TRNG I HC BCH KHOA TP.

H CH MINH
TS. NGUYN THNG

CP THOT NC
(Ti bn)

NH XUT BN XY DNG
H N I - 2 0 1 0
 LI M U

Cp th o t nc l mn h>c chuyn ngnh trong chng tr n h o to

k s N g n h X y dng. v l mn h.c cung cp cc k i n th c n h m
g i i q u y t cc v n lin quan n t.nh ton , thit k, q u y hoch m t h
th n g cp nc cho sinh hot, sn x.ut ca m t n v s d n g nc
hoc cho m t k h u vc . Tnh on thit k h thng th o t nc m a th
c n g l m t n i d u n g c h nh c Ctp tr o n g t i liu.

C un s ch s bao gm 2 phn: Ca.p nc v th ot nc . N i d u n g s

c gii thiu trong 9 chng v cc p h u lc. T rong m i ch ng , l
th u y t c bn s c gii thiu v c-c v d tn h ton m i n h ha c
trn h by. B n c s nm c ln tt hn th n g q u a cc bi t p c
li g i i cui m i chng.
T i liu c h o n th n h vi g i p v gp ca cc n g n g h ip
trong B m n K th u t Ti nguyn nr v trong K h o a K th u t X y
d n g T r ng i hc B ch khoa Th n p h H C h M inh.
Tro n g k h i bin son ti iu khng th tra n h khi n h n g sai st, rt
m o n g c s gp v p h binh cua bn c. Y kin x in g i v a ch:
Tr ng i hc B ch khoa Thnh p h H C hi M in h , K h o a K th u t X y
d n g , B m n K th u t T i nguv nc,

T c g i

3
 Chng 1

NHU CU DNG NC V NGN NC

1.1. (II T H I t

Trong gio trnh nv, chn ti s aii thiu ch yu n cc vn lin quan n

vn chuyn nc trong cc cna trnh dn nc, mng li ng ng phn phi nc
v rong h thng ng ng cng thot nc ma v nc thi. Cc vn lin quan
n x lv nc s c gii thiu trng ti liu khc.
Nc s dng c khai thc ch vu n t cc ngun nc ngt sau:
- N c mt, hin din trong cc h, cc (lng chy (sng sui).

- Nc ngm, thng dng khoim ha manh.

S sau v trnh by chu k s dung nc mt cch tng qut trong khai thc :

Mang li

i t . l : C h u k ( liu ii* \((k

K h i d u nc s dc ly t mi n^un nc (h ch a, s n g .. . ) n h vo m t c n g
i n n h ly nc. Cni n h ly nc ny ty theo trnu h p s c t h :
 - Ly nr n gin nh vo mt ng ng dn dt chm vo trong sng (h).
- Ly nc c s la chn nhiu chiu su khc nhau trong sne.

Trong mt vi trng hp, c th phi xy dng trm bm (trm bm cp I) hoc mt

p dng to h cha nhm iu tit lu lng trong Irng hp dng chy c Uru
lng khng m bo cho nhu cu ly trong chu k nc km.
Cc cng trnh dn nc (knh, ng ne c p) s dn nc th v khu vc cn cap
nc. Nu nc k h n g tiu chun v sinh, chng ta s x lv n trong mt trm
lm sch (khu x l) trc khi phn phi v cc ni liu th nc cui cng. Neoi
ra, bt k cht lng ngun nh th no, nc lun lun c kh trng (ph bia l
s d n g chlore).

Khi nc tr thnh su dng c (sch), ngi ta s phn phi trong vng quy
hoch cho n tn cc thit b dng nc cui cng, nh vo mt mng li ng ng
dn nc c p. Sau khi c s dng, v nguyn tc nc s mt di cc cht lng sch
cn thit v tr thnh nc thi. T , h thng ng ng cng s c nhim v thu
tho nc thi ny ra khi khu quy hoch.

Ta phi lu , theo nguyn tc, vic x l nc s dng trong mt trm xtr l

nhm trnh lm nhim mi trng ni nc thi tr v thin nhicn l iu bt buc.
iu ny cho php cc h dn khu quy hoch nm ve ha lu ca cc v tr ca x c th
s dng nc vo cc mc tiu khc nhau ironu d c nc dnn cho ,inh hot. Nirc d
c x l v lm sch li s c dn v khu vc tip nhn bi dng dn gi l knh
d n vi n h i m v k n h d n ny l ho m s pha lo n g t Iilit c th t r o n s ng u n

nc thin nhin.

Cui cng, trong mt con sng, nc s chu mt qu trnh lm sch t nhin m la

gi l qu trnh t lm sch (kh nii t lm sch cng cao khi sng cng ln). Trong
qu trnh ny, cc tp cht c hi s dn dn c gim i mt phn.
Ngoi ra, khi nc s dng dc tr v trong mt con snu hoc h cha, trong
m t s trng hp c th mau chng ha nhp vo ngun cp nc v n khng th t
trn ln tt trong tng th mi trng nc. L do, c th do khi ln ling ca n
khc, hoc c th do c tnh thy lc ca mi trng. Ta ni rng trong trng hp ny
c mt hin tng ni tt: qu trnh t lm sch khng xv ra, trong trng hp ny
ngun nc c th b nhiin bn nghim trng.

1.2. S H T H N G CP NC

H t h n g c p n c v thot 1111'c l IT1I tp h p cc c n g trnh: ihu nc, x l nc,

d tr nc, trm bm, h thng mns li phn phi nc dn ni tiu dng, h thnu
thu v thot nc.

6
 S tng qut c dng nh sau

_ _ _
p n

1-----
-{'1-

1-

/ - N ^ t i n c cp 2- c r/ih th u nc
3~ T r t hn c p 4 - T r m x nc
5 ' B ch a n c .sch 6- T i n i h t)in p 2
7 ' n\> ns> ch n h (S1- H his c p nc bn o i

9 - D n v ti n thu nc 10- D i tti c

I - H h i HC th i 2- T r m \ nc th i
13- c i th o i i( 4 - H fh !i! s ti r r i U f( h i

H n h 1.2: S(/(! h thiy cp m tc

1.3. C LN DN S V THI GIAN KIIAI TH C C N G T R N H

1.3.1. c ln dn s phc v cp nc

Dy l mt giai on bt luic cn thit cho thit k mt h thng cp nc. Ngi k

s phi xc nh c quy i dn s hin ti cho klui \ v dng v c nh gi cho s
pht trin trong tng lai trong sut ai on khai Ihc ca h thng cng trnh. Ty
theo nhu cu ca d bo la c 2 loi c lny v quv m dn s: c lng ngn hn
(M 0 nm ) v c lng di liiin (10-30 nm).
R rng bi ton d bo di hn l mt vn kh, hi v c qu nhiu yu t khng
chuc chn khi xt trong mt tng lai xa. Tron 1 trnu hp ny, c th tin hnh phn
tch ng cong biu th dn s troni qu kh (l nh gi c xu th v c xem xt
cc yu t x hi, kinh t, thi lp hay di i ca cc Cng ty X nghip, tc ng n
s tng trng ca vng. Ni chun; , phn ln cc phng php c lng thng ch
chu php nghin cu s bin ng ti >ng mt chu k tng i ngn.

1.3.2. Thi gian khai thc cng (rnh d kin

Hit k cc cn. trnh ronu ngnh cp thot nc nhm mc ch tha mn nhu cu

hin ti v cho tne lai cho mt vng quv hoch. Tui th cng trnh l khong thi
ian k t lc a cng trnh vo kliai thc n cui thi kv m cng trnh vn cn c
tluli gi iha mn cc vu cu k Ihut v kinh t trong khai thc. Xc nh thi gian
khui ihc hiu qu ny da vo mt phn tch ti chnh trong d la s k n cc vn :
- Du t.
- Chi ph khai thc (nhf'n cng, din, ha cht,...).
- Li sut.

7
 - S thun tin cho php chng ta c th ni rne CII trnh hay thm vo cc thit b
(v d ta s d dng hn khi thav th mt bm hav nia tni cng sut trm bm hon l
m rng mt tunel hoc mt cng trnh ly nc).
- C th ci tin cng ngh.
Bng sau y trnh by tui th cc cng trnh ta c th tham khao trong thit k cac
cng trnh trong lnh vc cp thot nc v lm sch nc. Ta nhn xt c ha nhm tui
th: nhm t 5 n 20 nm cho cc loi thit b s dni nh an h v thay th d dng;
nhm c chu k s dng t 20 n 30 nm cho cc thit b kh khn hn v tn kem khi
mun thay th; v nhm ln hn 50 nm khi thit b l rt dt v rt kh [hay th lioac
m rng.

Bng 1.1. Tui tho cng trnh tiu biu

1101 tho
Cng trinh c tnh
(nm)
c / ( ony IU litn (l Mi mu I tiOix.
p hoc tune Rt kh v dt khi m lng 50-7:
Ly nc v dng dn chnh Tng i kh khi m rn 2S-.S0
Trm x l v mang li Nu uia lng dn s v tv sut li nhun:
- B 2S
- Ln 50
ng dn c ng knh > 300 mm i lin khi Ihiiy th 2VH)
ng dn c dng knh < 300 mm Xy dim d IS-20
Trm bm:
- Kt cu Tng quy m e dang 20
- Bm Tng cim su dng, nhanh VO
Cc i ?i> trnh (lm* ( iit v ni MH i nc:
ng dn ph c dng knh < 375 I1111 Xy clim cle 20
Cc cng trnh thu, knh tho Kh v dt khi m rng 30-50
Trm x l Nu gia lne dn s va IV sut li nhun:
- B 20-30
- LI 10- 5
Trm bm M rng kh 10-20
Bm chuyn nc vo trm x l Thay th d dng 5-10

Tm lai, chng ta c th khai thc V ' su d u 11i- nc nut. nc nu m . iiL l va t a

nc bin sau khi d c thu v x l Irona mt trm tliii tiu chuan v s phn p h o i
I1 nh vo mt mng li phn phi. v plin nc d s dng sc dc lliu hi I|u;i 1l
thnt cng v hng c h n s di vo mt trm x l loi ho cc tp chai co hai trc
khi tr n v thin nhin. T ro n mi trng ny qu trnh t lm sacli s c lii! hnh
v s hon chinh s thanh lc. Chu k s C1I nc d khp kn v chii ta la i :o llic
khai thc n d da vo s duii.

8
1.4. N H U C U D N (; NC

T h e tc h v lu lnu nc d na thay i rt nhiu ty (heo di u kin a ph ng,

phu thuc vo mc sng ca khu vc nghin cu. Vi mt khu vc nghin cu cho
trc, lng nc cn tng cn bao gm: nc s dng cho gia dng, nc cung cp
cho thng mi, cho cng nghip v nc s dng cho cc mc tiu cng cng (v sinh
d n g s. c h a ciiv...).

1.4.1. Nc sinh hoat

Nc sinh hot trong mt chu kv dng nc (thng tnh l I12 V m) thay i theo
thi gian tionu nsv. Biu sau trnh by mt biu nc sinh hot cho ngy dng
nc ln nht i n hnh.

c i:

Qivit 111.1 lu lng nuy dng nc ln nht (m'/ng).

Q , h = Qnj.ci-,iu\/24 - lu l n g t r u n g b n h g i ( m 7 h ) .

Q, - lu lne gi ili i (in'/l).

Q h nl K - lu lnu gi ln nht ( m l/h).

K, = Q ,/ Qlb - h s klng icu ha gi th 1 (nh ngha thng s dng trong cc

phn mm m phng dng chv c p trong mng li, v du EPANKT).
K|t in 1X= Q h m,n / lh - li so khng diu ha gi ln nlit.

Q (m 7h)

i i 1 3 . B i r i i ( n ( l i i k v (ii h n h

( i c h : Trong mt s trirna h p ngi la cn ci ml i ngha h s khng dicti ha gi

nh sau :
k, = ,/ U n ). gi in k( tra phu c 3 ph ilmc vo K|vm N

9
 1.4.1.1. Tiu chun d n g nc
Tnh theo bnh qun u ngi lng nc dng trong mt ngy m, lt/ngy-m.
Theo tiu chun cp nc hin hnh TCXD 33 : 68.

Bng 1.2

Tiu chun dng H s khng

Trang b tin nghi trong nh 11C q lb iu ha gi
(1/ngi/ngy-m) <Kh-ma^
- Loi I. Nh bn trong khng c h thng cp thot nc v 40-60 2,5-2,0
dng c v sinh. Nc dng lv t vi nc cng cng.

- Loai II. Nh bn trong chi c vi ly nc. 80 100 2,0-1,8

- Loi III. Nh bn trong c h thng cp thot nc, c 120-150 1,8-1,5

dng c v sinh, khng c thit b tm.

- Loi IV. Nh bn trong c h thng cp thot nc, c 150-200 1,7-1,4

dng c v sinh, c thit b tm thng thns.

- Loi V. Nh ben Irong c h thong cp thot nc, c 200-300 1.5-1,3

dng c v sinh, c chu tm v cp nc ncmg cc b.

1.4.1.2. Lu lng nc sinh hot tnh ton

Lu lng nc cho trong bng trn y ch gi tr trun hnh dng nc trong mt
ngy m. Lu lng nc sinh hot tnh ton trong Iit ngy m c tnh cho naay
dng nc ln nht. Cng thc sau dy cho php xc nh gi ti ny:

Q sh-ngJ = ^ 5 ~ K ng c l-n m (m V n g d ) (1 .1 )

trong :

Qsh-ngi!' *u lung tnh t0i*n nc sinh hot ngy d n s nc ln nht, (m Vng).

Kngt|.m.ix - h s khng iu ho ln nht ngy, gi tr thay i trong khoim (1,35-1,5),
ph thuc vo c tnh kh hu tng vng.
q lb - tiu chun dng nc truna bnh c nhn irong 1 ngy m (1/ng-ng).
N - dn s d bo cho khu quv hoch (ngi).
Ngoi ra, s s dng nc trona mt ngy m thay i theo tng thi tlim trone
ngy. Lu lng nc sinh hot ln nht xc nh theo cne thc sau :

( , /],) (1.2)

10
trong :

Q ^ h - lu lng tnh ton gi dng nc ln nht (irv/h) .

Kh.m;ix - h s khng iu ho ln nht gi.

Cilii ch : Trong nhiu trng hp, chng ta m phng s thay di : lu lng, p sut,... ca
nc trong mt mng li cp nc theo thi gian. Khi , cc h s khng iu ho gi
s irc s dng.

1.4.2. Nc phc v cng nghip

Tiu chun cp nc cng n g h i p xc nh trn c s dy chuyn cng ngh ca x

nghip do c quan thit k hav qun l cp. Tiu chun nc xc nh trn s n v sn
phm. Cng mt loi x nghip, nhng do dy chuyn cng ngh khc nhau, lu lng
s ng nc c th khc nhau. Bng sau y cho php tham kho mt s yu cu dng
nc cho sn xut.

Bng 1.3

Tiu chun
Cc loi nc n v o dng nc Ch thch
(m Vi cin v o)
- Nc im sch trong nh my nli din 1000 KW/h 160-400 . Tr s nh dng
- Nc cp li hi nh my nhiel ilin 1000 KW/h 3-5 cho cng sut
- Nc lm ngui dng c t trong 1 c v /h 0,015-0,04 nhit in ln.

- Nc khai thc than tn than 0,2-0,5

- Nc lm giu than 1 tn than 0,3-0,7
- N c vn chuyn than theo mng 1 tn than 1,5-3,0 B sung cho h
thong tun hon.
- N c lm ngui i lu vn gang ] tn gang 24-42
- Nc lm ngui l Mac tanh 1 tn thcp 13-43
- Nc cho xng cn ng 1 tn 9-25
- Nc cho xng c thp tn 6-20
- Nc d xy cc loi gch 1000 vin 0,09-0,21
- Nc ra si d b tng 1 m1 1,0-1,5
- Nc ra ct d b tng 1 m' 1,2-1,5
- Nc phc v d 1 m ' b tng m' 2,2-3,0
- Nc d sn xut cc loi gch 1000 vin 0,7-1,0
- Nc e san xut nui 1000 vi n 0,8-1,2

Ticu chun dng nc cho nhu cu n ung v sinh hot ca cng nhn sn xut ti
cc x nghip lv theo bng sau.
 Hng 1.4

Tiu chun H s khng diu ha gi

Loi phn xtrng
(/ngi/ca) (Kh-max)

- Phn xng nng ta nhit ln hn 35 2,5

20 Kcalo cho 1 mVh
- Phn xng khc 25 3.0

1.4.3. Nc ti cv, ti ni

Tiu chun nc dng d ti cv. vn hoa, qung trng, ng ph trong cc li

th c ly khong 0 .5 - 1 l //ITT, phu thuc vo loi ng, loi cy trng, diu kin kh
hu. Thng thng ti dng c thc hin t 8h n I6h, ti cy t 5h n 8h v
t I6h n I9h hng ngy. Lu lng nc ti ng, ti cy c xc nh theo
cng thc:

Q. ..1 = q ,F, (m '/ng) (l.3a)

Q,
QI h (l-3b)

liong :
q, - tiu c h u n nc ti nu. li c ( m V n r - n g ) .

F, - din tch ti ( 1 1 1 )
Q| ngi! lng nc li trong I11I ntv m ( m 1).
, h - lng nc ti u ong mt gi (i Vh)-
T - Ihi gian ti trone mo( ngy dm (h).

1.4.4. Nc sinh hoat ciia cng nhn khi lm vic ti nh my

c xc nh theo cng thc sai :

= MnN i + C1/N : <m'/ca) (1 .-a)

r,\ o ?
v ,h - c ,
u ; h- h
(m 7h) (1.4b)
T,

trong :

- lung nc Snh hot cua cng nhn trong mt ca, mt gi'.

q n, l \ - tiu chun dR nc sinh hot cua cng nhn trong phn xng nni. lanh
(mVng-ca).
N, N 2 - s c n g nhn lam vic trong phn xng nng v lanh trong tny ca
T () - s gi lm v c trong mt ca (h).

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 1.4.5. Nc tm ca cng nhn khi lm vic ti x nghip

c xc nh theo cng thc sau :

Qf_Nh = 0 , 5 n (m7h) (1.5a)

(m-Vng) (1.5b)

trong :

Q ^ d,Qf_Nh - lng nc tm ca cng nhn trong mt ngy m, trong mt gi

(thi gian tm quy nh l 45 pht vo thi im sau khi tan kp lm vic),
n - s bung tm hng sen b tr trong nh my.
c - s ca kp lm vic trong nh my.

1.4.6. Nc dng trong cc nh cng cng

Theo quy phm TCXD 33 : 68.

1.4.7. Nc r r t m ng li phn phi

Lng nc ny khng c tiu chun r rt, ty theo tnh trng m ng li c th ly

t 5% n 10% tng cng sut ca h thng. Trong trng hp m ng li c, t l
nc mt c th ln n 5 c/o-20% tng lng nc a vo h thng.

1.4.8. Nc trong khu x l

c tnh ton s b c th ly theo t l 5% n 10% cng sut trm x l(tr s nh

dng cho trng hp cng sut ln hn 20000 mVngy-m). Lng nc ny dng cho
nliu cu k thut ca trm: b lng l,5% -3%; b lc 3%-5%; b tip xc 8%-10%.

1.4.9. Nc cha chy

c xc nh theo TCXD 11 : 63. C th tham kho trong bng sau y:

Bng 1.5

Lu lng nc cho 1 m chy, //s

S dn
S m chy Nh 2 tng tr xung Nh hn hp cc Nh 3 tng tr ln
(1000
ng thi vi bc chu la tng khng ph khng ph thuc bc
ngi)
I, II, III IV, V thuc bc chu la chu la
n 5 1 5 5 10 10
10 1 10 10 15 15
25 2 10 10 15 15
50 2 15 20 20 25
100 1 20 25 30 35
200 3 20 30 40
300 3 40 55
400 3 50 70
500 3 60 80

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 1.4.10. C n g sut cp nc

Trn c s cc nhu cu dng nc trnh by trong mc 1.4, cng sut cp nc trong

mt ngy m cho mt khu quv hoach trong trng hp tng qut c xc nh theo
cng thc sau:

Q = (aQ * ,x+ Q ,+ Q + Q f N+ Q ) b c (mVng) (1.6)

trong :

Q sh-m XQt Qsx ' lu l(?n nc sinh hot ca khu dn c; lu lng ti

ng, ti cy, nc sinh hot, nc tm ca cng nhn, nc sn xut ca cc
nh mv. Tt c cc s hng c tnh trong mt ngy m (m Vng).
a - h s k n lng nc dng cho cng nghip a phng, tiu th cng nghip
(thng ly a = 1,1).
b - h s k n lng nc do r r (ph thuc vo iu kin qun l, b = 1,1^1,15.
c - h s k n lng nc dng cho bn thn trm cp nc (ra cc b lng,
l c ,...), c = 1,05 -r 1,1. Tr s ln cho cng sut trm cp nc nh v ngc li.
thuii tin cho tnh ton, ngi ta thng lp bng tng hp lu lng nc tiu
th theo lng gi trong mt ngy m nh sau:

Bng 1.6. Tng hp lu lng nc dng theo gi

Ca, R Tng cng

Q-h a-Qo, Ti, m ' X nghip, m 1
cng r
Gi
Q sh-m nx
m' m' ng Cy Q^r Q ,x c r m' m1 ni1 %

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12)
0-1
1-2

22-23
23-24
1
I
Tng
1

Ghi ch :
(1) tra hang ph lc 3. phu thuc vo Kh.rn.ix.
(12)= 100 X 11 1)/ X ( l l ) .
Ct (12) s c s dng nh cc h s patterns trong bi ton m phng mng li cp
mrc theo thi gian (v d trong phn mm EPANET).

14
1.5. N (U N N C

1.5.1. Gii thiu

Nc trong thin nhin thng c tn ti hai dng sau: nm l thin trn mt t

v nm ngm di t. Nc ma sau khi ri xung mt t mt phn thm vo trong
t qua cc tng thm nc v c gi li tng khng thm nc to thnh ngun
nc ngm , phn nc cn li chy trn mt t theo a hnh thp dn tp trung hnh
thnh sui, ao, h, sng,...

Hnh 1.4: c/ii k vn chuyn nc

Trong k thut cp nc ngi ta thng s dng hai loi ngun nc ngt sau:
ngun nc ngm (m ch nng, mch trung bnh, mch su), ngun nc mt (ao, h,
sng ngi).
Ngoi ra, cn c ngun nc ma l ngun b sung cho nc ngm v nc mt.
nhng vng khng c hoc khng khai thc c hai ngun nc trn th nc ma l
ngun nc quan trng nht.
Khi thit k h thng cp nc, mt trong nhng vn c tm quan trng bc nht
l chn ngun nc. N gun nc s quyt nh lnh cht v thnh phn cc hng mc
cng trnh, v n cng quyt nh kinh ph u t xy dng v gi thnh sn phm. La
chn ngun nc cn phi da trn c s kinh t - k thut ca cc phng n.

1.5.2. Ngun nc ngm

Nc ngm l nc nm trong t c lc v gi li trong cc lr<p t cha nc

(thng l: ct, si, cui,., c c ht v thnh phn khong cht khc nhau), i vi nc
ngm c p thng nm gia cc lp cn nc (thng l t st, t tht, v .v ...). Ngun
b sung cho nc ngm l nc ma, nc t h, ao, sng ngi thm qua cc lp t.
Nc ngm c th tn ti cc trng thi sau:
- th kh: cng vi khng kh nm trong l rng ca t .

15
 - th bm cht: bao quanh cc ht t bng mt lp rt m ng, gn cht vi t bng
cc lc dnh, iu kin bnh thmi khng th tch ra c.
- th mng mng: nm bao quanh cc phn t t ct bng lc phn t, c th di
chuyn trong lng t di nh lii! ca lc phn t nhng khng th truyn c p sut.
Nc mao dn: cha y trong l rng nh ca t, chu tc dng ca sc cng mt
ngoi v trng lc. Nc mao dn c th di chuyn trong t v c th truyn c p
sut. Vng nc m ao dn nm trn mc nc trng lc.
Nc trng lc hay nc thm: cha y trong l rng cua t, chuyn ng di tc
dng ca trng lc v c th truyn c p sut.
Trong cc dng tn ti ca nc ngm nu trn th ch c nc thm l c tr
lng ng k v c kh nng khai thc c.

1.5.2.1. Phn loi

Phn loi theo v tr tn ti so vi mt t:
Nc ngm mv nng: nm nay trong tng t trn mt, thng c su t
3-1 Om, khng p. Lu lng, nhit , v cc tnh cht khc ca n chu nh hng
nhiu ca mi trng bn ngoi. Dao ng mc nc gia cc m a kh ln (2-4in). tr
lng t v c nhim bn ln.
Nc /Igni su rni bnh: nm su khng ln so vi mt t, c su
t 10-20m, thng l nc ngm khng p, i khi c p cc b. Tnh cht ca loi nc
ngm ny tng t nh Iic ngm mch nng nhng cht lng tt hn, n thng s
dng cp nc.
Nic igcm mch su: mch nc nsm c chiu su H > 20m, nm trong cc tng
cha nc, cht lng nc tng i lt v c tr lng nc phong ph.
Phn loi theo p lc:
Nc ngm khni p: l lp nc nm trn tng cn nc u tin, thng c su
khng ln nn cht lng nc khi t dc tt lm. Pha trn lp nc thm c gii
hn bi mt t do v p sut ti mi liicm trn mt t do ny u bng nhau.

V 7

2
Ghi ch: 3 ch tng a cht -hm yu
Inh . 5: Nc /im bn p

16
 Nc ngm c p: l lp nc nm gia hai tng cn nc, thng nm su
tng i ln nn c lc s b khi thm qua cc lp t v t chu nh hng ca
mi trng hn ngoi do cht lng tt hn so vi nc ngm khng p.
Q
T b

w \\\\\\\\\\\\\\\\\\\ . \ \ \ \ \ \ \ \ \ \ \ 2' \\WWW'

'. \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ A\\\\\\\\\\ .\\\\\\\''

Ghi ch: 3 ch tng a cht khng thm

Hnh 1.6. Nc nini l p

Phn loi theo thnh phn ha hc:

Nc ngt, nc l, nc mn.

1.5.2.2. u khuyt im

u (lim:
- nhim ban t, trong sch.
- X l n gin nn gi thnh r.
- C th xy dng phn tn nn ng knh ng dn nh.
- m bo an ton cp nc.
Khuyt im:
- T hm d, khai thc kh khn.
- Thng b nhim st, nhim mn nht l cc vng ven bn.
- Tr lng khai thc hn ch.

1.5.3. Ngun nc mt

Nc mt l loi ngun nc tn ti l thin trn mt t nh: sng, sui, h ..

Ngun b sung cho nc mt l nc ma. 0 nc ta ngun nc Iit kh phong ph v
lnt ma nhiu v c mng li sng, sui phn b khp ni y l ngun nc quan
irng c s dng trong cp nc. Nc mt bao gm cc dng sau:
Nc SII y:

L loi ngun nc mt ch yu cp nc, nc ta h thng sng ngi kh

phong ph c chiu di khong >5.000 km, nn tr lng nc sng rt n. N c th
p ng y nhu cu phc v cho sn xut v i sng. Nc sng c cc c im sau:

17
 - Gia cc m a c s chnh lch ln v mc nc, lu lng, hm lng cn v nhit
nc.
- H m lng m ui khong v s nh.
- c cao nn vic x l phc tp v tn km.
- Nc sng l ngun tip nhn nc ma v cc loi nc thi x vo. V vy, n
chu nh hng trc tip ca mi trng bn ngoi. So vi nc ngm , nc mt thng
c nhim bn cao hn.
N c su i:

Nc sui cng l ngun cp nc quan trng. C cc c tnh sau:

- K hng n nh v cht lng nc, mc nc, lu lng, vn tc dng chy gia
m a l v m a kit.
- V m a l. nc sui thng b c v thng c nhng dao ('ng t bin v mc
nc v vn tc dng chy.
- V m a kh th nc sui li rt trong nhng mc nc thp. Nhiu khi mc nc
q u thp khng su cn thit d thu nc. Nu s dng nc sui cp nc th
cn c bin php d tr, nng cao mc nc v bo v cng trnh thu hp l.
N c h, m :

Ty thuc vo a hnh v yu cu s dng, c th dng h, m nc t nhin (nu

tha m n yu cu s dng), hoc thit k h cha theo yu cu s dng. Nc h, m
c cc c tnh sau:
- T hng trong, c hm lng cn nh.
- cc h ln, ven h c sng nn nc ven h c th b c.
- Nc trong h, m thng c vn tc dng chy nh nn rong ru v cc thy sinh
vt pht trin nn nc thng c mu, c mi v d b nhim bn.

u khuyt im

u im:
- Tr lng nc phong ph.
- Khai thc, vn hnh d dng.
K huyt im:
- nhim bn v vi trng ln.
- H m lng cn cao.
- Cng trnh x l ln v t tin.

1.5.4. N gu n nc ma

N gun nc m a nc ta kh phong ph (lng ma trung bnh khong 1500-2000

m m /nm ). Tuy nhin vic s dng trc tip b hn ch do ph thuc nhiu vo thi tit,

18
ma, khu vc. N thng ch thch hp cho cung cp nhng vng ni cao, cc vng
nng thn v cc hi o thiu nc ngt th ngun nc ma l quan trng nht. Nc
ma tng i sch, tuy nhin n cng b nhim bn nu ri qua vng khng k h b
nhim, mi nh... Nc ma thng thiu cc mui khong cn thit cho s pht trin
c th con ngi.

1.5.5. La chn ngun nc

Vic la chn ngun nc phi da trn c s kinh t k thut ca cc phng n

nhng cn lu cc im sau:
- Ngun nc phi c lu lng trung bnh nhiu nm theo tn sut yu cu ca i
tng tiu th. Tr lng ngun nc m bo khai thc nhiu nm.
- Cht lng nc p ng yu cu v sinh theo TCXD 33 : 68, u tin chn ngun
nc no d x l v t dng ha cht.

- u tin chn ngun nc gn ni tiu th, c sn th nng tit kim nng lng,
c a cht cng trnh ph hp vi yu cu xy dng, c iu kin bo m v sinh
ngun nc.
- Cn u tin chn ngun nc ngm nu lu lng p ng yu cu s dng. V
nc ngm kinh t trong khai thc, qun l v c nhng u im khc nh nu
phn trn.
Cht lng nc dng cho sinh hot phi tha mn cc ch tiu sau y:

Bng 1.7: Ch tiu cho php nc sinh hot

Chi tiu Yu cu
Mi v v 20c Khng
mu theo Platin cobal 10
c, hm lng cn 5mg/l
pH 6.5-8,5
Hm lng st 0,3mg/l
Hm lng mangan 0,2mg/l
cng 12 c

1.5.6. Bo v ngun nc

ngun nc trnh nhim bn do nc thi sinh hot, cng nghip,... ngi ta cn

plii quan tm ng mc n vic bo v ngun nc. Nh nc ban hnh cc quy
nh bo v v sinh cho ngun nc c cc ni dung ch yu nh sau:
i vi ngun nc ngm :
K h u vc bo v :

- Nu tng bo v dy > 6m, bn knh bo v ly bng 50m.

19
 - Nu tng bo v dy < 6m. bn knh bo v ly bng lOOm.
- T rong khu vc ny nghim cm xy dng.
K hu vc bo v II:
L khu vc hn c h quanh khu vc I,ch cho php xy dng cc cng trnh ca h
thng cp nc nu tng bo v c bn knh300m. Nu t khu vc IIthm nc th ty
theo thm m bn knh bo v ly t 50 - 300m (ph thuc vo c ht ca tng
bo v).

i vi ngun nc mt:

K hu vc :
N ghim cm xy dng, tm git, lm bn bi v x nc vo ngun trong phm vi v
thng ngun > 200-500m , v h ngun < 100-200m ty lu lng, vn tc v nh
hng ca thy triu n dng sng.
K hu vc II:
K hng cho php x nc bn vo pha thng ngun:
- T 15 - 20 km i vi sng ln.
- T 20 - 40 km i vi sng va.
- i vi sng b th ton b thng ngun khng cho php x nc bn.
K hu vc IU:
Hn c h nhng cho x nc thi c x l v phi tnh ton hiu qu t lm sch.

i vi h cha:
- N ghim cm x nc bn vo h.
- N ghim cm xy dng, chn nui, trng trt trong phm vi 30-500m gn b nu
vng t bng phng v ton b lu vc nu mt t dc v pha h.
- K hu vc hn c h l 300-50()m k tip .

20
 BI TP

Ii 1. Mt mng li cp nc c quy hoch cung cp nc cho mt khu c

cc thng s sau :
- Khu dn c bao gm 2 tiu khu A v B. Khu A c 15 nghn dn vi tiu chun dng
nc l q lb = 120 //(ng-ng), c h s khng iu ha ln nht ngy K ng_max = 1,2 v gi
KjVlnaK = 1,3. Khu B c 3 nghn dn vi tiu chun dng nc l q lb = 200 //(ng-ng), c
h s khng iu ha ln nht ngy K ng[1.max = 1,3 v gi K h.max = 1,5.
- Mt nh m y ngy lm vic 2 ca, mi ca 6 gi v c 500 cng nhn (ca 1 t 6h n
12h, ca 2 t 13h n 19h). Nc dng cho sn xut trong mi ca l 300 n r/c a . Nc sinh
hot cho cng nhn trong mi ca l 24 //(ng-ca).
- Din tch ng, cy xanh cn ti l 10000 m2, vi tiu chun ti l qt = 2 //(m2-ng).
Thi gian ti t 15h n 19h.
Cho bit h s dng nc cho sn xut nh trong khu l a = 1,1; r r do m ng li
ng ng b = 1,15; h s dng nc cho trm x l c = 1,04.
Xc nh :
a) Lu lng ngy dng nc ln nht, lu lng gi dng nc ln nht v lc lOh-
I lh ca khu dn c A.
b) Cng sut cp nc ca trm bm cp I v cp II (nr/ng).
c) Lp bng phn phi lu lng trong mt ngy m cho ton khu.
Bi 2. Mt mng li cp nc c quy hoch cung cp nc cho mt khu c
cc thng s sau:
- Khu dn c c 25 nghn dn vi tiu chun dng nc l q tb= 125 //(ng-ng), c h
s khng iu ha ln nht ngy Kng max = 1,25 v gi K h.max = 1,5.
- Mt nh m y ngy lm vic 2 ca, mi ca 5 gi v c 1000 cng nhn (ca 1 t 6h
n l l h , ca 2 t 12 h n 17h). Nc dng cho sn xut trong mi ca l100 mVca.
Nc sinh hot cho cng nhn trong mi ca l 20 //(ng-ca). Nh m y c n = 6 nh tm
hng sen.
- Din tch ng, cy xanh cn ti l 20000 m2, vi tiu chun ti l q t = 4 //(rrr-ng).
'[Tii gian ti t 16h n 19h.
Cho bit h s dng nc cho sn xut nh trong khu l a = 1,1; r r do m ng li
dng ng b = 1,15; h s dng nc cho trm x l c = 1,0.
Xc nh:
a) Lu lng ngy dng nc ln nht, lu lng gi dng nc ln nht v lc
14h - 15h ca khu dn c.
b Cng sut cp nc ca trm bm cp I (mVng).

21
 c) Lp bng phn phi lu lng trong mt ngy m cho ton khu.
Bi 3. M t m ng li ct c thit k cho mt khu vc quy hoch nh sau:

Khu dn c A c 20000 dn, c tiu chun dng nc l 120 //ng/ng. H s khng

iu ha ln nht ngy K ng_max= l,2 v gi l Kh_max= l,5 . Din tch ti cho ng s v
cy xanh l 20 ha. Thi gian ti l t 17h - 20h trong ngy.
Nh m y F hot ng 2 ca trong ngy. Ca 1 t 7h -12h v ca 2 t 13h -18h. Mi ca c
500 cng nhn lm vic vi tiu chun dng aic cho sinh hot l 30 //ng-ca. Lu lng
nc cho sn xut cho khu cng nghip l 300 mVca. T rong nh m y c 9 nh tm c
trang b vi sen.
Xc nh :
a) Lu lng ngy dng nc ln nht, lu lng gi dng nc ln nht v lc
13h - 14h ca khu dn c.
b) Lu lng nc trn on ng 1-2 v 2-3 lc 17-18h.
c) Vi a = b = c = 1 tnh cng sut cp nc ca trm bm cp I (n r/n g ).

22
 Chng 2

CNG TRNH THU NC

2.1. (I I TH IU

Nc trong thin nhin c khai Ihc t nhiu ngun khc nhau. i vi mi loi
ngun nc khi khai thc cn c cc bin php cng trnh thch hp. Hnh thc cng
trnh khai thc ngun nc cn ph thuc vo nhiu yu t khc: a hnh, a cht cng
trnh, a cht thy vn, thy lc....

2.2. C N G TRNH TH U NC N(M

2.2.1. G ing khi

Ging khi l cng trnh thu nc ngm mch nng, thng khng c p hoc c p
lc yu, c ng knh D = 0,8-2,Om, chiu su H = 3-20m, phc v cp nc cho mt
gia nh, hay mt s i tng dng nc nh. Khi cn lng nc ln hn c th xy
dng mt nhm ging khi ni vi ging tp trung bng cc ng xiphng.

H n h 2.1: Cn to yiii kh<ri

/- (x \;n tm Iic; 2- thnh {n thu nc;
vch; 4 - ia c, /Im ni bn

V tr ging nn chn gn nh nhng phi cch xa cc chung nui sc vt, h x ti

thiu l 7-10 m.
Nc thu vo ging c th ly t y, t thnh bn, hoc c t y v thnh bn.
Trong mt s trng hp tng lu lng ging c th s dng thm cc nhnh thu
nc hnh nan quat.

23
 Cu to tng lc y ging gm 3 hoc 4 lp ct si, chiu dy ca mi lp ti thiu
lOOmm (lp di cng l ct, lp trn l si c kch thc ln dn t di ln trn). Nu
thu nc t thnh bn, b phn th phi nm trong tng cha nc v c cc khe
thu nc.
ng knh ging c xc nh ph thuc lu lng cn thu, tnh cht ca tng
nc, cch thu nc, loi thit b bm t trong ging v bin php thi cng. Thng th
ng knh ging khng nn chn qu 3-4m, nu ng knh ln nn dng nhm ging.
Vic tnh ton ging khi l xc nh: s lng ging, ng knh ging, su
ging theo lu lng yu cu vi iu kin h su mc nc trong ging khi biri
khng vt qu h mc nc cho php. Khi tnh ton cn ch phn bit: ging hon
chnh l ging c vch v phn thu xuyn ht tng ngm nc v ging khng hon
chnh l ging c vch v phn thu khng xuyn ht tng ngm nc.

Khi ly nc tcy:

Nu khong cch t y n tng cn nc ln hn ng knh ging (T > 2r), lu

lng c th xc nh theo cng thc V.D.Babuskin:
--------- 27tKSr (21)

" + --(1 + 1 .1 8 - ? - )
2 T 4H
trong :
r - bn knh trong ca ging.
K - h s thm.
s - h mc nc trong ging khi bm.
R - bn knh nh hng.
T - khong cch t y ging n tng cn nc.
H - chiu su mc nc tnh tnh n y cch thy.
Nu H v T rt ln th c th b qua v phi ca mu s.
Khi T > lOr v R < 10H c th tnh lu lng ging theo cng thc:
Q = 4KSr (2.2)

Khi ly nc qua thih bn:

C th s dng cng thc tng t nh vi ging khoan khng hon chnh khng p:

K S |2 ( H - T ) - S |
Q = 1,36------' --------------------------------------------------- i(2.3)
I K
lg
r
Ngoi ra cng c th xc nh theo cng thc sau (tnh nh ging khoan):
Khi thu nc t y:
Q ,= F , .V , (2.4)

24
 Khi thu nc t thnh bn:
Q 2 = F 2.V2 (2.5)
Khi thu nc t v v thnh bn:

Q = Q, + Q 2 (2.6)
trong d:

F - din tch y ging;

F 2 - din tch phn thu nc thc t ca ging c tnh bng phn din tch xung
quanh ca ging c b tr khe thu nc v nm trong mc nc ngm.
V ,- vn tc nc chy qua tng lc y vo trong ging. Theo C.V.Idbacser:

V, = a P K ( l - p ) ( r i - l ) (2.7)

vi:
a = 0,5 - 0,6 - h s an ton,
p - h s ph thuc cu to lc.
p - rng ca lp vt liu lc.
T|- h s nht ng hc ca nc.
V-, - vn tc nc chy qua thnh bn vo ging:

V2 = 6 0 n/ k (2.8)

K - h s thm (m/ng).
S b tnh ton c th xc nh lu lng ging khi theo cng thc sau:

q = zl ! v m 7s) (2.9)
4 cp
d - dng knh ca ging (m)
V - vn tc cho php ca nc chy vo ging.

B ng 2.1: Tc ti hn ca dng nc qua y ging khi

ng knh d50 (ram) ng knh d50 (mm)

Vm,(m/s) Vfh(m/s)
lns cha nc tng cha nc

0,05 0,01 0,7 0,09

0,1 0,02 0,8 0,10
0,2 0,03 1,0 0,11
0,3 0,04 1,5 0,14
0.4 0,06 2,0 0,16
0,5 0,07 3,0 0,18
0,6 0,08 - -

25
 n %hm lgaii tm l c:
L cng trnh thu nc ngm mch nng vi cng sut ln hn t vi chc n vi
trm m 5ngy. su tng nc khng qu 8m.

Mt t t nhin

- -
\ 7 4 \ 7 5
*!

i1
1
1

1
1

1
1
1

1
V - L - T
.12 ... _

H n h 2.2: S ( (II to hn liim Niant thu nc

- (tm; hm lin nc; 2- iii tp t i i t i i ; m c lir troiH in^;
4- mc Iic tih tron l tm; cha; 5- li'fjy (li cha nc ; 6- iiii cn nc

Cu to ng hm ngang thu nc gm c:
- H thng ng thu nc (bng snh hoc btng c l d = 8m m hoc khe rng
lO-lOOmm, ngoi ra c th xp dm, d lng) nm ngang t trong lp cha nc, c
dc nc t chy v ging tp trung.
- G ing tp trung.
- G ing thm: trn ng hm thu nc khong 25-50m v ti nhng v tr ng
hm i hng th cn b tr ging tlim kicm tra nc chy.
ng hm c th b tr kiu hon chnh hoc khng hon chnh.

Tnh ton (uy /ithn thu IIt

Xc nh lu lng ng hm da trn c s cc nh lut v dng thm ca Darcy.

Gi thi tng Ciri nc pha dy l mt nam ngang, trng thi chuyn ng ca nc
ngm t tng cha n ng him ! trng thi chv tng.

Mt d tnhin
Mc nc tnh i R
* -----------------------------

Hnh 2.3: Hm thu ii' hon ( htih

26
 p dng cng thc Dupuid:

L K (H 2 - h 2)
+ Khi thu nc 1 bn: Q ( 2. 10)
2R

L K (H 2 - h 2)
+ Khi thu nc 2 bn: Q = (2.11)
R
Mt t t nhin
i
Mc nc tnh

Hnh 2.4: Hm hu nc kht hon chnh

Lu lng xc nh theo cng thc A.V.Romanop:

Q = KLS + ( 2 . 12)
R , L 67T R
2,3 lg - + ---
7i.b 2T
trong :
L - chiu di ng hm.
b - chiu rng ng hm.
T - khong cch t y hm n tng cn nc.

2.2.2. Ging khoan

G ing khoan l cng trnh thu nc ngm mch su vi cng sut ln t 5 - 500 //s,
chiu su t vi chc n vi trm mt v c ng knh D = 100 - 600 mm.
a) b c) d)

' Hnh 2.5: Ci loi >iil khoan

777? rrrrrrT^T

27
 Ging khoan gm cc loi sau:
- Ging khoan hon chnh (a), khai thc nc ngm khng p, y ging khoan n
tng cn nc u lin.
- Ging khoan khng hon chnh (b), khai thc nc ngm khng p, y ging nm
cao hn tng cn nc.
- Ging khoan hon chnh (c), khai thc nc ngm c p.
- Ging khoan khng hon chnh (d), khai thc nc ngm c p.
a) b)

6 ____
_
.4 5$

p 5 I
V7-,

H n h 2.6: S d i ii lo yi/i khoaII

1- miU cih; 2- n v c h ; d a i lin kt, 4- IH lc; 5- UII lii; - cn ni
) n ; vcli ni vi lc htn> (lai lin kt; h) Om; vch ni vi IH lc hhi cn ni

S b tnh ton c th xc nh theo cng thc sau:

H2 - h 2
Q = I.K. (2.13)
2.R

I - chu vi ng thu.
K - h s thm (m/h). Khi khng c s liu thm d, c th tham kho s liu trong
bng 2-2.
H - chiu dy tng cha nc.
h - chiu cao mc nc trong ging tnh t y ng thu.

Bng 2.2 : Gi tr h s thm K c tnh ca mt s loi t

K (m/ngd)
Ln nht Trung bnh Nh nht
Si sn 100
Ct khng u, ln si sn 100 40 20
Ct ht th 15 12 10
Ct ht mn 10 5 1
Ct pha 2 I 0.2
St pha 0,1 0,05 0,01
St 0,08 0,01 0,005

28
2.3. C N G T R N H TH U NC M T

2.3.1. N him v v c im

Cng trnh thu nc mt ngoi chc nng ly nc cn c nhim v x l s b qua

song chn v li chn rc. Do v tr tn ti v tnh cht ngun b sung m ngun nc
mt c nhng c th ring, khc hn vi ngun nc ngm. No chu nh hng trc
tip ca cc iu kin mi trng bn ngoi v tc dng do s hot ng ca con ngi.
Khi tnh ton cng trnh thu nc mt cn quan tm n mt s vn khc m n c
ngha quan trng sau:
- T l gia lu lng thu v lu lng nc sng khng qu 15%. Nu lng nc
thu vo ln qu s gy nh hng n ch thv vn ca sng.
- Ch thy vn trn sng nh hng nhiu n kt cu v cch thu nc ca cng
trnh. Trc ht cn quan tm n MNmax, MNmin, tnh hnh bin ng ca dng chy
v hi lng ph sa chn v tr ca thu nc hp l. Cc sng gn bin cn xt n s
nh hng ca thy triu.

c)

H n h 2.7: Cc lii mt ct SI1

29
 - Dng mt ct ngang sng nh hng rt ln n kiu loi cng trnh thu. Ty theo
dc h sng v hnh dng ca n, mt ct ngang sng c th chia lm bn loi:
- Dng b thoi (a).
- Dng b dc (b).
- Dng dc dng ng (c).
- Dng c thm (d).
Cu to a cht b sng v lng sng c nh hng n v tr v kt cu ciia cng
trnh. Ty theo bn vng v n nh ca t m quyt nh s dng cng trnh thu
kiu kt hp hay tch bit vi nh my bm.
Cng mt ngun nc nhng c th c nhiu mc ch khc nhau nn cn kt hp
hi ha cc mc ch s dng nc vi nhau.

2.3.2. Phn loi cng trnh thu

Thng thng c th phn loi theo cc yu t sau:

- Theo ngun thu: knh, sng, h cha,...
- Theo tnh cht xy dng: c' nh, ni, di ng.
- Theo thi gian phc v: lu di, tm thi.
- Theo v tr ly nc: gn b, xa b.
- Theo cch b tr cng trnh: ring bit, kt hp.
- Theo kiu vnh.

2.3.3. V tr t cng trnh thu

Thng chn thng ngun so vi khu dn c v cng nghip. Cn bo m cc

yu cu sau:
- Bo m ly lng nc yu cu cho trc mt v tng lai c cht lng tt v
c iu kin bo v ngun nc.
- C h thy lc ngun nc thun dng.
- B sng, lng sng n nh.
- a cht tt.
- Gn ni tiu th, ngun in, giao thng,...
- Qun l, vn hnh thun li.
- Trn on sng cong nn b tr 1/3 on cui b sng lm.
2.3.4. Cng thu nc ven b

p dng khi b sng dc su v cht lng nc cng tt nh gia sng. Cng trnh
thu nc v nh my bm c th b tr kt hp khi b c a cht tt hoc b tr tch
bit khi c b t xu.

a) L o i k t li)

Thng c th b tr theo cc s sau:

30
 - G i a n mv c b tr cao hn mc nc thp nht trong gian ht. Cng trnh loi
nv c s dng vi nn t chc, n nh. Khi vn hnh my bm phi mi nc.
- G i a n mv c c a o sn bng cao y cng trnh thu, thng c chiu cao ht
H s < 0 nn khi vn hnh mv bm khng cn mi nc. Loi ny c khi lng xy
dng ln v iu kin a cht km hn loi trn.
- G i a n m y b m kt hp vi gian thu v gian ht nc c 2 trng hp:
+ Dao ng mc nc sng nh, sn ng c b tr cao hn mc nc I1 nht v c
chiu cao ht Hs < Hckcp (chiu cao chn khng cho php).
+ Dao ng mc nc ln, s dng loi bm chm.
C n g tr nh thu loi ny c khi lng g i m hn nhiu so vi 2 loi trn.

3) b)

n h 2.8: c n trnh thu nc ven b

kt h(p

() N chi:
b) Nn n khn u, hi rc *am>
c) Nn ln khn u, ht trc (ii>
/- nyn thu nc
2- phU ct m y hn
3- l ti chu rc
4- bcrt ly tr rc m*an
5- hn /v tm trc ny
6- ca thu nc

C h ; Khi xy dng cng trnh kiu kt hp cn c bin php chng thm hp l

cho gian my.

b) L o i tch bit

Do iu kin a cht nn nh my bm phi t li xa vo trong b. Trong iu kin

cho php nn b tr NMB cng gn cng trnh thu cng tt, v s gp phn nng cao cao
trnh sn gian my.

31
 Hnh 2.9: Cni trnh thu nc loi rch hit
- ntn thu nc; 2- nn h t ; n i ll; 4- m y brti; 5- trm hni cp I

2.3.5. Cng trnh thu nc xa b

Nu b sng mc nc qu nng, b sng thoi, mc nc dao ng ln ngi ta

thng ly nc gia lng sng. Nc c l) vo t ca thu (hng thu) gia lng
sng v dn qua ng t chy vo cong irnh thu nuc nm st b. Nh my bm c th
b tr kt hp hoc lch bit cng trnh thu. Theo cch dn nc v ngn thu nc, cng
trnh c th chia lm 2 loi nh sau:
L o i dirn m> t chy:

Thng c s dng khi b sng thoi, su t ng khng ln lm. Nu dao ng

mc nc gia 2 m a ln, c th b tr 2 hng thu 2 cao khc nhau.

Hnh 2.10: Cn trnh thu nc xa b loi tch bit

1- Iih thu nc; 2- tii t c h y ; IHI tliu; 4- trm Ixmi cp ; 5- Nitn lt; 6- hn chn rin

32
 L o i il/i n xiphii:

Thng c s dng khi b sng khng thoi lm. Nu t ng t chy th su

t ng ln, iu kin thi cng v qun l kh khn, nn ng t chy s c thay th
bng ng xiphng. Do trong cng trnh cn b tr thm bm chn khng mi ng
xi phng. Khi nc sng ln n mc nc cao nht th ng xipng s lm vic nh ng
t chay.

H n h 2.11: CiU trnh tltu ni xa h loi kt h

- II .xi p l iii; 2- hovi chm khuv,. 3- ian m v

2.3.6. Loi kt hp thu nc xa b v ven b

Thng c ng dung vi b<* sng urng dc hoc c thm, v ma l thu nc

qua ca ly nc (2) cn ma kit ly nc qua hng thu (1).

H n h 2 .12: c'IH n inh thu lit vei v xa h loi kt hp

- hiii thu IIc; 2- ca thu nc

Khi lulng ca cng trnh nh, nc sng tng i sch v t rc c th dng

bm ht trc tip nc sng. Loi nv c u im l chi ph xy dng thp. Nhng do
mc nc sng dao nc v ng ht cli nn 2 an dt my bm thp hn mt t nhiu
bao dm iu kin ht nc ca mv bm. Vic qun l ng ht c kh khn hn.

33
 H n h 2.13: Hn thu nc
- / ht; 2- b dt n I h t ; s o n ; clin rc; 4- l thu nc; 5- si

2.4. TN H T O N M T s H N G M C C N G T R N H

2.4.1. Song chn rc

Thng c b tr ca thu nc ca cng trnh. Cu to ca n gm nhng thamh

thp c tit din trn <>8 hoc 10, hoc tit din ch nht (6 X 50m m ) t song lOing
vi nhau v hn vo mt khung thp. Khong cch gia cc thanh thp t 4 0 -5 0 n m .
Song chn rc c nng th nh rng rc hoc ti quay tay b tr trong ngn qu.i 1.
Hnh dng song chn rc cn ph hp vi hnh dng ca thu nc. Din tch cn t.c
ca song chn rc c xc nh theo cng thc:

co = K ,.K 2.K 3 (2.14)

v.n
trong :
Q - lu lng tnh ton ca cng trnh (nr/s);
V - vn tc nc chy qua song chn rc (m/s). Theo TCN 33 : 85 vn tc ny nr ly
t 0,4-0,8 m/s;
K - h s co hp do cc thanh thp, tnh theo cng thc:

K,= (2.1:5)
a
a - khong cch gia cc thanh thp;
d - ng knh cc thanh thp;

34
 - h s co hp do rc bm vo song. Thng ly K2 = 1,25;
K , - h s k n nh hng hnh dng ca thanh thp:
- Vi tit din trn lv K3 = 1,1;
- Vi tit din hnh ch nht K 3 = 1,25.
n - s ca thu nc.

2.4.2. Li chn rc (dng phng)

Cu to gm tm li cng trn khung thp. Tm li an bng cc dy thp c

d n g k n h <> = l - l , 5 m m . mt li 2 x 2 - 5 x 5 m m .

Trong mt s trng hp tng kh nng chu lc ca li cn b tr thm mt tm

li na c kch thc mt li 25x25 mm an bng dy thp c ng knh () = 2-3mm.

Din tch cng tc ca li c xc nh theo cng thc:

(!> = K ,.K 2.K, (2.16)

v.n
trong d:
Q - lu lnu tnh ton ca cnII trnh ( m /s);
V - vn tc nc chv qua li chn rc (m /s);
Li phng lV V = 0,2 - 0 .4 m/s;
Li quay ly V = 0,15 - 0,8m/s.
n - s c a thu nc;
K| - h s c o hp tnh llico c n g thc:

K( = (a + d r _(1 + p) (217)
a"
a - kch thc mt li;
d - dng knh dy an li;
K - h s co hp d o rc hm vo li. T h n g ly K t = 1,5;

K, - h s nh hng ca hnh dng thanh thp, K , = 1,15-1,5;

p - t l gia phn din tch khung v cc kt cu khc chim so vi din tch cng tc
ca li.

35
 BI TP

Bi 1. M t ging khoan c cu to:

ng vch : ng knh Dv = 50cm, chiu di L v = 25m;

ng lc : ng knh D|0 = 40cm , chiu di L|0 = 36m;
ng lng : ng knh D|a = 40cm , chiu di La = 5m;
Ti khu vc xy dng c mt ct a cht nh sau:
Lp 1 : ct c chiu su H | = 17m, dn sut thy lc K = 8m/ng
Lp 2 : st nng c chiu su H 9 = 8m (tng khng thm Ko = 0)
Lp 3 : ct, sn c chiu su H 3 = 40m , dn sut thy lc K 3 =25m/ng
Lp 4 : st cht kh su (tng khng thm K 4 = 0)
Mc nc ngm tnh tnh ton c cao trnh -15m (tnh t mt t), bn knh a ,h
hng ging khoan c xc nh qua kho st c R = 120m.
a) Cho bit tn loi s tnh ca ging khoan trn? V hnh v ghi ch cc thni s
tnh ton?
b) Xc nh mc nc ng trong ging khi bm ra lu lng Q = 200m 7ng
p s: b) -1 7,06m
Bi 2. Mt ging bm ng knh 50cm, lu lng bm 300ni'/gi' t mt tng tham
nc c p chicu dv 50m. H s thm k = 10 m/no. Cch trc ging 200m, ct nc
o p c ghi n h n l k h n c di v c CLIO + 15 0 m . G i n g d c k h o a n x u y c n q u a
ton b chicu dv tn s thm nc. y tnt thm nc cao + 30m.
a) Tim phng trnh ng ct nc o p.
b) Tnh gim ct nc o p ti thnh ging.
p s: a) H = 120 - 2.3 Ln(200/r);
b ) 15 .4 in .

Bi . M t tng thm nc k h n g p c y nm ngang cao + lOm.

K = lOm /ng. Noi ta k hoan mt ging ng knh 50cm n tn dv tang thm
nc. Trc khi bm , cao mt bo ho l + 30m . T ro n e khi bm , mc nc trong
g i n a c du y tr cao + 28m v ccli trc ging 2 0 0 m , cao d mt bo lio
c ghi nhn l k hn g di.
a) Tim phng trnh ng ct nc o p.
b) Tnh lu lng bm (m Vg).
p s: a) IT = 400 -1 1,37Ln( 200/r);
h ) 1 4 . 8 8 m :/g.

36
 Chng 3

THIT B V CNG TRNH PH BIN

TR O N G H TH NG C P NC

3.1. G I I T H I U

m t h thng cp nc hot ng trong khai thc, vn hnh, sa cha cn c mt

s thit b v cng trnh h tr. Trong chng ny s gii thiu m t s cc thit b
thng g p v cc cng trnh c xy dng trong m t h thng cp nc.

3.2 C C T H I T B V C N G T R N H PH B I N

3.2.1. Bm tng p

T ro n g trng hp p lc nc trong m ng li ng ng c nhng ni cc b khng

p ng gi tr yu cu ti thiu ngi ta s dng bm tng p. Thng thng, nc cp
n tt c cc ni trong khu vc thit k s c m bo nh vo cc bm tng p (gi
l bm c ct nc cao); cc bm ny s ly nc t cc bn cha nc iu ha ca h
thng. K hc vi ch lm vic trm lc, loi bm ny phi m bo tha m n cc
nhu cu ti mi thi im s dng nc. Ct nc s dng ti trm bm tng p bin i
theo a hnh ni xy dng, theo nhu cu nc, theo kt cu ca m ng li phn phi,
theo kch thc ng ng (ng knh). Vi cc vng t tng i bng phng, p
sut s d n g bin i trong khong 300 kPa n 600 kPa (30 n 60 m nc).
V tr lp t cc bm tng p c th ngay trong m ng li, hoc phi hp vi cc
bn cha nc v d nh i cha. Ty theo a hnh khu xy dng, c th trong mt s
trng h p p sut gia tng qu ln (v d, vng y ca thung lng hoc chn ca mt
sn i). Trong trng hp thng phi s dng mt thit b gim p.
Tron.e trng hp a hnh khu vc nghin cu thay i nhiu, khi quy hoch m ng
li c th chia ra lm cc tiu lu vc. vi mi tiu lu vc c a hnh tng i ng
u. T rong trng hp , chng ta s b tr cc van gim p nu chng ta phi gim p
(nc n t vng cao hn) hoc bm tng p nu chng ta phi gia tng p lc nc
(nc n t cc vng thp). Tm li, khi thit k m ng li ngi ta c gng thit k
to thnh tng vng trong p lc nc khng qu cao v cng khng qu thp.

3.2.2 . Van iu khin

T ro n g cng tc qun l, vn hnh mt h thng phn phi nc i hi mt s thit

b ch u y n dng. Trong s ny, van gi mt vai tr rt quan trng, bi v n cho php

37
iu tit dng chy trong mng li. Mt s van iu lit lu lng c trnh bv trong
hnh 3.1 sau.

b) c)
ng

d)

Hnh 3.1 : Cu lao mt s loi ran diu tit don ' chy
u) Van rb inet; h) Van hrii; 1) Va/ clap! mt <liicu,
(I) Van iim p trni thi n ; r m

Van /l^t (a, b) cho php chng ta tch mt vi on ng cn kim tra (thay th hoc
bo tr) ra khi mng li. Vi cc ng ng c ng knh ln (> 350 mm), la s
dng van bm, vi cc ng ng nh hn ta dng van robinet. Thng thng, van ph
trch cho cc on ng ng khng nn di qu 150-250 in. Vi cc ng ng chnh,
chiu di ny c th t n 300-365 m. Mt cch l tng, van nn t cc v tr
ng ng giao nhau.
Van clupet I cliin (c) cho php
dng chy i theo mt chiu duy Ngun nc cp

nht. Chng thng lp t trn

ng ng ni ca m ng li ca hai
< 250rr
tiu vng c p sut khc nhau, hoc
Irn ng ng y ca bm, hoc
trn ng ng lp t ng h nc. < 250m
van
Van im p (d) cho php a
p lc cao v p lc tiu c hu n
Hnh 3.2: B tr van troiy, i li
thit k.

38
 Van p h a o thng lp t v tr v o ca mt bn cha nc a hnh cao; khi nc
trong bn ny t n cao trnh mc nc ti a, van phao s c t ng ng li di
tc dng ca p lc nc. Mt dng van phao khc dng khng ch mc nc trong
cc b nc da vo nguyn l cho phep ni (ngt) mch in khi ng my bm.

3.2.3. Ni ng ng

D lin kt cc ng ng thnh mt mng li ngi ta phi thc hin cc ni

ng ng. C ba phng php ni c bn c th hin hnh 3.3.

a) b)

H L ,

c)

H n h 3.3 : Ct p l n plip Iii (Ii m;

li) N i c hc; b) N i lni>; (') N i vn kp

Hai loi ni (a) v (b) c dng cho ng ng

chn trong t. Loi mi ni (c) cho lin kt cc ng
cng hem c dng ni cc ng ng bn trong
cc kt cu (trm bm nc thi, trm x l nc
sinh hat, ...).

3.2.4. Ct ly nc cha chy

c b tr trn mng li ng ng cho php

ly nc e phc v cha chy. Phm vi phc v ca
mi ct ly nc ph thuc vo lu lng cn
cha chv; s lng cng nhiu v cng gn nhau khi
lu lng cn ly ln.
T hng thng, khong cch gia 2 ct lv nc
cha chv dc theo ng l khng vt qu 200 m
trong khu ph dn c. Trong cc khu ph thng mi
v nh cao cp, khong cch ny thng 100 m. N
cn c b tr ti cc giao l quan trng, dc theo Hnh 3.4: Ct nc cha chy

39
ng ph c m t din ko di, trong cc hm ct, trong sn ca cc c s c quy m
ln v xe cha chy c th vo c. Kt cu chi tit ca ct ly nc c gii thiu
hnh v bn cnh.

3.2.5. Bn cha nc

M t h thng phn phi thng thng c nhiu bn cha k c bn cha khu x l

nc trung tm. M i bn cha c cc nhim v sau y:
- Bo m s hot ng thng xuyn ca nh m y nh vo s cung cp nc t bn
cha trm x l trung tm: trong chu k c nhu cu dng nc nhiu, s vt qu ca
nhu cu so vi kh nng cp nc ca trm x l ti m t vi thi on, nc s c h
sung ly t cc bn cha.
- Cung cp m t phn lng nc khi c ha hon.
- T h a m n m t phn nhu cu nc khi c s c trm x l hoc s c trn ng
ng dn nc chnh hoc ph.
- G im s thay i qu nhiu ca p sut trong ng ng bng cch s d n g nhu
bn cha trong m ng li trong chu k s dng nc nhiu.

3.2.5.1. P hn loi bn cha

Ta c th phn loi bn cha theo cc tiu chun khc nhau:
P hn loi theo m c ch s d n g bn cha:
Bn cn bng: Trong chu k hot ng 24 gi ca m ng li, khi nhu cu nc vt
qu kh nng cp ca trm x l trung tm, bn cn bng s hot ng. Bn cha trm
x l trung tm lc ch c th m bo nhu cu nc dng mt phn. T heo kinh
nghim , th tch bn cha cn bng chim khong 20% lng nc s dng trong ngy.
Cp nc cho m t khu ph, m t thnh p h s c tnh cho ngy tiu th ln nht.
Bn cha d tr nc cho ha hon: phng ha hon, trong thit k chng ta
phi d kin m t th tch nc nht nh d tr phc v cho m c ch ny. T h tch
cn thit s c quy nh t quy phm vi cc yu cu cn phi tha mn nh sau:
- Lu lng cn thit chng m t hay nhiu ha hon ng thi.
- Thi gian dp tt ha hon.

- p lc nc yu cu ti thiu ti cc a im ly nc phng ha hon.

M t cch tng qut, ta d kin cho trng hp ch xy ra mt trn ha hon trong

thi im phi cung cp nc cho ngy s dng ln nht. K hng xt cho trng hp tiu
th gi ln nht.
Bn cha nc d tr cho trng hp khn cp: y l lu lng cn thit trong
trng hp xy ra khng lng trc c trn m ng li, v d: h ng n g dn
chnh hay bm.

40
 Bn cha nc cho sn xut: D tr trong trng hp khi c s c' xy ra cho trm x
l trung tm. Lng nc d tr ny thng ly bng 4 gi hot ng ca trm v nm
ngay v tr trm x l trung tm.
Phn loi bn cha theo v tr:
T hng thng ta c hai loi bn cha: i nc v bn cha m t (xy dng cao
lng ng vi m t t).
i nc: Bn cha nc s c thit k nm trn mt kt cu (cao n 20m-30m)
Nc s c a ln i nh vo m t bm tng p (nu cn thit) trong chu k s dng
nc t v s chy ra khi i i vo m ng li, di tc dng ca trng trng, trong
chu k s dng nc nhiu. T hng thng nc vo v ra khi i s i trn cng mt
dng dn. Hnh v sau y trnh by s lm vic ca mt i nc:

, ___ Dng ct nc
/ o p

H n h 3.5: H o t (n i nc tro n h thng

U im :
- S phn phi nc c sn trong i nc l khng gin on khi c s c ca bm
tng p hoc ng dn nc chnh, ph.
- Bm dng cp nc vo h hot ng khng cn lin tc.
- S la chn v tr hp l ca i nc cho php gim s thay i p sut theo khng
gian trong mng li (phn phi p sut trong mng li iu ha hn).
Khuyt im:
- V tr la chn ca h cha phi bo m sao cho duy tr c p lc cn thit trong
mng li khi nc trong i v tr thp nht; trong m t s trng hp, m t phn nng
lng dng a nc vo h b lng ph.
- Th tch d tr i nc ti a l gii hn, bi v chng ta ch c th lp t cc
loi bn cha c trong th trng.

41
 - Trong mng li, p lc to ra t i nc c th b thay i sau khi lp t i
nc bi v ta khng th thay i li thit k chiu cao i nc.
- Trong chu k s dng nc t, nht l trong giai on mi a vo s dng, chng
ta s khng s dng nc d tr trong mt thi gian di (c th n nhiu thng). Tht
vy, do p lc to ra chn i nc ca cc bm tng p c th vt qu gi tr i
nc cp nc i vo mng li. iu nv c th nh hng n cht lng ca nc.
- Mt phn dung tch ca i nc s khng c s dng trong mt s iu kin. V
d p lc trong m ng li l thp hn so vi d kin v lu lng s dng ln hn so vi
trc . Mc nc nh nht trong i c th xc nh khi thit k.
Tm li, s xy dng i nc trong h thng ngoi nhim v to ra th tch nc d
tr trong m ng li, i nc cn to ra v iu ha p lc nc trong mng li. p lc
nc sinh t i hon ton ph thuc vo mc nc ti thi im kho st, khng th
kim sot c. Tuy nhin ta c th kim sot d dng trong trng hp nu s dng
bm tng p trong h thng.
Bn cha b mt: Nc d tr cng c ih c c nh vo cc bn cha xy dng
cao trnh mt t (c th cao hoc thp hn mt t so vi mt t). Cc trm bm tng p
ly nc t cc bn cha a nc c p vo m ng li khi p lc nc trong mng
li gim. Cc u im ca loi b cha mt ny nh sau:
- Gi thnh xy dng v khai thc loi hn nv thp hn so vi i nc.
- Cht lng nc trong hn loi ny thng tt hn, c t nguy c nc b tn lu
ngy trong bn cha.

- p lc nc d dng kim sot nh vo bm.

- V mt m quan, s hi ha ca loi bn cha ny vo khng gian vi mi trng
chung quanh d dng hn.
- V tr t bn d xc nh.
- C th ch ng thit k v chn kcn thc bn m khng ph thuc vo th trng.

3.2.5.2. D u n g tch iu ha
Dung tch iu ha, theo nh ngha, l dung tch cha nc ln nht cn c ca
cc i nc (b cha nc) b sng vo mng li cp nc khi nhu cu s dng ln
hn kh nng cung cp ca trm bm cp 2, trong mt chu k hot ng. Nh vy, theo
nh ngha, dung tch iu ha s ph thuc khng nhng vo ch s dng nc, m
cn ph thuc vo ch cp nc vo h thng. Ni mt cch khc i. s khc
bit gia nhu cu s dng v c h cp nc cng t, dung tch iu ha yu cu s b,
v ngc li. Do , trong mt h thng cp nc, gim nh dung tch iu ha, ta c
th b tr hot ng ca trm bm cp 2 theo nhiu cp lu lng khc nhau, thay v
trm hoi ng vi lu lng khng i Irong sut mt chu k hot ng (ngy).

42
 S tiu th nc cho mt ngy in hnh c th trnh by bi s sau y:

H n h 3.6: Dng hiu d tiu th nc

V d 1. Mt h thng cp nc sinh hot cho khu dn c c lu lng tnh ton ngy

dng nc ln nht W (m ). Cho bit h s khne; diu ha gi dng nc ln nht l
K-h-max = Nc c cu ng cp bi trm bm cp 2 hot ng theo c h mt cp lin
tc v c lu lng khng i trong ngv. Xc nh dung tch iu ha cho h thng.

Gi 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9

Dng % w 1,50 1,50 1,50 1,50 2,50 3,50 4,50 5,50 6,50
Cp % w 4,1667 4,1667 4,1667 4,1666 4,1667 4,1667 4,166 4,1667 4,1667
Dng - Cp -2,667 -2,667 -2,667 -2,667 -1,667 -0,667 0,333 1,333 2,333
Cng n -2,67 -5,33 -8,00 -10,67 -12,33 -13,00 -12,67 -11,33 -9,00

Gi 9 -10 10-11 11-12 12-13 13-14 14-15 15-16 16-17 17-18

Dng % w 6,25 6,25 6,25 5,00 5,00 5,50 6,00 6,00 5,50
Cp % w 4,1667 4,1667 4.1667 4.1667 4,1667 4,1667 4,1667 4,1667 4,1667
Dng - Cp 2,083 2,083 2,083 0.833 0,833 1,333 1,833 1,833 1,333
Cng dn -6,92 -4,83 -2,75 -1,92 -1,08 0,25 2,08 3,92 5,25

Gi 18-1 19-20 20-21 21-22 22-23 23-24

Dng % w 5.00 4.50 4.00 3,00 2,00 1,25
Cp % w 4,1667 4,1667 4,1667 4,1667 4,1667 4,1667
Dng - Cp 0.833 0,333 -0,167 -1,167 -2,167 -2,917
Cng dn 6.08 6.42 6,25 5,08 2,92 0,00
Dung tch iu ha \ v lh = 6.42f' \v - ( - 1 3 , 0 m v = 19.42% w

43
 3.2.5.3. D u n g tch ca b v i nc

Trn c s dung tch iu ha, dung tch ca b hoc i nc c xc nh nh sau:

(3.1)

W b = w dh + w b l + w j (3.2)

trong :
w , w b - dung tch i nc, b cha nc.
w h- dung tch iu ha i cha, b cha.
w , - dung tch nc d tr cha chy trong 10 v trong 3 gi.

w bt- lng nc dng cho bn thn trm x l, ly s b bng 5-10% cng sut
ca tram.

3.3. T H N G S C H N H T R O N G H T H N G C P NC

3.3.1. p sut ti thiu v p sut ti a

tha mn nhu cu ca ngi s dng, nc cung cp t m ng li n ni tiu th

cui cng phi t c mt p sut ti thiu. Nc phi n c cc tng bn trn ca
h tiu th nc, cho php s dng mt cch c hiu qu cc thit b gia dng: my git,
vi ly nc... l l do ti sao h thng phi m bo mt p sut ti thiu ti im
ly nc vo dn v s dng. p sut yu cu ph bin l 150 kPa (14 m H 20 ) , ta thy
y cng l p sut cn c ct ly nc cha chy. Trong thc t, cc loi my git,
my ra hot ng tt, p sut ti thiu phi t n 225 kPa (21 m H 20 ) . Trong nh, p
sut ti a cho php l 500 kPa nhm m bo an ton cho cc mi ni ng ng. Vi
p sut 500 kPa, nc c th cung cp cho cho m t nh 5 tng, khng cn phi b tr
bm tng p b sung.

3.4.2. Vn tc dng chy

ng ng phn phi nc th n g thng c th i t k vi vn tc gii hn
V m;lx = 2,2-3,0 m/s. iu ny nhm trnh hin tng mt nng lng (tnh bng m H 20 )
sinh ra do ma st gia nc chy v ng ng dn qu ln. Vn tc ln nht cho php
ny cn c tc dng lm chm qu trnh xm thc ng dn. v vn tc ti thiu, theo
kinh nghim m bo cht lng nc ta nn chn V mln khng nh qu 0,3 m/s.
Cng phi lu n vic hn c h hoc loi tr hin tng nc va xy ra trong ng
ng; l hin tng gia tng (gim) p sut t ngt khi c s ng (m) van nhanh
hoc dng (khi ng) bm t ngt.

44
 BI TP

Bi 1. Mt h thns cp n ir c sinh hot cho khu dn c c lu lng tnh ton ngy

cins nc ln nht W(m'). Cho bit h s khne iu ha gi d n g nc ln nht l
K|vniax = 1,5. Nc c cung cp bi trm bm cp 2 gm 2 bm ging nhau, hot
d n g theo c h 2 cp. Bm 1 hoai ng lin tc 24h v bm 2 hot ng t 3h v kt
thc lc 19h. Xc dinh dung tch iu ha cho h thnu. Hy cho bit lc no mc nc
trong i cao v thp nht.

Gi 0-1 2-3 3-4 40 5-6 6-7 7-8 8-9

Dng% w 1,50 1,50 1,50 1,50 2,50 3,50 4,50 5,50 6,50
( 'prr w (bm 1) 2,5 2,5 2 5 2,5 2,5 2,5 2,5 2,5 2,5
'p( w (bm 2) 2,5 2,5 2,5 2,5 2,5 2,5
1)na-Cp -1.0 -1.0 -1,0 -3.5 -2,5 -1.5 -0,5 0,5 1,5
( ono dn - .0 -2.0 -3,0 -6.5 -9,0 -10.5 -11,0 -10,5 -9,0

Ci MO 10-1 1 11-12 12-13 13-14 14-15 15-16 16-17 17-18

1)ngf>f w 6,25 6,25 6,23 5,00 5,00 5,50 6,00 6,00 5,50

( ' p c ( vv (bm ) 2,5 2,5 2.5 2,5 2,5 2,5 2,5 2,5
( apO w (bm 2) 2,5 2,5 2,5 2,5 2,5 2,5 2,5 2,5 2,5

Dnu-Cp L2S 1,23 0.00 0,0 0,5 1,0 1,0 0,5

( V)im
Cr don -7,75 -C0 -5,25 -5,25 -5.25 -4,75 -3,75 -2,75 -2,25

(i 1<S-10 19-20 20-21 1 \-2~> 22-23 23-24

1
l ) n a r' vv 5,00 4,50 4,00 3,00 2,00 1,25
( p rY\v (bm 1) 2,5 2,5 ' 2,5 2.5 2,5 2,5

( a p c; \v (bm 2) 2,5 0 0 0 0
0
Pnu-Cp 0.0 2,0 1,5 0,5 -0,5 -1,25
( 'ne dn -2.25 -0.25 1,25 1,75 1,25 0,00

Duni tch iu ha : \ V lh = \ v - (-1 l,())fV\V = 1 2 , 7 5 % w

Bi 2. S liu hai n h hi 1. Xc nh duiiu lch dicu ha trong trng h p b m 2 bt
(iu 1c 5h v kt (hc lc 21 l.

p s : W th 8,75% w

45
 Bi 3. S liu bi nh bi 1. Gi thit bm 2 chy lin tc 15h trong ngy. Xc nh
thi gian bt u v kt thc bm 2 dung tch iu ha h thng b nht.
Bi 4. Cho mt h thng cp nc sinh hot cho khu dn c c lu lng dng tnh
ton trong 1 ngy dng nc ln nht l w (rrv). C h dng nc theo tng gi c
cho trong bng sau :

Gi 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9

%w 0,815 0,815 1,282 1,903 3,868 3,158 4,072 8,716 8,541

Gi 9-10 10-11 11-12 13-14 14-15 15-16 16-17

%w 6,619 5,532 5,532 5,005 3,668 5,416 8.813

Gi 17-18 18-19 19-20 20-21 21-22 22-23 23-24

%w 7,901 6,271 1,843 2,076 2,093 0,900 0,629
cung cp cho nhu cu ny, trm bm cp 2 hot ng theo ch bm 1 cp vi
lu lng khng i t 4h n 20h. Xc nh dung tch iu ha. Hy cho bit lc no
mc nc trong i cao v thp nht.

B i gii:

Ci 0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8

Dng p>w 0,815 0,815 1,282 1,903 3,868 3,158 4,072 8,716
Cp% w 0 0 0 0 6,25 6,25 6,25 6,25
Dng-Cp 0,815 0,815 1,282 1,903 -2,38 -3,09 -2,18 2,466
Cng dn 0,815 1,63 2,912 4,815 2,433 -0,66 -2,84 -0,37

Cii 8-9 9-10 10-11 11-12 13-14 14-15 15-16

Dng r/fW 8,541 6,619 5,532 5,532 5.005 3,668 5,416
Cp % vv 6,25 6,25 6.25 6,25 6,25 6,25 6,25
Dng-Cp 2,291 0,369 -0,72 -0,72 -1,25 -2,58 -0,83
Cng dn 1,92 2,289 1,571 0,853 -2,11 -4,69 -5,53

Gi 17-18 18-19 19-20 20-21 21-22 22-23 23-24

Dng^/ w 7,901 6,271 1,843 2,076 2,093 0,9 0.629
Cp9f w 6.25 6.25 6,25 0 0 0 0
Dng-Cp 1,651 0,021 -4,41 2,076 2,093 0,9 0,629
Cng dn -1,31 -1,29 -5,698 -3,62 -1,53 -0,63 0

Dung tch iu ha : w dh = 4,815 - (-5,698) = 10,5 13%w.

46
 Chng 4

H TH N G CP NC CHO KHU v c

4.1. G I I TH IU

Nh trnh by cc chng trc, mt trong nhng cng tc u tin ca mt k

s thit k h thng cp nc l phi xc nh lu lng nc cn phi cung cp cho khu
vc thit k nhm tha m n cho nhu cu s dng hin ti v k c d kin pht trin
trong tng lai. Cc nhu cu c bn bao gm: nc sinh hot, nc cho cng nghip,
cho thng mi cng nh nc d kin trong cha chy... Kt hp vi cc s liu v quy
hoch h tng v cc cng trnh khc trong khu vc, s tin hnh thit k mng li
phn phi thch hp. Trong chng ny s gii thiu cc ni dung cn thc hin v
phng tin cn c mt k s tin hnh thit k mt mng li cp nc mi hoc
phn tch, nh gi hot ng mt mng li hin hu,
Mt mng li phn phi nc bao gm nhiu loi ng ng dn khc nhau, ta c
th phn loi theo:
+ Nhim v;
+ Kch thc (ng knh):
- ng ng chnh.
- n g n g ph.
- ng ng cc b.
ng ng chnh
ng ng chnh c nhim v chuyn nc t trm x l trung tm hoc cc trm
bm n cc khu ph khc nhau ca thnh ph. ng knh ti thiu ca ng chnh l
300 mm. Trn cc ng ng ny c cc bung thot nc nhng im thp (tho cn
nc khi cn thit) v cc l thng cc im trn cao (dng rt kh ra hay bm kh
vo tv theo yu cu). Ch i vi ng ng chnh s khng cho php c nhnh r
ly nc trc tip vo n v s dng.
ng ng ph
Loi ng ng nv c ng knh dao ng t 250 mm n 300 mm. N s rp ni
cng vi cc ng ng chnh to nn mt mng li, ta thng gi l mng li cp
nc bn ngoi. Cc ng ng ph cch nhau khong 1000 m. C th thc hin cc
nhnh r vo tng n v s dng nc trn loi ng ng ny.

47
 ng ng c c b
Cc ng ng cc b thng c kch thc nh hn ng ng ca mng li ni
trn. ng knh khng nh hn 150 mm nu m un m bo chng li hin tng ha
hon. Ngoi ra, theo nh ngha, loi ng ng nv ch phc v cho mt vi ng ph.

Nt, vng v im ly nc
- Nt c nh ngha l im - ni ni lin hai hay nhiu ng ng, hoc ti v tr
nc ly ra khi hay a vo m ng li.
- Ta gi vng l mt cu trc c to bi ba hay nhiu hn cc ng ng hnh
thnh mt mch khp kn. Thng thng, mt mng li phn phi nc l mt mng
li c to bi nhiu vng.
- im ly nc l cc v tr trn m ng li, nc s c a vo hay ly ra d
phc v cho n v s dng nc. Theo quy c, im ly nc s c thc hin cc
im nt ca mng li hay ti cui cc ng ng dn cc b.

Hng pht trin

Hnh 4.1: Mi li vm*

13 X 14 15 yt

Hng pht trin

&

5 6 7

Gh ch;
* 10 11 X 12

: ng ng chnh Hng pht trin
: ng ng ph
C^) : Bn mrc
2 : Trm bm cp 2 H n h 4 2 : M t * l ri CH

48
 V nguyn tc, mng li vng sc lm vic an ton v mt cp nc hn l m ng li
c t . tr o n g khi m n g li ct thng cho gi thnh thp hn.

4 .2 . YU CU I VI M NG LI

e s phn phi nc hot ng mt cch bnh thng, mt m ng li phi tha cc

tn h cht sau:
- p sut cn thit.
- Lu lng v th tch nc nhn c theo im vu cu trong sut qu trnh hot
n g ca h thng.
l l do ti sao ngi k s phi xc nh c cc tnh hung bt li nht c
th thit k mng li hot ng mt cch hiu qu trong bt k trng hp no. Vn
s dc cp chi tit hn trong cc mc sau y.

4.2.1. S tiu th nc vo gi cao im

Ngi thit k phi hao m rng mng li phi hot ng mt cch hiu qu cc
gi cao im cho hin tai cne nh trong tng lai. Theo kinh nghim, ngi ta nhn
tliv lu lng gi ln nhi trorm mt nm, bin thin t 2,25 n 4,5 lu lng gi
trung bnh trong nm.

4.2.2. Tiu th nc ngy ln nht v trng hp c xy ra ha hon

Trong thit k phi cnh gi s hot ng ca m.ina li trong trng hp c ha

ho an xy ra trong nguy ticu th nc ln nht trong nin. Kinh nghim cho thy lu
lng ny dao ne l 1.5 dn 2 ln lu lng trung bnh ngy ca nm tng ng.
N goi ra, ta cng phi (l kin trng hp c hai ha hon xy ra ng thi trong khu
vc v lu kho sl cho cc trng hp c v tr xy ra ha hon khc nhau.
4.2.3. Tiu th nc ngy ln nht trong trng hp c s c mt ng ng
chi nh hoc ng ph
Trong vn hnh, vn nghin cu ch vn hnh ca h thno mng li trong
trng hp mt on ng ng c s c v k lng hot ng xy ra trong ngy c tiu
thi nc ln nht l rt quan trng v thng hay gp. Trng hp ny ta phi tin hnh
bo tr hoc sa cha ng nR . iu ny khn? c ngha l ta loi ra khi mng
li nhng ng ng quan trng nghin cu vi mc ch thay vo mt ng
n;j dn mi song song vi n trong h thng. Mc ch cho nghin cu ny nhm kho
st s phn phi li dng chv trong tnh hung nh vy v s a vo mt s hiu
chinh m ng li cho ph hp hn, trong trng hp cht lng phc v ca mng li b
n h hng ng k.

4.2.4. Cc trng hp c bit

T r o n g thit k cn thit phi m phng c h thy lc h t h n g t ro n g m t s tr ng

h p vn hnh c bit. V d, i cha nc c th dc lm y sut trong mt chu k,
n h t l v b a n m . khi s tiu th nc l nh nht.

49
4.3. CC BC T H I T K M N G LI PH N PH I N C

Thit k mt mng li phn phi nc bao gm nhiu bc v ni dung trc khi

a ra phng n chn sau cng. Cc ni dung c bn c th tm tt bi s sau y:

Nhn nhim v
K ho st dch v hin hu:
Mng li cng thu
Mng li phn phi
N ghin cu khu vc thit k v nc
cc nhu cu hin ti v tng Mng li phn phi gaz
lai: Mng li phn phi
a hnh in
a c h t Mng li phn phi
in thoi.
Ngun nc
Quy hoch th
Dn s
Cc loi i tng tiu th
nc
Nhu cu nc cng nghip N ghin cu cc phng n
kh thi v nghin cu kinh
t.

H n h 4 3 : N i duni thit km n t li phn phi HC

4.3.1. Nhn nhim v

Ngi k s thng nhn cc yu cu mt cch c th, chn h xc v chi tit t cc

t chc c trch nhim (thng l cc t chc nh nc ch u y n ng nh). T rong , ta
s xc nh ranh gii thit k ch o khu nghin cu m t cch chnh xc cho hin ti v
c tng lai.

4.3.2. Kho st cc cng trnh hin hu

Ngi k s s nhn c t c quan chc nng v c thm quyn cc ti liu quy

hoch mi nht lin quan n cc m ng li cng thu nc cng nh cc bn ch dn
v cc mng li phn phi gaz, in, in thoi... Cc ti iu ny phi th hin y
cc thit b v cc cng trnh hin hu: ng dn, trm bm, van, bn cha...

4.3.3. Nghin cu khu vc, xc nh cc nhu cu nc cho hin ti v tng lai

Cc ni dung nghin cu bao gm cc vn sau:

Nghin cu tm tt mi trng vt l v a cht.
Nhn dng s phn b hin ti v tng lai ca khu vc: phn vng, nhn khu...
nh gi s tiu th nc hin ti v tng lai nh vo cc thng tin hin c (sn
lng nc ca nhng nm gn y, s s dng nc ca cc Cng ty, X nghip, cng

50
nghip, thng mi... da vo ng h nc). Cc k s c nhim v xc nh vi
chnh xc cao nht c th c c:
- Lng nc tiu th sinh hot.
- Lng nc tiu th cho thng mi.
- Lng nc tiu th cho cng nghip.
- Lng nc tiu th cho cc cng trnh cng cng: cy xanh, cng vin...
- Lng nc tiu th cho cc c quan hnh chnh s nghip.
- Tn tht.
- Lng nc bin ng ca cc s dng ny.
- Biu s dng nc ngv ln nht ca nhng nm cui.
. Thit lp cc tiu chun cho php nghin cu mng li hin hu v pht trin trong
tng lai.
. Xc nh cc tiu chun gii hn cho php, theo nu vt qu phi thit k li
m ng li.
Nghin cu s thay i v p sut, lu lng ca mng li vi cc iu kin hin
ti. V d, so snh kt qu m phng c t m hnh v s liu o c trn thc t.

4.3.4. Phng n kh thi v phn tch ti chnh, kinh t ca d n

Cc vn sau y s c gii quyt:

C c p h n g n tu y n khc n h a u c h o n g ng chnh v ph .
. nh gi s m rng vng phc v cho mi nt v tnh ton lng nc ly t cc
nt ny tv theo cc trng hp ti hn khc nhau.
M phng mng li vi nhiu tnh hung ti hn khc nhau.
Phn tch ti chnh v kinh t: gi thnh thc hin, gi bo tr, khai thc cho nhiu
phng n kh thi khc nhau.

4.3.5. Chon phng n

S la chn phng n cui cng s da vo:

- Mng li tha mn tt nht cc yu cu v k thut v kinh t.
- Lp bng bo co chi tit cho c quan chc nng, trong trnh by r phng n
chn, gi thnh thc hin v tin thc hin.

4.4. NI DUNG TNH TON M A N G LI

tin hnh nghin cu thy lc mt mng li phn phi nc, ngi k s thng
c mt vi phng tin v cng c m ta s cp sau y. Cc kin thc thy lc cn
thit phi c v pht trin cc phng trnh ton c s dng phn tch v thit k
m ng li thy lc cho dng chv c p.

51
 4.4.1. Chn s b ng knh ng ng

Trc khi c th m phng mng li cho nhiu trng hp khc nhau v tiu th
nc, ngi k s phi la chn s b kch thc v v tr ng ng. D nhin iu ny
i hi mt kinh nghim nht nh v ng thi p dng mt vi nguyn tc, quy phm
v tiu chun s gip cho vic la chn d dng hn.
Cc tiu chun v nguyn tc c bn nh sau:
- ng dn c ng knh nh hn 150 m m ch c th cho php nu khng phi bo
m vic bo v chng li ha hon.
- Trong mng li, khi ng ng dn ng knh 150 m m di hn 180 m, cc ng
ng giao nhau phi c ng knh t ra cng 200 mm. iu ny nhm gim thiu s tn
tht thy lc.
- Trong cc nhnh ct hoc cc h thng c m ng li tng phn, ngi ta yu cu
s dng ng ng c ng knh ti thiu cng 150 mm.
- i vi ng ng dn ph, thng c li hn khi ta d kin hai ng dn c
ng knh nh hn trong mt vi ng ph thay v chn duy nht mt ng c ng
knh ln. Trong trng hp ny khai thc mng li s c linh ng hn.
- Khi mun vt qua ng xe la, sng, xa l (hoc tt c cc vt cn c quy m
tng ng), nn chn phng n c nhiu im vt nhiu v tr. iu ny cn c
li cho php khai thc mng li mt cch linh ng.
- Chiu di mi cnh m ng li ti a l 350 m.
- Chiu di mi cnh ng ng ph ti a l 900 m.
- Tc dng chy trong ng trong iu kin khai thc bnh thng nn dao ng
trong khong t 0,8 m/s n 2,5 m/s.
- Vn tc ti thiu ca dng chy trong ng trong chu k s dng nc t, v d ban
m, khng c nh hn 0,3 m/s ( phng hin tng lng ng cc cht l lng
trong ng ng).
- p sut nc nh nht trong m ng li dng trong mc ch phng chy khng nh
hn 150 kPa.
- p sut ln nht ti tng h tiu th khng c vt qu 500 kPa.
Cc m phng s hot ng h thng thng qua vic tin hnh gii cc bi ton tnh
thy lc m ng li cho php nh gi cc la chn ban u ny. T phn tch kt qu s
pht hin cc v tr c p lc nc qu b hoc qu ln. Cng thng qua cc m phng
s b ny ta s xc nh c cc ng ng c vn tc dng chy qu ln hoc qu
nh. T tin hnh cc thay i thit k cn thit v tip tc thc bin cc m phng
mi cho n khi tm c li gii cui cng.
Xc nh ng knh ng ng theo kinh nghim
Xc nh ng knh ng ng l mt bc quan trng trong thit k h thng mng
li bi v gi thnh ca n gi mt t l quan trng trong tng gi thnh ca h thng.
Gi s vi ng ng dn trn ta c:

52
 7d
Q = coV = V (4.1)

do : d=. $ = f ( Q .V ) (4.2)

vi:
Q - lu lng qua ng.
to, d - tit din, ng knh ng ng.
V - vn tc trung bnh dng chy trong ng.
Ta thy, dn mt lu lng Q cho trc, khi Vtng th d gim v ngc li. Ngoi
ra, khi V tng ta s chu tn tht nng lng (ct nc) ln v ngc li. Ta c th minh
ha tm tt hin tng bng th sau y:

Chi ph u t cho
ng ng (T2)
Tng chi ph
(T )

min
Chi phi do tn tht
nng lng (T,)

V (m/s)
opt

H n h 4.4: Q uan h ii a vn i 17/ ( hi p h i

vi T : c h i />///, V . vn t c n u i hnh r o /.

Theo biu ta nh ngha V gi [ vn tc kinh t, l vn tc cho php ta cc

tiu ha gi thnh ca tng th cne trnh. Trn c s gi tr V J ta s xc nh c
dng knh kinh t tng ng ca ng ng.
Trong mt s trng hp v thiu d kin thit k, ta c th xc nh ng knh kinh
l s b nh vo kinh nghim sau y:

Bng 4.1: ng knh kinh t S b theo vn tc

(mm) 100 150 200 250 300

vp,(m/s) 0.15-.86 0,28-1,15 0,38-1,43 0,38-1,47 0,41-1,52

ci(mm) 350 400 450 500 600

vp,(m/s) 0.47-1,58 0.50-1,78 0,60-1,94 0.70-2,10 0,95-2.6

53
 Ngoi ra cng thc kinh nghim sau y c th dng xc nh s b ng knh
ng d (m) khi bit lu lng qua ng Q (mVs):

d = (0,8 + 1,2)Q '42 (4.3)

Trong khai thc, ta c cc loi ng ng c bn sau y:

- Ong b tng ct thp, c cc loi <>400, (>500, 600, ()700, () 1000 chiu di thng
L = 4 m. ng c th chu p lc p e ( 10-20) N/cm 2
- ng gang c cc loi <)50, ()75, () 100, () 150 c th chu p lc n p = 30 N/cm :
- Ong nha (>e( 15-300) c th chu p lc n 20 N /cm 2
Trn c s cc ng knh s b, s la chn ng knh cui cng s da vo tnh
ton Ihy lc mng li nhm tha mn cc ch tiu k thut yu cu.

4.4.2. Q uan h gia lu lng v tn tht ct nc trong np ng c p

Mt cch tng qut quan h gia tn tht nng lng dng chy dh v lu lng Q
trn mt ng ng c dng nh sau:

dh = K Q m (4.4)

trong :
K - mt hng s. ph thuc vo c tnh hnh hc ca ng v n v s dng,
m - mt thng s ph thuc vo ch dng chy trong ng (chy tng, chv ri,
chy qu ). Trong m e [ l ; 2 ] ; m = 1 trng hp dng chy tng v m > l
tng ng cho dng chy qu hoc hon ton ri.
Trong trng hp dng chy trng thi qu , cng thc thc nghim ca hai tc
gi Hazen-W illiams c s dng rng ri nht. dc thy lc J = clh/dx theo cc tc
gi nh sau:
I ,X52
6,827 V
J= 67 (4.5)

t().54 .0.63
hay: V = 0 , 3 5 4 4 x C HW X J X d (4.6)

hoc tnh dc thy lc theo lu lng Q (n r/s) nh sau:

dh 10,679 _ q !. x s 2
J= 1 4. s 71 I. X5 2
(4.7)
L d C|w

trong : C |1W ty thuc vo loi ng ng, gi tr nh sau:

Bng 4.2. H s C,IW

Loi ng ng st c Ong b tng ng nha ng ihp

cw 130-140 120-140 140-150 140-150

54
V1 quan h gia lu lng v tn tht nh sau:
0, 63
0, 54
Q =A X V =
4
xO ,849xC HVV '- 1
v4 J (4.8)

trong :
dh - vi phn tn tht nng lng tnh bng mHjO.
L - chiu di on ng tng ng.
d - ng knh ng ng dn.
C1IW- h s theo Hazen-Williams.
J - dc thy lc (dh/L).
T ta c quan h sau:
0, 54
Q = K '( h L) (4.9)

85:
hoc: dh KQ (4.10)

PL
vi: K = (4.11)

Bng lp sn sau y cho php xc nh gi tr ca p theo cc n v tnh khc nhau

Bng 4.3: Gi tri 1^ theo cc on v s dung khc nhau

dh (m)

Q mVs 1/s 1/s m7s

d m mm cm mm
L m m m m

p 10,679 1,218x10"' 163874 4,38x10'-

Mt kt qu thc nghim khc c th tham kho ca tc gi Blasius nh sau:

, 0,316 V2
J 77s~ x (4.12)
IC 2gd

vi Rc biu th s Reynolds p dng trong trng hp 400 < Rc < 10" v l ng trn.
Trn c s ny ta s bin di cng thc v dang tng t nh ta lm cho trng
h p c a Hazen-Wlliams ni trcn.

4.4.3. ng ng tng ng

Trong mt s trng hp c th. gim khi krng tnh ton cho mt mng li
ngi ta c th thav th nhiu ng ni trong mang li bi mt ng ng tng
ng (ng ng tng tim). Mt cch tng t, d tnh ton p lc, ta c th thay

55
th mt vi phn t trong m ng li (co, ni, van...) bi ng ng tng ng. V
nguyn l, trong tnh ton c th thm vo cc ng dn cc ng ng c cng ng
knh v chiu di cn thit sao cho s tn tht nng lng dng chy trn bng vi
tn tht xy ra trong thc t.
Sau y s nghin cu lm th no n gin ha m ng li nh vo cc ng ng
tng ng cho cc trng hp c bn: thay cc ng ng song song hay ni tip bi
ng ng tng ng; thay th cc thit b gy tn tht ct nc (kha ni, b phn
lin kt...) bng ng ng tng ng.
ng ng ni tip
Mt ng ng tng ng vi hai ng ng ni tip l mt ng ng ti cng
lu lng v c tn tht ct nc bng vi tn tht ct nc gy ra bi h thng hai
ng ng ni tip ban u. Tt c cc ng ng tha m n cc tnh cht trn c gi
l ng ng tng ng. Vi gi thit l tn tht ct nc nh nhau, c th xc nh
tn tht dng chy trong ng ng tng ng trong trng hp hai ng ni tip nh
vo phng trnh sau y:

(<">L ) = ( * - ) , + ( ^ > 2 = ? ( * , . ) ,
i
ngoi ra d h L = K Q m ta c:

(dhL) = K lQ " ' + K Q m= = K lQ '

i
vi dng chy theo Hazen-W illiams ta c:

mequ = m = m 2 = m = 1.852
J

Do : ( d h L)e = K , Q m' + K 2Q m2 = K ^ 1'1*52+ K 2Q'-852 = Q ,s52 K i = K equQ , x52

A:\ Q
d2.K2.(CHw)2.m /'

:* ; &
w
L1 L2
Hnh 4 .5 : D iii iii i tip

vi:

(dhL) - tn tht dng chy trong ng ng tng ng;

(dh| )j - tn tht dng chy trong ng ng th i;
Q, - lu lng dng chy trong ng ng th i;
Kj - h s c trng ca ng ng th i;

K = Z K ; - h s dc trng ca ng ng tng ng.

56
 p = 10,679
L, - chiu di ng ng th i (m).
d, - ng knh trong ng ng th i (m).
(C ||W)j - h s nhm ca ng ng th i theo Hazen-W illiams.
T :

irong : Q l lu lng trong ng ng ni tip (mVs).

Ghi ch: Trn c s (dhL)cqu tnh c, nu cn thit ta cng cth tnhc ng knh
(lng ng tng ng da vo quan h dH = KQm.
L lun trn y cng c th p dng cho trng hp nhiu ng ng ghp ni tip.
ng ng mc song song
Mt ng ng tng ng vi hai ng ng mc song song l mt ng ng ti
lu lng bng tng ca hai lu lng qua hai ng ng mc song song v tn tht
nng lng tin ng ng tng ng bng vi tn tht ct nc gy ra bi mt trong
hai ng ng song song (ch tn tht ct nc l bng nhau cho hai ng ng ghp
song song). Trong trng hp , ta c th biu din tn tht ct nc trong ng ng
lng ng nh sau:

( d h L)tq = ( d h L), = ( d h L)2 = d h L

Ngoi ra ta cn c: Q c ^ Q .+ Q ^ lQ ,

v trong mi on ng ng th i ta c:

( d h L)] = K 1Q ' " ' = K 1( Q i ),n

vi m cqu = iti = m 2 = m = 1,852.

d- .Q- ,L-J,rn(C|_|y,H

H n h 4.6: D i i mc son Sony

57
 Ta c:
1/ m

1
l/m I / I . X5 2

"D
( d h L) ( d h L)

_)
Qi =
K, K, K,

v t Q cqu = Q | + Q 2 ta c:
1/ m |- ]/ m I/ m I/ m
'dhL' dh dh dh
. K cqu_ K,
+
Y -
= 1 K

1/m ]/ m 1/ m 1/m /1X52

1
do :
. K cmu. K
+
K
= 1 K:
=x K

Ghi ch: C gi tr Kt.qil ta s xc nh c ng knh ng ng tng ng.

Lp lun hon ton ging nhau trong trng hp ta c nhiu hn hai ng ng mc
song song.

4.4.4. Tn tht nng lng trn ng ng c lu lng ly phn b u theo

chiu di

Trong mt s trng hp ta c th gp trong mng li cc on ng ng c ch

lm vic nh sau:

Qv(m 3/s) --------- !-----------1 Qr(m7s)

t t t V q (m3/s.m)
v t t I
/m
Hnh 4.7:
SV
/V
d
w / /t
lti I
lfi> lv
i1/ //(it / I 1 * 1 +11,* # I* < I 1 4^ 1 / 1 / 1 * \ , t t 1
lin c m t o n 011 t
/\ II .

Vi Q v (m 3/s) i lu lng i vo u Sng, Q r (mVs) l lirulng i ra khi ne v

q (m 3/s.m) l lulng n v ly dc theo ng. Theo nguyn l cn bng lu lng
ta c:

Q v = Q r +C x L 1 (4 I 3 >
vi L, l chiu di ng ng.
Gi dh l tn ilit ct nc trn ml on ng c chiu di (dx) v tr cch nt i mi
on l x:

dh = K Q mdx (4.14)
vi Q l lu lng ti v tr on ng xt; K l h s c trng ng ng.

58
 Vi Q = Q v - qx ta c: tlh = K ( Q V - q x ) m dx
n m+l _ n m+l
do : d h = f d h = [L,K ( Q v - q x ) mdx = K ^ ------ ^ ----- (4.15)
J -*1 (m + l ) q
Ghi ch: Trong irng hp dng chy trong khu sc cn bnh phng (m = 2) v lu lng
ra Q, = 0 la c ln tht ct nc cho on ng ng (ij) l:

dh = ^ KQv

4.4.5. Q u y i lu lng tr n n g ng c lu l n g Iv p h n b u th e o
chiu di
T r o n g thc t khai Ihc c th g p cc n g n g c lu l ng ly ra s u t trn dc
c h i u di n g ng. T u y nhicn trong tnh ton thv lc m n g li, t h n g n gi n
lu lng ly ra hoc a vo m n s li ch thc hin ti u h o c cu i o n n g
ng. Do d trong trng hp nh vv ngi ta s quy i R tr lu lng ly trn sut
tu y n n g v lu lng ly ti u v cui n g tng ng.
L

1 i
q (m3/s-m)

H n h 4.8a: So' ( iii i(n\> ly cn tic trn t (O ns

Xt trng h p n gin lu lng laV l phn phi u trn s u t c h i u di n g vi

c n g ly l q(inV s.m). Php bin i urng dn g thc hi n c h o o n n g n g (j)
c c h ie u di L n h s 4.8b:
L
--------------------------------- ---------------------------------

n h 4.8b: S d hicn di i (Xi (if(fn\

tr on g d: , = Q } = q L / 2 (mVs)

V d 1:

T n h d n u knh rm cua mt die dn c chiu di 150m t ng n g vi 2 n g

n s di 150 m dc m c s o n so nu. C ho bit cc vu t sau y:

d = 200 m m
d 2 = 150 m m
(C[i\v)| = ( C i w )2 ~ C MW = 120

59
 G i i:
Ta c: 1/m = 1/1,852 = 0.5
PL,
K: = 4.871/-,I,X52
c HW
vi p = 10,679 nu L, v dj tnh bng m.
... ,_ w n , v _ 1 0 ,6 7 9 x 1 5 0
Vi ng ng d = 200 mm ta c: K = -- 7^77
4,S7,--------- = 573,67
x I 2 0 I,X52
0 ,2

1 0 ,6 7 9 x 1 5 0
Vi ng ng d = 150 m m ta c: K 2 = = 2329,37
0, 154,x71 X 12 0 1852

V gi tr Kcqu c tnh nh sau:

0,54 0,54 0,54
1 11 1
+ = 0,047578
KeHU_ _5 7 3 ,67 . 2 3 2 9 ,37_

T : K equ = 281,48 m
v gi tr ca ng ng tng ng c tnh nh sau:
1/4,871 1/4,871
PL 10 ,6 7 9 x 1 5 0
d eHu '1.852 = 0 ,2 3 2 m
equ HW _ 2 8 1 ,4 8 x 120IX52_

Trong tnh ton ng ng tng ng ta thng chn ng knh ng ng

c s dng trong mng li (c cho ng ghp ni tip hoc song song) hoc l
ng knh c s dng trong th trng. Ngoi ra, n gin trong vic tnh ton, ta
nn chn cc gi tr l hng s, nu c th, lin quan n d, L, CMW. Thng thng trong
tnh ton hay chn cc ng ng tng ng c kch thc sau: d = 255 mm. L = 350 m
v CMW= 120.

4.5. TNH THY L c MNG LI NG NG H

Tnh ton mng li h s cn c vo phng trnh lin tc v phng trnh nng
lng vit cho mi on ng ng.
Q-
Phng trnh lin tc
Q
Ti mi nt bt k, phng trnh lin tc (bo ton Q1
khi lng) cho php vit phng trnh cn bng gia
lu lng vo v ra khi nt nh sau:
XQ, =0 (4.16)
' I l n h 4.9: Nityn l rn Ixhii!
vi Q, - lu lng trong ng ng th i c quy c du l" htns ' i lli
dng hay m khi dng chy i vo hoc ra khi nt. Ta thng quy c dng chay di
vo nt mang du dng (+) v dng chy i ra khi nt mang du m (-).

60
 T a c ti n t i: Q| + Q, + Q4 = Q 3

Phng trnh nng lng

T r n m i o n d ng ng, p h ng trnh n n g lng c d n g :
H , = H J + dh,j (4.17)

tror .H : H = z t- - c t n c o p ti n t i.
Y
i

dh,j - tn tht nng lng dng chy trong on ij.

Lu phng trnh (4.17) l mt dng ca phng trin h Bernoulli khi ta gi thit
r n g mi oan ng ng c ng knh khng i (gi tr n g nng l nh nhau).
T r n m i tu y n n g ng ta c p h ng trnh nng l n g n h sau:

Ha = H B+ Z d h , (4.18)
I

trortg : H A = Z.A + :H|, = Z| + - ct nc o p ti u v cui tuyn.

Y Y
]Tdh - t n g t n llit n n g l n g t r n c c o a n n g t A n B.
I
M ng li dng ng h l loi mng li dn gian v mt kt cu c v mt thy
lc. N thng c thit k trong trng hp khu cp nc b. Ta c th s ha
m a n g li h nh sau:

(I) C t dc / nv n; h) B nh </<;

G hi chu: (^) : d i nc; ABCD: d n g n g chinh; BH, CF: ng ng ph

p\
Z A: c a o trnh mt t t nhicn ti A; H A = + ZA : ct inrc o p ti A
y

61
 Ta c th gp 2 loi bi ton sau y:

Bi to n loi 1: Xc nh ng knh ng d, v cao trnh mc nc tnh ti A (ct

nc o p). Cc s' liu khc bit.
Thc hin tnh tuyn ng ng chnh trc.

- Xc nh lu lng trong mi on dj bt u t cui mng tin dn v hng

ngun. Ti mi nt s c iu kin cn bng v lu lng. V d cho s trn:

Q cd = Q d

Q b c = Qd + Q f

Q a b = Q d + Q f + Qe
- C Qj cho mi on ng s xc nh dj t iu kin vn tc kinh t V e theo kinh
nghim (cng thc kinh nghim tnh d theo Q).

- C Qj, Lj, d xc nh tn tht ct nc hj trn ng ng chnh, theo cng thc:

Theo Hazen-Williams:

_ 1 0 ,6 7 9 X L; - I.X52
~~ .4,X71r l,X52 ^
a '-'HW
q 2

(Nu tnh theo Manning: dh| = y L | vi Kj = coc V r , trong (0 tit din ng

Kf
ng, c h s' Chzy, R bn knh thy lc).
- Tnh cao trnh mc nc trong i nc:
HA = H D+ X dh,
i
vi i ch cc on ng trn tuyn ng ng chnh.
i vi cc on ng nhnh (v d BE), vi H B v H E bit, do tn tht ct nc
s l:

d h B[i = H B- H E

T , ta s xc nh ng knh ng ng nhnh. V d xc nh d BE theo Hazen-

W illiams bi cng thc:

j 4 ,X7 l _ 1 0 , 6 7 9 x L j ^ 1 X52 vA
d BB = - . - y r W 2 Q ^ d BH
d h BE X

Bi to n loi 2: Xc nh ng knh ng d. Bit L j , Qi , ct nc o p ti i nc

A v ct nc t do yu cu ti D. Cao mt t ti cc im nt bit.
Cng ging nh trn ta s gii cho ng ng chnh trc.
- dc thy lc trung bnh trn ton tuyn chnh s l:

62
 ^ L ; - tng chiu di ng ng chnh.
i
- N h bi ton loi 1, ta tnh c lu lng trong tng on ng ng. Trn tng
on ng ng chnh th i, ta tnh ng knh ng ng theo cng thc Hazen-
VVilliams nh sau:

j 4 .87l 1 0 ,6 7 9 Q ; 1,852 , J
di = r ils2------ >d.
tb HW

- Vi gi tr d, chn cho ng ng chnh, ta tnh c tn tht ct nc trn ng

ng chnh. T ct nc o p ti cc im nt trn ng ng chnh s c
xc nh.
- C ct nc o p ti cc im nt trn ng ng chnh v ct nc o p cn c
ti cc im ly nc trn ng ng nhnh, ta tnh c dc thy lc J cho tng ng
nhnh. T tnh ng knh ng ng theo cng thc nh bc trn.
V d 1. Xt cho trng hp s trn vi cc s liu nh sau:

AB = CD = 1000 m; BC = 500 m; BE = CF = 250 m; Q D = 0,2 mVs; Q k = 0,1 mVs;

Q : = 0,4 m Vs. Cao trnh mt t t nhin l nh nhau ti mi v tr trn mng li. Yu
cu ct nc t do (p/y) cui ng ng chnh hoc ph t nht l 16 m H 20 . Dng
chy tun theo quy lut ngh bi Hazen-W illiams, ng ng c C HW = 140. Ngoi
ra, cng thc kinh nghim sau y dng xc nh s b ng knh ng d (m) khi
bit lu lng ng phi ti qua Q (mVs) nh sau:

d = 0 , 8 x Q '42

Cho bit ng knh ng ng (tnh theo m m ) l 200, 300, 400, 500, 600, 700,
800, 1000. Xc n h ct nc o p ti i nc A v ct nc o p ti cc im ly
nc E, F.
V d 2. Cho m ng li c s v nhu cu dng nc nh v d 1. Gi s chiu cao
i nc l 20 m. Cao trnh mt t ti A l +23m, ti cc im B, c , D, E, F l 22m.
Quy lut thy lc tnh theo H-W, vi C HW = 120. Xc nh ng knh cc ng ng.
Do nhu cu dng nc, ct nc t do yu cu ti thiu ti cc im ly nc l 16 m.

4.6. TNH THY L c MNG LI VNG BNG PHNG PHP HARDY

CROSS

Trong thc t ta thng hay gp cng trnh dn nc bn ngoi cho mt khu quy
hoch di dng mt mng li. Do vn tnh ton thy lc cho n cng c phn
phc tp hn so vi trng hp va trnh by trn. tm c li gii trong trng hp
ny i lc ta phi thc hin bng phng php ng dn v h phng trnh thng l
h phng trnh c cha phng trnh phi tuyn. Sau y ta s cp dn cc phng
php c bn trong tnh ton.
Phng php Hardy-Cross c l l phng php c in nht v c s dng kh
ph bin nghin cu mng li phn phi nc. y l mt phng php lnh lp c
th tin hnh tnh th cng hoc nh vo my tnh.
Phng php Hardy-Cross cho php tnh ton c th: hoc lu lng, hoc l tn tht
ct nc l n s (ty theo s thit lp bi ton v h phng trnh chn la). Phng
php tnh cho php hiu chnh gi tr c lng ban u (lu lng, tn tht ct nc)
sau mi ln lp. Ph bin nht l phng php Hardy-Cross p dng cho bin lu lng
trong mi on ng m ta s cp sau y.

4.6.1. Xc nh lu lng hiu chnh trong phng php H ardy-Cross

Gi s trong mi vng khp kn ta c lu lng c lng cho mi ng dn.

Nu ta gi Q, l lu lng c lng trong ng ng th i v AQ l lu lng hiu
chinh cho vng kn tng ng ny; lu lng trong ng ng sau ln lp s l:

Q = Qi + AQ (4.19)
Gi tr Q ny s l gi tr lu lng mi Q, cho ln lp n, c th l lu lng cui
(khi li gii t chnh xc theo yu cu). AQ c nh ngha l lu lng hiu
chnh, c th dng hoc m, s c b sung vo gi tr lu lng gi nh ca mi
on ng ng trong vng kn tng ng.
Tn tht ct nc trong mt on ng ng s l:

dhL = K (Q ,+ A Q )m

hay: dh = KQ
V Q | J

vi khai trin a thc trn trong loi b cc s hng b bc cao s cho ta (gi thit
A Q Q ):

m ,, AQ 1-...
dh, = KQ 1 + m ------
Q,

Ngoi ra ta bit rng tng i s ca cc tn tht ct nc trn mt vng khp kn s

bng 0. Cho mi vng khp kn ta c:

X ( d h L) = 0 = l K Q r + m A Q K Q r '
i 1 t I
Trn c s quan h ny gi tr i s ca lu lng hiu chinh AQ c tnh nh sau:

64
 - IK Q " - X ( < M
1____________ _ ______1
AQ = (4.20)

vi m = 1,852 (phng irnh Hazen-Williams).

K thav i theo tng on ng ng kho st.
Lu V rng theo quy c, lu lng chy theo chiu kim ng h s mang du dng
v ngc li s mang du m. Trong mi on ng ng kho st, du ca tn tht ct
nc s cng vi du ca lu lng. T nu AQ dng, lu lng dng s gia tng
vi AQ v vi lu lng m s gim vi AQ.
Tin hnh tnh lp cho n khi nhn c li gii t n chnh xc theo yu cu.
C ngha l cho n gi tr AQ nh theo yu cu ca k s thit k v c tnh ca bi
ton. Ta nhn thy s ln lp s ph thuc vo chnh xc ca lu lng chn ban u
trong cc ng ng. Lu lng ban u chn cng gn vi thc t s cn s ln lp t v
ngc li. Trong mt s trng hp nu li gii chn ban u qu xa vi thc t, cc ln
lp s khng a li gii hi t v li gii ng, trong trng hp ta phi chn li lun
lng v tin hnh tnh lp li.
Ghi ch:
- Trong bc ny, phi ch l phn . hi nc trong mi vng bt k l d c lp vi cao
ca nt. Tuy nhin, cao ny s anh hng ln p ic trn cc v tr khc nhau ca vng
khp kn.
- Sau mi ln lp ta phi c |max( AQ)11 gim dn bo m li gii hi t

4.6.2. Cc bc tnh ton trong phng php Hardv-Cross

Cc bc lnh ton c tm tl nh sau:

Xc dnh cc vng khp kn, chn chiu dng quv c theo chiu kim ng h.
C k n s tiu th cc nt nu c. c lng cc lu lng trong cc ng
ng dn vi ch l ti mi nt phi c s cn bn lu lng ( X Q V1 = X Q r .1 ) Trng
thc hnh nu M l s on ne v N l s nt trong mng li, s gi tr lii lng
ii thit trong mng li l (M -N +l). Cc gi tr lu lng trong cc ng cn li s xc
nh bng cc phng lnh cn bng lu lng li nt. Nn bt u t cc nt n
g i n rc.

Tnh ln tht ct nc (d h L) ch cc na ng dn nh vo quan h theo Hazen-

VVilliams:

(4.21)

(du cua dh cng du vi Q^.

65
 Tnh tng i s tn tht ct nc lin quan n ng dn ca tng vng kn. Vi
lu l gi tr tng ny thng s khng bng 0, bi v lu lng chn ban u thng
cha phi l li gii ng ca bi ton, do X ( d h L) * 0
i

Tnh gi tr ca X ( d h L) / Q i c h mi vng khp kn trong khng k n du

i
bi v ta bit H| v Q, lun lun cng du.

Tnh gi tr lu lng hiu chnh AQ cho tng vng khp kn nh vo quan h sau y:

- S ( d h L),
AQ = (4.22)
. & LJ i
m i
Q ,

So snh max(AQ) vi [AQ]. Nu max(AQ) < [AQ]. Kt thc bi ton. Ngc li, tip
tc bc k.
a lu lng hiu chnh vo cc on ng cho tng vng khp kn:

Trng hp ng ring: (Qj)mj = Q, + AQn

Trng hp ng chung: (Q,)ml = Q, + AQn - AQm

(AQn lu lng hiu chnh vng ang xt, AQm lu lng hiu chnh vng bn cnh).

Tin hnh li cc bc lp cho n khi nhn c chnh xc yu cu. Mt cch

tng qut, qu trnh lp s dng khi gi tr AQ nh hn mt gi tr cho php xc nh
trc. Gi tr cho trc ny s ph thuc vo tng bi ton c th v mc chnh xc
theo yu cu.
Ghi c h :
Khi du t cc p lc bit ti cc nt, k c cao (p lc ti v tr ra ca trm x l, p
lc cn thit cho cc thit b dng nc ...) c th tnh p lc ttccc nt ca ton mng
li nh vo p dng phng trnh Bernoulii ln lt theo cc nt thch hp. Nhc li phng
trnh Bernoulli cho on ng gia 2 nt A v B nh sau:

Pa V? P b + _V B
+ z, = dh,
Y 2g Y 2g
trong trng hp nu ng knh ng ng khng thav i t A n B v khng c ly lu
lng dc theo ng ng ta c:

4* z + z = dh
Y y
vi d h j , Q, d bit, cc dc trng hnh hc ca ng ng v cao hnh hc ciia A v B d
bit, khi ta c p sut ti A la s xc nh c p sut ti B.

66
 4.6.3. C c h n ch ca p h n g p h p H a rd y -C ro ss

Vi s xut hin ca mv lnh, ngi ta s dng tin hnh phn tch hoc hiu
chnh mng li hin hu hav thit k mt mang li hon ton mi. Tuy vy
trong p dng ta c th gp cc vn kh khn sau:
- Tc hi t v li gii ng chm.
- Trong ml s trng hp ta hon ton khng th gii bi ton khi khng th xc
inh iu kin cn bng lu lng ton mng li trang thi ban u.
iu ny thc y cc nghin cu kv thut c th p dng my tnh nhm gip
cho cch tnh hiu qu hn. Trong mt vi phn mm, ta phi hp vi cc phng php
tnh khc nh phng php Newton-Raphson hoc phng php tuyn tnh ha ca
W ood-Charles. Vi cc phng php ny cho php ta x l cc phn t nh trm bm,
cc van gim p, cc bn cha... thun li hn nhiu so vi phng php Hardy-Cross
n thun.
V d 1. Cho int mang li ng ng nh hnh 4.11:

nh 4.

c trng cc ng ng nh sau:

on ng AB BC AC

D (mm) 200 200 305

L (m) 1500 1000 1000

S dng phng php Hartlv-Cross xc nh lu lng trong cc ng ng. Sai s

ti a cho php 0.1 l/s. Cho bit tn tht nng lng ct nc dh tun theo quy lut
(Hazen-Williams):

6.827L ' V r
d u ,
V 90 J =
10.68L
d 4S7
UoJ
Q
trona : V chi vn tc truna bnh (m/s) v D l dnt! knh ng (m).

B i gii:
Gi s phn b lu lng ban du trong m nc li nh sau:

67
 on ng AB BC AC
Q /s) 50 10 50

Ln lp 1:

Lu lirng D L dh dh/Q
on
(m'/s) (m) (m) (m) (s/nr)
AB 0,05 0,200 1500 35,27 705,42
BC 0,01 0,200 1000 1,20 119,74
CA -0,05 0,305 1000 -3,02 60,33
33,45 885,49
33 45
A. = --------------------------------- ------ = - 0 ,0 2 0 4 m Vs
11 1,8 5x 8 8 5 ,4 9

Ln lp th 2:

Q D L dh li/Q
on
(m7s) (m) (m) (m) (s/irf)
AB 0,0296 0,200 1500 13,36 451,51
BC -0,0104 0,200 1000 -1,29 124,00
CA -0,0704 0,305 1000 -5,68 80,72
6,38 656,23

= ---------------------- ^ --------= - 0 , 005 3 m Vs

12 1,8 5x 6 5 6 ,2 3

Ln lp th 3:

Q D L dh dh/Q
on
(mVs) (m) (m) (m) (s/rrr)
AB 0,0243 0,200 1500 9,30 382,36
BC -0,0157 0,200 1000 -2,75 175,45
CA -0,0757 0,305 1000 -6.49 85,81
0,06 643,62

A n = ------ - - 6 - -0 ,0 0 0 0 5 11 1 -/s
1 1,85 x643,62

Ta thy A 3 nh hn sai s' cho php (0,05 //s < 0,1 /-). Ta chp nhn kt qu tnh
sau ln lp th 3.

68
 V d 2.

Cho mng li cp nc nh hnh bn cnh.

Cho bit tn tht nng lng dh(m) tnh theo
cng ihc sau:

1 0 .6 7 9 1 / ^Q s' l'x5
d h (m ): D 4.87
140

trong : L(m) chiu di ng, D(m) l ng

knh ng. Q(mVs) lu lng chy qua ng. Gi
nh phn phi lun lng ban u trong AB v
Hnh 4.12
BC nh hnh 4.12. Hy xc nh cc lu lng
hiu chnh AQ,(mVs) cho cc vng v t xc nh lu lng trong vng khp kn sau
ln lp th 1, 2,... chnh xc yu cu l 0,5 //s.
Cho bit c tnh cc ng ng nh sau:

B n g 4.4

AB BC CD DE EA BF FG GC
D(mm) 0,30 0,20 0,20 0,30 0,30 0,20 0,20 0,20
L(m) 1000 500 500 1000 1000 500 500 500
Lu lng ti cc im ly iuo:
B ng 4.5

im B c D E F G
q /s) 20 10 30 20 20 20

B i gii:

L n lp 1

Vng khp kn ABCDE:

Q D L dh dh/Q
on
//s (m) (m) (m) m/(//s)
AB 60,0 0,300 1000 2,941 0,0490
BC 10,0 0,200 500 0,385 0,0385
CD -10,0 0,200 500 -0,385 0,0385
DE -40,0 0,300 1000 -1,389 0,0347
EA -60,0 0.300 1000 -2,941 0,0490
-1,389 0,210

69
 -1 389
AQ abcdf = ------- - 3,58 (//s)
V abcde i ?85 X 0,21

Vng khp kn BFGC:

Q D L dh dh/Q
on
//s (m) (m) (m) m/(//s)
BF 30,0 0,200 500 2,940 0,0980
FG 10,0 0,200 500 0,385 0,0385
GC -10,0 0,200 500 -0,385 0,0385
CB -10,0 0,200 500 -0,385 0,0385
2,555 0,214

A Q bfcc = - , ^ ' 5n5 5 , , . = 5,47 < //s )

1,85x0,214

L l lp 2
Vng khp kn ABCDE

Q D L dh dh/Q
on
//s (m) (m) (m) m/(//s)
AB 63,6 0,300 1000 3,2743 0,05150
BC 20,0 0,200 500 1,3946 0,06957
CD -6,4 0,200 500 -0,1697 0,02643
DE -36,4 0,300 1000 -1,1681 0,03207
EA -56,4 0,300 1000 -2,6251 0.04653
0,706 0,226
0,706
AQ \B C D E = - 1 ,6 9 (//s)
1,85x0,226

Vng khp kn BFGC:

Q D L dh dh/Q
on
//s (m) (m) (m) m/(//s)
BF 23,5 0,200 500 0.004 0,00016
FG 3,5 0.200 500 0,000 0.00003
GC -16,5 0,200 500 -0,002 0,00012
CB -20,0 0,200 500 -0,003 0,00014
- 0,001 0,00045
-0 ,0 0 1
AQ BFGC 1,04 /s)
85x0,00045

70
 L a n l p 3

Vng khp kn ABCDE:

Q D L dh dh/Q
on
//s (m) (m) (m) m//s)
AB 61.9 0,300 1000 3,1153 0,05034
BC 17,3 0,200 500 1,0639 0,06144
CD -8.1 0.200 500 -0,2614 0,03223
DE -38,1 0,300 1000 -1,2702 0,03333
EA -58,1 0,300 1000 -2,7722 0,04771
-0,125 0,225
0,125
A Q
ABCDE 0,3 (//s)
1.85x0.225

Vng khp kn BFGC:

Q D L dh dh/Q
on
//s (m) (m) (m) m/(//s)
BI-' 24,6 0,200 500 0,004 0,00017
FG 4,6 0.200 500 0,000 0,00004
(C -15,4 0.200 500 -0,002 0.00011
CB - 17.3 0,200 500 -0,002 0,00012
0,0004 0,00044
0,0004
\ lil-GC = -0 ,4 9 (//s)
1 .8 5 x 0 .0 0 0 4 4

Vi ln lp th 3. ta tliv lu lne hiu chnh ln nht nh hn sai s cho php l

0,5 //s. Ta chp nhn li aii cui hc tnh th 3.

4.7. TNH THY L c MN LI v m ; b n g p h n g p h p m a t r n

Trong mc 4.5 d trnh by phnt php lnh thuv lc mng li bng phng php
d n s dn. Phng php nv s 2 p kh khn khi khng th xc nh dicu kin cn bng
lu lng cho toan h thng. V d h thng c nhiu di nc, bm... lm vic ng
thi. Vi s pht trin ca mv tnh, c tho s cinu phng php sau d gii bi ton
thy lc mng li.
Xt on n s th i c cc nt (k,j) vi cc quv c k liu nh sau:

q;

71
 Xt quy lut tn tht nng lng cho mt on ng c bn th i trong m ng li
bt k:

Ti nt k: = kA H 1 = ki ( h ; - H )

v ti nt j: Qj = - k | -H j j

Vit di dng ma trn cho mi phn t on ng:

Qic" - K; 1 -l" H/
k
'

X -1 1
, h;_
hay: Q' = Kj H'

4.7.1. H thng phng trnh cho ton m ng li

thit lp h phng trnh biu din cho ton m ng li, ta s da vo nguyn tc

cn bng lu lng ln lt ti cc nt. n gin, ta xt v d cho mt m ng li sau:

S mn ; li

Ta gi Cj l lu lng vo (hoc ra) ti nt j vi quy c:

Cj > 0: lu lng i vo nt
Cj < 0: lu lng ra khi nt
Phng trnh cn bng lu lng ti mt nt bt k j:

Z Q = C ,
i
vi ch s i biu th tt c cc ng ng hi t v nt j.
V d ti nt j = 5 cho mng li nu trn ta c phng trnh cn bng lu lng nh sau:

Ql+Q]+Q5 = c 5
Xt phn t ng ng i = 5 ta c:

Q " 1 -l" "H s '

= k5
-1 1 _H 2.
_q 52 .

72
 Xt phn l ng ng i = 7 ta c:

1
]
-U
/ O
1
"H /
= k 7/
QL
- 1 1
_H 5_
Xt phn t ng ng i = 8 ta c:

1
X
" 1 ' h 3'

'-*J
o
V
- K s

ac
0X
1

<Vr'j
- 1

1

Thay vo phng trnh cn bng nt v thu gn ta c:
- k 5H 2 - k 8H 3 - k 7H 4 + ( k 5 + k K+ k 7) H 5 = c 5

V d ti nt j = 1:
Vi nt ny ta c 2 phn t i = 1 v i = 2 lin kt vo nt. Xt phn t i = 1 ta c:

Q -1 H
= k
1 H
Q!
Xt phn t i = 2 ta c:

Q H
= k
-1 1 H
Q
Thay vo phng trnh cn bng nt ta c:

(k, + k 2)H , - k , H 2 - k2H, = c ,

Trn c s hai v d Irn, ta c th tng qut ho ra quy lut chung cho php vit
phng trnh cn bng ti bt k nt no trong mng li. Tng hp li tt c cc
phng trnh ny cho ton h Ihng v vit di dng ma trn tng th nh sau:
1

-k2 0 0 0 ' 'c ,

+

(k, +k, +k,, +k,) 0 h2 c2

(k2 +k, +k fi + k 8) -K
- k f, 0
(k4+k +k7+kj -k7 -K
(k,+k7+ k) 0
K,
Ch : Ma trn K, i xng.

4.7.2. iu kin bin

Trc khi tin hnh gii h phng trnh tuyn tnh trn, cc iu kin bin p dng
ong mng li phi c a vo h phng trnh. Thng thng ta c 2 loi iu kin
bin c bn sau v:
* H ;: bit
* Q,: bit

73
 Trong trng hp th 1, vi Hj bit trc, gi tr ny s c x l vo h phng
trnh bng 1 trong 2 phng php sau:

Phng php 1:

Gi nguyn h phng trnh ca m ng li, ch tin hnh bin i hng th i trong h

phng trnh. Cho tt c cc h s kjj = 0 nu i * j, kjj = 1 nu i = j v thay Cj = Hj (gi tr
ct nc bit ti nt i). y l phng php c s dng rng ri trong cc bi ton ca
phng php phn t hu hn.

Phng php 2:

Thay gi tr H| bit vo phng trnh v bin i thch hp nhn h phng

trnh mi c s phng trnh t hn (khng c phng trnh cho Hj bit). Gi s c II
gi tr H, bit, s phng trnh cn li s l (N - n) vi N l s nt ca m ng li.

V d .
Cho h thng m ng li nh hnh v. Gi thit l dng chy tng v c cc d kin
sau y. Xc nh lu lng qua mi ng nhnh.

H| = 10 m; c 2 = -2 rrr/s; L| = L2 = 1000 m; | = 0,1 m; 2 = 0,2 m; V = ] 0 f rrf/s v

dng chy tng c k = .

128|iL
1

Ci

B i gii:

Trn C s s liu ta tnh c: k| = 0,024 iTf/s v k? = 0,385 n r / s

Ma trn c bn cho phn t i = 1:

0 ,0 2 4 -0 ,0 2 4 ' rH .1
X

- 0 .0 2 4 0,0 24
r1
1

Ma trn c bn cho phn t i = 2:

f ' 0,385 -0 ,3 8 5 ' H.

-0 ,3 8 5 0,385 _H 2
Q .
Ma trn tng th cho h thng s l:
l

1
+

'H ,' 'c ,'

1
1
r1

r J

_ ( - k ,- k 2) (k, + k 2 ) _ 12 _ c:

74
 0,024 + 0,385 -0 ,0 2 4 -0 ,3 8 5 H, c,
-0 ,0 2 4 -0 ,3 8 5 0,024 + 0,385 h 2 c2

T iu kin H| = 10 m v C-, = -20 m '/s ta c:

-0,409H| + 0,409H 2 = -2 => H2 = 5 , l l m
T :

Q, = k,(H, - H 2) = 0,024(10 - 5 . 1 1) = 0,1173 n r / s

Q 2 = k2(HI - H2) = 0,385(10 - 5 ,1 1 ) = 1,8826 m 7s

V d 2.

Cho mng li nh hnh v. Ly V = 1 0 6 m 2/s v c cc s liu nh sau:

Phn t L(m) d(m) kj(m2/s)

1 1000 0,4 6,164
2 1000 0,2 0,385
3 2000 0,283 0,772
4 2000 0,283 0,772
5 2000 0,573 12,977

Xc nh lu lng v ct nc ti cc v tr cha bit.

B i g i i:
Ma trn tng th cho mang li nh sau:

[(6 .1 6 4 + 0 .3 8 5 ) -6 .164 -0 .3 8 5 0 20" ct

. (6 .1 6 4 10.772 + 0 .7 7 2 ) -0.7 7 2 -0 .7 7 2 H, 10
0 .3 8 5 + 0 .772 + 12.977) -12.977 H, 10
(0.772 + 12.977) 10 c 4.

Gii h phng trnh trn ta c:

H 2 = 19.443 m; H 3 = 11,495 m; c , = 6,7 m 7s; C4 = -26,7 mVs

75
4.8. PHN TCH S LM VIC H THNG CP NC

Trong mng li cp nc s hot ng ng thi ca bm, i nc v h thng

ng ng phi tha m n cc quy lut hot ng ca cc hng mc. i vi bm, quan
h gia lu lng bm hot ng v ct nc bm to ra phi tha mn ng cong c
tnh ca tng loi bm. i vi i nc, lu lng ra hay vo i ty thuc vo ct
nc ca i v p lc nc ti nt m ng li ni ni vo i vo cng thi im. Mt
cch tng qut dng ng cong c tnh ca bom c dng nh sau:

H(m)

>
Q (m3/s)

Trong Q tk v Hlk ch lu lng v ct nc thit k ca bm. Khi hot ng vi

cc thng s thit k ny bm s c hiu sut r| cao nht. VI mt l do no , bm phi
hot ng trong iu kin khc gi tr thit k hiu sut s gim v s gim hiu sut s
cng tng khi s khc bit cng ln. th sau trnh by mt cch tng qut hiu sut T|
ca bm.
H (m)
/ n = 95%

Q (m3/s)

76
 i vi mt on ng, quy lut thuv lc biu th quan h gia tn tht nng lng
dli (m) v lu lng i qua Q(mVs), mt cch tng qut c dng sau:

H n h 4.15: Dm> dn ton thin niii; hrin tronV (tiH n\> c p

Ghi ch: Khi dng ng ti qua lu lng Qo tn tht nng krng tng ng s l dhn.
Sau y s kho st mt vi s d hot dng c bn tronp h Ihng mng li
cp nc:
Tnni h]) :
Gi thit bm s dng c xc dnh (bit na cong c tnh bm) v mt on
ng ng (ij) vi c trng hnh hc cua oiii d cho trc (chiu di, ng knh, h s
nhm, quy lut tn tht nng lng). Cui dng ng dn, nc c a n mt cao
trnh H ( bit. Xc nh lu lng Q() qua ng.
Vi h thng cho trn, gi tr lu lng qua ng (cng l lu lng bm) xc nh
nh sau: gi Q x l lu lng gi nh qua ont. T ng cong quan h tn tht nng
lng xc nh c (h + v 2/2g) tng ng. Ngoi ra, khi bm hot ng vi lu lng
v t ng cong c tnh bm xc nh c "t iic bm H Do , ci nc o p
tai cui dng ng l:

Hx = H - ( d h + v 2/2 g)

So snh gi tr H x v Hj: nu lu lng Q x s gim n khi no H x = H r

Trng hp nu H x > 1-^ lu lng s tng n khi no H x = H r D nhin trona qu
trnh thay i Q x gi tr (dh + v :/2g) thay i theo.
T phn tch ny ta nhn ihy lu lng hin khng phi l gi tr p ot "ch quan
vo h thng m n l kt qu t s cn hng lm vic phi hp gia c tnh ng
ng, bm v iu kin "bin".
Ti itv l ]) 2:
Kho st mt h thng n gin grn I)JM1 di nc. 1'ii licn om v i nc l mt
ng ng vi cc thng s bit. (jia thit ti mt thi im kho st mc nc trong

77
i d xc nh Hd v bm ang hot ng vi lu lng Q b. Xc inh ting thi nc
ra, vo h v lu lng ly ra ti cui ng ng.
Khi bm hot ng vi lu lng Q 0, t ng cong c tnh bm xc nh c ct
nc bm H h. T ng cong quan h tn tht nng lng v lu lng qua ng ng
xc nh c tn tht ct nc qua ng ng dh. Do , ct nc o p ti cui
ng l:

H| = Hb - (dh + v 2/2g)

So snh gia Hj v H, t xc nh trng thi nc ra hay vo i nc cng nh

xc nh lu lng tng ng Q d. Trn c s Q b v Q t, xc nh lu lng ti nt J.

Trong trng hp nc vo i, lu lng ra ti nt j l:

Q j = Q b - Q d

V trong trng hp nc ra khi i, lu lng ra ti nt j l:

Q j = Q b 4 Q d

Ti i i l ]) 3 :

Kho sl mt h Ihng n gin gm bm, i nc. Ni lin bm v i nc l mt

ng ng vi cc thng s bit. Gi thit ti mt thi im kho st mc nc trong
i xc nh H v lu lng ly ra ti nt j ng ng l Qj. Xc nh lu lng hot
ng ca bm v trng thi nc ra, vo h.
Trong trng hp ny xc nh im hoi ng ca bm phi xc nh bng cch
ng dn. Cc bc tnh ng dn nh sau:

- Gi thit gi ti lu lng ra (vo) i Q x t xc nh lu lng qua ng

ng Q 0.

- Vi Q(l l dng cong quan h tn tht nng lng v lu lng qua ng ng xc

nh c tn tht ct nc qua c ng ng dh v t ng cong c tnh bm xc nh
H h. Do , ct nc o p ti cui ng l:

Hj = H b - (dh + v 2/2g)
T Hj v Ht) xc nh lu lng ra (vo) i Q cl.

- So snh x v Q (| gi thit. Li gii s chp nhn khi sai bit ca Q x v Q d nh

hn gi tr cho php.
T cc phn tch cho mt s s lm vic n gin nu trn ta nhn thy trong mt
h thng mng li cp nc khi c bm hot ng, lu lng ca bm khng ph
thuc vo p t "ch quan" m lu lng bm s thav i theo tng tnh hung c th
ca h thng. y l im cn phi lu khi m phng h thng mng li cp nc
theo thi gian s dng t cc phn mm.

78
4.9. PH \ N rCH H THNG CP NC VI M HNH EPANET

4.9.1. Gii thiu

Cc phng php va trnh by trn dng phn tch mt mng li trng thi
tnh. Ni mt cch khc i, y l phng php cho ta xc nh phn b ct nc v lu
lng trong mng li ti mt thi im cho trc. Trong thc t khai thc mng li,
c th gp trng hp khne nhng ta phi xc nh li gii ti mt thi im
chn, ta cn phi nh gi c qu trnh thav di ea n trong mt khong thi gian
(gi. ngy...). v l mt vn rt ph bin, VI ta bit rng lu lng cp cng nh s
clng trn mt mng li lun lun thav i theo thi gian. V d lng nc s dng
gia dng s b vo ban m, nc phc v sn xut thay i theo cng sn xut...
Phn mm EPANET c th p dn nghin cu bi ton m phng thy lc mng
li theo thi gian.
m phng bi ton, cc phng trnh c bn v thy lc m t hin tng nh sau.
Phng trnh tn tht nng lng cho mi on ng ng (i,j):

H i-H -h ^ rQ " (4.23)

V ti m i nt ta c:

Z Q ,1 " Z Q i j - li = 0 (4 24)
' J

trong :

Q,, - lu krug ti on g d ng ng (ij);

H, - chiu cao ct nc do p ti nt i (th nng + p nng);

q k - lu lng tiu th (+) hoc cp vo (-) tai nt k.
gii h phng trnh trn, c th s dung phng [>hap sai phn hu hn. y ia
hi ton m phng theo ihi gian khi cc lu lng ly ra hoc a vo mng li thay
di theo thi gian.
4.9.2. V du
12
Cho mt mng li nh hnh sau. Dng 1
HPANET m phng hot ng ca
m ng li trong 72h. 2 3 5

*
n v s d n s trong m phna:
- Lu lne (//s)
1. *4T
- Tn tht nng lng dng di trong
nt theo quy lut Hazen-Williams 9 10 2
^ a i ( .... .. w
- Chiu di (m)
TVT /
- ng knh ng (min)
- Cao trnh (m) S (l m ii* h)7

79
 Thi gian m phng: 72 h.
S liu ban u cho mng li nh sau:

Nt 2 3 4
Cao 10 10 12 13
L.u lng (//s) 20 15 20 20
N" Pattern 1 2 1 2

S liu v patterns nh sau:

Pauerns N 1:

Time 1 2 3 4 5 6 7 8 9 10 11 12
0.7 0,7 0,7 0.7 0.8 0.8 0,8 1,2 1,2 ,2 1.2 1,2

Time 13 14 15 16 17 18 19 20 21 22 23 24
1.2 .2 1,2 1.2 1,2 1,2 1.2 1.2 0,8 0,8 0.8 0.8

Patterns N" 2:

Time 1 2 3 4 5 6 7 8 9 10 l 12
0.9 0.9 0,9 0.9 1,2 1.2 1.2 1.2 1,2 1,2 1.2 1.2

Time 13 14 16 17 18 19 20 21 22 23 24
15
1.2 1.2 1,2 1.2 1.2 1.2 1,2 1,2 1.2 0 0 0

S liu ng ng;

ng 1 2 3 4 5
L(m) 500 1000 1000 500 40
D (mm) 200 200 150 150 300

S liu v i nc s 12.

Cao y di nc (m) 32
Chiu su nc ban u (m) 7r'
Chiu su nc min (m) 2
Chiu su max (m) 7

ng knh di (m) 8

( h i c h : Thng thng chiu su nc ban u cho trong i nc l chn ngu nhn, do

d vi m phng ln du th sau chu k mc nc i s khng v ng nh ban cu gi
(lnh. hiu chinh chi cn ly s liu mc nc di cui chu k m phng v g ngi tr
nay cho mc nc ban au cua i.

80
 S liu v bm 6 v 10.

N bm 10 6
Lu lng bm (//s) 65 65
Ct nc bm (m) 45 45
N dng c tnh my bin 15 15
Pattern 10 6
Bm s 10 s hot ng lin tc 24h (pattem N 10) v bm s 6 s chy t lOh n
20h (pattern N" 6).

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81
 - nh righa thi gian ko di rn phng: 72h
Vo ca s Browser chn: / Options / Times
Chn Total Duration > 72

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Times Qptions n Data Map

Property Hrs:Min Options
Total Duration =72 Hydraulics
Hydraulic Time Step 1:00 Qualiy
Reactions
Quality Time Step 0:05
Pattern Time Step 1:00 Energy

PaUern Slart Time 0 00

Repoting Time Slep 1:00
Repoit Start Time 0:00
Clock Start Time 12 am
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StatsHc None

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Map Options

Ndes 7 D isp lyN odelD 's

P D spiayN deV alues

Links

w Display LinkDV
Labels
V Dsplay LinkValues
Notaiion
~ U se r a n s p a r e n te x t

Simbols
t zoom of 11 QQ j

FbwArrows
Pont S26

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K Cancel Help

- Hin th ln s tnh c k hiu hng dng chy:

Chn theo ng dn sau: View / Options / Flow Ai rov s v chn:
Arrows Style: Opel)

82
- Nhp s liu nt: V d cho nt 2.

H & S E H H H H M |x

Property Value -

Munction ID i7

X-Coordinate 1469.93
Y-Coordinale 6659.24
Description
Tag

xElevation 10
Base Demand 15
Demand Pattern 2
z

- Nhp s liu pattern: v d pattern N (l cho nhu cu dng nc.

P a tte m E d ito i

PUein ID DiCiplior

Time Petiod 1 2 3 4 5 6 7 8

Multiplier 0.7 0.7 0.7 0.7 .8 0.8 0.8 1.2

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G h i ch: T io ns trng hp pattern cho nhu cu nc sinh hot trong mt chu k tnh ta c
gi ir trunu bnh cc h s b n s l : Avg. = .

83
 Nhp s liu pattern: v d pattem N6 cho hot ng bm s 6.
1 M ap J
Pattein Ertoi
PUem 10
Patens
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TimePenod 8 9 10 11 12 13 14 15

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 18 20 21 22 23 24
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Ghi ch: C th dng pattem ny xc nh gi hot ng ca bm trong chu k dng nc.

- Nhp s liu ng ng: V d cho ng ng 1 chiu di Length = 500m, ng
knh Diameter = 200mm.

1Pipe 1 'm
Propert V alue
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Start N o d e 1 ---

KEnd N o d e 2

Description

a g

"Length 500

Diameter 200
kH ___ 1_____ 4 Art d

- Nhp s liu i nc s 12.

Data I Map I
Property Vlue
Tank ID 12

X-Coordinate 4387 53 1

Y-Coordinate 7750.56

Oescription

Tag

*Elevation 32

Initial Level 7
vMinimum Level 2

"Mximum Level 7
X
Diameter 8
.................... H

84
Nhp s liu bm nc s 10 v 6.
Bm s 10

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"Pump ID n 1

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"End Node 1
Description
Q
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"Pump ID 6
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Irutial Status opan '& X g

s liu dng c tnh my bm (Pump Curve) kv hiu ID 15.

Curve Editoi Data I Map

Curve ID Deciiption

Cmve Type Equation

PUMP [ I Head = BO QCl 0 2 0 761F10wI^2 00
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Q EPANETt vlduepanetl .net -[ Time Seres Plot - Flmr for Seiected Urtks]
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0 2 4 6 8 101214 16 182022 24 28 2830 32 34 36 38 40 42 4446 48 5 0 5 2 5 4 56 5 8 6 0 6 2 64 6668 70 72
Time (hours)

86
 p sut nc trong i nc TANK 12:

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87
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88
 4.9.3. Mo p hng s khuech tn cc cht x l nc tr ong m n g li

Bi lon dai ra n h m uia qu y t vn clc k h u c h tn c a c h t k h t r n g (v d c lo ) c

d u a vo mni li. Nsioi h p h n e trnh thy lc sii th i u trn, ta c n c p h n g
trnh tli lu (s hunu "adxectioii") cua cht a vo n h sau:

(4-25)

t r o n e d:

c - n n g d chai kh trnti r on u o n ng im (ij); c x c in n h l m t h m s

th e o k h o a n g cch v thi gian; Cjj = Cj j ( X j j , t )k e / m \

X - c h i u di d c theo n e (ij).
Hi - lu lig r one ng n (ij).
A - tit di n n g n g (ij).

()(ci| I - tv l cht kh trne trong ng ng (ij), k/m^ngy.

89
 BI TP

Bi 1. Ml mng li ct c thit k cho mt khu vc c quy hoch nh sau:

Hnh
Cc c trng ng onu nh sau:
Bng 1.1

ng ng AB BC CD BE CF CG
D(m) 0.915 0,915 0,61 0,405 0,405 0,405
L(m) 3000 2500 5000 1500 1500 1500

Lu lng ly ra ti t cc diem trn mng li nh sau:

B ng 1.2

im B c D E F; Ci
Q(mVs) 0,25 0,08 0,30 0,15 0,10 0,12

Bit rng ct nc o p cui ng ng chnh (D) cn c l 10 m. Tn tht nng

lim ct nc tun theo quy lut (h a7.en-Williams):

J 1 0 .6 7 9 Q V'*5
D 4'*7 1 120,
trong Q chi lu ln trong ng (n r/s) v D l ng knh ng (m).

Hv xc nh (a) c! nc o p H A(m) ti i nc A v (b) CI nc o p H /m ) ti

cc im E, F, G.

B i gii:
a) v l loi mng li ct, ta s tin hnh gii trn ng ng chnh ABCD trc
tin. Lu lng trn mi on ng s c tnh bng phng php cn bng lu lng
nt. Thc hin php tnh t cui ngun v u mng li. Kt qu tnh dc irinl by
trn hng sau:

90
 B ng 1.3

ng ng (mVs) D(m) L(m) dh(m) H(m)

CD 0,3 0,61 5000 9,11 19,11

BC 0,6 0,915 2500 2,28 21,38

AB 1 0,915 3000 7,03 28,42

Trong bng dh(tn) ch tn tht ct nc trn don ng tng ng v H(m) ch ct nc

o p ti im u on ng ng. Kt qu cho thy ct nc o p ti A l 26,92 m.

b) Tnh trn cc on ng nhnh:

Bng 1.4

ng ng Q(mVs) D(m) L(m) dh(m) H(rn)

BB 0,15 0,405 1500 5,57 15,81

CI; 0,1 0,405 1500 2,63 16,47

CCi 0,12 0,405 1500 3,69 15.42

Trong d dh(in) chi tn tht ct nc trn on ng tng ng v H(m) ch ct nc

tlo p ti diein cui don dung ng. Him) duc tnh hng hiu s gia ct nc o p
li u mi ng ng (kt qu cu a, cc im tng ng trn ng ng chnh) v
h(m) tng ng.

Bi 2. Mi mang li ct c thit k cho mt khu vc quy hoch nh sau:

Hnh 2

91
 Cc c trng ng ng nh sau:

Bn 2.1

ng ng 1-2 2-3 3-4 4-5 2-6 3-7 .-S

D(mm) 1000 800 400 400 400 250 250
L(m) 3000 2500 5000 3000 2000 2000 4000

Lu lng ly ra ti t cc im nt trn mng li nh sau:

B ng 2.2

im 5 2 4

Q(mVng) 100 500 100

Khu dn c A c 20000 dn, c tiu chun dng nc l 120 1/ng-ng. Din tch ti
cho ng v cy xanh l 20 ha. H s khng iu ha ln nht ngv dem v l lan
lt l Kng(|.max = 1,2, Kh.max = 1,5. Khu dn c B c 5000 dn, c tiu chun dnu noc
l 200 l/ng-ng. H s kling iu ha ln nht ngy m v gi ln lt l Kn(t mix = 1,2,
Kh.m.ix = 2,0. Din tch ti cho ng v cy xanh l 15 ha. Tiu chun ti l 1.5 //nr/ngd.
Nh my F hot ng 2 ca trong ngy. Ca I t 7h-12h v ca 2 t 13h-18h. Mi ca c 500
cng nhn lm vic vi liu chun dng nc cho sinh hot l 30 //ng-ca. Lu li>
nc cho sn xut cho khu cng imhip l 300 mVca. Trong nh my c 9 nh tm c
trang b vi sen. Lu lng lv dc tuyn on 4-5 l 0.1 mVnR-m v trn on 3-4 l
0,08 m 7ng-m . Thi gian ti thc hin t 18 n 20h trong ngv.
Bit rng ct nc o p cui ng ng chnh (5) cn c l 10 m. Tn tht ct
nc tun theo quy lut (Hazen-Williams):

= 10,679 Q VX5
D 4*7 l l 2 0 ,
trong : Q ch lu lng trong ng (m '/s) v D l ng knh ng (m).

a) L4p bng tnh lu lng gi cho ngy s dng nc ln nht. T xc nh lu

lng cho gi s dng nc dn dng cao im trong mi on ng.

b) Vi kt qu cu (a) xc nh ct nc o p H A(m) ti i nc 1 v (b) ct nc

o p H(m ) li cc im 2, 3, 4, 6, 7, 8 vo lc 8h-10h (gi thit lu lnz tnh ton khu
B gina nh cu (a)).
Bi 3. Cho mt mng li thot nc nh hnh v. Hy s dng phng php Hary-Cross
xc nh lu lng trong mi on ng vi sai s ti a cho php l 1 //s. Cho bit h
s Hazen-W illiams ca tt c cc ng ng l 140.

92
 Qa = 301/s

Qc = 301/s
Qd = 801/s

Hnh 3

Cho bit chiu di L v ng knh d ca cc on ag ng nh sau:

Bng 3.1

AB AC CD BD
L(m) 2000 1500 2000 1500
d(m) 0,2 (',2 0,2 0,2

B i gii:
Ln lp th 1

L dh dh/Q

tim; (m) (ms//)

2000 2,45 0,16
0,200 1500 -8,82 0,25
0,200 2000 18,72 0,42
0,200 I 500 ,84 0,12

9,29 0,95
A Q = -5,26 l/s

Ln lp th 2

D 1. dh dh/Q
on k Q
(//s) (m) (m) (m) (ms//)
AB ! -20.3 0,200 2000 -4,28 0,21
BD -40,3 0.200 1500 -11,43 0,28
CD 39,7 0,200 2000 14,87 0,37
AC 1 9'7 0,200 1500 0,83 0,08
L_
- 0,01 0,95
A Q 0,00 /s

93
 Sau ln p th 2 la thy li gii d tha mn icu kin sai s cho php.
T m l i:
Lu lng trong on ng AB l 20,3 //s, theo chiu t B n A.
Lu lng trong on ng BDl 40,3 //s, theo chiu t D n B.
Lu lng trong on ng CD l 39,7 //s, theo chiu t D n c.
Lu lng trong oan ng AC l 9,7 //s, theo chiu t c n A.
Bi 4 Cho mt mng li thoi nc nh hnh v. Hy s dng phng php Hardv-
C.TOSS xc nh lu lng trong mi don ng vi sai s ti da cho php l 1,5 //s. Xc
nh c liu dng chy irong mi on ng v tn tht ct nc trong lng on. Gi s
nc c cp t mt i cha nc cch D l 3000m c ng knh d = 0.40m. Gi s
cao trnh mt t cc dim A, B, c , D l nh nhau v bng 25 m. Cao trnh mt dt ti v
tr i nc l 33 m. Xc nh chiu cao i nc. B qua ct nc to bi chiu su
nc trong i. Ct nc o p cn thit ti A l 10 m. Cho bit h s Hazen-W illiains
ca tt c cc ng ng l 120.

Qa = 501/s
Q d = 401/s

Q d = 1301/s

Qc = 401/s

Ilnh 4

Cho bit chiu di L v dng knh d ca cc on ng ng nh sau:

Bng 4.1
AB AC CD BD
I.(m) 2000 1500 2000 1500
d(m) 0.25 0,25 0,25 0,25

B i gii:
Ln lp I

Q D L h dh/Q
on
1 (//s) (m) (m) (m) (ms//)

AB -10,00 0,250 2000 -0.520 0.052

BD ! -50,00 0.250 1500 -7.654 0,153
CD 80.00 0.250 2000 24,346 0.304
AC I 40.00 0.250 15()0 5,065 0,127
21.238 0,636
AQ = -18,05//s

94
 Ln lp 2

Q D L dh dh/Q
on
(//s) (m) (ni) (in) (ms//)

AB -28,05 0,250 2000 -3,503 0,125

BD -68,05 0,250 1500 -13,537 0,199

CD 61,95 0,250 2000 15,170 0,245

AC 21,95 0.250 1500 1,669 0,076

0,201 0,645

AQ = 0 ,1 7 //s

Sau ln lp th 2, li gii tha iu kin sai s cho php l 1,5 //s.

T m li:
Lu lng trong AB l 28,05 //s, theo chiu t B n A.
Lu lng trong BD l 68,05 //s, theo chiu t D dn B
Lu lng trong CD l 61,95 //s, theo chiu t D n c
Lu lng trong AC l 21,95 //s, theo chiu t c n A.
Tn iht ct nc t i nc n D l:
10 679
''
n = -^ r -11.' rX ^^ Q lx sx L = 0 ,0 030 28x 300 0 = 9,08 m
11, K / I /
d C|W
Chiu cao i nc ti o l:

H = Ha + h|)_| + h() |)+ (Z |,- z 0 ) = 10 - 3.501 ( 13.5 > 9,U8 + (25-33) = 28,1 Im

Bi 5. Cho mt mng li thot nc nh hnh v. Hy s dung phng php Hardy-

Cross d xc inh lu lng trong mi an n vi sai s ti a cho php l 1 //s. Cho
bit h s Hazen-Williams ca tt c cc ng ng l 120.

Qe = 201/s

Hnh 5

95
 Cho bit chiu di L v ng knh d ca cc on ng ng nh sau
Bng 5.1

li 1

i
i
m
m
r \
AC = EF = BD CF = FD

>
1

L(m) 2000 1500 2000
d(m) 0,25 0,25 0,25

B i gii:

Ln lp 1
Vng khp kn AEFC:

Q D L dh dh/Q
on
/s) (m) (m) (m) (ms//)
AE -30,0 0,250 2000 -3,966 0,132
EF -10,0 0,250 1500 -0.390 0,039
FC 30,0 0,250 2000 3,966 0,132
CA 20,0 0,250 1500 1,405 0,070
1,015 0,374
A Q ,= 1,47//s

Vng khp kn EBDF:

Q D L dh dh/Q
on
/s) (m) (m) (m) (ms//)
EB -40,0 0,250 2000 -6,753 0,169
BD -60,0 0,250 1500 -10,724 0,179
DF 50,0 0,250 2000 10,205 0,204
FE 10,0 0,250 1500 0,390 0,039
-6,883 0,591
A Q 2= 6,30 //s
Ln lp 2
Vng khp kn AEFC:

Q D L dh h/Q
on
(1/s) (m) (m) (m) (ms/1)
AE -31.5 0,250 2000 -4,333 0,138
KF -17,8 0,250 1500 -1.129 0,064
l-c 28,5 0,250 2000 3,615 0,127
CA 18,5 0,250 1500 1,220 0,066
-0,627 0,394
A Q ,= 0 ,8 6 //s

96
 Vnu khp kn EBDF

on Q L dh dh/Q
r ' i7 ~
(//s) (m) (m; (m) (ms/1)
HB 0.250 2000 -4,919 0,146
l._ '.7
HI) ^ 3 .7 0,250 1500 -8,735 0,163
DI- 56,3 0,250 2000 12,710 0,226
1
IH ! 17,8 0,250 1500 1.129 0,064

0,185 0,598
AQ 2= - 0 ,1 7 //s

Sau ln lp th 2 ta thy li gii d tha m a n iu kin sai s c h o p h p l 1.5 1/s.

T m li
Lu lng trong EB i 33,7 //s, dng chy chiu t B n E.
Lu lcmg trong BD l 53.7 /s, dng chy chiu t D n B.
L u lng trong DF l 56,3 // s, d n g chay chiu t D n F.
Lu lng trong FE l 17,8 //s, dng chy chiu t F n E.
Lu lng trong A E i 31.5 //s. d n g c hy ch iu t H n A.
[.u lurng trong FC l 28,3 //s, dng chy chiu t F n c .
L u UrnR troni C A l 18,3 //s, d n p c h v ch i u l c n A.

Hi 6. Cho mt mang li cp nc nh hnh v. Hy s dng phng php Hary-

C i o s s e xc dn h lu lng trong mi o n ng vi sai s ti a c h o p h p l 1,5 //s. Xc
i n h c h i u d n g clv trong mi oa n n g v ton tht ct n c t ro n g tng o n . G i s
nc c cp t mt di cha nc c c h D l 500()m bne mt ng ng c ng
knh d = 0 ,4m . Gi s c a o trinh mt t cc ic m A , B ,C ,D l n h n h a u v b n g 15 m.
Cao trnh mt t ti v tr i nc l 19.8 m. Xc nh chiu cao i nc. B qua ct
nc lao bi chiu su nc trong i. Ct noc vu cu ti A l 10 IT1. Cho bit h s
H a z e n - W i l l i a i n s cu a tt c cc ng ng l 120.

Hnh 6

97
 Cho bit chiu di L v ng knh d ca cc on ng ng nh sau:

B ng 6 .

AE = EB AC = EF = BD AD CF = FI)
L(m) 2000 1500 2500 2000
d(m) 0.3 0,3 0,3 0,3

B i gii:
Ln lp 1
Vng khp kn AEFC:

Q D L dh dh/Q
on
(// s) (m) (m) (m) (ms/)
AE -15,0 0,300 2000 -0,453 0,030
EF -5,0 0,300 1500 -0,044 0,0)
FC 35,0 0,300 2000 2,170 0,062
CA 15,0 0,300 1500 0,340 0.2 >
2,013 0.124
AQ| = -8,79 l/s
Vng khp kn EBDF:

Q D L dli dh/c.
on
/s) (m) (m) (m) (ms/)
UB -30,0 0,300 2000 -1.632 0.05-1
BD -50,0 0,300 1500 -3.149 0.063
DF 50,0 0,300 2000 4,199 0.08-
I;E 5,0 0,300 1500 0,044 0,000
-0,538 0,210
A Q 2= 1,38 //s
Ln lp 2
Vng khp kM AEFC:

Q D L dh dh/c;
on
(//s) (m) (m) (m) (ms//
AE -23,8 0,300 2000 -1.063 0,045
EF -15,2 0,300 1500 -0,347 0.02;
FC 26,2 0,300 2000 1,271 0,04
CA 6,2 0,300 1500 0,066 0,01.1
-0.073 0,12'
A Q ,= 0,31//s

98
Vng khp kn EBDF:

on Q D L dh dh/Q
(// s) (m) (m) (m) (ms//)
EB -28.6 0,300 2000 -1,495 0,052
BD -48.6 0,300 1500 -2,990 0,061
DF 51,4 0.300 2000 4,416 0,086
FE 15,2 0,300 1500 0,347 0,023
0,278 0,223
A Q, = -0,67 //s

Sau ln lp th 2 li gii tha mn iu kin sai s cho php l 1,5 //s. Tm li:
Lu lng trong on ng EB l 28,6 //s, dng chy chiu t B n E.
Lu lng trong on ng BD l 48,6 //s, dng chy chiu t D n B.
Lu lng trong on ng DF l 51,4 //s, dng chy chiu t D n F.
Lu lng trong on ng FE l 15,2 //s, dng chy chiu t F n E.
Lu lng trong oan ng AE l 23,8 //s, dri chy chiu t E n A.
Lu lng trong don ng FC l 26,2 //s, dng chy chiu t F n c.
Lu lnR trong oan ng CA l 6,2 //s, dnti chv chiu t c n A.
Tn tht ct nc t i nc dn D l:

h0 X L - 0,001864 X 5000 = 9.32 m

d C||\\
Cliiu cao di nc ti 0 l:
H = Ha + h|.;.A+ h| |.: + h) H+ ho.) + (Z|) - z ())
= 1 0 + 1 .0 6 3 + 1,495 + 2,99 + 9.32 + (15-19,8) = 20 m

99
 Chng 5

H THNG CP NC BN TRONG

5.1. (I T H I U

Chng nv ch yu da vo "Quy chun cp thot nc trong nh v cng trnh" do

B Xv dng ban hnh thng 12-1999 (gi tt l QCCTNTN 1999), thay th mt
phn nhng quy nh c ca TCVN 4513:1988. Mt s im khc bit chnh s ac
gii thiu. Nhng chi tit cha c quy nh r trong quy chun rri s c trnh bv
theo quy nh ca tiu chun c.
H thng cp nc bn trong (HTCNBT) c nh ngha l nhng h tlir.g c;,p
nc cho nh dn dung cc cp, cng trnh cng cng, chung c, trng hc, bnh vin,
x nghip,..
H thng cp nc bn trong bao gm cc thnh phn:
- ng ng cc loi,
- Phu kin ni ng,
- Cc thit b v sinh,
- Cc thit bi trn ng ng.
- Cc thit b cha chy.

5.2. C U T O H T H N G C P N C B N TRONC

Yu cu c hn di vi ng iig cp nc bn trong l:
- C bn cao v mt ha hc, c hc v nhit.
- Trng lng ling nh.
- D ni v kn nc, mi ni chc chn.
- C cc loi b phn ni ng, to iu kin da dang cho vic b tri v thit k
V mt vt liu, cc loi ng c s dng ph bin nht trong HTCNBT l ii nha
p v c v nu thp trng km (galvanised Steel). Cc loi ng ng hav nha phc hp
(thnh im lm bng kim loai, c lp ph bng nha) thng c s dng cho h [hng
cp nc nnu.

5.2.1. n knh dan h nh

im dc s dung c dng knh danh inh ND (thm gn hng lnu kinh nuoai
cua ne) tnh theo li do lng M (inch) hay h SI (m).

100
 Cc c ng thng dng dng cp nc bn trong c ng knh danh nh l 21 mm
(3/4"), 27 mm (1"), 34mm (1 1/4"), 42 mm (1 1/2"), 49 mm (1 3/4"), 60 mm (2"), 75
(76) mm (2 1/2"), 90 mm (3"), 110 (114) mm (4"), 140 m m (5"), 160 (168; mm (6"),
200 inm v 220 mm (8"). Nhng gi tr ny c ghi trc tip trn thnh ng. Tuy nhin
trong cc bng tra, kch thc ng v thit b c ghi theo ng knh trong. Cc gi tr
tng ng thng vo khong 0,8 ca ND: 15 mm (21), 20 mm (27), 25 mm (34), 32
inm (42), 50 mm (60)...
Khi thit k, cn phi chn la ng knh ng da theo quy cch sn xut hin c
trn th trng. Lu rng ng knh danh nh ca ng khng th hin kch thc hu
hiu (ng knh trong) ca ng. Do cn tham kho nh sn xut v b dy thnh
ng ng vi cc p sut hot ng khc nhau hiu chnh cho thch hp. Gn ng c
th ly ng knh hu hiu cua ng nha v ng thp ln lt l 0,9 v 0,8 ca ng
knh danh nh. Chiu di sn xut thng thng ca ng nha l 4m, v ca ng thp
trng km l 6m.

5.2.2. p su t d a n h nh

p sut danh nh (thng c vit tt l NP, ghi trn thnh ng) ph thuc vo vt
liu ch to ng, b dy thnh ng v ng knh ng. Cc loi ng nha PVC c N P t
4 n 15 bars<n. c ghi ngay trn thnh ng. Tuy nhin trn thc t, i vi ng nha
p v c cc gi tri p sut hot ng thit k nn xc nh vi h s an ton t 1,5 n 2
gim thiu s bin dng ca cc mi ni, l nguyn nhn chnh gy ra s r r hay tch
ri li cc mi ni ng. Cc loi ng thp trng km c NP ln n 10-20 bars hoc cao
hn, thng c s dng trong cc cng trnh quan trong hay nh cao tng. Vic chn
ng p sut danh nh ca ng l yu cu rt quan trng v mt k thut v kinh t.

5.2.3. C c yu cu k th u t
- H thng thng xuyn lm vic trong iu kin p lc cao (t 10 m i vi nh trt
n hng trm m trong trng hp nh cao tng), do tuyt i khng xy ra hin
tng r ri bt k b phn no. Do s r ri nc trn ng ng cp nc bn trong
ngoi vic c th dn dn s ph hng cc mi ni rt kh sa cha, cn gy ra thm
loang trong nn hav tng cng trnh.
- H thng phi m bo yu cu rt nghim ngt v v sinh, do khng c
xy ra hin tng chy ngc (backflow hay back siphonage) ti cc thit b v sinh hay
b nhim do h thng thot nc gy ra. Bin php thng c s dng l tun th
cc quy nh v khong lu khng ti thiu (air-gap separation) cho bi quy phm.
Trong mt s trn hp c bit cn cn phi s dng cc thit b chng chy ngc

1 I htr n 1* l i r t n i i VO I i i p M i d i I Inty li) J J m I oi n(

101
(backflow preventer) hot ng theo nguyn tc thng p chn khng hay gim p. Vn
ny s c trnh by chi tit trong phn thit b trn ng ng.
- ng ng phi m bo hon ton trung tnh, k hn g gy ra s thay i cht
lng nc trong qu trnh vn c h u y n v khn g b nh hng bi cc tc nhn n
m n ha hc.
- tin cy ca h thng phi tuyt i, khng cho php gin on v bt k l do g.
- p sut trn h thng phi tng i ng u v c gi tr hp l ty theo mc
ch s dng. p sut qu ln ngoi vic lm tng kh nng h hng hay r r ca h
thng, cn gy ra tn hao nc mt cch khng cn thit v thm ch nguy him cho
ngi s dng. p sut thp hn 5 m c th lm cho m t s loi thit b nh my git,
m y nc nng trc tip,... khng hot ng c.
ng ng thng c du kn trong cng trnh m bo yu cu v m thut.
Tuy nhin nn hn c h vic chn lp ng to iu kin d dng cho vic bo tr v
sa cha h thng.

5.2.4. Cc ph kin ni ng
Cc ph kin ni ng hin c trn th trng rt a dng v chng loi. Nhng loi
ph kin ng thng dng l:

- ng lng (mng sng): dng ni hai on ng thng. M ng sng nha PVC c

dn bng keo chuyn dng. Mng sng thp trng km c kt ni bng cch to rng
trong. Hin nay trn thc t cng c loi ng nha c c h to vi mt u loe sn v
c th c ni trc tip vi nhau khng cn m ng sng.
- Co thng gc (90) v co li (135): dng chuyn hng ng.
- Ch T: dng chia nhnh ng ba theo gc vung. Ni ch T c th c ba u ng
bng nhau hay T gim (c u ng chia nhnh nh hn, VD: T gim 60-21 cho php ni
cc ng nhnh 21m m vo ng ng chnh 60mm).
- Ch Y : dng chia nhnh ng ba theo gc nhn.
- Ch thp: dng chia nhnh ng t.
- Nt: dng bt kn u ng. C hai loi: nt d n v n t rng (rng trong hoc
rng ngoi)
- Ni rng trong: dng gn vi cc thit b dng nc c rng ngoi (vi nc, bc
phun ma cu ha, . . . ) .
- Ni rng ngoi: dng gn vi cc thit b v sinh c rng trong.
- Ni gim: cho php ni chuyn tip hai u ng c ng knh khc nhau.

ng thp thng c to rng ngoi c th ni c vi cc ph kin khc. Ch

ni c lm kn nc bng cch qun bng Telon (keo la) hay ch gai c tm sn
chung quanh rng trc khi gn vo ph kin, n g v cc ph kin nha PVC c ni

102
bng keo c bit c cha dung mi Xylen c kh nng ha tan nha to ra mi hn
chc chn. Trong vi trng hp cng c th ni bng rng hay mt bch.

5.2.5. Cc loi thit b trn ng ng

- Vi m nhanh: ch dng cho p sut nh hn 10 m. C vi thng dng c ng
knh c rng l 21 mm, ng knh ming vi 15mm, thng c dng cho cc thit b
v sinh loi nh.
- Vi m chm: khng tin dng bng loi m nhanh, tuy nhin li an ton hn i
vi vn gim p lc nc va trong h thng.
- Van kha (shuto valve): dng c lp hon ton hay mt phn h thng cp
Iic khi cn bo tr hay sa cha. Cc loi van kha c th c m hon ton hay mt
phn. Cc loi van kho c ch to theo nguyn tc m nhanh nh van cu (ball
valve) hay m chm nh van cng (gate valve). Van m chm c lc ng m nh,
thng c s dng trn ng ng chnh hay ng nhnh quan trng, trong khi van
m nhanh thng c s dng trn cc ng nhnh nh, t quan trng. Van bm
(butterfly valve) l loi van m nhanh c lp t trn ng ng ln do c lc ng
m nh.
- Van mt chiu (check valve): Van mt chiu thn c t ti u di ca ng
ht m y bm hay ti nhng v tr thch hp theo thit k nhm duy tr dng chy theo
mt chiu duy nht nh trc. Van mt chiu nn c b tr hn ch trnh gy ra
tn tht nng lng Ltk: b khng cn Ihit.
- Van an ton (relie valve): dng d ho v cc on xung yu trong ng ng. Khi
p lc tng cao, van s l ni m ra x bt nc b dn nn. C loi van an ton
hot dng theo nguyn lc ngi mch in (piessure breaker) my bm khi p sut ti v
tr b tr van vt qu hay thp hn mt gi tr nh trc.

103
 - Van gim p (pressure reducing valve): thng c dng trong cc h thng cp
nc nh cao tng gim bt p sut d cho cc tng bn di. Van gim p cng c
th c b tr trn cc u ng nhnh khi p sut yu cu trn cc nhnh ny khc bit
nhau ng k, nhm phn phi lu lng trn cc ng ng nhnh mt cch hp l
hn. bo v ng ng v thit b, p sut ti a cho php ti trc van chnh khng
c vt qu 50 m.

ng h p lc
Khoen kn nc ^ y an chn pc

Khoen chm 1 __ _ tlii Vt chnh

L

H i n h 5 .2 : V a n ini p

- Van phao: dng ng m t ng mi khi mc nc trong b cha vt ra ngoi

mt gii hn nh trc.
Van phao

' Nc vo b

Nc ra khi b

I n h 5 .3 : V a n khi ch m c n c hm> p h a o

- Van cao (altitude valve): c dng khng ch t ng dng chy vo v ra

ca b cha trn mi hay sn thng. Khi mc nc dng cao hn gii hn cho php,
van s ngt in my bm, ngc li khi mc nc trong b h thp hn mt gi tr nh
trc, van s ng in my bm hot ng tr li.

- Van t (solenoid valve): l loi van ng m theo nguyn l t tnh. Van t hoi
ng theo hai nguyn tc khc nhau: thng m (van trng thi m khi khng c in)

104
hay thng ng (van trng thi ng tr khi c dng in chy qua). Van t thng
dc ch to hot ng bng in xoay chicu 220 VAC hay 24 VAC. Khi dng in
chay qua, cun dy s to ra t trng ht li thp kch hot vic ng m ca van t.
Van t l mt thit b rt ph bin v tin cy, thng c s dng trong cc h thng
cp nc t ng ho tng phn hay ton b.
- Van x kh (air reiease valve): khng kh c th lt vo ng ng theo ng ng ht
ca bm, theo cc ch ni khng kn hay do khng kh ho tan trong nc. Vic tch t
cc ti kh thng xy ra ti cc v tr cao ca h thng ng ng v lm gim tit din
thc t ca ng dn v tng sc cn i vi dng chy. Van x kh, do , thng c
h tr ti cc v tr ni trn nhm loi b cc ti kh. Van x kh loi n gin hot ng
theo nguyn l qu cu ni. Khi ti kh xut hin, qu cu khng c nng bi sc y
ca nc s ri xung v m ng cho khng kh thot ra bn trn. Khi ti kh gim
(ln, mc nc tiong ng dng cao ln tr li lm cho qu cu ng dn li, ngn khng
cho nc thot ra bn ngoi.

l n h 5.4: l7an x klii

- Thy lng k (flowmcter): dng theo di lng nc s dng trong h thng

cp nc. Thy lng k dc thit k theo nguvn tc c hc hay t tnh, c ng
knh u ni t 2 1min tr ln. Thy lng k thng c b tr nm ngang gim sai
s. Thy lng k c hc c ch to theo hai nguyn l:
Loi cnh q u t: c kch thc ming vo di 50mm v lu lng danh nsha t
1 - 1 0 IT1'/a.
Loi rnrhine: c kch thc ming vo t 50mm tr ln v lu lng danh ngha t
I5in'/gi tr ln.
Tn tht p lc qua thy lng k c hc c xc nh theo cng thc sau y:
H| = s . q 2 (m) (5.1)

trong :
H - tn tht p lc (m);
q - lu lng lnh lo n (//s);
s - h s cn cho trorm bne sau:

105
 Bng 5.1: H s sc cn ca thy lng k (mm )

D (mm) 15 20 32 40 50 80 100 150 200

H s cn 14,4 5,1 1,3 0,32 0,265 0,0207 0,0067 0,00013 0,00004
Ngun: TCXDVN 4511:1988.

- Thit b ngn dng chy ngc (backflow preventer): Nc trong HTCNTN phi
c bo v chng li s nhim do dng chy ngc thng qua ng ng v cc thit
b dng nc. Hin tng chy ngc gy ra bi hai nguyn nhn chnh: s gim p sut
trong ng ng chnh hay khi ng ng chnh b v v s tng p lc trn cc thit b
dng nc. Ti cc thit b v sinh, vic lp t cao vi qu thp so vi bn cng c
th gy ra s chy ngc. i vi cc thit b v sinh nh bn tm, chu ra m t,...
dng chy ngc c th trnh c bng cch to khong lu khng cn thit (air gap).
K hong lu khng ny thng c quy nh khng nh hn 2 ln ng knh ng cp
nc vo thit b v khng nh hn 25 mm. Vic ngn cch gia HTCNTN v h thng
cp nc cng cng c th c thc hin thng qua b cha trung gian b tr ngm hay
trn mi nh. Tuy nhin gii php ny c nhc im l lm trit tiu p sut d ca h
thng bn ngoi khi chy vo b v do cn phi c bm tng p cho HTCNTN.
- Thit b cm bin p sut hay mc nc (pressure transducer): Trong cc h thng
cp nc t ng ho, cc b cm bin thng c lp t theo di p sut trong h
thng hay mc nc trong b cha. Cc tn hiu ny s c c h u y n i ra tn hiu
dng in p. Cc tn hiu ny c th c pht hin v ghi n h n iu khin thc
hin cc hot n g ca m y bm , van t, van kh a hay nhng thit b khc trn h
thng cp nc.

Bng 5.2: K h on g lu khng ti thiu dng cho thit b phn phi nc (mm)

Cc thit b dng nc c ng knh hu hiu

Cch xa tng * Gn tng
D ca vi
D < 15mm 25 38
D < 20mm 38 60
D < 25mm 50 76
D > 25mm 2D 3D
N ii ii: Q iiv t h u n h t h i H c p l i o t i i n c h n t r o i i v CII t r n l i . B Xh' D ii, 1999.
* p dng khi khong cch t mp irong ca vi n tng bn ln hn 3D (trng hp tng n)
hay 4D (trng hp tng giao nhau).

Thit b lc trn ng ng (in-line filter): Nu nhng thit b dng nc c l thot

nc nh hn lm m , cn phi b tr thit b lc trn ng ng chng hin tng tc
nghn gy ra bi cc cn th. Cc thit b lc ny p dng nguyn tc lc bng li
(screen filter) c lu lng nh hay lc bng a (disk filter) c lu lng t nh n
lrun< bnh. Cc b lc ny cn c sc ra nh k chng tc nghn.

106
5.3. B TR N G N G C P N C BN T R O N G

5.3.1. Yu cu k thut

ng ng cp nc bn trong phi c b tr sao cho n c mi thit b v sinh

bn trong vi tng chiu di l ngn nht c th. Cch b tr v lp t phi to iu kin
d dng cho vic kim tra, sa cha, thay th. H thng ng ng phi c neo gi
mt cch chc chn vo cc b phn kt cu ca nh. v mt m quan, ng cp nc
nng v lnh c th c b tr chung trong hp ng t gc tng, c lp vi tuyn
cp in, in thoi, tivi, gas. Hp ny c np c th m ra khi cn thit. phn
bit, cn phi nh du ng bng k hiu mu theo quy nh.
Tuy nhin nn tun th cc quy nh sau y:
- Khng c b tr xuyn ngang qua phng . nn b tr dc theo tng.
- Khng nn chn kn di nn hay trong tng, gii php thng c p dng l
treo v du ng bn trn trn gi.
- Cc ng ng xuyn tng khng nn b tr chung vi ng ng thot nc, h
thng in hay in thoi, ng cp tivi,... Cc hp k thut c lp nm cnh nliau l
gii php l tng.
- Mi ng nhnh khng nn ph trch qu 5 thit b (mi thit b c lu lng chun
0,2 //s) v khng nn di qu 5 m.
- Ngoi tr cc khu nh quan trng, ncn b tr theo dng nhnh ct tit kim ng.
S cp nc bn trong v cng trnh thng c phn ra thnh 2 loi: cp t di
(up-feed) v cp t trn xung (down-feed).

5.3.2. S cp nc t di ln

Trong cc khu nh hay cng trnh thp, h thng nc lnh t di c th c cp

trc tip nh vo p sut ca h thng ng ng cp nc cng cng hay thng qua h
thng bm tng p (booster pump) v bn p lc (pressure tank). H thng phn phi
loi ny thng c p dng cho nh c chiu cao ti a khng qu 8-10 tng. Trong
trng hp chiu cao nh vt qu 10 tng, cn phi phn vng p lc v s dng cc
van gim p thch hp cho tng vng.

5.3.3. S cp nc t trn xung

i vi cc to nh c chiu cao trn 8-10 tng, gii php c th c chn la l

bm nc ln cc b cha trn mi (roof storage tank), t ng ng s dn nc
xung cp cho cc thit b v sinh. b phi lun lun d tr mt lng nc phc
v cho mc ch cu ha. Nhiu h thng b cha v ng ng cp xung c th c
b tr cnh nhau, hot ng song song nhng c th h tr qua li khi cn thit. Trong
gi t dng nc, mt b c th ngng hot ng sc ra hay sa cha nu cn. Vic
kim sot hot ng ca bm cp nc vo b c t ng ho nh cng tc in ng

107
in bng phao (float-operated electric valve)2. Thng thng nn b tr bm d tr
m bo h thng cp nc khng bao gi b gin on. Cc tng di cng cng c th
ap dng s cp nc t di ln, trong khi cc tng trn nhn nc t trn xung.

Hnh 5.5: B tr h th)is> i p nc bn tron\> (s cp HC t di)

Khi my bm hot ng ht nc t ng ng cng cng cp nc ln b, p lc

ng ng ny c th b gim ng k lm nh hng n cc khu vc ln cn. trnh
lnh trng ny, phi b tr b thu nc pha di ca nh. B cha ny c b sung t
dng nh ng ng cp nc bn ngoi. T my bm s ht nc t b thu cp
ln b cha trn mi.
Theo quy pham, i vi cc loi nh c h thng cha chy bt buc (xem phn
di), nc cp cho cha chy phi c tr trn b mi c th hot ng trong iu
kin mt din. Khi h thng cp nc t trn xung c th p ng cho c hai mc
ch. Nu p sut d ca ng ng cp nc cng cng bn ngoi nh h<m 6 m hay
khng n nh irong ngy, nht thit phi b tr b thu nc t ni hay ngm.
i vi nh cao tng, h thng phn phi nc c chia ra thnh nhiu vng p sut,
mi vng dc phc v bi mt h thng cp nc t trn c lp vi nhau. Ring cc
tang di cng, c ih p dng h thng cp nc t dui ln, c c ung cp bi p lc
liong mng cng cng.

5.4. T H I T K H T H N G C P NC BN T R O N G

5.4.1. Ti liu thit k

Ti liu dng d thit k h thng cp nc bn trong bao gm:

- Bn v mt hng v chi tit chung quanh khu vc, ch nhng chi tit cn thit nh
cao d mi ai. v tr. ng knh v chiu su t ng ca tuyn ng cp nc bn ngoi.

Kf,, liiH ntiiX ,lum,; ictt (ii Hi cho phK phao rct ni vn s n\t din tif> cho mx h/; Htyi lt J i i mc
nn\A x itii \h)h (cn di ii( (HX (/, phao di S (n c tiii h cp (i/ cho nuy htn. Kii<>(in
r / 7 / Iin hu! nih nKi ny khni nn (it nh ' trnl f/h rng hm h ni tn iir i nu ro iii m i thi lti \n.

I08
 - Bn v m t b ng cc tng nh v m t ct ca nh trong c m t v tri lp t ca
c c thit b v sin h .

- S liu v p lc dm bo ca dng ng nc cng cng bn ngoi.

- c tnh k thut ca ng v phu kin.
- Dc tnh k thut ca my bm.

H n h 5 . 6 : o n U' l n u i i ( (//> \ i. i n \ h i :'fi H o n ^ . \ ( f ( n ( ) l i i /i)

5.4.2. Ni d u n g thit k

Ni d u n g ihit ke huo g m thit k kv lliui va lp d ton. i vi n h n g c n g trnh

ln. c a n phi c th m phn thit k thi co ng . Phn bn v thiet k bao g m :

- ln v mt bn i khu nh li l 1/500, tron li d ch ghi r V tr, c a o , c h i u di

v u n g k n h cu a cc luyn onu cp vo nh.

- In V i' h tr mi bim h hna c p nc cho cc lnu n h t i 1/100 - 1/200. Ch

V m o (a k c c c h i tl i s a u d y : VI tr v e h u n e l oa i tlCl hi v s i n h v t h i t b d n g n c

kh c, c h i u dai- d n u knh \ kv hiu cua cc oan 011 trong h ihn g.

- Bn v h nh chiu Irc do (3D) c u a h thng VI t! l dii 1/50 - 1/100 v t l

ngaiiL 1/100 - 1/200. Cn th liin r cc thit bi l\ nc h nu kv hiu th eo q u v nh,
ili s hicu. c h i u ci v dnu knh cc o a n n^ nm Miianii v n u , ch iu c a o lp dt
ihii hi YC sinh.

- L p haH hyct m in h ve pho na p h p tnh toan, iroii d c nu r v cc vu cu

thit kc, tiu cliun kv tluit, inh mc d n m d si unti. p h n g p h p v s liu tnh

109
thy lc ng ng v cc hng mc cng trnh lin quan. Ch phn tch so snh v
la chn phng n k thut.

- Lp bng thng k vt t v thit b ca d n. Cc loi ph kin ng ng v

nhng vt l ph thng c tnh theo s lng ng da trn nh mc hin hnh.
Nhng loi vt t v thit b c bit c thng k theo thc t s dng. Ch m t
chnh xc cc thng s k thut yu cu i vi ng ng v thit b chng hn nh
ng knh danh nh, p sut lm vic, cng s u t,.. v cc quy cch k thut khc.
- Lp bng d ton cho h thng theo n gi v cc h s c quy nh. Cc chi tit
phc tp ca h thng cn c gii thch r bng bn v thi cng nh: chi tit cm my
bm, bn tng p, b cha mi, b thu nc, chi tit cm ng h nc, chi tit v cc l
cha sn khi thi cng cng trnh v chi tit v hp k thut.

n g nc i ni I 0 ) I Dng h o nc

ng nc i ngm Van x nc
" - r
*-) Vi nc chu ra
* - 1 Vi nuc u tiu

I I I Van ng m (khng gian)

h-
Vi nc bn cu
-------co Van ng m (m t bng)
1
------ Van m t chiu (khng gian) B vi tm hng sen

---------^ Van m t chiu (m t bng)

Vi cha ch y

My bm (m t bng)

Vi trn nc nng lnh

l^ My bm (khng gian)

H n h 5.7 : C c k hin quy c v li thm; ( p nc troii niu)

5.4.3. Thit k h thn g ng ng

Cc d liu sau y s c thu thp:

- p sut ti thiu ca ng cp nc bn ngoi.

- p sut lm vic yu cu ca cc loi thit b dng nc s c lp t.

Tnh ton lu lng

Phc tho s b tr cc luyn ng chnh, ng nhnh, v tr lp t thit b v
sinh v s lng thit b. T n h ton ng lng cho tng tuyn n g theo nguyn tc
cng dn ng lng. Xc nh lu lng tnh ton ch o tng tuyn ng ca tt c
cc cp trong h thng hng cch tra theo tng ng lng c a tuyn trn biu
trong hnh 5.8.

I 10
 Bng 5.3: ng lng tnh ton ca cc thit b v sinh

T nhn Cng cng

[.oi thit b s dng mrc ^mn c Gia S dng Tp the
(mm) thn nh1 chung4 ln'
Chu ra (lavatory) 15 1 1 2
lin tm hoc kt hp vi hoa sen 15 4 3,5
Chu bp 15 1.5 1 1,5
My gii gia nh 15 4 2,5 4
My ra chn 15 1.5 1 1,5
Vi hoa sen gia nh 15 2 2 2
Vi hoa sen tp th 15 5
u tiu 3,8 lt /ln x 15 4 5
u liu ln hn 3,8 lt /ln x 15 5 6
Bn cu t ng 6 lt/ln x 15 2,5 2,5 2,5 4
Bn cu t ng 13,3 lt/ln x 25 7 7 8 l
Vi gn ng mm 15 2,5 2,5 2,5
Vi phun nc 20 4
Vi phun ma l 1 1
Chu ra trong bnh vin 15 1

N s it n : Q u y c u t n h h n y ( p th o i n c hn tro n g v ( n g r n . B XY t ig , 1 99 9.

CHI TIT BIU XC NH NHU CU DNG Nc

0,0 L J _ L .._ L J _ L .. M 1 M I M 1. M I 1-1 1 I.. LJ. 1 I J

20 40 60 80 100 120 140 160 180 200 220240
NG LNG THIT B

* H id dinh c 3 'If i r lc i
1 Ap (n f o (loanh nl). ho mi, c nghip.
' Ap (u /li ; cho cc km ct -H. hch san, khu nh th, t ti hoe, h i trng, sn vn (/, nh th i (u. nh
i , hn ve...

111
 B ng 5.4

Van (?ng lng 10 20 40 60 80 100 120 140 160 180 200 220 240
xa
dinh L u hrns 1.72 2.17 2.89 3.37 3,75 4.12 4.49 4.84 5.15 5.43 5.68 5,90 6.12
lng yu cu //s)

ng lng 5 20 40 60 80 100 20 140 160 180 200 220 240

K!
\a Lu lne
0.313 0.90 . 55 2.02 2.38 2.7 2.98 3.25 3.5 3.75 4,0 4.24 4.48
yu cu (//s)

BIU XC NH NHU CAU DNG NC

NG LNG THIT BI

H n h 5.S: V! ln lu lm; tinli lon heo (i(<fiii I/I\>

B ng 5.5

Van x 1 ng lng 0 500 1000 1500 2000 2500 3000

dinh k
lirnu ! Lu lng yu cu (//s) 1,26 9,03 13.04 16,93 20,63 24,02 27,23

ng lng 0 500 1000 1500 2000 2500 3000

Kt x
1.tru lirii}: yu cu (//s) 1.26 8.01 13.04 16,93 20.63 24,02 27.23

I 12
 Tnh ton chiu di tng ng
tnh ton tn tht p lc cc b, cn xc nh chiu di tng ng ca tt c cc
on ng bng cch cng chiu di thc ca on ng tnh ton vi tng chiu di quy
i ca cc ph kin lp trong on ng y.
Khi tnh ton mng li cp nc bn trong, quy phm T C V N 4513:1988 cho php
xc nh gn ng tn tht p lc cc b nh sau:
- Sinh hot cho nh v nh cng cng: 30% tn tht chiu di.
- Sinh hot kt hp cha chy cho nh v nh cng cng: 20% tn tht theo chiu di.
- Sn xut kt hp cha chy: 15% tn tht chiu di.
- Cha chy: 10% tn tht chiu di.
Xc nh tn tht p sut cho php trn tuyn kim tra:

[Hl ] = H , - H 2

trong : H (m ) l ct nc o p ti thiu ti u tuyn.

H| = Z| + P

trong : Z |(m ) l cao ti v tr u ng cp nc chnh v Pj(m ) l p sut d ti

thiu ti . H 2(rn) l ct nc o p cn thit ti thit b dng nc.

h 2 = z 2+ p2

trong : Z 2(m) l cao lp t ca vi ly nc v p^(m) l p sut hot ng yu cu

ti . p sut hot dng yu cu thay i ty theo loi thit b.
Thng thng, p lc hot ng khong 10 m u tha mn cho hu ht cc loi thit
b dng nc gia dng c yu cu p sut hot ng cao nh vi hoa sen, my git, my
tm nc nng trc tip.
Theo TCVN 4513:1988, p lc nc t do cn thit ca cc vi nc v dng c v
sinh l 1 m v vi hoa sen l 4 m. Quy chun h thng cp thot nc nm 1999 ca B
Xy dng da theo Unibrm Plumbing Code do hip hi IA PM O ban hnh nm 1997
theo p sut hot ng ti thiu c cho trong bng sau.

Bng 5.6: p sut hot ng ti thiu cho nhng thit b dng nc

Loi thit b p sut hot dng (m) Lu lng (//pht)

/ 2 .?
Vi ra sn 5,8 11,4
Vi ra sn [ dng 8,7 9,5
Vi ra la va b loi 10 mm 7,2 17
Vi ra la va b oai 15 mm 3,6 17
My ra chn 10,9- 18
 1 2 3
Bn tm 3,6 22,7
Chu git 3,6 18,9
Vi hoa sen 8,7 11,4
Van cu w .c 10,9 11,4
Van ra w .c 7,2 - 14,4 56,8
Van ra u tiu 10,9 56,8
ng mi trong vn, 15m l \an 21,8 18,9
N gun: b s M e rrit and J . T. Rickets, 1994. Buiding design and construcion handhook.

Trong mi trng hp p lc hot ng ca cc thit b v sinh khng vt qu 6>0 m.

Tnh ton tn tht p sut n v cho php [S] ca tuyn thit k:
[S ] = [ H J / L, trong L(m) l chiu di tng ng ca on ng ang xt k c
ph kin.

Tnh ton s b ng knh n g

T heo H azen-W illiam , cng thc xc nh ng knh ng theo s c cho bi:
.85 V ' 205
10,666Q
D 1,85
(5.2)
sc
trong :
D - ng knh trong ca ng (m);
Q - lu lng tnh ton ca tuyn (m7s);
c - h s nhm iheo Hazen-W illiam, i vi ng nha PVC v ng thp trng km
c = 1 3 0 - 140.
B ng 5.7: Chiu di tng ng cho nhng ph kin khc nhau

ng Co gc Co li Ch T, chy Ni hoc ch T Van Van Van

knh ph 90" 45" i hng chy thng cng cu gc
kin (mm) (mm) (ram) 'mm) (mm) (mm) (mm) (mm)
10 305 183 457 91 61 2438 1219
15 610 366 914 183 122 4572 2438
20 762 457 1219 244 152 6096 3658
25 914 549 1524 274 183 7620 4572
32 1219 732 1829 366 244 10668 5486
38 1524 914 2134 457 305 13716 6706
50 2134 1219 3048 610 396 16764 8534
64 2438 1524 3658 762 488 19812 10363
76 3048 1829 4572 914 610 24384 12192
100 4267 2438 6401 1219 823 38100 16764
125 5182 3048 7620 1524 1006 42672 21336
150 6096 3658 9144 1829 1219 50292 24384
Ngii/I. Quy nnti h tig ( ]} thot H C hn trong v cny trnh, B X\' (lng, 999.

114
 Trong trng hp tng ng lng nh hn 450 c th dng bng 5.8 chn ng.
Chn ng knh ng ca tuyn ang xt theo quy cch sn xut. V cn xc nh lu
lng tnh ton cho tng on ng v cho ton b ngi nh phc v cho vic chn
my bm v ng knh ng.
Vn tc trong ng ng cp nc bn trong nn c khng c h gim ting n v
chng xi mn thnh ng.
T h e o T C V N 4513:1988:

V max = 1 , 5 - 2 m/s i vi ng ng v ng chnh.

V max = 2 m /s i vi ng nhnh ni vi thit b v sinh.
V max = 1,2 m /s i vi ng ng, ng chnh dng cho nhu cu sn xut.
V max = 10 m/s i vi cc thit b cha chy t ng.
Quy chun cp thot nc 1999 ch cho php ly vn tc ti a l 3m/s.

K im tra li clio cc tuyn nhnh khc

Nu ngi nh c b tr mch vng, tng tn tht p lc tng ng c ly ng vi

phn na vng. Nu chnh lch tn tht tnh theo 2 chiu dng chy ch k^ng qu 5%
th tnh ton kt thc.
Kim tra li p sut cc tng nh khc nhau , nu cn thit, s b tr cc van gim
p ti cc u ng nhnh.

Bng 5.8: ng knh ng v ng h km theo xc dnh theo ng lng thit b

Mc p sut t 2 kG /cm 2 n 3,2 kG /cm 2

ng h Chiu di ln nht cho php (m)

Cp cho
o v
nh v
ng
nhnh
chnh 12 18 24 ^0 46 61 76 91 122 152 183 213 244 274 305
(min)
(mm)

20 15 5 4 3 2 1 0 0 0 0 0 0 0

20 20 16 16 14 12 9 6 5 5 4 4 3 2 2 2 2

20 25 29 25 23 21 17 15 3 12 0 8 6 6 6 6 6

25 25 36 31 27 25 20 17 15 13 12 10 8 6 6 6 6

20 32 36 33 31 28 24 23 21 19 17 l 16 13 12 11 11

25 32 54 47 42 38 32 28 25 23 19 17 14 12 12 1 11

40 32 78 68 57 48 38 32 28 25 21 18 15 12 12 11 11

50 40 85 84 79 65 56 48 43 38 32 28 26 22 21 20 20

40 40 150 24 105 91 70 57 49 45 36 31 26 23 21 20 20

50 40 151 129 129 110 80 64 53 46 38 32 27 23 21 20 20

N ^ u ii; Q u y h it /1 h ig c p o /IC hn ro n \ v c trn h B Xy d n g , 9 99 .

115
 5.4.4. S lng thit b v sinh ti thiu

nh mc v s lng thit b v sinh ti thiu c b tr ty thuc vo loi cng

trnh. (Tham kho chi tit bng 4.1 trong Quy chun h thng cp thot nc bn trong
v cng trnh. B Xy dng, 1999).

5.4.5. Tnh ton b cha nc

B cha nc c b tr ngm bn trong cng trnh hoc trong khun vin ln cn.
Cc trng hp bt buc phi b tr b thu nc l:

- p dng s cp nc t trn i vi nh cao tng, c bm cp nc ln b cha

mi. Tc dng ca b ch yu l tch ri hot ng ca bm ra khi m ng li cp
nc bn ngoi cng trnh.

- p lc nc trong m ng li ng ng cng cng khng n nh, khng kh

nng cp nc thng xuyn. Trong trng hp ny b thu nc c tc dng iu tit
lu lng ngy.
Ngoi ra b cha nc cn c th c s dng d tr nc sinh hot hay cha
chy cho cng trnh trong trng hp c s c v ng ng bn ngoi.
Ty theo cng dng, dung tch b nc c th c tnh ton theo nguyn l iu tit
trn c s lng nc chy n v c h lm vic ca my bm (xem phn tnh ton
iu tit dung tch i nc) hay chn theo cu to:

(5.3)

(5.4)
n
trong : n - s ln ng m m y bm bng tay trong ngy.
Trong trng hp c h thng cha chy bn trong, cn phi d tr thm vo dung
tch b mt lng nc cha chy (xem mc tnh ton b cha trn mi). Trong trng
hp ny cn b tr cao trnh ca ng ht sao cho lng d tr cha chy khng c
dng vo cc mc ch khc.

5.4.6. Tnh ton b cha trn mi (kt nc)

Dung tch b cha trn mi:

(5.5)

116
 - Khi khng dng m y bm th ly bng tng lng nc dng trong thi gian thiu
nc trong ngy.
- Khi c dng m y bm vn hnh t ng: ly khng nh hn 5% ca lng nc
d n g Q n(1. Khi vn hnh m y bm bng cch ng m nhiu ln trong ngy:

w = (5,6)
4n
trong :
Q b - lu lng thit k ca my bm (mVgi);
n - s ln m m y bm mi ngy, ly bng 2-4 i vi mv bm kt nc h, 6 - 1 0
i vi m y bm dng vi bn p lc (pressure tank).
w - dung tch phng chy, ly bng lng nc cha chy trong thi gian bng 10
pht i vi h thng cha chy vn hnh bng tay v bng 5 pht i vi h
thng cha chy t ng.
Ch khng nn ly dung tch mt kt nc qu 25 m \ Nu cn dung tch ln hn,
c th chia ra thnh nhiu b hot ng song song. Chiu cao t b cha trn mi phi
m bo p lc cn thit cho tt c cc thit b dng nc v hng cha chy kt hp
nu c.
B cha trn mi phi c y cc thit b km theo:
- ng dn nc vo: c van kha v phao mc nc, mp trn ca ng cch mt di
ca np 100-150 mm.
- Ong dn nc ra (ng phn phi): ni thnh b pha trn lp nc d tr cha
chay, c van kha v cch thnh b ti thiu 50 mm.
- O n s trn: c ng knh ln hn hoc bn ng dn nc vo.
- ng x cn: c van kha t pha trc ch nhp vo ng x trn.
Trng hp ng dn nc c kt hp vi ng phn phi phi c van mt chiu v
van kha trn on ng phn phi nc.

5.4.7. Tnh ton bn p lc

Bn p lc l mt gii php thay th cho b cha trn mi hay i nc loi nh. Bn

p lc c th c p dng i vi nhng cnt trnh cn lu n vn m quan trong
kin trc hoc khng ch b tr b cha trn mi. Tuy nhin th tch ca bn p
lc thng khng xt n lng nc d tr cha chv gim gi thnh. Bn p lc
hot ng da theo nh lut Boyle-Maiiottc (P.v = const) l thit b d Ir p nng
thav v th nng nh trong trng hp b cha trn mi.
Bn p lc c lm bng thp, c dant hnh tr. pha trong c chia ra lm hai
ngan b'i mt mng n hi. Ngn cha pha nn c np vo mt lng kh nn to
ra mt p lc ban du. Bn p lc c b tr u mng ngay sau van kha chnh. Khi
bm hot ng, nu ing nc dng trong h thng nh hn lu lng cp cia bm, p

117
lc tng ln lm cho ti kh b nn li. Khi lu lng dng trong h thng tng ln t
ngt, p lc hot ng ca bm gim xung, ngn kh nn s gin ra b vo h thng
bng p lc d tr trong bn.
Th tch ca bn p lc c xc nh da theo lun lng cp nc v c cung cp
bi nh sn xut. C th xc nh s b dung tch bn W p theo cng thc sau:

w p = 7 w <ih (m 3) (5.7)
H 1-
trong :
k v w dh - xc nh nh ca kt nc trn mi;
a - t l gia p sut nh nht v p sut ln nht ca bn, ly t 0,7-0.8.

5.5. H T H N G C P NC CH A C H Y

Theo QPV N 4513 : 1988, h thng cp nc ~ha chy phi c b tr trong nhng
ngi nh sau y:
- Nh cao t 4 tng tr ln.
- Nh tp th, khch sn, ca hng cao t 5 tng tr ln.
- C quan hnh chnh, trng hc cao t 3 tng tr ln.
- Nh ga, kho bi, bnh vin, nh tr ,... c khi tch t 5000 m 3 tr ln.
- Rp ht, chiu bng, cu lc b, nh vn ha c t 300 ch ngi tr ln.
- Khn i sn vn ng c t 5000 ch ngi tr ln.
- Nh my, x nghip tr nhng trng hp c quy nh di y:
Cc loi cng trnh khng cn thit k h thng cha chy bn trong bao gm:
- Trong cc khu vc sn xut c bo qun hay s dng nhng cht c th pht chy,
n khi gp nc.
- Trong cc khu vc sn xut c bc chu la I v II, c thit b v vt t l loi
khng chy.
- Trong cc nh kho lm bng v liu khng chy, cha hng ha khng chy.
- Trong cc khu vc sn xut hng D, E bc chu la III, IV, V nhng c khi tch
khng qu 1000 m \ ...
Tham kho thm chi tit trong TCV N 4513:1988 v cc quy nh khc.

5.5.1. H thng cha chy thng thng

Lu lng tiu chun ca mt vi phun khng nh hn 2,5 //s. S' ct nc cha chy
s dng ng thi l 1 cho nhng cng trnh nh c khi tch di 25000 m ' v 2 cho
trng hp khi tch ln hn 25000m 3 hay c chiu cao t 12 n 16 tng. Cc quy nh
chi tit c cho trong bng 3, TCV N 4513 : 1988.
H thng ng ng cha chy c th s dng kt hp vi h thng cp nc sinh
hot bn trong. Trn mi lng phi b tr it nht 1 hp cha chy t nhng v tr d

118
thy v d tip cn. Khong cch gia cc hp cha chy c chn sao cho hai vi
phun c th hot ng ph ln nhau.
Vi phun cha chy thng c dng nn ct c ng knh l thot nc t 10-20 nim.
Vi c ni vi hp cha chy thng qua ng cun m m lm bng vi gai. Nhng
khp ni u l loi ni nhanh (quick coupling).

p lc cn thit hp cha chy c xc nh nh sau:

Hcc = Hv + H l (5.8)
trong :
Hv - p lc hot ng cn thit ti u vi:

Hv = , _ LdT (5-9)
1- c p a L d
Ld - chiu di phn c ca ct nc phun (m), t sau chiu di ny, nc b phn tn
ra thnh ma bi.Theo TCVN 4513:1988 Ld c ly tnht bng 6 m v c th
phun n im cao v xa nht ca khu vc do vi ph trch.
9 - h s vi phun c ly theo ng knh ming vi phun dv nh sau:
0,25
5.10)
d v + 0 , 0 0 1 d:
trong :
d v - ng knh ming vi phun, tnh bng mm.
a - h s c gi tr trung bnh bng 1 ,2 .
th sau y cung cp gi tr p lc yu cu ti vi phun H v cho cc trng hp
dng knh vi dv v chiu di ct nc c Ld.

Lu lng cha chy Q v ty thuc vo p lc u vi phun H v (m) v ng knh

ming vi. C th xc nh Q v theo cng thc sau:

Q v = 0,0025H ';9x9 (//s ) (5.11)

dv = 12mm
dv = 14mm
dv = 16mm
.....
dv = 18mm
dv = 20mm

L d (m )

H n h 5.9: A p l(' Ch i cua vi p h u n la c h y

119
 Tn tht p lc H[ ca ng vi gai c th c xc nh bng cng thc sau y:

H l = C Q L h (m ) (5.12)

trong :

c - h s sc cn ca ng, cho trong bng sau

L 0 - chiu di ng (m).

ng knh ng (min) ng vi gai thng ng vi gai c trng cao su

50 0 ,0 12 0,0075
66 0,00385 0,00177

5.5.2. H thng cha chy t ng

H thng cp nc cha chy t ng c s dng trong nhng ni c nguy c chy

rt cao nh kho cha hng d chy, siu th... hay trong nhng ni thng xuyn c
ng ngi nh cao c vn phng, rp ht. H thng cp nc cha chy t ng c
iu khin bi cm bin khi v nhit s t khi ng cc vi phun nc.
Mng li ng ng c b tr tch ri vi trng hp cp nc sinh hot v h
thng cha chy thng thng. Ton b ng ng c lm bng thp, lin kt vi
nhau Iheo dng nhnh ct. Khong cch cc vi phun c b tr cch u trn ng
nhnh sao cho c th bao ph c ton b din tch cn bo v. Vi phun cng c
lm bng kim loi, hot ng vi p lc nc t 0,5 kG /cm 2 tr ln.

5.5.2.1. Thit k h thn g cp nc cha chy t ng

C h n la loi vi pliun:

ng knh ca l phun c chn la sao cho tha mn iu kin v lu lng cn

thit. 1 am phun ca tng loi vi do cu to ca vi v p hrc nc quy nh. Cn tham
khao bng c tnh k thut ca vi phun bit c quan h gia ng knh l phun,
p lc nc v lu lng tng ng ca tng loi vi.
B tr vi phun v ng nhnh: khong cch ca cc vi piiun trn nhnh thng c
ly vo khong 1 , 2 - 1 ,4 ln bn knh phun ng vi p lc thit k ca vi.
Tiili ton (III knh hi nhnh v 0 /1 chnh:

ng knh ng c xc nh da theo tng lu lng do ng ph trch. Lu rng

lu lng ny ph thuc vo gi tr p lc c th ti cc v tr vi. Ngc li. cc gi tr
p lc ny l: thay i theo tn tht trn tuyn ng, ngha l theo lu ln dn trn
ng ng. Do , bi ton thy lc ca vi phun c th dc gii quyt theo phng
php tnh lp. Thut ton lp c th c tin hnh nh sau.

120
 5 .5 .2 .2 . X c nh dng kinh ng ca he thng cp UC cha chy t ng

- Chn s b ng knh ng cc ci-).

- Gi nh mt quy lut phn b p lc ty trn mng (c th chn phn b gim
clu hay phn b u).
- Tnh lu lng ca mi vi theo cnc thc (5.11) hay da theo c tnh k thut ca
vi phun do nh sn xut cung cp.
- Tnh li tn tht thu lc (theo cng thc Hazen-William) ca tng on ng theo
nguyn tc cng dn lu lng.
- Xc nh li gi tr ca p lc ng iii ti cc v tr vi.
- Lp li 3 bc sau cng cho n khi li aii hi t (sai bit v gi tr lu lng gia
2 ln tnh lin tip nh hn gi tr sai s cho php).

Bi ton tnh lp cho h thng vi phun cha chy c th c tin hnh kh n gin
rn EXCEL.

V d 1:
Chung c cao 10 tng, c 200 cn h vi s nhn khu trung bnh l 4 ngi/h.
Chiu cao mi cn h l 3,8 m, chiu di 16 rn v b rng l 4 m. Chiu di ti a ca
luyn nhnh mi tng c c lne l 10 0 m, chiu di ti a ca tuyn nhnh
mi cn h l 30 m, tng chiu di qu\ i tng dng ca cc ph kin trn tuyn
dc c lng bng 45% ca chiu d] [hc. Chung c c trang b thit b v sinh
lion chinh cho mi cn h bao gm: 1 bon tm, 1 vi sen, 4 lavab ra mt, 1 hn cu
t dng v 2 v tr vi nc ra trong bp Bm c vn hnh t ng a nc ln
b cha trn Iii v p dng s cp nc t trn.

Y a i t t :

a) Xc nh lu lng tnh ton cho tng cn h, cho tr,o tng v cno c chung c.
b) Xc nh ng knh ng cho tng cn h, cho tng tng v cho c chung c.

B i gii:

Tng s ng lng dng nc trone 1 cn h:

N ,, = 3 .5 + 2 + 4 X 1 + 2 . 5 + 2 X 1 = 1 4 ,0

Tng s dng lng ca mt tng:

N, = 20 X 14.0 = 280

Tng s ng lng ca chung c:

N = 280 X 10 = 2800

121
 Tra biu trong hnh 5.8:

Qh = 0,001 mVs

Qtng = 0,0063 mVs

Qchung = 0,0265 mVs

i vi tng cn h c ng lng tng c n g l 14,5 c th c h n ng 34m m
(D t[ = 2 5 m m ) lp t cho ng ng bn trong. Cc ng ng nhnh dn n tng
thit b v sinh s c xc nh theo yu cu ng knh ng ti thiu cho trong bng 2 .
xc nh ng knh ng ph trch cho mi tng ta kim tra cho cn h xa nht ca
tng. Chn trng hp kim tra l vi sen lp t cao 2 m so vi cao trnh mt sn
ca tng h, gi tr p sut hot ng cn thit ca thit b l 8,7 m. Nh vy ct p cn
thit l 2 + 8,7 = 10,7 m.

Gi nh p sut d sau van gim p mi tng khng nh hn 20 m. dc tn tht

nng lng trung bnh ca tuyn kim tra l:

s = (2 0 - 10,7)/145 = 0,064

p dng cng thc Hazen-W illiam xc nh ra ng knh ng cn thit:

1.85 ^ ' 2()5

10,666 Q
D 1,85
= 0 ,0 6 6 m
sc 0 ,0 6 4 x 1 3 0 '

Phng n : chn ng 76 m m lm ng nhnh cho mi tng

Kim tra vn tc: V = Q/A = 0,0063/(3,14 X 0,0662 / 4) =1,84 m/s < 2,5 m/s

Phng n 2: chn 2 ng nhnh cho mi tng

p dng cng thc Hazen-W illiam xc nh ra ng knh ng cn thit:

/ I x s V 1' 2 0 5
/ 10 ,6 6 6 Q 1-*5 1 0 ,6 6 6 x 0 ,0 0 3 1 5 1'*5
D= 1,85
= 0 ,0 5 m
s c 1'85 0 ,0 6 4 x 1 3 0

Nh vy c th chn b tr 2 ng c ng knh danh nh 60 mm lm ng nhnh

cho mi tng.

xc nh ng knh ng ng dn nc t b cha trn mi xung n tng tng

(b tr thng ng xuyn qua cc tng), ta chn s b ng knh ng theo nguyn tc
gii hn vn tc V max = 2 m/s.

4Q 4 X 0,0265
D = = 0,130 m
7lV V 3, 14 16 X 2,0

122
 ng knh ng dng c chn l 140 nim theo quy cch sn ;ut.

Vic b tr b cha trn mi phi c xc inh sao cho m bo p lc trn ng

ng ng ti mi v tr khng nh hn gi tr 20 m gi nh trn. Trong trng hp
kh khn, c th xem xt gim nh gi tr ny.
K im tru li tn tht p sut trn ng n< ni

p dng cng thc Hazen-William, tnh ra c s = 0,038 m/m. Nh vy gim p

sut trn ng ng chnh (vo khong 0,15 m/tng) khng ng k so vi s tng p
sut do gim cao ca mi tng (3,8 m/tng). iu ny cho php kt lun nu m bo
p lc trn ng ng ti v tr trc van gim p ca tng trn cng ln hn 2 kG /cm 2 th
s gi thit v p lc sau van s ng i vi cc tng bn di. Trong trng hp h
thng nh, c th chn ng knh ng cp nc bn trong theo bng 5.8 (xem v d 2).
V d 2: s dng s liu ca v d trn, dng hai luyn nhnh cho mi tng:

p sut lm vic sau van gim p: 2 kG/cin 2

Chiu di tuyn di nht ca tng: 10 0 m

Chiu di tuyn di nht ca cn h: 30 m

ng lng cho 1 cn h: 14,0
ng lng cho 1/2 tng: 140

Tra bng 5.8 ta c:

ng knh hu hiu ca tuyn nhnh chnh trong cn h l 25 mm, ta chn ng 34 mm.
ng knh hu hiu ca tuyn nhnh trong mi tng l 50 m m , ta chn 2 ng 60 mm.

123
 BI TP

Bi 1. Ml cn h c 6 nhn khu. Chiu cao cn h l 3,8 m, clu di 20 m v b

rng l 4 m. Thit b v sinh hon chnh trong cn h bao gm: 1 bn tm, 2 vi sen, 4
lavab ra mt, 2 bn cu t ng v 2 v tr vi nc ra trong bp. Bom c vn hnh
t ng a nc ln b cha trn mi v p dng s cp nc t irn.
a) Xc inh ng knh thy lng k (ng h nc) v ng knh ng chnh cn thit.
b) S dng s liu ca bi tp 1, hy xc nh dung tch b cha v kt nc mi cp
bng bm t ng. Bit rng tiu chun dng nc l 200 //ngi-ngy.
c) Xc nh cao trnh b tr ca kt nc trn mi sao cho m bo p lc d ti thiu
ti cc thit b l 8 m. Nhn xt g v kt qu ny?
d) Hy xem xt v ngh cc gii php thay th cho kt nc mi.
e) Hy thit k li h thng cp nc trong nh vi s cp nc t di v khng
dung kt nc mi.
Bi 2. Hy thit k h thng cp nc v cha chy vn hnh bng tay cho mt ngi
nh c 8 nhn khu. Chiu cao nh l 5x3,8 m, chiu di 20 m v b rng l 4 m. Thit
b v sinh hon chnh trong nh bao gm: 1 bn tm, 2 vi sen, 4 lavab ra mt, 2 bn
cu t ng cho mi tng v 4 v tr vi nc ra trong bp. Bm c vn hnh t ng
a nc ln b cha trn mi v p dng s cp nc t trn.

124
 Chng 6

H THNG THOT NC BN TRONG

6.1. GII TH IU

Ni dung trnh bv trong chng ny ch yu da theo Quy chun Cp thot nc

trong nh v cng trnh 1999 ca B Xv dng. So snh vi quy phm c c ban hnh
nm 1988. c th nhn thy nhiu im khc bit co bn.
H thng thot nc bn trong (HTTNBT) c nhim v:
- Thu tt c cc loi nc thi v sinh.
- Thu cc loi nc thi c ngun gc sn xut.
- Thu nc ma trn mi nh.
Ty theo tnh cht khu vc v iu kin c th, h thng thot nc bn trong c th
c ni trc tip vi h thng thot nc d thi hay phi x l s b trc . Trong
trng hp khu vc c lp, xa mng li thot nc khu vc, HTTNBT phi gm c
cng trnh x l thot nc thi ti ch.

6.2. P H N L O I H T H N G 1 H O T N C B N T R O N G

Tv thuc vo ngun gc ca nc Ihi trong nh, c th phn HTTNBT ra lm cc

loi sau y:
- H thng thoi nc sinh hot: dn nc thi chy ra t cc dng c v sinh.
- H thng thoi nc ma: dng tliu nc ina trn mi nh hay trong sn.
- H thng thot nc sn xut: ty theo ngun gc v tnh cht nc, nc thi c
ngun gc sn xut c th nhp chung hay tch ri vi cc h thng cn li.
Cc ng dng thot nc bn trong c th c lm bng kim loi (gang, ng,
thau, thp), nha (ABS, PVC) hay ng snh cng cao. Cc loi ng bng kim loi
khng dng cho h thng thot nc ngm. ng cng bng b tng c s dng vi
ng knh ti thiu l 10 0 mm. ng cng v ph kin phi c ni bng m cao su
mm. Khng s dng xi mng Portland lm mi ni tr trng hp sa cha.

6.3. H THNG THOT NC SINH HOT

H thng thot nc sinh hot bao gm cc b phn sau:

- Cc thit b thu nc thi (thit b v sinh hay phu thu nc).
- B phn chn.
- Mng li ng ng thot.
- Cc loi cng trnh.

125
 - Trm bm.
- Cng trnh x l cc b.
6.3.1. Cc thit b v sinh

Cc chi tit k thut ca mt s thit b v sinh thng dng c cho trong bng 6 .1.
- Bung tm hng sen.
- Bung tm c vi hoa sen c kch thc ti thiu 0,9 X 0,9 m, chiu cao lt gch
men ti thiu 1,8 m k t sn. Sn c dc t 1% n 2% hng n phu ha rnh
thu nc.
- ng thu nc trong bung tm bn di phu c ng knh t 50 n 10) nm.
Rnh thu nc c b rng khng nh hn 0,2 m, chiu su ban u 5 cm; dc khng
nh hn ] %, hng v phu thu nc.

Bng 6.1: c im ca cc thit b v sinh

Kch thc D ng D ng Dng

Loi thit b cap thot t'n
L (cm) B (cm) H (cm)
(mm) (mm) (nm)
Bn tm 150-180 70-100 40-60 21 42 11
Vi sen 40-70 21 54 21
Lavab 60 - 75 3 0 -60 12- 17 21 34 21
Chu ra nh bp 4 0 -45 1 5 -2 0 21 42 11

- Phu thu nc
Phu thu nc gm c phn li chn rc, phu thu ni n ng thot nc Kch
thc phu thng dng ln lt l 150 X 150 X 135 mm v 250 X 250 X 200 mm tng
ng vi ng knh ng 50 m m v 100 mm.
ng lng thot nc ca mt s loi thit b v sinh c cho trong brg 6.2.
Nhng loi khc c th tham kho thm trong Q uy chun cp thot nc bn trcng nh
v cng trnh (1999), gi tt l QCCTNTN 1999.

Bng 6.2: ng lng thot nc ca cc thit b v sinh

T nhn Cng ccng

ng knh nh
Thit b v sinh nht ca xi S S
>3
1 ngi dng cng
phng (mm) ngi
chung hiu
/ 2 .? 4 5
Chu ra nh bp 32 2 2 2

My ra chn 38 2 2 2

My git 50 3 3 3
Bn tm hoc vi sen v kt hp 38 3 3

126
 1 2 3 5 6
("hu ra s 32 1 1 1 1
Nhm 2-3 chu ra s 38 2 2 2 2
Iung tm hoa sen 50 2 2 2
Au tiu 38 4 5
In cu x trng lc 6 lt/ln x 76 3 3 4 6
ln cu x trng lc 13 lt/ln x 76 4 4 6 8

Lu lng nc thi ca thit b v sinh c cho trong bng 6.3. ng lng thot
nc ng vi cc c xi phng c xc nh theo bng 6.4.

Bng 6.3: Lu lng nc thi ca cc thit b v sinh

Lu lng nc thi ng knh ng ti thiu

Loi thit b
' /s) (mm)
Chu ra mt, ra tay 0,15 34
ln tm c vi trn 0,8 42
Hn tm c bnh nc nng 1,1 42
Vi hoa sen 0,2 - 0,3 42
Vi nc nng lnh 0,4 42
Bn cu t ng (git) 1,4 - 1,6 50
ln cu di 1-1,4 50
"-/1

ln tiu c vi bn rni 42
1
0

II1 tiu 0,1 - 0,2 42

Mng tiu (cho 1 m di) 0,1 34
Vi ti 0,3 42
Vi phun nc ung 0,05 27

6.3.2. M n g lui ng ng thot nc sinh hot

Mng li ng thot nc bn trong bao gm nhiu oan ng c chiu di v ng

knh khc nhau, ni t cc thit b thu nc th; hay mng thu nc ma ra n h thng
thot nc ng ph. Nc thi t cc thit b v sinh c x vo h thng thot nc
cng cng theo nguyn tc t chy. Hnh 6.1 m t cc b phn thng gp trong mt
h thng thot nc trong nh.

Bng 6.4: ng lng thot nc ca xi phng

ng knh xi phng (mm) ng lng thot nc

127
 Thot nc ma

Hnh 6.1b: H t i* th o t n c rin\> h i t

 n g thu nc mi n g ng thu nc bn n g thu nc ma

H n h 6 .c: hny thot c chun

Vic i hng dng chy trong h thng ng ng thot nc trong nh c thc

hin lling qua cc ph kin c gc ni thun, trnh s dng gc ni 90".

a) im nguna

O ng thot nc nm imang c nhim v chuyn nc t thit b v sinh vo ng

n ihot nc. O ne nhnh c th c t trong sn nh (trong lp x bn gia c
nn - doi vi Irim hp tng trt); hay c treo bn di trn nh (c lp trn gi
c h e kn b n d i).

Kch thc ca ng thot nc c xc nh t tng s ca tt c cc ng lng

thit b ni vi Yi. ng knh li thiu ca ng ngang khng nn nh hn 50 mm.
dc ti thiu ca ng thot nc ngang l 2% hng n im thi. Trong trng hp
bt li v a hnh hay i vi nhng ng c ng knh t 10 0 ram tr ln, cho php ly
dc li thiu l 1 %.
V i c h tr n a n h n h ph i t u n th c c q u y lc s a u y :

- Khng dc treo ns qua phng , nh bp.

- Chiu su chn m han u k h n g n h hn 1 0 CITI.

- dc du (de thni tc) v khng qu ln (d b tr).

- Tron trng hp II thot phn, ng knh ng nhnh khng nh hon 100 mm.

129
 - Gia ng nhnh v thit b v sinh phi b tr cc xi phng chn ngn khng cho
hi thot ngc tr li.

b) ng ng

Ong ng c nhim v lp trung nc t cc ng nhnh v chuyn xuyn qua cc

tng a xung pha di. ng knh ng ng c xc nh theo tng s' ng
lng do ng ph trch v chiu di ca ng (xem bng 6 .6 ).

ng ng c b tr theo nhng nguyn tc chung sau y:

- Nn b tr tp trung gn cc thit b v sinh gim chiu di ng ngang.
- C ng knh khng nh hn 50 mm v khng nh hn ng knh ng nhnh ni
vi n.
- ng thot phn uc b tr ring v c ng knh khng nh hn 10 0 mm.
- Nn gii hn s ng ng cng nh cng tt.

Bng 6.5: ng lng thot nc ca ng tnh theo lu lng thi

Lu lng thi (//s) ng lng thot nc

<0,5 1
0,5 0.95 3
1 - 1,89 4
1,95-3,15 6

Bng 6.6: ng lng ph trch v chiu di ti a ca ng thot nc v thng hoi

ng knh
32 38 50 64 76 100 125 155 200 250 300
ng (mm)
ng lng ti a
J(2,
n.
00

ng ng" 1 2 () 161-" 32(1) 256 600 1380 3600 5600 8400

Ong ngang" 1 g(> 7 2 0 (. 2640'5 4680(5) 8200'
1 1 14, 35<4) 216(M 428<m
ng thng hi 1 8 24 48 84 256 600 1380 3600
Chiu di ti a (m)
Ong ng 14 20 26 45 65 91 119 155 228
ng ngang 14 18 37 55 65 91 119 155 228

Ghi ch:
(1) Khng bao gm tay xi phng.
(2) Ngoi tr cc chu ra, u tiu v my ra chn.
(3) Ngoi tr 6 ng xi phng v bn cu.
(4) Nu chi c 4 bn cu hoc 6 ng xi phng th c thot vo bt c ng ng no. Nu ciii co
3 bn cu hoc 6 ng xi phng th c thot vo bt c ng nhnh hoc ng ngang no.
(5) Da trn dc 2%. Trong trng hp d dc 1%, nhn s ng lng vi h s 0,8

130
 c) ng x (ng thot)
- ng x c nhim v chuyn tip t cui ng ng sn nh ra ging thm hay cng
thot nc ng ph.
- Mi ng ng c ni vi mt ng x.
- C th b tr nhiu ng x tp trung vo mt ging thm.
- ng knh ng x ly t 50 mm n 150 mm.
- Chiu di ti a ly t 10 m (i vi ng nh) n 20 m (i vi ng ln). Nu
khong cch gia nh v ging thm qu xa, c th b tr thm mt ging thm cch nh
t 3m n 5m; ging thm cn li c b tr ti v tr nc tp trung vo cng thot
nc ng ph.
- ng x nu t di mng nh phi c bo v trnh nt gy c hc do ln.
d) ng thng hi
- ng thng hi c b tr nhm mc ch thot cc kh d chy v c mi kh chu
t ging thm len li vo ng ng. Ngoi ra ng thng hi cng gip khc phc hin
tng nghn kh trong ng ng. ng thng hi c th c ni trc tip vi ng nhnh
gip cho khng kh len li vo trong h thng thot nc thi, gi cho c c xi phng
lm vic c bnh thng.
Thng kh

131
 - ng knh ca ng thng hi ring bit c xc nh da theo chiu di ng v
tng s thit b v sinh ni vi ng nh c nu trong bng 6 .6 khng nh hn 32 min
v khng nh hn ng knh ng thot nc m n ni vo. ng thng hi khng c
c chiu di on nm ngang vt qu 1/3 tng chiu di.

Ngoi ra vic b tr ng thng hi cn c quy nh bi cc nguyn tc sau:

- u trn ca ng phi vt cao hn mi nh t nht l 150 m m v cch tng ti
thiu l 300 mm.

- ng thng hi phi cch xa ca s, ca i, ca ly gi, ban cng t nht l 3m hoc

cao hn t nht l 900 mm.

- Cc ng thng hi c th i ring hay kt hp li bng cc ng ln hn c kch

thc bng tng cc ng n l.
- Mi ng ng thot nc chy sut t 10 tng tr ln cn c ng thng hi h sung.
iig thng hi b sung ny chy song song vi ng ng thot nc, v thng vi ng
ng ny cc v tr cch nhau 5 tng mt. Kch thc ca ng thng hi b sung ny
khng nh hn bt k ng knh ng thot nc hay thng hi no khc.
e) H thng thot nc v thng hi kt hp

Quy pham cho php s dng chung mt ng ng va thot nc va thng hi. H

thng thot nc v thng hi kt hp ch s dng trong nhng trng hp m kt cu
cng trnh khng cho php p dng kiu thng hi ring bit bnh thng.
ng ng thot nc v thng hi kt hp phi c ng knh ti thiu gp i so
vi ng thng hi ring. H thng thot nc v thng hi kt hp ch yu c s dng
nhng ni thot nc sn c din tch ln. Ngoi ra khng c php p dng h
ihng kt hp cho nhng thit b v sinh t cao hn mt sn hay nhng thit b v sinh
d gy tc ng.

Khi cha c php ca c quan qun l th khng c s dng ng ng lm ng

thng hi.

0 Xi phng
Mi thit b v sinh, ngoi tr nhng thit b c xi phng gn sn, u phi c lp
xi phng ngoi. Mi xi phng c th ph trch Ihiu thit b cng loi, gn k nhau v
c cao trnh ngang nhau. Khong cch thng ng t ming thot ca thit b v sinh
n l trn ca xi phng cne ngn cng tt v khng vt qu 600 mm.
Mi xi phng ca thit b u phi c ng thng hi ni vi tay xi phng. Khong
cch t im ni ny n ming thot ca xi phng ly theo quy nh (bng 6.7) nhng
klng c nh hn 2 ln ng knh tay xi phng.

132
 Bng 6.7: Khong cch nm ngang ca cc tay xi phng

ng knh tay xi phng Khong cch t xi phng ti ng thng hi

(mm) (ram)

32 760
40 11 0 0
50 1500
76 1800
> 100 3000

H n h 6.2b: Tln kh cho cc ni; nhnh.

a) S d kt hp; h) S(f c rini hit; c) S vng.

g) Ca thng tc
Ca thng tc dc b tr trn ng thot mi tng, c dng nm ngang (ng kim
tra) hay co 90 (ng sc ra). u ng kim tra-sc ra c np vn, khi cn sc ra, np
y c m ra c th thng ra bng nc p lc cao hay dy my do. Cng c th
dng cc loi dung dch lm tan cn cu trong ng. Khong cch ln nht gia cc ng
kim tra-sc ra c cho trong bng 6 .8 . Trn ng ngang thot nc ti nhng ch c
dng ct 135 chuyn hng u phi t b sung mt ca thng tc.

Ca thng tc phi c b tr v tr thun li cho vic lm v sinh ng ng v

phi c lp t ng chiu dng chy. Khng cn b tr ca thng tc nu chiu di
ca on ng di 1,5 m hay c dc ln hn 32%.
h) Be lng ct
Cc b lng ct c th c xv dng bng gch b tng, thp hay cc vt liu khng
thm khc. B c cu tao thnh hai ngn. Th lch ca ngn vo c xc nh theo
lu lng:

133
 Bng 6.8: Khong cch ln nht gia cc ng kim tra - sc ra

Khong cch ln nht (m)

ng knh ng
Sinh hot, Sn xut c nhiu Loi thit b
(mm) Sn xut sch
sn xut bn cht l lng
50 15 12 10 ng kim tra
50 10 8 6 ng sc rra
100-150 20 15 12 ng kim tra
100-150 15 10 8 ng .sc ra
200 25 20 15 ng kim tra

- Nu Q < 75,7 //pht th W mjn = 0,2 nr

- Nu Q > 75,7 //pht th c mi 16,9 //pht tng thm cng thm 0,09 nr

Ngn ra c th tch li thiu phi bng th tch ngn vo. ng ng vo v ra c

cM!g kch thc v khng nh hn 76 mm. Vch ngn c hai l c cng ng knh
dc b ir so le vi cc l vo v ra khng to ra dng chy tt qua b.
i) B lng cn
Khi nc thi t mt thit b hoc ng ng thot nc c cha cht thi In (ch
yu l cc nh my hoc c s sn xut, ch bin) c th gy ra tc nghn trong h
thng chung. B lng cn dng thu bn t v cc loi cht thi sn xut khc c th
dc xy dng bng gch, b tng, thp hay cc vt liu khng thm khc. Dung tch b
c lv bng lng nc chy vo b trong thi gian t 5 n 10 pht. Din tch mt
ct ngang ca b c chn sao cho vn tc dng chy qua b t 0.00 V(),005m/s.

6.3.3. Tnh ton m ng li thot nc trong nh

a) ung ng thot nc thi sinh hot

ng knh ng thot nc cc cp trong cng trnh c xc nh trn c s tng
ng lng ca cc thit b do ng i ph trch (xem bng 6 .6 ).
b) Lu lng nc thi sinh hot cho cc x nghip
Lu lng nc thi sinh hot tnh ton cho cc x n g h ip c cho trong cng
thc sau:

<6 -'

trong :

Q lh - lun lng nc thi tnh ton;

q - lu lng nc thi ca tng thit b v sinh cng loi trong on ng tnh ton;
n - s thit b v sinh cng loi trn on ng tnh ton;
p - h s hot ng ng thi ca cc thit b v sinh, ly theo bng 6.9.

134
 Bng 6.9: H s hot ng ng thi p ca cc thit b v sinh trong x nghip

S' lng thit b trn on ng tnh ton

Lo;.i thit b v sinh
1 3 6 10 20 40 60 100 200

Chi ra mt, tay 100 100 100 100 100 100 100 100 100
Bn :iu t ng 100 100 60 40 15 10 10 10 10
Bn :iu treo tng 100 70 50 40 35 30 30 25 25
Bn l u t ng 100 30 25 20 15 10 10 10 5

6.4. i T H N G T H O T N C MA

Nic ma t mi nh, sn bi s c thot ra h thng cng thot nc ma ring

bit h}c cng chung trong trng hp khng th b tr h thng cng ring. Nc ma
khn c php thot ra h thng cng dnh cho mc ch thot nc thi v sinh,
ngoi tr nhng n ng ip c bit c quy nh bi c quan c thm quyn.
ing ng thot nc ma bn trong cng trnh phi c lm bng kim loi (gang,
tlip r n g km, ng, thau...) hay nha (ABS, PVC).
H thng cng bn ngoi cng trnh c lp t chung quanh chu vi ca cng trnh
ni gia h thng Ihol nc ma bn trong vi knh mng thot nc hay h thu nc
l ng. H thng thot nc ma nn c b tr v thit k theo nguyn tc t chy.
Trong trng hp khng th gii quyt bng gii php t chy, nc ma c th c
tp trung v h ga thu nc c trang b my bm thot nc t ng.

6 A l . C u to

H thng thot nc ma mi chnh bao gm ng mng, m ng xi thu nc ma (s

n), ng ng v ng ngang. Trong trng hp cc mt chn nc hay cc kt cu khc
c cao trnh cao hn mi chnh th cn c thm h thng thot nc ph c lp.
H thng thot nc ma mi nh c thit k trn c s mt trn ma ln nht lin
tc cc chu k lp li l 1 nm hoc trn ma 60 pht c chu k 10 0 nm.
Mi:n \ i thu nc ma:
Cc th c b tr mt bn (thng dng khi chiu di hng nc < 12 m) hay hai bn
mi m. Mng xi c b tr bn ngoi hay trong tng bao ty theo yu cu kin trc.
Chiu r n g s n 50 - 6 0 cm; c h i u su n c trong m n g t h a y i t 5 - 10 CI1 ( u
mng) v tng dn dn 20 - 30 cm ( cui mng). Trn s n c b tr li chn rc
gi ki l cy cn bn v iu tit bt lu lng trn khi ma qu ln bo v ng
ng ng knh li chn v pliu thu ly t 1,5 n 2 ln ng knh ng ng, chiu
cao trn 10 cm, dc lng mng chn t 0 ,0 0 2 - 0 ,0 1 .
i di thu II HIHI:

ing knh ca ng dng c chn khng nh hn 100 mm. Nu c ng nhnh,

ng rhnh phi c ni vi ng ng chnh theo dc > 5%, on thng ng ca
ng m nh 1 - 1,2 m.

135
 Lu lng tnh ton cho ng ng v phu thu nc ma c cho trong bng 6.10
sau y:

Bng 6.10: Kh nng thot nc ca phu v ng ng

ng knh phu hay ng ng (mm) 80 100 150 200

Lu lng tnh ton cho mt phu thu (//s) 5 12 35

Lu lng tnh ton cho mt ng ng thu (//s) 10 20 50 80

6.4.2. Tnh ton tliy lc thot nc ma mi nh

a) Lim lng thot nc Hli nh'.

Phng p hp i :
1. Da vo cng . ma (bng 6.12), c th xc nh din tch mi cho php ti a
ng vi ng knh ng ng cho trc.
2. Chn ng knh ng v xc nh lu lng tnh ton q ca ng ng theo bng 6.11.

3. Xc nh s ng ng cn thit: n > -----.

Qixl

Bng 6.11: Din tch mi tnh ton cho php theo dng knh ng dng

Din tch mi tnh ton cho php ti a (m2)

D ng
Lu lng ng vi cc cng ma khc nhau
ng
( 1/s) 25 50 75 100 125 150
(mm)
m/h m/h m/h m/h m/h m/h
50 1.5 20 2 10 1 67 51 40 34
75 4,2 600 300 200 150 12 0 100
100 9,1 1286 643 429 321 257 214
125 16,5 2334 1117 778 583 467 389
150 26,8 3790 1895 1263 948 758 632
?0 0 57,6 8175 4088 2725 2044 1635 1363

Bng 6.2: Gi tr cng ma thit k q 5

Trm kh tng qSm, (//s-m2) qsmax (mm/h)

1 2 3
Ban M thut 0,03877 139,57
Bo Lc 0,05063 182,27
C Mau 0,05074 182 66
Lt 0,04162 149,83

136
 2 .?

Nng 0,03706 133,42

Hu 0,03706 133,42

Nha Trang 0,02817 101,42

Phan Thit 0,03261 117,40
Pleiku 0,03923 141,23
Qung Ngi 0,04162 149,83
Qung Tr 0,04219 151,88
Quy Nhem 0,03421 123,16
Sc Trng 0,04504 162,14
Tuy Ha 0,03569 128,48
TP. H Ch Minh 0,04960 178,56

Cng c th chn trc s lng ng ng da theo iu kin kt cu v kin trc. T

d xc nh lun lng thot nc ph trch ca mt ng. Sau da vo gi tr lu
lng cho trong bng 6 . 1 1 xc nh ra ng knh ng ng cn thit.
4. Tnh ton tng din tch phu thu nc ma sao cho > 2 ln din tch mt ct ca
ng ng.

Phng plp 2:

Lu lng thot nc ma trn mi c tnh theo cng thc sau:

Q = KFq5 (//s) (6.2)

trong :
Q - la lng nc ma;
K - h s, ly bng 2;
F - din tch mi thu nc, (m 2). Nu pha trn mi c tng ngn thng ng th:
F = F mi + 0.3 F tng.

q 5 - lp nc ma tnh ton ng vi thi gian tp trung nc l 5 pht v chu k trn

cng p = 1 nm.

b) Tnh ton miy xi:

Pli((>'iivt il p I : s dng bng tra

K c h th c m n g thot nc d n g b n nRuvt c th c x c n h n h a n h c h n g
b'mg cch s dng bng 6.13.

137
 Bng 6.13: Xc nh ng knh mng thot nc ma dng bn nguyt

D mng Din tch mi lnh ton cho php ti a (m2)

(mm) ng vi cc cng ma khc nhau
dc 0,5% 50 mm/h 75 mm/h 100 mm/h 125 mm/h 150 mm/h
75 31,6 21 15,8 12 ,6 10,5
100 66,9 44,6 33,4 26,8 22,3
125 116,1 77,5 58,1 46,5 38,7
175 178,4 119,1 89,2 71,4 59,5
150 256,4 170,9 128,2 10 2 ,2 85,3
200 369,7 246,7 184,9 147,7 123,1
250 668,9 445,9 334,4 267,6 223
dc 1% 50 mm/h 75 mm/h 100 ram/h 125 mm/h 150 mm/h
75 44,6 29,7 22,3 17,8 14 J
100 94,8 63,3 47,4 37,9 31,6
125 163,5 108,9 81,8 65,4 54,5
150 252,7 168,6 126,3 100,8 84,1
175 362,3 241,5 181,2 144,9 120,8
200 520,2 347,5 260,1 208,1 173,7
250 947,6 631,7 473,8 379 315,9
dc 2% 50 mm/h 75 mm/h 10 0 mm/h 125 mm/h 150 mm/h
75 63,2 42,2 31,6 25,3 21
100 133,8 89,2 66,9 53,3 44,6
125 232,3 155 116,1 92,9 77,5
150 356,7 237,8 178,4 142,7 118,9
175 512,8 341,9 256,4 204,9 170,9
200 739,5 494,3 369,7 295,4 246,7
250 1338 891,8 668,9 534,2 445,9

dc 4% 50 mm/h 75 mm/h 100 mm/h 125 mm/h 150 mm/h

75 89,2 59,5 44,6 35,7 29,7
100 189,5 126,3 94,8 75,8 63,2
125 328,9 219,2 164,4 131,5 109,6
150 514,7 343,3 257,3 206,2 171,9
175 724,6 483,1 362,3 289,9 241,4
200 1040,5 693 520,2 416,2 346,5
250 1858 1238,4 929 743,2 618,7

138
 Phig php 2: p dng cng thc thy lc
1 . Chn s b dc lng mng theo yu cu dc ti thiu.

i = 0,003 i vi dng lng mng bn nguyt,

i = 0,004 i vi dang ch nht.
2. su nc trong mng > 5 cm; vt cao an ton Ah =10-20 cm.
3. Chn cu to 1 m 2 din tch hng nc 2 cm 2 tit din t ca s n t gi nh
kch thc s b ca s n.
4. Kim tra lun lng tho nc v chiu su nc ca s n theo cng thc Manning:

V = I r ^ 2 v Q = coV = ( 0 . - R M 2
n n
Mng ch nht: R = b.h /(b + 2h);
Mng trn: R = 2T2.h / (3T 2 + 8 h2).
Vi h - chiu su nc trong mng (m);
b - kch thc y mng ch nht (m);
T - b rng mt ct t ca mng trn (m).
nhm n c chn ty theo loi vt liu:
B tng n = 0,011 - 0,015;
Gch n = 0 ,0 1 2 -0 ,0 1 7 ;
Tn n = 0,013-0,017.
5. Kim tra vn tc cho php trong mng theo quy phm 0,6 m/s < V < 4 m/s.
6 . Kim tra lu lng tho so vi yu cu
Lu lng ph trch ca mi oan s n c tnh theo lu lng thot nc ca mt
ng ng b tr cui on mng (xem phn trn).
c ) Tnh ton l thot nc.
L u lng tn h t o n c a cc l thot nc n m nga ng, tit d i n c h nh t, c c h i u c a o
t nht bng hai ln chiu su ca lp nc tnh on c cho trong bng 6.14.

Bng 6.14: Lu lng tnh ton ca cc l thot nc tit din ch Iiht

Chiu cao ct nc B rng ca l thot nc (mm)

(mm) 150 300 450 600 760 900
12,7 0,4 0,8 1,2 1,6 2 2,4
25,4 1,1 2,2 3.3 4,5 5,6 6,8
38 2 4 6,1 8,2 10,3 12,4
5] 6,2 9,4 12,6 15,8 19,1
64 8.6 13,1 17,5 22 26,5
76 11 ,2 17,1 23 28,9 34,8
89 21,4 28,8 36,3 43.7
102 26 35,1 44.2 53,3

139
6.5. CNG THOT NC BN NGOI CNG TRNH

6.5.1. Cu to

Cc cng thot bn ngoi cng trnh (nm ngoi phm vi m ng cng trnh) tip nhn
nc t ng x v c ni vi cng thot nc cng cng. Cng thot nc ngoi cng
trnh phi c t trn m ct trn sut chiu di v chn lp cn thn. Vt liu ch'
to cng thng l b tng ct thp. Vic u ni cng thot nc ngoi cng trnh vi
h thng thot nc cng cng phi tun theo quy nh ca c quan c thm quyn.
S lin kt gia HTTN bn trong v ngoi nh c cho di y:

"- HTTN HTTN r* HTTN

HTTNBT sn nh tiu khu V cng cng

6.5.2. Nguyn tc b tr

M ng li thot nc sn nh c xy dng song song vi tng nh v cch m ng

t nht l 0,6 m v cch mt t ti thiu l 0,3 m ngoi tr trng hp cng c lm
bng loi vt liu c php s dng cho h thng thot nc bn trong cng trnh.
Cng thot nc bn ngoi cng trnh phi c b' tr sao cho khong cch ti thiu
so vi cc loi cng trnh d nhim bn nh c quy nh trong bng 6.15.

Bng 6.15: K hong cch an ton ti thiu so vi cc loi cng trnh bn ngoi

Hng mc Khong cch ti thiu (m)

Cng trnh hoc b phn cng trnh 0,6

Ging cp nc 15(l)
Sng sui 15
ng ng cp nc sinh hot cho ngi nh 0,3
ng ng cp nc cng cng 3
) K h o n g c ch n y c t i d c g i / x u n g c n 7,5 n i c ii n g th o t n c c n i h /ii ( c
o a i v t li u c p h p s d ig hn tro n g c /i trn h .

Ni chung, cc cng thot nc c lm bng snh hay cc loi vt liu khc khng
tiu chun c chp thun s dng bn trong cng trnh th khng c b tr
chung trong cng mt ng ho vi ng ng cp nc, ngoi tr trng hp m bo
c cc yu cu sau:
- nh cng thot nc phi thp hn y ca ng ng cp nc t nht l 300 mm,
- ng ng cp nc c c nh v cch cng thot nc t nht l 300 mm theo
phng nm ngang.

140
 6.5.3. Xc nh kch thc cng thot nc bn ngoi v cng x

Kh nng ph trch ti a ca cng thot nc bn ngoi cng trnh v cng x c

th c xc nh theo bng 6.16. Kh nng phu trch ca cng tng theo dc lp
t. Do nu c th c, nn xem xt cc phng n b tr dc cng ln tit
kim na knh ng. Bng 6.16 cng c th c dng xc nh ng knh ng
nhnh thot nc trono nh.

Bng 6.16: Kh nng thot nc (tnh theo ng ng thit b v sinh)

ng knh 'n dc t ng (%)

(mm) 0,5 1 2 4
50 21 26
60 24 31
76 42 50
100 180 216 250
125 390 480 575
150 700 840 1000
200 1400 1600 1920 2300
250 2500 290(1 3500 4200
300 ?OQQ 4600 5600 6700
380 7000 8300 10000 12000

6.5.4. Ca thng tc

Ca thng tc c th c b tr bn trong hay bn ngoi cng trnh v tr gn dim

ni ia cng thot nc bn trong v bn ngoi cng trnh. M ing ca ca c xy
thng bn trcn ng II v cao bng vi mt nn. Ngoi ra dc theo tuvn cng, cc
ca thng tc dc b tr cch khong 30 m v lai cc v tr chuyn lun cng.
ng knh ng thot khng nh hn 125 mm. Cc tuyn ca h thng thot nc
tiu khu c ng knh ln hn 150 min.
Ging thm - kim tra phi c b tr ti tt ca nhng giao im ca cc h thng
thot nc, hav ti cc ch ngot di hng ca ng na. Ngoi ra trn cc tuyn ng
qu di, cng b tr ging thm cch khong t 50 in (i vi ng nh hn 600 m m) n
75 m (i vi ng ln hn 600 mm n 1400 mm).

V d:
Tnh ton thot nc cho mt chung c TP. 1l Ch Minh. Chung c mi bng c
din tch mi B X L = 24 X 100 m.

S cn h l 2 dy X 20 cn h X 5 tng (xem s d).

141
 Bit rng chung c c trang b thit b v sinh hon chnh cho m i cn h bao
gm : 1 bn tm , 1 vi sen, 2 lavab ra mt, 1 bn cu t n g v 2 v tr v: nc
ra trong bp.
L = 20 X 5m
< 12 m

<N
II
C2

B i gii:
I .Thot nc v sinh:

p dng Quy chun cp thot nc trong nh v cng trnh, 1999. Gi s ti: chn
phng n b tr 20 ng ng ng cho mi cm gm 2 cn h cng tng X ) tng
(xem s ). Nh vy mt ng ng ng ph trch cho 10 cn h. ng n thot
phn c b tr ring v cng ph trch cho tng cm 1 0 cn h.

ng knh ng knh ng knh

Thit b ng lng
ng thot (ND) xi phng (mm) ng thng kh (mrn)

Bn tm 3 42 42 42
Vi sen 2 42 42 42
La va b 1 34 34 34
Bn cu 3 hoc 4 42 hoc 49 42 hoc 49 42
Vi ra bp 2 42 42 42
Tng 14- 15

- Thng k ng lng thot nc v chn ng knh ng thot nc cho c: thit

b v sinh (bng 6.2 v bng 6.3):
- Tng ng lng thot nc cho mt CP h l 15. S dng bng 6 .6 , ng knh
n g th o t n c n g a n g c c h n l 6 4 m m ( n g c N D = 76 m m ) . d c n g ch ng
nh hn 2%.

- Tng ng lng thot nc cho m t ng ng l 10 X 15 = 150.

S dng bng 6 .6 ng knh ng thot nc ng c chn l 100 mm (c'ng c

ND = 114 mm). Chiu di ti a cho php ca ng ny l 91 m, nh vy l t y u ; u .

Ong rlni kh chnh:

S dng bng 6.6 ng vi ng lng 150, ta chn c ng knh ng thig kh
chnh l 100 mm, ng vi ng c ng knh danh nh bng 114 mm.

142
 0/1 tf x:
Ong x c b tr y ca ng ng thot nc ra cng bn ngoi cng trnh.
Gi s ng x c b tr bi dc thun l 1%, tra bng 6.16 ta c ng knh cn
thit l 76 mm ng vi 180 ng lng. Theo quy phm, cng thot nc bn ngoi
khng c chn nh hn cng thot nc bn trong, do ta chn b tr ng x bng
vi kch thc ca ng ng ND = 1 1 4 mm.
2. Tnh ton thot nc tmt
Tnh ton ng ng
Phng p h p I :

Trm ma i biu cho khu vc l trm Tn Son Nht c cng ma q 5 l

178 m m/h (0,0496 //s-m2). Bng cch s dng gi tr trong bng 6.11, ta thy din tch
ph trch ca mt ng ng thot nc ma c tnh ra trong bng sau:

ng knh ng ng Lu lng ph trch Din tch ph tich

(mm) (//s-m2) (m 2)
50 1,5 30,2
75 4,2 84,7
100 9,1 183,5
125 16,5 332,7

150 26,8 540,3

200 57,6 1161,3

Do chiu rng nh >12 m ta s b tr mng xi v ng ng thot nc ma c 2

mt ca chung c. Da theo s lng cn h trn mt dy, gi s s ng ng l 2 X 10 = 20
2400
ng. Din tch ph trch ca 1 ng: = 120 ITT.
20
Theo kt qu trn ta chn b tr ng c ng knh 100 min (ND 114 mm).
Ph/ii p li ) 2 :
Lu lng thot nc ma:

Qm = K * F * q ' . 2 i2W -ty

10 0 0 0 10 000

Gi s ta chn b tr tng s' ng ng thot nc ma l 20.

20
Lu lng phu trch ca mi m l 6 // s
20
Theo bna 6 .10. la chon dc dnc knh ng dni cn thit l 80 mm. Do quy nh
kch thc ca ne na thot nc ma khng nn ly nh hn 10 0 mm trnh b

143
nght, ta chn ng knh ng d = 100 mm. ng knh li chn v phu thu nc trn
m ng c chn l 150 mm.
Tnh ton mng thu nc ma
Chn m ng xi c dng bn nguyt, ta s dng bng 6.13 thit k m ng xi. Do
cng ma cung cp trong bng 6.13 ch ti a n 150 m m /h, cn phi tnh ton
ngoi suy cho trng hp ca trm Tn Sn Nht (178 m m /h)1' 1. Do cch b tr s lng
ng ng nh trn, ta tnh c chiu di ti a ca mt on m ng gia hai ng ng
thot nc l 10 m, din tch ph trch ca mt on m ng xi l 10 X 12 = 120 m 2.
Bng cch ngoi suy gi tr trong bng 6.13, ta tnh c din tch ph trch ca int
mng xi bn nguyt ng vi cng ma 178 m m /h l:

ng knh mng (mm) Din tch ph trch ti a (m2)

200 105
250 191

Nh vy kch thc mng xi c chn l khong 220 - 250 mm.

BI TP

Bi 1. S dng s liu ma ca TP. H Ch Minh hy xc nh:

- Din tch mi nh ph trch bi cc ng ng c ng knh 75 v 100 mm.
- Din tch mi nh ph trch bi cc mng xi c tit din bn nguyt, c ng
knh ln lt l 15 v 17,5 cm.
Bi 2. Tnh ton cc ng knh ng cn thit (ng ngang, ng ng, ng thn? kh)
cho mt h thng thot nc (v sinh v nc ma) cho mt cn h icn hnh TP. H
Ch Minh. Bit rng nh mi bng 3 tng c din tch mi B X L = 4 X 20 m.
Bit rng nh c trang b thit b v sinh hon chnh bao gm: 2 bung tm (1 bn
tm, 1 vi sen, 1 lavab ra mt, 1 bn cu t ng); nh bp ( 2 vi nc ra).

1 N g o a i suv a y ih

144
 Chng 7

CNG TRNH X L NC THI SINH HOT

QUY M VA V NH

7.1. G I I THIU

Nc thi th l t hp h thng phc tp cc thnh phn vt cht. Trong cht

nhim bn thuc ngun gc hu c v v c thng tn ti di dng khng ha tan,
dng keo hoc dng ha tan. Thnh phn v tnh cht nhim bn ph thuc vo mc
hon thin ca thit b, thnh phn nc thi cng nghip, nc thi sinh hot, tp qun
sinh hot, mc sng x hi ca ngi dn v tiu chun thot nc. Do tnh cht hot
ne ca th m cc cht nhim bn c trong nc thi thay i theo thi gian.
tin li trong s dng, ngi ta quy c i vi nc thi sinh hot c gi tr bnh qun
khng i. Trong chng ny chi gii hn kho st v x l nc thi sinh hot c quy
m va v nh.

7.2. CC PHNG P H P X l l NC THI

7.2.1. M c x l nc thi

m ho iu kin v sinh mi trng, nc thi th phi c x l t tiu

chun trc khi x vo ngun nc mt theo tiu chun xy dng TCXD 188: 1996
nh sau:

Bng 7.1: T C X D 188:1996 Nc thi th - Tiu chun nc thi

Gi tr gii hn
TY Thng s n v
Loi A Loi B
1 2 4 5
1 Nhit c 40 40
2 pH 6-9 5-9
3 mu Pt/Co 20 50
4 dc NT 50 100
Tng cht rn l lng m g// 50 100
6 Tn? cht rn ha lan mg/v 1000 3000
7 COD mg// 50 100
8 BOD5 mg II 20 50
9 Clorua (CT) mg// 250 1000

145
 / .9 3 4 5
10 Sulat (S042-) mg// 200 1000
11 Nitrit (NCM mg/l 0,1 2,0
12 Nitrat (NOy) mg// 50
13 Du m khong mg// 0,001 1,0
14 Clo d mg/l 1,0 2,0
15 Coliorm MPN/lOOm/ 5000 10000

Ghi ch: Nng gii hn cc ch tiu nhim khc khng nu trong bng ny c th xc
dnh theoTCVN 5945: 1995.
Mc x l nc thi c xc nh da trn quy m i tng thot nc v kh
nn tip nhn nc thi ca ngun. Nng gii hn cho php cua cc cht nhim
trong cc loi ngun nc c quy nh theo tiu chun mi trng TCVN 5942: 1995
v cac TCVN 5943: 1995, TCVN 3773: 1995, TCVN 6774: 1995.

Bng 7.2: Nng gii hn mt s ch tiu nhicm trong cc thv vc nc mt

theo quy nh ca B Khoa hc Cng ngh Mi trng

TCVN 5942-1995 TCVN TCVN TCVN

TT Thng s
'
Loi A Loi B 5943-1995 6773-2000 6774-2000
1 pll 6-8,5 5,5-9 6 ,5-8,5 5,5-8,5 6 ,5-8,5
2 BODs, mg// 4 25 20 10
3 COD, mgll 10 35
4 Oxy ha tan, ma// 6 2 4 2 5
5 Cht rn l lng, mg// 20 80 25 100
1,49 (pH = 6,5)
6 Amoni, mg// 0,05 1 0,1
0.93 (pH = 8 )
7 Nitrat, mg/l 10 15
8 Nitrit, mg// 0,01 0,05
9 Du m, mg// Kh.ig 0.3 Khng Khng
10 Cht ty ra, mg// 0,5 0,5
11 St, mg// 1 2 0,1
12 Xianua, mg// 0,01 0,05 0,01 0,005
13 Asen, mg// 0,05 0,1 0.05 0,05-0,1 0,02
14 Phenol tng s, mg// 0.001 0,02 0,001
15 Tng ho cht bo v thc
0,15 0,15 0,05
vt, mg//
Theo chi s
16 Tng cht rn ha tan, mg 1000
SAR
200 cho vng
17 Calilbrm, M3N/100ml 5000 10000 1000
irng rau

146
 Ghi ch:
TCVN 5942-1995 Cht lng nirc - Tiu chun cht lng nc mt (A: ngun cp nc
cho trm x lv inrc cp, B: ngun cp nc cho mc ch khc).
TCVN 5943-1995 Cht lng nc - Tiu chun cht lng nc bin ven b.
TC V N 6773-2000 Chl lng nc - Cht lng nc dng cho thy li.
TCVN 6774-2000 Chi lng nc - Cht lng nc ngt bo v i sng thy sinh.

7.2.2. La chon phng php v cng trnh x l nc thi

S la chn phng php v cng trnh x l nc thi da trn cc c s sau:

- Q uy m v c im ca di tng thot nc ( th, khu dn c, bnh vin).
- c im ngun tip nhn nuc thi v kh nng t lm sch ca n.
- Mc v cc giai on x l nc thi cn thit.
- c im kh hu, thi tit, a hnh, a cht thy vn... khu vc.
- iu kin cung cp nguyn vt liu x l nc thi ti a phng.
- Din tch v v tr t c th s dng xy dng trm x l nc thi.
- iu kin kinh t v ti chnh.
T heo c ch qu trnh t lm sch, cc phng php x l nc thi sinh hot quy m
va v nh c phn ra nh sau:

a) X l nc thi bi phng php c lic: l cc thit b nh song chn rc, b

lng ct, b tch du m... y l cc thit b. cng trnh x [ s b ti ch tch cc
cht bn tli nhm dam bao cho h thng thot nc hoc cc cng trnh x l nc thi
pha sau hot dng 011 nh.
b) Xi l iih thi buiii )ht(n\> p .sinh hc k khi: Qu trnh x l c da trn
c s phn hv cc cht hu c nh s ln men k kh. i vi cc h thng thot nc
quv m va v nh ngi ta thim dng cc cng trnh kt hp gia vic tch cn lng
vi phn hy ym kh cc cht hu c trong pha rn v pha ing. Cc cng trnh c s
dne rna ri loai nv l: b t hoai, ging thm, b lng hai v, b lng trong kt hp
vi nen ln men, b lc ngc qua tng cn k kh.

r j X l ni thi hni phng plip sinh hc hin kh: Qu trnh x l c da trn

s oxv ha cc cht hu c c trong nc nh oxy ha tan. Nu oxy c cp bng thit
b h o c n h c u t a o CI1 t r n h , th l q u t r n h x l s i n h h c h . _ u k h t r o n g i u k i n

nhn to. Nec lai. d l qu trnh x l sinh hc hiu kh trong iu kin l nhin,
c ong trnh x l hiu kh trong icu kin nhn to thng da trn nguyn tc hot ng
ca bn hot lnh (be aeroten. knh oxy ha tun hon) hoc mng sinh vt (b lc sinh
hc, a sinh hc). X l sinh hc hiu kh trong iu kin t nhin thng c ihc
hi n t r o n g h (h sinh vt oxv ha, h sinh vt n n h ) h o c tro ng t g p n c (bi
loc, m ly nhn to).

147
 () x /v nc thai hn phc/ni p h p ha hc: l cc qu trnh kh trne nc
thi bng ha cht (clo, ozon). X l nc thi bng phng php ha hc thng l
khu cui cng trong dy chuyn cng ngh x l nc thi trc khi x ra ngun tip
nhn nc c yu cu cht lng cao.

e) X i l ) II c n HC t h i: Trong nc thi c cc cht khng ha tan nh rc, ct,

cn lng... Cc loi ct (ch yu l cc cht v c c t trng ln) s c phi kh v
san nn, rc c nghin nh hoc ch v bi chn lp rc. Cn lng c gi li
trong cc b lng t mt (gi l cn s cp) c hm lng hu c ln c kt hp vi
bn th cp hnh thnh trong qu trnh x l sinh hc nc thi. Hn hp s c x l
theo cc bc tch nc s b, n nh sinh hc trong iu kin vm kh hoc hiu kh
v lm kh. Bn cn sau khi x l c th dng lm phn bn.

7.3. X L NC TH I BNG p h n g p h p sin h h c k k h

Trong iu kin khng c oxy, cc cht hu c c th b phn hy nh vi sinh vt v

san phm cui cng ca qu trnh ny l cc cht kh nh metan (CH4) v cc carbonic

( C 0 2) c to thnh. Qu trnh chuyn ho cht hu c nh vi khun k kh ch yu

din ra theo nguyn l ln men qua cc bc sau:

- Bc 1: Thy phn cc cht hu c phc tp v cc cht bo thnh cc chi hu c

n gin hn nh monosacarit, axit amin v cc mui pivurat khc. y l ngun dinh
dng v nng lng cho vi khun hot ng.

- Bc 2: Cc nhm vi khun k kh thc hin qu trinh ln men axit, chuycn ho cc

cht hu c n gin thnh cc loi axit hu c thng thng nh axit axetic hoc
glixerin, a x e ta t...

C H 3C H 2COOH + 2 F 20 -> CH 3CO O H + C 0 2 + 3 H 2

axit priionic axit axetic
CH3CH2CH2 COOH + 2 H20 2 CH3COOH + 2 H2
axit butiric axit axetic
- Bc 3: Cc nhm vi khun k kh bt buc ln men kim (ch yu l cc loi vi
khun ln men metan nh Metliaiosurciiu v Metlianothri.x) chuvn ho axit axetic
v hvdro thnh CH 4 v C 0 2.

C H 3COO H -> c o 2 + c h 4

axit axetic

H C O 3 + 4 H 2 -> CH 4 + OH + 2H 20

148
7.4. B V SINH T HOI

7.4.1. T n g q u t

B t hoi l mt cng trnh nhm thu v x l nc thi t nh v sinh gia nh hoc

lp th. v l cng trnh x l nc thai theo nguyn l sinh hc k kh. Cng trnh bt
buc phi c mt h th ng lm sch c vai tr m bo s oxy ha hi bc ra t cc b
t hoi. H thng cng trnh ny c u im l chu k bo tr lu (hng nm). Lu l
hin tng ha lng trong b t hoi chi c th xv ra khi khi n nhn c mt lng
nc nhiu, v quy m, b t hoai c th thit k vi quy m t n 300 ngi
s dng.

7.4.2. B phn thu v s ha lng

Trong mt b t hoi ang vn hnh tt. cc cht rn tch tr di y b t hoi chu

s ln men k kh trong mi trng kim. S tch ly bn trong b t hoi s lm gim
dn th tch hu ch theo thi gian s im. Do , s no vt s c thc hin theo
chu kv.

N guyn tc hot n g
Phn thi ca ngi cha cc cht hu co' co nit, m to ra amoniac c hi cho cc
VI khun khi hm lng ca n vt qua gioi hn. Hm lng tng cng nit, m ca

nc phn trong bc l hoi c biu th theo NH 4 khng th vt qu 200mg//.

bo m yu cu ny, th tch nc sch yu cu phi s dng trung bnh khong

401/imi/ngy-m. T rong trng hp nu c nc ( nh bp i vo b t hoi n phi
dc loi cc cht bo, du 111 v tt hon htl divo ngn th hai ca b t hoi. Ti
dy cc cht bo cn st c th c oxv ha v tiu tn trn b mt nc. Trong trng
hp nc c ngun gc t bn tm, my uit_rt c hi cho s hot ng ca vi khun.
Do , v nguyn tc cc loi nc ny phi ngn khng cho vo b t hoi. Ngoi ra,
n c m a c n g n h n c ra v sinh: nh. xe.... k h n g c p h p c h o v o b t hoi.

Cc cht thi rn trong sinh hot gia nh: rau b, bng, tro,... khng c cho i vo
b t hoi. Trong qu trnh lm v sinh nh cu, cn phi m bo khng cho nc Javel
hoc cc cht lng acid... i vo b t hoai. Cc cht ty ra nv c tc hi lm cht cc
vi khun cn thit cho qu trnh hot ni cua b t hoi.

7.4.3. K ch thc b t hoi

The tch b t hoi xc nh trn c s tne th tch cht lng m cng trnh phi
cha. Trong trng hp ch nhn nc l van, kch thc b t hoi theo quy m s
l m^: n aw i s d u n CT c t r n h b y troiiii b n LI ^^sau:

149
 Bng 7.3: Kch thc b t hoi theo s lng ngi s dng

S ngi s dng
Th tch b cn thit (m )
Nh nhl Ln nht
1 4 1,0
2 6 1,5
2 8 2,0
3 10 2,5
3 12 3,0
4 14 3,5
4 16 4,0
5 18 4,5
5 20 5,0

Trong trng hp s lng ngi s dng ln hn, c th tnh s b trn nguyn tc

khong 300 1/ngi l ti thiu.
Trong trng hp nc sinh hot cng c a vo b, th tch b lc s c yu
cu gp i.
Trong thit k cn lu n cc trng hp cng trnh tp th nh: bp trng hc,
vn phng, ... khng hot ng thng xuyn, th tch yu cu b t hoi c th gim
xung. Cc gi v th tch b ti thiu yu cu sau y c th tham kho trong thit k:
- Trng, vn p h n g ,... bn tr: 200 //ngi.
- Ngoi tr: 100 //ngi.
Cc ngn ca b t hoi cho php tch cht lng v cht rn mt cch c hiu qu.
Theo kinh nghim, s phn chia th tch trong mt b t hoi nh sau:
- Trng hp b t hoi ba ngn (hnh 7.1): 1/2 cho ngn u v 1/4 cho hai ngn k.
- Trng hp b t hoi hai ngn (hnh 7.2): 2/3 cho ngn u tin v 1/3 cho ngn k.

Hnh 7.1: S d cu to h t hoi hu iii

150
 . 7 ' 'T 7" ' 1 11 ..... * * 1: ;* ***!*

f*7 * T t' * T * ? * *T*T *Tn*

B tng chng thm

B tng lt
t t nhin

Hnh 7.2; S cu to h hoi hai nqn

/- \ dn nc tldi vo; 2- ch ni tH,' 3- ch np qan; 4 ch * fhnq i >;tv7

5- chi i d nc ra. Cao tnh hi n v kch thc tnh bn { n.

O-

A-A
B-B
60

n c D
1010 / M c?

0 85_; 10 85 W / 10 10 10
2 0 0 ..
A %
5 JL L . 200. ,j5
23 23

Hnh 7 3: B h o a i c vch nsn, lu \ nc hdi sinh hot 25nrlnm'iv

151
 Trong trng hp kt cu c v tr thu nc tiu ring, nc tiu pha long phai
dn v mt trong nhng ngn cui cng.
Cc l chuyn nc trong cc ngn s b tr khong 1/3 chiu su k t dy, v
nc trong.
Chiu su nc trong b thay i t lm n 2m trong b u tin. Chiu su nv c
th gim cho cc ngn k. Thit k y b nghing cho php d dng tp trung bn lng
y.
ng ng dn cht thi c th cm su vo hoc khng vo b t hoi. Trong mi
trng hp n phi c b tr sao cho trnh c s khuy ng qu mc khi b nhn
cht thi.
Ming lp ng thot cho php hiu chnh mc nc nm ngang trong tt c cc ngn
ca b. ng c th c dng gp khc.
Np y b t hoi phi thit k cho php tip cn cc ngn khi cn thit phi lm v
sinh, b o q u n b. K c h thc ti u l l , l m X 0 , 7 m , c h o p h p t ro n g t n h h u n g cn
thit cng nhn c th vo c. L ny phi c bo v bng tm li nhm trnh s
xm nhp ca cc cn trng.
Kh thi ra trong qu trnh cc vi sinh vt hot ng trong b phi dc cho thot ra
mt cch ch ng vi v tr ming ra phi cao hn mi mt chiu cao an ton.

7.4.4. P h n g p h p xy d n g

Tnh kn nc ca b t hoi l mt iu kin quan trng nht. N phi m bo ngay

t u v khng c vi phm trong bt k tnh hung no. Kt cu b phi chu c
tc dng ca tt c cc ti trng tc dng ln cng trnh, ngav c trong cc trng hp
khai thc c bit. Cc chiu dy ti thiu sau y phi c tha mn ty theo loi vt
liu s dng:
- xy bng va hoc b tng thng: 0.35m
- Gch xy bng va: 0,33m
- B tng ct thp ti ch: 0,15m
- B tng ct thp c sn: 0,08m
Cc chiu dy nu trn cha k n chiu dv lp va trt.
Xi mng s dng nn l loi xi m ng c kh nng chng li cc hin tng xm thc
t cht lng trong b v xm thc t kh thi ra. Xi m ng Portland s dng khng thch
hp lm trong trng hp nv.
B tng s dng nn l loi b tng vi si nh v hm lung xi m ng 3 5 0kg /m 5
b tng nhm mc ch ngn naa s thm mt nc.
B mt ca b t hoi phi c bo v bng mt lp va trt bng xi mng Portlan
dy khong 2cm. Tng t cho y vi lp va dv khong 3cm. Cao trnh lp va trn
vch vt mc nc trong b t hoi t nht 0,25m.

152
 Tuy nhin, lp va trt ny c th khn cn trong trng hp cng trnh c xy
dng bng h tiiii dm nn bang thit b rung c hc v dng vn khun bng kim loi.
Trong tt c trn hp 1 phai dam bo tnh kn nc.
Trong thc t. c nhiu loai b t hoi loai ch tao trc. N d dng lp t vi cng
nhn khng i hoi tay nshc cao. Cc loi b ny c the bng: b tng, kim loi, nha
c gia c sn.

V tr
B t hoai nn chn v tr pha rmoi phm vi nh. Trong trng hp bt buc phi
xy dng b trong nh, v tr ming b bt buc phi c bt kn v v tr phi l ni
thng gi tt v khnti lin thng trc tip vi phng sinh hot trong nh. V tr cn phi
cho php lin thng vi hn nsoi d dng thc hin cng tc bo tr thun li.

R o tr
be t hoi vn hnh ti, nn thc hin cng tc thu dn cht cn lng di y
tlico chu kv (thng l 1 hoc 2 nin). Tuy vy. khng nn ly i ton b cht cn trong
mi ln bo tr. Theo kinh nghim, nn gi li khong 1/5 cht lng ng trong tng the
cht cn ti cn no vt.
Troni mt s [rng hp. c th d kin dne sn phm ln men trong b khi bt u
da b vo s dna hoc ngay sau khi no vt bo tr nh k. Cht nv c tc dng to
diu kin thun li qu trnh ln men ca cc vi khun khi phn hy phn thi sinh hot.

7.4.5. Pho php lm sch sau l)

Cc phim p h p sau y c h o ph p lm sch han e cc hot d n g c a VI k h u n hiu
kh ti v ir ra ca cc b l hoai:
- Bi mt sn phi c tnu lc vi s hot ng cu a vi k h u n.
- Bi mt liii mrc iem c chiu su b.
- Bi mt sn tham.
Kch thc toi thiu loi sn phi c tn 2 lcc ph th u c vo s lng n S i m c n g
trnh cn phc v v chiu dv tniz lc. Kch thc loi sn phi c tng lc dc trnh
by tm ne bunu sau. Cliicu dy taii lc khns c b hn 0,7m. Kch thc ht lng
lc thay- di Iroiiic khon
c 1Omni n 50mm.

Bng 7.4: Kch thc sn lc nc th i sau b t hoi

Cliiou ilv Din tch b mt sn vi N nturi cn phc v (rrr)

U|m lc 1( 111) N = 1-> 5 N=6 N=7 N=8 N=9 N = 10 N > 10
1---------
:
o

1,0 o.s 0.6 0,7 0.8 0,9 1,0

II

0.9 o / 0.75 0.85 1.0 1.1 1.2

O.K 0.8 0,95 1.1 1,25 1.4 1.55
0.7 1.0 1.25 1,45 1.65 1.85 2,0

153
 Gi tr trong bng trn tng ng trng hp nc n t van. Trong trng hp cng
trnh cn phi nhn nc n t nh bp, nh v sinh din tch phi c gp i.
V loi sn lc, vi kt cu y dng 2 lp l thch hp nht. N cho php s lun
chuvn nc d dng, iu ny cng c ngha l s thng kh tt. y l mt yu t cn
thit cho s hot ng ca vi khun hiu kh.
Trong khi do chiu dy sn lc b nn phng php thi gi b mt khng hiu
qu nhiu. Khng kh a vo trong mi trng c th thc hin thng qua cc phng
php ph bin sau:
- a cc ng dn kh i su vo trong lp nc.
- S dng lc ca gi v d nh qut c ng c.

Thit b ht kh tnh c

Hnh 7.4 : Sn lc vi hot (I1 vi khun hin k li c th i t b ht k h lil

Vi kt cu ny cn c mt ging thm cho php tin hnh bo li nh k. Cn ch

l vi kt cu sn lc ny to ra mt s chnh lch v mc nc vo v ra khi b
mt cch ng k.

154
 Chng 8

H THNG THOT NC CHO KHU vc

8.1. G I I TH IU

Q u trnh th ha dn dn mt vng dn c dn n s gia tng rt ln t l phn

trm din tch b mt khng thin nc (s gia tng do cc ng b tng nha, tm lp,
ng lt vo cc nh xng...). Hu qu ca hin tng ny s lm gim, khi ma,
th tch nc c th thm vo lng t v do lm gia tng lng nc chy trn trn
mt. Lng nc chv trn ny l mt vu t quan trng, nh hng n quy m cng
trnh, cn phi xc nh khi thit k h thng thot nc cho khu vc.

V vn tho nc, xt cho mt lng nc ca mt cn ma, s to dng chy s

xy ra nhanh hn nhiu v lu lng ln nht cng ln hn rt nhiu sa khi vng
nghin cu c th ha so vi trc (c th n 100 ln ln hn). Ngi k s
chu trch nhim qun l vn (l nv phi tm cch eim thiu ti a cc iu ht li hay
cc tc hi do dne nc ma gy ra (v c nc thi dn dng trong h thng cng).

Trc khi xut mt h thng thot nc ma c kh nng ti c lu lng ra

khi khu vc theo yu cu ca khch hng, ngi kv s phi vt qua cc bc theo th
t sau y:

a) Tim cc ti liu cn thit: bn a hnh (bn gii thiu cao a hnh cng
nh cc kin trc hin c), bn a cht, quy hoch cho th v vng.

b) Xc nh gii hn vng thot nc, xc nh cc gii hn cho cc lu vc v tiu

lu vc, xc nh din tch tng ng. Xc nh v tr dng giao thng v cc ng
cnu dn.

c) Xc nh din tch cc b mt khng thm (l ng, ng, ng vo cc

garage, mi lp...) da vo quy hoch th. quv hoch vng v a hnh. Chng ta phi
phn bit hai loi mi: loi mi nh ngoi c cc mng thu v c bao quanh bi 1
khu vn, v loi mi thng thng bng phns. cho cc nh lin k xy dng cho cc
vng c mt dn c cao. Trone trng hp th nht, ta d dng (thng l bt buc)
hng dng chay c c di qua cc be mt thm bao bc chung quanh nh: ta quan
n i m m i trong trn S hp nv l be m t k h n g th m c t h o g i n tip. T r o n g trn g

155
hp 2 , nc nhn c t mi c chuyn qua cc nhnh ca cc ngi nh: loi mi
nv c gi l b mt khng thm c tho trc tip.

d) Thit lp (nhn bit) ng cong IDF (cng ma - thi gian ma - tn s xut

hin) ph hp vi khu xv dng v chn tn sut ma ri ph hp vi a phng (thna
thng l 5 nm).
e) Xc dnh h s Manning lin quan n cc b mt lu vc khc nhau v ns dn.
f) Xc nh lng nc thm vo t.
a) Tnh thi gian nc vo h thu nc lin quan n cc tiu lu vc khc nhau nh
vo cc m hnh, v d m hnh ca Kerby.
h) Xc nh lu lng cn ti, chn ng dn v dc ca n.
Trong chng ny chnc ta s cp n cc phng php cho php nh gi lng
nc ma phi tho trong mi nng th khi xy ra ma; tnh ton lu lng tho ln
nht lin quan n cc dng khc nhau ca a hnh, cc m hnh ma khc nhau; cui
cng s cp n mt vi bin php ph bin gim lu lng tho nc ma.

8.2. MA V DNG C H Y T R O N G MI T R N G TH

Lu vc thot nc c xem l din tch hng nc v s thu v 1 im duy nht.

Vi tt c cc lu vc thot nc, d cho lu vc nv c nm trong khu thnh th hay
khng, khi tnh th tch v lu lng nc ca dng chy to ra do ma s phi k n:
- c tnh ca cn ma: cng , thi gian ko di cn ma, s phn b theo khng
gian v thi gian;
- Cc c tnh v b mt ca lu vc (thin nhin, t l din tch thm nc, dc,
quv hoch);
- Cc quy lut v dng chy mt.
Bng sau y trnh by h qu logic quan h hin hu gia mt cn mua (v cc dc
trng ca n), mt lu vc (v cc c trng ca n) v cc c trng thy d ca lng
nc xut hin cn phui tho ra khi lu vc.

Bng 8.1

Quan trc Tnh chi

Niuin: Ma Trong khna kh

- Phn b iheo khng gian v thi gian ca ma: biu d thc hoc tm tai
Bin i: lu Vl l
vc thot nc - B mt
* Khng thm v tho trc tip

156
 / 1
Bin di: lu * Khng thm v tho gin tip
vc thot nc * Thm khng tho (khng ni licn V I mng li cng)
* Thm v tho
- Nc c ei lai bi:
* Do b mt thm
* Do b mt khng thm
- iu kin ma trc
- Mc lc nc trong t trong khi ma
Vn chuyn: Thy lc
mang li cng - c tnh mang li cng tho;
- S lan truven thy dng chy trong mane li cng;
- Tch nc (trong cc ng dn hoc h cha).
Kt qu: thy Thit lp thv dng chy.
dng chy

8.2.1. Ma
Nc ma ri trn mt lu vc s tri qua ba giai on chnh:
- Lm m b mt lu vc v cc thit b lp t ni d:
- Mt phn thm vo lng t v ha nhp vo tng nc ngm;
- Mt phn s hnh thnh dng chy mt cho n cc im thu nc (h ga, ming
cong, sng sui).

8.2.2. C h u k

Ta nh ngha chu kv l khong thi gian trung bnh tch ri cho 2 cn ma c cng
cng : l nghch o cua tn s. Mt cch khi qut, v d, mt cn ma c chu
k l 10 nm s xv ra (mt cch trung bnh, 1 ln c mi 10 nm). Khi chn chu k
cng ln, lu lng dng chy ln nht (tnh t phng trnh thch hp) s cng ln. D
nhin vic chn chu kv ln thit k n c ngha tt ve quan if-m bo v chng li
h hi do dng chy sy ra, tuy nhin gi thih u t vo cng trnh cng s ln. S
la chn chu k thit k do s ph thuc vo cc quy trnh, quy phm hoc cc quy
c theo thng l trong vng, ni ta thc hin vic nghin cu. Cc yu t khc cng
c th nh hng n s chn la nh: gi tr ti sn cn bo v trong khu nghin cu
hoc mc quan trng cc tn tht do s c h thng thot nc gy ra.
T hng thng h thng cng thot nc ma chu kv thit k s dng ph bin l 5
nm. Chng ta lu khng nht thit gi thnh thit k h thng cng thot nc l t l
tuyn tnh vi chu k ma thit k (ta ch c th ni chc chn l c t l ng bin).
Theo kinh nghim. 11 si ta nhn thy rng gi thnh mng li thit k vi chu k ma
xut hin l 0 nm thna vt 10% so vi gi thnh m ans li thit k vi chu k 5%;
ui trung bnh ca 1 th tch nc thot b sun l thp hn gi trung bnh ca th tch

157
tng th nc cn thot: iu ny thng c gi l hiu qu kinh t ty thuc vo quy
m cng trnh.

8.2.3. Cng ma

Vn p dng phng trnh thch hp i hi chng ta phi chn gi tr cng

ma I. y l mt thng s ph thuc vo v tr, vng trong c lu vc kho st.
c s xc nh hp l, trc ht phi nh gi thi gian tp trung nc ca lu vc, trong
ta mun tnh lu lng dng chy ln nht. Tip theo, ta phi xc nh chu k ma
xut hin s p dng trong tnh ton. iu ny d nhin ty thuc vo cc quy dnli c
tnh cch php l.

8.2.4. Cng - Thi gian ma - Tn s (ng cong IDF)

Cc ng cong IDF theo nh ngha, l th gii thiu s thay i ca cng

trung bnh ca ma, l hm ca thi gian ko di cn ma cho loi ma ko di trong
thi gian ngn (< 3 gi, i khi < 1 gi) v cho cc chu k xut hin khc nhau. Dng
tng qut ca ng cong IDF c th biu th bi phng trnh ton hc c cr dng
khc nhau sau y:

CNX
( 8 . la)
(a + t)"

M
( 8 .1 b)
t+ B
M
( 8 . 1 c)
tn + B
trong :
N - tn s ca lng ma (1/nm),
t - thi gian ko di cn ma (pht),
a, M, c , B, X, n - cc hng s lin quan n tn s tnh ton cho ma v vng nghicn cu.
V d cho vng Montral, Canada, tc gi Mitci thit lp biu tnh cng
ma dng I = M/(t+B) nh sau:

Bng 8.2: Cng ma cho vng Montral

Chu k ma xut hin (nm) Cng ma (mm/gi)

0,25 533,4/(1+5)
0,50 863,6/(t+7)
1 1244,6/(1+9)
2 1778,0/(t+12)
5 2184,4/(1+12)
10 2743.2/(1+14)

158
 Thi gian ma (pht)

n h 8.1: (V// ( rm(a cho vns Qibec

8.2.5. Dng chy

Trong mi trng d tli, vn e qun l nc gy ra do ma thng khng c
ntiha ln nh trong muc ch bo v i sng con ngi ging nh trong khun kh
qun l dng chy trong cc vng nh hng ca cc con sng ln c th gy l lt.
v ch yu l c phng v loi b cc tc hi ca nc ma trn ln cc ti sn.
C rt nhicu phng php (lc ngh dng tnh ton lu lng dng chy trong
mi trng th. theo c thc chng ta ch quan trn n lu lng ln nht hoc
chng ta quan tm n s thay i lu lng dng chy theo thi gian (thy ). Bc
M, phng php gi l phng php "thch hp" cho php tnh c lu lng ln nht
vn c s dung rng ri. Thm vo , nh vo s pht trin ca my tnh, nht l cc
my tnh c nhn nhni c b nh trung tm tng i mnh, cc k s ngy nay c th
lp cc m hnh cho php tnh ton v thit lp cc thy mt cch nhanh chng cho
cc trng hp khc nhau ca ma. cc dng lu vc khc nhau, cc dng kt cu h
tng dng e ihu nc khc nhau. Nh vo cng c ny, chng ta cn c th tnh ton
th tch cn cua h cha nc tm thi mt cch hiu qu, kh nng tr nc ca cc
ng 0 112 , thi gian nc ciiv trong ng...

8.2.5.1. H s dng chy

H s dng chay, nh vo n ta nh gi t l ma cn li to thnh dng chy mt
tron l khu nahin cu. Cc vii t nh hng n h s nh sau:
- Tinh trn ti t nhin ca b mt nc chy qua.

159
 - dc trung bnh ca b mt khu vc dng chy i qua theo hng thot nc chnh.
- Cng ma.
- T l th tch nc tch c trong vng "trng" ca a hnh.
- iu kin bu kh quyn trc : v d chu k kh hn, chu k m t.
Chng ta c th xem h s dng chy l 1 h s biu th tnh cht khng thay i ca
mt din tch b mt nghin cu hay ngc li, gi tr ca n thay i ty theo cc tnh
hung khc nhau.

8.2.5.2. H s dn g chy kh n g i
Thng thng chng ta xem h s dng chy khng thay i trong sut qu trnh cn
ma xy ra v gi tr ny s khng i theo cc c tnh khc nhau ca cc cn ma.
l l do ti sao ta gi l h s khng i. Cc bng sau y trnh by tm tt gi tr cc
h s dng chy lin quan n cc b mt khc nha v lin quan n cc khu dn c c
cch sinh hot khc nhau.
Mt cch tng qut, ngi ta yu cu xc nh gi tr h s dng chy ca mt lu
vc hay mt vng xc nh no trn c s s tnh n t l c c bi cc loi !>
mt khc nhau ca vng c trng cho lu vc hay vng kho st. Cch xc nh nh
vo cng thc sau y:
n

c = n ( 8.2)
IA ,

vi A, - din tch ca b mt c tnh cht i,

c, - h s dng chy lin quan n din tch A; A; = A.

Bng 8.3: H s dng chy c theo cc loi b mt khc nhau

B mt H s dng chy, c
ng b tng, trng nha 0,70-0,95
ng lt ch, gch 0,70-0,85
Mi lp 0,75-0,95
Trng c, t loi c nhiu ct
- Bng phng (< 2%) 0,05-0,0
- dc trung bnh (t 2% n 7%) 0,10-0,15
- dc ln (> l/c) 0,15-0,20
Trng c, t cht
- Bng phng (< 2%) 0,13-0,17
- dc trung bnh (t 2% n 7%) 0,18-0,22
- dc ln (> 7%) 0,25-0,35
ng vo garage c lt 0,15-0,30

160
 Bng 8.4: H s dng chy c theo cc khu vc khc nhau

Loi khu ph H s' dng chy, c

Thng mi
- Trung tm thnh ph 0,70-0,95
- Ngoi 0,50-0,70
Nh
- Nh ring bit 0,30-0,50
- Nh lin k, tch ri 0,40-0,60
- Nh lin k, theo tng dy 0,60-0,75
- Nh khu ngoi km pht trin 0,10-0,25
- Nh khu ngoi 0,25-0,40
- Chung c 0,50-0,70
Cng nghip
- Mt trung bnh 0,50-0,80
- Mt cao 0,60-0,90
Cng vin, ngha trang, ng c 0,10-0,25
Sn chi 0,25-0,35
t b hoang 0,10-0,30

V d: Xc nh h s dng chy cho mt khu dn c thnh th c din tch 1420000 m 2

(142 ha) trong t l cc loi b mt phn chia nh sau: mi 25%, ng nha 14%, l
ng b tng 5%, ng vo garage lt 7%, t trng c c dc b 49%.

B i gii:

A .C ,
S dng phng trnh: c = 1=1
n

i=l A'
v kt qu trnh by trons bng sau

Din tch A, H s dng chy, Din tch "khng thm" AjC

Loi b mt
(ha) c (ha)
Mi 35,5 0,90 31,95
Dng nha 19,9 0,85 16,92
L ng b tng 7,1 0,90 6 39
ng vo garage lt 9,9 0,25 2,48
t trng c c dc b 69,6 0,15 10,44
Tng cng 142 68,18

H s dng chy cho khu ph nh sau:

A ,C ,
68,18
c = i=ln 0,48
142
1=1

161
 82.5.3. H s dng chy thay i theo thi gian

ma (ph)

Hnh 8.2: Bin di h s d n chy, c c yi tr tO n 100 hiu h l ph n trm

din tch b m t kny thm (h ti, asphale,...) ca kiit vc.
a) Thm thu h m t thm: t;
h) Thm thu b m t thm: tntn bnh;
c) Tham thu b m thm: nhiu

162
 Trong thc t h s dng chy cho mt lu vc khng phi l hng s. H s ny s
thay i theo din bin cn ma: n thng b vo u cn ma, bi v vo thi im
ny, mt phn nc ma ri s thm vo lng t v lm cho t tr nn trng thi bo
ha, mt phn khc s lm y cc vng trng ca a hnh. l l do ti sao mt vi
tc gi ngh tin hnh tnh ton vi gi tr h s dng chy tng theo thi gian ko di
cn ma. Trong khi , cng thc xc nh cng trung bnh ma gii thiu trc
(phng trnh thch hp) khng cho php k n s thay i theo khng gian v thi
gian. Do vn a vo h s bin i theo thi gian rt t nh, i hi chng ta phi
rt thn trng, t nht l vn lin quan n vic thit lp thy . Trong thc t, vic
p dng h s lu lng thay i theo thi gian ch c d dng vi s tr gip ca
m y tnh.

8.2.5.4. Q uan h gia hnh dng lu vc v h s dng chy

Hnh dng ca lu vc c mt nh hng quan trng trn lu lng ti a ca
d n g chy v trn thi gian xut hin ca lu lng ny. C hng ta phi lu khi s
d n g phng php thch hp trong thit k khi dng lu vc k h n g phi l ch nht
hoc vung.

Lu'II vc dm; tam c u (hnh 8.3a)

Trong trng hp lu vc c dng ca mt tam gic u, v tr thot nc nm gia

1 cnh no , quan h gia thi gian ko di cn ma (di dng t l phn trm so vi
thi gian tp trung nc) v din tch lu vc thc s Iham gia to dng chy (di dng
t l phn trrn so vi din tch lu vc) cho kt qu trnh by trong bng sau. Khi cn
m a cn g k o di so vi thi gian tp trung nc, tng th din tch khu vc s cng
tham gia lo dng chy.

o)

c)
Inh 8.3

163
 Bng 8.5: T l phn trm din tch ca lu vc tham gia to dng chy
trong sut cn ma vi thi gian tp trung nc l 10 pht

Thi gian Hnh tam gic u Hnh qut Hnh ch nht Hnh vung
ma (pht)
%A %tc %A %tc %A %tc %A %tc
0 0 0 0 0 0 0 0 0
2 25 20 4 20 18 20 8 20
4 63 40 16 40 39 40 30 40
6 83 60 36 60 59,5 60 58,5 60
8 96 80 63 80 80 80 83 80
10 100 100 100 100 100 100 100 100
12 100 12 0 100 12 0 100 12 0 100 120

Trong trng hp ny, gi s mt t l phn trm quan trng ca din tch lu vc

nm gn v tr thot nc lu vc, dng chy s gia tng nhanh chng sau khi cn ma
bt u. Lu lng dng chy l ln nht trong trng hp cn ma c thi gian ko di
l b hn thi gian tp trung nc ca lu vc: tht vy, vi mt chu k ging nhau, ma
c thi gian ko di ngn s c cng ln hn theo kt qu t tch s AI trong
phng trnh thch hp Q = KCIA ln hn (chng ta chp nhn l h s dng chy l
hng s v ng nht trong trng hp ny).

Lu vc c dng /lnh qut (hnli 8.3b)

Trong trng hp lu vc c dng hnh qut, v tr thot nc chnh nh trcn hnh v,

quan h gia thi gian ko di cn ma (di dng t l phn trm so vi thi gian tp
trung nc) v din tch lu vc thc s tham gia to dng chy (di dng t phn
trm so vi din tch lu vc) cho kt qu trnh by trong bng trn. Khi u cn ma,
lu lng dng chy gia tng mt cch t t. Khi cn ma ko di hn thi gian tp
trung nc, tng th din tch khu vc s cng tham gia to dng chy.
Lu vc dng ch nht hnh 8.3c)
Theo quy c, y l lu vc kh' c chiu di ln hn chiu rng t ra l 4 ln. V tr
thot nc trung tm nm trung im cnh ngn ca pha h lu lu vc. Kt qu tm
tt trong bng trn.
Lu vc dn vung (hnh 8.3J)
Vi mt lu vc dng vung v v tr thot nc chung nm trung im ca cnh
lu vc, kt qu trnh by trong bng trn.
Bi v phn ln lu vc thot nc thnh th thng c dng vung hoc ch nht,
mt cch tng qut chng ta c th xem, khi u ca 1 cn ma, t l phn trm din
tch, % A , ca lu vc tham gia to dng s gia tng theo cng t sut ca thi gian ko
di cn ma (tnh theo phn trm vi thi gian tp trung, % tc). Khi thi gian ma ko
di hn thi gian tp trung nc, tt c din tch lu vc, 1 0 0 %A, tham gia to dng
chy. Hnh v sau y trnh by li kt qu trn di dng th.

164
 Thi gian ma (%t)

H n h 8.4: Quan h ia thi tin ko di cn ma (% tt)

v din tch i vc tham a to dnq chy ( %A)

8.2.6. Thi ian tp trung nc

Thi gian tp trung nc lin quan n mt lu vc l thi gian di nht cn thit

git nc ma ri v tr "xa nht" trong lu vc di chuyn n v tr thot nc ca
lu vc.
Trong mi trng th, cc lu vc nh, cc tiu lu vc c mt din tch b mt
tng i b (v d, 11 hnh thnh trn c s 1 vi khun vin xy dng v cc cng
trnh nh trn v mt on dng ph) v ni thot chnh l mt ming cng. Ta gi
thi gian i vo tc, chnh l thi >;ian tp trung cho mt tiu lu vc dc nh ngha
nh trn.

Vi mt lu vc l th ln, n chnh c hnh thnh t cc tiu lu vc ni trn.

Thi gian tp trung nc ca n dc tnh trong iu kin bnh thng chnh l tng ca
thi gian i vo tc cua ticu lu vc u tin ( l tiu lu vc nm v v tr xa nht v
thng lu ca lu vc theo quan im thy lc) v thi gian nc chy trong ng cng

165
tf tnh t tiu lu vc ny cho n v tr thot nc chung cho lu vc. Do , thi gian
tp trung nc s c tnh nh sau:
t L. = t c + t f (8.3)

8.2.6.1. Thi gian te

Thi gian i vo te ca mt tiu lu vc l thi gian di nht cn thit nc trong

tiu lu vc ny i n c ming thu nc. N ph thuc vo:
- dc trung bnh b mt khu vc theo hng m ing thu nc;
- Khong cch nc phi di chuyn, chy trn trn mt, n m ing cng thu nc;
- Tinh trng t nhin ca b mt a hnh nc chy qua.
Thi gian i vo cho mt tiu lu vc, mt cch tng qut, dao ng t 5 pht n 30
pht ty theo quy m ca tiu lu vc v cch b tr cc v tr thu nc. Trong vng dn
c rt ng c, t l din tch b mt khng thm ln nn thi gian i vo tc s
ngn. Trong khi , vi cc vng dn c, nh dng cc h c th v th t tng
i bng phng, thi gian vo te dao ng trong khong 5 pht n 10 pht. nh gi
thi gian vo, ngi ta ngh nhiu m hnh nh: m hnh ca Kerby,
m hnh ca Kirpich, m hnh ca Schaake, m hnh ca C quan Hng khng Lin
bang M.
M l/ih Kerby-. M hnh ny cho php nh gi thi gian cn thit cho mt lp nc
mng chy trn mt b mt c cc tnh cht thay i. Phng trnh ngh bi Kerby
trong te c tnh bng pht nh sau:

/ 2 ,1 8 7 n L x'467
te = 0 .5
(ph) (8.4)
s
trong :
L - khong cch ln nht nc phi di chuyn trn mt (m). M hnh trn chi p dng
cho L < 365 m; khi L vt qu gii hn ny, trong thc t nc s chy nhanh
hn so vi gi tr tnh bi m hnh;
n - h s nhm b mt tnh theo M anning (xem bng sau);
s - dc trung bnh ca a hnh nc phi chy qua.

Bng 8.6: H s nhm n theo M anning

B mi n
Khng thm, nm ngang 0,02
Ph c v nm ngang 0 ,10
t nn cht v nm ngang 0 ,10
Ph c nhng khng bo tr tt, trng trt 0,20
Bi chn nui 0,40
Rng ph l 0,60
Rng thng 0,80
Rng ph l v c cao 0.80

166
 M hnh K irp ic h : Tc gi ngh phng trnh sau y, thng p dng cho vng
nng thn, trong tc tnh bng pht:

0,0195L'77F
te = (8.5)
.0 .3 X 5

trong :
L - khong cch ln nht nc phi di chuyn trn mt (m). Vi m hnh ch p dng
cho 30 m < L < 3050 m.
s - dc trung bnh ca a hnh nc phi chy qua.
F - yu t ph thuc vo loi b mt t; cho php p dng phng trnh trong cc
vng khng phi l nng thn

Bng 8.7: H s F cho m hnh Kirpich

B mt F
t s.an bng sch v b mt l phng (lu vc nng thn) 1,0
C 2,0
Lt b tng hoc nha dng 0A
Chy trong knh bng b tng 02

M hnh Schaake: Tc gi d ngh phng trnh sau y cho cc tiu lu vc th

(rong c ng ph v cc ming thu nc t dc theo cc l ng hay cc ng
bao q u a n h vi tc tnh bng pht:
0.24
1, 8 L
(3.6)
's irip

trong :
L - khong cch ln nht nc phi di chuyn Irn mt (m) dc thec ;c ng bin
(va h) cho n ming thu nc,
s - dc trung hnh ca da hnh nc phi chy qua;
A im - t l din tch tng cng ca tiu lu vc khng thm (mi che, ng trng
nha, l dng...)
M hnh ca C (iia n HnI khni Lin ba/i> M. M hnh sau y c ngh
tnh th ot nc cho vng phi trng vi tc tnh bng pht:

3 ,2 6 (1 ,1 -C )L " -5
t., = n .v , (8.7)

trong ;:
L - k ho ng cch ln nht nc phi di chuyn trn mt (m).
c - ih s dng chy.
s - dc trung bnh ca a hnh nc phi chv qua.

167
 8.2.6.2. Thi gian nc chy trong ng ng
Thi gian nc chy tf, trong ng ng tnh nh vo phng trnh ca M anning
nh sau:

( 8. 8 )
n
trong :
n - h s nhm;
R h - bn knh thy lc tng ng vi chiu su h ca dng chy trong ng;
J - dc ng ng.
Khi ng dn chy y vi lu lng, chng ta c th bin i phng trnh
M anning v nhn c phng trnh sau y, trong tf tnh theo pht:

L d ^ ___
(8.9)
tf 7 6 ,3 9 4 4 Q P

vi:
L - chiu di ng dn (m);
d - ng knh ng (m);
Qp - lun lng chy trong ng y (rrv/s).

8.3. T H Y

Hy xem mt lu vc nh sau:

T if' 1- ........
Ranh gii
lu vc

t=t

A ng ng tp
trung nc

im tp trung ne A

Hnh 8.6: Lu vc v d n\ thi an tp runs nc

168
 H nh 8.7: Thx d (IIII chy cho m! con nua c cn
khi (i ri trn hfi( vc tiotti thi a n At

thit lp biu trn, chng ta da vo cc ng ng dng chy (theo nh

ngha l cc im t nc cn phi c cng thi gian tp trung v im tp
trung khu vc). Cc ng ng dng chv ny s xc nh cc din tch A |, A 2, Aj...An
(trong Aj c nh ngha l din tch gii hn bi 2 ng ng dng chy tj_| v tj).
Bin t ch thi gian tri qua ca cn ma. Trong khun kh gii thiu phng php,
chng ta la chn cc ng ng dng chy nh sau:

t, - t At

12 = l 2 - t (l - 2 Al

t =t -t =3At

jAt

= n A t
= n

Chng ta s xt cho 3 trng hp sau y:

Trng hp 1. Gi s, ma ri trn ton b lu vc c cng I l hon ton ging
nhau v ko di trong khong thi gian At. Chng ta cng gi thit Cj l t l ma ri
trn din tch AI s to nn dng chy (h s dng chy). Chng ta c th tnh lun lng
Q(t) thot ra lu vc nh sau:
lc t = 0 , Q( 0 ) = 0
lc t = At, Q (tI) = AlC

lc t -7 = 2At, Q(t2) = AtICt

lc tj = j A t , Q ( t j) = AjICj

lc tn = nAt, Q (tn) = AnICn

169
trong :
A|1 - th tch nc ma ri trn din tch A t lc khi u ma cho n thj im
l| = At;
A|IC| - th tch nc ca dng chy (trong thi on At), tho ra khi lu vc, n u A|.
Trong th trn, chng ta gii thiu thy dng chy, c ngha l lu lng tho
thay i the o thi gian Q (t) ra khi k h u vc (ti v tr t h o n c lu vc). l S thay
i lin tc tng ng VI cn m a k o d i t ro n g thi o n At, c n g k h n g I. rai
xung ton b lu vc
Trng li) 2. Trong trng hp ny ta cng xt cho ma c cng khng i nh
trng hp trn, nhng vi trng hp thi gian ma ko di gp i 2At, v ri ung
ton b khu. Thy tng ng cho trng hp ny s c thit lp trn nguyn da
vo thy trng hp I v cng thm vo thy ny nhng l ;h i mt th on
Ai. Chng ta c th tnh lu lng thot ra khi lu vc ny nh sau:
lc 1 = 0. Q(0) = 0
lc 1 | = At, Q(t) = A |IC ,

lc I-, 2At, Q (t 2 ) = A |IC + A 2 IC 2

lc I, = 3 At, Q3) = A 2IC2 + A3IC3

lc I, = jAt, Q(tj) = A ^ IC .i + A jICj

Ic tn = nAt, Q(tn) = A n_IICn. I + A nICn

lc In+I = (n+l)At, Q (tn+|) = A nICn

Trii hp J l a vn xi cho trn mua c cng khng i, I, nhng xtt cho
irng hp thi gian ko di cn ma l n t v ri xung ton b lu vc. Chn ta s
tnh lu lng tho ra khi lu vc nh sau:
lc 1 = 0, Q(0) = 0

lc t| = At, Q(t) = A lC

lc t. jAt, Q(tj) = A kIC,

k= l

lc tn = IIAt, Q(tn) = A n.,IC n., + A nICn

lc In+| = ( n + l ) A t , Q(tn+|) = A nICn

I i ong 3 trng hp gii thiu trn, cng nh cc trng hp tng t khc m ta c
: d dng ihit lp. xt cho ma c cng khng i v xy ra u trn ton l lu
vc v chng la c th rt ra kt lun nh sau:

a) Nu thi gian ma tn bng thi gian cn thit mt git ma ri v tr Xi nht

v n cng thot nc cho lu vc, ta thy trng hp ny tng th iu vc s than gia

170
tao nn lu lng tho Q(t) thay i theo thi gian. iu na\ co ngha l n tiu din tch
Aj tham gia vo s to dng.

b) Nu thi gian ma ri l ln hn tn, gi tr lu ln ihao ra khi lu vcQll^) ln tai

trong mt khong thi gian chnh bng s sai bit gia thi gian ko dicn ma v ln.
c) Chng ta s nhn c lu lng tho ln nht khi ihi gian ko i cn ma bng
vi tn (y l thi gian ta thng gi l thi gian tp trung IIc cua lu vc Ic); iu ny
c ngha l ton b din tch lu vc c c hi tham gia vo s tai) dng thoi ra khi
lu vc.

d) Khi thi gian ko di cn ma b hn tn, lu lng dong chay thoi ra khi lu vc

th b hn lu lng ln nht.

8.4. T H I T LP PHNG PH P T H C H HP

L u l ng thot ra d o m a c c n g k h n g i 1. ri x u n g ton b lu vc ko

di trong khong thi gian tn bng vi thi gian tp 'rung nc 1L ca lu vc nh vo

phng trnh sau v:

Q ( ' n ) = Q ( 0 = A l ICk = * t-K

k=l k=l
Ta gi v l phng trnh thch hp v ta thng vit di dang:
Q = KC1A (8.11)
vi K l h s quy i n v.
T r o n g bng sau y c h n g ta n h n g h a cc bin ca ph ng trnh v n VI tng
ng ca n:

Bng 8.8: Bin trong phng trnh thch hp v dn vi tng nj

Bin n V

Q: lu lng ln nht m Vs m 7s
A: din tch lu vc ha knv
1: cng d ma mm/h mm/h
C: h s dng chy khng dn v khng tni Vi

K: h s quv di 2,75 X 101 0.275

8.4.1. Phng php thch hp

Phng php thch hp, c nghin cu p dng trc khi ra i my lnh, cho phpI
tnh ton mt cch nhanh chng cc lu lng dne chy ln nht cho cc m hnh ma
u ri xunc cc lu vc lng i b (< 5 kn r); do vy y l phng php hon lon
thch hp cho nshin cu cc lu vc thnh th.

I7 I
 Theo ti liu, c l phng php thch hp c s dng ln u vo nm 1851
Irlande. Tuy vy, ngi ta ghi nhn c ch n nm 1889 phng php ny mi c
bit n Bc M, khi tc gi Kuichling s dng nghin cu hot ng ca cc mng
li thu nc ma khc nhau trong mi trng th. Ngi ta a phng php ny
vo Anh nm 1906 v y n c bit di ci tn phng php Lloyd-Davis. Mt
cuc thm d c thc hin vo nm 1975 tren 37 th ti Canada cho bit khong
9 7 % tro n g s n y s d n g p h n g p h p th c h h p n g h i n c u v thit k h th n g
cng thot nc ma.

8.4.2. C s ca phng trnh thch hp

S dng phng trnh thch hp da trn c s cc gi thit sau y:

- Cng ma l khng i trong sut qu trnh ma ri;
- Cng ma l ging nhau trn ton b lu vc;
- Ma ri trn lu vc ko di trong sut qu trnh ma;
- H s dng chy c gi tr khng i trong sut qu trnh ma v h s ny khng
ph thuc vo cng ma, I. Tuy nhin trong thc t, ta thy gi tr ny c xu hng
gia tng trong thi gian ko di cn ma;
- Vi bt k ma c cng khng i no, dng chy to ra s cc i khi thi
gian ma bng vi thi gian tp trung nc c trng cho lu vc;
- Cc b mt c xem l khng thm (ng, mi che, sn ph vt liu khng
thm...) phn phi u trn ton b din tch ca lu vc;
- Tn s xut hin lu lng ln nht chnh l tn sut ma s dng tng ng. Ni
mt cch khc i, v d nu chng ta chn ma xut hin trung bnh 10 nm mt ln
tnh th lu lng ln nht tng ng cng l lu lng s xut hin mt cch trung bnh
10 nm 1 ln;
- Vi lu vc c dng hnh ch nht, tip theo s khi u ca mt cn ma c cng
khng i, t l din tch ca lu vc tham gia vo s to dng ti ni thot ra khi
lu vc th gn bng vi t l gia thi gian .ko di cn ma v thi gian tp trung nc
ca lu vc.
Ta gi lu lng ln nht tiu chun tnh c t phng trnh thch hp khi tt c
cc iu kin trn tha mn. Tuy y l cc gi thit c n gin ha, phng trnh
thch hp cho php d dng tnh c gi tr ln nht ca dng chy gy ra do ma. Kt
qu tnh c tng i chnh xc cho php chng ta thit k phn ln cc mng li
thot nc khng ln lm (trong phm vi 5 km 2 tr xung).
Ngoi ra, ta cn c cc phng php tnh ton khc c chng trnh ha s dng
trn cc my tnh thng c im li hn l n cho php tnh c tl c cc lu lng,
k c lu lng ln nht. Nhiu iu kin bin khc nhau rng buc bi ton cng c th
a vo thun tin di vi cc phng php ny (ma c cng thay i theo khng
gian v thi gian, h s d ng chy thay i,...).

172
 8.4.3. Cc gii hn ca phng php thch hp

Chng ta khng th lun lun s dng phng trnh thch hp trong mi tnh hung
thit k. Phna php chi cho chng ta mt vi kt qu lin quan n lu lng tho ra
khi mt vi dng lu vc cho trc. Chng ta c th lu n vi gii hn ca phng
php nh sau:
- Khi chng ta tnh ton lu lng ln nht thot ra khi luru vc bng phng php
thch hp, chng ta gi thit l ma ri phn b mt cch u n trn ton b ca
lu vc ko di trong mt khong thi gian chnh bng thi gian tp trung nc ca lu
vc ny. Chng ta ch nhn c mt gi tr lun lng duy nht v chng ta c rt t d
kin lin quan n thy ca dng chy.
- Chng ta chi c th s d n s phng php thch hp cho mt vc nh m thi. Mt
s tc gi khuyn co ch nn p dng phng php ny vi cc lu vc nh hn 5 km 2.
- Do phng php cho chng ta bit rt t v hnh dng ca thy dng chy,
phng php thch hp khng cho php tnh kh nng ca h tch nc trong lu vc
c thit k nhm iu ha ho lu lng dng chv.
- Phng php thch hp ch c th k dn 1 phn nh hng ca m ng li cng ln
thy dnt chy. Chng ta khng th tnh ton mt cch chnh xc thi gian nc
c hy trong ng. t, trong khi gi tr Ihi gian ny tham gia vo gi tr thi gian tp
trung nc ca lu vc, tL.
- Chng ta bit tng i 1! s hin i lu lng ti noi thot nc chnh ra khi lu
v c (th y d n g c h y ), d o v y vi c n h g i d un g tc h ch a cn th i t c th ch
d n g i u ha lu lng l k h n g th c (thy d hi u c h i n h d o c c a n th i p c n g
trnh tch nc tm trong lu vc).
- Phng php thch hp khng k n cc iu kin ma ri trc ; ngoi ra
chng ta bit rng dng chy to la do ma trn 1 lu vc thay i rt nhiu theo iu
kin lu vc l kh (tnh trng khn c ma ko di mt thi gian lu trong lu vc)
hay m t (lu vc xy ra ma cch cn ma thit k khng lu). y l l do chnh
ti sao ngi ta li ngh phng php thch hp c ci tin vi h s dng chy thay
di theo thi gian.
- Phng php thch hp khng k n lng nc ma tch ti cc vng trng ca
(la hnh hoc trong cc rnh c th cha nc.
- Phng php thch hp ch gii hn trong nghin cu cho ma ri mt cch u n
trn lon lu vc hoc 1 phn lu vc.
V d : Cho mt h thng thot nc ma nh s sau. Nc ma sau khi tp
trune s thoi v nt s' 5. Cho bit cng trn b tne c h s nhm n = 0,015. Cho bit
cng trn th trng gm cc loi c ng knh D = l,0m ; l,2m ; l,5m ; l , 8 rn v 2,Om.
Nc ma thu trn cc din tch tng ng, chy tp trung v cc h ga nh hnh v.
Cho bit cim ma I tnh theo phng php thch hp trong khu vc l:
18125,6
trong : T c tnh bng pht. Cho bit thi gian nc trn v cc h ga l te = 10 pht.
Xc nh ng knh ng ng theo phng php thch hp.

ng 1-3 2-4 3-4 4-5

i 0,0034 0,004 0,005 0,007
L(m) 400 400 800 1000

B i gii:

IC .A ,
L(m) i(%) n c i
T(ph) I (//s/ha)
ng
(1) (2 ) (3) (4) (5) (6 ) (7)
1-3 400 0,0034 0,015 0,5 2,75 10 ,00 388,13
2-4 400 0,004 0,015 0,6 3,00 10,00 388,13
3-4 800 0,005 0,015 0,4 5,15 14,40 354,73
4-5 1000 0,007 0,015 0,3 9,05 2 1 ,1 1 313,53
27,69

Q = ICAj(m'7s) F(h/D) Dch(m) co (m2) V(m/s) Tf = L/V(ph)

ng
(8 ) (9) (10 ) (1 1 ) ( 12 ) (13)
1-3 1,07 0,27 1,0 0,70 1,52 4,40
2-4 1,16 0,28 1,0 0,72 1,62 4,12
3-4 1,83 0,39 1,2 0,92 1,99 6,71
4-5 2,84 0,51 1,2 1 ,1 2 2,53 6,58

y: Gi tr trong cc ct (1), (2), (3), (4) c t s liu ban u.

Ct (5) ch din tch khng thm ng ng phc v (tnh cng dn).
Ct ( 6 ) tnh bng thi gian tp trung nc n im tp trung nc l u ng ng
xt: TC= TC+ T f.

174
 Ct (7) tnh t ct (6 ) vi cng thc tnh cng
ia i trn lu vc.
Ct ( 8 ) = (5) X (7) ch lu lng Q qua ng.
Ct (9) c tnh theo cng thc Manning cho dng
chy u khng p trong ng trn nh hnh v:
Chy khng p trong ng trn
T phng trnh Manning:
5/3
nQ 0)
.2/3
= F (h /D ) (8.12)
V X'
trong : 0) l din tch t, X chu VI t, i dc t cng, n h s nhm, Q lu lng
qua ng. Gi D l ng knh ng chn; h/D ch y.

nQ
Vi gi tr F(h/D) = (tra ph lc 3), vi D kin ngh (ct 10), xc nh
/
c co ct ( 1 1 ) trong bng tnh.
Ct (12) = ( 8 ) / ( 1 1 )
Ct (13) = (l)/(12)/60. Gi tn ny s tham kho khi xc nh thi gian tp trung nc
cho cc on ng sau nu cn.
V d 2: Cho mt h thng thot nc ma nh s . Nc ma sau khi tp trung s
thot v nt s' 5. Cho b i t cn trn h tng c h s nhm n = 0,015. Cho bit cng
trn th trng gm cc loi c dng knh D = l,2m; l,5m ; l , 8 m v 2,0m. Nc ma
th u trn c c d i n tch tng ng, chy tp trung v c c h g a n h h n h v. C h o bit
cng ma I tnh theo ph(nj; php thch hp trong khu vc l:
6520
(mm/h)
X + 3 6 ,7

trong : Tc tnh bng pht. Cho bit thi gian nc trn v cc h ga l te = 10 pht.
Xc nh ng knh ng ng theo phng php thch hp.

A=10ha
A=12ha
00,4
c=0,5

A=7ha A=9ha
00,4 c=0,3
1

S liu v dc t cng i v chiu di cng L nh sau:

ng 1-3 2-4 3-4 4-5

i 0,005 0,005 0,005 0,007
L(m) 500 500 1000 1000

175
 B i gii:

IC .A ,
L(m) i(%) n c T(ph) . I (mm/h)
ng i

(1 ) (2 ) (3) (4) (5) (6 ) (7)

1-3 500 0,005 0,015 0,5 6,00 10 ,0 0 139,61
2-4 500 0,005 0,015 0,4 4,00 10 ,0 0 139,61
3-4 1000 0,005 0,015 0,4 9,60 13,90 128,84
4-5 1000 0,007 0,015 0,3 15,70 21,42 112,18
27,11

Q^IIC.A.mVs) F(h/D) Dch(m) co (m2) V(m/s) Tf = L/V(ph)

ng
(8) (9) ( 10 ) (1 1 ) (12 ) (13)
1-3 2,33 0,49 1,20 1,09 2,13 3,90
2-4 1,55 0,33 1,20 0,82 1,89 4,40
3-4 3,44 0,73 1,50 1,55 2 ,2 2 7,52
4-5 4,89 0,88 1.50 1,67 2,93 5,69

8.5. PH NG PH P CNG G II HN

Phng php c xut bi p. F. Gorbachep. y l phng php da trn gi

thit ban u cng ging nh phng php thch hp, trong ta chp nhn thi gian
ko di cn ma tnh ton chnh bng thi gian tp trung nc. Ni mt cch khc i, ta
xc nh lu lng tnh ton nc ma cn c vo thi gian tp trung nc. Lu lng
tnh ton nc ma c xc nh bi quan h sau:
Q = CqF (8.13)

trong :
c - h s dng chy;
q - cng ma (//s-ha);
F - din tch lu vc thot nc ma (ha).

8.5.1. Thi gian ma tnh ton

Cng tng t nh phng php thch hp gii thiu trn, trong phng php ny
chng ta cng tnh thi gian ma tnh ton (theo gi thit y cng chnh thi gian tp
trung nc):

it = + tr + t l (8.14)

trong : tm - thi gian tp trung nc ma trn b mt t im xa nht n rnh, ph

thuc vo kch thc a hnh ca lu vc, cng ma v loi mt ph.

176
 Theo L. T. Abramov:
1 c 0,61(),6

z 1 I
( Ph) <8 -1 5 '

trong :
z - ch h s lp ph;
n - h s nhm;
i - dc b mt;
I - cng ma (mm/pht);
/ - chiu di on nc chy.
Trong trng hp thiu ti liu v tnh ton s b tm c th c ly nh sau:
- Nu trong tiu khu khng c h thng thot nc ma: tm = 10 pht.
- Nu trong tiu khu c h thng thot nc ma: tm= 5 pht.
tr - thi gian nc chv trong rnh:

t r = 1,25 (s) (8.16)

vr

vi /, -chiu di rnh v v( vn tc nc ma chy cui rnh ; h s 1,25k n s

tng dn vntc ca dng chv nc ma l u rnh (vr = 0 ) n lc t c
v n tc cui rnh.

\ j - th i g ia n nc chy Iro n g n g n ti t (H i tn h to n

. , = ^ ( S ) (8 .1 7 )
v <>

vi /0 - chiu di ng; v0 vn tc nc chy trong ng v M - h s tnh n s chm tr

ca dng chy nc ma v c ly nh sau:
M = 2 khi a hnh lu vc thot nc ma bng phng ;
M = 1,2 khi a hnh lu vc thot nc ma dc (> 0,5%).

8.5.2. Cng ma

T h e o ph ng php nv, cng m a c xc n h n h sau:

Theo L Cmi X (c ):

^20n q 20 (1 + C .lg P )
- ( 8 . 18 )
tLlln
trong :
n, c - ph thuc vo dc im kh hu tng Yna.
q 2() - cnu tl ma Irong khong thi ian 20 pht, \i chu k lp li mt ln trong nm.
p - chu k lp li nn imra tnh ton, chnh bn khong thi gian xut hin mt trn
ma c cng d vt qu cng tnh ton (nm).

177
 Theo tc gi Trn Vit Lin, vi s liu ca 47 trm theo di ma v p dng phng
php hi quy tc gi ngh cng thc tnh q nh sau:

( 2 0 + b ) " q 2 ( l + C . l g P )
q=!=-------------- ----------------------------------------------------(8.19
/ I \n
(lu + b )
Cc gi tr ca cc thng s b, c , n, q 20 c trnh by trong bng sau.

Bng 8.9
Cc thng s
rr Trm
b c n q 20 (//s-ha)
1 2 3 4 5 6

1 Bc Cn 25,66 0,2615 0,9142 256,6

2 Bc Giang 26,92 0,2158 0,7082 423,4
3 Bo Lc 27,20 0,2251 1,0727 328,9
4 Ban M Thuc 12,09 0,2139 0,8996 224,7
5 Ca Tng 49,95 0,2999 0,7369 237,9
6 C Mau 13,29 0,2168 0,8872 310,5
7 Lng 2,61 0,2431 0,6666 303,9
8 Nng 2,64 0,3074 0,5749 226,5
9 H Giang 19,03 0,2115 0,7862 269,6
10 H Bc 19,16 0,2534 0,8197 267,0
11 H Ni 11,61 0,2458 0,7951 289,9
12 Hng Gai 11,13 0.2433 0,7374 303,6
13 Ha Bnh 11,30 0,2404 0,8016 295,0
14 Hng Yn 18,32 0,2513 0,8158 280,7
15 Hi Dng 15,52 0,2587 0,7794 275,1
16 H Nam 19,66 0,2431 0,8145 274,0
17 Hu ,07 0,2603 0,5430 239,3
18 Lo Cai 5,92 0,2528 0,8092 266,3
19 Lai Chu 11,64 0,2186 0,7446 225,4
20 Lin Khng 31,52 0,2321 1,0230 240,9
21 Mng Ci 25,24 0,2485 0,7325 342,6
22 Nam nh 11,73 0,2409 0,7607 252,7
23 Ninh Bnh 17,01 0,2477 0,7945 310,5
24 Nha Trang 12,90 0,2738 0,8768 156,4
25 Ph Lin 21,48 0,2530 0,8434 283,4
26 Plycu 19.06 0,2329 0,8990 242,2
27 Phan Thit 20.01 0,2533 0,9064 187,0
28 Qung Tr 6 ,21 0,2513 0,5843 216,3

178
 1 2 3 4 5 6

29 Qung ngi 24,51 0,2871 0,7460 259,5

30 Quv Nhn 14,61 0,2745 0,6943 216,3
31 Sapa 6,58 0,1781 0,6075 173,8
32 Sn La 12,45 0,2489 0,8677 217,3
33 Sn Ty 8,51 0,2314 0,7403 298,0
34 Sc Trng 20,05 0,2291 0,9281 261,9
35 Tuyn Quang 28,87 0,2483 0,9316 274,4
36 Thi Nguyn 17,47 0,2570 0,7917 382,5
37 Tam o 3,42 0,1650 0,6693 346,0
38 Thi Bnh 17,85 0.2497 0,7870 305,6
39 Thanh Ha 1 1 ,1 0 0,2730 0,7003 262,1
40 Ty Hiu 13,54 0,2506 0,7785 247,7
41 Tuy Ha 3,57 0,3400 0,6972 197,2
42 Tn Sn Nht 28,53 0,2286 1,0750 302,4
43 Vit Tr 20,04 0,2480 0,9076 306 6
44 VTnh Yn 17,81 0,2451 0,8267 279,4
45 Vn L 19,12 0,2491 0,7708 287,3
46 Vinh 14,87 0,2827 0,6780 279,1
47 Yn Bi 21,64 0,2367 0,8362 293,4

8.5 .3 . H s dng chv

Tng t nh trong phng plip thch hp, ngi ta nh ngha h s dng chy c
nh sau:

C=^ ( 8 .2 0 )
<r

trong : q r, qc - lng nc ma ri trn 1 ha v lng nc ma chy vo mng li

thot nc ma t 1 ha y.
H s dng chy ph thuc vo tnh cht, dc v lp ph b mt, cng ma,
thi gian ma v c xc clnh nh sau:

C = Z,bq 0'Y u ( 8 .2 1 )

trong :
q - ch cng ma (//s-ha);
t - ch thi gian ko di cn ma (pht);
Z lb - h s biu th mt phtrung bnh ton lu vc, l i lng trung bnh ca h
s z (c trng cho tnh cht b mt ph) ca b mt.

179
 Khi din tch b mt khng (hoc t) thm nc ln hn 30% din tch ton lu vc
tnh th h s dng chy c cho php ly bng gi tr trung bnh c 0 v khng ph thuc
vo cng (q) v thi gian ko di cn ma (t).

Gi tr h s mt ph z v h s dng chy c 0 theo cc loi mt ph khc nhau c

tham kho trong bng sau:

B n g 8.10

H s dng chy
Dng b mt H s' z
Co
Mi nh v mt ng b tng 0,95 0,240
Mt ng nha v o 0,60 0,224
Mt ng hc 0,45 0,145
Mt ng dm khng c cht dnh kt 0,40 0,125
ng trong vn bng si 0,35 0,090
Mt t 0,30 0,064
Bi c 0,15 0,038

8.5.4. H s ma khng u
Khi xc nh lu lng tnh ton nc ma trn mt lu vc ln (> 300 ha) ta phi k
dn h s' ma khng u. Khi cng thc tnh lu lng tnh ton s l:

Q = ilC q F (8.22)

trong : r| - ch h s ma khng u hay cn gi l h s phn b ma c xc nh

nh sau:

(8.23)
Qmax
trong :

q lb - ch cng ma trung bnh trn ton b din tch thot nc ma;

q mi)X - ch cng ma ln nht ti mt im no trong lu vc tnh ton.
Trong trng hp khng c ti liu, h s ma khng u c th tham kho gi tr
trong bng sau:

B ng 8.11

Din tch lu vc
300 500 1000 2000 3000 4000
(ha)

Tl 0,96 0,94 0,91 0,87 0,83 0,80

180
8.6. PHN TCH H THNG THOT NC MA VI M HNH SYVMM

8.6.1. G ii thiu

Phng php thch hp ni trn khi thit k ch xc nh lu lng ln nht i qua

cc ng ng thit k. Thi gian ko di trn ma nguy him c xc nh bng vi
thi gian tp trung nc ca lu vc xt n tng im thot nc kho st. Ma cng
c gi s l xy ra ton b trn lu vc. Trong trng hp lu vc khng tha mn cc
gi thit ca phng php yu cu, vic s dng phng php thch hp s b hn ch.
Ngoi ra, trong trng hp khi chng ta mun kho st s thay i lun lng trong h
thng ng ng trong sut qu trnh xy ra ma v ko di sau nu cn, phng
php thch hp khng p ng c. c th m phng hin tng chng ta c th s
dng m hnh SWMM.
8.6.2. V d
Xt lu vc thot nc c s v s liu nh sau:

m
C3w
C1

Ou t 1 C5 J4 C4 J2 C2
-4
////

Gage 1 C6
p

S liu ban u nhu sau:

- Tiu lu vc:

Lu vc SI S2 S3 S4

Tram m a lin h G agel Gage 1 G ag el G agel

im thot nc J5 J1 J3 J6
T l din tch khn thm (%) 50 50 50 50
Din tch (ha) 10 10 10 10
Chiu rng trung bnh (m) 400 400 400 400
dc trung bnh (c'<) 0.5 0,5 0,5 0,5
M hnh thm GREEN GREEN GREEN CiREEN
AMPT AM PT AMPT AMPT

181
 - ng ng trn dn nc:

ng C1 C2 C3 C4 C5

^rnax(m) 0,75 0,75 0,75 1,0 1,0

L (m) 700 500 800 600 500

n 0.01 0.01 0,01 0,01 0,01

- S liu v nt:

Nt J1 J2 J3 J4 J5 J6 Outl

Cao y ng (m) 19,5 19 19 18 19,5 19,5 17

Chiu su t y n mt t (m) 2 2,5 4 2,5 2 2

iu kin bin FREE

- Ma trn lun vc:

Trm ma G agel trn lu vc. S liu ma di dng chui thi gian, tnh bng
mm/h.
- Chn n v v loi m hnh ng lc cho lu vc:
H n v SI: lu lng LPS (//s)
M hnh thy lc loi sng ng lc: dynamic wave
M hnh thm vo t: Green Ampt

Data

Map
i
Simulation Options I
General Dates Tim eSteps ; Dynamic W a ve J[ Files
Categories
Title/N otes A.
Options
Flow Units Inikraion Model
Climatology
6 Hydrology o C-'S 0 CMS o Horton
Rain Gages
Subcatchments O gpm LPS 0 Green Ampt
nuiffirs v
O mgd O mld o Curve Number

>0
Routing Method

ptions o Steady Flow 0 llow Ponding

General
Dates o Kinematic W a ve 0 Report Conrol Actions
Time Steps
Dynamic W a v e Dynamic W ave

Interace Ples

182
 - Xc nh thi gian m phng (trong thi gian 3h cho ngy 27/11/2004):

D k m H
Simulation Options
D a t a M a p

G e n e r a l D a t e s T i m e S t e p s ; D y n m i c W a v e ! l F i l e s J
C a t e g o r i e s

i t l e / N o t e s A
O p t i o n s

D t e ( M / D / Y ) T i m e ( H : M )
C l im a t o l o g y

1 H y d r o l o g y
1 1 / 2 7 / 2 0 0 4 0 0 : 0 0
S t a r t A n a l y s i s o n V '
R a m G a g e s

S u b c a t c h m e n t s

A A !
AntJfftrs v : S t a r t R e p o r t i n g o n 1 1 1 / 2 7 / 2 0 0 4 V 0 0 : 0 0
V .

A.
E n d A n a l y s i s o n 1 1 / 2 7 / 2 0 0 4 V [ 0 3 : 0 0
* !

p t i o n s
ta rt S w e e p m g o n
01/01
General
D t e s
; 1 2 / 3 1
E n d S w e e p i n g o n L ..
T i m e S t e p s

D y n a m i c W a v e
A n t e c e d e n t

I n t e a c e F ie s
r y D a y s

- S liu nhp cho tiu lu vc Sl:

Subcatchm ent S i I IM._ IM... ............................ I ,

---------------------------- ...... ...... ........................... . 1
P r o p e r t y V a l u e

R a i n G a g e G a g e l

u t e t J 5

r e a
[in
W i d t h 4 0 0

/ S l o p e 0 . 5

% I m p e r v 5 0

N - l m p e r v 0 . 0 1

N - P e r v 0 . 1

D s t o r e - l m p e r v 0 . 0 5

D s t o r e - P e r v . 5

% Z e r o - l m p e r v 2 5

S u b a r e a R o u t i r i g Q U T L E T

P e r c e r i t R o u t e d 1

I n i l t r a t i o n G R E E N _ A M P T

183
 - S liu ng ng C 1 :

C o n d u t C1
P r o p e r t y V a l u e

N a m e C 1

I n l e t N o d e J 1

u t l e t N o d e J 2

D e s c r i p t i o n

T a g

S h a p e C I R C U L A . R

M a x . D e p t h 0 . 7 5

L e n g t h [ 7 0 0 ..........................................................................1

R o u g h n e s s 0 . 0 1

I n l e t O f f s e t 0

O u t l e t O f f s e t 0

I n i t i a l H o w 0

E n t r y L o s s C o e f f .

S' liu nt J 1:

J u n c t i o n J IH D
P r o p e r t y ! V a l u e

N a m e J 1

X - C o o r d i n a t e 5 7 0 2 . 7 6

Y - C o o r d i n a t e 6 5 6 6 . 8 2

D e s c r i p t i o n

T a g

l n f l o w s N 0

T r e a t m e n t N 0

I n v e r t E l . 1 9 . 5

M a x . D e p t h 2

I n i t i a l D e p t h 0

S u r c h a r g e D e p t h 0

P o n d e d A r e a

184
 - Trm ma trn lu vc G a g e l. Cng ma biu th bng (m m/h) theo thi gian
(tn file Mua-Intensity):

Rain Gage Gage JE3

P r o p e r t y

N a m e G a g e l

X ' C o o f d i n a t e 3505.35
Y - C o o d i n a t e 3359.24
Description

Tag

R a i n F o r m a t I N T E N S I Y

R a i n I n t e r v a l 0:01
S n o w C a t c h F a c t o r

D a t a S o u r c e T I M E S E R I E S

TIME SERIES:
S e r i e s N a m e M u a - l n t e n s i t y

IDATA RLE:
F i! e N a m e

S t a t i o n N o .

Rin Units MM

Cng ma thit k trn khu vc:

Time Series Mua-lntensity i

90
80
70
60
50
40
30
20
10

Time (hours)

185
 K h ai thc m t s kt qu tnh ton in hnh:
- Mc nc trong trc dc tuyn J5-J2-J4-O utl sau 45' ma:

?{| n 2 (i1 % ^ ; Cl vM

Water Elevation Proile: Node J5 - Out1

Distance (m)
11 / 27/ 2004 00-45: 0)

Qu trnh thay i mc nc ti cc im nt:

Graph - Node Depth w i i

N o d e D ep th
--------Nde J5 -------- Node J1 Node J 2 --------Node J6 Node J3 Node J4
1

Elspsed Time (hours)

186
 Lun lng thot ra khi lu vc ti nt O utl

Graph - Nod 0ut1 Total lnflow M iK

N o d e Out1 T otal ln flo w

Elapsed Time (hours)

Vn tc dng chy trong cc ng C4, C5:

Link Velocity
Link c s Link C4

Elapsed Time (hours)

8.7. BIN PHP GIM LU LNG DNG CHY

Vn du t thc hin cc cng trnh nhm d ch ng dn nc v kim sot

c lu lns ln nht (n xy ra tng i him, t 5 nm n 10 nm) thng tng
i ln, do d nhim v ca ngi k s l phi tm cc bin php hu hiu gim mt
cch ng ke lu lng ny.

187
 c th t n mc tiu ny, chng ta c 2 phng php c bn:
- Pht trin cc k thut nhm gi nc ti ch, du ch c th l vi pht;
- To cc h cha c kch thc ln trn lu vc tr nc tm thi.

8.7.1. Lm chm nc tp trung

Vn qun l nc chy trong mi trng th cng ngy cng c nhn bit l

rt c ch khi gi nc ca dng chy nu chng ta m un hn c h ti a cc h hi gy
ra do t cc dng chy nhanh v lu lng ln. M t gi c bn l ta nn lm chm
vic tho nc ra khi ni pht sinh. T , chng ta c th gim m t cch ng k gi
thnh xy dng cc cng trinh h tng dng thu nc.

gi hoc lm chm dng chy, chng ta c th:

- iu ha vic tho nc ma ri ln cc mi lp;
- Tho nc i qua cc b mt ph c cho nc ri trn cc mi lp;
- iu ha vic thot nc ma ri trn cc bi t trng (sn chi, bi u xe...;;
- Tho nc trong cc h cha nc hay ngay trong c cc khu dn c.

8.7.2. S lm chm hoc gim dng chy nh vo h cha trong lu vc

Khi chng ta c th, mt phn hay ton b, gi hay lm chm dng chy bng mt
trong cc phng php trnh by sau y, chng ta c th gim mt cch ng k cc
lun lng ln nht ca dng chy nh vo cc h cha tch tr nc tm thi trong lu
vc. Chp nhn l cc h cha ny tch tr nc, n s c tc dng gim mt cch ng
k lu lng ln nht, c th hin qua vic gi tr nh ca thy s gim xung khi
c k n cng trnh tch nc trong h thng. Th tch v din tch trung bnh cn thit
ca h cha nc ph thuc vo:

- Th tch nc ln nht m ta cn gi li;

- S thay i ln nht ca mc nc chp nhn c;
- Hiu qu kinh t thc hin c lin quan
n vic xy dng h thng thu nc th
vng h lu ca h gi nc;

- Cc s dng cho mc ch khc c th

c ca h cha (cc dng th thao di nc).

Hnh v sau y trnh by s lm vic

ca mt h cha nc tm thi. Tuy vy,
chng ta khng c qun rng thit k mt
h tr nc, chng ta phi bit thy ca
dng chy i vo h gi nc d kin. H nh 8.8: H tr nc tm

188
 H nh 8.9: Thv d dn cldv trc v sau khi xv cln%h tr nc

Th tch tham gia iu ha nc ma ca h c xc nh theo cng thc sau:

W = K Q ltt (8.24)

trong : K - h s ph thuc vo mc iu ha ca h a (t s gia lu lng

c iu titv lulngnc ma tnh ton ti vtr x vo h, a < 1 ) v h s n
trong cng thc xc nh cng d ma.

a = Q 4 / Q (8.25)

vi: Q It. lu lng nc ma tnh ton v tr ni vi h;

tu - thi gian ko di cn ma tnh ton ca ton b lu vc.
Gi tr h s K dc ly theo bng sau y:

Bng 8.12

K K
a a a K (khi n bt k)
n > 0,6 n < 0,6 n > 0,6 11 < 0,6

0 ,10 1,50 - 0,40 0,42 0,47 0,70 0,13

0,15 1,10 1,50 0,45 0,36 0,38 0,75 0 ,10
0.20 0,85 1,13 0.50 0,30 0,32 0,80 0,07
0.25 0,69 0,87 0.55 0,25 0,27 0,85 0,04
0,30 0,58 0,69 0,60 0,21 0 ,22 0,90 0,02
0.35 0.50 0,57 0,65 0.16 0. 17

Tng lng nc iu ha ca h cn c x di bng ng ng ring c ng

knh khng c nh hn 200 mm, vi thi gian x khng nn vt qu 24 gi k t lc
ma tnh. Trong trng hp ring, thi gian x s c xc nh da trn c s tnh kinh
t k thut v iu kin v sinh.

189
 Lu lng tnh ton cho on cng sau h iu ha c xc nh nh sau:

Q = a Qit + Q i + Q x

trong : a Q u ch lu lng khng c x vo h, Q | ch lu lng tnh ton n: mua

chy trc tip vo on ng sau h v Q x ch lu lng trung bnh x ra khi h S1 U khi
ma tnh.
C th s d n g phn m m SW M M m p h n g h th n g khi kh ng c v ; h
iu ha. V d ly m ng li nh trong m c 8.6.2. G i thit m a xy ra trn luu vc
c d ng sau:

Time Series Mua lntensityl

1
140

120
100

80

60

40

20

0
0 1 2 3
Time (hours)

Kt qu m phng dng chy trong tuyn ng J5 -J2-J4-O utl sau 45' ma:
Prole - Node J5 - Out1 g j i l

Distance (m)
11/27/2004 00:45:00

Kt qu cho thy lu lng vt qu kh nng ca tuyn ng ng ny.

gim nh lu lng qua tuyn ny gi s thit k mt h cha nc tm hm ch
nht c din tch mt thong 2000m 2, su 2m, k hiu 15. Mt knh hnh thang c :hiu
rng y 4m, su l,2 m ni h v nt J2. Mt ng ng ng knh l , 2 m ni t h) n
nt J4.

190
c trng h tr tm s 15:

Name p5 A
X-Coordinate 4538.77

Y-Coodmate 4025.47

Desciption

Tag

lnlows NO

Treatrrient NO

Invet El. 18

Max. Depth 2

intial Depth 0

Ponded Area 0

Evp. FCtOf 0

Shape Cufve TABULAR

S mng li trong trng hp c h tr tm:

Kt qu m phng sau 45' nh sau:

Water Elevaton Protle: N o d e siL; Out1

1.600 1.400 1 ,Q30 800 600

Distance (m)

11 /27/2004 00:45:00

191
 Kt qu cho thy lun lng qua tuyn ng gim ng k so vi trng hp khng
c h iu ha ti cng thi im.
Mc nc trong h iu ha nh sau:

Graph - Node 15 Depth

Node 15 Depth

Elapsed Time (hours)

Lun lng dng chy trong cc ng dn CIO v C 1 1 nh sau:

rGraph - Link Flow

Link Flow
Lmk C10 Link C11

Elapsed Time (hours)

8.7.3. G i m lu lng vi thit b iu h a xoy

Khi lu lng dng chy trong mng li ln, chng ta c th gim bng cch lp
vo thng lu ng ng dn ta cn bo v, m t thit b iu ha lu lng trn nguyn
tc thit b ny s to nn cc dng xoy thy lc (xem hnh v sau). S tn tht nng
lng (ct nc) do thit b gy ra ko theo s y li mt phn lu lng trong ng
dn pha thng lu hay trong h tr nc. Chng ta cng c th lp t thit b ny
trong cc h ga.

192
 H nh 8.10: Thit b iu ha hi lng
a) khnq c xoy, lu ln%b ; b) c xoy, lu lng ln

BI TP

Bi 1. Xc nh h s dng chy cho mt khu vc thcmg mi c thi gian tp trung

nc ca khu vc l 30 pht. B mt khu l loi t st v mt nc ngm y nm
tng i nng. Cc yu t ca khu vc nh sau:

Mi lp: 40% ; thm c. c dc ln (dt cht): 6 %; lng ng: 18%; l ng:

6 %; bi xe: 25%;ng vo garage: 5%

p s: 0,7< R < 0,91

Bi 2. Khi tnh ton dne chv gy ra do ma trong mi trng th, hy gii thch
s khc nhau gia h s dng chy l hng s v h s dng chy thay i theo thi
gian. Khi no ta s dng n.
Bi 3. Thi gian tp trung nc ca 1 lu vc hnh ch nht c cnh di gp 4 ln
cnh ngn l 30 pht. Gi s nc s chv theo hng song song vi cnh ngn v v tr
thot nc trung tm nm Irung im cnh di pha a hnh thp. Gi s h s dng
chy l hng s, xc nh lu lng ln nht thot ra ti v tr thot nc trung tm theo
phng php thch hp trong cc trng hp:
a) Ma ri cng 100 mm/h trong vng 10 pht;
b) Ma ri cng 25 mm/h trong vng 40 pht.
p s di dng AR m Vs
p s: 0,092A R mVs; 0,069AR m '/s
Bi 4. Cho mt h thns thot nc ma nh s sau. Nc ma sau khi tp trung
s thot v nt s 12. Cho bit cng trn b tng c h s nhm n = 0,015. Cho bit

193
cng c trn th trng gm cc loi c ng knh D = l,0m; l,5m ; l , 8 m v 2,Om.
Nc ma thu trn cc din tch tng ng, chy tp trung v cc h ga nh hnh v.
Cho bit cng ma I tnh theo phng php thch hp trong khu vc l:

6520
I= _ (m m /h)
Tc + 36,7

trong : Tc - tnh bng pht. Cho bit thi gian nc trn v cc h ga l te = 10 pht.
Xc nh ng knh ng ng theo phng php thch hp.

ng 1 -2 3-4 5-6 7-8 2 -6 4-8

i 0,0025 0,0025 0,0025 0,0025 0,003 0,003
L(m) 400 400 400 400 500 500

ng 6 -10 8 -1 1 9-10 1 0 -1 1 1 1 -1 2

0,004 0,004 0,004 0,006 0,0065

L(m) 500 500 400 120 0 1000

194
 Chng 9

L c TC DNG LN NG NG CHN TRONG T

9.1. G I I T H I U

ng ng dn nc khi c chn trong lng t, s chu tc dng bi cc lc thay

i theo: chiu dy lp t pha bn trn; loi t bao bc, phng php t ng, kch
thc h mng; cc lc tc dng ng hoc c nh khc (lc c nh gy ra t mt ti
tc dng khng i, v d lp o nha ng ca ng nm bn trn ng). Cng vi
loi lc ny, phi k n cc dng ti trng ng gy ra do xe di chuyn tc dng ln
trong trng hp ng t di nn ca ng c xe qua li. Trong chng ny s cp
n phng php tnh lc tng cng d kin tc dng ln ng v trn c s s xc
inh loai ng ng hp l.
tnh ton lc gy ra do cc nguyn nhn khc nhau ln ng ng, phi bit
phng php (s lp t) thi cng lp t v tnh cht c hc ca ng ng. Sau
d y s a ra c c n h n g h a cho cc th n g s c h n h s c s d n g trong t n h to n
lip theo.

Ti trng dng
Ti trng c nh do lp l ph
bn trn gy ra.
(Fc ic tng ng)

Lc ma st
gia t ph v
t t nhin thnh h mng

t t nhin

H n h 9.1: L p d i on

Xay cls tng (oi. nu n s c t tng on vo rnh tng i hp o

trong lng t, sau lp t li ln ng ng cho n cao trnh ban u ca t t
nhin. Cc s c trnh bv sau y cho thy oia lp t ph v cc thnh vch
ca h o s xut hin cac lc ma sat s phi cp n trong tnh ton.

195
 t t n h i n
a) b)

H n h 9.2: Kv hin cc bin c s dng

tron tnh ton c gy ra do i rnq t inh

Chn ng. ng ng c t trn mt t t nhin ca h o, sau lp t li.

xc nh cc lc tc dng ln mt ng ng, phi lu n cc s lp ng
ng khc nhau:
- Lp t trn ng theo s p dng (9.3a): ng ng s c t trong on
h mng tng i cn v sau s lp t ln n cao trnh cao hn mt t t nhin.

t p -
t p _ - ! t p

t t nhin

aj b) c)

H n h 9.3
a) tt p (Kim : 7 rn /H n< cao hn m t t o.
b) t clp trun tnh: Trn ns> n nian vi m t t do.
c ) t p m : T r n ( n ri! thp h n m t t o .

- Lp t trn ng theo s t p trung tnh (9.3b): khi ng ng t trong h'

mng v c cao trnh trn ng gn bng cao trnh mt h mng.
- Lp t trn ng theo s t p m (9.3c): ng ng s c t trong on h
m ng tng i su v sau s lp t ln n cao trnh cao hn mt t t nhin.
ng ng lp t trong i hm. ng ng c th c lp t trong ng
hm o trong , hoc ng hm o di t. l trng hp phi ti lu lng
ln, ng ng c th c xy dng nh l mt ng hm. K n s trt va chng
thm thnh v sau cng s thi cng mt lp o bc b tng hon chnh ng ng.

196
 Chin riii han on ni. Khi chiu rng h m ng ln hn gi tr ny, lc ma
st gia t p v thnh h mng s xem nh khng ng k khi tnh ton lc lc dng
ln ng ng.

9.2. L c TC DNG LN NG NG TRONG H MNG HP

c th hiu r cc cng thc dng tnh ti tc dng ln cc ng ng, mt s
k hiu sau v s c dnR:

/lr - chiu rng h mng tai cao trn ng ng, cho bt k dc ca vch h
mng no. Trng hp sau khi thi cng la' hin trng cc kt cu chng
thnh h mng, chiu rng /lr c tnh bng chiu lng h mng tr i chiu dy
cc kt cu ny.
h - khong cch thng ng tnh t trn ng n mt t sau khi san lp (cng trnh
hon thnh).
d ,x - ng knh ngoi ca ng ng.
X- k h o n g c c h thng ng tnli l nn n g n c a o trnh m t t t nhin h m ng
sau khi o.
p - c dng khi t p dng (p = x/dex).
p' - c dng khi t p m ( p' = x//,r).

r S(1 - thng s ch c tnh ln dng ch s h thp tng i ca t lp pha trn

ng (trong on h mng) v ca t t nhin. Nu rsj m, t lp ln nhiu hn
l t t nhin; lc gy ra bi khi t ]p ln ng ng s c gim nh mt
phn bi lc ma st gia khi t p v thnh h mng. Trng hp ng c
chn, rsd dng biu th bi t s gia ln ca khi t nm pha bn trn
ng ng v ln (. a khi t p nm bn cnh ng ng. Bng 9.1 sau
y gi chn gi tr khc nhau c th chp nhn cho rsd.
f.i - h s ni ma st ca dt p.
l-i' - h s ma st gia t (lp v thnh h mng.
k - h s Rankine, t s ci! cc p sut hng v p sut thng ng trong vt liu
t p.

Bng 9.1: G i tr r sll

C ch t ng Yu t ln, Isd Cch dt ng Yu t' ln, rsd

t p dng t p m
+ 1.0 p' = 0,5 -0,1
t ct +0,7 p '= 1,0 -0,3
t st +0,3 p - 1,5 -0,5
^

o
11 i

Dt dp trung tnh 0 1 ,0

1
1

197
 1 1 3 4 5
Vdex

H n h 9.4: Gi tri clio tntiH hp t lp hng ct lioc si

Trong mc ny s trnh by phng php tnh lc gy ra do ti trng t p khng

i tc dng thng xuyn ln ng ng c chn trong mt h m ng tng i hp.
C ngha trong trng hp ny ta s k n nh hng ca lc ma st gia t p v
thnh h mng. Mt cch tng qut ta c 2 loi ng ng: ng ng cng (dng ng
bng b tng ct thp hoc b tng) v loi ng ng khng hon ton cng (v d
ng ng bng vt liu nha, tle gn sng).

9.2.1. ng ng cng
Lc gy ra do t p tc dng ln ng ng da vo phng trinh ca Marston nh sau:
F = c dm g/ (9.1)
trong :
Fc - lc lc dng ln ng ng (N/m);
m - khi lng n v ca t p (kg/m ,);
/tl. - chiu rng h mng ti cao trnh trn ng (m);
Ct| - thng s (hnh 9.5) ph thuc vo:
- H s ni ma st t p, |A:
- H s ma st gia t p v thnh h m ng, i-i';
- H s Rankine, k;
- T s h//lr
o - gia tc trng trng (9,81 rn/s2).

198
 cd
H n h 9.5 : Gi tr h s C,I dii* tnh lc iy ra do
r i triH rnh lc dtn ln nv, t tro n i h m n i hp

Trn th, cc ng A, B, c , D, E tng ng tronp c c trng hp sau:

A - k f.i' = 0,1924: vt liu ht khng dnh;
B - kf.i' < 0,165: ct, si;
c - k |i' < 0,150: t c ln c;
D - ki' < 0,130: t st bnh thng;
K - kp.' < 0 , 1 1 0 : t st bo ha.
V d:
Ngi ta mun p t mt ng ng trn c ng knh trong l 1200 mm
(dcx=1474 m m ) trong mt h mng c chiu rng ti cao trnh nh cng l /lr = 2,60 m.
Bn trn trn cng lp bng lp ct v si c chiu dy l 11 m v c khi lng ring l
1900 k g / m \ H mng c o trong nn t ct. Tnh lc thng xuyn tc dng ln
ng ng.
B i g i i

Tnh li knh m>oi (n l II, ex

Vi ng ng c ng knh trong 1200mm s c ng knh ngoi l
d . x = 1474mm.
T n h c h i n r ii ii litiii c a h , (I,r) !rans

tnh gi tr ny, xem dng n c chn, sau khi c t ln nn h m ng loi

t ct vi cc c tnh: p =1,0 (p = x/dcx= dcx/cx = 1 ). Hn na, nn l loi t ct do

199
 chn t bng 9.1 c rsd = 0,7
vi h/dex = 7,46 (11,0 m /1,474 m)
v rsdp = 0,7 tra biu 9 4 c
L = 2,7.
Do : /l r - 2,7 = 2,7x1,474
= 3,98 m
y l chiu rng gii hn ca
h mng. Hnh 9.6: ni /H cu dt rom> h ninv, hp
Bi v chiu rng o h mong
(2,6m) nh hn gi tr gii hn va tnh (3,98m), xem nh ng ng lp t trong iu
kin ca h m ng hp, do ly /tr = 2 ,6 m.
Tnh lc c nh tc dng ln ng:
h//~ = 11/2,6 = 4,23
Vi h//Ir- 4,23 v t p l loi ct si, c d = 2,3 (ng B trn th 9.5); lc tc
dng l:
Fc = C dm g/
= 2 , 3 X 1 9 0 0 X 9 ,8 1 X 2 , 6 2 = 2 8 9 8 0 0 N / m

9.2.2. rig n g khng cng tuyt i

Tnh lc gy ra do p tc dng ln ng ng da vo phng trnh ca Marston

nh sau:

Fc = c dmg/,rd ex (9-2)
Phng trnh trn c khai trin trong c k n s bin dng ca ng, ko theo
s ln ca khi t p pha bn trn ng ng. Hin tng ny s lm gia tng lc ma
st gia khi t p v thnh h mng, lm gim i mt phn lc do khi t pha trn
sinh ra tc dng ln ng.
Ngoi ra, ngi ta quan st c, do s bin dng ca ng, trng lng ca khi t
lng tr nm ngay bn trn ng ng i khi to ra mt ti ln hn gi tr tnh t cng
thc va nt'u trn Do vy, ngi ta khuyn nn tnh trng lng khi lng tr t p c
chiu rng l ng knh ngoi ng ng v chiu cao l chiu cao ca khi t p.
Nu ti trng tnh bng phng php ny ln hn gi tr cho t cng thc nu trn ta s
dng gi tr ny tnh ton.

9.3. L c TC DNG LN NG NG TRONG H MNG RNG

Khi ng ng c t ln t hay trong trng hp h m ng t ng c chiu rng

ln [/lr > (/lr)tr;ms], s khng cn s gim ti nh vo lc ma st gia t p v thnh h
mng nh trng hp trc. Sau y s xc nh lc gy ra do lp t bn trn cho 3
trng hp khc nhau: ng ng c t lp dng, ng ng c t lp trung tnh,
ng ng c t lp m.

200
 9.3.1. ng ng c t lp dng

Trong trng hp ny, cao trnh trn

ng s cao hn cao trnh t t nhin
y h mng. Lc tc dng sy ra do
t p ln ng ng c xc nh
bi phng trnh sau v:

Fc = C cm g d ^ (9.3)

trong : Cc l h s ph thuc vo t s
h/dcx v tch s rs lp cho bi th 9.7.

V d:
Mt ng ng bng b tng c
ng knh trong 12 0 0 mm v ng Cc
knh ngoi 1474 mm, dc t trong nn
H n h 9.7: H s c , dtni th lc tc dni ln
t ct theo s nh hnh 9.8. Lp t
chrn n p iln
lp c chiu cao 10 m so vi trn ng v (chiu 1'ii h rnm> .xem nh v hn)
c khi lng ring l 1760 kg/m \ Tnh
lc tc dng ln ng ng, cho bit trn
cng t cao trnh 0,7dCN (p = 0,7) phi
trn y h mng t nhin.

Li gii:

Vi nn t ct, rs I = 0,7; p -- x/d,.x - 0,7;

rsdp = 0,7 X 0,7 = 0,49.

Ngoi ra, h/d.x=l 1/1,474 = 7,46. Vi

1M|P = 0 ,5 v h/d ,x= 7 ,4 6 , tra d th 9 . 7 i n h 9-8: n x n H c (ct lp dng

c Cc = 10,3. Do ti trona lc dng s l:

F. = C cmgd^x

= 10.3 X 1760 X 9,81 X 1,4 742= 3 8 6 3 79 N/m

9.3.2. ng ng c lp t lp m

Trong trnfc> hp nv, dng ng dc t trong mt h m ng tng i cn v cao

trnh trn no cao hn cao ninh int v h ca t t nhin. Sau t c lp n
cao trnh mt dt chuim cua khu vc. Lc tc dng ln ng ng tnh nh sau:

F , = C nm g/ (9.4)

110112 : Cn l h s phu thuc vo cc gi tr h//lr, rsd. v p' trnh by trong cc

th 9.9.

201
 b)

0 1 2 3 4 5 6 7 8 n 0 1 2 3 4 5 6 7 8 'n

c) d)

Hnh 9.9: Gi tr li s' C n clm lnh lc y ra do tci tnh (lp t dp m )

a) p' = 0,5; h) p' = 1,0; c) />'=] ,5; d) p' = 2

9.3.3. ng ng c t lp trung tnh

Lc gy ra sau khi lp t c tnh ging nh trng hp c lp t lp dng

nhng vi lu cho trng hp ny l p = 0 hay rS(ip = 0 .

V d:
Mt ng ng dn bng b tng c ng knh trong 1200 mm v ng knh ngoi
1474 mm, c dt trong nn t ct theo s nh hnh 9.10. Lp t lp c chiu cao

202
] 1 m so vi trn ng v c khi lng ri n g 1900 k g /m \ Tnh lc tc dng ln ng
n g trong trng hp h m n g rng 2 m v khong cch thng ng gia cao trnh mt
h' m ng t nhin v c ao trnh trn ng l X = 2m.

Cao trinh 1131 it lp sau khi xy dng

L i gii

X 2
Gi tri p' = - = = 1, vi gi tr ny ca p' cho php chn gi tri ca rvl1 = -0,3 (xem
^lr 2
bng 9.1); do rs(, p '= (-0,3) X 1 - -0,3. Ngoi ra, h//lr = 11/2 = 5,5. Vi h//, r= 5,5;
d = -0,3 v p' =1,0 ta c Cn = 3,6 t th 9.9b.
Ti trng gy ra do lp t ph bn trn s l:

F = :C r n g . / , 2r = 3 ,6 X 1900 X 9 ,8 1 X 22

~ 268402 N/m

9.4. L c T C DNC, LN NG NG DO T I T R N G N G T P TRU NG

Trong khai thc, ng ng di khi cn phi chu tc dng gy ra bi cc loi xe di

chuyn pha bn trn, ta gi l lc ng. Hmh AI 1 cho thy mt cch nh tnh s phn
b trong t ca mt lc gy ra do mt xe ti di chuyn pha trn ng ni t ng. Ti
trng ca xe c truvn xune nen thng qua 2 bnh xe. T hp nguy him ca ti v
mt tc dng ca ti thay i theo chiu v ca lp t lp trn ng. Bng 9.2 gii thiu
3 trng hp nguy him.

B ng 9.2: Ba trng hp nguy him di tc dng ca ti trng do xe

Chiu cao t p Ti Irng xe Din tch b mt chu lc

(m) (kg) (m2)
h < 0,4 7250 (0,25 + 1,75h)/(0,5 + l,75h)
0,4 < h < 1,25 14500 (0,25 + ,75h)/(l,7 + l,75h)
1.25 < h 21750 (1.45 + 1,75h)/( 1,7 + l,75h)

203
 p sut do ti ng tc dng ln ng ng c xc nh bi phng trnh sau y:

Pgl
Pl (9.5)
A

trong :
PL - ng sut trung bnh trong mt phng nm ngang di tc d ng lc p (N /m 2)
p - khi lng tp trung (kg).
I - h s truyn ti, ph thuc vo su chn ng.
A - din tch b mt nm ngang ti v tr mun tnh ng sut (m 2).
g - gia tc trng trng.

Hnh 9.11: Ti trii n tc chini ln dirti

Ta nhn thy khi cng i su vo lng t din tch chu lc s gia tng. Trong thc t
din tch ny thay i gn nh dng ca mt hnh nn c nh l ni tc dng ca bnh
xe ln mt t v cnh bn nghing mt gc 0 (xem hnh 9.13) so vi trc. Trong trng
hp ph bin khi lp t p l ci hoc si, ta c th ly 0 = 26.6, tng ng vi
mt dc 2:1. y ca hnh nn kho st nm cao trnh trn ng ni mun xc nh
p sut ca lc bn trn gy ra.

204
 Vi s xc nh h s I (bng 9 3), p iu.t s c xc nh.

a) b)

H n h 9.13: Anh hiii ri t! n< dn< ln un n:

a) Phn b lc trong t; h) D i n lch s dng tnh lc tnq CI tc ilnnt ln n.

Bng 9.3: G i tr ca I

Chiu cao lp d ph ln ng (m) H s I

T 0 m n 0,3 l 1,3
T 0,31 rn dn 0,60 m 1,2

T 0,61 m n 0,()0 m 1,1

T 0,91 m tr ln 1,0

T gi tr lc m ng ng phi chu xc nh bi phng trnh sau y:

F = p l x L x / ( 9 .6 )

trong :
Ftot - lc tng cng gy ra do ti trng ng tc dng ln ng (N)

P - p sut tc dng trn mt phng nm ngang ti cao trnh trn ng (N/m 2= Pa).

L - chicu di on ng ng chu lc F 10l tc dng (m). Chiu di ny thay i theo

phn phi hnh nn ca lc trng t.

/ - chiu rng ng ng chu lc Fuu tc dng (m). Trong trng hp ng trn,

chnh l ng knh ngoi dcx ca ng ng.
Trn c s kt qu ny, lc tc duns ln m chiu di ng ng c tnh nh sau:

205
trong :
Fv - lc tc dng ln 1 m chiu di ng ng (N/m);

L - chiu di hiu dng ng ng di tc dng ca F(ot;

F v - c th tnh mt cch n gin nh sau:

c PI
Fv = ^ p (9.8)

trong :
Cs - h s ph thuc vo ng knh ngoi ca ng ng v chiu cao lp t p
bn trn ng (bng 9.4).
p - ti trng ng (N).
I - h s (bng 9.3).
L - chiu di ng trn c ti phn b.

Bng 9.4: Gi tr h s C s dng tnh F v v Fc trong (9.8) v (9.9)

l/(2h) hay U(2h) (ti phn phi u hoc ti trng dng tp trung)

dex/2h 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,2 1,5 2,0 5,0

0,1 0,019 0,037 0,053 0,067 0,079 0,089 0,097 0,103 0,108 0,112 0,117 0,121 0,124 0,128

0,2 0,037 0,072 0,103 0,131 0,155 0,174 0,189 0,202 0,211 0,219 0,229 0,238 0,244 0,248

0,3 0,053 0,103 0,149 0,190 0,224 0,252 0,274 0,292 0,306 0,318 0,333 0,345 0,355 0,360

0,4 0,067 0,131 0,190 0,241 0,284 0,320 0,349 0,373 0,391 0,405 0,425 0,440 0,454 0,460

0,5 0,079 0,155 0,224 0,284 0,336 0,379 0,414 0,441 0,463 0,481 0,505 0,525 0,540 0,548

0.6 0,089 0,174 0,252 0,320 0,379 0,428 0,467 0,499 0,524 0,544 0,572 0,596 0,613 0,624

0,7 0,097 0,189 0,274 0,349 0,414 0,467 0,511 0,546 0,584 0,597 0,628 0,650 0,674 0,688

0,8 0,103 0,202 0,292 0,373 0,441 0,499 0,546 0,584 0,615 0,639 0,674 0,703 0,725 0,740

0,9 0,108 0,211 0,306 0,391 0,463 0,524 0,574 0,615 0,647 0,673 0,711 0,742 0,766 0,784

1,0 0,112 0,219 0,318 0,405 0,481 0,544 0,597 0,639 0,673 0,701 0,740 0,774 0,800 0,816

1,2 0,117 0,229 0,333 0,425 0,505 0,572 0,628 0,674 0,711 0,740 0,783 0,820 0,849 0,868

1,5 0,121 0,238 0,345 0,440 0,525 0,596 0,650 0,703 0,742 0,744 0,820 0,861 0,894 0,916

2,0 0,124 0,224 0,355 0,454 0,540 0,613 0,674 0,725 0,766 0,800 0,849 0,891 0,930 0,956

Bng trn y gii thiu cc gi tr ca h s Cs c s dng tnh lc F v tc dng

ln ng ng sinh ra do mt ti trng ng tp trung. N cng dng tnh lc Fc gy

ra do ti trng c nh phn phi u trn mt t v i xng so vi ng ng
(dcx/(2h) i vi ti ng tp trung v L/(2h) cho ti trng phn phi u).

206
 Tuy vy, trong thc hnh ngi ta t dng cch t.nh ni trn khi m un nh gi lc
gy ra do lc ng t xe di chuyn bn trn. Cc bmg lp sn thng c s dng khi
tnh ti trng ng tc dng ln cc ng ph chai trng nn (y l trng hp nguy
hin 1 nht xy ra vo thi im xy dng ng). Trong cc bng ny s cho tnh lc tc
dng ln ng ng cho cc ng ng c -ng k.nn khc nhau c t di ng
b hoc ng st; v cho c cc chiu dv lip t (p khc nhau pha trn ng ng.
Cc gi tr ny c tnh khi k n h s I trong trng hp chiu cao lp t p b
hn 0,9 m.

B n g 9.5: T i trong ng ca n g b (k g/m )

t c d n g ln ng nsg trn

Chiu cao lp t ph b n ; rn dng ng m)

d,n dex
(mm ) (m)
0.15 0,30 0,45 0,61 0,76 0,91 1,0*6 \2 2 1 52 1,83 2,13 2,44 2,74

300 0,40 5620 3090 2190 1610 1130 820 67 J 570 430 340 280 240 190

375 0,49 6310 3510 2590 1900 1340 980 800 m 520 420 340 280 240

450 0,58 6120 3880 2930 2170 1530 1120 920 770 590 480 390 330 280

525 0,67 5830 4200 3260 2410 1710 1250 10?0 <360 670 540 450 370 310

600 0,76 6100 4480 3570 2650 1890 1380 mo 950 740 590 490 420 360

675 0,85 5770 4370 3850 2870 2050 1SQ0 1B0 1040 30 650 540 450 390

750 0,94 5390 4210 4120 3080 2200 1600 13?0 1120 m 710 580 490 420

900 1,12 4750 4180 4360 3470 2480 1830 15?Q 1280 1000 820 670 560 490

975 1,21 4480 3970 4240 3630 2620 1920 1600 1350 1060 860 710 610 520

1050 1,29 4260 3790 4120 3810 2740 2020 16fc 1410 T20 910 760 640 550

1200 1,47 3850 3470 3900 3690 2960 2190 1830 1550 1220 1000 830 700 610

1350 1,65 3510 3200 3700 3510 3050 2350 1960 1670 1320 1090 910 770 650

1500 1,83 3230 2960 3650 3350 2920 2500 2080 1770 1*10 1160 970 830 710

1650 2,01 2990 2750 3750 3210 2800 2440 2200 1870 1500 1240 1040 880 760

1800 2,19 2780 2570 3840 3260 2690 2340 2250 1980 1580 1310 1100 940 800

2100 2,54 2450 2290 4060 3410 2690 2170 2100 2020 1730 1430 1210 1030 890

2400 2,89 2190 2050 3590 3410 2800 2230 1980 1890 1660 1550 1310 1120 970

2550 3,07 2070 1960 3420 3260 2840 2280 2010 1850 1920 1590 1350 1160 1010

3000 3,61 1800 1710 3010 2870 2530 2200 2110 1900 2080 1740 1470 1280 1120

3300 3,96 1650 1580 2780 2S80 2350 2050 1980 1920 V 70 1810 1550 1340 1180

3600 4,32 1520 1460 2590 2480 2200 1930 1860 1800 V 90 1900 1620 1400 1240

( h i c h : G i t i i h i t vois tn ( n i tii ( h ti.h . frt>nv t h p h ic u ca o l p d ) p h

n h lu m 0 ,9 m.

207
 Bng 9.6: Ti trng ng ca ng st (kg/m) tc dng ln ng trn

Chiu cao lp t ph bn trn ng ng (m)

(mm) 0,3 0,6 0,9 1,2 1,5 1,8 2,1 2,4 2,7
300 5400 5060 4550 4020 3480 2990 2560 2200 1870
375 6590 6160 5530 4910 4260 3650 3120 2680 2290
450 7770 7280 6530 5790 5010 4300 3690 3170 2710
525 8960 8380 7530 6650 5770 4950 4240 3650 3120
600 10130 9480 8530 7540 6530 5610 4810 4120 3530
675 11320 10590 9520 8440 7290 6260 5370 4610 3940
750 12500 11700 10520 9300 8060 6900 5920 5090 4360
900 14880 13910 12500 11060 9600 8210 7050 6060 5180
1050 17260 16070 14490 12810 11110 9520 8180 7010 6000
1200 19640 18300 16520 14570 12650 10830 9300 7980 6830
1350 22020 20530 18450 16368 14170 12140 10420 8930 7650
1500 24400 22770 20530 18150 15620 13450 11530 9890 8470
1650 26630 25000 22470 19790 17260 14760 1266C 10860 9300
1800 29020 27230 24400 21580 18750 16070 13780 11830 10120
2100 33780 31550 28420 25150 21720 18750 16070 13750 11750
2400 38540 36010 32440 28720 24850 21280 18300 15620 13410
2550 40920 38240 34370 30360 26340 22620 19340 16670 14220
3000 47320 44340 39880 35270 30500 26190 22470 19190 16520
3300 52080 48660 43750 36690 33480 28720 24700 21130 18150
3600 56840 53120 47760 42260 36600 31400 26930 23060 19790

B ng 9.6 (tt): Ti trng ng ca dng st (kg/m ) tc d n g ln n g trn

Chiu cao lp t ph bn trn ng ng (m)

(mm) 3,1 3,7 4,3 4,9 5,5 6,1 7,6 9,1
300 1620 1310 1070 880 730 620 430 310
375 1980 1590 1310 1070 890 760 520 370
450 2340 1870 1530 1250 1060 910 610 450
525 2690 2160 1770 1440 1200 1040 710 510
600 3050 2440 2010 1640 1370 1180 800 580
675 3410 2720 2230 1830 1530 1320 890 640
750 3750 3010 2470 2020 1700 1460 1000 710
900 4460 3590 2950 2400 2010 1730 1180 850
1050 5180 4150 3410 2780 2340 2010 1370 980
1200 5890 4720 3870 3170 2650 2280 1550 1120
1350 6610 5300 4340 3540 2980 2560 1730 1250
1500 7310 5860 4810 3930 3290 2830 1920 1380
1650 8020 6430 5280 4310 3620 3110 2110 1520
1800 8740 7010 5740 4690 3930 3380 2290 1650
2100 10150 8140 6680 5460 4570 3930 2680 1920
2400 11580 9280 7620 6220 5210 4480 3050 2190
2550 12280 9850 8080 6610 5530 4760 3240 2320
3000 14220 11400 9360 7630 6400 5510 3750 2680
3300 - 15620 12530 10280 8410 7040 6040 4120 2950
3600 17110 13670 11220 9170 7680 6590 4490 3210

Ghi ch: H s dc s d n g d tn h cc g i t r i ro ig b n g trn hin th in t 1 ,4 (cho tr g u/? riiu

ca o 1 p h b m 0 ) n ,0 c i ca o y p h h i h o c x n g 3 ,0 n).

208
9.5 . L c T C D N G L N NG N G 11)0 T I T R N G PHN P H I U
V I X NG
tnh lc gy ra do mt ti trng phn phci u trn b mt, ln mt ng ng
chn trong t, c th s dng phng trnh au dv:
Fc = C sm gdex (9.9)
trong :
Fc - lc tc dng ln 1 m chiu di ca ng ng (N/m);
Cs - h s ph thuc vo cc kch thcc (L, /) cua ti v ca chiu cao t p trn ng (h)
(bng 9.4);
L - chiu di ca ti phn phi u theo piirnig ng ng (m);
1 - chiu rng ca ti phn phi u theo phmg thng gc ng ng (m);
m - ti phn b u (kg/m 2);
g - gia tc trng trng (9,81 m/s2);
dcx - ng knh ngoi ng ng (m).

Ti phn b u
bn trn

Mt t

(n V! i i i.) ?
H n h 9.14: Ti t r tn h p )'(Ai di x !(>pha trn ng n%

9.6. Lc T N G HP T C DN( LN N G N G
Cc ng ng chn trong dt phi chu c t hp lc: tnh v ng. tnh tng
hp lc ny, ta c th dng cng thc sau:

(9.10)

trong :
F lol - lc tng hp tc dng ln ng Yic:
^ F c - tng cc ti trng tnh (N/m);
X tng cc ti trng ng (N/m);
d , x - ng knh ngoi ng n> (nini;
FS - h s an ton;
L r - h s ph thuc vo s gi ta ca ng (bng 9.9).

209
 Bng 9.7: Gi tr Lf

Loi nn lt H s' Lf

A 4,8; 3,4 hay 2,8 ty theo cht lng ct thp

B 1.9
c 1.5
D 1.1

A - nn ll bng b tng
B - nn lt bng dm c m cht
c - nn t c m cht
D - ncn t t nhin, t p khng c m cht

c) d)

Hnh 9.15: C c d a n %p h h in n% b tns> c t thp

a) cti i% r n c t thp n ;

b) ns ni (rn ci thp kp;

c) d ^ if tr n c thp kp c n tli m J t th p d i e ls e ;
() d V ns> tr n c thp lini e llip s e n.

9.7. K C H TH C T I T H I U M T C T N G A N G H M N G

Lp t mt cch thch hp ng ng i hi kch thc h m ng phi tha mn

mt s yu cu, c th k n: loi t nn o h' mng; mi dc h mng; khng gian
ti thiu c th thao tc cc thit b m nn; kch thc ng ng.

210
 9.7.1. M i dc h m ng

Mi dc thng c quy nh trong cc cm nang thi cng nhm bo m an ton

lao ng. Mi dc s c th ly 1:10 trong trmg hp h' m ng thi cng trong nn v
1:2 trong trng hp vt liu khc. Trong m t s trng hp, ta c th p dng phng
php c mi dc thay i, pha di dc b' v tin v mt t s c dc ln hn. Tm
li, c s vic chn h s mi dc ph thuc vo iu kin tnh'n nh mi dc.

9.7.2. C hiu rng y h mng v ch iu dy lp lt

Chiu rng /lr y h mng v chiu dy d lp lt y ng ph thuc vo ng

knh ng s d n g v mi dc ca h m n g . Hnh 9.16 sau y gii thiu m t ct h
m ng in hnh.

Chiiu rng y h mng r

Hnh 9.16: Mt c hmn

B ng 9.8: C hiu dy lp lt v ehiu rng y h m ng cho cc to trmg ng

ng knh khc nhau

Nn khng phi (mi dc 2.) Nn (mi dc 10:1)

ng knh ng
(mm) Chiu dy lp lt Chiu rng y Chiu dy lp lt Chiu rng y
(mm) h mng (mm) (mm) h mng (mm)

/ 1 4 5
< 150 150 900 150 950
20 150 900 150 1000
225 150 900 150 1000
250 150 900 150 1050
300 150 950 150 110 0
350 150 1000 150 1150
375 150 1000 150 1200
400 150 1000 150 120 0

211
 1 2 3 4 5
450 150 1050 150 1250
500 150 110 0 150 1300
525 150 110 0 150 1350
600 150 1150 150 1450
675 200 1350 150 1650
750 200 1400 150 1750
900 200 1500 150 1900
1050 200 1600 150 2050
120 0 200 1750 150 220 0
1350 250 1800 150 2400
1500 250 1900 150 2550
1650 250 2000 150 2700
1800 300 2050 200 2850
1950 300 220 0 200 3000
2 10 0 300 2300 200 3200
2250 300 2400 200 3350
2400 300 2500 200 3500
2700 300 2700 200 3800
3000 300 2950 200 4150
3600 300 3400 200 4800

9.8. L P L T Y NG

Mt ng ng s chu tt hn di tc dng ca lc khi di y h mng s c

chun b sao cho phn bn di ca ng ng tip xc vi tt c cc im di y h
mng. S la chn vt liu lm nn cng gi vai tr khng km quan trng. Hn na, khi
c s gia tng tip xc vi nn hai bn thnh ng cho php phn phi lc truyn c
u n hn. Kh nng chu lc ca >ng cng tng khi nn h m ng c m nn tt.

9.9. PH NG PH P LP T LN NG N G

Thng thng thi cng lp h mng sau khi lp ng ng c thc hin tng lp
dy 300m m. v mi lp s c m cht theo ng quy phm. Trong trng hp ng
ng xy dng bn ngoi ng, c th mt vi on ng c lp t m khng cn m
nn. Vi cc ng ng c ng knh nh hn 900m m , s lp lp dy 300m m pha trn
trn ng bng vt liu ht nh. T cao trnh ny tr ln, c th tn dng vt liu ti ch
c th m nn c tr loi t c qu nhiu cht hu c. Vi cc ng ng c ng
knh ln hn hoc bng 900m m s lp bng vt liu ht nh cho n cao bng na
ng knh ng ng, sau l cc vt liu nh trong trng hp trn. Kch thc vt
liu ht nh bin thin t 0 n lOmm hay t 0 n 2 0 mm.

212
 BI TP

Bi 1. M t ng ng bng b tng ct thp c ng knh trong d = OOmm, c

t trong m t h m ng nh hnh v. Pha trn ng ph bng m t lp ct v si c khi
lng ring l 1900 k g / m \ Xc nh lc tc dng ln ng ng (N/m). Chn mt loi
nen t ng, chn loi ng.

ng c xy tng on.

Loi nn t ng B c L f = 1,9 (bng 9.7).

p s: 67424 N/m

Bi 2. M t ng ng m m c ng knh ngoi d , x = 9 lOmm t trong mt h

mng c chiu rng 1350mm, c lp bi mt lp ct si dy 365cm c khi lng
: ing l 1900 kg/rrv. Xc nh lc tc dng ln ng (N /m ). Tinh trng h mng?

p s: Theo M arston 41216 N/m;

tnh t ti do khi t p ngay bn trn 61909 N/m.
H mng qu hp.

213
 Bi 3. Mt ng ng b tng c ng knh trong 1200mm, c t vo t nh
hnh v, sau s c lp li bi m t lp t dy 975cm. t c khi lng ring
2 0 0 0 k g /m \ Xc nh lc lc dng ln ng (N/m).

p s: 39175. N/m
Bi 4. M t ng ng b tng ct thp c ng knh trong 1200 mm, t trong mt
h' m ng nh hnh v sau. Cho bit gi tr rsd = -0,3- Xc nh lc tc dng ln Eg khi
c t p c khi lng ring 2000 kg/m 3 bn trn.

p s: 252941 N/m.
B i 5. Mt dng ng b tng ct thp c ng knh trong 600m m c trr cng
cch mt ng 91cm. Tnh ti trng ng ng ng c th chu c.
p s: 13535 N/m
Bi 6 . M t ng ng b tng ct thp c ng knh trong 600rnm c trr cng
cch mt ng st 90cm. Tnh ti trng ng ng ng c th chu c.
p s: 8 367 9, N/rn

214
 Ph lc 1

CH UYN I H T H N G N V us V SI

Chiu d
H thng us Tng ng
] foot = 12 inches(in) I inch =2,54 001
1 yard = 3 feet 1 foot = 0,3045 m
1 mile = 5280 feet 1 mile = 1,609 km
] mile hi = 1,1516 mile I m il e h i l = 1,853 km
1 arce - din tch hnh vung c canh 11208,71 ft
Din tch
H th /S Tnq n
1 ft2 = )44 square nches 1 sq inch = 6,45 cm 2
I square yard - 9 ft2 1 sq foot = 0,0929 m 2
1 arce = 43560 ft2 1 sq yard = 0,836 m 2
sq mile = 640 arces 1 sq mile - 2,59 km 2
1 arce = 0,4 ha
Th lch
H thong us ng ng
1 fr' nc li 39,1F = 62,425 lbs 1 inch* = 16,387 cm'
1 ft - 1728 in' 1 ft3 = 0,0283 m 3
= 7,480519 U Sgalons 1 ycf = 0,765 m 3
1 yard- = 2 7 ft' 1 u s liquid gallon = 3,785 litre
Khi lng & trng lng
Dn v IIS Tn %ng
1 lb = 1 6 ounces 1 ounce = 28,35 grams
1 ton = 2000 lbs 1 Ib = 0,4536 kg
Ib = 4,448 N
kip - 4,448 kN
i kip/i = 14,594 kN/m
1 lbs nc 39,1F = 27,681217 in 1

Ap sut
Dn v us
1 fcel nc ti 39,1F = 62,425 psf (pounds per square foot)
= 0,4335 pound per square inch
= 0,0295 atmospherc
1 pound nc ti n 1 in2 = 2,3094 ft nc

215
 1 m H20 = 9,81 kPa
1 Pa = 1 N/m 2
1 atm = 101,33kPa/m2
1 bar = 100kPa = 105 N/m 2
1 lb/in2 = 6,895 kPa (kN/m2)
1 lb/ft 2 = 47,88 Pa

Lu lng
n v S Tng ng
1 gpm = 1 gallons / pht 1 cfs = 0,028317 mVs
1 cfs = 1 ft3/s 1 USgalon/pht = 6,31.10' 5 mVs
= 60 ft Vpht 1 milli s galon /ngy = 2,629 mVph
= 448,83 .s gallon / pht
Nhit
Nhit ng c ca nc = 32 Fahrenheit
= 0 Celsius
Nhit bc hi ca nc =212 Fahrenheit
= 100 Celsius
0 Celsius = 32 Fahrenheit
1 Celsius = 1,8 Fahrenheit
1 Fahrenheit = 0,556 Celsius
Nhit tuyt i
K = 273 + c
R = 460 + F

Nhit lng
1 cal = 4,187 J (nhit lng cn thit a 1 gam nc tng 1K).
1 Btu = 252 cai (nhit lng cn thi i a 1 lb nc tng 1R).

216
 Ph lc 2

TNH THY L c DNG CHY

TRONG NG TRN BNG TH

Phng trnh c bn
Nm 1769, Chzy ngh mt phng trnh da trn thcnghim, cho phptnh vn tc
ca dng chy u (dng chy c biu phn b vn tc l ging nhau trong sut chiu di
dng chy).

Phng trnh Chzy nh sau;

V = < W

trong :
V - vn tc trung bnh ca dng chy;

Cc - h s Chzy;

Rh - bn knh thy lc;

J - dc thy lc (J = i trong trng hp chy u).

Tnh dng chy trong ng trn bng phng php d th

Phng php M anning

Trn c s l thuyt ca Manning, th sau y c thit lp phc v cho tnh ton thy
lc dng chy va y trong ng n.
V d 1: Mt ng ng b tng ct thp ng knh trong d = 600 mm (ng knh thc
610 mm) l 0,002 m/m. Xc nh kh nng ti lu lng khi ng ng chy y di p sut
10] ,3 kPa (p sut kh quyn), bit rng h s Mannmg ca b tng l n = 0,013.

Xc nh vn tc nc chy trong ng.

Bi gidi:

T th, v ng thng i qua im trn trc biu th dc c gi tr 0,002 v qua im

trn trc biu th h s nhm Manning c gi tr n = 0,013. ng thng ny s ct trc chun
gia thi ti mt im. V ng thng qua im ny v im trn trc biu th ng knh
dng ng d(m). Ko di ng thng ny s ct 2 trc biu th lu lng Q(mVs) v trc biu
th vn tc V (m/s).
Ta c: Q = 0,3 rrr/s
v: V = i m/s
Chng ta c th kim tra kt qu ny bng cch s dng trc tip phng trnh Manning.

217
 40
800 -_

30
600
500
20
400

300
ng knh
110 d(cm)
200 9
5,0
7
6
h 5
100 -=
4
80

60
: 3 96*1
50 84-1
r 2
40 72 h

"" 1.0
20 1-0P 8
90

0.C01
0C008
0.C006
0.C005
0.C004

0,C003

0,(002

0.C001
0,(0008
- 0,2 0,(0006
0,C0005
0.C0004
O.C0003

4-L r 0.C0002

.u lng
0.C0001
Q (m 3/s) O.COOOO
0,01 O.COOOO
0.C0000
ocooo*

6.0-3

th tnh clm> chy va dy tron { n theo M anning

Phng php Hazen-W illiam s

Trong khi , phng trnh theo Hazen-Williams c s dng rng ri nht tnng vng
hp nghin cu dng chy trong ng ng c p. Phng trnh nh sau:

218
 V = 0,8 4 9 C HWR (h,'fi-J'54

trong d: Cj|W h s nhm theo Hazen-Williams.

th sau y gii thiu cch gii theo Hazen-Williams tng ng vi trng hp
C(\v - 130 (trng hp gp ph bin trong thc t).

0.03 0,03 0.8

0,04 0,04 0.25
0,05 0,05 0.9
0,06 0,06
-
1.0 0.3
0,08 =- 0.08
0.1 - 0.1 u-
r
1.2 -
1.3-
0.2 0.2 ---- 0,4

(m /1 0 0 0 ) - =

70
7
! 8
1 .8
- 3
150 ~z ="150
200 9
200
- -
10
300 300
400 400

D i ii in <s' -7/c/v c p tron h h t ' 0 Hazen -W i/li(im s (C m = M ))

219
 V d 2: Xc nh p sut ti B ca ng ng A-B nm ngang, chy c p. ng ng c h
s Hazen-Williams l 130. Cho bit lu lng qua ng l 200 //s, dng chy i t A n B, p
sut ti A l 300 kPa. ng c chiu di L = 2565 m, ng knh trong d = 350 mm (ng knh
thc 355 mm).

Bi gii:

T gin Hazen-Williams (CHW = 130), ta c tn tht l 10 kPa cho chiu di ng ng

100 m. Chng ta c th vit:
2565
H to t X10 = 256,5kPa
100
Do p sut ti B s l:
PB = PA - H toI = 3 0 0 - 2 5 6 , 5 = 4 3 , 5kPa

V d 3: Tm p sut ti B ca ng ng trong v d trn, trong trng hp cao trnh B thp

hn A l 25 m.
Bi gii:

Ta c:
PB = PA - H lot + y z A = 3 0 0 - 2 5 6 , 5 + 9 ,8 1 x 2 5 = 288,75kPa

Ch : Phng trnh Bernoulli cho php biu th nguyn l bo ton nng lng gia 2 im
A v B. S sai bit nng lng (th nng + p nng + ng nng) gia 2 im A v B chnh l
tng cc tn tht khi cht lng di chuyn t A n B:

Pa Pb
Z A +
ZB + = H
y 2 g y 2g

trong :

Hw - tn tht (m);
z - tung tm mt ct (m);
pA/y - ct nc do p nng (m);
v?/ 2 g - ct nc do ng nng (m).
Ch trong phng trnh Bernoulli cc s hng thng biu th di dng ct nc (m hay
bng kPa). Phng trnh Bernoulli tng qut hn phng trnh ca Hazen-Williams. Phng
trnh theo Hazen-Willaiams s c s dng khi s hng ch sai bit ng nng gia A v B l
b, c th b qua.

Tnh dng chy khng y trong ng trn bng phng php th

Trong mng li thot nc ma v nc bn, thng thng ch thy lc trong ng l

chy khng p (chy khng y ng).
Chng ta c th xc dnh cc iu kin thy lc trong ng ng trn chy khng y nh
vo cc ng cong trong biu sau y.

220
 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2
1,0

0,9

0,8

0,7

0,6

0,5

0,4

0,3

0,2

0,1

0
0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0 1,1 1,2

A/Api Q/Qp; V/Vp

th tin h d n g c h y kh ig y tro n g n g tr n

V d 4: Trong mt ng ng trn ng knh d(m), chiu su nc chy l 2d/3 c lu

lng l Q 2/3 = 0,3 m7s. Khi ng chy vi lu lng nh nht Q min= 0,09 mVs, vn tc dng
chay l Vmin= 0,6 m/s. Cho h s nhm Manning l 0,015, tnh ng knh d, d dc s ca ng.

Bi gii:

Vi lu ing Q 2/3 ta c:
h/d = 2/3
T quan h ng cong trong th ta c:

Q 21I/3
= 0,79
Q,

0,3
l d: Q o - ^ = ------ = 0,38 mVs
p 0,79 0,79
(lu lng khi ng chy y)
v ta c: Q mJ Q = 0,09/0,38 = 0,24

vi Q min/Qp= 0,24, tra t d th ta c:

hmin/d = 0.34

v m m /v p = - 82

l : V = 0,6/0,82 - 0,73 m/s (vn tc khi chv dy ng)

Do: Q = 0,38 in 'h v vp = 0,73 m/s ta c :

221
 A = Qp/Vp = 0,52 m'

v: d= = 810m m

C th chn mt trong hai loi ng c ng knh 750mm hay 900 mm, l 2 loi ng c
sn xut trong th trng gn vi ng knh l thuyt. Gi s ta chn ng 750mm, t th lu
lng ln nht s l 0,38mVs, dc s l 0,0015 v vn tc l 0,86m/s. Vi cc yu t5 mi ny,
ta s tnh li cc iu kin ca dng chy hmin v vmin.
V d 5: Trong mt ng ng trn ng knh d(m), chiu su nc chy l 3d/4 c lu
lng l Q 3/4 = 0,14 mVs. Khi ng chy vi lu lng nh nht Qmin = 0,03 mVs, vn tc dng
chy l Vmm = 0,6m/s. Cho h s nhm Manning l 0,015, tnh ng knh d, dc s v lu
lng ln nht ca ng.

Bi gii:
T quan h ng cong trong th ta c:

Q<>.
^ = 0,915

Q(),75d _ 0,14 3.
t : Q, r _ - = _ = 0,153 m /s
0,915 0,915

(lu lng khi ng chy y)

v: Qmin/Qp = 0,0 3 /0 ,1 5 3 = 0 ,2 0

VI Qmin/Qp = 20 tra t th ta c: hmin/d = 0,31

vi h m ,n/d = 3 1 ta c : v m in /v p = ' 7 7

Ngoi ra vi vmin = 0,6 m/s ta c:

vp = vmin/0,77 = 0,60/0,77 = 0,78 m/s (vn tc khi chy y ng)

T : A = Qp/vp = 0,153/0,78 = 0,20 m 2

v: d= = 500 ram

Tng t nh v d trn, ta s chn ng ng c sn xut gn nht vi ng knh ng

ng l thuyt ny v s tnh li cc iu kin hmin v vmin.

222
 Ph lc 3

T N H TH Y Lc D N G C H Y U T R O N G N G T R N
BN G PH NG PHP TR A B N G

F (h /D ) = - ^
vi
Bng 3-1
D (m)
0,20 0,40 0,60 0,80
h/D F(h/D) co(h/D) F(h/D) (0(h/D) F(h/D) 0)(h/D) F(h/D) co(h/D)
0,99 0,0043 0,031 0,0274 0,125 0,0807 0,282 0,1738 0,502
0,98 0,0043 0.031 0,0274 0,125 0,0807 0,281 0,1739 0,500
0,97 00043 0,031 0,0273 0,125 0,0806 0,280 0,1735 0,498
0,96 0,0043 0,031 0,0272 0124 0,0802 0,279 0,1728 0,496
095 0,0043 0,031 0,0271 0,123 0,0798 0,277 0 1719 0,493
094 0,0042 0,031 0,0269 0,123 0,0793 0,276 0,1707 0,490
0,93 0,0042 0,030 0,0267 0,122 0,0786 0,274 0,1694 0,487
0.91 0,0041 0.030 0,0262 0,120 0,0772 0,270 0,1662 0.480
089 0,0040 0.030 0,0256 0,118 0,0755 0,266 0,1626 0.473
0.87 0.0039 0,029 0,0250 0 116 0,0736 0,261 0 1586 0,464
0,85 0,0038 0,028 0,0243 0 114 0.0716 0,256 0.1542 0,455
0.83 0,0037 0,028 0,0236 0,111 0.0694 0,251 0,1496 0,446
0.81 0,0036 0.027 0,0228 0,109 0,0672 0,245 0,1447 0,436
0,79 0,0035 0,027 0,0220 0,106 0.0648 0,240 0,13% 0,426
0,77 0,0033 0,026 0,0212 0,104 0,0624 0,234 0,1343 0.415
0,75 0,0032 0,025 0,0203 0.101 0,0599 0,227 0 1289 0,404
0,73 0X031 0,025 0,0194 0,098 0,0573 0,221 0,1234 0,393
0,71 0,0029 0,024 0,0186 0,095 0,0547 0.215 0,1179 0,382
0,69 0,0028 0.023 0,0177 0,092 0.0521 0,208 0,1123 0,370
0,67 0,0026 0.022 0,0168 0,089 0,0495 0.201 0,1067 0,358
065 0,0025 0.022 0,0159 0,086 0,0469 0 195 0,1010 0,346
0,63 0.0024 0 021 0,0150 0,083 0,0443 0 188 0,0954 0,334
0,61 0X022 0.020 0,0142 0.080 0,0417 0,181 0,0899 0,321
0,59 0X021 0,019 0,0133 0,077 0.0392 0*174 0,0844 0,309
0,57 0,0020 0 018 0,0124 0.074 0,0367 0,166 0,0789 0,296
0.55 0,0018 0,018 0,0116 0.071 0.0342 0,159 0,0736 0,283
0,53 0,C017 0 017 0,0108 0.068 0,0318 0,152 0,0684 0,271
0,51 0,0016 0,016 0,0100 0,064 0,0294 0.145 0.0633 0,258
0.49 0,0014 0.015 0,0092 0.061 0.0271 0,138 0,0583 0,245
0.47 0,0013 0.05 0,0084 0,058 0.0248 0,131 0,0535 0,232
0.45 0 0012 0,014 0,0077 0,055 0,0227 0.123 0,0489 0 219
0.43 0,0011 0.013 0,0070 0.052 0.0206 0,116 0,0444 0,207
0,41 0.0*010 0.012 0,0063 0.049 0,0186 0.109 0,0401 0,194
0 39 0,0009 0 011 0,0057 0.045 0,0167 0,102 0,0360 0,181
0,37 0,0008 0,011 0,0051 0.042 0 0 4 9 0.095 0,0321 0,169
0.35 0.0*007 0.010 0,0045 0,039 0.0132 0.088 0,0284 0,157
0.33 0,0006 0.009 0,0039 0.036 0.0116 0 081 0,0249 0 145
CUI 0,0005 0.008 0.0034 0.033 0.0101 0,075 0,0217 0,133

223
 Bng 3-1 (tt)
D(m)
1,00 1,20 1,50 1, 30 2,00
h/D F(h/D) co(h/D) F(h/D) co(h/D) F(h/D) C(h/D) F(h/D) 0)(h/D) F(h/D) 0)(h/D)
0,99 0,3151 0,784 0,5124 1,129 0,9290 1,764 1,5106 2,540 2,0007 3,136
0,98 0,3153 0,782 0,5127 1 126 0,9296 1759 1,5116 2,533 2,0019 3,127
0,97 0,3146 0,779 0,5116 1,121 0,9275 1/752 1,5083 2,522 1,9976 3,114
0,96 0,3133 0,775 0,5095 1,116 0,9238 1,743 1,5022 2,511 1,9895 3,099
0,95 0,3116 0,771 0,5067 1,110 0,9187 1,734 1,4939 2,497 1 9786 3,083
0,94 0,3095 0,766 0,5033 1 103 0,9125 1,724 1,4838 2,482 1,9652 3,065
0,93 0,3071 0,761 0,4993 1,096 0,9054 1*713 1,4722 2,466 1,9498 3,045
0,91 0,3014 0,750 0,4901 1,081 0,8887 1,688 1,4451 2,431 1,9138 3,002
0,89 0,2948 0,738 0,4794 1,063 0,8693 1,661 1,4136 2,392 1,8721 2,954
0,87 0,2875 0,725 0,4676 1,045 0,8477 1 632 1,3785 2,350 1,8257 2,902
0,85 0,2796 0,712 0,4547 1 025 0,8244 1,601 1,3405 2,305 1,7754 2,846
0,83 0,2712 0,697 0,4409 1,003 07995 1,568 1,3000 2,258 1.7217 2,787
0,81 0,2623 0,681 0,4265 0,981 0,7733 1,533 1,2574 2,208 1,6653 2,726
0,79 0,2530 0,665 0,4115 0,958 0,7460 1,497 1,2131 2,156 1 6067 2,662
0,77 0,2435 0,649 0,3960 0,934 0,7179 1,460 1,1674 2,103 1,5462 2,596
0,75 0,2337 0,632 0,3801 0,910 0,6891 1,422 1,1206 2,047 1.4842 2 527
0,73 0,2238 0,614 0,3639 0,885 0,6598 1,382 1,0730 1 990 1,4210 2,457
0,71 0,2137 0,596 0,3475 0.859 0,6301 1,342 1,0247 1,932 1,3571 2,385
0,69 0,2036 0,578 0,3310 0,832 0,6002 1 301 0,9760 1.873 1,2926 2,312
0,67 0,1934 0,559 0,3144 0,805 0,5701 1,259 0,9271 1,812 1,2278 2,237
0,65 0,1832 0,540 0,2979 0,778 0.5401 1,216 0,8782 1,751 1,1631 2,162
0,63 0,1730 0,521 0,2813 0,751 0,5101 1,173 0,8295 1,689 1,0986 2,085
0.61 0,1629 0,502 0.2649 0,723 0,4804 1,129 0,7812 1,626 1,0346 2,007
0,59 0,1530 0,482 0,2487 0,694 0,4510 1,085 0,7333 1,562 0,9712 1,929
0,57 0.1431 0,462 0,2327 0,666 0,4220 1,041 0,6862 1,498 0,9088 1,850
0,55 0,1335 0,443 0,2170 0,637 0,3935 0,996 0,6398 1,434 0,8474 1,770
0,53 0.1240 0,423 0,2016 0,609 0,3655 0,951 0,5944 1 369 0,7872 K691
0,51 0,1147 0,403 0,1866 0,580 0,3383 0,906 0,5501 1,305 0,7285 1,611
0,49 0,1057 0,383 0,1719 0 551 0,3117 0,861 0,5069 1,240 0,6714 1,531
0.47 0,0970 0.363 0,1577 0,522 0,2860 0,816 0,4651 1,175 0.6160 1,451
0,45 0,0886 0,343 0,1440 0,494 0,2611 0,771 0,4246 1,111 0,5624 1 371
0,43 0,0805 0,323 0,1308 0,465 0,2372 0,727 0,3857 1,046 0,5108 1,292
0.41 0,0727 0,303 0,1182 0,437 0,242 0,682 0,3484 0,982 0,4614 1,213
0,39 0,0652 0,284 0,1061 0,408 0,1923 0,638 0,3127 0.919 0,4142 1,134
0,37 0,0582 0.264 0,0946 0,380 0,1715 0,594 0,2788 0,856 0,3693 1,057
0,35 0,0515 0,245 0,0837 0,353 0,1517 0,551 0,2467 0,794 0,3268 0,980
0,33 0,0452 0,226 0,0734 0,325 0,133 0,509 0,2165 0.732 0,2867 0,904
0,31 0,0393 0,207 0,0638 0,299 0,1158 0,467 0,1882 0,672 0,2493 0,830
Ghi ch: D (m) - ng knh hnh trn. Q (mVs) - lu lng.
h (m) - chiu su nc. i - dc y ng.
n - h s nhm.

224
 TNH THY L c DNG CHY U t r o n g n g v u n g
B N G PH NG PH P TR A BN G

F(h /D ) - -
vi
Bng 3-2
B(m)
1.6 1,8 2.0 2,2 2,4
h/B F(h/B) C(h/B) F(h/B) m(h/B) F(h/B) t(h/B) F(h/B) tu(h/B) F(h/B) m(h/B)
] .00 1,684 2,56 2,305 2,88 3,053 4,00 3,936 4,84 4,964 5,76
0.99 1,663 2,53 2,277 2,85 3,015 3,96 3,888 4,79 4,903 5,70
0.98 1,642 2,51 2,249 2,82 2.978 3,92 3,840 4,74 4,843 5,64
0.97 1,622 2,48 2,220 2,79 2,941 3,88 3,792 4,69 4,782 5,59
0.96 1,601 2,46 2,192 2,76 2,904 3,84 3,744 4,65 4,722 5,53
0,95 1,581 2,43 2,164 2,74 2,867 3,80 3,696 4,60 4,661 5,47
0.94 1.561 2,41 2,136 2,71 2,829 3,76 3,648 4,55 4,601 5,41
0.93 1,540 2,38 2,108 2,68 2,792 3/72 3,600 4,50 4,541 5,36
0.92 1,520 2.36 2,080 2,65 2,755 3,68 3,553 4,45 4,481 5,30
0,01 1,499 2,33 2,053 2,62 2,718 3,64 3,505 4,40 4.420 5,24
0.90 1,479 2.30 2,025 2,59 2,682 3,60 3,457 4,36 4.360 5,18
0.89 1,459 2,28 1,997 2,56 2,645 3,56 3,410 4,31 4,300 5,13
0,88 1.438 2,25 1,969 2,53 2,608 3,52 3,362 4,26 4,241 5,07
0,87 1,418 2,23 1,941 2,51 2,571 3,48 3,315 4,21 4,181 5,01
0,86 1.398 2.20 1,914 2,48 2,534 3,44 3,268 4,16 4,121 4,95
0,85 1,378 2,18 1,886 2,45 2,498 3,40 3,220 4,11 4,061 4,90
0,84 1.357 2.15 1,858 2.42 2,461 3.36 3.173 4,07 4,002 4,84
0,83 1,337 2.12 1,831 2.39 2,425 3,32 3,126 4,02 3,943 4,78
0,82 1.317 2.10 1,803 2.36 2,388 3,28 3,079 3,97 3,883 4,72
0.81 1.297 2.07 1,776 2,33 2,352 3,24 3,032 3,92 3,824 4,67
0,80 1.277 2.05 1,748 2,30 2,315 3,20 2,985 3,87 3,765 4,61
0.79 1,257 2.02 1.721 2,28 2,279 3,16 2,938 3,82 3,706 4,55
0,7S 1.237 2.00 1,693 2,25 2,243 3,12 2.892 3,78 3,647 4,49
0,77 1.217 1.97 1,666 2,22 2,206 3,08 2,845 3,73 3,588 4,44
0.76 1.197 1.95 1.639 2,19 2,170 3,04 2,798 3,68 3,529 4,38
0,75 1.177 1.92 1,611 2,16 2,134 3,00 2,752 3,63 3,470 4,32

(hi ch: B(m) - cnh hnh vung. Q(m Vs) - u ng.

h (m) - chiu su nc. i - dc y ng.
n - h s nhm.

225
 Ph lc 4

H S PH N B LU LNG NC SIN H H O T
V X N G H I P C N G N G H I P (K,) T H E O G I T R O N G N G Y
(% lu lng ngy hoc ca)

Bng 4.1. Khu vc dn c

Gi ^h-max
ki 1.25 1,30 1,35 1,5 1,7 2,0 2,5
0-1 3,23 3,20 3,00 1,50 1,00 0,75 0,60
1-2 3,25 3,10 3,20 1,50 1,00 0,75 0.60
2-3 3,30 3,20 2,50 1,50 1,00 1,00 1,20
3-4 3,32 3,20 2,60 1,50 1,00 1,00 2,00
4-5 3.25 3,20 3,50 2,50 2,00 3,00 3,50
5-6 3,40 3,40 4,10 ->,50 3,00 5,50 3,50
6-7 3,85 3,80 4.50 4.50 5.00 5.50 4.50
7-8 4,45 4,60 4,90 5,50 6,50 5,50 10,20
8-9 5,20 5,40 4,90 6,50 6,25 3,50 8,80
9-10 5,05 5,00 5,60 6,25 5.50 3,50 6,50
10-11 4,85 4,80 4,90 6.25 4,50 6,00 4,10
11-12 4,60 4,60 4,70 6,25 5,50 8,50 4,10
12-13 4,60 4,50 4,40 5,00 7,00 8,50 3,50
13-14 4,55 4.40 4.10 5,00 7.00 6.00 3.50
14-15 4,75 4.60 4,10 5,50 5,50 5,00 2,00
15-16 4,70 4,60 4,40 6,00 4.50 5,00 6,20
16-17 4,65 4,40 4,30 6,00 5,00 3,50 10,40
17-18 4,35 4,30 4.10 5.50 6,50 3,50 9,40
18-19 4,40 4,40 4,50 5,00 6,50 6,00 7,30
19-20 4.30 4,50 4,50 4,50 5,00 6.00 3,80
20-21 4,30 4.50 4,50 4,00 4,50 6,00 1,70
21-22 4,20 4,80 4,80 3,00 3,00 3.00 1,10
22-23 3,75 3,80 4,60 2,00 2.00 2,00 0,80
23-24 3,70 3,70 3,30 1,25 1,25 1,00 0,70
Tng (%) 100,0 100,0 100,0 100,0 100,0 100,0 100,0

Ghi ch: Kh_max

226
 Bng 4.2. Khu vc khc

Bnh vin,
Tim tm git Nh n Tim n Trng hc,
Gi khch sn Nh tr
k tc x

L/
K = 2,5

II
K= 1 K = 3,0
0-1 0.00 0.00 0,20 4,50 0,00 0,15
1-2 0,00 0,00 0,20 4,50 0,00 0,15
2-3 0,00 0,00 0,20 3,80 0,00 0,15
3-4 0,00 0,00 0,20 3,60 0,00 0,15
4-5 0.00 0,00 0,50 3,60 0,00 0,15
5-6 0,00 0,00 0,50 3,70 0,00 0.25
6-7 0,00 12,00 3,00 4,00 5,00 0,30
7-8 0,00 3,00 5,00 4,00 3.00 23,50
8-9 6,25 1,00 8,00 3,00 15,00 6,80
9-10 6.25 18,00 10,00 4,90 5,50 4,60
10-11 6,25 18,00 6,00 4,60 3,40 3,60
11-12 6,25 2,00 10,00 4,00 6,40 2,00
12-13 6.25 1,00 10,00 4.00 15,00 3.00
13-14 6,25 2,50 6,00 4,80 8,10 6.25
14 15 6.25 2.50 5,00 4,80 5,60 6,25
15 16 6,25 4.00 8?50 4,00 4,00 3,00
16-17 6,25 4,00 5,50 4.50 4,00 4,00
17-18 6.25 6,00 5,00 4,00 15,00 3,60
18-19 6,25 3,00 5,00 4,90 3,00 3,30
19-20 6.25 6,00 5,00 4,20 2,00 5,00
20-21 6,25 7,00 2,00 4,10 2,00 2,60
21-22 6,25 10,00 0,70 4,10 3,00 18,60
22-23 6.25 0,00 3,00 4,30 0,00 1,60
23-24 6,25 0.00 0,50 4,10 0,00 1,00

T n g (%) 100,0 100,0 100,0 100,0 100,0 100,0

227
 Bng 4.3. X nghip cng nghip
(% tng lun lng trong mi ca 8 gi)

Gi Nc nh Nc nng
0-1 12.5 12,5
1-2 6,25 8,12
2-3 6.25 8.12
3-4 6,25 8,12
4-5 18,75 15,65
5-6 37,5 31.25
6-7 6,25 8,12
7-8 6,25 8,12
Tng (%) 00.0 100.0

Bng 4.4. Tiu chun nc ti, ra ng

Tiu chun chcnnt

Mc ch dng nc v cch ti, ra n v
ln ti (//rrr)
- Ra mt dng, qung trng hon thin bng c gii. ln ra 1,5-2,5
- Ti mt ng, qung trng d hon thin bng c gii. ln ti 0,4-0,3
- Ti va h, mt ng hon thin bng th cng. I ln ti 0,4-0,5
- Ti cy xanh h. ln ti 3-4
- Ti thm c, bn hoa. 1 ln ti 4-6
- Ti cy trong vn m cc loi. 1 ngy 6

Bng 4.5. Tiu chun nc dng cha chy v s m chv ng thi

trong cc khu dn c

Lu lng nc cho mt dm chy (//s)

Dn s S dm
Nh 2 tng tr xung VI Nh hn hp cc Nh 3 tng tr ln
(nghn chy ng
bc chu a tng khng ph khng phu thuc
ngi) thi
i'
\ I.II v l i r IV v V thuc bc chu la bc chu la
.

n 5 V 1 5 5 10 10
n 10 10 10 15 15
n ;
n 25 ) 2 10 10 15 15
n 50 2 15 20 20 25
n 100 2 20 20 30 35
n 200 3 20 30 40
n 300 3 40 55
n 400 3 50 70
n 500 3 60 80

228
 Ph lc 5

Hnh PL5.: Kt cu in hnh i nc dng tr

229
 Mt ng

Hnh PL5.2: Kt cu in hnh cng thu nc

230
 TI LIU THAM KHO

[ 1] Trng i hc Kin trc H Ni. G io trnh C p thot nc. NXB Xy dng.

[2] PGS. TS Hong Hu, KS. Phan nh Bi. M ng li thot nc. NXB Xy dng.

[3] Trn Hiu Nhu, Trn c H, Hi, ng Quc Dng, Nguyn Vn Tn. Cp
thot nc. NXB Khoa hoc v k thut.
V I

[4] Michcl BOLDUC. Drainqe e Aimentoi en eu ouhle des btiments. Les

ditions Le Griffon tTargile.

[57 Francois G. Brere. Disribion e colece des eaux. ditions de r cole

Polytcchnique de Montral.

[6 ] Les eaux ises CUS les aqqom m tions arbaries ou rurales. Le traitement.
Gom clla ct Guerree. Editions Eyrolles.

[7] TS. L nh Hng. H dn s dng Chng trnh E P A N E T . B mn KTTNN,

Khoa Kinh t xy dng, Trng i hc Bch khoa TP. H Ch Minh.

[8 ] E .w . STEEL and Tcrence J. M cHGEE. Mc. Graw-Hill. Waer Suppy and

Sexveraye. Book Company.

[0 ] Moder Se\ver Desin. American lron and Steel lnstitutc.

[ 10] Guerrin A. Dunoci. Trait de b ton arr. Paris (1968).

[ 1J Tran c H. x l nc thi sinh iot quy m nh v v. NXB K hoa hc v

k th u t.

[12J B Xy dng. Quy chun h thng cp thot nc roti nh v cm> trnh. NXB
Xy dng. H Ni 2000.

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 MC LC

Li ni u 3

C hng 1. Nhu cu dng nc v ngun nc

1.1. Gii thiu 5
1.2. S h thng cp nc 6
1.3. c lng dn s v thi gian khai thc cng trnh 7
1.4. Nhu cu dng nc 9
1.5. Ngun nc 15
Bi tp 21
C hng 2. C ng trnh thu nc
2.1. Gii thiu 23
2.2. Cng trnh thu nc ngm 23
2.3. Cng trnh thu nc mt 29
2.4. Tnh ton mt s hng mc cng trnh 34
Bi tp 36
C hng 3. T hit b v cng trnh ph bin trong h thn g cp nc
3.1. Gii thiu 37
3.2. Cc thit b v cng trnh ph bin 37
3.3. Thng s chnh trong h thng cp nc 44
Bi tp 45
C hng 4. H thng cp nc cho khu vc
4.1. Gii thiu 47
4.2. Yu cu i vi mng li 49
4.3. Cc bc thit k m ng li phn phi nc 50
4.4. Ni dung tnh ton mng li 51
4.5. Tnh thy lc mng li ng ng h 60
4.6. Tnh thy lc mng li vng bng phng php Hardy Cross 63
4.7. Tnh thy lc mng li vng bng phng php m a trn 71
4.8. Phn tch s lm vic h thng cp nc 76
4.9. Phn tch h thng cp nc vi m hnh Epanet 79
Bi tp 90
C hng 5. H thng cp nc bn trong
5.1. Gii thiu 100
5.2. Cu to h thng cp nc bn trong 100
5.3. B tr ng ng cp nc bn trong 107
5.4. Thit k h thng cp nc bn trong 108
5.5. H thng cp nc cha chy 118
Bi tp 124

232
Chiig 6. H thng thot nc bn trong
(6 . Gii thiu 125
(5.2. Phn loi h thng thot nc bn trong 125
(5.3. H thng thot nc sinh hot 125
(5.4. H thng thot nc ma 135
(5.5. Cng thot nc bn ngoi cng trnh 140
tBtiup 144
Chinig 7. Cng trnh x l nc thi sinh hoat quy m va v nh
'7.1. Gii thiu 145
7.2. Cc phng php x l nc thi 145
'7.3. X l nc thi bng phng php sinh hc k kh 148
7.4. B v sinh t hoi 149
Chinig 8. H thng thot nc cho khu vc
<8.1. Gii thiu 155
8.2. Ma v dng chy trong mi trng th 156
'8.3. Thy 168
8.4. Thit lp phng php thch hp 171
<8.5. Phng php cng gii hn 176
<8 .6 . Phn tch h thng thot nc ma vi m hnh SVVMM 181
8 .7. Bin php gim lu lng dng chy 187
iBi itp 193
Chinig 9. Lc tc dng ln ng ong chn trong t
(9 .1. Gii thiu 195
'9.2. Lc tc dng ln ng ng trong h mng hp 197
a) . L c tc dng ln ng ng trong h mng rng 200
9.4. Lc tc dng ln ng ng do ti trng ng tp trung 203
(9 .'i Lc tc dng ln ng ng do ti trng phn phi u v i xng 209
9/). Lc tng hp tc dng ln ng ng 209
9.7. Kch thc ti thiu mt ct ngang h mng 210
9.H. Lp lt y ng 212
9.0. Phng php lp t ln ng ng 212
Bui Hp 213
Phiu lic 1. Chuvn i h thng n v u s v SI 215
Phi l<c 2. Tnh thy lc dng chy trong ng trn bng th 217
Phi |(C 3. Tnh thy lc dng chy u trong ng trn bng phng php tra bng 223
Phiu ||(C 4. H s phn b lu lng nc sinh hoat v x nghip cng nghip (kj)
theo gi trong ngy 226
Phi Ihc 5. 229
Tii liui th a m k h o 231

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