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Chng 5. Nhng quy nh chung Bin son: GS.TS Ng Tr Ving

5.1 Phn loi cng trnh tho l

Trong u mi cng trnh thu li h cha nc, ngoi mt s cng trnh nh p

dng, cng trnh ly nc, cng trnh chuyn mn, cn phi lm cc cng trnh tho

nc l tha khng th cha c trong h, c lc t su m nhn thm vic tho

cn mt phn hay ton b h cha khi cn thit phi kim tra sa cha hoc tho bn ct

trong h. C cng trnh tho l th h mi lm vic c bnh thng v an ton.

C nhiu loi cng trnh tho l. Cn c vo cao trnh t, c th phn lm hai loi:

cng trnh tho l kiu x su ( l tho nc ) v cng trnh tho l trn mt (ng trn l).

1.Cng trnh tho l kiu x su c th t di y p trn nn (cng ngm), qua

thn p b tng (ng ng), c th t trong b (ng hm) khi iu kin a hnh a

cht cho php. Vi loi ny c th tho c nc trong h bt k mc nc no, thm

ch c th tho cn h cha. Loi ny khng nhng dng tho l m cn tu cao trnh, v

tr v mc ch s dng c th dn dng thi cng lc xy dng, tho bn ct lng ng

trong h cha hoc ly nc ti, pht in...

Do iu kin c th m c th kt hp nhiu mc ch khc nhau trong mt cng trnh

tho nc di su.

2.Cng trnh tho l trn mt thng t cao trnh tng i cao. Do cao trnh ca

ngng trn cao, nn n ch c th dng tho dung tch phng l ca h cha. Cng trnh

tho l trn mt bao gm cc kiu sau y.

- p trn

- ng trn dc

- ng trn ngang ( mng trn ngang)

- Xi phng tho l

- Ging tho l

- ng trn kiu go

Cng trnh tho l c th phn thnh:

- Cng trnh tho l trong thn p (p trn, xiphng tho l, cng ngm, ng

ng...) v cng trnh tho l ngoi thn p (ng trn dc, trn ngang, ging tho l,

ng hm...).

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- Cng trnh tho l ct nc cao v cng trnh tho l ct nc thp. Ct nc cao khi

60m. Phn loi ny ni ln c im, ch lm vic.

i vi tng loi u mi cng trnh thu li, cn phn tch k c im lm vic, iu

kin a hnh, a cht v thu vn, cc yu cu v thi cng, qun l khai thc chn loi

ng trn thch hp.

5.2 Nguyn tc b tr cng trnh tho l.

Do iu kin lm vic, c im a hnh v tnh cht cng trnh ngn nc m c th

c nhiu cch b tr v nhiu hnh thc cng trnh tho l.

C th b tr cng trnh tho l tch khi cng trnh ngn nc hay c th cng trnh

tho l ngoa lng sng chnh.

i vi p b tng, b tng ct thp, xy thng b tr cng trnh tho l ngay trn

thn p, nh h thng Bi thng, lng, Thch Nham, Tn Giang th p va lm

nhim v dng nc v trn nc.

i vi cc loi p khc(p vt liu a phng, p t, p ..) cng trnh tho l

thng c tch khi cng trnh dng nc.

ng trn tho l c th c ca van khng ch, cng c th khng c. Khi khng c

ca van th cao trnh ngng trn bng cao trnh mc nc dng bnh thng, ng trn

lm vic t ng. Khi c ca van khng ch th cao trnh ngng t thp hn mc nc

dng bnh thng, khi cn c d bo l, quan st nc trong h cha xc nh thi

im m ca van v iu chnh lu lng tho.

Khi cng tc d bo l tng i tt th ng trn c ca van khng ch c th kt

hp dung tch phng l vi dung tch hu ch, lc hiu ch s tng thm. Cho nn vi h

thng cng trnh tng i ln, dung tch phng l ln, khu vc b ngp thng lu rng

th thng dng loi ng trn c ca van khng ch. i vi h thng cng trnh nh, tn

tht ngp lt khng ln, thng lm ng trn khng c ca van.

Khi thit k cc h thng thu li, cn nghin cu nhiu phng n chn cch b tr,

hnh thc, kch thc cng trnh tho l cho hp l v mt k thut (tho l tt nht, an

ton, ch ng) v kinh t (vn u t ton b h thng t nht).

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5.3 L thit k v l kim tra i vi cng trnh tho

l.

Khi thit k cng trnh tho l cc u mi h cha nc cn bit c l thit k v

l kim tra, tng ng iu tit l ca h c mc nc thit k (MNTK) v mc nc kim

tra (MNKT). Cc tn sut lu lng ny c quyt nh theo cp cng trnh.

I. Cc tiu chun ca Vit Nam

1. TCXDVN 285-2002 (Cng trnh thu li cc quy nh ch yu v thit k).

Tn sut lu lng v mc nc ln nht tnh ton thit k v kim tra nng lc x

nc, n nh kt cu, nn mng ca cc cng trnh thu li trn sng v ven b, cc cng

trnh trn tuyn chu p, cc cng trnh trong h thng ti tiu khi thng ngun cha c

cng trnh iu tit dng chy c xc nh nh bng 5-1.

Bng 5 - 1. Tn sut lu lng v mc nc ln nht thit k v kim tra cng trnh thu.

Cp cng trnh Loi cng trnh thu

I II III IV V

1. Cm u mi cc loi (tr cng trnh

u mi vng triu); h thng dn thot

nc v cc cng trnh lin quan khng

thuc h thng ti tiu nng nghip; cng

trnh dn tho nc qua sng sui ca h

thng ti tiu nng nghip

-Tn sut thit k (%) 0,10,2* 0,5 1 1,5 2

-Tng ng vi chu k lp li (nm) 1000500 200 100 67 50

-Tn sut kim tra (%) 0,020,04* 0,1 0,2 0,5

-Tng ng vi chu k lp li (nm) 50002500 1000 500 200

2. Cng trnh u mi vng triu; cng

trnh v h thng thot nc lin quan trong h

thng ti tiu nng nghip (tr cng trnh dn

tho nc qua sng sui ni 1)

- Tn sut thit k (%)

- Tng ng vi chu k lp li (nm)

0,2

500

0,5

200

1

100

1,5

67

2

50

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Ch thch * Tn sut nh p dng cho cng trnh c dng l phc tp thng xut hin

min ni, trung du. Tn sut ln p dng cho cc cng trnh c dng l n nh thng

xut hin vng ng bng.

2. Tiu chun TCXD 250 2001 p dng cho d n thu in Sn La

Cng trnh thu in Sn La l cng trnh c bit nn c mt tiu chun ring. Cc

cng trnh ch yu c ly tn sut l thit k p = 0,05% c Q0,05%, kim tra ng vi p =

0,01% cng thm lng DQ = 20% Q0,01%.

Qktra = Q0,01% + DQ0,01% .

L ln nht kh nng (PMF) c tnh ton i chng.

II. Tiu chun ca cc nc khc

1. Tiu chun ca Lin bang Nga

Quy phm ny tng ng vi quy phm Vit Nam, nhng c thm iu kin khi cng

trnh c s c gy nn hu qu nghim trng th cng trnh c tnh ton kim tra vi lu

lng ln nht tng ng tn sut p = 0,01% cng thm lu lng hiu chnh DQ nhng

khng vt qu 20%, trong quy phm khng cp n tnh ton l ln nht kh nng

(PMF).

2. Tiu chun ca Trung Quc

Theo tiu chun ca Trung Quc GB50201 94 c hiu lc t 1995, cng trnh thu

cng thuc u mi thu li thu in, tu theo n thuc nhm u mi no, tc dng v

tm quan trng ca n, c th chia thnh 5 cp. Nhm u mi, tu theo quy m, hiu qu

v tnh cht ca cng trnh trong nn kinh t quc dn , chia thnh 5 nhm (bng 5 - 2).

Bng 5 - 2. Cp cng trnh

Cp cng trnh lu di Nhm u mi

Cng trnh ch yu Cng trnh th yu

Cp cng trnh tm

thi

I I III IV

II II III IV

III III IV V

IV IV V V

V V V

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Tiu chun phng l ca cng trnh thu cng, tu theo cp c xc nh ph thuc

vo v tr cng trnh ( vng ni i hay ng bng, ven bin) v vt liu xy dng cng trnh

nh bng 5 - 3.

Bng 5 - 3. Tn sut l thit k v kim tra.

Tiu chun ( thi gian lp li/ tn sut %)

Vng i ni Vng ng bng, ven bin

Kim tra Cp cng trnh Thit k

p b tng

xy

p t v

Thit k Kim tra

I 1000500 50002000 PMF hoc

10005000 300100 20001000

(0,10,2) (0,02 0,05) (0,01 0,02) (0,3 0,1) (0,050,1)

II 500100 20001000 5000200 100 50 1000300

(0,21,0) (0,050,1) (0,020,05) (1,0 2,0) (0,10,3)

III 10050 1000500 20001000 50 20 300100

(1,0-2,0) (0,10,2) (0,010,1) (2,05,0) (0,31,0)

IV 5030 500200 1000300 2010 10050

(2,03,0) (0,2 0,5) (0,10,3) (1 10) (1,02,0)

V 30 20 200 100 300 200 10 5020

(3,05,0) (0,5 1,0) (0,3 0,5) (10) (2,05,0)

p t khi s c xy ra gy tc hi ln i vi h lu, tiu chun kim tra phng

l ca cng trnh cp I cn s dng l PMF hoc l 10.000 nm (P = 0,01%); cc cng trnh

cp II IV tiu chun kim tra phng l c th nng ln 1 cp.

- p b tng v p xy nu l trn nh cng gy ra nhng tn tht nghim trng,

tiu chun kim tra phng l cho cng trnh cp I, nu c lun c y v chuyn mn c

th s dng l PMF hoc l 10.000 nm ( p =0,01% ). Nu theo phng php kh tng thu

vn tnh c l PMF cho kt qu hp l th dng tr s PMF ; nu theo phng php phn

tch tn sut, tnh c l 10.000 nm v nu l PMF v l 10.000 nm vi tin cy tng

ng nhau th dng gi tr trung bnh ca hai s hoc dng gi tr ln hn.

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3. Tiu chun ca Hi ng p ln th gii (ICOLD)

H cha c chia thnh 4 nhm A,B,C, D.

Nhm A. H cha khi b s c gy tn tht v ngi v tn tht v ti sn rt nghim

trng cho h lu :

L thit k = l PMF

Nhm B . H cha khi b s c c th gy tn tht v ngi v tn tht ti sn nghim

trng cho h du :

L thit k = 0,5 l PMF hoc l tn sut 0, 01%

Nhm C. H cha nc khi b s c gy tn tht khng ng k v ngi v ti sn

cho h du:

L thit k = 0,3 l PMF hoc l tn sut 0,1%

Nhm D. H cha nc khi b s c khng gy tn tht v ngi v tn tht ti sn cho

h du.

L thit k = 0,2 l PMF hoc tn sut 150 nm 1 ln ( P = 0,66%).

4. Tiu chun ca M

Cc cng trnh tho l ca cc h cha u c tnh tho c l PMF. L PMF

c tnh t ma cc hn PMF xy ra ti lu vc trong vng 72gi.