22TCN 262-2000-Quy Trinh Khao Sat Thiet Ke Nen Duong o to Dap Tren Dat Yeu

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MC LC Trang

I. Cc quy nh chung (nh ngha, ngun gc, phn loi t yu) ......................... 2 II. Cc yu cu v tiu chun thit k ........................................................................... 4 II.1 Cc yu cu v n nh ...................................................................................... 4 II.2 Cc yu cu v tiu chun tnh ton ln ............................................................ 5 II.3 Cc yu cu v thit k v b tr h thng quan trc trong qu trnh thi cng nn

p trn t yu . ................................................................................................. 7 II.4 Xc nh cc ti trng tnh ton ........................................................................... 9 III. Cc yu cu v kho st phc v vic thit k nn ng qua vng t yu ... 11 III.1 Cc yu cu chung ............................................................................................ 11 III.2 Cc quy nh v kho st a hnh .................................................................... 12 III.3 Cc quy nh v kho st v th nghim a k thut ........................................ 12 IV. Cc gii php thit k nn p trn t yu ......................................................... 15 IV.1 Cc yu cu chung v cu to nn p trn t yu ........................................ 15 IV.2 p trc tip trn t yu ................................................................................ 16 IV.3 o mt phn hoc hoc o ton b t yu ................................................ 18 IV.4 Gii php p b phn p ................................................................................ 20 IV.5 Tng ct m ..................................................................................................... 20 IV.6 Cc bin php thot nc c kt theo phng thng ng (s dng ging ct

hoc bc thm) ................................................................................................ 21 IV.7 S dng vi a k thut tng cng n nh nn p trn t yu .......................................................................................... 23 IV.8 Cc nguyn tc la chn gii php thit k .................................................... 26 V. Tnh ton n nh nn p trn t yu ................................................................ 27 V.1 Phng php tnh ton .................................................................................... 27 V.2 Nhng ch khi vn dng phng php tnh ton phn mnh c in v Bishop .................................................................................. 29 V.3 Cc trng hp tnh ton n nh v thng s tnh ton tng ng ................ 31 VI. Tnh ton ln nn p trn t yu ........................................................................ 33 VI.1 Tnh ln c kt Sc ........................................................................................ 33 VI.2 D tnh ln tng cng S v ln tc thi Si .............................................. 35 VI.3 D tnh ln c kt theo thi gian trong trng hp thot nc mt chiu theo phng thng ng ................................................................................ 36 VI.4 D tnh ln c kt theo thi gian trong trng hp thot nc 2 chiu (c s dng ging ct hoc bc thm) ...... 38 VI.5 Nhng ch khi d tnh ln ............................................................................ 41 Ph lc 1 : Xc nh tr s p lc tin c kt v cc ch s nn ln ca t yu ............. 43 Ph lc 2 : Tnh ton ng sut nn (p lc) thng ng zi do ti trng nn p hoc ti trng phn p gy ra trong t theo ton Ostezberg .......................... 48

www.vncold.vn www.vncold.vn www.vncold.vn_______________________________________________________________

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(Ban hnh theo Quyt nh s 1398 /Q - BGTVT ngy 1 / 6 / 2000 ca B trng

B GTVT)

I. CC QUY NH CHUNG I.1 Quy trnh ny c p dng khi tin hnh kho st thit k nn ng t p

trn t yu, bao gm c nn p ng cao tc v nn p ng t cc cp. Ngoi ra cng c th c tham kho p dng i vi nn p ca sn bay trn vng t yu.

Trong quy trnh ny quy nh r cc yu cu cn phi thc hin i vi vic kho st a hnh, iu tra v th nghim a k thut trn vng t yu c tuyn ng i qua; ng thi cng quy nh r cc yu cu v tiu chun thit k cn phi m bo t c khi thit k nn p trn t yu cng vi cc yu cu cu to v cc phng php tnh ton tng ng, cng nh vic la chn gii php v phm vi p dng ca mi gii php thng dng xy dng nn p trn t yu (khng cp n cc gii php c bit nh x l t yu bng in thm, bng cc vi, cc xi mng, cc b tng, cc ct )

I.2 Khi tin hnh kho st thit k nn ng qua vng t yu, ngoi vic phi

tun theo cc quy nh quy trnh ny cn cn phi tun theo cc tiu chun v quy nh chung v thit k nn ng trong cc TCVN 4054-1998 ng t - Yu cu thit k, TCVN 5729-1997 ng t cao tc - Yu cu thit k.

Cc quy nh trong tiu chun ny v gii php s dng bc thm v vi a k thut v c bn l khng khc vi cc quy nh Quy trnh thit k x l t yu bng bc thm trong xy dng nn ng - 22TCN 244-98 v Tiu chun thit k thi cng v nghim thu vi a k thut trong xy dng nn p trn t yu - 22TCN 248-98. Trong trng hp c nhng yu cu khc nhau v kho st thit k nn p trn t yu th nn thng nht p dng cc quy nh tiu chun ny.

I.3 Trong quy trnh ny, t yu c xc nh iu I.4 l ch cc loi t c sc

chng ct nh v tnh bin dng (p ln) ln, do vy nn p trn t yu, nu khng c cc bin php x l thch hp thng d b mt n nh ton khi

CNG HA X HI CH NGHA VIT NAM

B GIAO THNG VN TI

QUY TRNH KHO ST THIT K NN NG T

P TRN T YU

TIU CHUN THIT K

22TCN 262- 2000

C hiu lc t 15/ 6 / 2000


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hoc ln nhiu, ln ko di nh hng n mt ng, cng trnh trn ng v c m cu ln cn. Chnh v th m mc tiu ca cc quy nh trong quy trnh ny l nhm m bo cho kch thc v cc yu t hnh hc ca nn ng trn vng t yu (k c cao nn) lun duy tr c ng thit k trong qu trnh thi cng nn p cng nh trong qu trnh khai thc ng sau .

I.4 Ty theo nguyn nhn hnh thnh, t yu c th c ngun gc khong vt hoc

ngun gc hu c. I.4.1 Loi c ngun gc khong vt thng l st hoc st trm tch trong nc

ven bin, vng vnh, m h, ng bng tam gic chu; loi ny c th ln hu c trong qu trnh trm tch (hm lng hu c c th ti 10 - 12 %) nn c th c mu nu en, xm en, c mi. i vi loi ny, c xc nh l t yu nu trng thi t nhin, m ca chng gn bng hoc cao hn gii hn chy, h s rng ln (st e 1,5 , st e 1), lc dnh C theo kt qu ct nhanh khng thot nc t 0,15 daN/cm2 tr xung, gc ni ma st t 0 - 10 hoc lc dnh t kt qu th nghim ct cnh hin trng Cu 0,35 daN/cm2. Ngoi ra cc vng thung lng cn c th hnh thnh t yu di dng bn ct, bn ct mn (h s rng e > 1,0, bo ha G > 0,8).

I.4.2 Loi c ngun gc hu c thng hnh thnh t m ly, ni nc tch ng

thng xuyn, mc nc ngm cao, ti y cc loi thc vt pht trin, thi ra v phn hy, to ra cc vt lng hu c ln vi cc trm tch khong vt. Loi ny thng gi l t m ly than bn, hm lng hu c chim ti 20 - 80%, thng c mu en hay nu sm, cu trc khng mn (v ln cc tn d thc vt). i vi loi ny c xc nh l t yu nu h s rng v cc c trng sc chng ct ca chng cng t cc tr s nh ni I.4.1.

t yu m ly than bn cn c phn theo t l lng hu c c trong

chng: Lng hu c c t 20 - 30% : t nhim than bn Lng hu c c t 30 - 60% : t than bn Lng hu c trn 60% : Than bn I.5 Phn loi trng thi t nhin ca t yu nh gi s b v tnh cht cng trnh ca t yu, t bc u xem xt

cc gii php thit k nn ng tng ng, t yu c phn loi theo trng thi t nhin ca chng nh di y:


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I.5.1 t yu loi st hoc st c phn loi theo st B:

BW W

W Wd

nh d

= (I.1)

Trong : W, Wd, Wnh l m trng thi t nhin, gii hn do v gii hn nho ca t yu.

Nu B > 1 th c gi l bn st (t yu trng thi chy) Nu 0,75 < B 1 l t yu do chy. I.5.2 V trng thi t nhin, t m ly than bn c phn thnh 3 loi I, II, III:

Loi I: Loi c st n nh; thuc loi ny nu vch t o thng ng su 1m trong chng vn duy tr c n nh trong 1-2 ngy;

Loi II: Loi c st khng n nh; loi ny khng t tiu chun loi I nhng t than bn cha trng thi chy;

Loi III: t than bn trng thi chy. I.6 Khi tuyn ng i qua vng t yu do chy, bn st ni iu I.4.1, I.5.1 ;

vng c bn ct, bn ct mn ni iu I.4.1; vng m ly than bn ni iu I.5.2 th cn phi c bin php kho st thit k tng ng (c cp cc phn sau ca quy trnh ny) m bo nn ng n nh v cng v bin dng, k c trng hp pha trn cc lp t yu c tn ti mt lp t khng yu.

Ring vi cc cng trnh ng cao tc v cc cng trnh c ngha c bit khc, nu chiu cao nn p cao t 8 - 10 m tr ln th cc loi t st v st do mm (c st B trong phm vi t 0,5 - 0,75) cng nn p dng cc bin php kho st thit k nh vi t yu.

II. CC YU CU V TIU CHUN THIT K NN P TRN T YU II.1 Cc yu cu v n nh Nn p trn t yu phi m bo n nh, khng b ph hoi do trt tri

trong qu trnh thi cng p (p phn nn theo thit k hoc p cao hn cao thit k gia ti trc) v trong sut qu trnh a vo khai thc s dng sau . m bo yu cu ny phi m bo c ng thi cc tiu chun c th di y:


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II.1.1 Mc n nh d bo theo kt qu tnh ton i vi mi t p (p nn v p gia ti trc) v i vi nn p theo thit k (c xt n ti trng xe c dng xe ti a trn nn) phi bng hoc ln hn mc n nh ti thiu quy nh di y :

Khi p dng phng php nghim ton n nh theo cch phn mnh c in vi mt trt trn khot xung vng t yu v cc thng s tnh ton c xc nh theo mc V.3 th h s n nh nh nht Kmin = 1,20 (ring trng hp dng kt qa th nghim ct nhanh khng thot nc trong phng th nghim nghim ton th Kmin = 1,10 ;

Khi p dng phng php Bishhop nghim ton n nh th h s n nh nh nht Kmin = 1,40 ;

II.1.2 S liu quan trc ln theo chiu thng ng v quan trc di ng ngang ca

vng t yu hai bn nn p trong qu trnh p nn v p gia ti trc phi khng c vt qu tr s quy nh di y:

Tc ln y nn p ti trc tim ca nn ng khng c vt qu

10mm/ngy m.

Tc di ng ngang ca cc cc quan trc ng hai bn nn p khng c vt qu 5mm/ngy m.

Cch b tr quan trc ln v quan trc di ng ngang c nu r iu II.3.1 v II.3.3.

II.2 Cc yu cu v tiu chun tnh ton ln II.2.1 Phi tnh ton d bo c ln tng cng S k t khi bt u p nn cho

n khi ln ht hon ton p phng ln (p rng thm b rng nn ng so vi b rng thit k). B rng phi p thm mi bn ca nn ng (bm) c xc nh theo cng thc:

bm = S . m (II.1)

Trong : 1/m l dc ta luy nn p thit k S c tnh theo phng php quy nh VI.2 v VI.3 vi 2 thnh phn Si (ln

tc thi do bin dng ngang khng thot nc, xt n kh nng n hng ca t yu di nn p) v ln c kt Sc (do nc l rng thot ra v t yu b nn cht di ti trng p).


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II.2.2 Khi tnh ton ln tng cng ni trn th ti trng gy ln phi xt n ch gm ti trng nn p thit k bao gm c phn p phn p (nu c), khng bao gm phn p gia ti trc (nu c) v khng xt n ti trng xe c.

II.2.3 Sau khi hon thnh cng trnh nn mt ng xy dng trn vng t yu, phn

ln c kt cn li S ti trc tim ca nn ng c cho php nh bng II.1 di y:

Bng II.1- Phn ln c kt cho php cn li S ti trc tim ca nn ng sau khi hon thnh cng trnh

V tr on nn p trn t yu Loi cp ng

Gn m cu Ch c cng

hoc ng dn sinh chui di

Cc on nn p thng

thng 1. ng cao tc v ng cp 80 2. ng cp 60 tr xung c tng mt cp cao A1

10cm

20cm

20cm

30cm

30cm

40cm

Ghi ch bng II.1:

Phn ln c kt cn li S l phn ln c kt cha ht sau khi lm xong o ng ca on nn p trn t yu. Tr s S c xc nh theo cng thc (VI.9) ty thuc c kt U t c vo thi im lm xong o ng;

Chiu di on nn ng gn m cu c xc nh bng 3 ln chiu di mng m cu lin k. Chiu di on nn p c cng hoc c li chui qua ng di c xc nh bng 3-5 ln b rng mng cng hoc b rng li i qua ng;

Nu phn ln c kt cn li S vt qu cc tr s cho php bng II.1 th mi cn phi c cc bin php x l gim S cp cc mc IV.3, IV.5, IV.6. Nu tha mn cc tr s cho php bng II.1 th khng cn p dng cc bin php tng nhanh c kt;

II.2.4 i vi cc ng cp 20; 40 v ng ch s dng kt cu o ng mm cp

cao A2 tr xung th khng cn cp n vn ln c kt cn li khi thit k.

II.2.5 Yu cu v quan trc d bo ln


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Ngoi vic tnh ton d bo cc thnh phn ln ni iu II.2.1 lm c s cho vic xut cc gii php x l v cu to nn p trn t yu, cn phi da vo kt qu quan trc ln theo cc quy nh iu II.3.1 v II.3.2 so snh, i chiu v hiu chnh li kt qu d bo theo tnh ton kim tra ln v tc ln cho php quy nh cc iu II.2.3 v II.1.2, cng nh xc nh khi lng t hoc ct b ln thc t s c thanh ton sau khi cng trnh hon thnh.

Yu cu c th ca vic quan trc ln l:

Xc nh c khi lng t hoc ct p ln chm vo trong t yu (so vi mt t t nhin trc khi p).

V c biu quan h gia ln tng cng S vi thi gian (c ghi r thi gian tng t p nn v p gia ti). Da vo biu ny x l tch ring cc phn ln tc thi (l cc phn ln tng t ngt trong thi gian cc t p) v lp ra biu ln c kt St theo thi gian t k t khi kt thc qu trnh p nn v p gia ti trc;

Miu t quan h St = f (t) thc t quan trc c mt cch gn ng nht bng mt hm s ton hc dng St = Sc (1 e-t ) vi v l cc h s hi quy t s liu quan trc ln, lm c s d bo phn ln c kt cn li ni iu II.2.3.

II.3 Cc yu cu v thit k v b tr h thng quan trc trong qu trnh thi

cng nn p trn t yu II.3.1 i vi cng trnh xy dng nn p trn t yu, trong mi trng hp, d p

dng gii php x l no, d kho st, tnh ton k vn phi thit k h thng quan trc ln, ch tr trng hp p dng gii php o vt ht t yu, h y nn p n tn lp t khng yu. H thng ny phi c b tr theo cc quy nh sau:

Mi phn on nn p trn t yu c thit k tnh ton khc nhau, hoc mi phn on thi cng ring r phi c b tr quan trc ln ring (khc nhau v chiu cao p, v loi t yu vi cc ch tiu khc nhau r rt v vi chiu dy lp t yu khc nhau r rt);

Mi on ni trn, nu di 100 m th cn b tr 3 bn o ln trn cng mt mt ct ngang chnh gia phn on (1 bn ti tim nn ng v 2 bn v tr mp vai nn ng) nu di > 100 m th ti thiu phi b tr 2 mt ct quan trc ln nh trn v c thm 100 m li b tr thm 1 mt ct (b tr ti nhng ni c kh nng ln nhiu);


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H thng mc cao dng cho quan trc ln phi c b tr ni khng ln v phi c c nh chc chn;

Bn o ln c kch thc ti thiu l 50 50 cm c b dy cng ( 3 cm) gn vi cn o tht chc chn, cn o phi bng thp c ng knh nh hn ng knh ng vch chn t p (khng cho t p tip xc vi cn o): ng vch khng c gn vi bn o ln. Nn dng cn o c ng knh 4 cm. Cn o v ng vch nn lm tng on 50 ~ 100 cm tin ni theo chiu cao p.

Bn o ln c t cao bt u p nn ng: vt, o t yu n

u t bn o ln ; nu c tng m ct th t trn mt tng m ct, nu c lp v cng trn t yu th t trn mt t v cng t nhin, nu c ri vi a k thut th t trn mt vi a k thut. Trng hp phi t bn o trn mt nn t yu th phi o t yu su 30 cm trong phm vi din tch bn o ln thay bng ct ri mi t bn o ln ln.

Bn o ln phi c bo v chc chn, lu di t nht cho dn khi bn giao cng trnh.

II.3.2 Phi quy nh ch quan trc ln ngay trong n thit k :

o cao lc t bn ln v o ln mi ngy mt ln trong qu trnh p nn v p gia ti trc, nu p lm nhiu t th mi t u phi quan trc hng ngy;

Khi ngng p v trong 2 thng sau khi p phi quan trc hng tun; tip quan trc hng thng cho n ht thi gian bo hnh v bn giao cho pha qun l khai thc ng c h thng quan trc ( h tip tc quan trc nu thy cn thit);

Mc chnh xc yu cu phi n mm. II.3.3 Khi p dng cc gii php x l nn p trn t yu c i hi phi khng ch

tc p th cn phi thit k h thng quan trc di ng ngang theo di mc n nh trong qu trnh p nh ni iu II.1.2, h thng ny c b tr nh sau:

Trn mi mt ct b tr quan trc ln, pha ngoi cch chn ta luy 1 m b tr mt dy cc quan trc di ng ngang thng gc vi tim ng t 3 - 4 cc vi c ly t 5 - 10 m, dng cc hoc cc b tng tit din 10 10 cm ng ngp vi t yu t nht l 1,2 m v cao trn mt t yu t nht l 0,5 m (nu ln nhiu v nu c ngp nc th cng phi cao); trn nh cc c


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cm cht nh du im quan trc. Yu cu cc phi cm hoc chn chc trong t yu.

Trong qu trnh p nn v p gia ti trc (nu c) hng ngy phi o c s di chuyn theo hng ngang (hng thng gc vi tim nn ng) ca cht nh du trn nh tt c cc cc ni trn bng my kinh v chnh xc theo phng php tam gic c vi hai nh tam gic nh v c nh nm ngoi phm vi nh hng ca ti trng p. ng thi phi o cao nh cc theo di b mt t yu c b y tri ln khng. Sau khi p xong, hng tun phi tip tc quan trc cho n khi thy r nn ng n nh. chnh xc ca my kinh v phi bo m sai s v o c ly l 5 mm, v o gc l 2,5 .

II.3.4 i vi cc on nn p trn t yu c quy m ln v quan trng hoc c

iu kin a cht phc tp nh on c chiu cao p ln, hoc phn b cc lp a cht khng ng nht (c lp v cng...) khin cho thc t c nhng iu kin khc nhiu vi cc iu kin dng trong tnh ton n nh v ln th nn b tr thm h thng quan trc p lc l rng (cng vi cc im quan trc mc nc ngm) v cc thit b o ln su khc nhau (thit b kiu gung xon...). Nh c h thng cc thit b quan trc ny, cng d dng thc hin c cc yu cu ni iu II.2.5 v nh to iu kin thun li cho vic rt ngn thi gian thi cng cng trnh. Trong trng hp ny, vic thit k b tr lp t cc h thng thit b quan trc ni trn c xem l mt ni dung thit k c bit do cc k s chuyn ngnh thc hin v phi c ch qun u t xt duyt ring.

II.4 Xc nh cc ti trng tnh ton II.4.1 Cc ti trng tnh ton dng khi kim tra n nh v d bo ln ca nn p

trn t yu gm ti trng p nn v p gia ti trc, ti trng xe c, ti trng ng t nh ni iu II.1.1 v II.2.2. V vic tnh ton u a v bi ton phng, do vy cc ti trng tnh ton u c xc nh tng ng vi phm vi phn b trn 1 m di nn ng.

II.4.2 Ti trng p nn v p gia ti trc c xc nh ng theo hnh dng p

trn thc t (hnh thang vi mi dc c dc thit k, c th c thm phn p hoc trong trng hp o bt t yu trc khi p th c thm hai di ti trng phn p v hn hai bn).

II.4.3 Ti trng xe c c xem l ti trng ca s xe nng ti a cng mt lc c th

kn khp b rng nn ng (hnh II.1) phn b trn 1 m chiu di ng;


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ti trng ny c quy i tng ng thnh mt lp t p c chiu cao l hx xc nh theo cng thc sau:

hn G

Bx= .

. . l ; (II.1) Trong :

G l trng lng mt xe (chn xe nng nht), Tn

n l s xe ti a c th xp c trn phm vi b rng nn ng (nh s xp xe hnh II.1)

l dung trng ca t p nn ng, T/m3 l l phm vi phn b ti trng xe theo hng dc, m (nh hnh II.1)

C th ly l = 4,2 m vi xe G =13 tn, ly l = 6,6 m khi xe c G =30 tn, ly l =

4,5 m vi xe xch c G = 80 tn.

Hnh II.1- S xp xe xc nh ti trng xe c tc dng ln t yu

B l b rng phn b ngang ca cc xe (mt) c xc nh nh s hnh

II.1 theo cng thc sau:

B = n.b + (n 1)d + 2 ; (II.2) Trong thng ly b = 1,8 m vi cc loi t, b = 2,7 m vi xe xch; d l

khong cch ngang ti thiu gia cc xe (thng ly d = 1,3 m); e l b rng lp i hoc vt bnh xch (thng ly e = 0,5 - 0,8m); cn n c chn ti a nhng phi bo m B tnh c theo (II.2) vn nh hn b rng nn ng. Nh vy khi tnh ton c xt n ti trng xe c th ti trng p xem nh c cao thm mt tr s hx.


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II.4.4 Ti trng ng t c k n khi tnh ton kim tra mc n nh ca nn p trn t yu chnh l lc qun tnh do ng t ca bn thn khi trt, lc ny xem nh t l thun vi trng lng bn thn khi trt:

Wi = Kc . Qi (II.3)

Trong :

Wi l lc ng t tc dng trn mt mnh trt i (hoc khi trt i) (Tn), Wi c im t l trng tm mnh (hoc khi trt) v c phng nm ngang t pha trong nn ng ra pha ngoi mi ta luy nn p;

Qi l trng lng ca mnh trt i (hoc khi trt i), Tn;

Kc l h s t l c ly ty thuc cp ng t nh bng II.2. Bng II.2 - H s t l Kc

Cp ng t 7 8 9 10 11 12

H s K c 0,025 0,05 0,1 0,25 0,5 0,5

Phn vng ng t ca nc ta c th tham kho Quy chun Xy dng Vit

Nam v ch nhng vng c th c ng t t cp 7 tr ln th khi tnh ton mi phi xt n lc ng t. Ngoi ra cn c th tham kho cch tnh lc ng t Tiu chun ngnh 22TCN 221-95.

III. CC YU CU V KHO ST PHC V VIC THIT K NN

NG QUA VNG T YU III.1 Cc yu cu chung III.1.1 Phi iu tra xc nh c phm vi phn b ca vng t yu c v din phn

b, chiu su phn b v dc ngang y lp t yu di cng xem xt cc phng n cho tuyn vng trnh hoc cho tuyn ct qua t yu ch t bt li nht. Cng cn iu tra xc nh ngun gy m, kh nng thot nc, cng nh v tr v kh nng khai thc cc m t dng p nn ng.

III.1.2 Phi ly mu v tin hnh cc th nghim trong phng v thc hin cc th

nghim hin trng cn thit v a k thut xc nh c:

Loi t v cc ch tiu ni iu I.5.1, I.4.1 v I.5.2 khng nh vng tuyn i qua l vng t yu v xc nh loi t yu phi x l;


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Cc ch tiu phc v cho vic tnh ton kim tra mc n nh ca nn p trn t yu, c th l: Sc chng ct khng thot nc c xc nh bng phng php ct cnh ti hin trng (hoc c xc nh bng phng php ct nhanh trong phng th nghim, nu khng c thit b ct cnh ti hin trng), dung trng t nhin v mc nc ngm ( xc nh vng t yu chu tc dng ca lc y ni). Cc ch tiu ny phi c xc nh ring cho mi lp t yu khc nhau. Ngoi ra, cng phi xc nh cc ch tiu lc dnh C, gc ni ma st v dung trng i vi t dng p nn ng (ng vi trng thi cht v m ca t p);

Cc ch tiu phc v cho vic tnh ton d bo ln tng cng v ln c kt theo thi gian thng qua th nghim xc nh nn ln trong iu kin khng n hng, h s rng ban u eo, ch s nn ln Cr v Cc , h s c kt theo phng thng ng Cv (cm2/giy) v p lc tin c kt p. Cc ch tiu ny cng phi c xc nh ring cho mi lp t yu khc nhau ( ngha k hiu cc ch tiu ni trn xem mc VI).

III.2 Cc quy nh v kho st a hnh III.2.1 Khi tin hnh lp d n kh thi, i vi vng t yu phi o c lp c bnh

t l 1:500 1:1000 vi chnh lch cc ng ng mc 0,50 m dc theo cc phng n tuyn qua vng t yu. Trng hp vng t yu phn b rng ln (nh vng m ly...) th cng c th s dng phng php o c hng khng kho st a hnh, a mo ca c khu vc. Trong giai on ny, cc mt ct dc v mt ct ngang phc v cho vic thit k tnh ton nn p trn t yu c th c xc nh thng qua bnh a hnh lp.

III.2.2 Trong giai on thit k k thut v thit k lp bn v thi cng phi o c

mt ct dc v mt ct ngang theo tuyn ng thit k vi cc cc chi tit c c ly tng ng vi quy nh mi giai on, ngoi ra c b sung cc cc ti v tr khoan thm d, ly mu th nghim t yu v ti v tr d kin b tr cc h thng quan trc ni mc II.3.

III.3 Cc quy nh v kho st v th nghim a k thut III.3.1 t c cc yu cu ni iu III.1.1 v III.1.2 phi kt hp thm d

khng ly mu (bng cc thit b khoan xon, xuyn tnh hoc ct cnh ti hin trng) v thm d c ly mu (bng thit b khoan ly mu nguyn dng em v th nghim trong phng) sao cho tit kim nht. Vi din thm d rng trong giai on lp d n kh thi nn tn dng ti a cc bin php thm d khng ly mu kt hp vi khoan ly mu th nghim mc ti thiu. Trong giai on


13

thit k k thut v thit k chi tit lp bn v thi cng phi b sung bng bin php khoan ly mu, ch b sung thm d khng ly mu khi tht cn thit (khi cn m rng din thm d hoc khi vic thm d khng ly mu giai on lp d n kh thi cha nh ni iu III.3.2). V tr v s lng cc im thm d phi do Ch nhim d n quyt nh sau khi c d kin cc phng n thit k.

Khi thm d bng khoan, xuyn, ct cnh nn tham kho cc quy trnh hu quan di y :

Quy trnh khoan thm d a cht 22 TCN 259-1999

Ct cnh : ASTM D2573 v TCXD 205-1998 ca B Xy Dng

Xuyn : ASTM D1586 III.3.2 * Bc lp d n kh thi. Sau khi tin hnh khoan thng thng m pht

hin t yu th tin hnh khoanh vng v b tr l khoan trn tim tuyn vi khong cch t 250 n 500 mt (nu cn thit c th b xung cc im thm d nh : ct cnh, xuyn v.v.. pht hin phm vi t yu, nhng vic b xung thm d ny khng ly mu th nghim). Ch khoan trn mt ct ngang khi thit k ngh v c Ch u t chp thun.

* Bc thit k k thut. Cng tc thm d a cht cng trnh bng nhng l

khoan c b tr cch nhau thng thng t 50 n 100 mt trn tim tuyn (trong k c khi lng tin hnh bc lp d n kh thi).

- Trong trng hp c bit c ly ny c th rt ngn hn. - C cch 100-150 mt tin hnh 1 mt ct a cht cng trnh theo chiu ngang

vung gc vi tim tuyn, trn c 3 l khoan. Mi khu vc t yu phi c ti thiu hai mt ct ngang a cht i din.

- su khoan thm d phi n di y lp t yu, vo lp t khng yu thm 2 m hoc nu t yu c chiu dy ln th khoan n ht phm vi chu nh hng ca ti trng p. Phm vi ny c xc nh tng ng vi su ti c ng sut do ti trng p (do nn p v phn p gia ti trc nu c) gy ra bng 0,15 ng sut (p lc) do trng lng bn thn t yu gy ra (c xt n lc y ni nu tn ti nc ngm).

- Trong mi trng hp phi tin hnh th nghim ct cnh hin trng. Th nghim ny c th c tin hnh c lp hoc trong l khoan.

* Bc kho st lp bn v thi cng l s dng kt qu cc l khoan hoc cc

th nghim hin trng tin hnh bc thit k k thut. Khi lng kho st ch b sung cho bc thit k k thut cha thc hin ht theo quy nh. Trong trng hp c bit khi pht hin thm v tr t yu th c th tng kh lng kho st a cht, s lng tng thm do Ch chim nghip v xut v c Ch u t chp thun nhng khng vt qu 20% khi lng thc hin bc thit k k thut.


14

III.3.3 Mt ct thm d ct cnh v c khoan ly mu phi c b tr ch p tng i cao nht v c s phn b cc lp t yu tng i c trng nht.

III.3.4 Trong mi l khoan ni iu III.3.2 tu thuc vo chiu di on t yu

ly mu: *Chiu di on t yu n 200m th c 1-2 m su li phi ly mt mu t yu nguyn dng. *Chiu di on t yu trn 200m th khi lng ly mu do Ch chim nghip v xut v c Ch u t chp thun nhng ti thiu gia mi lp t phi ly mt mu t nguyn dng. Phng php ly mu, bao gi, vn chuyn v bo qun mu nguyn dng phi c thc hin ng nh cc quy nh Tiu chun Vit Nam TCVN 2683-91.

III.3.5 Vic th nghim xc nh cc ch tiu c l ca t yu ni iu III.1.2 phi

c thc hin vi tt c cc mu nguyn dng ly theo cc quy nh sau:

Th nghim xc nh cc ch tiu sc chng ct (lc dnh C v gc ma st ) phi tun theo phng php v cc quy nh Tiu chun Vit Nam TCVN 4199-95, trong phi xc nh c theo phng php ct nhanh v ct nhanh c kt (ch tiu ct nhanh kim ton mc n nh ca nn p trong qu trnh p v ch tiu ct nhanh c kt c dng kim ton n nh ca nn p khi a chng vo s dng);

Th nghim xc nh tnh nn ln trong iu kin khng n hng c thc

hin theo Tiu chun Vit Nam TCVN 4200-86. Ring vic xc nh tr s p lc tin c kt pz c thc hin theo hng dn Ph lc I ca bn quy trnh ny;

Cc ch tiu khc c xc nh theo cc Tiu chun Vit Nam tng ng. III.3.6 Vic th nghim xc nh cc ch tiu c l ca t hoc ct p nn ng

cng c thc hin theo cc tiu chun tng ng ni iu III.3.5 vi cc mu ch b bng vt liu p ly t m t hoc ct c cht v m tng ng nh thc t. Ring vi ch tiu sc chng ct th ch p dng phng php ct nhanh.

III.3.7 i vi mi ch tiu dng trong tnh ton nn c t nht 6 s liu th nghim v

tr s tnh ton c xc nh theo cng thc: t = tb ; (III.1)


15

Trong : t l tr s tnh ton ca ch tiu tb l tr s trung bnh s hc ca cc s liu th nghim l lch bnh phng trung bnh

( ) = A Ani tb

2

1

n

; (III.2)

Vi: Ai l tr s ca ch tiu mi ln th nghim xc nh c; n l s ln th nghim i vi mi ch tiu. Khi quyt nh chn tr s tnh ton ca mt ch tiu cn phn tch k cc iu

kin thc t nh hng n cht lng mu t yu trc khi em th nghim cng nh nh hng bt li ca mi ch tiu n kt qa tnh ton.

Ngoi ra, khi quyt nh nn kt hp vi kinh nghim ca cc chuyn gia a k thut.

III.3.8 Cc s liu th nghim hin trng bng thit b xuyn tnh hoc ct cnh cng

c x l a v tr s tnh ton nh ni iu III.3.7 (tham kho thm cc quy trnh v tiu chun ni iu III.3.1, kt hp vi kinh nghim ca cc chuyn gia a k thut).

IV. CC GII PHP THNG P DNG THIT K NN P TRN T YU IV.1 Yu cu chung i vi cu to nn p trn t yu IV.1.1 Cu to ca nn p trn t yu phi bo m hn ch c cc tc dng bt

li ca nc ngp v nc ngm:

t p phi dng loi n nh nc tt, tuyt i khng dng cc loi t bi (theo phn loi TCVN 5747-1993);

cht, chiu cao p ti thiu trn mc nc ngp v mc nc ngm cng cc yu cu cu to khc ca nn ng (nh p bao ta luy khi thn nn ng l ct...) u phi tun theo cc quy nh TCVN 4054 -1998 v TCVN 5729 -1997.

IV.1.2 Trong phm vi 20 m t chn ta luy nn p ra mi bn phi san lp cc ch

trng (ao, chum...) v tuyt i khng o ly t trong phm vi .


16

IV.1.3 C gng gim chiu cao nn p to iu kin d bo m n nh v gim

ln; tuy nhin, tr trng hp ng tm, chiu cao nn p ti thiu phi t 1,2 ~ 1,5 m k t ch tip xc vi t yu, hoc phi l 0,8 ~ 1 m k t b mt tng m ct (nu c) m bo phm vi khu vc tc dng ca nn mt ng khng bao gm vng t yu. Tr s cao ca chiu cao p ti thiu ni trn c p dng cho nn p ng cao tc v cc ng c nhiu xe ti nng, tr s thp p dng cho nn p cc ng khc.

IV.2 p trc tip trn t yu IV.2.1 C th p dng gii php p trc tip (khng dng mt bin php x l no

khc) khi tnh ton n nh v ln ca nn p trc tip trn nn thin nhin (bao gm c t yu di) hoc trc tip trn nn t yu u tha mn c cc yu cu v tiu chun ni mc II.1 v II.2. Phng php tnh ton n nh c quy nh mc V v phng php tnh ton ln c quy nh mc VI ca bn Quy trnh ny.

Trong mi trng hp p trc tip trn t yu u nn c tng m ct dy ti thiu 50 cm v rng thm so vi chn ta luy nn p mi bn 0,5 ~ 1,0 m.

IV.2.2 Cc trng hp sau y c th xt ti vic p dng gii php p trc tip.

Trn vng t yu c lp t khng thuc cc loi t yu ni mc I.4 v I.5 (thc t thng gi l lp v trn b mt t yu). Nu lp v dy 1~2 m th chiu cao nn p trc tip c th ti 2 ~ 3 m, nu lp v dy trn 2 m th chiu cao p trc tip c th ti 3 4 m ;

Trn vng than bn loi I hoc t yu do mm c b dy than bn di 1 ~ 2 m;

Trn vng bn ct, bn ct mn (loi ny c h s c kt thng ln nn ln nhanh).

Ngoi ra, i vi cc trng hp cc trng hp nn p c d bo ln t v ln nhanh nhng nu p ngay n cao thit k s khng bo m n nh theo tiu chun ni iu II.1.1 th vn c th p dng gii php p trc tip km vi bin php khng ch tc p (p tng t ; gia cc t p c thi gian ch c kt) bo m yu cu n nh (xem iu II.1.2) ch tr khi vic khng ch tc p dn ti qu ko di thi gian, khng bo m c yu cu v tin thi cng i vi ton b cng trnh ng th mi cn ngh n cc gii php x l khc.


17

IV.2.3 Cng ngh p t vng nn thin nhin l t khng yu ra vng t yu thi cng nn p trc tip trn t yu.

Khi thc hin cng ngh p cn bo m c cc iu kin sau : p b, ht kh nc trn b mt t yu; vt liu p phi l loi n nh nc tt nh ct cc loi, cp phi si cui,

hoc cc ph liu cng nghip phn c p ch l phn nm di mt t yu t nhin v vic lu ln vn

phi thc hin t nh (my i ) n nng (lu nng) cho n khi vt liu p khng tip tc ln vo t yu na, tc l n khi to c mt bng thi cng vng chc trn t yu.

phn nn p k t mt t t nhin tr ln phi c p tng lp v bo m t c yu cu m nn quy nh).

IV.2.4 to iu kin thi cng p trc tip trn t yu c thun li (to iu

kin cho xe my i li trn vng t yu v to iu kin m cht cc lp t p u tin) c th s dng vi a k thut ri trn mt t yu trc khi p nh ch dn bng IV.1 di y:

Bng IV.1: Chn vi v kt cu ng tm phc v cho xe c i li trn vng t yu

Cc ch tiu yu cu i vi vi a k thut

Loi vt liu p

ng tm

Kt cu ng tm

Cng chu ko t (kN/m)

dn di khi t (%)

Cng chu x rch

(kN)

H s thm

m sm/

ng knh l

lc 95 (m)

1- Mt lp vi trn p 50 cm 12 25 0,8 0,1 125

I. Ct, hn hp ct si thin nhin

2- Hai lp vi trn mi lp p 25 cm

8

15-80

0,3

0,1

125


16

15-80

0,5

0,1

80-200

1- Mt lp vi trn p 30 cm 25 25 1,2 0,1 200

II. Cp phi tt

2- Mt lp vi trn p 50 cm 12 25 0,8 5.10-2 200


20

15-80

1,2

5.10-2

200

Ghi ch Bng IV.1:

H s thm c th nguyn l s-1 v l m/s trn mt n v b dy mu vi a k thut em th;


18

ng knh l lc ca vi l tng ng vi ng knh ca ht vt liu ln nht c th theo nc thm qua vi; c ht ln nht ny c ly bng D95 (l ng knh ht m lng cha cc c nh hn n chim 95%);

Vi phi ri ngang (thng gc vi hng tuyn) v ph chng ln nhau t nht l 0,5 m hoc khu chng nhau 10 cm; m nn t hiu qu cao ngay lp p u tin th phi chn vi c cng chu ko t ti thiu t 25 kN/m tr ln.

IV.3 o mt phn hoc o ton b t yu IV.3.1 Gii php ny thng rt c li v mt tng n nh, gim ln v thi gian

ln; do vy tr trng hp trn t yu c tn ti lp v khng yu ra, trong mi trng hp khc ngi thit k u nu u tin xem xt p dng hoc kt hp vic o mt phn t yu vi cc gii php khc. c bit thch hp l trng hp lp t yu c b dy nh hn vng nh hng ca ti trng p. Dng s cng ngh o t yu bng my xc gu dy, o n u p ln n th chiu su o c th thc hin c l 2 - 3 m. iu ch yu l phi thit k b tr mt bng thi cng hp l, thun li cho vic y t p ln nhanh chng sau khi lung o hnh thnh; t yu o ra c th v pha 2 bn on p ln xong to nn b phn p. Chiu su o t yu cn thit c th xc nh c thng qua tnh ton hng dn V.2.6 trn c s tha mn c cc yu cu ni mc II.1 v II.2.

IV.3.2 Mt ct ngang phn t yu phi o ch cn thit k dng hnh thang vi y

nh pha di su c b rng bng ng phm vi b rng mt nn ng, cn y ln trn va bng phm vi tip xc ca nn p vi mt t yu khi cha o (phm vi gia hai bn chn ta luy nn p). iu ny c ngha l, chiu su o t yu ch cn bo m t c trong phm vi b rng nn ng, cn hai bn ta luy chiu su o c th gim dn.

IV.3.3 Cc trng hp di y c bit thch hp i vi gii php o mt phn

hoc o ton b t yu : B dy lp t yu t 2m tr xung (trng hp ny thng o ton b t

yu y nn ng tip xc hn vi tng t khng yu); t yu l than bn loi I hoc loi st, st do mm, do chy; trng hp

ny, nu chiu dy t yu vt qu 4-5m th c th o mt phn sao cho t yu cn li c b dy nhiu nht ch bng 1/2 1/3 chiu cao p (k c phn p chm trong t yu).

IV.3.4 Trng hp t yu c b dy di 3 m v c cng qu thp o ra khng

kp p nh than bn loi II, loi III, bn st ( st B >1) hoc bn ct mn th c th p dng gii php b chm n y lp t yu hoc b kt hp vi


19

p qu ti nn t ln n y lp t yu. Gii php ny c bit thch hp i vi trng hp thit k m rng nn p c khi ci to, nng cp ng trn vng t yu.

phi dng loi kch c 0,3 m tr ln v c t pha trong y t yu ra pha ngoi, sau khi nh ln khi mt t yu th ri ct, nh hoc cp phi ln v lu ln t nh n nng dn. Nu nh th c th dng lng, r an thp hay lng bng cht do tng hp trong ng p.

IV.3.5 Dng cc tre ng 25 cc/m2 cng l mt gii php cho php thay th vic o

bt t yu trong phm vi bng chiu su cc ng (thng c th ng su 2 -2,5 m). Cc tre nn dng loi c ng knh u ln trn 7 cm , ng knh u nh trn 4 cm bng loi tre khi ng khng b dp, gy. Khi tnh ton c php xem vng ng cc tre nh trn l nn ng p. Trn nh cc tre sau khi p mt lp 30 cm nn ri vi a k thut (hoc cc loi geogrids c chc nng tng t) nh ni iu IV.2.4 to iu kin phn b u ti trng nn p trn cc cc tre.

Tng t, c th dng cc cc trm loi c ng knh u ln trn 12 cm, u nh trn 5 cm, ng su 3 - 5 cm vi mt 16 cc /m2.

IV.4 p b phn p IV.4.1 Gii php ny ch dng khi p nn ng trc tip trn t yu vi tc dng

tng mc n nh chng trt tri cho nn ng t cc yu cu ni II.1.1, c trong qu trnh p v qu trnh a vo khai thc lu di. Nu p nn v p b phn p hai bn ng thi th khng cn khng ch tc p, v vy c th thi cng nhanh. Tuy nhin gii php ny khng gim c thi gian ln c kt v khng nhng khng gim c ln m cn tng thm ln (do thm ti trng ca b phn p hai bn). Ngoi ra, n cn c nhc im l khi lng p ln v din tch chim rung t ln. Gii php ny cng khng thch hp vi cc loi t yu l than bn loi III v bn st.

IV.4.2 Cu to ca b phn p

Vt liu p b phn p l cc loi t hoc ct thng thng; trng hp kh khn c th dng c t ln hu c.

B rng ca b phn p mi bn nn vt qu phm vi cung trt nguy him t nht t 1-3 m (xc nh cung trt nguy him nht theo phng php ni iu V.1 v V.2). Mt trn b phn p phi to dc ngang 2% ra pha ngoi.

Chiu cao b phn p khng qu ln c th gy trt tri (mt n nh) i vi chnh phn p phn p; khi thit k thng gi thit chiu cao b


20

phn p bng 1/3 - 1/2 chiu cao nn p ri nghim ton n nh theo phng php mt trt trn ni mc V i vi bn thn b phn p v i vi nn p c b phn p, nu kt qu nghim ton t cc yu cu ni iu II.1.1 l c.

cht t p b phn p nn t K 0,9 (m nn tiu chun). IV.5 Tng ct m

IV.5.1 Tng ct m c b tr gia t yu v nn p tng nhanh kh nng thot nc c kt t pha di t yu ln mt t t nhin di tc dng ca ti trng nn p.

Tng ct m nn c s dng trong cc trng hp p trc tip trn t yu (IV.2.1 v IV.2.2) v bt buc phi c khi p dng cc gii php thot nc c kt theo phng thng ng (mc IV.6).

IV.5.2 Ct dng lm tng ct m cn phi bo m c cc yu cu sau:

Ct phi l loi ct c t l hu c 5% c ht ln hn 0,25 mm chim trn 50%, c ht nh hn 0,08 mm chim t hn 5% v phi tha mn mt trong hai iu kin sau:

DD

60

106> (IV.2)

( )DD D

302

10 60.> 1 v < 3 (IV.3)

Trong : D30 l kch c ht m lng cha cc c nh hn n chim 30%

D10 l kch thc ng knh ht m lng cha cc c nh hn n chim 10%.

IV.5.3 Chiu dy tng ct m t nht phi bng ln tng cng S ni iu II.2.1

nhng khng c nh hn 50 cm. cht m nn ca tng ct m ch yu cu t 0,9 cht m nn tiu chun (phc v xe my thi cng cc lp trn).

IV.5.4 B rng mt tng ct m phi rng hn y nn p mi bn ti thiu l 0,5

1 m; mi dc v phn m rng hai bn ca tng ct m phi cu to tng lc ngc nc c kt thot ra khng li theo ct, nht l khi ln chm vo t yu nc c kt vn c th thot ra v khi cn thit dng bm ht bt nc s khng gy ph hoi tng ct m.


21

Tng lc ngc c th c cu to theo cch thng thng (xp dy khong 20-25 cm) hoc bng vi a k thut c yu cu nh ni iu IV.5.5. Trng hp s dng vi a k thut th nn ri vi trn t yu, sau p tng ct m, ri lt vi bc c mi dc v phn m rng ca n lm chc nng lc ngc. Lp vi lm chc nng lc ngc ny phi chm vo phm vi y nn t nht l 2 m. Lc ny, cng nn li dng vi a k thut ri trc tip trn t yu kim thm cc chc nng khc nh tng cng thm mc n nh trong qu trnh p (xem mc IV.7) hoc cc chc nng ni iu IV.2.4.

IV.5.5 Trong trng hp s dng vi a k thut lm tng lc ngc nh ni iu

IV.5.4 th ng knh l lc ca vi phi m bo iu kin sau:

Of C.D85 (IV.4) Trong :

Of l ng knh l lc ca vi cn chn (m) D85 l kch c ng knh ht ca vt liu tng ct m m lng

cha cc c nh hn n chim 85% (m) C l h s ly bng 0,64

Vi a k thut kim thm chc nng no th ch tiu k thut ca vi cng ng thi phi tha mn cc yu cu tng ng.

IV.5.6 Nc c kt t tng ct m qua tng lc ngc thot ra cn phi c thot nhanh khi phm vi ln cn nn ng. Cn thit k sn cc ng thot nc v khi cn thit c th b tr bm ht tho nc (c bit l khi tng ct m ln ht vo trong t yu).

IV.6 Thot nc c kt theo phng thng ng (s dng ging ct hoc bc thm)

IV.6.1 Nh c b tr cc phng tin thot nc theo phng thng ng (ging ct

hoc bc thm) nn nc c kt cc lp su trong t yu di tc dng ca ti trng p s c iu kin thot nhanh (thot theo phng nm ngang ra ging ct hoc bc thm ri theo chng thot ln mt t t nhin). Tuy nhin, m bo pht huy c hiu qu thot nc ny th chiu cao nn p ti thiu nn l 4 m v khi thit k cn tha mn cc iu kin (IV.5a), (IV.5b) di y:

vz + z (1,2 1,5) pz (IV.5a)


22

( )( ) + + =

>

log log

log log

vz z pz

vz z vz

0 6, (IV.5b)

Trong :

vz l ng sut (p lc) thng ng do trng lng bn thn cc lp t yu gy ra su z (MPa)

vz = i . hi (IV.6)

i v hi l trng lng th tch v b dy lp t i nm trong phm vi

t mt tip xc ca t yu vi y nn p (z=0) n su z trong t yu; ch rng i vi cc lp t yu nm di mc nc ngm th tr s i phi dng trng lng th tch y ni (tr i 1).

z l ng sut (p lc) thng ng do ti trng p (phn nn p v phn p gia ti trc nu c, nhng khng k phn chiu cao p hx quy i t ti trng xe c) gy ra su z trong t yu k t y nn p (MPa); z c tnh theo ton Osterberg Ph lc II.

pz l p lc tin c kt su z trong t yu (MPa); pz c xc nh t th nghim c kt theo hng dn v quy nh Ph lc I.

iu kin (IV.5a) v (IV.5b) phi c tha mn i vi mi su z trong phm vi t y nn p n ht chiu su ng ging ct hoc cm bc thm.

Nu khng tho mn cc iu kin ni trn th c th kt hp vi bin php gia ti trc nh ni iu IV.6.8 tng z .

IV.6.2 Cc gii php dng phng tin thot nc c kt thng ng thng ch p

dng khi tng t yu dy (b dy tng t yu vt qu b rng y nn p) v nn p cao. V gi thnh xy dng cao nn thng ch p dng khi dng cc gii php khc khng th bo m c tiu chun v phn ln c kt cn li S ni iu II.2.3 trong thi hn thi cng quy nh.

IV.6.3 Khi s dng cc gii php thot nc c kt thng ng nht thit phi b tr

tng ct m vi cc yu cu quy nh cc iu IV.5.2, IV.5.3, IV.5.4, IV.5.5 v IV.5.6. Nu dng ging ct th nh ging ct phi tip xc trc tip vi tng ct m. Nu dng bc thm th bc thm phi cm xuyn qua tng ct m v ct d thm ti thiu l 20 cm cao hn mt trn ca tng ct m.


23

IV.6.4 Ct dng cho ging ct cng phi c yu cu nh ni iu IV.5.2 nhng ng thi phi tha mn c 2 iu kin IV.2 v IV.3.

IV.6.5 Bc thm dng lm phng tin thot nc c kt thng ng phi t c

cc yu cu sau: Kch thc l v lc ca bc

(xc nh theo tiu chun ASTM D4571) : 095 75 m H s thm ca v lc (ASTM D4491) : 1.10-4 m/sec Kh nng thot nc ca bc thm vi

p lc 350 KN/m2 (ASTM D4716) : qw 60.10-6 m3/sec Cng chu ko ng vi dn di di 10%

(ASTM D4595) nhm chng t khi thi cng : 1 KN/bc B rng ca bc thm ( ph hp vi

thit b cm bc tiu chun ho) : 100 mm 0,05 mm IV.6.6 Ging ct ch nn dng loi c ng knh t 35 45 cm, b tr kiu hoa mai

vi khong cch gia cc ging bng 8-10 ln ng knh ging. Nu dng bc thm th cng nn b tr so le kiu hoa mai vi c ly khng nn di 1,3 m v khng qu 2,2 m.

IV.6.7 Vic quyt nh chiu su ging ct hoc bc thm l mt vn kinh t - k

thut i hi ngi thit k cn phi cn nhc da vo s phn b ln ca cc lp t yu theo chiu su di tc dng ca ti trng p i vi mi trng hp thit k c th. Khng nht thit phi b tr n ht phm vi chu nh hng ca ti trng p (phm vi chu ln) nh ni iu III.3.2 m ch cn b tr n mt su c tr s ln c kt ca cc lp t yu, t tr ln chim mt t l ln so vi tr s ln c kt Sc d bo c sao cho nu tng nhanh tc c kt trong phm vi c b tr ging hoc bc ny l t c tiu chun v ln c kt cho php cn li ni iu II.2.3 trong thi hn thi cng quy nh.

Do vy ngi thit k phi a ra cc phng n b tr ging hoc bc thm khc nhau (v su v v khong cch). Trong mi phng n b tr v chiu su u phi m bo tha mn iu kin (IV.5a) v (IV.5b).

IV.6.8 Khi s dng cc gii php thot nc c kt thng ng nn kt hp vi bin

php gia ti trc v trong mi trng hp thi gian duy tr ti trng p khng nn di 6 thng. C th dng bt k loi t no (k c t ln hu c) p gia ti trc. Ta luy p gia ti trc c php p dc ti 1:0,75 v cht m nn ch cn t K = 0,9 (m nn tiu chun)


24

IV.7 S dng vi a k thut tng cng mc n nh ca nn p trn t yu

IV.7.1 Khi b tr vi a k thut gia t yu v nn p nh hnh IV.1, ma st

gia t p v mt trn ca vi a k thut s to c mt lc gi khi trt F (b qua ma st gia t yu v mt di ca vi) v nh mc n nh ca nn p trn t yu s tng ln.

Hnh IV.1

I l vng hot ng (khi trt) II l vng b ng (vng vi a k thut ng vai tr neo gi) F l lc ko m vi phi chu (T/m) Y l cnh tay n ca lc F i vi tm trt nguy him nht S dng gii php ny, khi tnh ton thit k phi bo m iu kin sau:

F Fcp ; (IV.7) Trong :

F l lc ko m vi phi chu (T/m) Fcp l lc ko cho php ca vi rng 1 m (T/m) IV.7.2 Lc ko cho php ca vi Fcp c xc nh theo cc iu kin sau:

iu kin bn ca vi:

FF

kcpmax= ; (IV.8)

Trong :


25

Fmax l cng chu t ca vi kh 1 m (T/m)

k l h s an ton; ly k = 2 khi vi lm bng plieste v k = 5 nu vi lm bng pliprpilen hoc plithilen

iu kin v lc ma st cho php i vi lp vi ri trc tip trn t yu :

F h fcp d i0

1

= l (IV.9)

F h fcp d i= 0

2l (IV.10)

Trong :

l1 v l2 l chiu di vi trong phm vi vng hot ng v vng b ng (xem hnh IV.1)

d l dung trng ca t p ; f ' l h s ma st gia t p v vi cho php dng tnh ton

hi l chiu cao p trn vi (thay i trong phm vi l1 v l2 , t hi = h n hi =0, (xem hnh IV.1); biu thc IV.9 v IV.10 l tng lc ma st trn vi trong phm vi vng hot ng v vng b ng:

= f k 23

tg ; (IV.11) Trong :

l gc ma st trong ca t p xc nh tng ng vi cht thc t ca nn p hoc ca tng m ct nu c ( ) ; k' l h s d tr v ma st, ly bng 0,66.

Vic xc nh tr s l1 v l2 c tin hnh ng thi vi vic kim ton mc

n nh ni iu V.1: gi thit lc F m bo h s n nh nh nht t c yu cu ni II.1.1 ri nghim li iu kin (IV.7) sao cho tha mn ng thi c (IV.8), (IV.9) v (IV.10); nu tha mn th cn c vo tr s Fcp nh nht theo cc quan h ni trn chn vi c Fmax tng ng.

IV.7.3 Vi a k thut dng tng cng n nh cho nn p trn t yu c th

c b tr mt hoc nhiu lp (1 - 4 lp), mi lp vi xen k ct p dy 15 - 30 cm ty theo kh nng lu ln. Tng cng chu ko t ca cc lp vi phi chn bng tr s Fmax c xc nh nh ni iu IV.7.2.


26

Ch : Cc lp vi pha trn nm trong ct p (mt trn v mt di u tip xc vi ct) th tr s Fcp tnh theo (IV.9) v (IV.10) c nhn 2, t tnh ra tng lc ma st cho php ca cc lp vi.

IV.7.4 Trong trng hp s dng gii php ny nn chn vi a k thut bng loi si

dt (woven) v c cng chu ko t ti thiu l 25 kN/m nh ni iu IV.2.4 m bo hiu qu m nn t trn vi nhm to h s ma st cao gia t v vi. i vi cc ch tiu khc ca vi cng nn tham kho s dng theo bng IV.1.

Nu kt hp s dng vi lm tng lc th cng phi m bo c v ng knh l lc nh ni iu IV.5.5.

IV.8 Cc nguyn tc v trnh t la chn gii php thit k IV.8.1 Trnh t tin hnh:

lm c s xut cc gii php thit k, trc tin pha t vn thit k cn phi tnh ton nh gi mc n nh v din bin ln i vi trng hp nn p trc tip trn t yu (khng p dng mt bin php x l no khc) theo cc phng php hng dn mc V v mc VI. Vic tnh ton nh gi phi c tin hnh ring i vi tng on c kch thc nn p v c cc iu kin cu to tng lp t yu cng nh c trng k thut cc t yu khc nhau. Nu kt qu tnh ton cho thy khng m bo c cc yu cu v tiu chun thit k ni mc II v iu IV.1 th mi xut cc phng php x l cho mi on , trc ht l cc phng n n gin nht (k c phng n thay i kch c nn p v chiu cao v dc mi ta luy), hoc cng c th a ra cc phng n kt hp ng thi mt s gii php trong cc gii php ni mc IV v c cc gii php khc cha cp n trong quy trnh ny (v d gii php ko di cu dn qua vng t yu ). i vi mi phng n xut li phi tnh ton nh gi v n nh v ln ri thng qua tnh ton, phn tch so snh v kinh t - k thut mt cch ton din la chn gii php p dng. Khi phn tch nn xt n c nh hng gy ln ca nn p i vi cc cng trnh nhn to hin c.

IV.8.2 Trong mi trng hp cn phi tn dng ht thi gian thi cng cho php: p

trn t yu phi khi cng sm nht v nu cn thit c th cho php ko di ti a ti k hn cui cng trong tin chung hoc chia lm nhiu t p, va p va ch c kt. Tn dng thi gian ti a nh vy l mt bin php em li hiu qu kinh t - k thut ng k, do nn kt hp p dng cng vi mi gii php x l khc.


27

IV.8.3 Trong qu trnh thi cng trn thc t, phi lun xem xt kt qu theo di h thng quan trc (mc II.3), so snh n vi cc yu cu khng ch v n nh v bin dng ni II.1.2 v II.2 kp thi iu chnh li tc p nu cn thit, ng thi c th iu chnh c cc gii php thit k theo hng c li hn v kinh t - k thut so vi thit k ban u. c bit l phi da vo quan trc ln thc nh ni iu II.2.5 d bo ln c kt cn li khi quyt nh thi im c th thi cng cc hng mc cng trnh c lin quan n yu cu khng ch ln ca nn p trn t yu (cc d bo ln theo tnh ton ch dng a ra cc gii php thit k).

IV.8.4 i vi trng hp chiu di tuyn ng qua vng t yu c cc c trng

a k thut tng i ng nht t 500 m tr ln th nn t chc thi cng lm th trn thc a mt on nn p di 30 - 50 m (khng nn ngn hn 2 ln b rng y nn p) c b tr cc thit b quan trc nh ni mc II.3 t chnh xc ho cc gii php thit k trc khi thi cng ng lot. Vic lm th ny phi c thc hin trong giai on thit k k thut v vic iu chnh sau lm th s c thc hin trong giai on thit k lp bn v thi cng chi tit.

i vi trng hp chiu cao nn p thp cng nn lm th. Thi gian theo di quan trc on th nghim lm th nn t 6 - 12 thng.

V. TNH TON N NH NN P TRN T YU V.1 Phng php tnh ton V.1.1 Trong quy trnh ny s dng phng php phn mnh c in hoc phng

php Bishop vi mt trt trn khot xung vng t yu lm phng php c bn tnh ton nh gi mc n nh ca nn p trn t yu.

V.1.2 Phng php phn mnh c in c tnh theo s hnh V.1 v h s n nh Kj ng vi mt mt trt trn c tm Oj c xc nh theo cng thc V.1:


28

Hnh V.1: S tnh n nh theo phng php phn mnh vi mt trt trn; (hx l chiu cao quy i ti trng xe c xc nh theo cng thc II.1)

( ) ( )( )[ ]K

c Q cos tg F Y / R

Q sin W Y /Rj

i i i j1

n

i i i i j1

n=

+ +

+

l i i

(V.1)

Trong hnh (V.1) mnh trt i rng di chu tc dng ca trng lng bn thn

Qi, lc ng t Wi (nu cn xt n); ngoi ra, nu c ri vi a k thut tng cng n nh th ton khi trt cn chu tc dng ca lc gi F (xem hnh IV.1 v iu IV.7.1). Wi c xc nh iu II.4.4, cn F c xc nh nh ni iu IV.7.1 v IV.7.2. Cc lc tc dng ny c cnh tay n so vi tm trt Oj l Yi (lc Wi) v Y (lc F). i vi mt mt trt trn c tm Oj th Yi s thay i theo v tr trng tm ca mnh trt, cn Y s l khng i.

li l chiu di cung trt trong phm vi mnh i

n l tng s mnh trt c phn mnh trong phm vi khi trt

i l gc gia php tuyn ca cung li vi phng ca lc Qi (hnh V.1) Rj l bn knh ng cong ca cung trt

ci v i l lc dnh n v v gc ma st trong ca lp t cha cung trt li ca mnh trt i (nu cung li nm trong vng nn p th dng tr s lc dnh v gc ma st trong ca t p). i vi vng t yu, khi dng kt qu th nghim ct cnh hin trng th p dng i = 0, cn ci c ly bng sc chng ct tnh ton Cui (xem V.3.2).

V.1.3 Khi tnh ton theo phng php Bishop th h s n nh Kj ng vi mt mt trt trn c tm Oj (hnh V.1) c xc nh theo cng thc sau :

( )

( )[ ]KQ tg

c m F Y R

Q W Y Rj

i i

ii i i j

i i i i j

n

n=+

+

+

cos

/

sin /

l1

1

; (V.2)

vi : m K tg tgi j i i= +

11

1

. ; (V.3) Cc k hiu trong (V.2) v (V.3) u c ngha nh trong (V.1) trn hnh

V.1 . Cch xc nh chng cng hon ton ging nh khi tnh ton theo phng


29

php phn mnh c in. Ch khc l qu trnh tnh ton theo (V.2) v (V.3) l qa trnh tnh lp m dn v mi (V.3) li ph thuc vo Kj ; do vy, nu s dng phng php Bishop th buc phi s dng cc chng trnh tnh trn my vi tnh.

V.2 Nhng ch khi vn dng phng php tnh ton phn mnh c in v Bishop

V.2.1 B rng mnh trt di khng c qu 2 m v phi phn mnh sao cho chiu

di cung trt trong phm vi mi mnh li phi nm trong cng mt lp t. Mi mnh trt bao gm tt c cc lp t k t mt trt tr ln (c th gm c tng ct m, phn p chm trong t yu, phn lp t khng yu, phn p phn p, phn p gia ti trc v phn chiu cao p tng ng vi ti trng xe c quy i).

V.2.2 Xc nh trng lng bn thn mi mnh trt Qi nh sau:

Q d . h i i k k1

N

= (V.4) Trong : hk l chiu cao ca mnh i trong phm vi mi lp t khc nhau c

dung trng th tch kh k khc nhau (N l s cc lp t khc nhau trong phm vi mnh i). i vi cc lp t yu nm di mc nc ngm th tr s k phi dng trng lng th tch y ni (tr i 1).

Ch rng, i vi cc mnh trt nm trong phm vi b rng ca nn ng th khi tnh Qi phi k n thm chiu cao quy i ti trng xe c hx xc nh theo cng thc (II.1) nh hnh V.1 v chiu cao p gia ti trc (nu c).

V.2.3 Phi tnh ton vi nhiu mt trt trn (Oj, Rj) khc nhau xc nh c mt trt nguy him nht v h s n nh nh nht Kj min (vit tt l Kmin). Tr s Kmin ny c dng nh gi i vi cc yu cu v n nh trt tri ni II.1. Ch rng phi v c (xc nh c) v tr mt trt nguy him nht d bo theo tnh ton lm c s cho vic thit k b tr cc gii php x l nh b rng b phn p (iu IV.2.4), chiu su b tr phng tin thot nc thng ng (iu IV.6.7) hoc xc nh vng hot ng khi tng cng n nh bng vi a k thut (hnh IV.1). Trong trng hp lp t yu mng, mt trt c th gm cc on cung trn kt hp vi mt on thng y lp t yu (c bit l khi y c dc trn 10).

V.2.4 Nu khng s dng my tnh th c th m tm mt trt nguy him nht bng

cch cho v tr tm Oj ca chng thay i trong vng "tm trt nguy him nht" nh th hin trn hnh V.2 :


30

Hnh V.2: S xc nh vng tm trt nguy him (I l im gia mi ta luy nn p, C l chn ta luy nn p)

Nu nn p bng ct (lc dnh c = 0) th giao im gia mt trt nguy him

nht vi b rng nn ng c th thay i trn c phm vi AB, cn nu p t c lc dnh ln th giao im ny thng qua im A hoc ln cn A (t A n gia tim nn p).

V.2.5 Cc chng trnh tnh trn my vi tnh xc nh h s n nh Kj v m tm

h s n nh nh nht Kmin phi c kh nng bo m c cc yu cu tnh ton ni cc iu V.1, V.2.1, V.2.3.

V.2.6 Khi nh gi mc n nh ca nn p trn t yu c dng cc gii php x

l khc nhau ni IV.2, IV.3, IV.4, IV.6, IV.7 th vn p dng cc phng php ni V.1 v nhng yu cu vn dng ni V.2 (c bit l iu V.2.1 v V.2.2) iu ny i hi trc khi gi thit cc mt trt v tin hnh tnh ton phi v mt ct ngang nn p vi y cc lp nn thin nhin pha di v cc cu to theo yu cu ca gii php x l tng ng (chiu su o t yu, tng m ct, b phn p, hnh dng khi t p gia ti trc, b tr cc lp vi a k thut...) trong chiu cao nn p phi k thm chiu cao quy i ti trng xe c.

V.2.7 Nu p dng cc gii php p thnh nhiu t th vic xc nh chiu cao p

cho php i vi mi on c lm nh sau:

Gi thit mt chiu cao p nn

Tnh ton mc n nh ca nn chiu cao p ny theo phng php ni V.1 v V.2 tng ng vi sc chng ct ca t yu c xc nh khc nhau cho mi t p (xem phn V.3). Nu kt qu nghim ton tha mn iu kin ni II.1.1 v tr s Kmin khng qu ln (nn tn dng Kmin = 1,2) th chp nhn chiu cao gi thit ni trn l chiu cao thit k cho mi t p, nu khng th gi thit li cho n khi kt qu nghim ton cho Kmin = 1,2.


31

Cho php s dng cc loi ton tra sn chiu cao p gii hn Hgh hoc cc cng thc tnh ti trng gii hn Pgh ty thuc cc c trng sc chng ct ca t yu a ra tr s chiu cao p nn gi thit ni trn mt cch nhanh chng nhng sau vn phi nghim ton li theo phng php mt trt trn ni V.1 v V.2 (ch rng Pgh = d . Hgh vi d l dung trng ca t p nn ng hoc p gia ti trc).

Nu s dng cc chng trnh tnh ton trn my vi tnh c sn th c th gi thit 3 - 4 tr s chiu cao p ri cho chy my xc nh tr s Kmin tng ng vi mi chiu cao v thng qua quan h Kmin = f (Hp) xc nh chiu cao p cho php tng ng Kmin = 1,2.

V.3 Cc trng hp tnh ton n nh v thng s tnh ton tng ng V.3.1 C 3 trng tnh ton n nh i hi phi s dng sc chng ct tnh ton

trng thi khc nhau nh di y: 1. Trng hp I: Nn p c xy dng trong iu kin t yu pha di cha

kp c kt hoc c c kt nhng mc khng ng k nh cc trng hp c th di y:

Trng hp tnh ton nh gi mc n nh phc v xut cc gii php thit k ni iu IV.8.1;

Trng hp p dng cc gii php p trc tip, p c ri vi a k thut (IV.2 v IV.7), o mt phn t yu (IV.3), dng b phn p (IV.4);

Trng hp p nn t u tin khi p dng gii php p thnh nhiu t (IV.8.2 v V.2.7), khi p dng gii php tng m ct (IV.5) v thot nc thng ng (IV.6).

2. Trng hp II: Nn p trn t yu sau khi hon thnh a vo khai thc s

dng, t yu pha di t mc c kt 90% tr ln. 3. Trng hp III: Nn p trong qu trnh xy dng vi gii php p lm nhiu

t, va p va ch c kt (IV.8.2), mc c kt ca t yu tng dn trong nhng t p th hai, th ba.

Nu kt qu tnh ton n nh theo trng hp I vi chiu cao p mt ln bng chiu cao nn p thit k cho thy m bo c cc yu cu ni II.1.1 th d p dng gii php x l no cng khng cn cp n vic tnh ton theo cc trng hp II v III.

V.3.2 i vi trng hp I, cc c trng v sc chng ct a vo tnh ton phi c xc nh nh sau:


32

i vi t nn p v lp ct m: Tr s lc dnh c v gc ma st c xc nh bng mu ch b cht v m ng nh thc t thng qua th nghim ct nhanh khng thot nc trong phng th nghim. Nu nn p b ngp nc hai bn th mu ct cn ch b m bt li nht tng ng.

i vi cc lp t t nhin yu hoc khng yu nm di nn p: S

dng kt qu th nghim ct cnh hin trng v tr s lc dnh tnh ton Cu c xc nh theo cng thc sau (xem nh gc ma st = 0):

Cu

i = . Ss (MPa) (V.5) Trong :

Ss l sc chng ct nguyn dng (MPa) khng thot nc t th nghim ct cnh hin trng

l h s hiu chnh (theo Bjerum) xt n nh hng bt ng hng ca t, tc ct v tnh ph hoi lin tip ca nn t yu ty thuc vo ch s do ca t nh bng V.1

Bng V.1: Tr s ty thuc vo ch s do Ip

Ip 10 20 30 40 50 60 70

1,09 1,0 0,925 0,86 0,80 0,75 0,70 (Ni suy bc nht gia cc khong trong bng)

Ch khi khng c cch no c c thit b th nghim ct cnh hin trng th mi c dng c trng sc chng ct theo kt qa th nghim ct nhanh khng thot nc trong phng th nghim (ci , i).

V.3.3 i vi trng hp II: c trng sc chng ct ca cc lp t yu v khng

yu nm di nn p (C v ) c xc nh vi mu nguyn dng thng qua th nghim ct nhanh c kt trong phng th nghim; i vi cc lp t p (k c tng ct m, nu c) vn c xc nh nh trng hp I.

V.3.4 i vi trng hp III: Cc c trng sc chng ct ca cc lp t v nn p

u c xc nh nh i vi trng hp I nhng tr s Ss trong cng thc V.5 nay c thay bng tr s Su xc nh nh sau:

Su = U [0,22.z + Ss(pz/vz)0,2] (V.6)

Trong :


33

U l mc c kt d bo c th t c k t lc bt u p nn t u tin cho n khi bt u p nn t II tip theo: U tnh bng phn s thp phn ca 1 (v d t c kt 50% th U = 0,5) v c d tnh theo cch ni iu VI.3.1.

Ss c ngha nh cng thc (V.5) vi th nghim ct nhanh hin trng t lc cha p (t trng thi t nhin): z, pz, vz c ngha v c xc nh nh cng thc (IV.5 v IV.6) vi ti trng p t u. Vi Su tnh c theo (V.6) s tnh c lc dnh tnh ton (tc l sc chng ct tnh ton) Cui theo cng thc (V.5) ty thuc mc c kt ca t yu sau khi p t u. Tr s sc chng ct tnh ton ny khi U = 1 phi nh hn tr s sc chng ct ca trng hp II

Su (z + vz) . tgi + ci (V.7)

Trong : ci v i c xc nh thng qua th nghim ct nhanh c kt nh ni V.3.3. Nu Cu tnh theo cng thc (V.5 v V.6) ln hn tr s v phi ca cng thc (V.7) th ch c dng tr s v phi ca (V.7) tnh ton.

Trng hp s dng kt qa ct nhanh khng thot nc trong phng th nghim tnh ton th tng ng vi mc c kt t c U , sc chng ct ca t yu lp i c xem l c tng thm mt tr s ci . ci = z . U . tgi (V.8) v tr s lc dnh a vo tnh ton theo cc cng thc (V.1) hoc (V.3) s l cU

i = ci + ci . Tr s sc chng ct tnh ton vi i v cUi ny cng phi tha mn iu kin (V.7).

V.3.5 Vic tnh ton n nh vi cc cch xc nh sc chng ct tnh ton ni trn

ch phc v cho nhng d kin thit k. Trong trng hp I v II m bo nn lun n nh trong qu trnh p phi thc hin y cc yu cu v quan trc ln v di ng ngang ni mc II.3.

VI. TNH TON LN NN P TRN T YU VI.1 Tnh ln c kt Sc VI.1.1 ln c kt Sc c d tnh theo phng php phn tng ly tng vi cng

thc sau:


34

( )S H1 e

C log / C logci

oi

i 1

n

ri

pzi

vzi

ci z

ivzi

pzi= + ++

=

(VI.1)

Trong :

Hi l b dy lp t tnh ln th i (phn thnh n lp c cc c trng bin dng khc nhau), i t 1 n n lp; Hi 2,0 m ; eo

i l h s rng ca lp t i trng thi t nhin ban u (cha p nn bn trn).

C ci ch s nn ln hay dc ca on ng cong nn ln (biu din di

dng e log ) trong phm vi i > pzi ca lp t i. C r

i l ch s nn ln hay dc ca on ng cong nn ln ni trn trong phm vi i pzi (t trng thi cha c kt xong di tc dng ca trng lng bn thn) v khi vzi > pzi (t trng thi c kt bnh thng) th cng thc (V.8) ch cn mt s hng sau (khng tn ti s hng c mt C r

i ).

b) Khi vzi < pzi (t trng thi qu c kt) th tnh ln c kt Sc theo VI-1 s c 2 trng hp :

Nu zi > pzi vzi th p dng ng cng thc (VI.1) vi c hai s hng ;

Nu zi > pzi vzi th p dng cng thc sau :

S H

1 e C logc

i

oi

i 1

n

ri z

ivzi

pzi= ++

=

(VI.1)

VI.1.2 Xc nh cc thng s v tr s tnh ton trong cng thc d tnh ln (VI.1)


35

Cc thng s Cri Cci v pzi c xc nh thng qua th nghim nn ln khng n hng i vi cc mu nguyn dng i din cho lp t yu i theo hng dn TCVN 4200-86 v cc hng dn b sung Ph lc I ca bn Quy trnh ny v iu III.3.5 v III.3.7.

Tr s ng sut (p lc) vzi c xc nh nh hng dn iu IV.6.1 (cng thc IV.6).

Cc tr s p lc zi c tnh theo ton Osterberg Ph lc II nh ni IV.6.1) nhng ch ng vi ti trng nn p thit k (iu II.2.2) v c xt n d phng ln nh ni VI.3.

VI.1.3 Chiu su vng t yu b ln di tc dng ca ti trng p hay phm vi

chu nh hng ca ti trng p za c xc nh theo iu kin:

za = 0,15. vza (VI.2)

Trong :

za l ng sut do ti trng p gy ra su Za (nu phc v cho vic tnh ln tng cng S th ti trng p cng ch gm ti trng p thit k)

vza l ng sut do trng lng bn thn cc lp pha trn gy ra su Za (c xt n p lc y ni nu cc lp ny nm di mc nc ngm)

Nh vy vic phn tng ly tng tnh ln tng cng theo (VI.1) ch thc

hin n su za ni trn v cng l su cn thm d khi tin hnh kho st a k thut vng t yu nh ni III.3.2.

VI.2 D tnh ln tng cng S v ln tc thi Si VI.2.1 ln tng cng S c d on theo quan h kinh nghim sau: S = m . Sc (VI.3)

Vi m = 1,1 1,4; nu c cc bin php hn ch t yu b y tri ngang di

ti trng p (nh c p phn p hoc ri vi a k thut...) th s dng tr s m = 1,1; ngoi ra chiu cao p cng ln v t cng yu th s dng tr s m cng ln.

VI.2.2 ln tc thi Si ni iu II.2.1 cng c d tnh theo quan h sau:


36

Si = (m 1). Sc (VI.4)

vi m c ngha v xc nh nh iu VI.2.1. VI.2.3 Trnh t tnh ton ln ca nn p trn t yu tnh ln tng cng S theo cng thc (VI.3) th phi tnh c ln c

kt Sc theo (VI.1) hoc (VI.1'), tc l phi xc nh c cc thng s v tr s tnh ton ni VI.1.2, trong tr s zi ph thuc vo ti trng p, ti trng ny bao gm c phn p ln vo trong t yu S. V lc u cha bit S, do vy qu trnh tnh ln l qu trnh lp th dn theo trnh t sau:

Gi thit ln tng cng Sgt (thng gi thit Sgt = 5-10% b dy t yu hoc chiu su vng t yu chu ln za; nu l than bn ln nhiu th c th gi thit Sgt = 20 - 30% b dy ni trn);

Tnh ton phn b ng sut zi theo ton Osterberg vi chiu cao nn p thit k c d phng ln H'tk = Htk + Sgt (Htk l chiu cao nn p thit k : nu p trc tip th k t mt t thin nhin khi cha p n mp vai ng; nu c o bt t yu th k t cao mt t yu sau khi o);

Vi ti trng p H'tk tnh ton ln c kt Sc theo (VI.1) hoc (VI .1') ty

trng hp;

Nu Sc tnh c tha mn iu kin (VI.4) tc l SS

mcgt= th chp nhn

kt qu v nh vy ng thi xc nh c Sc v S = Sgt ; nu khng tha mn iu kin ni trn th phi gi thit li S v lp li qu trnh tnh ton...

VI.2.4 Chiu cao nn p thit k c d phng ln H'tk c xc nh l: H'tk = Htk + S (VI.5)

Nh vy, cao nn p trn t yu phi thit k cao thm mt tr s S d phng ln. B rng nn p ti cao ng vi chiu cao H'tk phi bng b rng nn p thit k.

VI.3 D tnh ln c kt theo thi gian trong trng hp thot nc mt chiu theo phng thng ng


37

VI.3.1 Trong trng hp ny c kt U ca t yu t c sau thi gian t k t lc p xong nn ng thit k v p xong phn p gia ti trc (nu c) c xc nh ty thuc vo nhn t thi gian Tv nh bng VI.1.

T C

H tv

vtb

2= (VI.6) Trong :

C vtb l h s c kt trung bnh theo phng thng ng ca cc lp

t yu trong phm vi chiu su chu ln za (xem ngha iu VI.1.3)

C z

h

C

vtb a

2

i

vi

2=

(VI.7)

Vi hi l b dy cc lp t yu nm trong phm vi za (za = hi) c h s c kt khc nhau Cvi

Cvi xc nh thng qua th nghim nn ln khng n hng i vi cc mu nguyn dng i din cho lp t yu i theo TCVN 4200-86

tng ng vi p lc trung bnh vzi zi

2

+ m lp t yu i phi

chu trong qu trnh c kt

H l chiu su thot nc c kt theo phng thng ng, nu ch c mt mt thot nc pha trn th H = za cn nu hai mt thot nc c trn v di (di lp c t ct hoc thu knh ct) th H = 1/2 za

Bng VI.1: c kt t c ty thuc vo nhn t Tv ; Uv = f (T)

Tv 0,004 0,008 0,012 0,020 0,028 0,036 0,048 Uv 0,080 0,104 0,125 0,160 0,189 0,214 0,247 Tv 0,060 0,072 0,100 0,125 0,167 0,200 0,250 Uv 0,276 0,303 0,357 0,399 0,461 0,504 0,562 Tv 0,300 0,350 0,400 0,500 0,600 0,800 1,000 Uv 0,631 0,650 0,698 0,764 0,816 0,887 0,931 Tv 2,000 Uv 0,994


38

Ch l nu Cv tnh bng cm2/sec th hi v H phi tnh bng cm v t phi tnh bng sec (giy).

VI.3.2 ln c kt ca nn p trn t yu sau thi gian t ni trn c xc nh nh sau:

St = Sc . Uv (VI.8)

Trong Sc xc nh nh iu VI.2.3 cn Uv xc nh nh VI.3.1.

Phn ln c kt cn li sau thi gian t, S s l: S = (1-U) . Sc (VI.9)

VI.3.3 Da vo cc quan h (VI.6, VI.7) v bng VI.1 ngi thit k c th xc nh c thi gian cn thit phi ch sau khi p nn (bao gm c thi gian thi cng kt cu o ng) phn ln c kt cn li sau khi lm xong mt ng nm trong phm vi cho php ni iu II.2.3; t xem c cn p dng cc gii php tng nhanh ln hay khng.

VI.4 D tnh ln c kt theo thi gian trong trng hp thot nc 2 chiu (c s dng ging ct hoc bc thm)

IV.4.1 Trong trng hp ny c kt U t c sau thi gian t k t lc p xong

c xc nh theo cng thc sau:

U = 1 (1Uv) (1Uh) (VI.10) Trong :

Uv l c kt theo phng thng ng vn c xc nh nh ni iu VI.3.1,

Uh l c kt theo phng ngang do tc dng ca ging ct hoc bc thm (xc nh nh iu VI.4.2).

VI.4.2 c kt theo phng ngang Uh c xc nh nh sau:

( )U 1 exp 8T

F n F Fhh

s r= + +

(VI.11)

Trong : Th l nhn t thi gian theo phng ngang:


39

T C

thh2= l (VI.12)

Vi l l khong cch tnh ton gia cc ging ct hoc bc thm:

- Nu b tr ging hoc bc thm theo kiu vung

l = 1,13 D (VI.13) - Nu b tr theo kiu tam gic

l = 1,05 D (VI.14) D l khong cch gia cc tim ging hoc bc.

H s c kt theo phng ngang Ch (cm2/sec) cng c th c xc nh thng qua th nghim nn ln khng n hng i vi cc mu nguyn dng ly theo phng nm ngang theo TCVN 4200-86. Nu vng t yu c kt gm nhiu lp t c Ch khc nhau th tr s dng tnh ton l tr s Ch trung bnh gia quyn theo b dy cc lp khc nhau .

giai on lp d n kh thi, cho php tm dng quan h sau xc nh tr s Ch a vo tnh ton:

Ch = (25)Cvtb (VI.15) Vi Cvtb c xc nh nh ni iu VI.3.1.

F (n) l nhn t xt n nh hng ca khong cch b tr ging ct hoc bc thm, c xc nh ty thuc vo n = l/d (vi d l ng knh ca ging ct hoc ng knh tng ng ca mt bc thm) theo cng thc:

F(n) n

n 1ln(n)

3n 1

4n

2

2

2

2=

; (VI.16)

Fs l nhn t xt n nh hng ca vng t b xo ng xung quanh bc thm (lm h s thm trong vng b gim i).

Fr l nhn t xt n nh hng v sc cn ca bc thm.

Khi dng ging ct th khng xt n 2 nhn t ny (tc l xem Fs = 0 v Fr=0) cn khi p dng bc thm th chng c xc nh nh ni iu VI.4.3.

VI.4.3 Trng hp s dng bc thm lm phng tin thot nc thng ng th cc

nhn t F(n), Fs v Fr trong (VI.11) c xc nh nh sau:


40

Nhn t F (n) vn theo cng thc (VI.16) vi ng knh tng ng ca mt bc thm d tnh nh sau:

da b

2= + ; (VI.17)

Trong : a l chiu rng, b l b dy ca tit din bc thm

V d nh nn t s n thng ln v n2 >> 1, do vy c th tnh F (n) theo cng thc n gin sau:

F (n) = ln (n) 3/4 ; (VI.18)

Nhn t xt n nh hng xo ng:

Fs = (kh/ks - 1) . ln (ds/d) ; (VI.19)

Trong kh v ks l h s thm theo phng nm ngang ca t yu khi cha ng bc thm (t yu khng b xo ng) v sau khi ng bc thm; ks < kh v thng cho php ly ks = kv vi kv l h s thm ca t theo phng thng ng. Trn thc t tnh ton thng cho php p dng:

k

k

k

k

C

Ch

s

h

v

h

v= = = 2 5 ; (VI.20)

- Ch v Cv l h s c kt ca t yu theo phng nm ngang v phng thng ng .

- ds/d l t s gia ng knh tng ng ca vng t b xo ng xung quanh bc thm v ng knh tng ng ca chnh bc thm. Thc t tnh ton cho php p dng:

d

ds = 2 3 ; (VI.21)

Nhn t xt n sc cn ca bc thm:

F 2/ 3 L k

qr2 h

w= ; (VI.22)

Trong :

L l chiu di tnh ton ca bc thm (m) nu ch c mt mt thot nc pha trn th L bng chiu su ng bc thm, nu c 2 mt thot nc (c trn v di) th ly L bng 1/2 chiu su ng bc thm;


41

kh l h s thm ngang (theo phng nm ngang) ca t yu, cho php xc nh gn ng theo (VI.20) t h s thm theo phng thng ng kv hoc th nghim thm trc tip vi cc mu thm theo phng ngang (m/s).

qw (m3/sec) l kh nng thot nc ca bc thm tng ng vi gradien thy lc bng 1; ly theo chng ch xut xng ca bc thm. Thc t tnh ton cho php ly t s kh/qw = 0,00001 0,001m-2 i vi t yu loi st hoc st; kh/qw = 0,001 0,01 i vi than bn v 0,01 0,1 i vi bn ct;

VI.4.4 Trong trng hp s dng ging ct th khi thit k c th trc tip dng ton

hnh VI.1 biu th mi quan h (VI.11) vi F (n) theo (VI.16) v Fs=Fr= 0.

Hnh VI.1: Ton xc nh c kt theo phng nm ngang Uh theo Th v n

VI.4.5 ln c kt t c St v phn ln cn li S sau thi gian t trong trng hp thot nc c kt 2 chiu cng vn c xc nh nh cng thc (VI.8) v (VI.9) nhng thay Uv bng U tnh c theo (VI.10).

VI.5 Nhng ch khi d tnh ln VI.5.1 xt n nh hng ca thi gian thi cng p (ko di trong mt thi hn

nht nh ch khng phi p t ngt xong ngay) i vi din bin ln ca nn p trn t yu c th dng cch suy din n gin nh hnh VI.2 vi gi thit ti trng p tng tuyn tnh.


42

Trc ht v ng cong ln c kt theo thi gian St = Sc U vi trng hp ti trng p tc dng ngay mt lc (ng cong chm gch, ng 2 hnh VI.2)

Hnh VI.2: Din bin ln theo thi gian c xt n thi gian thi cng p nn

ln cui thi k thi cng ( thi im tc lc p xong) c xc nh bng ln ca ng 2 thi im p c mt na tc/2, trn hnh v t im 1/2tc dng xung gp ng cong 2 H, t H dng ngang gp ng dng thng ng t tc E.

Tng t, ln thi im t c xc nh xut pht t im K (ln thi im t/2 ca ng cong 2) dng ngang c N, ni ON ct ng dng thng ng t t M. Kt qu l v c ng cong d bo ln c xt n thi gian thi cng p nn (ng cong 1 qua OME trn hnh VI.1).

VI.5.2 Do mang nhiu gi thit gn ng v l thuyt v v thng s a vo tnh

ton nn kt qu d bo ln v c kt ch c s dng nh ni im II.2.5. Trong qu trnh thi cng lm th (IV.8.4) hoc thi cng thc t, phi thng qua kt qu quan trc ln thc t nh gi, iu chnh cc gii php v cc bc x l nh ni II.2.5 v IV.8.3.


43

PH LC I

XC NH TR S P LC TIN C KT pz V CC CH S NN LN CA T YU

TRNH T THC HIN : 1. Thc hin th nghim xc nh tnh nn ln khng n hng ca cc mu t yu nguyn dng ly su z theo ng TCVN 4200-86, bao gm c vic th nghim d ti sau cp ti cui cng nh ni iu 4.9 ca TCVN ni trn. Khng c dng phng php nn nhanh. 2. Da vo kt qu th nghim v ng cong nn ln e lg p (hnh 1) trong e l h s rng tng ng vi cc cp p lc p. Cng c th v ng cong nn ln ny di dng lg e lg p . 3. Xc nh tr s p lc tin c kt p :

a) Trn ng cong e lg p xc nh im A ch ti c cong ln nht

(bn knh cong nh nht). T A k ng nm ngang v ng tip tuyn vi ng cong nn ln. K ng phn gic ca gc to bi ng nm ngang v ng tip tuyn qua A ni trn. Giao im ca ng phn gic ny vi ng tip tuyn k t cui ng cong nn ln (on tip tuyn ko di) s xc nh im tng ng vi p lc tin c kt P (xem hnh 1).


44

b) Trn ng cong lg e lg p nu hnh thnh mt im gy (giao im ca hai nhnh thng c dc khc nhau) th chnh l im tng ng vi tr s p lc tin c kt (xem hnh 2).

c) Chn tr s no ln hn trong hai cch xc nh ni trn lm tr s s dng.

4. Xc nh cc tr s nn ln Tr s p lc tin c kt chia ng cong nn ln e log p thnh hai phn tng ng vi on < p (bn tri) v on > p (bn phi). T xc nh c cc ch s nn ln nh sau : a) Ch s nn ln C r on < p :

1p

p1r lglg

eeC

= trong : ep l h s rng tng ng vi p lc tin c kt p ;

e1 l h s rng tng ng vi p lc nn 1. Vic chn tr s 1 ty thuc vo thc t chu ti ca lp t i cn tnh ln. Thng c th ly 1 = 0,1 kG/cm2 tng ng vi cp p lc th nghim u tin theo TCVN 4200-86 i vi t yu; Cng c th tnh Cr theo nhnh d ti trn hnh 1.

b) Ch s nn ln Cc on > p :

p2

2p

lglg

ee

=cC

ep , p c ngha nh trn, cn e2 l h s rng ng vi p lc 2 . Vic chn tr s 2 ty thuc vo thc t chu ti ca lp t i cn tnh ln v nn chn sao cho tr s ivz + iz trong cng thc (VI.1) nm gia khong p v 2 .


45

Nu khi th nghim nn chn cp p lc ln nht ng nh ni iu 1.7 ca TCVN 4200-86 th c th ly 2 bng tr s cp p lc ln nht .

5. T kt qu th nghim xc nh p lc tin c kt cc lp t i khc nhau c th v biu p z ( su) nh hnh 3. Trn c th v ng v.z z (p lc do trng lng bn thn cc lp t yu) ng z z (p lc do ti trng p) v ng v.z+ o = f(z) kim tra iu kin (IV.5a) v (IV.5b) nh trn hnh 3. iu kin (IV.5a) v (IV.5b) nu khng c tho mn th khng nn p dng cc gii php dng phng tin thot nc c kt theo phng thng ng (ging ct hoc bc thm).

TH NGHIM NN Cng trnh : ....................................................................................

K hiu l khoan ................................ su ly mu : ............ (m)

S hiu mu : ...................... No S th nghim : ......................

p lc tin c kt : p = 0,620 (kG/cm2)


46

H s rng ban u : eo = 1.188

Ph lc I - Hnh 1

p lc tin c kt : p = 0,68 (kG/cm2) H s rng ban u : eo = 1.188

Ph lc I. Hnh 2 - Xc nh p lc tin c kt trn th loge - log p


47

(s liu th nghim nh vi hnh 1)


48

ng sut do trng lng bn thn ng sut do ti trng p ---------- ng sut qu kh ti a (p lc tin c kt)

Ph lc I . Hnh 3 - Kim tra iu kin (IV.5a)

PH LC II

TNH TON NG SUT NN (P LC) THEO PHNG THNG NG ZI DO TI TRNG NN P HOC TI TRNG PHN P GY RA TRONG T

THEO TON OSTERBERG


49

a- Ton xc nh ng sut nn thng ng do nn p gy ra trong t b- S ti trng v v d s dng ton Osterberg (trng hp ti trng ch nht s c

xem l hnh thang c t s a/z =0 0,01); Cc s trn hnh v l kch thc tnh bng m V d: b = a = 2 m b = b + a + b1+ b2 = 8 m V d s dng Osterberg 1. Xc nh ng sut zi ca im M1 :

a- Vi cc ti trng tc ng bn tri :


50

a

z

2

2 1= = v b

z

1

2 0,51 = =

Theo ton c It = 0,397

b- Vi ti trng tc ng bn phi:

a

z

2

2 1= = v b

z

3

2 1,52 = = If = 0,478

Vy zi = (0,397 + 0.478)q = 0,875q 2. Xc nh ng sut ti im M3 (ti trng ch nht) : Z3 = ( It + If )q Xc nh It khi a/z = 0 v b/z = 0,5 v If khi a/z = 0 v b/z = 1 c : Z3 = ( 0,278 + 0,410 )q = 0,688q 3. Xc nh ng sut ti im M2 (ng dng tnh ng sut do khi phn p gy ra ti im tim nn p su z ) : Z2 = ( Ilmnk Ilrsk )q

Ilmnk l ti trng hnh thang bn phi im M2 Ilrsk l ti trng hnh ch nht bn phi im M2

a- Tnh Ilmnk

az

= =22

1 v bz

= =82

4

Tra ton c Ilmnk = 0,5

b- Tnh Ilrsk

az

= 0 (tit din hnh ch nht) bz

b" a / 2

z

2 1

2 1,5= + = + =

Tra ton c Ilrsk = 0,46 Vy Z2 = (0,5 0,46) q = 0,04q Y Y Y Y Y Y Y Y Y Y Y Y


51

Y Y Y Y li li li li li li li li n=40 n=100 n=40 n=100 n=40 n=100 n=40 n=100 n=40 n=100 n=40 n=100 c kt ngang Uh % Nhn t thi gian Th c kt ngang Uh % Nhn t thi gian Th c kt ngang Uh % Nhn t thi gian Th c kt ngang Uh % Nhn t thi gian Th


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