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Phan tich vung anh hu'd'ng cua tai trong din coc ben trong ho dao trong
nen dat yeu
Ngay nhan bai: 15/10/2014 Ngay siia bai: 22/10/2014 Ngay chap nhan dang: 5/11/2014
Vo Trung Hieu, Le Trong NghTa
T O M TAT:
Cong trinh ho dao difijc nghidn ciiu nam Q u i n 8 - Tp. Ho Chi Minh tren nen dat cd ldp dSt ylu day ISm tif cao do - I m den -26m so vdi mat dat tii nhien vk cd chi s6 NSPT bSng khong. Khi tien hanh dao dat den cao trinh day dai mdng thi h^ tifdng vay cii Larsen IV c6 chuyen vj ldn lam day troi dat keo theo cac coc ong be tong cot thep dil ling lUc chong dd k i t cau ben tren bi nghieng va gay. O'ng xif cua coc trong qua trinh thi cong ho dao difcJc phan tich ngtfdc bang mo hinh Plaxis 3D vdi md hinh dat Hardening Soil. Kit qua md phdng cho thay dng xil cua cpe trong mo hinh tiiong duong vdi ket qua quan trac ngoai hien triidng. Tif do tiep tuc phan tich stf anh hifcfng ciia khdi dat dip vi chieu sau n g i m tUdng den chuyen vi cua coc ben trong ho dao. Ket qua xac dinh difpc viing ^ h hudng cua khoang each khoi dat dap den chuyen vi cua coc ben trong hd dko, chuyen vi cua coc khi ddi khdi dat dap ra xa, chuyfe vi cua cgc sau khi tang chieu dai ngam cua tildng.
Tvf khoa: Coc ong b e tong dtf ijfng life, md h i n h d i t , h o dao, chieu sau ngam tiftUng, dS,X dap, ph^ ho^i cgc.
ABSTRACT
The excavation case study is located at District 8, Ho Chi Minh City oo the 25 meter- thickness soft soil layer irom the EL -l.Om to the EL -26.0m with the SPT test N is zero. The spun concrete pile is used for foundation to support the superstructure. The existing piles inside the deep excavation were incline and failure when the foundation pit reached to 3.8m deep. PLAXIS 3D Foundation programe is used to back analyze the behavior of piles during construction stages of foundation pit. In the results, the pile behaviors during construction stages are same with in-situ observation data. In addition, the analysis the effect of surcharge load and the embedded legth of sheet pile to the existing spun piles inside the deep excavation in soft soil was carried out.
Keywords: Prestressed concrete pile, soil model, excavation, embedded length of wall, spun pile, failure.
Vo Trung Hi^u
Hoc vien cao hgc, Khoa Ky thuit XSy dyng, Trifcing Dai hgc Bach khoa Tp.HCM TSLe Trong Nghia
Giing vien, Khoa Ky thuat Xay dting, Tnfdng Dai hpc Bach khoa Tp.HCM Email: [email protected]
LDatvande
Ngay nay, nhu eau ve viee si!r dung ktiong gian ngam nhu tang ham ky thuat hoSc djch vu ciu'di cac nha eao tang, bai clau xe ngam, h6 thdng giao thong ng3m, he thdng xH ly nu'cic t h i i ngay cang gia tang trong cac khu do thj. Trong 36 c6 khong it eong trinh dUoe xay dung tren nen dat yeu, va tru'dng help cae coc ben trong hd dao m 6 bl pha hoai la sU co hay xu^t hien Cac su ed nay CO diem chung lei: sau khi thi cong phan cgc xong tien hanh cong tae dao dat hd dao thi x i y ra sU cd coc bj nghieng lech hay pha hoai, IWlgt sd nUdc tren t h ^ gicrt tien hanh thi cong hd dao trade khi thi eong coc de b i o ve coc dn dinh, nhUng no lai khdng phii hop trong dieu kien kh5ng gian thi eong chat hep vk khong eho phep dcio m d dac biet 1^ eong trinh eo nhieu tang h i m , Viec thi cong hd dao trong dSt yeu \k rat phiJe tap, khi dat yeu ehuyen vj ngang se tao ra phu t i l tren coe va khi chuyen vj qua miJc se gay moment udn I6n hcjn moment khang nilt eua coc dan den coc bi gay
Gan day cong trinh Khu dan eu 15 tang tai Quan 8, Thanh phd Hd Chi IWlinh cung x i y ra sU pha hoai eCia coc ben trong ho dao, Trong qua trlnh tien hanh thi cong dao dat de thi cdng dai m d n g t h i g a p s u c d c o c b i nghieng lech v i e h u y e n vi dau egc Icfn nhat ten den 60cm. Nguyen nhan Quae xac dinh do don vi thi eong da vSn chuyen dat trong h d dao va tap ket thanh khdi dat cao 4m va each m4p hd dao k h o i n g 12m,
Difa tren h d so k h i o sat dja chat vh sd lieu quan t r i e ehuyen vi dau coc cCia c6ng trlnh tren, t i c g i i da mo phong lai c i e giai doan thi cong hd dao bang chuong trinh Plaxis 3D Foundation.
Dua vao ket q u i phan tieh, t i c gia hieu ro nguyen nhan gay pha hoai coc ben trong ho dao va d i n h g i i do chinh xac ciia bo thong sd dau vao cua mo hlnh bai toan, Td do, tae g i i tiep tue s d d u n g bg thong so tren de phan tich sU i n h hudng eua khdi dat d i p va chieu sau ngam tudng den chuyen vj eua coe ben trong hd dao.
2. GiSi phap chdng p h i hoai coc ben t r o n g
ll.20l4^ili;[|9JX:85
h6 d t o trong nen dat y€u 2 . 1 . M& t i d u i n
Cong trinh khu d i n cu 15 tang, Quan 8 - IP- Hd Chi IVIinh eo quy mo 15 tang va 1 tang ham, sCr dung mong eoc be tong cdt thep dU ung ILTC de chdng 36 ket eau ben tren. Mat b i n g tdng the hd dao eong trinh the hien trgn Kinh 1 .Ci^ Larsen loai IV dai 6,0m dUOe diing de ch^n gi& hd dao trong q u i trinh thi eong t i n g ham. Ho dao co kich thu'dc 52.4mx33.9m, thi cong bSng bien phap dao m d va duoc g i i n g b i n g cae cgc neo phia sau tu'cmg
Hlnh2 SadoiiJingaicsii'dungphantlcti Cdc budc thi cong chinh cho hd dao:
Bu'dc 1: Tbi cong ep egc dng be tong cdt thep d u Lfng lu'e du'dng kinh 600mm dai 36m.
Bode 2:Tbi cdng tiidng cii Larsen IV dai 6m.
BUdc 3- Dao dat den eao dp -1.8m so vdi mat d i t t u nhien, 3ko den dau ti^n hanh g i i n g dau cCf den 36. van ehuyen dat qua khu vUe tap ket.
Bu'de 4: Dao dat den day dai co cao do -3.8m so vdi mat dat tif nhien 3i thi cong dai mdng.
2.2 Dac di^m dia chat
DSe diem dia chat khu vUe gom cd Idp set yeu day 25m cd so bua SPT bSng 0, ben dUdi Idp set yeu la Idp set yeu thir hai day S.Smcd sd bua SPT trung binh b i n g 3, va dadi cung la top cat min chat vUa dky 13 9m cd sd bua SPT trung binh b i n g 17.
Mgc nude n g i m each mat dat tU nhign -1.5m. Dua vao hd so khao sat dia chat edng trinh de x i e dinh eac thdng sd md hlnh dat cho mo phdng b&i toan h d d ^ o trong chuong trinh Plaxis 3D.Thdng sd sire chdng c i t hilu hieu c'vitp'lay t i i l h i nghiem 3 tiue CU. Md-dun eua dat trong md hinh Hardening Soil di/Oe x i e dinh nha sau:
Bang 1. Cae t h d n g sd d i t nen sCt d u n g trong phan m e m Plaxis 3D foundat i n
Ldp dat Thong sd
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ky
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18 18 8,64E-2 8.64E-2
28''00 0
1 1
H S / Undrained
15
8.64E-6 8,64E-6 5 6 17''00'
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1200
3600 1 0,9
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8.64E-5 8.64E-5 9.2 25<'00'
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8.64 E-3 8,64E-3 3.1 29°00'
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19,6
8,64E-6 8.64E-6 20.9 28''00' 0
30000
90000
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(c) D&i tdi khoi ddt ddp 5H
(d) Dai ldi litiSi ddt dSp 7H (e) Ddi tdi kiioi ddi d Ifinti 3, Cac trirdng tiop ddi ktioi flJit dSp trong mo hinti Plaxis 3D foundation
(f) Ddi tdi khoi ddt ddp UH
- Vdi cac Idp d i t set md-dun E^'=' = E^'^=as^, vdi s la sLfe chdng c i t khdng thoat nadc cCia Idp d a t . "
-Vdi ldp dat 3: Ckt lan bui rdi den chat vUz, ta chgn thdng sd md-dun E dUa vao B i n g cac mi^n gia trj cua mo-dun E vdi cac loai dat khac nhau [Bowles,l 988) hay B i n g cac gia tri dien hinh eCia md-dun E {Malcolm Puller, 2003)
- M d - d u n nen lai va d d t ^ i E^,'^= 3 Ej^"^
Oac trOng va thdng sd dja chat eua cac ldp dat daoc sLt dung cho phan mem Plaxis 3D Foundation trinh bSy trong B i n g 1
Vdi Idp dat dap la cat dagc chgn Lfng xCr thoat nude theo mo hinh Mohr-Coulomb va cd E'^ = lOOOOkN/ml
2.3. M d hmh phan tich
Md hinh da duoc phan tich trong trUdng hgp thuc te vdi phu tai eua may thi eong va cong trlnh l i n can dUflc lay 1^ 10 k N / m ' va each mep n g o i i tadng ea Larsen 2.6 m, dat d mat d i t tU nhien (MDTN), Ngoai ra, khi thi cong d^o, dat duge chuyen vh tap ket each hd clao k h o i n g 11 m tren
dien tich 200m' va cao k h o i n g 4 m n&n tac g i i lay b i n g 70kN/m^ Mac nadc n g i m each MDTN -1.5m. Trong trUdng hop nay ta t h i y s U i n h hadng cua khdi d i t d i p den cdc cgc b&n trong hd dao l i rat Idn, lam eho m d t sd cgc bj p h i hoai. D ^ khac phuc van de dd, chiing ta djch ehuyen khdi dat ra xa dan theo tCmg k h o i n g e i c h nhat dinh so vdi vi tri khdi dat ban d^u de p h i n tich su i n h hudng cua khdi d i t den c i c cgc trong hd dao v i eiing vdi viec d o t h i chung ta so s i n h TCVN 7888:2008 ve m o m e n t khang udn cOa coc trong cdng trinh.
Cac trudng hgp dUOc phan tich vdi k h o i n g eich tU khoi d i t d i p den t u d n g cif Larsen lan lUOt la 3H, 5H, 7H, 9H, 11H va trUdng hgp b 6 t i i khdi d i t d i p (vdi H la chieu sSu Idn nhat cOa hd dao)
Them m d t phaong an khac i^-jgc t^c g i i ti^n hanh m d phdng la bai toan \\\s ^ ^ j chieu s i u ngam tucmg, n h i m myc dicii / . , x^t k h i n i n g g i i m chuyen vj cua coc ber, tro:, h,^ d i o . T h e o s6 ligu cong trinh thUe te t h , ' jor, , , i^,^^^ ^5 e h i i u dai \k 6m, ta ti^n hanh ,, ,, ,- ^ ^ ^ . ^ ^^^
tnrdng h g p c h i g u sSu n g i m iuong dai g n r I2m-
861
"irnninir
a) Tudng ngam ddi 6m; b) Tudng ngdm ddi 9m: c)Tirdng ngdm ddi 12m, d)Titang ngdm ddi ISm;
Hlnh 4, Mo tilnli coc va tif&ng c6 chi^u siu ngam vao aSt thay doi
tri moment eiia cgc khi khdng xet tdi khdi d i t d i p xung quanh hd dao. Qua dd ta thay g i i tri moment udn Idn nhat eda egc gan tUdng g i i m xudng 3 lan khi ddi khdi d i t Kf 3H l^n 5H, v^ giam xudng 3,5 lan khi ddi khdi dat tU 3H ten 11H, Ung vdi trudng hgp khong xet t i i dat d i p lan cSn hd 3ho cho ket q u i mdmen udn Icim nhat trong coc chi b i n g khoang 60% momen khang udn cCia cgc nen eoc van cdn nguyen ven,
Pham vi anh hUdng Idn n h i t eua khdi dat d i p den ehuyen vi vh moment udn cua coc ben trong hd d^o khoang 3H vei sU anh hUdng nhd thi k^o
Hlnh 5. Bieu do the tiien hinli d^ng chuyen vi ngang ciia cocliong trudng hop dfl khdi dat dap ra xa ho dao va tniemg hop MiAag khSi dit dap khi dao den cao do -3,8m
18mnhuHinh5 2.4. Ket q u i ph&n ti'ch
Xet phuong an di chuyen khdi d i t d i p , trong giai doan dau khi d i o d i t den cao do -1.8m so vdi MEfTN coe cd xu the bi udn cong nhUng gia tri chuyen vj eiia egc edn nhd va ngi luc trong eoc p h i t sinh khdng \6n. Moment udn ldn n h i t ciia coc trong eac trUdng hgp v i n cdn nhd hon moment k h i n g udn ciia coc (M^, = 166.8 KN.m) n§n coe ehUa bj p h ^ hoai, khi ddi khdi dat ra xa thi g i i trj chuyen vi va moment cd g i i m nhung khdng dang ke. Giai doan sau khi dao dat den eao de -3.8m ta thay luc r\hy coc cd g i i tn chuyen vj k h i \6n, ddng thdi the hien ro rang sU thay ddi gi^
trj ehuyen vj Ong vdi tdng vi tri d i t t i i k h i c nhau ehuyin vj Idn n h i t cOa eoc trong trudng hgp khdi dat eich tudng 3H (theo trudng hop thUc t4, H la chieu s i u hd dao) ciia cac coc 150, cge 153, ege 155, cgc 158 l i n lUot cd gia tri 57.9em; 37.1cm;
24.9em; 23.6cm.Trong l i n xet khdi dat tai vj tri 5H Ihi chuyen vi g i i m xudng nhi^u, g i i tn Icm n h i t d i l edn 29.5em [tuong duong 50% gia tri chuyen VI eda eoc khi khdi d i t dap each tudng 3H) nhUng g i i tri nay van cdn cao. Khi tiep tuc xet den khdi d i t d i p tai eac vi tri 7H, 9H thi g i i trj chuyen vj tiep tuc g i i m xudng vdi cae gia trj chuyen vi Idn nhat eiia cgc 150 lan lugt \k 25.5em v i 22.7cm (tUdng duong 44% va 4 1 % g i i tri. ehuyen vi Idn n h i t khi t i i tai vj tri 3H) va khi x^t t a i l 1H thi g i i trj chuyen vj x i p xl vdi tnidng hgp khdng x « d^n khdi dat d i p xung quanh hd 3ko.
Vifec di chuyen khdi dat d i p ra xa hd dko se lam g i i m 3nh hOdng nhieu d i n ket q u i chuyen vi cua egc b^n trong hd d i o , g i i tri chuyen vi 1 ^ n h i t g i i m xudng 2 l i n khi ddi khdi d i t t U 3 H l^n
i
Cac tnnmg hpp dilt khoi dil d ^
S - L
Jlii ii : ^ £ L I I I
Cac tnrcmg hpp djl khoi dat dap
Hlnh 6. Bieu dd so sanh ket qui moment uon c£ia coc trong cac tru'cing hop dcii khSi dat dap ra xa ho dao ktii daodenGado-3,8m
5H va g i i m xudng 2,5 lan khi ddi khdi dat t a s H len 11H (vdi H l i chi^u s i u ciia hd 3ho).
Trong giai doan khi dao xuong -3,8m ta thay ndi lUc trong coc phat sinh rat Idn, moment udn ldn n h i t ciia coc trong trUdng hgp khdi dat eich tudng 3H cua cac cge 150, ege 153, cge 155, epc 158 t i n lUcrt cd gia trj 339,26 KN m, 125 kN.m; 67.21 kN.m va 43.65 kN.m. Gia trj cua ege 150 vUdt qua moment khang udn cua ccx: 166.8 kN.m (chiem 203%) lam cho coc bi pha hoai, cac cgc cdn lai thi g i n vcfi 80% g i i trj moment k h i n g udn ciia eoc v i n n i m trong trang thai gidi han eiia egc NhOng khi xet trUdng hcrp khoi dat d i p dat each tUdng 5H thi gia trj moment uon trong coc g i i m xudng dot ngdt chi edn k h o i n g 72,2%
moment khang udn ciia coc Khi xet trudng hgp ddi Midi dat dap ra xa dan hd dao 11H (tUc fa c i e h tudng c h i n 44m) thi moment cua coe g i i m xudng khdng deing ke v i g i i tri liic n i y x i p xi b i n g gia
dai trong pham vi r i t Idn k h o i n g 11H, Vi^c p h i n tieh nay se giiip ich cho viec bd tri vat li&u, m i y mdc thiet bi vdi mdt k h o i n g cieh h c ^ ly n h i t de g i i m i n h hudng den edng trinh
X6t trudng hop khi thay ddi ehieu sau n g i m tudng, t i l ket q u i tinh toan eua PLAXIS 3D Foundation theo md hinh Hardening Soil ta ve dugc cac bieu do chuyen vj ngang Idn nhat va moment udn Idn nhat eiia coc vdi k h o i n g cieh cgc den tUdng kh^c nhau khi chieu dai tUdng lan lUOt la 6m, 9m, 12m, 18m. Khi dao dat den eao do -1 8m (so vdi MEfTN) ta thay khi l i n luot tang ehieu dai tudng theo eic trudng hop neu tren thi ehuyen vi ngang eiia coe giSm r i t nhd.
NhUng khi dao d i t den cao do -3,8m, tU Hinh 9 ta thay khi tang chieu dai ngam tudng thi chuyen vi ngang eua cgc giam dang ke, c i c coc cd xu hudng bl udn cong va chuyen wi ciia eic eoc g i n
ii.20i4aoni[nHi 37
ifinh 7. Ket qiiS diuyen vi ngang ciia coc khi tang chieu sau ngam ti/img 9m, 12m, 18m trong giai doan dao den
Khoang cAch nrcijc d^
Hinti S, Bieu do so sanh chuyin vi ngang Idn nhat cua coc trong cac tru'dng hop tang d\m sau ng^m tUdng trong g i a [ d o a n d i a d l n - 3 8m
1
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Hlnh 9. Bieu do Moment uon ton nhat cua coc khi thay doi chieu sau ngam tirdng vao dat, trong giai doan dao den -3 8m
tudng (cgc 150,153) cd gia tri ehuyen vi Idn hon eie egc xa tUdng {eoc 155,158).
TnJdng hop dau khi tang ehieu dai ngam tudng t u 6m len 9m thi ehuyen vi ngang ciia egc g i i m , gici tri chuyen vi ciia cgc 150 la 482cm - g i i m 14% so vdi gia tr; ehuyen vi eiia trUdng hop tudng sau 6m ciia coc 150 (ege 150 la cge gan tudng n h i t vdi khoSng each JU cge den tudng la
4 J 4 7 m va eo gia tri chuyen vj Idn nhit). Khi ta tiep tuc lang chieu s i u tUdng len 12m thi chuyen vi ngang cua eic coe g i i m kha nhieu, g i i tri ehuyen VI cua egc 150 g i i m 24% so vdi gia tri chuyen vj trong trudng hdp tUdng sau 6m, tUong t y g i i tri ehuyen vi cua eic coc d xa tudng khoang eich 7.147m, 10.647m va 13.247m cung giSm. TrUdng hop eudi khi ta tang ehieu dai ngam tudng tU 6m
l e n l S m t h i t a t h S y k e t q u i iiuy.= j a nhdm coc khdng sai l#ch nhi4u • t ^ ' ^'^ ^ " 9 chi^u dki ngam tudng ISn " ^ ^ ^ 9 ^'^
tudng d i i 18m l i khdng k l n h . '
Xet ve moment udn IcJn nhat ciia egc trong c^c tn/dng hgp r\ky, ddi vdi moment udn trong coc tai vj tri c i e h tudng 4 5 4 7 m {cgc 150) khi t i n g chieu s i u ng^m tOdng 1^ 9m thi moment udn eua cgc la 263.3kN.m v i n ldn hon n h i l u moment chdng udn eda cgc M^ = 166.8kN.m nen cgc cd k h i nang bi p h i hoai. Khi tang chieu sau ng^m tudng la 12m v i 18m thi moment udn Idtn n h i t eua cgc 150 v i n ldn hcJn moment chdng udn M khien cgc bj nUt c i c cgc cd vj tri cieh tudng 7.147m cd moment trong cge x i p xl vdi moment chdng udn M„, M i e dii ta tang c h i l u s i u n g i m tudng I l n 18m nhung g i i trj moment udn trong coe g i n tudng n h i t v i n rat ldn,
Ta thay g i i tri moment u6n Idn n h i t ciia cge ed g i i m theo cac trUdng hgp tang chieu sau tadng nhung van edn Idn hOn moment khang udn eda egc nen hang coc g i n tUdng vSn cd k h i nang bj p h i hoai. Phaong i n tang c h i l u s i u ngkm tudng l i khdng hieu q u i .
S . K c f t l u i n
TCr k i t q u i md phdng b i i t o i n b i n g p h i n mem PLAXIS 3D Foundation theo md hinh Hardening Soil theo 2 phuang i n ddi khdi d^t d i p va tang c h i l u sau n g i m tudng, Ta t h i y vile di chuydn khoi d i t d i p ra xa hd d^o se lam g i i m i n h - h u d n g n h i l u d i n ket q u i chuydn vi eda coc b^n trong hd 3ko, gid trj c h u y i n vi Idn n h i t g i i m xudng 2 lan khi ddi khdi d i t tU 3H len 5H va g i i m xudng 2.5 l i n khi ddi khdi dittCrSH len 11H {vcfi H la c h i l u sSu eua hd d i o ) . Pham vi i n h hudng ldn n h i t eiia khdi d i t d i p den c h u y i n vj v i moment udn eua egc ben trong hd dao k h o i n g 3H v i sU i n h hudng nhd thi keo d i i trong pham vi r i t Idn k h o i n g 11H. Viec p h i n tich n i y se giup ich cho viee bd tri v i t lieu, mdy mdc t h i l t bi vdfi mdt k h o i n g c i e h h ^ 1;^ n h i t de g i i m i n h hadng d i n edng trinh.
Viec t i n g chieu sau n g i m tadng n h i m g i i m chuyen vi eiia cgc ben trong h6 dko cd hieu q u i khdng cao, can p h i i xem xet tinh kinh te khi sd dung g i i i p h i p nay.
LCftCAMON
N g h i i n cUu n i y duge t i i t r g bdi Dai hgc Qudc gia Thanh phd Hd Chi Minh (VNU-IHCM) trong khudn khd d4 t i i ma sd C2013-20-13.
TAIUCUTHAMKHAO
[1]. Vo Trung Higu. 2013. "Phan tfdi sU plia hoai cua coc iien trong ho dao s i u trang nen dai ye'u d khu v w T p H3 O i l Minh", Luan van Thacsi,{)aihocBldi Khoa-€KQGTp,Hr ,f/n„\f
[21. Hoang Xuan Hung, 2011.''Phar ho dao sau vdi coc ong^ Luin van Thac s u » Tp.H6ChiMinh
[3]. Kok, S.T„ Bujang, B.K.H,, JamoJuddm, andGue,Si.(2009-Acceptedforput)liQiion) A u s e s i u d u f ' ' pilesfeiiureinopenexiavafen.DFIJoumaUQl.j Uo 2 ' " ' ^ ^ ^ ' ^
•yen i n h hudng ciia ''achKhoa-eHQG
. ' ^ • " h d S a l e h , ) , ,
