Cong trinh Khoa hoc
PHAN TICH iTNG XtJ* CUA NEN MONG D U * 6 N G H A M BI/OC GIA CO B A N G H E COC XI MANG D A T
TS. TRAN THE TRUYEN KS. TRAN NGpC HOA ThS. CHU VIET BINH
Trir&ng Dai hoc Giao thong Van tai Tom tat: Bai bao nay se gop phan phdn tich dac diem ung xu cua nen ddt yeu dugc gia CO bang he cgc xi mdng ddl (XMD) phia dual nen mong duang ham. Mo hinh phdn tich phi tuyen bang phuang phap phdn tie huu han dugc thyc hi?n vai cdc so H$u thiet ke hinh hoc vd dia chat cua mot so du an da dugc dp dung a Viet nam nhu ham chui Kim Lien, ham duang ho tren dai Id Thdng Long. Ket qua linh loan sS lam ro truang irng .uidt. bien dgng vd chuyen vi cua nen ddt dual tdc dgng cua tai trong khai ihdc phia tren
Summary: This article contributes to analyse the behaviour of tunnel foundation on soft soil improved with sod cement columns. A nonlinear model by finite element method is carried out with geometrical and geotechinical characteristics of some projects in Vietnam like Tunne Kimlien tunnel, tunels on Thang Long Avenue. The results will clarijy stress, strain and displacement fileds of tunnel foundation under the action ofsevice loadings.
1. D A T V A N D E
X u ly nen m o n g d u a n g h a m d e d a m b a o o n djnh lun ciia nen c o n g trinh y e u cau bat bugc doi v a i c o n g trinh tren dia chat yeu. N e u khong xir ly tot se x a y ra hien t u g n g lun nen m o n g keo t h e o s u niit, h o n g v a sup do c o n g trinh. CJ n u o c ta, van d e xu' ly nen m o n g dutrng h a m dS d u g c t h u c hien bang c a c giai phap khac nhau t u o n g t u n h u khi xir ly nen mong d u a n g d a p cao tren dat yeu. Mgt trong so d o la giai phap gia c 6 nen dat yeu bang he cgc xi mang dat, hien da d u g c sir d u n g k h a rgng rai v a i m u c dich tang c u a n g kha nang chju tai c h o nen m o n g d u a n g ham; c6 the ke d e n m g t so d u an n h u ham chui K i m Lien, ham d u a n g b g tren dai Ig T h a n g L o n g , , . . So v6i mgt so giai phap gia c 6 dat yeu khac n h u c g c cat, coc da, bac t h a m , . . . giai phap sit d u n g he cgc X M D d u g c danh g i a la c 6 hieu q u a gia c6 tot h a n , dac biet la khi tang dat yeu t u o n g d6i day. T u y nhien, mgt so s u co c u n g d u g c ghi nhan lien quan den n u t ciia mat d u o n g ham bang be tong cot thep, dieu nay mgt phan c 6 nguyen nhan d o s u lun khong deu c u a phan dat yeu va phan cgc X M D phia d u a i n8n sau gia c 6 . S u lam viec d o n g thoi ciia c g c X M D va dat yeu sau gia c6 la van de m a neu chi thuan tuy tinh toan theo q u y trinh thi khong t h e nam bat d u g c . C a n thilt phai CO c a c phan ti'ch chi tiSt sir d u n g p h u a n g phap so v a c a c mo hinh phi tuyen wk irng xir ciia vat lieu d e m o ta t r a n g thai irng xir ciia nen dat sau gia c 6 . Bai bao nay se gop phan phan tich dajc diem i m g xir ciia nen d a t y e u d u g c gia c6 b a n g he cgc X M D phia dudi nen m o n g d u o n g h i m . T r a n g thai irng s u i t , bien d a n g ciia nkn d i t d u g c phan tich bang p h u a n g phap phan tir huu han la mgt tham chieu quan trgng cho c a c ho s a thiSt kS von chii y8u d y a tren cac c o n g thirc c h o san trong mgt s o lieu chuan thiet ke c u a cac n u o c .
2. B O T R I H E C O C X I M A N G D A T G I A C O N E N DUOfNG H A M
Tiiy theo m u c dich sii' d y n g c 6 the bo tri cgc theo c a c s o do Icriac nhau. Hai dang bo tri c g c dat xi mSng diSn hinh nhat khi gia c6 nen dat trong xay d u n g nhn d u o n g tren dSt ySu la
Tap chi KHOA HOC GIAO THONG VAN TAI So 44 - 12/2013
Cong trinh Khoa hoc
dang bo tri tarn giac va dang bo tri vuong goc (hinh ® @ ® ® W ]). Rienga Viet nam, so do vuong goc dugc sir dung ^ A ® S trong hau het cac truang hap can gia c6 nen mong -»
trong cac du an xay dung giao thong.
®
tanrf
Mat cat ngang nh duang him c6 gia c6 bang ^J)' ^..^ ^^ ^. ^ j ^^. ^.^^ ^^^ ^- ,„^.„g.
cgc xt mang - dat dugc bi6u dien nhu hinh 2. He cgc (a). Sa dd hoa mar. (b) Sa dd song .song xi mang dSt c6 thi dugc bo tri theo so do coc ma sat M6 hinh xdc dinh dieu kien dinh bdm hoac cgc chong tiiy theo dac diem dia chat ciia cac lap
dat tot phia duai tang dat yeu. Neu dat nen tot thi he cgc dugc xem la coc chong, neu khong thi dugc xem la he cgc ma sat.
3. PHAN TiCH iTNG iTNG XU" NEN MONG DirONG HAM
Bai toan tinh toan thi^ ki gia c6 nfin ddt ylu ^'"'^^'f^'% . , . (f')^lV""'^' . Hum 2. Giai phap coc chong bang he cgc dat gia c6 xi mang noi chung va gia c6 hoac cac ma sdi nen mong duong ham noi rieng can thoa man cac dieu kien ve cuang do. ve bien dang cung nhu yeu cau thoat nuac. Cho den nay, viec tinh toan he cgc xi mang - dat chii yeu dugc thuc hien theo cac du thao quy trinh thiet ke trong nuac hoac nuoc ngoai [6], [8]. Tuy nhien, cac ket qua thu dugc chiva that su du do tin cay. dam bao cho chu dau tu va nha thau hoan toan yen tarn trong qua trinh thi cong va khai thac. Co dieu nay la do cac tiep can tinh toan khac nhau v6i cac gia thiet khac nhau dii dua den cac ket qua nhieu khi c6 su khac biet dang ke. Cac tinh toan bang phuong phap so chua duoc su dung nhu la cong cii hu'u ich nham kiem cluing ket qua tinh loan theo quy trinh, tir do c6 cac de xuat ve thiet ke bo tri he cgc hgp ly. Nghien cuu nay se tap trung vao viec phan tich ung xir ciia nen mong duang ham sau gia c6 bang he cgc xi mang dai vdi cac mo hinh phi tuyen vat lieu cung nhu mo hinh bai toan phii hop.
3.1. Cac phu'O'ng phap tinh toan
3.1.1. Phinmg plidp linh tloi dejc trirng ca ly ciia vat lieu
Trong phuong phap tinh toan nay, nen dat sau gia c6 bao gom dat va cgc se dugc quy dfii thanh 1 nen tuong duong c6 cac dac trung co ly va hinh hgc dugc tinh theo cac dac trung ciia nen dat yeu (nen) va ciia cgc xi mang - dat (cgc). Cac tham so tuong duang bao gom mo dun dan h6i tuong duo'ng E|j, he so dinh ket Cn|, goc ma sat trong <p,j, trgng luong rieng ciia dat YIJ dugc: (p,(| = m(p^ut + (I- m)cp„e,i: C,d = mC^,K + {1- m)C„£„; E„i = mEt^,^ + (1- iTi)E„i„: ym = my,j^ + (1- m) Y„eii- Voi: ni = A^„t / Ano,,. A^IH. la tong dien tich cgc xi mang dat. A,,;;.,, la dien tich dat nen duac gia c6.
Nen dat tinh doi vdi cac dac trung co ly nhu tren se dugc xem nhu la mgt nen dSt d6ng nhat. Neu tang dat yeu co nhieu lop khac nhau thi cac dac trung linh doi se dugc quy doi cho m6i lap dat rieng biet. Mgt khi da quy ve nen tinh doi, hoan toan co the diing bai toan biln d^ng phang de mo phong tinh toan; khi do nen dat dap va nen dat \eu dugc xem xet tren mat phang cat ngang va vuong goc vai tim duong ham. Phuong phap tinh doi nay co thi diing de phan tich irng xii" ciia ca nhom cgc dudi duang liam.
Tap chi KHOA HOC GIAO THONG \ AN TAI S6 44 - 12/2013
Cong trinh Khoa hoc 3.1.2. Phuffng phap xem xet su lam viec ctpc lap iucrng dot ciio coc XMD
De mo ta su lam viec cua rieng re ciia nhom cgc gia co trong moi truong dat yeu, can thiet phai xet su lam viec cua cac cgc XMD theo cac phuang khac nhau. Phan tich khong gian 3D la hgp ly nhat de diing mo ta ung xir ciia nen dat y^u sau gia co. Tuy nhien, bai toan 3D kha phirc t^p, thai gian tinh toan lau. Khi ap dung tinh toan phan tich anh huang ciia cac tham so dau vao den ling xir ciia nin dat gia c6 thi phuong phap nay khong tien dung.
Nhieu tac gia c6 dk xuat tinh toan ling xir ciia he cgc lam viec rieng re vai dat yeu bang mo hinh bien dang phang; tuy nhien, mo hinh nay khong co tinh tong quat, chi dung vai mat cat cat ngang qua tim cac cgc XMD.
Mgt mo hinh phan tich dugc mgt so tac gia tren the gioi sir dung trong phan ti'ch nen dat yeu gia c6 bang he cgc XMD la mo hinh d6i xirng true [4], [5]. Mo hinh nay mo ta su lam viec dong thai ciia cgc xi mang dat va phan dat yeu xung quanh cgc. Khi do 1 cgc dai dien se dugc tinh toan voi viing dk xoay tron xung quanh cgc. Mo hinh doi xirng true dac biet phu hgp voi viing dat y6u can gia co co kich thuoc Ion. Viec tinh toan dien tich d4t y^u lam viec xung quanh 1 cgc XMD dugc tien hanh bang each quy doi dien tich xung quanh cgc ve mot hinh tron co dien tich tuang tu.
3.2. Mo hinh vat lieu
Cgc xi mang dat c6 do cirng kha Ian so voi dat yeu, vi the bien dang ciia cgc so vdi dat yeu la nho hon dang ke. De mo ta ling xir ciia cgc XMD, c6 the sir dung cac mo hinh co hgc danh cho be tong cap thap hoac dat da cirng. Mo hinh ling xir dan hoi tuyen tinh co th8 ap dung trong trudng hgp nay, tuy nhien se khong the hien dugc dac diem pha huy ciia cgc khi tai trgng ben tren qua Ion. Neu ham lugng xi mang Ion, keo theo cudng dg ciia vat lieu xi mang - dat Idn, mo hinh phi tuyen ve pha huy don be tong co thS ap dung hgp ly. Trong da so trudng hgp, vat lieu xi mang - dat co nguy co pha huy deo nhieu hon pha huy don, khi do, mo hinh dan deo tuyet doi dugc ap dung hgp ly. Mo hinh deo Mohr - Coulomb la mo hinh kha thong dung, co tinh tong quat CO the ap dung trong cac phan tich so bg, gSn diing; cac so lieu dau vko it va de xac dinh bang thuc nghiem.
Mo hinh Mohr - Coulomb cung cd the ap dung hgp ly cho dat yeu, dac biet cho cac tinh toan nhanh. Tuy nhien, de phan tich chi'nh xac ung xu ciia dk yeu c^n thiet phai sii' dung cac mo hinh vat lieu dugc phat trien rieng cho loai dat nay, dac biet la phai xet den su co ket va tir bien ciia dk theo thai gian.
Mo hinh dan deo tuyet doi cGng ap dung tot de md ta ling xu ciia cac lop dat tot bao gom lop dat cirng phia dudi tSng dat yeu hoac lap dem cat phia tren dau he cgc XMD. De cd do chinh xac cao han cd the sir dung cac mo hinh cho cac loai dat hoac da cung vdi cung co dang huang.
Vdi phan ket cau duang ham bang be tong phia tren phai sir dung cac mo hinh irng xu vat Ii?u be tong. Mo hinh dan hdi ap dung dugc trong trudng hgp bi8n dang ciia dudng ham nhd;
trudng hgp dudng ham liin nhieu va bj niit can thiet phai sir dung mo hinh phi tuyen ve pha huy don hoac phi tuyen deo de mo ta co che pha huy ciia dudng ham.
T^p chi KHOA HOC GIAO THONG VAN TAI So 44 - 12/2013
Cong trinh Khoa hoc 3.3. Vi du tinh toan 3.3.1. Mo td bai toan
Kk cau hSm dan (hkm hd) ciia h^m chui dudng sat (Km7+358 tren d^i 16 ThSng Long) dugc xay dung tren nSn dk yeu dugc gia cd bSng he cgc xi mang dk (phan ham kin tua tren mong la he cgc ep BTCT 35x35 cm). Doan hSm dan xem xet c6 he coc XMD duong kinh 0,6m dugc bd tri theo hinh vuong kich thudc 1,6 m x 1,6 m; chieu dai coc la 15,6 m; khoang each cgc thay doi theo cac doan ham la 1.2: 1,4 va 1,6 m.
Bang I. Cdc dgc [rung co' ly cua dia chdl khu vuc hdm xem xet
Vai li?u Dat nen D3t y€u Lop d^m ckt
Cgc XMD
Mo dun dan h6i E (Pa)
5E6 fl.78E6
2E8 I.75E7
He so Poisson, u
0.3 0.35 0.2 0.2
Khoi lircmg rieng. y (kg/m')
I.85E3 I.-54E3 2.4E3 I.9E3
Goc npi ma sat, tp (")
25 7 30 30
He s6 kat dinh. C (Pa)
1.25E6 I.18E4 1.95E6
•i 75 E6 He so gian
no, V) 0 0 0 0 Vi pham vi gia cd nen dat yeu tuong doi rpng va deu nen mo hinh doi xii'ng tryc se dugc diing de phan tich irng xu ciia nen mdng dudng ham dan sau gia cd. Ung xir ciia cgc xi mang dat, cua Idp dem cat dudi mdng hSm, cua dat y8u va ciia n^n dat tot phia dudi dugc md ta biing luSt phi tuyen dan deo tuyet doi Mohr - Columb vdi cac dac trirng dja chSt nhu mo dun dan hoi, he so ket dinh, goc ma sat dugc lay phii hgp vdi moi loai dat giong nhu so lieu dja chat ciia du an nay (bang I). So dd tinh toan va ludi phSn tu hiiu han dugc mo ta nhu tr6n hinh 3a va 3b.
Lien ket gifra cac phan vat lieu khac nhau dugc gia thifit la lien tuc.
C-BHSV^I 3
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T ~ .... P h i l dli tut pku
• <"> . . "" M (dl Hml, 3. Sa do Imh dai Arraj; Irvc (a), Imi phdn lu him han (b). phdn b6 x/i do lun (c) viAngs.
phuang Ihang diing cua nm duang him sou gia cS
Tap cW KHOA HOC GIAO THONG VAN TAI S6 44 - 12/2013
Cong trinh Khoa hoc Ung xir cua nen mong duai dudng ham dugc phan tich do tac dgng ciia tai trgng phia tren truyen xuong. Cac khoang each cgc 1,2; 1,4 va 1,6 m Ian lugt dugc danh gia nham xem xet anh hudng den do lun cua phan cgc XMD va phan dat yeu phia dudi mdng.
3.3.2. Kit qua tinh loan va nhan xet
Tren hinh 3c va 3d la bieu do phan bd dg liin va irng suat theo phirong thang dung ciia phan nen mdng phia dudi nen dudng ham. De dang nhan thay su khac biet ve do lun trong phan cgc XMD va phan dat ySu. Phan cgc XMD chju hdu h^t cac tai trgng phia tren truyen xudng vi cd dg cirng Idn han, vi the cd su chenh lenh ve irng suat kha Idn trong phAn cgc XMD va phan dat yeu; viing cd nguy ca bj pha huy deo Idn nhat la viing tiep xiic giua cac dau cgc vdi cac Idp dat phia tren va phia dudi. Phan bd iirng suat va chuyen vj thang dung kha deu trong phan dat tot phia dudi Idp dat yeu.
Inn -0.15 (m)
i
1
"' •
— • — -
*
- DM = -0.10
- D M =-0.15
- D M = - C 3 0
- K h o i n g c i d i tinh ttr tim coc XM&<m) - (a)
-0.26 D6 1 (•»)
1.20 1 30 l.flO 1 5 0 1.
U i o i u g cich c^c (m)
* —•—Smax CXMD
1 —•—Smax €>at yeu
50
Hlnti 4. Lun cua phdn cac XMD vd phdn ddl yeu (m) theo da lun cua day mdng duang hdm
Tap chi KHOA HOC GIAO THONG VAN TAI So 44 - 12/2013
Cong trinh Khoa hoc
Tren hinh 4a la bieu do do liin cua phSn cgc XMD va phin dat yeu d cao do day Idp dem cat theo do lun ciia day mdng dudng ham Hinh 4b la biSu dd do liin ciia Idn nhat ciia phan cgc XMD va dat y6u theo each bd tri ludi cgc XMD (1,2 ; 1,4 va 1,6m). Cd thi thSy rang, khi do liin cua day him mdng ham tang len thi chenh lech ve do liin giu^a hai phan cgc XMD va dat yeu cung tang len. Khi khoang each cgc tang len thi ca phSn cgc XMD va dat ySu deu tang do liin, tuy nhien gia tang do Iiin phan dat yeu la nhanh hon. Do liin ciia cgc va dat cd xu hudng deu nhau khi khoang each giiJa cac cgc giam.
5. KET LUAN
Giai phap gia cd nen dat yeu dugc gia co bang he cgc xi mang dat da dugc sir dung nhieu trong gia cd nen mdng dudng ham. Dac diem irng xir cua nen dat sau gia co dudi nen dudng ham la van de chua dugc quan tam nhieu. Nghien ciru nay da chi ra dac diem ve trudng irng suat, bien dang cua nen gia co khi tach rieng su lam viec tuong doi giira cgc va dat yeu. Vdi cac viing gia cd rgng, mo hinh doi xOmg tryc vdi cac md hinh phi tuyen vat lieu hgp iy cho phep md ta dac diSm irng xir cua nen gia cd tuong ddi chinh xac. Kk qua nghien ciiu nay cd the diing lam ca so tham khao cho cac tinh toan nen dat ySu gia co cgc xi mang dat noi chung va dudi dudng ham noi rieng ben cgnh cac tinh toan thiet ke theo cac quy trinh thiet ke.
Tii li^u tham khao
[ 1 ]. Hdsadydn ma rgng vd hoan thien duang Ldng-Hoa Lac
[2]. Huang, J., Han. J., and Porbaha, A. Two and Three-Dimensional Modeling of DM Columns under Embankments. GeoCongress: Geotechnical Engineering in the Technology Age. 2006.
[3]. Kitazumi M. Terashi..M, The deep mixing method: Principle, Design and Construction, Swets &
Zeitlinger Publisher, 2002
[4]. Navin, M. P. Stability of Embankments Founded on Soft Soil Improved with Deep-Mixing- Method Columns, Ph.D. dissertation, Blacksburg, VA, 2005
[5], Paulo. V.O, Joao. LP. P. Antonio.A SC. Numerical analyisis of an embankment buit on soft soil reinforced with deep mixing column. Computers and Geotechnics 38, p566-576 (2011).
[6]. Quy ph^m kj thu§t xir ly nin mong - DBJ08-40-94, Tieu chutn TP Thugng Hai, 1994.
[7]. Smith, M. E. and Filz, G. M. Settlement of Column Supported Embankments. VTRC, 2006.
[8]. TCXDVN 385: 2006 "Gia c6 nfin ddt y^u bSng tru dk - xi mSng".
[9], Venda Oliveira PJ, Lemos L/L. Numerical analysis of an embankment on soft soils considering large displacements. Comput Geotech 2011;38:88-93.
[\0].Zheng JJ, Abusharar S(V, Wang XZ. Three-dimensional nonlinear finite element modeling of composite foundation formed by CFG-lime piles. Comput Geotech 2008;35:637-43 •
Phan bien: TS. V\h Lan Huong
Tap chi KHOA HOC GIAO THONG VAN TAI S6 44 - 12/2013
