KHOA HOC & CONG NGHE
Tdng quan
ve danh gia sut lun mat dat do khai dao ngam
ThS. Phan Tu- Hmyni
T o m tat Hd Noi va TR HCM la hai dd thi 16n cd cao do tti nhien tiidng doi thap va d l bi ngap lut, dac biet la khi mifa ldn hoac trieu ciifdng. Hien cac do thi nay dang trien khai cac di^ dn difdng sat tren cao (mdt s6 doan di ngam) va tau di^n ng£m (TDN). Viec thi cdng vh sii dung cdc cdng trinh dd lam thay doi mdi triidng dia chat, dan den hien tifdng sut lun mat dat. Neu khong cd sU tinh toan va phong ngifa, hidn tUdng nay d§ gay pha v3 si^
can bang cua he thong ha tang ky thu^t do thi vd quy hoach trong khdng gian v6n rSt yeu kem nhif hien nay.
Do vay cdng tac dii bao hien tiidng siit lun mat dat do khai dao cong trinh ngam (CTN) Id h^t suCc can thiet, nham diia ra c&c bien phap phong ngiia, giam thieu cac tac hai cua hien tiiang nay gay
Abstract Ha Noi and HCM city are two large urban high natural levels are relatively low and prone to flooding, especially when heavy rains or high tides. Currently the municipality is implementing the project on the high rail (underground passages) and subway. The construction and use this project that changed the geological environment, leading to land subsidence. Without the calculations and prevention, this phenomenon easily disrupt the balance ofthe system infrastructure in urban and spatial planning which is very weak at present.
Therefore forecasting land subsidence phenomenon by underground excavation IS essential, in order to take measures to prevent and minimize the harm caused by this phenomenon.
ThS. Phan TvHie&tig Bp mdn Dja ky thugi. Khoa Xdy dimg.
DT 0913 532 322
1. Ddt van de
Vipc xdy dyng cdc cdng trinh ndm sau trong ldng d i t Id m{
trong nhu-ng bipn phdp dugc ua chudng nharn giai tod sy dfini due dan cu vd trd thanh mpt xu hudng tat yeu. Cdc nudc tiSi t i l n tren T h i gidi dd thyc hign nhieu CTN cho cdc muc dich ktjl n h a u n h u h l m n g a m , TDN... Viec xdy dyng cac cdng trinh do Sl d i n d i n hien tugng sut ldn mat dat d phia tren, ddc bidt la klii vyc cb nen d i t yeu vd kdm on dinh. Ti> dd phd vd sy cdn bini cua hd thdng hg tang ky thugt dd thj vd quy hogch trong kh6rj gian nhu gay nggp ung cyc bp, rdi logn hudng cCia hp thing thoj nudc, thay ddi cao db dja hinh, phd vd ket cau hd thdng ha l^ri!
nhu hp thdng c l p thoat nudc, xu ly nudc thai...
1.1. Phutmg phdp xac djnh dg lun be m^t
Khi khai ddo CTN kin, tren mat dat cd the xuat hipn nhung hi syt ldn, dat dd tren ndc h i m bj bien dgng vd pha huy. Hi§n tu^tli ndy xdy ra khi dat da phdn tren ndc ham kem dn djnh, CTN phSi bd gan mat dat. Neu dat da tren nbc CTN cb dp ben, bp on ^nl cao thi hidn tugng ndy khdng xay ra hope lun khdng dang M Hign tugng syt lOn mgt dat gdy mat on djnh cho cdc cdng trlnl xung quanh vd ngay cd doi vdi cbng trinh khai ddo nglm, dac bi^
Id khi cb sy tap trung nudc mgt chdy xuong.
D l xdc (^nh dp lun b l mgt, cd nhieu phuang phdp khdc nhai nhu theo ly thuyet dan hdi, p h l n t u huu hgn, bdn kinh nghipm,., cua nhilu tdc gia nhu Schmidt-Peck, Cording-Hansmire Atlkinson-Potts, Attewell, O'Reilly-New,... Dudi ddy xin gidi thi$i phuong phdp bdn kmh nghigm md hien tgi dang sCr dyng rOni rai nhat cua tdc gid Schmidt-Peck (hinh 3). Phuang phdp ndy li gid thuyit dudng cong lun theo phuang trinh (ggi Id dudng coni Gaussian) Tai tim h i m cho do iun Idn nhat (S^g^), dd liin gidn d i n khi cdch xa tim dudng h i m . Dp lun cua mpt d i l m b i t ky ntii sau:
L 2i'
Trong dd:
Smax - bien dgng Idn nhat tgi tim ham.
X - khoang cdeh tCr tryc ham d i n d i l m tinh lun S the phuang ngang.
S - dp lun be mat tai d i l m tinh.
i -khoang cdch cua true h i m den diem udn cong cii dudng bien dgng lun.
ZQ • dp sau cua tim ham.
R - bdn kinh cua ham.
^ Theo each tfnh tren, trong phgm vi phdn bd cua i, mgt dit c dp lun ldn. Od lun gidm dan t u i den 2i, 3i. Mbt sd lugng dan ke cac nghidn cdu lidn quan den quan t r i e ngodi hipn tardn vd kilm tra md hinh ddnh cho vi^c xdc djnh Smax vd i cho dii
28
TAP CH KHOA HOC K I E N T R O C - X A Y DUTIGpn d i t nen khdc nhau vdi d i l u kign khdng cb tai trgng hu them tren mgt. K i t qua xdc djnii gid trj i t u nhilu nhd ghidn ci>u khdc nhau dugc t h i lii^n trang Bdng 1.
;ang 1. Cdc phuvng phap xdc dinh gia trj i Tdc gid
Atkinson
& Potts (1979)
Attewell (1977) Clough &
Schmidt (1981) Mair (1993)
O'Reilly &
New (1982)
Peck (1969)
Gid tn i (• = 0.25(zo + R) vdi cdt xop.
i = 0.25(1.5Z(, + 0.5R) vdl cdt chgt hogc d i t set qud co kit.
R IR
i R^[iRj
0.8
i-OSz,
i - 0.43zii + LI v6i a l t dinh.
i-0.2S2„-0.l2 v&i d i t rtr'l.
R [2RJ
vdi n = 0.8 d i n 1.0
Ghi chCi
Co sd tu quan trie hien tn/dng va thi nghidm mb hinh.
Co sd tu quan trie cac CTN tai Anh Ca sd tu quan trdc cdc CTN tai Anh Co sd tu quan trie hi§n trudng tren the gidi vd thi nghiem ly tdm Ca sd td quan trie cdc CTN tai Anh
Ca sd tu quan trie hien trudng
1.2. XAc dinh d^ iUn be mat Icm nhat
Dg iLin b l mat Idn nhat S^^^ dugc nhieu nhd khoa hoc lua ra vdi nhieu phuang phdp tinh khdc nhau.
Atkinson vd Potts (1977) cung da xac djnh dugc quan le giua dg lun Idn nhat (Smax) vd t h i tich vung dat bj lun :u6ng (V^) tren mdt dan vi chilu ddi nhu sau:
Be ddnh gia muc dd dat bj mat di do lun, ngudi ta lung hp s6 G (%). G Id t^ s6 giua the tich p h l n mat dat ij lun x u i n g (VJ vd the tich p h l n dudng ham trong d i t Vg^c)- Bdng 2 vd 3 dudi day t h i hi$n gid tn G trong d i t linh vd d i t rdi.
Ngodi ra. chung ta cd t h i xdc djnh gia tri S^^^ theo dng thuc cua tdc gid Mair (1993):
_0.313K^(2J?)^
Trong dd:
VL - T i n t h i t d i t , Id t j s l giua the tfch d i t m i t di vd the ch 1 mdt chilu ddi h i m .
K - bdn kinh cua h i m .
Hinh 3. Mo hinh tinh lun be mat theo Peck (1969)
Hinh 5 la k i t qua so sdnh dudng cong lun b l mdt theo cdc phuang phdp tinh khac nhau. Theo k i t qud dd, phuang phdp cua tdc gid Clough & Schmidt cho dp lun Smax Ibn nhat vd dp lun giam nhanh khi lan ra xung quanh.
Ngugc lai, phuong phdp cua tac gid Mair & Attewell cho dp lun Sfnax nhd nhat vd dp lun giam chdm khi lan ra xung quanh.
S 6 18-2015 ? y
KHOA HOC & CONG NGHE
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Bang 2. Hp so G trong dat dinh theo O'Reilly vd Nn (1982)
i 13 IB 20 M 18 33
- - - -
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, -
•
V .
• z'
^
• 'r
i-a.IBZ~0.l3 ^ , y y
M fraMtw Mth
Dilu kien dja ting
Set cdng nut ne
Cdc tram tich dbng bang
Cac tram tich dbng bang
Cac tram tich set pha tre (C„=10-40KN/m2) Cdc tram tich set pha tre (C^=10^0KN/m2)
Cdng nghp thi cbng CTN
Cb chong dd hoac khbng (Shield or none) Cd chdng dd trong khi t y nhidn (Shield in free air)
Cd chong da trong khi nen
Cd chbng dd vdi khi ty nhien Cd chong da trong khi nen
G(%) Ghichij
So li^u ddng tin ciy, thbng
= 1 - 3 %
Khf nen su di,ing de dtlu khiln sy djch chuydn dit Kh6ng thich hpp Bdng 3. He sd G trong dat r d i theo O'Reilly vd ^ew
1
(1982)
Hinh 4. Mdl quan he giu'a i vdi zO (Reilly -1982]
Di4u ki0n dia tang c a chat Cat chat vL^a
G (%) 0.5-1.0 1.0-2.5
ChLing ta se thay ket qua d y bdo cua cdc Tdc gid la cd nhau. Nhung logi dat da dd khdc nhau v l dp bin, d§ fln sy khde nhau, neu d tdm liin nhilu thi lun xung quanh b l djnh, muc dd c6 k i t (ke cd cung thdnh phan, trgng thji) mgt gidm di vd ngugc lgi. Vi$c lya ehpn phuang phdp tinh se cd i>ng xu khdc ntiau vdi cung mdt tdc nhan gdy biSn phu hgp khdng dan gidn, can cd sy quan tdm thich dang dgng. Nhung van d l nay chua dugc xem xet ey thi trong cua cdc nhd khoa hoc. mb hinh tfnh todn.
2. Nhgn xet ve khd ndng dp dung tai Viet Nam Theo cdc phuang phdp tfnh toan d tren, phan ldn k i t qud d i u dua trdn quan trie thyc te hoac tren md hinh D i l u dd cd nghTa Id k i t qud tinh todn dp lun be mgt khi thi cbng CNT d i u cb qua trinh dy bdo, quan trie. Ti> ket qud so sdnh tu nhilu cbng trinh khac nhau, cdc Tac gia phdn tich vd tdng hgp lgi, t d db dieu chinh Igi cdng thuc ly thuyet cho sdt vdi thyc t l ,
Tuy nhien n l u su dyng cdc phuang phap tinh dd tai Vipt Nam. k i t qud tfnh toan khbng phCi hgp vd chac chdn cb sy sai lech. Ly do Id dilu kidn khi hau vd mbi trudng dja chit khdc nhau. Nhung nguyen chfnh nhan d i n den sy sat Idch db nhu sau:
- Dat da cb nguon gdc khdc nhau: Qua trinh hinh thdnh d i t da tgi Hd Nbi vd TP HCM rat phuc tap, chii y i u Id t r i m tich, b-lm tich bien, trim tfch hb d i m l l y . . T u db d i n den dia ting gbm logi dat da cb thdnh phln, tinh chat ca ly, trgng thdi cung nhu di§n phan bo trong khdng gian khac
- Myc nudc dudi dat: Hau h i t cac khu vyc tr&n ci myc nudc dudi d i t khd ndng vd b i l n doi theo mua. Ctiieii sdu myc nudc dudi d i t se anh hudng den db lun cOa^ai da lien quan d i n dp lye d l y n i l . Chilu sau ciJng nhu qui trinh dao ddng cCia myc nudc dudi dat se anh hudng den qud trinh lun be mat. Tuy nhien v l n de ndy chua dugciK cdp trong edc phuang phdp tinh todn.
- Qud trinh phdn huy hij-u ca cua cac Idp dat yeu: Hi|n tugng syt lun tie mat ndi chung lien quan d i n nin dat yen do qud trinh phan huy huu ca. Hogt dbng xdy dyng cong trinh cua con ngudi nhu khoan tham db, khai thac mflirc ngam... da hg t h i p myc nudc n g l m , Idm d i t dd tir mfli tnjdng ydm khi dugc t i l p xue vdi khdng khf, gdy nSn qui trinh phdn huy huu ca, ti> dd d i n d i n hl§n tugng syt Hin b l mgt Hipn tugng lun b l mat xay ra khd mgnh mS (^
the len den 2-3cm/nam) d khu vyc cd Idp^dlt y i u phan bo d phia tren vdi be day Idn. Ddy Id van de r i t phCpctai' cdc md hinh dy bao deu chua phu hgp vdi thuc t i l n quai t r i e d Ha Npi.
30
TAP CHI KHOA HOC K I E N T R O C - X A Y D U N GDistance (m) -10 0
Atkinson & Potts {1979) O'Reilly & New {1982) Mair (1993) &
Attewell 1 9 7 7 Clough & Schmidt (1981)
Hinh 5. So sanh du'dng cong lun be mat theo cac Tdc gia
- Cdc s y c6, v l n d l Oja c h i t cbng trinh nhu cdt chdy,
;yt vdm, m i t I n djnh vach,... eung ldm nguy co gia tang nue dp sut idn mgt dat.
Mdt d y an xdy dyng hp thdng c l p nudc ngam cua .hdnh pho H i Chi Minh bdng phuang phdp thi cbng kich 3ay vdo ndm 2005-2006 do Sd tdi nguyen mbi trudng dm ehu d i u t u , cdng ty NISHIMATSU thi edng. Chilu sdu Jgtong trung binh 11m, dudng kinh ngodi cua khien ddo 2.6m, myc nudc dudi d i t 2m tfnh t u mgt dat. Dat da phfa :ren cb cdc thdng sd nhy sau:
- Khdi tugng t h i tich ty nhien: 2.02 T/m^
- Gbc ma sat trong: 28 dp - Lye dfnh ket: 0
Qua k i t qud tinh todn theo cdng thuc thyc nghipm vd Ddn kinh nghidm (O'Reilly-New), gid trj S^^gx bang 3.8mm.
rheo phuang phdp tfnh p h l n ti> hOu han (GTS, Pfaxis), Jd Ibn Idn n h i t S^g^ = 1.9mm. Nhu vdy, giua 2 k i t qud :d s y chdnh l^ch khd Idn. CTN cd quy md Idn han ndn
!d ldn sd nhilu han, khd nang sai Ipnh giOa cdc phuang jlidp tfnh cdn cao han nua.
3. Ket lugn
Cbng tdc khai ddo ngam se dan d i n syt lun b l mat d i t . Muc do syt lun didn ra phuc tap, phy thubc vao nhieu y i u td khach quan cung nhu chu quan. 6l nudc ngodi, cdng tac du bao vd tfnh todn dp lun ndy da dugc tfch luy tu nhieu nam tren ca sd qud trinh quan trie thyc te hoac tu cdc mb hinh tinh todn.
Tgi Vidt Nam, CTN Id hang muc cdng trinh khd mdi me, chCi y i u v i n la cdc HMS cho edc nhd cao t i n g , cdn edng trinh dang ham ngam keo ddi h i u nhu chua ddng ke. Da cd nhieu sy co lien quan den HMS do s y hilu bilt hgn che, chu quan cung nhu nggi chi phi tdn kem cua cd chu dau t u , t u vdn thilt k l , gidm sdt vd don vi thi cbng.
Do vdy c i n cd qud trinh nghien cuu, so sdnh vd quan trgng nhat Id quan t r i e trong qud trinh thi cdng. T u dd cd nh&ng hieu chinh thfch hgp khi dp dyng cac phuang phdp tinh tgi Vipt Nam. Cbng vipc ndy c i n sdm triln khai, trdnh nhung sy cd cung nhu cdc tinh hudng khdng mong mudn khi edc dy dn TDN dang chuan bi tnen khai./.
Phdn bien: PGS.TS. Nguyen Due Ngudn T a i l i e u t h a m khao
/. Peck RB Deep excavation and tunneling in soft ground. Stale of Ihe an report. In Proc Till intconfsail mechanics and found engineenng, Mexico, 1969 pp 225-90
2 Atkinson JH, Polls DM. Subsidence above shallow tunnels in soft ground J. Geoiech. Eng. Div. ASCE 1977.
3. Mair RJ. Gunn MJ, O 'Reilly MP Ground movements around shallow tunnel in soft clay lOlh intconfon soil mechanics and foundation engineering. Stockholm. 1983.
4. NewBM. O'Reilly MP. Tunneling induced ground movemeiils.
predkting iheir magnitude and effects. Proc 4th canf on ground movemcnis and structure.. Cardiff, 1991.
5. Schmidt B Prediction ofseillemenis due to tunneling in soil three case histories In' Proc 2nd rapid excavation tunneling conference. San Francisco. CA. 1969
6 Clough GW, Schmidt B. Design and performance of excavation and tunnels in soft clay. In Soft clay engineering Amsterdam:
Elsevier: 1981.
7. O 'Reilly MP. New BM. Settlements above tunnels in U.K- their magnitude and prediction. Tunneling'82, 1982.
8. Takahiro Aoya^ Representing Settlement for Soft Ground Tunneling. 1995
9. Mair RJ. Developments in geotechnical engineering reserch - Application lo tunnels and deep excavations. 1993.
W. Biii Thanh Mai. Ngo Dang Quang. Nguyin Xudn Huy. Tinh todn lun bi mgi gdy ra bai thi cdng CTN theo cdng ngh? kich 11. Cdc tdi lipi khdo sdt Dja chdl cang trinh tpi khu H
TP HCM.
'-HdNpivi
