toi cong tac thiet ke va thi cong cong trinh giao thong ngam
tai Ha No!
Ths. Vu Hoang Ngoc *
Tdm t i t : Bai bdo de cop tdi van de sut lun ddt nen do thi do bdn thdn nen ddt yeu, do khai thdc nUdc ngam tuy tien vd dnh hudng cua nhu'ng van de do tdi cdng tdc thiet ke, thi cong cdng trinh giao thong ngam (thi cdng theo phuong phdp ddo ngam) tai Ha Noi hien nay.
TU khda: Nudc ngam, dat yeu, thi cong, cong trinh, giao thdng ngam.
Abstract: The article mentions the issue of urban soil background subsidence due to soft soil, groundwater extraction and effects of these problems to the design and construction of underground traffic works (following the underground excavation method) in Hanoi, today.
Key words: Groundwater, soft soil, construction, works, underground traffic Nhdn ngdy 10/02/2014. chinh sda ngdy 14/02/2014, chdp nhan ddng ngay 20/02/2014.
1 . Anh hudng cua viec khai thac niidc ngam tdi dat nen Ha Noi Theo sd lieu cua Sdlai nguyen va Mdi trUdng Ha (Moi, cdng suat khai thac nude tai Ha No; cho den nhUng nam 1950 dat khoang 25.000 mVngd. Nhung nam 1960 dat cdng suat khai thac 141-000 mVngd va tang len 173.000 mV ngd trong nhdng nam 1970.
TU nam 1985, vdi nUdc sach Phan Lan, tai phia Nam sdng Hdng cong suat khai thac nudc tang dang ke td 200.000 mVngd (1985) den 320.000 mVngd (1994), cdn phia Ble sdng Hdng cdng suat dat 21.300 mVngd'".
Hinh I: So do ddng dp tdng chda nudc Pleistocen tai Hd Npi Hien nay, tong mde khai thac nudc ngam cua toan TP. Ha Npi vao khoang 700 000 mVngd Du bao, den nam 2020, khai thac se tang len mUc 1,4 trieu mVngd.
Do qua trinh khai thac nen mUc nudc cua tang chda nUdc da hinh thanh ph§u ha thap mUc nude khu vUc, pheu CO hinh elip vdi true dai gan song song vdi Sdng Hdng tU Nhdn den Ngoc Hoi, true ngan vudng gdc vdi sdng Hong t d Yen phu den Ha Ddng, trong pheu ha thap chung cdn hang loat cac pheu ha thap nhd lien quan den cae gieng khai thac nudc ngam (Hinh 1).
Ket qua theo ddi cho thay pheu ha thap mUc nude dudi dat md rdng lien tye cave dien lan chieu sau. SU ha thap mUc nudc ngam gay ra hieu Ung nen chat tram tich trong tang chda nudc, tao ra hien tupng lun be mat.
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2. Anh hudng cua lun dat tdi cong trinh xay dtfng
Cdng tac khai thac nUdc dUdI d I t da hinh thInh nen d c phlu ha thap muc nude cua cle tang chda nude, khi dd ap luc nude 16 rong chuyen boa thanh I p luc hdu hieu, gay ra hien ttlpng t u lun cua d c Idp dat t d muc nude ngam xudng den chieu sau nhat dinh. Vl d e pheu cd kich thudc rat Idn so vdi chieu day d c Idp dat n l n , nen hau h i t eac tac g i l khi nghien cdu
dung phuong phap phan tich ngUdc trong qua trinh tinh toan.
Hien tupng sut lun mat dat thUdng lien quan true tiep den sued mat cua tang dat lap, dac biet I I nhijng viing cd mat tang y l u (bun, than bun, dat hdu cd, set - set pha deo chay, chay), be d l y v l dien phan bd cua chung.Tai HI Ndi, Idp bun phan bd tai phan Idn cac khu VUc, vdi chieu day Idn va len tdi gan 20m (Gilng Vd, Thanh Cdng:
16,7m;PhapVan: 19,3m) -
Hinh 2: SU bien doi mUc nudc du& ddt - do Idn ndm 1998-1999 tai Hg Dinh van de nay d l u ap dung md hinh cd k i t mdt chilu cua Terzaghi de d i n h g i l va du bao qua trinh sut lun mat daL Tuy nhien, q u i tnnh lun phu thudc r l t n h i l u yeu t d va bien doi theo thdi gian. De danh g i l v l dU bao q u i trinh sut lun mat dat dat dp chinh xac cao ban, hien nay d n h i l u ncfi ngUdi ta dat mang ludi quan trie nudc dudi dat, do ap lue nudc lo rong va do dp lun, ddng thdi I p
Hien tupng lun nut, bien dang cdng trinh di kem vdi ha mUc nude ngam chu y l u x l y ra ddi vdi cac cdng trinh xay dung cd thiet k l n l n mdng va k i t cau khdng phu hpp vdi d u true n l n dat yeu.
Vao eudi nhOng nam 80, tdc la khi chucmg trinh nudc sach Phan Lan di vao boat ddng, h l n g loat d e cdng trinh tilp tue lun, lun lech va lun rat manh, g l y ndt ne, khdng dap dng
dieu kien sd dung binh thudng, tl chi gay hU bdng cfflig trinh. Tdi 90%*
cua tOTig so 200 ngdl n h l lap ghep tai d c chung cUvdi quy md 4 - 5 t m g f l duoe xay dUng eudi nhOng nam 70 d ^ nhthig nam dau 80 khu Giang Vot Thai Thinh, Ba Dinh, l a n Mai, Tn/png
£>jnh,TrungTU, Kim lien, NghTa Ddu CO tdng do lun t d 10 d i n 40 cm. Trong do cd khoang 50 n h l bi lun nut d mde dd da va dang d n d l u tu, sda chOa ^ . CIc ngdi n h l bj lun manh tiiudng II mdng I ndng tren nen d I t tU nhien, mdt so a gia cd nen nhU dem cat, cpc d t ; o tbapi- Cd 2 hi^n tupr>g lun diln hinh nhUsau:
- H'Kn tuang toe dd lun khmg gHk hodcgidmittheothdigian:Chuyeu}iief I ra d cac cortg trinh xay dUrig tren nln ] dat yeu cua Ha Npi nhU Gilng Vd (A2, A3, A6, C6, C7, E6k_), Ngoc Khanh (A2.
81, B^ B8_), Tan Mai (C5, C6, OJ, Thanh Cdng (B7, E3, E4, E6, E7, K 7 ^ ' |
Theo 1]? t h u y l t c6 k i t tham va tren thUc te, dudi t i e dung cua tli trpng khdng ddi, n l n dat bi lun vl dai lupng nay g i l m d i n theo thdi gian. Cho d i n mot thcri gian nao d l , nen dat dupc c6 k i t h o l n toan, khi do se khong cdn hien tupng lun nda.
TCr hien tupng tdc dp lun cua mot so cdng trinh neu tren khdng giam hoac giam it theo thdi gian, dio
pi
Nguyin nhdn lun ndt cdng tnnh xdy dung lien quan den cdu true nen vd nin ddt yeu
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Hinh 3: Thi cdng ham giao thdng trong do ^i phep gia t h u y l t x u l t hien mot li ngoai tac dung phu them cung v t l i trpng cdng trinh va g l y lun thei cho nd. Luc tac dung phu them chic chan lien quan tdi viec ha thap n nudc khi khai t h l c nUde dudi dat t^
Ha Ndi '*'
- Hien tupng tdc dp lun dot n h i ^ tang trd lai sau mdt thdi gian dai ld|
it hole ngdng lun: Hien tUpng n l y b i l u hien thdng qua su xuat hien nhanh chdng vdi cudng dp cao d e hu hdng t r l n cdng trinh l l u nay v I n sd dung binh thudng va an toan. Tuy nhiln, d c hu hdng ndi tren dudng nhu it p h I t t r i l n them sau mdt thdi gian p h I t t r i l n manh me*"
Trong d e cdng trinh khIc, mot sd chuyen gia nglnh Dja chat cdng trinh da cdng bd nhieu k i t q u i nghiln cdu xung quanh cau triie nen d I t y l u , nguyen nhan Idn ndt cdng trinh xay dUng lien quan d i n d u true n l n v l nen d I t y l u .
H I Npi d3 cd quy hoach tdng t h i tdi nam 2020, cung vdi mdt sd quy hoach chi t i l t . NhUng HI Ndi hoan t o l n chua cd quy bo^cb khdng gian ngam. .Nhu vly, elc tai lieu ve dat n l n va nude n g l m se gdp phIn lam Cd sd cho viec phdi hpp quy hoach xly dung ndi va n g l m , cdng nhu edng tac khai thac t l i nguyin, phIt t r i l n kinh t l va b i o ve mdi trudng mdt elch hop 1^. CIc cdng trinh d l u tUOng t i c vdi n l n dat thdng qua mdng cua chung. Tiiy theo quy md edng trinh vdi dang i l l trpng dac trung va d I t nen se q u y l t djnh cle dang n l n mdng thieh hpp.
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tdt chilm Uu t h i tuong ddi thuan Ipi cho phat t r i l n xly dUng ngam. CIc quan ndi thanh v l cle huyen phia Nam sdng Hdng dat yeu k h i phd b i l n va phIn bd phdc tap tren mat bang, cung nhu theo chilu sau. Ngoli d e Idp dat bun y l u cdn ed d c Idp cIt bui, d t mjn cung ed y nghia rat quan trpng d i n van de dn djnh va biln dang eda cdng trinh ngam v l dac biet la cdng nghe thi cdng chung.
Dat y l u ed the phat sinh sut vdm ham, vieh ham, bung nen, eung nhu x l y ra d t chly, dat chly, xdi n g l m , buc nude khi khai dao, hda Idng khi ed t l i trpng ddng lam hU hdng cdng trinh.
Hinh 4. Mdt log! khiin ddo hSm • ! :dnbdng dp li/c guong ddo cua Nh^t Bdn
Trong tuong lai, d l dap dng su phIt t r i l n v I n minh, hien dai, TP. H I ; Ndi se p h l i xly dUng h i thdng giao thdng n g l m nhu Metro (Hinh 3), d c n h l ga nglm, d e dUdng nglm dl bd, d c kho n g l m v l nhllu dang edng trinh n g l m khIc nhau.
K i t q u i nghiln cdu v l d I t y l u i H I Ndi cho thIy, elc huyen phia Ble sdng Hdng v l sdng Dudng vdi dat
y l u phia t r l n hang dao cd chieu day hdu ban, chuyen dich nay cd t h i I n h hudng tdi b l mat d I t . Q u i trinh nay t i l p tuc cho den khi thiet lap sU d n b l n g mdi eda trang thai dng suit - b i l n dang trong khdi dat bao xung quanh hang dIo.
Theo cae sd lilu ve b i l n dang lun mat dat trong d c tai lieu nghien edu ed the dUa ra cle nhin xet sau: Khi thi cdng ham bang khien dao (TBM - Tunel Boring Machine) thdng thUdng thi dp lun khdng vupt qua 30 - 50mm, tuy nhien trong mdt sd trudng hpp dp lun dat d i n 100mm v l Idn hon.Dp lun xuat hien khi thi edng h i m bang khien dao khdng cd I p luc can blng d
3. Qng suat-bien dang cOa khoi d^t xung quanh ham
Xly dung ham se t i e ddng len khdi d I t bao quanh guong dIo, g l y ra sU thay ddi trang thai dng suit - b i l n dang t u nhien cda khdi dat, g l y ra sU bien dang cua khdi dat xung quanh gUong d I o v l mat dat khu vUe phia tren ham. Bien dang nly se g l y t i c ddng bat Ipi d i n d c cdng trinh xay dUng gan ke trong pham vi I n h hudng cua viec dao ham.
Q u i trinh chuyin djch cua d I t dudi t i c ddng eda viec dao h i m b i t d l u xung quanh hang d I o v l d i l n ra lien tue, khi tdn tai Idp dat
gUdng dao Idn hdn d i n g k l so vdi khi thi edng ham b l n g khien d I o cd I p luc d n bang d guang d I o (Khiln dao can b l n g I p lUc - Hinh 4).
Cd rat nhilu y l u td I n h hudng den q u i trinh b i l n dang cua khdi dat, trong dd cle y l u td l i l n quan d i n edng nghe xay dUng, d i l u kien dia chat xhu^ van v l die d i l m ket d u eCia ham gid vi tri quan trpng:
- Trong dat rdi am, bien dang cda dat xly ra vdi tdc dd nhanh ban r l t nhilu so vdi d I t dinh.
- Dp Idn cda b i l n dang tang len eung vdi sUtang kich thUdc mat c I t ngang h i m ;
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- Anh hudng cua d c cdng trinh xay dung gan ke den bien dang cua khdi dat hen quan den su xuat hien cac b i l n dang ban d l u cua khdi dat;
- Chieu sau dat ham anh hudng true tiep den qua trinh dich chuyen va bien dang. Ddi vol ham dat ndng (khi H/ D dai 2 ^ 3) dd lun mat dat xuat hien nhanh va gia trj ciia chung tang len khi giam chieu sau dat han^' - Anh hudng cua k l i c l u vd h l ' ^ den bien dang va chuyen dich cua mat dat lien quan den bien dang vd ham, cdng tac bom vUa nen sau vd him va cac ly do khac:
- Dd iun xuat hien khi thi cong ham blng khien dao. thdng thudng cd gia In nhd hon so vdi cac phuong phap dao md.
- Khi dao ham blng khien dao xual hien cac bien dang ed kit, bien dang keo dai va bien dang lUc thai (ngIn han) cua dat.
- Bien dang cd ket mang dac tinh phu thudc vao thdi gian va dupc quy dinh bdi dac tmhthuy ddng t u nhien va ap luc nudc Id rdng thay ddi do sU di ehuyin cua khien dao.
Hinh 5. Nguyen iy khien ddo hdm cdn bdng dp lUc guang ddo:
AC- dp luc ddt trudc guong ddo. B,D-dp luc ddt sau gUdng ddo
Vdi dieu kien dia chat edng trinh va dia chat thdy van Ha Ndi nhu da phan tich d tren, cdng trinh giao thdng ngam nen duac thiet ke vdi vd him nhieu Idp (tren mat cat ngang v6 ham tU trong ra la Ldp hoan thien tao kien true, ldp vd be tong cot thep lap ghep chiu lue, eac ldp vd chdng tham va tao li^n ketvdikhdidatxungquanhddngthdichenkhehdlhicdng), ket clu vdham duoc tinh toan vdi so dd tuong tac cung lam viee vdi khdi dat xung quanh, phuong phap thi cdng dao ngam sd dung khien dao ham can blng ap luc./.
* Trudng khoa Qudn ly Xdy dung - Hoc vien MAC
TAI LIEU THAM KHAO
1 ,: 2 :.De tai nghien cdu khoa hgc vd cdng nghe trong diem cdp Thdnh phd Ho hgi nam 2002 do Trudng Dgi hoc Mo - Dia chdt thuc hien: Thu thdp, kiem chiing cdc tdi lieu ad cd, nghien cdu bd sung Idp bdn do phdn vdng ddt yeu Hd Ndi phuc vu phdt tnen ben vdng thu do'. Md so: TC-OT/06'02-3.
(3). Dieu tra ddnh gid, du bdo bien dang lun be mat ddt khu vuc Hd Ndi do thay doi muc nude ngam, xdc lap ca sd hodn thien he thdng cdc tram quan trdc bien dang lun cua thdnh phd Hd Ngi - Bdo cdo tong hop. ndm 1998-1999.
(4), (5;. Nguyen Vdn Quang, Nguyin HClu Khdng vd Udng Dinh Chdt (1996). Nen
•.a mdng cdc cdng tnnh ddn dung cdng nghiep, Nxb Xdy Dung, Hd Ndi.