DIA MOI TRUONG V 6 l KHAI THAC
VA Sir DUNG HIEU QUA KHONG GIAN NGAM DO THI HA NOI
T h S . N C S . N G U Y E N D U G M A N H , ,,, • ,, : ,, Bg mdn Dja Ky thudt
Khoa Cdng trinh
KS. NGUYEN NGOC LAN Bg mdn Vgt lieu Xdy dung
Vien KH&CNXD GT
Tru&ng Dai hgc Giao thong Van tdi
Tdm tdt: Viic khai thdc vd su dung khdng gian ngdm cd y nghia dgc biit quan trgng ddi vai nhung do thi nhu thu do Hd Ngi. Nhimg dgc diim dgc thii ciia khdng gian ngdm vung Hd Ndi vd su biin ddi dia mdi trudng do hogt dgng khai thdc lanh thd ciia con ngudi, cd dnh huong lan din su an todn vd dn dinh khi thi cdng cung nhu khai thdc cdc cdng trinh ngdm vd cdng tiinh trin mat
Summaiy: The exploitation and use underground space mean special important for mimicipalilies as the Hanoi capital. The particular characteristics of underground space in Hanoi and the variation in local geological environment due to mining activities of human territory, have a great influence safety and stability when construction as well as exploitation of the underground and on the suijace. . . .
L D A T V A N D E
Khdng gian ngam Ha Ndi la ngudn tai nguyen dat xay dung rat quan trpng, da, dang va St; dugc khai thae sir dung vdi cac muc dich khac nhau nhu: bd tri cac cdng trinh ha tang ngam (thoat-nude, cap nude, cap dien ...), phan ket cau ngam hay tang ham cac tda nha Cling nhu cac he thdng giao thdng ngam (metro, ham vupt, bai dd xe . . . ) . Sir dung hgp ly ngudn tai nguyen nay gdp phan lam tdt hon mdi trudng sdng ciia con ngudi, ddng thdi cho phep bao tdn tdi da canh quan tu nhien va kiijn tnic dd thj da cd.
Viec phan tich va danh gia anh hudng den trang thai dja mdi trudng cd y nghia quan trgng va tinh chat nguyen tac khi vach chien lupc. Cling nbu lap du an quy hoach khai thae su dung khdng gian ngam tai Ha Ndi. Nghia
la, can phai xem xet tdng hgp va dieu kien tuong tac, cac qua trinh chuyen ddi tu nhien, ciia thach quyen, thiiy quyen va sinh quyen dudi tac ddng ciia cac boat ddng ky thuat, cac dac diem viec xay dii-ng va khai thae cdng trinh tren mat va cdng trinh ngam. Dac diem va cudng dp sir phat trien cac qua trinh nay thudng dupe quyet djnh bdi cau triic dja chat, cac dieu kien dja chat thiiy van va dja chat cdng trinh, ciing nhu bdi sir dac thii va miic dp tac ddng nhan sinh trong trong khdng gian ngam. ,, . . ,. ,,..
II. DAC DIEM DAC THU K H O N G GIAN N G A M HA NOT
Chii yeu lanh thd Ha Ndi nam trong ddi Slit dia hao trung tam ciia trung Ha Npi thupc mien kien tao Ddng Bac - BSc Bg, ddi nay nam kep giua cac dirt gay sau Sdng Chay d
T51P chi KHOA HQC GIAO THONG VAN TAI So 29 - 03/2010 65
phia Tay Nam va Sdng Ld phia Ddng BSc, ddng thdi cat qua cau true Trung Tam va Ddng Bac thupc he chuan udn nep Ddng Viet Nam, cdn phia Tay Nam giap vdi he udn nep Tay Viet Nam. Vdi dac diem nhu vay, lanh thd Ha Ndi gan lien cac dac diem chung ciia trung Ha Ndi, vdi cau tnic kien tao rat phiic tap, mii-c dp ddng va dap vd vd trai dat manh.
Ngudn gdc ctia mpi van ddng ni5i sinh lanh thd Ha Ndi chju anh hudng ciia sir van hanh hai he diit gay Sdng Hdng va Ddng Trieu.
Tren mat cat Kainazoi lanh thd Ha Ndi phat trien day dii cac thanh tao Oligocen (E3), Neogen (N) va de Tir (Q). Vdi nen tram tich de Tir kha day, cd the dat tren 120m, den nay va trong tuo-ng lai ddi tugng nay chii yeu dugc khai tbac va sir dung cho muc dich xay dung cdng trinh tai Ha Ndi. Tir dudi len tren, cac thanh tao de Tir vimg Ha Ndi gdm he tang Le Chi (aQi'lc), Ha Ndi (a,apQ|--^hn), Vinh Phiic (a,lbQi'vp)> Hai Hung (m,lb,bQ2''-hh) va Thai Binh(a,alb,aQ2-'tb)[l].
Cac thanh tao tram tich sdng he tang Le Chi, tir dudi len gdm cudi, sdi, cat lan bdt set cd nai la bdt set d ben tren. Cac thanh tao de Tir cti nhat nay phan bd phd bien d vimg Ha Ndi, khdng Id ra tren mat, thudng gap d dp sau 45 - 69,5m, vdi tdng be day 25 - 30m. He tang Ha Ndi phan bd rdng khap pham vi Ha Ndi, dupe Id ra d phSn ria ddng bang (vimg doi gd Sdc Son), phan cdn lai bj phii bdi cac tram tich tre ban. La cac thanh tao sdng va sdng lii. thanh phan gdm cudi, sdi, cat, nhieu nai cd cat pha hay set pha d ben tren. Vdi gia trj md dun tdng bien dang kha cao (>70 MPa), cac tang cudi sdi Le Chi va Ha Ndi la ldp chju lire quan trpng cho mdng cpc ddi vdi cac cdng trinh ldn tren dja ban thanh phd. Cac tram tich Pleistocen mudn - he tang Vinh Phiic cd nguon gdc sdng, hd va hd - dam lay dupe
phan bd rdng rai trong vung Ha Ni3i. Chimg Id ra tren mat d Ddng Anh, Sdc San va dien nhd d Cd Nhue - Xuan Dinh va khu vuc Nghia Dd, gdm cd hai tap tram tich. Tap dudi la cac tram tich rdi, gdm cat nhd den thd, cd khi lan san sdi, cdn tap tren gdm cat pha, set pha hoac set mau loang Id dac trung cd chd lan tan tich huu CO-. Nhung thanh tao tram tich cudi, sdi va cat ciia cac he tang Le Chi, Ha Ndi va Vinh Phuc la tang chira nude Pleistocen (qp) phong phu va quan trpng ciia Ha Ndi. Cac thanh tao Holocen dudi - giua he tang Hai Hung cd ngudn gdc hd-dam lay, bien va dam lay.
Thanh phan gdm set, set pha deo chay den chay lan tan tich huu co-, set xam xanh dac trung va than bim. Cac thanh tao chira huu ca Hai Hung cd tinh dj hudng cao, mirc dp thanh da thap, thudng nam tren be mat khdng bang phang ciia cac tram tich set bdt tang Vhih Phiic va phan bd khdng lien tuc, tao nen tinh phirc tap ciia dieu kien dja chat cdng trinh tai nhiing noi chimg cd mat. He tang Thai Binh la tram tich de Tir tre nhat, phan bd rdng rai, gdm hai phu he vdi tdng be day cd the dat 46m. Phu he tang Thai Binh dudi la cac thanh tao tram tich sdng, sdng - hd - dam lay, phan bd rdng rai d be mat ddng bang trong de, thanh phan gdm cat thd, cat vira cd khi lan san, cat nhd va cat bdt (nam dudi) va bdt set, set bdt hay cat set cd nai lan tan tich hu-u ca (nam tren). Phu he tang Thai Binh tren la cac tram tich bai bdi va ldng sdng, phan bd ngoai de sdng Hdng, Dudng, Ca Ld, ..,, vdi thanh phan gdm cudi, sdi, cat lan it bdt set (nam dudi) va bpt set, cat bdt (nam tren). Cac thanh tao cat he tang Thai Binh la tang chira nude Holocen (qh) kha phong phii.
Vdi ba tang dat yeu Vinh Phiic, Hai Hung va Thai Binh la cac tram tich ngudn gdc hd - dam lay va dam lay, cimg vdi cau tnic
66 Tap chf KHOA HQC GIAO THONG V^N TAI S6 29-03/2010
kien tao phirc tap tao nen tinh dac thii ciia khdng gian ngam vung Ha Ndi.
III. ( A( \ AN DK DIA MOI TRUONG Kill KHAI n i A C N .\ SL DUNC; KHONG (MAN N ( ; A M HA NOI
Nhu da biet, da phan dien tich Ha Ndi nam viing anh hudng true tiep ciia he dirt gay Sdng Hdng. He nay khdng chi gdm cac diit gay sau phuong Tay Bac - Ddng Nam (dirt gay Sdng Hdng, Sdng Chay, Vinh Ninh. Phiic Yen-Yen Vien, Sdng Ld), ma cdn cac dirt gay Ddng Bac - Tay Nam (diit gay dudng 6), cac dirt gay nhanh a kinh tuyen va a vi tuyen.
Hoat ddng ciia cac dirt gay nay dugc ghi nhan boi cac dj thudng nhiet, trugt dat, nirt dat ngam va dac biet dat Ha Ndi trong pham vi ddi ddng dat cap 7 - 8 . Vdi tren 30 diem nirt dat ngam dugc xac nhan d lanh thd Ha Ndi, se la nhung yeu td nguy hiem khdng the khdng tinh den khi vach chien luge khai tbac khdng gian ngam trong vimg nay, ddng thdi chinh nd tao kenh dan ngudn d nhiem xudng cac nude va dat ben dudi. Hai tran diing dat cudng dp 5,1 Ricbtcr (8/1278 va 10/1285) va rat nhieu tran nhd hon da dugc ghi nhan tren dja ban Ha Ndi, rd rang hien tugng ddng dat va hau qua tham hga ciia nd ludn thdi sir va rat quan trgng ddi vdi xay dirng. dac biet la xay dirng cdng trinh ngam. Sir cd mat cac thanh tao dat loai cat chira nude, dac biet cat kem chat he tang Thai Binh phan bd gan mat dat, muc nude ngam ndng va vdi ham lupng bat bui kha cao (22,5 - 68,3%), chimg hoan toan cd the xay ra su hda Idng khi xay ra di5ng dat cap 7 - 8. Tai cac khu vuc phan bd thanh tao hd-dam lay (dat yeu tang Vinh Phiic. Hai Hung. Thai Binh), tinh chat bat lt)i dja chan se tang len dang ke ddi vdi nen dat va cdng trinh khi ddng dat. Theo y kien ciia mdt nha dja chat, vj tri vd de (1915) sau dd hinh thanh dam tai
Thanh Tri va nhieu diem sat Id bd sdng Hdng nhieu nam qua nam trong pham vi ddi pha biiy ciia dirt gay kien tao.
Vdi sir cd mat cac tram tich cat (Thai Binh, Vinh Phuc) dpe theo sdng Hdng va Sdng Dudng, nhieu trudng hgp nam ngay dudi cac Idp dat loai set cd be day nhd (2 - 3m) trong mat cat cau tnic nen de, ket qua lam hinh thanh nhung khu vuc trong de dang cao muc nude ngam vao miia mua. Khi dd, ngoai anh hudng den sir thay ddi trang thai va giam do ben ciia dit do ngap nude, can chu van de tang ap lire ddng tham gay bien dang tham (cat chay, xdi ngam), tang ap luc nude Id rdng trong dat, sut Id hay bimg nen khi thi cdng hd mdng, khai dao ngam, ciing nhu sir lam viec ciia cac he thdng cdng trinh ngam khu vuc dgc theo va nam trong de. Mat khac, sir chiem chd ciia cac he thdng cdng trinh ngam Idn (Metro, collector ...) nam trong cac tang chira nude qp hay qh, lam gmm ldp dan mrdc va gay dang mirc nude ngam cue bd, de dpa den su dn djnh lau dai khi khai tbac chimg.
Cac tang dat cat he tang Thai Binh va Vinh Phiic, tai nhieu khu vuc trong khdng gian ngam Ha Ndi cd tinh chat cat chay rd ret, the hien bdi he sd khdng deu deu bat kha nhd (q = 2,6 - 9,7) va dp dn djnh huyen phii cd khi phan tich thanh phan hat kha cao (cd khi
>24cm' ), hay kha nang xdi ngam (ri = 16,2 - 21,7). Nghia la, khi khai dao ngam, hd mdng hay khoan cpc nhdi trong cac tang dat cat d Ha Ndi, qua trinh bien dang tham (cat chay, xdi ngam) hoan toan cd the xay ra khi thda man dieu kien ap lire tham, gay trd ngai khi thi cdng, ddi hdi bien phap thi cdng chuyen biet va cd the gay bien dang hay pha hiiy nen dat. Chinh su hinh thanh nhirng mach dim, mach siii d nen de sdng Hong trong miia mua nhiing nam qua, la dang bi^u hien ciia bien
67
dang tham phat trien d vimg Ha Ndi.
Nhu nhieu nghien cu-u da cho biet. tdc do liin mat dat do ha thap muc nude ngam (khai thae nude ngam) nhirng nam qua dien ra vdi tdc do kha ldn (5 - 35min/nam), cac pheu ha thap muc nude ngay cang md rdng va dp ha thap ngay cang ldn. Su bien ddi mdi trudng dja chat nay, khdng chi gay bien dang cac cdng trinh tren mat, vd hieu hda cac he thdng thoat nude, ngap img cue bd trong thanh phd, ma se la mdt trong nhQ-ng nguyen nhan quan trpng gay bien dang cac cdng trinh ngam, dac biet vdi cac he thdng dudng ngam Metro hay cac nut giao thdng ngam se xay dung tai Ha Ndi. Cd le, chinh nguyen nhan nay gay ra sir bien dang khdng deu ham Kim Lien, lam nirt khe CO gian dan den rd ri nude ngam nhu hien nay.
Trong mat cat tram tich de Tir khdng gian ngam Ha Ndi. cd mat hai tang chira nude phong phii Pleistocen (qp) va Holocen (qh).
Nhieu khu vuc tren dja ban Ha Ndi, cac tang nude nay da va dang bj d nhiem ngay cang nghiem trpng, tao dieu kien hinh thanh mdi trirdng yein khi khi cd mat cac vat chat huu co- tir nhien hoac do d nhiem trong dat. Dac diem nay dupe the hien bdi dai lugng the d xi hda khir (Eh) khdng cao ciia cac tang nude qp (-88 - -H40 mV, thudng -^20 ^ +70mV) va qh (-63
•^ +132 mV, thudng +16 - +80inV), va cd xu the giam do d nhiem d mdt sd noi (bai rac cu trong thanh phd). Va do se la dieu kien thuan Ipi cho qua trinh an mdn dien hda ddi vdi cac ket cau thep va mdt sd kim loai trong dieu kien mdi trudng thieu d xi. Mat khac, dp pH ciia cac tang chira nude bien ddi trang pham vi ning, vdi qp (3.7 - 8,4) va qh (4,0 - 8,6), nghia la tai mdt sd khu vuc tren dja Ha Ndi.
nude ngam cd tinh an mdn axit ddi vdi be tdng va be tdng cdt thep thdng thudng. Tinh
chat an mdn nay ciia nude ngam viing Ha Ndi can dugc xem xet ca qua trinh dien bien theo ngudn gay d nhiem chiing khi lua chgn vat lieu xay dung cho cac cdng trinh ngam, hay phan ngam cac cdng trinh tren mat phan bd trong cac tang dat chira nude nay.
Yeu td nhiem ban mdi trudng ngam thanh phd bdi sir rd ri tir cac he thdng thoat nude thai va cac bai rac thai sinh boat cd y nghia dja mdi trudng quan trgng. Cac he thdng thoat nude thai dugc xem nhu ngudn cue bd cua su d nhiem vd co-, hiTu ca va vi sinh ciia khdng gian ngam thanh phd.
Nbu da biet, d khu vuc ndi thanh Ha Ndi, nhieu tuyen cdng thai dugc xay dung tir nhiing nam 30 the ky trudc, den nay xudng cap nghiem trgng. Su rd ri thudng xuyen tir cac he thdng cdng thai sinh boat, sir tham thau tir nhung he thdng kenh mirong va sdng thoat nude bj d nhiem nghiem trpng, gay d nhiem nude ngam va dat trong khdng gian ngam Ha Ndi ngay cang manh. Su keo dai va thudng xuyen bj nhiem ban bdi cac ddng nude thai sinh boat, gdp phan thiic day qua trinh thay ddi bat Ipi ve thanh phan hda hpc ciia nude ngam, ddng thdi tao dieu kien thay ddi trang thai va tinh chat ciia dat da chii-a nude dd. Sir hinh thanh mdi trudng khir do sir d xi hda cac chat huu ca thudng dugc phat hien trong cac tang tram tich bj d nhiem bdi cac ddng thai smh boat. Sir d nhiem khdng gian ngam lanh thd thanh phd cdn dirge tang nhanh va lam nghiem trgng them tir pha Idng giau hiiu ca, dugc tham tir cac bai chdn lap rac trirdc day (Thii Le, Thanh Cdng, Thai Ha, Nggc Khanh, Me Tri, ...).
Khi cac thanh phan gay d nhiiim (vd co-, huu ca, vi sinh) xam nhap vao cac dat phan tan chira nude, tao mdi trudim thuan lai cho vi
68 Tap chi KHOA HQC GIAO THONG V^N TAI S6 29 - 03/2010
sinh phat trien ciing nhu qua trinh chuyen hda cac chat protit. Ket qua chiing dugc hiit vao trong cac phan hat khoang cua dat phan tan.
Su tich tu thanh khdi vi sinh huu ca la ket qua ciia sir day manh boat ddng vi smh vat trong dieu kien ir dpng ciia nude dudi dat. Dieu dd dan den su tang len ham lugng nhdm hat keo, gdp phan lam cac Id rdng ciia dat nhd hon, lam giam tinh tham va kha nang nha nude ciia dat cat. Sir tich tu nay cd the lam cho dat cat chuyen sang trang thai "chay", dat loai set thay ddi tinh deo va tinh truo-ng nd va phan ldn chuyen sang trang thai chay.
Su phat trien dfr ddi cac dieu kien khir dxi trong khdng gian ngam do sir dxi hda huu CO- thudng kem theo sir chuyen ddi cac hgp chat sat ba ve dang linh ddng sat hai. Cac hgp chat sat ba nay ddng vai trd la hgp the va xi mang gan ket trong dat phan tan. Ket qua sir chuyen ddi nay gay ra sir ha thap dd ben va kha nang chju lire ciia dat d nen cac cdng trinh va tda nha bien cd. Ngoai ra, khi sir nhiem ban nude ngam bdi cac ddng nude thai, noi cd qua trinh khir dxi ciia luu huynh vdi sir tham gia cac vi hiiu co- cylphat bda, dan den sir thanh tao hydro sunfua va hidrotroilit. Si,r tich tu cac khi gas sinh hda it tan (CH4, N;, H2 ...) vdi viec tang ddng thdi khdi vi sinh gay ra sir ndi long (giam chat) cac ldp dat, kem theo dd la si,r giam di5 ben va md dun tdng bien dang ciia chimg, ddng thdi tao dieu kien hinh thanh tinb chiit xiic bien va tang do nhay ciia dat vdi tai trpng ddng. Sir bao hda khi trong cac tram lich cat lam giam gdc ma sat trong ciia chimg, dieu nay lam tang si,r chuyen tiep cat sang trang thai Idng.
Hien tuang lim bd sium sau thdi sian dai
dn djnh ciia nhieu tda nha va cdng trinh d Ha Ndi cd lien quan den su suy giam tinh bien dang ciia dat nen do d nhiem dat gay ra. Vi du cdng trinh nha 2 tang 87 Hai Ba Trung, xay tren mdng bang nam 1925, sau thdi gian dai dn djnh den dau nhung nam 90 the ky trudc xuat hien lim bd sung. Hien tugng lim bd sung tuong tu ciing xay ra vdi tda nha tru sd BCH TU Dang (xay nam 1910), tda nha thu vien khoa hgc ky thuat va nhieu cdng trinh khac.
Ngoai ra, khi phan tich nguyen nhan lun bd sung va lim qua gidi ban cho phep ciia cac cdng trinh cu xay tren mdng cgc d dja ban Ha Ndi, sir giam dp ben va tang tinh bien dang ciia dat do d nhiem khdng gian ngam can dupe nghien ciru va tinh den.
Su xau dan ciia tinh trang dja mdi trirdng trong khdng gian ngam thanh phd khdng chi chuyen ddi trang thai tieu cue va tinh chat ciia dat, ma cdn la su nang cao mirc dp an mdn ciia mdi trudng ngam vdi cac vat lieu xay dung. Sir dao ddng sinh hda manh me cac chat hda tan trong nude ciia cac khi (CO2, HjS) ciing vdi sir tich tii cac san pham cua sir chuyen hda vi sinh, gdp phan nang cao tinh an mdn cua nude ngam va dat ddi vdi vat lieu xay di.rng dupe sir di,ing trong cac ket cau ngam va he thdng cac cdng trinh ngam. Nghia la, khi khai tbac khdng gian ngam cac do thj ldn trong cac dieu kien cudng dp tang cao va sir suy giam tinh trang dja sinh thai manh nbir d Ha Ndi, can chii y dac biet ve van de lira chpn vat lieu xay di.rng, chimg phai dugc dn djnh trong cac dieu kien tinh an mdn cao ciia mdi trudng va dam bao tin cay khai thae cdng trinh ngam va he thdng ky thuat ngam.
(Xem tiip trang 158)