BAl HOC Ttr s u C6 SAP B6 VlfiN KHOA HOC XA HOI VUNG NAM B 6 a THANH P H 6 HO CHI MINH
PGS.,TS.NGUY§NBAK^
Vien KHCN xay dung
Tdm tat : Bai bao trinh bay cac budc trong each dieu tra va phan tich mgt su co cu the trong thuc te xay dung tang ham a nude ta hien nay. Mgt so bai hgc bo ich va hudng khac phuc khiem khuyet trong thi cdng theo phuang phap md cdng trinh ngam dugc rut ra tCr sued nay.
Viec thi cdng hd mdng s§u phuc vu x^y dung tang ngam nha cao tang d nude ta da lam hu hdng va tham chi gay sap dd nhieu nha va cdng trinh hien hOu lien ke. Su sap dd nha 2 tang ciia Vien Khoa hgc Xa hdi vung Nam Bd tai thanh phd Hd Chi Minh khoang 19 gid ngay 9 thang 10 nam 2007 do thi cdng hd mdng tang ngam cua cao dc Pacific ben canh la su cd nen mdng dien hinh thugc loai nay va cho den nay van chua cd su phan tich ky ludng ve mat ky thuat de tU dd rut ra mgt sd bai hgc nham phdng tranh su cd tuong tu trong tuong lai. Bai bao nay thir cd gang lam viec do tren co sd nhdng tu lieu da thu thap dugc.
1. Dac diem cong trinh cao 6c Pacific /. /. / / tri va quy mo cong trinh
Cdng trinh cao dc Pacific nam tai sd nha 43-45-47 Nguydn Thi Minh Khai, phudng Ben Nghe, quan 1, TP.
Hd Chi Minh; phia Bac tiep giap tda nha Yoco cao 12 tang ciia bao Tudi tre, phia Ddng Bac tiep giap dudng Nguydn Thi Minh Khai, phia Ddng Nam tiep giap tda nha 2 tang ciia Vien Khoa hgc Xa hdi vimg Nam bd, phia Tay giap Sd Ngoai vu (hinh 1).
Hinh 1. Vl tri cong trinh cao dc Pacific
Tda cao dc Pacific dugc cap phep xay dung thang 2/2005, dien tich mat bang 1.750 m^ cao 78.45m, gdm ba tang ham va 1 tang ky thuat (chieu sau 11.8m); 1 tret va 20 tang lau; tdng dien tich san x^y dung la tren 22.000 m l Tuy nhien trong qua trinh thi cdng, chii dau tu cao dc Pacific da dieu chinh thiet ke (tuy chua dugc Sd Xay dung thanh phd cho phep) len thanh sau tang ham (chieu sau 21.1m), mgt tang tret, 21 lau, tdng dien tich san xay dung len tdi hon 41.000m^ vdi he khung gdm 16 cdt cd tiet dien 1400x1400 mm va san ngang.
Cdng trinh sir dung mdng be BTCT dat tren 65 cgc barrette kich thudc 2.8x1.2m sau 67m. Theo thiet ke, he tudng vay gdm 50 tam panel kich thudc tU 2.8 den 5.7m, day lm sau 45m nhung khi thi cdng Cdng ty Pacific da thay ddi thanh 24 panel kich thudc 2.8 den 7.7m, day lm sau 45m. Gioang each nude gida cac tam panel khdng dugc chi dinh chieu dai trong thiet ke nen ddn vi thi cdng chi dat den day tang ham, tdc khoang 22m.
Thi cdng cac tang ngam theo phuong phap "ban ngugc" (semi top-down) sir dung he chdng dd ngang la he dam san BTCT day 230mm va 250mm tua len cot bien tao ra he chdng ngang phia trong tudng vay.
Chu dau tu va quan ly du an: Cdng ty TNHH mgt thanh vien Bia Thai binh duong.
Don vj thiet ke cao dc: Cdng ty Tu van xay dung dan dung ciia Bd Xay dung.
Don vj thi cdng: Chii dau tu tu td chirc thi cdng.
Don vj tu van giam sat: Chii dau tu tu lam.
Don vj chUng nhan chat lugng phu hgp: Cdng ty CP tu van thiet ke xay dung CIDECO.
2.2. Dieu kien dat nen
Cac bao cao ve khao sat dja chat cdng trinh va dja chat thiiy van cho cdng trinh gdm cd:
- Bao cao khao sat dja chat cdng trinh do Cdng ty TNHH tu van xay dung Nam Thien lap thang 4 nam 2002 cd 2 Id khoan sau 45m va 50m;
THI CONG XAY LAP - KIEM OJNH CHAT LUONG - Bao cao dja chat cdng trinh do Trung t§m cau dudng phia Nam lap thang 02 nam 2006 vdi 1 lo khoan sau 80m;
- Bao cao khao sat dia chat cdng trinh do Trung tam Nghien ciru Cdng nghe va Thiet bi cdng nghiep Trudng Dai hgc Bach khoa thanh phd Hd Chi Minh lap thang 1 nam 2009 kiem tra "d bim" va mach nude ngam cung nhu hieu qua chdng tham tai nhii'ng chd ndi giua cac tam tudng sau khi bdm phut xi mang gdm 1515 sau 25m/ld;
- Bao cao ciia Lien hiep Dia ky thuat nen mdng cdng trinh lap thang 3 nam 2009 phuc vu kiem djnh chat lugng he ket cau cac tang ham gdm 2 Id vdi do sau 80m/ld.
Theo cac tai lieu tren, dia tang khu vuc cdng trinh tU tren xudng, nhu sau:
- Ldp 1: Dat san lap cd chieu day lm;
- Ldp 2: Set pha, xam nhat nau vang, trang thai deo mem; Be day Idp 4,2m;
- Ldp 3: Set pha san, xam trang xam vang, xam xanh, trang thai deo cUng. Chieu day Idp 4.1m;
- Ldp 4: Cat hat nhd den hat trung, nau nhat, nSu vang, xam trang, nau dd, trang thai chat vUa den chat.
Chieu day Idp 29m;
- Ldp 5: Set nSu dd, vang nhat, trang thai cdng den rat cirng. Chiiu day Idp 15,1m;
- Ldp 6: Set pha mau vang, xam xanh, xam trang, trang thai nira cdng. Chieu day Idp 2,3m;
- Ldp 7: Cat hat trung, nau vang, xam xanh, trang thai chat den rat chat. Chieu day den het hd khoan (- 80,45m).
Muc nude ngam trong khu vuc la -9m tU cdt cao mat dat tu nhien, tuong ddi dn djnh. Cac chi tieu co ly ciia cac Idp dat cho d bang 1 cdn mat cat dia chat cdng trinh xem hinh 2.
Nhu vay, chan ciia tudng vSy vUa vao mai Idp set (sd 6) cdn mui cua cgc barette vao mai ciia Idp cat pha (sd 8).
MATCXT DIACHAT
C O N C TfiiNH; CAO 6c PACIHC
D|A D i f M . 4J.45.47 NGUYEN TH| MINH KHAI - QUAN I . T P . H 6 CHI MINH
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Hinh 2. Mat eat dia chat eong trinh dudi nen eao dc Pacific Bang 1. Chi tieu ca ly cua eic Idp dat
— - — — _ _ _ ^ l ^ d p dat
Chi tieu ~ Hat soi %
Hat cat % Hat bui % Hat set %
Od am tu nhien W%
1 - 55.7 25.0 19.3 18.59
2 - 56.9 19.1 24.0 21.20
3 29.0 32.0 17.0 22.0 18.19
4 - 57.2 20.6 22.2 18.65
5a 10.1 44.4 27.5 18.0 14.67
5 9.1 80.0
5.8 5.1 17.55
6 - 45.2 22.7 32.1 17.80
7 - 61.0 16.2 22.8 17.26
8 4.3 84.3
6.2 5.2 17.03
50 Tap KHCN Xdy dung - so 3/2010
Dung trpng tu nhien x„,, T/m^
Dung trong khd y^., T/m' Dung trong day ndi y^^ ,T/m^
Ty trpng A,T/m^
Do bao hda G%
Do rdng n%
He so rdng, s^
Gidi han chay W, % Gidi han deo W„%
Chi so deo, I^
Dp set, B
Goc ma sat trong, ^ ° Luc dinh C, daN/cm^
SPT
1.96 1.65 1.04 2.70 79 39 0.636
23.7 12.8 11.0 0.53 11°38' 0.132 7-9
1.99 1.64 1.03 2.71 88 39 0.652
30.7 16.0 14.7 0.35 12°05' 0.242 16-20
2.01 1.70 1.09 2.77 80 39 0.626
30.7 15.7 15.0 0.17 13°17' 0.253 11-14
2.03 1.71 1.08 2.71 86 37 0.585
27.3 14.6 12.7 0.32 13''04' 0.244 10-12
1.93 1.68 1.06 2.70 65 38 0.607
22.0 11.8 10.2 0.28 15''13' 0.187 22
2.02 1.72 1.08 2.67 85 36 0.553
- - - - 24°28' 0.055 12-31
2.06 1.75 1.11 2.72 87 36 0.556
38.7 19.8 18.8 -0.11 16°35' 0.380 46 ->50
2.04 1.74 1.10 2.71 84 36 0.557
31.9 17.1 14.7 0.01 15''45' 0.307 35 ->50
2.01 1.72 1.08 2.67 82 36 0.553
- - - - 26''04'
0.055 29->50 2. Ho scrsiTco
21. DiSn bien sWcd
Do khdng cd he quan trac de theo ddi didn bien (luc va chuyen vj/bien dang) cua he ket cau chdng giii' hd dao va cdng trinh chung quanh nen nht/ng thdng tin sau day chii yeu thu thap tU cac phuong tien truyen thdng va ngudi chUng kien luc xay ra su cd.
- Thang 5/2007, cdng trinh bat dau thi cdng san tang ham, den thang 10/2007 thi cdng dugc bdn tang ham va bat dau thi cdng tang ham thir 5. Trudc khi xay ra su cd da thi cdng xong cac panel tudng vay, cgc barrette va thi cdng dd be tdng den san tang tret tai cac true 1-3 va 6-8. Phan khoang hd tU true 3 den true
6 sir dung cac thanh thep 1400 de lam he thanh chdng dd tudng vSy;
- Ngay 9/10/2007, khoang 18 gid 30 khi dang dao dat de chuan bj dd be tdng mdng thi d vi tri tiep giap tudng vay tai cao trinh am 21m so vdi cdt nen tang tret ciia cdng trinh Pacific, tudng vay xuat hien Id thiing rgng 30-35 cm, dai 168 cm. Do ap luc manh ciia nude ngam tai vj tri Id thiing nen gay tran nude va Idi dat phia ngoai tudng vao trong tang ngam (hinh 3a) do dd khoang 19 gid thi day nha tru sd Vien Khoa hgc Xa hgi vimg Nam Bd gdm 1 tret 2 lau bat ngd dd sap, bj vui sau dudi Idng dat hdn 10m; phan cdn lai ciia khu nha cung cd nguy co dd sap (hinh 3b).
Hinh 3. Hien trang tang ngam Pacific (a) va Vien khoa hoc Xa hgi vung Nam Bg (b) sau su cd ngiy 9/10/2007
THI CONG XAY LAP - KIEM OJNH CHAT LUONG
- Luc17 gid ngay 23 thang 1 nam 2008, hdn 2 thang Rode, quan 1, dau lung vdi cao dc Pacific, sut lun mdt Id sau su cd sap Vien Khoa hgc Xa hgi vung Nam Bd, trong rgng 10m^ sau 3m lam 4 xe gan may roi xudng hd (hinh khu vuc de xe ciia Sd Ngoai vu tai sd 6 Alexandre de 4a) va nirt tudng d khu ve sinh (hinh 4b).
(a) (b)
Hinh 4. Hien trang nen tai nha de xe (a) va nCrt tudng khu ve sinh (b) eua Sa Ngoai vu sau su cd ngay 23/1/2008 2.2. Dieu tra sWco
Dieu tra dinh tinh: Dua vao tai lieu thu thap dugc tU chinh quyen dja phuong va co quan quan ly thi trudc khi xay ra su cd da xuat hien nhieu dau hieu canh bao su khdng binh thudng ciia nhung cdng trinh lien ke nhu la:
- Sau khi cdng trinh cao dc Pacific thi cdng dugc mdt thdi gian thi thang 11/2006, Vien Khoa hgc Xa hgi (KHXH) cd cdng van giri cac cd quan chirc nang TP.
Hd Chi Minh khieu nai don vj thi cdng trinh cao dc Pacific khdng dam bao an toan, lam nirt tudng va cd nguy cd lam sap Vien Khoa hgc Xa hgi. Cac don vj quan ly trat tu dd thj phudng, quan khao sat, lap bien ban vi pham va bao cao vu viec len co quan quan ly nha nude cd tham quyen.
Ngay 7/12/2006, Thanh tra Sd Xay dung TP. Hd Chi Minh da cd Quyet djnh sd 112/SXD dinh chi thi cdng phan mdng cdng trinh cao dc Pacific tiep giap vdi Vien KHXH cho den khi thuc hien cac yeu cau ciia Thanh tra Sd Xay dung vdi ly do cdng trinh nay vi pham trat tu an toan xay dung gay ran nirt va chan dgng tru sd Vien KHXH. Thanh tra Sd Xay dung TP.
Hd Chi Minh yeu cau chii dau tu cdng trinh la Cdng ty TNHH Thai Binh Duong va nha thau ngung ngay phan thi cdng phan mong cdng trinh, khac phuc su cd; di ddi
ngay ngudi va tai san ciia Vien KHXH neu cd nguy co xay ra su cd,... Ngoai ra, Thanh tra Sd Xay dung TP.
Hd Chi Minh cung yeu cau phia chii dau tu cdng trinh phai thue don vj tu van giam sat; khdng the vUa la chu dau tu vUa la tu van giam sat.
Ngay 4/1/2007, Sd Xay dung TP. Hd Chi Minh da ra quyet djnh xii phat vi pham hanh chinh vdi mUc phat 29 trieu ddng ddi vdi don vj quan ly cdng trinh cao dc Pacific la Cdng ty TNHH xSy dung mdt thanh vien Thai Binh Dudng. Ngay 4/6/2007, Cdng ty TNHH mgt thanh vien xay dung Thai Binh Duong va phia Vien KHXH da thda thuan dugc viec khac phuc su cd do cdng trinh cao dc Pacific gay ra va hai ben tien hanh ky bien ban nghiem thu cac hang muc sijra chUa, tram tret cac vet nUt tai cac phdng lam viec ciia Vien KHXH.
- Chi nira thang sau, ngay 18/6/2007, phia Vien KHXH lai cd cdng van giri den cac co quan quan ly nha nude TP. Hd Chi Minh tiep tuc "keu cUu" viec thi cdng cdng trinh cao dc Pacific tiep tuc gSy sat nirt va cd nguy cd gay sap tru sd Vien. Qua khao sat, ghi nhan hien trang vu viec ciia co quan quan ly trat tu d6 thj thi mdc do lan nay nghiem trgng hon lan trudc.
Ngoai cac vet nUt cu da dugc xir ly, tram tret tam bg, nay lai xuat hien nhieu vet nUt khac. Nhung mUc do xir
52 Tap KHCN Xdy dung - so 3/2010
ly lan nay chi dUng lai d cap quan khi ngay 17/7/2007 UBND quan 1 ra quyet djnh xir phat vi pham hanh chfnh trong xay dung ddi vdi Cdng ty Thai Binh Dudng vdi muc phat 2 trieu ddng va budc don vi nay phai khac phuc hau qua.
- Ngay 9/10/2007, khi dang dao dat de chuan bi dd be tdng mdng thi tai vj tri tiep giap tudng vay d cao trinh am 21m so vdi cdt nen tang tret cua cdng trinh Pacific, tudng vay xuat hien Id thiing rgng 30-35 cm, dai 168 cm. Do ap luc manh ciia nude ngam tai vj tri Id thiing nen gay tran nude va dat phia dudi nen Vien KHXH, lam hai day nha tru sd Vien Khoa hgc Xa hdi bat ngd dd sap, tai lieu luu trii' va may tinh bj viii sau dudi dat hon 10m; phan cdn lai ciia khu nha cung cd nguy co dd sap.
- Sau dd cdng trinh tam ngUng va sir dung bien phap chdng tham tai cac mdi ndi giUa cac tam tudng tang ham do Cdng ty Ddng Minh (Trung Qudc) thi cdng bang khoan phut tao thanh 2 hang cgc xi mang dat cd dudng kinh d = 40 cm. 17h chieu ngay 23/1/2008, hon 2 thang tfnh tU ngay Vien khoa hgc xa hdi phia Nam bj sap, Sd Ngoai vu ke ben cdng trinh nay tiep tuc bi sut nen. Nguyen nhan vu sut lun dugc xac dinh la do anh hudng ciia viec bom nude trong hd dao khi xay dung tda nha cao dc Pacific.
Qua cac tai lieu vUa neu chi cho biet tinh trang cdng trinh ve mat dinh tinh (nUt va nguy hiem) chua
\ ..JM ' ». sl -^ 7 ^mt t I. ^
chi rd sd lugng vet nUt, be rdng va be sau vet nurt cung nhu su phat trien cua chiing theo thoi gian..., so vdi bien dang cho phep de phan cap nguy hiem va tU dd de ra each xir ly thfch hgp.
Dieu tra dmh lugng: Sau khi xay ra su cd, theo yeu cau ciia co quan quan ly va chii dau tu cung nhu CO quan dieu tra,... da tien hanh dao, chup anh, kiem tra chat lugng be tdng bang sieu am, do chuyen vi va bien dang mgt sd cdng trinh lien ke,... va cho biet mdt sd ket qua nhu sau:
- Tudng vay bj thung, nUt tU vai cm den 20-30 cm, d tang ham thir 3 va 4 Id cdt thep chju luc tU vai cm den 20, 27, 80 cm, chan tudng bj nghieng nen phat sinh khe hd chd tiep giap/mdi ndi (xem hinh 5);
- Cudng do trung binh ciia be tdng tudng vay kiem tra bang sieu am R,(, «264 daN/cm^ thap hdn mac thiet ke con theo ket qua thir mau be tdng tudi trudc khi dd vao hao tudng do Trung tam cau dudng phfa Nam thuc hien thi Rtb =453 daN/cm^ dat yeu cau thiet ke.
- Theo ket qua do va theo ddi ciia Cdng ty kiem djnh xay dung Sai Gdn den giffa thang 2 nam 2008 thi mdng nha xe va nha sach cua Sd Ngoai vu liin 30- 40mm so vdi cac thang trudc, cd chd tdc do lim den 2mm/thang, gach lat nen bong rdp tren dien rgng, cira ra vao khd ddng md. Cao dc Yoco cua toa bao Tudi tre chua cd dau hieu hu hdng.
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(a)_ (b) Hinh 5. Vet nirt (a) va khe ha eho tiep giip giffa 2 tam tuang vay(b) eua tang ngam cong trinh Pacific
2.3. XWly tam thdi nhan, chu dau tu da ky hgp ddng vdi Cdng ty Ddng Nham han che su phat trien ciia su cd, cdng trinh Minh (Trung Qudc) thi cdng khoan phut xi mang va tao tam ngUng mdt thdi gian trong liic chd tim nguyen ra 2 hang cgc xi mang dat co dudng kinh 40cm de
THI CONG XAY LAP - KIEM DJNH CHAT LUONG
chdng tham dgc cac vi tri tiep giap giffa cac tam panel tudng vay. Nhd dd lugng nude ngam chay vao tang ngam da giam di ro ret. Cung chfnh Cdng ty nay da thuc hien bom cat va xi mang vao chd sut lim nen nha So Ngoai vu de han che sup dd day chuyen cd the xay ra sau su cd ngay 23 thang 1 nam 2008.
3. Phan tich nguyen nhan sUco
De tim nguyen nhan gay ra su cd, nhat la cac su cd phUc tap, thudng xem xet cac van de sau day.
3.1. Kiem tra thiet ketang ngam
So dd ket cau tang ngam nhu mieu ta d muc 1, phan "nen mdng cdng trinh" tren day.
So dd tfnh theo cac giai doan thi cdng nhu hinh 6 va viec tfnh toan theo hd so thiet ke (vi khdng cd hd so hoan cdng) dugc thuc hien bang phan mem PLAXIS vdi cac thdng sd dat nen dung trong tfnh toan cho d bang 2.
Dao giai doan 1
Hinh 6. Sa do tinh toan tang ngam cong trinh Pacific Bang 2. Cic thong sd dung trong tinh toin
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Ket qua tinh toan ndi luc (M, Q) va chuyen vj (UJ dugc dugc trinh bay tren cac hinh 7 va 8
54 Tap KHCN Xdy dimg - so 3/2010
• ; 0 . Q 0 -10 0 0 OOC 10 0 0 2 0 0 0 M O t « 00 50 00 60 00 70 00 60 00 flO M ^ iZO.U
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Hinh 7. Bien dang tong cua cong trinh tai giai doan thi cong tang ham cuoi Ut^t - 0.6m
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M^3, = 241Tm/m LUc cit Q™,= 108T/m Chuyen vj ngang U,^3, = 0,2m Hinh 8. Momen, luc cat vi chuyen vi ngang Idn nhat eua tudng tang ham Ket qua kiem tra cho thay:
- Md men trong tudng Idn nhat cd gia trj 241 tan m/m nhd hon gia trj 318.67 tan m/m dimg de tinh toan thep cho tudng vay trong thuyet minh tinh toan ket cau do Cdng ty tu van Xay dung dan dung Viet Nam (VNCC) lap thang 6 nam 2006.
So bd tudng vay dii kha nang chju luc trong qua trinh thi cdng.
- Tdng chuyen vi ciia tudng U=0,6m (tUc do Idn ciia vecto chuyen vi) trong khi chua xay dung cac tang phia tren nen do lun luc nay rat nhd, do dd chuyen vj nay la do dat dudi day tang ham bj trdi len do bang chdng tham giffa cac tam tudng chi cam den day tang ham (-21m), dieu nay se lam cho nude d Idp cat phun
trao vao hd mdng va dat quanh hd mdng bj lim sut xudng, cd the day cung la mgt trong nhffng nguyen nhan lam nen Vien Khoa hgc Xa hgi va nen Sd Ngoai vu bj sap dd.
- Chuyen vj ngang cua tudng 0,20 m la qua Idn.
Theo kinh nghiem nude ngoai (Han j,1997) khi ket cau tudng chan chuyen vj ngang qua 30mm hoac 0,2%H (H la do sau hd mdng) thi cdng trinh d each hd mdng 5m se bj hu hdng nghiem trgng hoac rat nghiem trgng va theo ket qua quan trac cac hd mdng sau d Bangkok, chuyen vj ngang Idn nhat cua tudng den 100mm khi hd mdng sau tren 20m (Phienwej,N.2003).
Tdng hgp 2 loai chuyen vj vUa neu dugc the hien tren hinh 9.
THI CONG XAY LAP - KIEM OJNH CHAT LUONG
D
Hinh 9. Sa dd mo ta nguyen nhan gay su ed cong trinh lan can hd dio
1. Nguyen nhan lam dat rong va gay chuyen vi; 2. Dat bi dao hoac chuyen vi the tich: 3. Phan bd chuyen vi the tich;
4.Chuyen vi lun cua mat dat; 5.Chuyen vi cua ket cau vi nghieng lech; 6.Hu hong ket cau; 7.Dat dich chuyen vio hd mong; d.Day mong bi day trdi /ning len
3.2 Kiem tra chat IWcfng thi cong
Qua khao sat chat lugng thi cdng tudng ve be tdng va do kfn khft ciia cac khe ndi giffa cac panen sau khi xay ra su cd thay rang:
Tudng bj thiing va ndt d nhieu chd, chan tudng bj nghieng lech (xem hinh 5) do dd nude ngam cd do chenh thuy luc cao (khoang 13m) trong Idp dat cat (sd 5) se d§ dang mang cat chay tran vao hd mdng gay sup dd nhanh chdng Vien khoa hgc Xa hdi vimg Nam bg nam lien ke va ngay phia tren Idp cat vUa neu.
Co che gay su cd hd dao do nude dudi dat cd the minh hoa tren hinh 10.
TTTzr-
Chay qua OT\C luong bj niJr. vo
Hinhl 0. Dong nude dudi dat chay vio hd dao Mdt sd ghi nhan liic xay ra su cd cung nhu ket qua khao sat (dao dat chd nude trao va cac vet nirt cung nhu do do lech tao ra khe hd giffa cac tam tudng...) da chUng td nguyen nhan chinh gay sup dd Vien Khoa hgc Xa hgi vimg Nam Bg cung nhu d nen Sd Ngoai vu la do tac ddng ciia nude dudi dat qua chd ndt, khe hd bdi thi cdng kem chat lugng cua tudng vay. Dieu nay cung dugc khang djnh khi Cdng ty Ddng Minh bdm phut xi mang chd tiep giap giffa cac tam tudng thi lugng nude phun trao vao hd mdng giam han vi liic nay he sd tham cua dat da giam tU 10'^ cm/s cdn 10"^
cm/s.
Mdt sd khuyet tat/su cd thudng gap khi xay dung phan ngam cdng trinh, trong dd cd trudng hgp ciia cdng trinh Pacific, nhu la mdi ndi giffa cac tam tudng bj hd(hinh 11a) va tham qua tudng (11b).
(a) Mdi ndi bj tach
Hinii 11. Mot sd khuyet tat thudng gap
(b) Tham qua tudng trong thi cong phan ngam cong trinh
56 Tap KHCN Xdy dung - so 312010
4. Mot sd bai hoc
Qua phan tfch cac mat cd lien quan den su cd nhffng cdng trinh lien ke vdi cao dc Pacific cd the rut ra mdt sd bai hgc kinh nghiem sau day:
- Ve mat quan ly: kinh nghiem cua nhieu nude (Washington - My; Frankfurt - CHLB DUc; Thugng Hai - Trung Qudc.) ngudi ta bat budc cac du an cdng trinh ngam (thiet ke' va thi cdng) cd do sau tren 5m deu phai qua co quan quan ly xay dung nha nude tham dinh, neu dat yeu cau mdi dugc phep thi cdng. Muc dich ciia viec nay la de giam riii ro cho cdng trinh va dam bao an sinh cho cdng ddng. Cd le d ta chua quy djnh chat che van de nay va sin sang chuyen sang
"chu dau tu chju mgi trach nhiem" chang? Nha thau thi cdng tang ngam phai la nha thau cd nang luc va kinh nghiem dugc chgn qua canh tranh, tu van giam sat phai la don vi ddc lap. 6 cdng trinh nay hinh nhu khdng thuc hien dieu dd;
- Tai lieu khao sat dat nen phuc vu cho thiet ke tang ngam vdi cgc sau tdi 67m nhung chf cd mdt Id khoan sau 80m, rat it thdng tin ve dieu kien thuy van nen ddng thai nude ngam khdng dugc sang td, tff dd cd the lam cho ngudi thi cdng khdng cd dieu kien de danh gia day dii tac ddng bat Igi ciia nude ngam ddi vdi phan ngam ciia cdng trinh;
- Ve mat thiet ke: tuy tudng du kha nang chju luc nhung thieu han phan tfnh chuyen vj ciia tudng trong cac giai doan thi cdng. Theo ket qua tfnh toan cho thay chuyen vj ciia tudng, theo kinh nghiem nude ngoai la qua Idn. Tuy rang trong cac tai lieu thiet ke cua nude ta chua quy djnh cac chuyen vi gidi han ciia he ket cau chdng giff hd dao cung nhu ciia cdng trinh lan can, nhung dieu nay khdng thieu tai lieu de ngudi thiet ke tham khao;
- Ve chat lugng thi cdng: trach nhiem cac ben trong thi cdng khd phan djnh va khdng kiem soat chat che trong qua trinh thi cdng. Hon nffa, khdng dat he thdng do dac va quan trac cdng trinh tang ngam cung nhu cdng trinh lien ke, do dd khdng kiem tra dugc chat lugng ciia tugng (do ddng nhat cua be tdng va do thing dffng ciia tudng...) cung nhu dgng thai ciia cdng trinh lan can (nut, nghieng va cac bien dang khac,...).
Do dd, hien tugng phat trien cac vet nirt tuy xay ra nhieu lan d Vien Khoa hgc Xa hdi viing Nam Bg nhung khdng dugc danh gia mgt each nghiem tuc de tU dd cd bien phap ddi phd thfch hgp va kip thdi nham ngan chan su cd. Cung cd the nhffng ngudi thiet ke, thi cdng chua cd dii kinh nghiem va kien thUc can thiet de du bao va ngan chan/phdng ngUa su cd.
- Ldp cat (sd 6) vdi muc nude ngam cao va tudng vay thi cdng chat lugng kem la nguyen nhan chu yeu gay ra su cd. 6 day khdng phat hien cd su dj biet gi ve mat dja chat can phai chu y so vdi cac su cd khac da tUng xay ra tai Sai gdn Residence (11D Thi Sach ,quan 1), sap nen trudng Ludng Djnh Ciia (phudng An Phu, quan 2).
- Thiet hai ve kinh te
Theo sd lieu ciia chii dau tu cung cap thi so bg gdm nhffng khoang chi phi sau su cd nhu:
+ Chi phf cho viec khoan bd sung hai Id khoan mdi Id sau 80m:?;
+ Chi phi cho viec thi cdng chdng tham hon 3,51^;
+ Chi phi den bii cho cdng trinh Sd Ngoai vu: 5,01^;
+ Chi phi den bu cho Vien KHXH vimg Nam Bd:
12,0 ty;
+ Chi phi tra lai vay ngan hang trong thdi gian ngung thi cdng: 24,0 t^;
+ Chi phi bj cham 2 nam rudi khai thac cdng trinh udc tfnh 150,0 t^y';
+ Tdng cgng khoang 200 ty.
Cai gia dat nhat la da gay ra mdt du luan khdng tdt ddi vdi nganh xay dung trong xa hgi.
TAI LIEU THAM KHAO
1. NGUY§N VAN DAT, NGUYEN BA Ki, TRAN BINH.
Ket qua kiem djnfi he ket cau cac tang tiam cao dc Pacific tiianh ptid Hd Chf Minh, thing 5 nam 2009.
2. NGUY§N VI£T TUAN. Tfnh toan kiem dinh ket cau tudng vay tang ham cao dc Pacific. Vien KHCN xay dung, thing 8 nam 2008.
3. Vietnam Net, ngay 12 thang 10 nam 2008.
4. HAN J.;CHENG L.K; SONG FA. Issues on the design and application of anchored pile/wall structure for deep foundation pit. Computer Methods and advance in Geomechanies.Yuan (ed)1997,Ballkema Rotterdam.
5. PHIENWEJ N.iGAN CM. Characteristics of Ground Movements in Deep Excavations with concrete diapharm walls in Bangkok soils and their Prediction.
Journal of the Southeast Asian Geotechnical Society,December,2003.
6. NGUY§N BA K£'. Xay dung cdng trinh ngam dd thj theo phuang phap dao md. Nhi xuat ban Xiy dung. Ha Ndi, 2006.
Ngay nhan bai: 7/7/2010.