Lai Ngoc Hung Tap chi KHOA HOC & CONG NGHE 128(14). 23-27
BANK GIA PHirONG PHAP DU^ BAO SlTC CHIU TAI CUA COC KHOAN NHOI SU" DUNG KET QUA CAC THI NGHIEM XUYEN CPT VA XUYEN SPT
Lai Ngoc Hung' Dai liQC Ky thuat Cong nghiep - DH Thai \guyiin
TOM TAT
HiSn nay trong thiit kk cpc khoan nh6i, sue chiu tai (SCT) ciia cgc thudng tinh dua tren ket qua thi nghiem xuyen CPT hoSc xuyen SPT, su dung he so an toan Fs tir 2-3 do do ket qua kh6 xac dinh chinh xac. Thuc te de ki^m tra SCT thong dung su dung thi nghiem nen tTnh (TNNT) cpc sg cho ket qua rat tin cay. De giai quyet v3n de moi tuong quan giiJa SCT cua cpc khoan nhoi tinh toan dua tr6n kSt qua xuyen CPT, SPT va sue chiu tai tir TNNT cpc, tdc gia tien hanh thu thap ket qua nen tmh cpc khoan nhoi tren mot so khu vuc dien hinh ciia thanh pho Ha Noi va tinh toan SCT cpc dua tren kdt qua xuyen CPT, SPT. Ket qua nghien cuu chi ra moi tuong quan gitta SCT cua cpc theo kgt qua thi nghiem xuyen CPT, SPT vdi SCT tir TNNT thong qua he so tuong quan K, voi xuySn CPT co K = 0.654- 1.405, vdi xuyen SPT co K = 0.837-1.42.
Til* kh6a: Sue chiu lai cua coc. cpc khoan nhdi. thi nghiem xuyen CPT. thi nghiem xuyen SPT, thi nghiem nen tinh cpc
DAT VAN DE
Trong xay dung hien dai, dac biet vdi nha cao tang, mdng cpc khoan nhoi iudn la giai phap thiet ke dugc uu tien lua chon do cd nhieu uu diem nhu sue chju tai Idn, do liin khong dang ke, su anh hudng den dia chat va cdng trinh xung quanh khi thi cdng cd the kiem soat tot...
Hien nay de du bao sire chju tai cua cgc ndi chung va cgc khoan nhdi ndi rieng, cd the sir dung nhieu cdng thiic khac nhau, trong do cdng thuc dira vao ket qua tu' cac thi nghiem xuyen( CPT va SPT) duge dung rat pho bien.
Trong thuc te tinh toan thiet ke, cac ky su tu van dugc siJ' dung he sd an toan rat Idn (tir 2- 3), neu ehiing ta cd nhirng so sanh tin cay ket qua tinh sue chiu tai cgc khoan nhdi dua vao ket qua cac thi nghiem xuyen vdi ket qua thi nghiem nen tmh tren cgc thuc te cua cdng trinh, ehiing ta cd the sir dung he sd an toan thich hgp han, tang hieu qua kinh te cua cac du an dau tu xay dung khi su dung ege khoan nhdi, tranh gay lang phi tai nguyen trong dieu kien mdi trudng xay dung hien dai.
Tei 0988 906921. Email: ngochungktcnt%gmail com
CAC PHUONG PHAP XAC DINH SUC CHIU TAI COC KHOAN NHOI DUA VAO KET QUA THi NGHIEM XUYEN VA THI NGHIEM NEN TiNH
Phirong phap du'a vao cac thi nghiem xuyen Dua vao ket qua khao sat bang cac thiet bj thi nghiem xuyen (CPT va SPT), chiing ta tinh toan dugc cac thanh phan sire ma sat ben ciia thanh cgc vdi dat nen (Qs) va thanh phan sue khang cua dat d mui coc (Qp), tir dd tinh duoc sire chju tai ciia cpe theo phuang dien dat nen la nguyen ly chung cua viec tinh sire chiu tai cgc dua vao cac thi nghiem xuyen.
Sue chju tai gidi ban: Qi, = Qs+Qp (2.1) Sire chiu tai tinh toan Qa - Q„/Fs trong do Fs la he so an toan lay tir 2-3.
Vdi Qs la sire khang thanh ege, Q,, Sue khang mui ege
- Theo ihi nghiem xuyen tieu chuan SPT
Q,= K2,N,i,As (2.2) Qp-K,N.Ap (2.3) Trong dd: N - chi sd SPT trung binh trong
khoang ID du'oi mui cgc va 4D tren mui cgc (D la dudng kinh cpc nhdi), N,b - chi sd SPT trung binh cac lap dat dpc than cpc.
23
Lai Ngoc HiJng T^p chi KHOA HOC & CONG NGHE 128(14): 23 • ^7 K| -he sd lay bang 120, Ki -he s6 lay bSng
1.0, Ap la dien tich tiet dien cgc. As la dien tich xung quanh than cgc.
'Theo Ihi nghiem xuyen tieu chuan CPT
Qp=Ap.(q,„.Ky (2.5) Trong dd:
U|, l| : ehu vi va chieu dai cpc di qua lap thu i, K, he so phu thudc loai dat.
^7.-.- *?---. S'-''^ khang mui xuyen trung binh cua lap dSt thir i. thu n.
Ap dien tich tiet dien ege.
Thi nghiem nen tinh doc true coc Nguyen ly thi nghiem:
Tac dung Ien cgc thi nghiem tai trgng coi la tmh, xac dinh quan he tai trgng - do liin (chuyen vi coc) tren ca sd dd xac dinh duge sire chju tai gidi han ciia cgc ve phuang dien dat nen Pj,|, ( hay Q,,) tir do suy ra sue chju tai tinh toan Q^,
Kit qua thi' nghiem: Theo quan diem bien dang: tir gia tri bi6n dang cho phep da hieu chinh S* suy ra P^i, theo sa do nhu hinh I.
Pgh (Pgl^ PmaxTN
S*=5(S)
Hinh I. Xdc dinh sue chiu tai cua coc tic ket qua thi nghiem nen tTnh DANH GIA DO CHJNH XAC KET QUA TINH s u e CHIU TAI COC KHOAN NHOI DUA VAO KET QUA THI NGHIEM XUYEN V6l THi NGHIEM NEN TINH Chuan bi so lieu
Tren ea sd phan viing dja chat d Ha Ndi, tac gia da thu ihap.tai lieu, thdng ke va linh toan 24
ndi suy cac sd lieu khao sat dja chat va sd lieu nen tTnh cpc khoan nhdi theo tieu chuan Viet Nam hen hanh
S^ X.
- Vi
/
-.pf") • M \
}
r V
^ „
Hinh 2. Phan viing dja chdt Hd Ndi Vdi 5 vCing dja chat dien hinh dd (nhu hinh 3.1), tac gia da thu thap, tdng hgp cac sd lieu nen tmh cpe khoan nhdi cho eac cdng trinh thudc cac vimg tuang irng.
So sanh ket qua tinh to^n va ket qua thi nghiem nen tinh tai hien trirtfng Sue chju tai gidi han ciia coc khoan nhdi theo cdng thirc ly thuyet sii' dung ket qua thi nghiem xuyen (Q„), sue chju tai cho phep ciia cpc (Qa) lay vdi he sd an toan chung la 2,5.
Theo thi nghiem nen tTnh tai hien trudng: gia tri sue chju tai gidi ban Qu. ciia cpc khoan nhdi dugc tinh dua vao dudng eong nen S-P theo gia tri dp liin cho phep ciia coc, gia trj nay dugc quy dinh trong TCXDVN cd th^ ISy theo hai gia tri sau:
+ Theo S ' - ^.S,|, (vdi ^ = 0,1; S,„ - do liin gidi han cdng trinh), vdi cdng trinh xay dung' dandling thi S'= 0,1.8 = 0,8 cm
+ Theo S* = 1%. D (D - dudng kinh cpc) Sire chiu tai cho phep cua cgc \ky theo dg liin cho phep ciia cpc: Qa = Qu/1.25
Lai Ngoc HCing Tap chi KHOA HOC & CONG NGHE 128(14): 23-27 Tien hanh tinh toan va so sanh, nghien cuu
thu dugc cac ket qua sau:
y&i viine A (Khu Phu Diin, Mai Dich, NghTa Tan)
Tinh toan cho cdng trinh vdi cgc dudng kinh 1,2m; chieu dai 30 m (cam vao Idp cuoi sdi khoang 2m)
- Ket qua nen tTnh: Lay trung binh eua 5 cgc cd dudng kinh 1,2m, irng vdi S'^^.S^i, ed Q.n.Htinh= 690 T, irng vdi S*='0,01D cd Qan=,.llni.= 825 T
- Ket qua tinh sue chju tai cua cgc dua tren ket qua thi nghiem xuyen:
Bang 1. Ket qua Q„, Qa vdi dang dla chdl A1 Cong thuc tinh
1. Xuyen CPT 2, Xuyen SPT
Qs(T) Qp(T) Ou(T) Qa(T) 671.20 678.6 1349.8 539.9 197,20 1357.2 1554.4 621.6 Bang 2. Ket qua Q,., QaVai dgng 3ia chdl A2 Cong thiic tinh
1 Xuyen CPT 2. Xuyen SPT
Qs(T) Qp(T) Qu(T) Qa(T) 714.10 1017 881731.96 692.8 219.07 1357.171576.24 630.5 Bdng 3. Kel qua Qu, Q„ vat dang dta chdt A3 Cong thuc linh
1 Xuyen CPT 2, Xuyen SPT
Qs(T) Qp(T) Qu(T) Oa(T) 386.84 1017.88 1404.72 561.9 148.42 1357.17 1505.59 6022 V&i viim B: (Khu Co Nhiie, Ddng Nggc):
Tinh toan cho cdng trinh vdi cgc dudng kinh 1,2m; chieu dai 33 m (cam vao lap eudi sdi khoang 2m)
Ket qua nen tTnh: lay trung binh cua 3 cgc CO dudng kinh 1,2m, irng vdi S'=^.Syh co Oaniiiii.ih~760 T, irng vdi S = 0,01D ed
QanemTiih" 8 8 0 T
- Ket qua tinh sire chju tai ciia cgc dua tren ket qua thi nghiem xuyen:
Bang 4. Ket qua Q„. Q„ vdi dgng dla chdt Bl Cong thuc tinh
1. Xuyen CPT 2. Xuyen SPT Bangs./^e'/
Cong thirc tinh 1. Xuyen CPT 2. Xuyen SPT
Qs(T) 754.10 258.07 qui g,. 1
Os(T) 434.84 262.42
Qp(T) Ou(T) Oa(T) 1123.881877.98 751.2 1356.171614.24 645.7
£?u v&i dgng dia chdt B2 O P ( T ) O u m Oa(T)
1017.88 1452.7 581.1 1327.15 1589.6 635.8
V&i vans C: (Khu My Dinh, Mi Tri. Dgi Md) Tinh toan cho cgc dudng kinh 1,2m; chiSu dai 34 m (cam vao Idp cuoi sdi 2m)
- Ket qua nen tTnh: lay trung binh ciia 3 cgc cd dudng kinh 1,2m, li'ng vdi S'=^.Si,h cd Qanen.rnh=751 T, irug vdi s'= 0,0ID cd
Qanenllnh= 9 5 0 T
- Ket qua tinh sire chju tai ciia cgc dua tren ket qua thi nghiem xuyen:
Bang 6. Ket qua Q,„ Qavdi dgng dla chdt CI Cong thirc tinh
1, Xuyen CPT 2 Xuyen SPT Bang 7. Kit Cong th He tinh 1. Xuyen CPT 2. Xuyen SPT B i n g 8. Kel Cong thirc tinh 1. Xuyen CPT 2 Xuyen SPT Bang 9. Kit Cong thuc tinh 1. Xuyen CPT 2. Xuyen SPT
Qs(T) 1467 9 341.7 qua Q,, Q
Os(T) 1503,7 442 8 qua Q„ Q
Qs(T) 1036.1 333,71 qua Q,„ Q
Qs(T) 2658,2 345.4
OP(T) OU(T) Oa(T) 678.6 2146.5 858 6 1357.2 1698.9 6796 a vai dang dla chdt C2
On(T) Ou(T) Q»(T) 1017,9 25216 10086 1357,2 1799 9 719,9 n vat dang dia chdt C3
Qp(T) Qu(T) Qa(T) 1017.9 2053.9 821.6 1357.2 1690.9 676,4 I, vol dang dia chdl C4 Qp(T) Q u ( T ) Q a ( T ) 678,6 3336.8 1334.7 13572 1702.6 6810 V&i viine D: (Khu Trung Yen, Ngoc Khanh) - Tinh toan cho cgc dudng kinh 1,2m; chieu dai 45 m (cam vao Idp cudi sdi 2m)
Ket qua nen tTnh: lay trung binh ciia 3 cgc, ung vdi S'=^.Sj,i, cd Qa„e„iiiii,=660 T, ung vdi S ' = 0 , 0 I D c d Q a n e n , r n h - 8 5 3 T
- Ket qua tinh sue chiu tai ciia cpc dua tren ket qua thi nghiem xuyen:
Bang 10. Ke, C8ng thirc tinh 1. Xuyen CPT 2. Xuyen SPT B a n g l l . / f e ' , C6ng thuc tinh 1. Xuyen CPT 2, Xuyen SPT
f quo Q,i, Qs(T) 653.4 277.9 f qua Q,„
Qs(T) 1535.36 409.68 Bang 12. KSl qua Q,„
Cong thuc tinh 1. Xuyen CPT 2. Xuyen SPT
Qs(T) 1588.34
'.n.n
Q„ vai dang dig chdt D!
Qp(T) Qu(T) Oa(T) 1017.9 1671.2 668.5 1357,2 1635,1 654.3 QB vai dgng dig chgl D2 O P ( T ) Q U ( T ) Oa(T) 1 1187.5 2722.9 1089.1 13572 1766.8 706.7 Q„ vai dang dig chdl D3 O P ( T ) Q U ( T ) Oa(T) 1 1085.4 2673.7 1069.5
1251.5 1678.6 671.4
Lai Ngoc Hung Tap chi KHOA HOC & CONG NGHE 128(14)-23-27 Bang 13. Kel qug Q„
Cong thuc tinh Qs(T) l . X u y g n C P T 1704.13 2. Xuyen SPT 474 67
Bang 14. Kel qua Q„
Cong thuc tinh Qs(T) 1 Xuyen CPT 458.39 2 Xuyen SPT 124.67
2u vai dgng dia chdl D4 Qp(T) Qu(T) Qa(T) 1187.5 2891.7 1156.7 1357.2 1831.8 732 7 Qa vai dang dia chdl D5
Qp(T) Qu(T) Qa(T) 10179 14763 59051 1357 2 1481 8 592 74 Vo'i viine E: (Khu Dgi Kiin, Linh Dam, Phap Van, Thanh Tri)
- Tinh toan cho cgc dudng kinh 1,2m; chieu dai 42 m (cam vao Idp cudi sdi 2m)
Ket qua nen tTnh: lay trung binh ciia 3 cgc, irng vdi S =E,.Sj,i, co Qanenrinii~744T, li'ng vdi S'= 0,01 DcdQ,n„„Tnh= 992 T
Bang 15. Ket qua Q,„ Qavdi dgng dia chdt El Cong thiic tinh
1. Xuyen CPT 2. Xuyen SPT
Qs(T) 1079.55 308.76 Bang 16. Ket qua Q„, Cdng thiic tinh 1 Xuyen CPT 2 Xuyen SPT
Qs(T)
miAi
521 21
Qp(T)Qu(T) Qa(T) 1855.5 2935.1 1174 2120.6 2429.3 971.7 Q„ vat dang dia chdl E2
Qp(T) Qu(T) Qa(T) 1237 2514.5 1005 8 2 1 2 0 5 2 6 4 1 . 7 1056.7 Tir cac ket qua tren, tac gia diing he sd tuang quan K = Oa,„,i„oan/Qanenimi, de danh gia mii'c do tin cay ciia sue chju tai cho phep tinh toan du'a tren ket qua thi nghiem xuyen va ket qua sue chiu tai cho phep ciia cgc tii thi nghiem nen tTnh, thu dugc ket qua nhu sau:
- Dua vao thi nghiem CPT, cd K = 0.782- 1.778 ngu tinh S'=^.Sgh va K = 0.654- 1.405 neu tinh S*= 0,01D (nhu hinh 3.2).
| i 8 - , H e s a K . I
!"^ K . . A
- ^ S g h - - . — S'=0.01O
Hinh 3. Bang he so K giua liit qua theo thi nghiem CPTvd Ihi nghiem nen tinh coc - Dira vao thi nghiem SPT, c6 K = 0,837-1.42 neu tinh S'=^.S,i, va K = 0.695- 1.065 neu tinhS'=0,01D(nhirhinh3)
26
1 2 1 1 0 9 0 7 0 6
-.^
'-
- • \ ' .
Hinh 4. Bdng he sd K giira ket qua theo thi nghiem SPT vd thi nghiem nen tmh coc.
K E T L U A N
Vdi he sd K thu dugc trong nghien cii'u, sii'c chiu tai cho phep cua cpc tinh dua vao ket qua thi nghiem CPT va SPT (vdi he sd an toan Fs=2.5) deu cd sai khac vdi sire chiu tai eiia cpc tir thi nghiem nen tTnh cgc, tuy nhien sai khac nay la khdng qua nhieu.
- Sii'c chiu tai cho phep ciia cpc tinh theo ket qua thi nghiem CPT va tii' thi nghiem nen tTnh tinh ung vdi bien dang S = 0,01 D la tin cay ho'n (cd K = 0.654- 1.405) so vdi tinh li'ng vdi bien dang S'= ^.Syi,(cd K = 0.782-1.778).
- Sue chiu tai cho phep eiia cgc tinh theo ket qua thi nghiem SPT va tii' thi nghiem nen tTnh tinh ling vdi bien dang S*= £,.S^i, la tin cay han (cd K = 0.837-1.42) khi tinh ling vdi biSn dangS*=0,01D.
- So sanh vdi sire chju tai cho phep ciia cgc tir thi nghiem nen tTnh cgc thi sire chiu tai cho phep ciia cgc tinh theo ket qua thi nghiem SPT tin cay han tinh theo kk qua thi nghiem CPT (vi vdi thi nghiem SPT cho K = 0.837- 1.42, thi nghiem CPT cho K = 0.782-1.778).
TAI LIEU THAM KHAO 1. Vu C6ng Ngir, 2006, Thi nghiem ddt hien trudng va irng dung trong phan tich n^n mong, Nxb Khoa hoc va ky thuat.
2. Le Due Thang, tai ban 1999, Tinh toan m6ng coc, Nxb Khoa hoc ky thuat,
3 TCXDVN 205 : 1998', Mong cpc tieu chuSn thigt k^.
4. TCXDVN 269:2002, Cpc - Phuang phap thi nghifm bang tai trpng tTnh dp dpc true.
Lai Ngoc Hiing Tap chi KHOA HOC & CONG NGHE
S U M M A R Y
A S S E S S M E N T O F M E T H O D S A P P L Y I N G T O D E T E R M I N E T H E L O A D C A P A C I T Y O F B O R E D P I L E S U S I N G R E S U L T S F R O M C P T A N D S P T T E S T S
Lai Ngoc Hung College of Technology - Th U
Recently, the pile load capacity using in designs is commonly estimated based on the results of Cone penetration tests (CPT) or Standard penetration test (SPT). This calculations must apply a safety factor Fs from 2 to 3 because the pile load capacity is difficult to determine accurately that possibly leads to a wasteful design. In practice, to determine the load capacity of piles, the static load test method is commonly performed and provides reliable results. To solve the problem of the relationship between the load capacity of piles according to calculations based on experimental results of CPT or SPT and other regular capacity from static load test, the author has conducted static load test results of piles located in some typical areas of Hanoi, pile load capacities calculated theoretically based on CPT and SPT.This research focuses on establishing a correlation between the pile load capacity as a result of tests CPT, SPT with the capacity received from static load test through a correlation coefficient K, with CPT have K = 0.654- 1.405, with SPT have K = 0.837-1.42.
Keywords: Loading capacity of pile, bored pile, cone penetration test CPT, standard penetration test SPT, static load test
Ngdy nhan bdr 15/8/2014: Ngdy phan bien. 30/8/2014. Ngdy duyet ddng 25/11/2014 Phan bien khoa hoc: ThS. Hdn Thi Thuy Hdng - Trudng Dal hoc Ky ihudl Cdng nghiep - DHTN
Tei 0988 906921. Email: ngochungktcn%gmail com
