TRONG XUf LY DAT YEU 6 MIEN NAM VIET NAM

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B A N H GIA H I E N T R A N G SLf DUNG BACTHAM TRONG XUf LY DAT YEU 6 MIEN NAM VIET NAM

ABSTRAG

A 40,000-kni^ soft ground area in the southern Vietnam is big obstmction for infrastructure development of the country. PVD is the most popular technique applied to treat soft clay in Vietnam. However, field perfomtance of the PVD based on field monitoring is quite discrepant from prediction. This study aims at better understanding of PVD field perfonnancevia case studies. The four complete projects using PVD for soft ground improvement were utilized for back analysis. Field monitored settlement agrees well with predicted settlement when the field settlement has experienced a settlement of O i m or less. The predicted settlement exceeds the field monitored settlement about 2044%

when the field settlement reaches 0.8 m or larger. The result indicates that degree of filed consolidation was less than 90% and large field settiement keeps occurring during the service stage of highway and may cause settiement excess allowable settlement

H6T1ilLanHiRmg

Tnidng Dai hoc Bdch Khoa TR HCM Email; [email protected]

Itin NguySn Hoing Htkng

B6 m6n d u Oudng - Khoa Ky thult xSy dumg - Trudng OH Bich khoa TP. HCM Email: [email protected];

tnhhung^maiLcom b

1. Gidi thidu

LOn sut d eac cdng trinh cau dudng dang Id vdn dd bde xdc ma du luan quan tam, ddc bidt cdc cdng trinh d khu vuc mien Nam, nOi ed dja chat phdn Idn Id dat ydu [5]. Hdng loat cdng trinh trong dllm Quoc Gia sau khi thi cdng vda dua vao khai thde dd ed hidn tupng xulng cdp, Idm gidm tde dp luu thdng, gay mdt an todn, vd gidm my quan eda edng trinh, Tuy nhidn, nguydn nhdn gay Idn sut ehUa dUac nghidn cdu mpt each hd thdng hda vd khoa hpc.

Bde thdm (prefabricated vertical drains - PVD) kdt hpp vdi gia tdi thudng dupc sd dung d l xd ly n i n dat yiu. Thd! gian cd k i t eda dat dupe rut ngdn do nudc thodt d i n PVD theo phuong ngang (9] nhd hon rat nhilu so vdi chilu ddy eua Idp dat yeu [5]. Tuy nhidn, khd ndng Idm vide eda bic thdm bi dnh hudng bdi rdt nhieu yiu td [1,9, 10,11,16,17, 18, 20].Vi vdy, dd idn quan trde hidn trUdng thudng nhd hon dp lun thilt k l .

Bdi bdo ndy tdp trung vao ddnh gid hidn trang Idm vide cua PVD thdng qua md phdng phdn tieh ngupe mdt sd dy an thpc td (ease studies). Theo tidu chudn hifn hdnh 22 TCN 244-9S, PVD dupe gid thilt Idm vide ly tUdng, tUc Id bd qua edc tdc ddng hidn t r U ^ g d i n khd ndng Idm vide eda PVD theo thdi gian. Md phdng dupc thUe hidn theo phuong phdp gidi tieh (22 TCN 244-98) vd phUOng phdp phan td hull h?n (Finite Element Method - FEM) (phdn mIm Plaxis 2D v8.5).

2. Phuong phdp nghien ciiTu 2.1 Phifang dn nghUn cCfu Kit qud Idn quan trac t d cae dy dn thyc te da thi cdng hoan chlnh dUpc ddi chidu so sdnh vdi k i t qda tinh lOn bdng phuong phap gidi tieh dua vdo 22TCN 244 -98 vd FEM (phan mIm Plaxis 2D v8.S). Nghidn cUu ndy tdp trung vdo phdn tfch ddnh gid cho 4 dy dn thye t l ed ede vj trf xuydn sudt tUTp. HCM d i n ddt Mui Cd Mau:

DUdng ddn vdo cdu Phd My, Dai Ld Eldng - Tdy, dudng dan vdo elu Cdn Tho, doan thi nghidm eda cdng trinh dudng Nam Cdn.

2.2Ctfsifl:^thuyit

2.2.1 Bd cd kit n4n ddt y&JxHIysCt dung PVD Dd Idn cd k i t todn phdn S, (khi nin chUa cd PVD) tinh theo phuong phdp epng Idp phdn td

HoThjL Tran Nguyen Hoang Hung [2] (Phuong trinh 1,2}

s,=y-V[c;iog4=--c;iog^

=-?^r-'°'- oL (2)

Neu o'„ aa|„ thi S, sd tinh theo cdng thde (1) vdi c;=0; niu t^„<<^^ se cd 2 trudng hop khi o^ + (^„>a'p, thi S^ tinh theo (1), khi

<^. + f^w < oL thi S, tinh theo (2).

Trong ad: h,: chieu ddy Idp ddt tinh Idn thd i (h^ £ 2 m), e',: hd sd rdng eda Idp ddt thd i 6 tr^ng thdi ty nhidn ban ddu (khi chua ddp ndn);

C^: chl sd ndn lun hay dp ddc eda doan dUdng eong ndn Idn; C,: chf s6 ndkhi ddtdi, hay dd ddc eda doan dudng cong ndn Idn; &^ dp luc tiin cd kit Idp ddt thd i; o'^ ap lye do trpng lupng bdn than eda cde idp dat tu nhidn ndm trdn Idp thd i;

o'^dp lUc do cdng trinh gdy ndn.

€)d Idn cd kit theo thdi gian, S^ (khi ndn dd thi cdng PVD) Id dd lun ciia ndn dudng sau thdi gian duoc tinh theo [2]:

S, = S^.U ^ ^ (3) Tron^ 3d: S-. do lun ed kit todn phdn tfnh theo (1) hoac (2); U: dd c l k i t ndn ddt ydu sau thdi gian, t, vdi PVD.

Dd cd k i t chung, U, khi ddng bde thdm thoat nudc theo [8]:

U = U„ (4) Xde djnh dd cd k i t theo phUcmg ngang

theo [81:

U, = 1-exp{-8T/F(n)} (5) Trong dd:T^. nhan t l thdi gian theo phuong

ngang, T^ = C^.t/D'^ D^: dudng k/nh anh hudng cua bae tham; D, =1.13i, khi PVD bd tri theo kilu h1nh vudng; D,= 1.0S.S, khi PVD bd trf theo kilu tam gide; S: khodng cdch gii3a cde tim PVD;

C^: he sd cd kit theo phuong ngang, F(n): nhan td xet d i n dnh hufnig eda khodng cdch PVD;

F(n)=[nV(n'-1)].ln(n)-[(3n'-l)/4n1; n= D / d ^ d^:

dudng kInh tuong duong eda PVD, d^=(a+b)/2;

a: chieu ddy PVD; b- chilu rdng PVD.

2.2.2 Md phdng FEM

Plaxis 2D v8.5 (FEM) khdng cd phdn t d ddc bidt de md phdng PVD mot cdch true tidp.

Nghien edu ndy sCr dgng hai phuong phap md phdng thdng dung: (i) phuong phdp vung tuong duong theo [4), (ii) phuimg phdp xem

B155

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B d n g i L A p d I t

l a 3e 3d

Chl tidu CO ly f » y 1 2 3 52 1 7 J

Cdc Idp ddt tai km 2 + 343 V k N / m '

14.9 14.6 13.S

b 1.24 1.25 1.46

1 3 ^ 2 ' WA9' 14''18'

c k N / m '

9 3 0 9.00 10.20

k.

m/nqdy 2.76E-05 2.60E-0S 1.86E-05

kh m/ngdy 3 3 1 BOS 3 . 1 2 E ^ 2.23E-05

C mVnqay 2.0SE-02 2J9E-02 2.62E-02

C. mVmfiy 4.10t(fi 4.58&Q2 5.24E^)J

Hlnh 1. M$t cdt dadng vdo clu Phu My tai km 2-I-343 Bdng 2. Chi tidu eo iy edc Idp ddt t^l km 2 + 320

Hlnh2.Kftqui(Iolun va qud trinh gia tdi Hinh 3. Kit quj phan tfdi hidn trudng tal km 2+343, duimg djn vdo c3u Phu My.

Ldpdft

l a

k 3d

Ddy m 123 5.2 17.5

V k N / m '

14.9 14.6 13.5

e . 1 J 4 I J S 1.46

9 (°) 1837 19.83 1930

c k N / m '

15.30 14.50 16.20

k.

m/ngdy 2.76E-05 2.60E-05 1.86E-05

kk m/ngdy 331E-05 3.12E-05 223E-05

C mVnqSy 2.0SE-02 2.29E-02 2.62E-02

G, mVnqdy 4.10E-02 4.58E-02 5.24E-02

Kinh 4. M$t cJt t\^g yio d u Riu My t^i km 2+320

iiir^!

Hlnh 5. Ket qui do lun vd qua trinh giatji

Hinh 6. KA qud phan tidi hien trudng tai km 2+

320, lucmg din vdo cdu Phii M^.

PVD Id vdt lidu ddn hdi cd hd sd thdm theo phuang ddng tuong ty nhuPVD theo [12].

a. Phuong phdp xem PVD Id v^t lidu ddn hdi c6 hd sd thim tiieo phuong ddng tuOng ty nhu PVD tfieo (12} dupc vidt tdt Id FEM-1

Trdn t h i ^ t l , PVD dng xy theo md hlnh mjc ddl xdng (TDX), nhung dupe md phdng theo md hlnh phdng (MHP) trong phdn mIm Plaxis 2D v8J. VI v|y, hd sd thdm ngang. k^ vd hd sd dUng, k ^ dupe quy ddl tuong duong trong md phdng bdng cdc phuong trinh (6,7)

L 0.67 .

" [ln(n)-0. .75

Tmng dd: k^: hd s i thdm ngang cua MHP;

k^: hd sd thdm ngang eua TDX Xdc djnh hd sd thdm eda bde thim trong

Trong dd: k : hd sd thdm eda ble thdm trong MHP; q„^: khd ndng thodt nudc cua bae tiidm trong MhlP, c\^-2B.qJn.W; q^: khd ndng thodt nude eda bde thdm trong md hlnh Q)C[,

*U = K.Ji-'^w K«' ^^ so tfidm cua ble thdm trong DXT; 2b^: b l rpng Idp ddt md phdng PVD trong MHP.

b. Phuong phdp vdng tuong dUong theo [4]

dupc vidt tdt Id FEM-2

Vdng cdm PVD trdn thyc t l , dupe md phdng tiieo MHP trong phdn mdm Plaxis 2D v8 J bdng mdt kSp ddt tuong duong ed hd sd tiilm, k^

quy ddi bdng phuong trinh (8)

. f , 2.26,Pk,\

Trong dd: 1 (m): chilu ddi ddng thdm; k,^ hd sd thdm theo phuong ngang trong TEOC; 1^ ^ sd tham theo phuong ddng trong TDX; F= ^ { ^ nhan td xdt din dnh hUdng eda khodng dot

PVD. ' ^ "

22.3. Xdc dmh qf s i ch&nh ISch tuangddl(H Oe ddnh gid khdc bidt gida edc kit qud tinh todn, ty sd chdnh Idch tuong ddi, A(%) dupcld xuit de xde djnh sy chdnh Idch gida k i t qud tMi toan v ^ kit qud thyc tl.Ty so chdnh Idch tUDOg ddi Id ti so gida hidu eda dd Idn tinh todn vd d(

Idn quan trdc vdi dd lUn quan trde tich lOy Mn

nhat.

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Bdng 3. Chi tidu co ly cde Idp dat tai km 17 + 320 LdpdCt

L d p l L 6 p 2 L d p 3

D * y m 15.53 6.27 15.13

v

k N / m ' 14.50 15.40 1 9 ^ 0

• a

2.55 0.92 0.92

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9.08 8.10 1 0 3 0

c kN/m*

8.80 8.80 720

k.

m/nqdy 1.21 E-04 1.47E-05 2.76E-05

kh m/nqay 3.63E-04 4.41 E-05 3.10E-05

Cv m ' / n gay 2.53E-03 5.43E-03 4.30E-O2

mVnqay 5.06E-03 1.09E-02 8.60E-02

Hlnh 7. Mdt cat vt trf nghidn Cdu. Hinh 8. Ket qud do liin va qud trinh gia tdi

Hlnli 9. Ket qud phdn tid) hien trudng tai km 17 + 320, dudng Sal la flong-Tdy

Bdng 4. Chl tidu CO 1]? edc Ldpdit

L d p i L d p 2

Ddy m 27.7 2 3 3

d p d d t t ^ i k m 1 + 5 6 0

v

k N / m ' 16.50 17.50

e g

1.54 1.15

<P

C) 13.32 15.49

c kN/m^

13.00 2 0 3 0

k.

m/nqay 2.16E-04 1.45E-04

kh m/nqdy 2.59E-04 1.74E-04

C.

m'/nqay 2.28E-03 2.82E-03

Ch mVnqdy 4.55E-03 5.64E-03

Kinh 10. Mdt cdt Vi trf nghidn cihi

di= •^^!—^.100% (9)

Trong dd: A: TJ- sd chdnh Idch tuong ddi; x,:

gid trf d^ Idn quan trie; x,: gid trj dd Idn tinh Mdn, x,:Q4 Idn quan trdc tieh IQy Idn nhlt.

3. NghMn cdu hlf n trtittng 1 & 2 dU dn

diflRig din v i o clu Phd M9

l . a G M ( M ^ d ^ d n

Cdu Phu tiA9 bde qua sdng Sdi Gdn ndi Qu?n 2 vd Qudn 7, TP. HCM. Cdu dUpc thilt k l (gdm cdu chlnh vd cdu ddn) cd ehllu ddl 2031 m. Hal vj tri nghidn cdu ndm trong do?n dudng ddn vdo Cdu Phd M^ v l phfa Qudn 2, td km 2 + 183 J8 din km 2 + 371.43, cd chilu ddi 187.95 m.Vjtrfl cd ly trinh km 2 + 343 vd vj tri 2 cd ly trinh km 2+ 320.

Hinh ll.Ketquddo lun va qua trinh gla tdi

3.1 Nghlin oUtu hiin tnfimg 1 3.1.1 Mat cStvj tri nghlin cdu Mdt cdt vj tri nghidn edu tai km 2 + 343, cdch md cdu Phd My 160 m dUpc t h i hidn d Hlnh 1. Bac thdm dupe thi cdng vdi ehllu sdu 14.5 m, bo tri theo ludi tam gide, khodng cdch gida hai bac tham, S = 2 m. Lo^i bae thdm eda Singapore, FD747, ed kfch thUdc 4 x 100 mm.

Khd ndng thodt nudc; q_ = 1324 mVnSm. Cde ehi tidu eo iy tOtig Idp ddt dUpc trinh bdy trong Bdng 1 [6].

3. UQud trinh ddp nin vd quan trdc Qud trinh gia tdi t ^ vj tri nghidn edu theo Hlnh 2. Vj tri nghidn cijfu dUpe bd tri thilt bj do Idn t9i tim ndn dudng E3 (Kinh 1). Kit qud quan trde quan sdt trong 331 ngdy. bdt ddu td ngdy 13 tiidng 1 ndm 2008 din ngdy 27 thdng 12 n3m

Minh 12. Ket qud phan tfch hten tnfdng tai km 1 + 560, dudn Cau CdnTho

2008 vd dupe t h i hidn d Hlnh 2 [6].

11.3 Kit qud nghiin a3u

Kit qud md phdng tai km 2 + 343 dupc thi hien d H1nh 3. Dua vao sd lidu quan trie dd t h i hidn d Hlnh 2, kit qud Idn bdng phuong phdp gidi tich theo [2] vd 2 phuOng phdp FEM (Plaxis 2D v8.5) theo [4,12] vdi gid thiet PVD lam vide 1^ tudng.

3.1.4 Nhdn xdt

Kdt qud eho thdy ty Id chdnh Ideh tuong ddi Idn nhat gida dp lun tinh todn vd quan trde. A, theo 3 giai doan: (1] giai doan eo dd Idn < OJ m Id 8%, (2) khi dd Idn 0.81 m Id 283%, vd (3) glai do^n ed dd lun > 0.95 m Id 14.1%. Theo kit qud md phdng eho thdy FEM-1 vd FEM-2 song song vdi nhau nhung ed sy khdc bidt.

3.2 Nghiin cifu hiin tnOng 2

03J012nMi1Bai 5 7

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Bdng 5. Chi tieu eo ly cdc tdp ddt tai km 33 + 620

Ldpdft Ddy V e.

m kN/m' L d p l 10 15.00 2.19

9 6J3

c kN/m^

11.30 k.

m/nqdy 3.80E-04

kh m/nqay 7.60EO4

C, mVngdy 1.64E-02

&

mVnqdy 328^02

^L

U PVD S'bo ai hfoi lunli MB (iic

Hlnh 13. Mdt cdt vi tn nghien cim

3J.T Mdt cdt vi trf nghiin cOu Mdt cdt vj trf nghidn cdu km 2 + 320, cdch md cdu Phd M^ 36 m dupe t h i hidn d Hlnh 4.

Bde thdm dupc thi cdng vdi chidu sdu 14.5 m, b d tri theo ludi tam gide, khodng c^ch gida hai i>ac thdm (FD747), S = 1 3 m. Cdc chi tieu co ly tdng I d p ^ dupe trinh bdy trong Bdng 2 [6].

3JJi Qud trinh ddp nin vd quan trdc Qud trinh gia tdi t^i vj t r i nghidn edu theo Hlnh 5. \^ tri nghidn cdu dupc bd t r i t h i l t bi do lun Q i t i m ndn dudng E2 [Hlnh 4). K i t qud quan trdcquan sdt trong 331 ngdy, bdt ddu t d n g d y 13 thdng 1 ndm 2008 ddn ngdy 27 thdng 12 ndm 2008 vd dupe thd h i d n d H i n h 5 [10).

323 Kit qud nghiin cdu

K i t qud m d phdng t^i km 2 + 320 dupc t h i hidn d Htnh 6. Dya vdo sd lidu quan Udc dd t h i hidn d Hlnh 5. k i t qud Idn bdng phuong phap gidi tich theo [2] vd 2 phuong phdp FEM (Plaxis 2D v 8 3 ) theo [4,12} vdi gid thidt PVD Idm vide

\jtUdTyg.

3.1.4 Nhdn xit

K i t qud eho t h i y t y Id chdnh Ideh tuong d d i Idn nhdt gida d d Idn tinh todn vd quan t r d c &.

theo 3 giai d o ^ n : (1) giai do^n ed d d Idn < 0 3 m Id 1 1 % , (2) khi d p Idn 0.93 m Id 44.1%, vd (3) glai d o ^ n ed d p Idn > 1.20 m Id 11.7%. Mdt cdch tuong ty, kdt qud t d FEM-1 vd FEM-2 khdng tidm cdn nhau.

4 . N g h i d n cihi h i d n t r u d n g 3 d U l n Oai I d O d n g - T l y

4.f6MtfiJ#u

O^i Id D d n g Tdy, Id con duOng d e p n h l t Tp.

HCM. c d chidu ddi todn tuydn Id 21.89 km, d i qua dja bdn cdc qudn 1, 2, 4, 5, 6, 8, fflnh Tdn vd huydn Blnh Chdnh, t^o thdnh mpt t u y I n n y c giao thdng Odng - Tdy, vd kdt ndi hai ddu Odng Bic - T3y Nam thdnh phd.

V) t r i nghidn cUu km 17 + 320. ndm trong d o ^ n tU hdm Thd Thidm ddn cdu vUpt Cdt Ldi, thupc khu d d thj mdi Thu Thidm. Mdt cdt vi t r i

Hlnh14.Ketquddolun vaqua^nhglatai

nghidn eiJU dupe t h i hidn d hllnh 7. Bac t h i m dupc thi cdng vdi chidu sdu 21.5 m, bd tri theo hinh vudng, khodng cdch gida hai bde thdm, S = 1 2 m. Loai bac tham Chikami cua Nhat Bdn (A6) cd kich thude 4x100 m m . Khd ndng thoat nude, qw, 1000 mVnam. Cdc chl tidu co 1^ tCmg Idp ddt dupc trinh bdy trong Bdng 3 [19].

4.2 Qud trinh dip nin vd quan trdc Qua trinh gia tdi t^i vi tri nghidn cdu theo Hinh 8. \^ tri nghidn cdu duoc b d t r i thiet bj do Idn tai t i m ndn dudng E5 (Hlnh 7). K i t qud quan trdcquan sat t m n g 1019ngdy,t>dt dau t d n g d y 06 thdng 5 nim 2006 ddn ngdy 18 thdng 02 ndm 2009 vd dUpc t h i hidn d Hlnh 8 [11 ] .

4L3 Kit qui nghiin cdU

Kdt qud md phdng tai k m 17 + 320 dUOC t h i hidn d Hinh 9. Dya vdo sd lidu quan trdc da t h i hidn d Hinh 8, k i t qud Idn bdng phUOng phdp gidi tich theo [2] vd 2 phuong phdp FEM (Plaxis 2D V8.51 theo |4,12] vdi gid t h i l t PVD lam vide ly tudng.

4.4 Nhdn lat

Ty Id ehdnh Ideh tUOng ddi Idn nhat gida do Idn tinh todn vd quan trde. A, theo 3 giai doan:

(1) giai doan e d d d lun < 0.5 m Id 9.8%, (2) khi d d Idn 1.75 m la 19.8%, vd (3) glai d o ^ n cd d d Idn >

2.20 m Id 9.4%. K i t qda t d FEM-1 vd FEM-2 tidm can giai doan dau, nhung khi d d idn > 2.0 m thi dudng FEM~2 cd xu hUcmg tdch rdi xa d u d n g F E M - I .

5. N g h i d n cihj hidn t n / d n g 4 d y d n dudng d i n c l u C i n T h o

5.1 Gidl tiitiu

Cdu Can Tho bde qua sdng Hdu ndi thanh p h d Cdn Tho vd tinh Vinh Long v& c h i l u ddi todn b d tuydn d y dn Id 15.35 k m , trong d d cdu chinh vd cdu ddn Id 2.720 m vd dUdng dan 12.63 km. Vi & i nghidn cdu t^i km 1 + 560, doan d u i m g tUQudc LA I A re vdo cdu C I n T h o . M^t dt vj t r i nghidn cdu dupe t h i hidn d Hlnh 10. Bae thdm dupe thi cdng vdi e h l l u sdu 29 m. b d trf theo

Hinh 15. Kit qud phan tfch hi@n tn/dngt^l km 33 +

620, du dn dudng Nam Can

ludi tam giae, khoang edeh giiJia hai bde thSm, S

= 1.0 m. Loai bde thSm FD 747 eda Singapore cd kich thude 3 3 x 96.7 m m . Khd ndng thodt nudc q ^ = 4451 m V n a m . Cde chl tidu eo ly timg Idp dat dupe trinh bay t r o n g Bdng 4 [20].

5 ^ Qud trinh dip nin vi quan trie Qud trinh gia tdi tai vj trf nghidn cdu theo Hinh 11. Vi t r i nghidn cdu dupe bd trf t h i l t bl do Idn tai t i m nen dUPng 52 (Htnh 10). K i t qud quan udc quan sdt trong 728 ngdy, bdt ddu t d ngay 15 thdng 5 nam 2006 d i n ngdy 5 thdng 11 ndm 2008 vd duoc t h i hidn d Hlnh 11 [14].

53 laftqui nghiin cdu

Ket qud m d p h d n g tai km 1 + 560 dupc thd hidn d hfinh 12. Dua vdo s i lieu quan trdc da ti^

hidn d Hlnh 11, kdt qud idn bdng phuong phdp gidi tich theo 12] vd 2 phuong phdp FEM (Plaxis 2D v 8 3 ) tiwo (4,12] vdi gid tiiilt PVD Idm vide ly t u d n g .

5 . 4 N M n x A

Ty Id ehdnh lech t u o n g ddi Idn nhdt gida dO Idn tinh todn vd quan trdc, A, theo 2 glai do^n:

(1) giai doan ed d d lun < 0.25 m Id khdng ddng ke (2) khi d d lun 0.65 m Id 11.7%. K i t qud FEM-1 vd FEM-2 tidm edn nhau.

6. Nghidn cClu h i d n t r U d n g 5 dUdn dUAng N a m C i n

6.1 GHHOtiiu

Vj t r i nghidn cUU k m 33 + 620, ndm trong doan t h i nghidm thupe d y dn d u d n g Ndm Cdn n d i O L I A vdi ddt mui Cd Mau.Ddy Id v£ing trdng, ehju ngap nUdc sdu vd kdo ddi trong ndm, do vdy ed nhidu vat lidu sdt vd hdu co Idng dpng.

t r o n g mdt e l t dja chdt t d trdn xudng ddn dd sdu 30 m Id b u n sdt [3].

Mat cdt vj t r i nghidn cdu dupe t h i hien d Hinh 13. Ble t h a m dupe thi edng v A c h i l u sdu 1 2 3 m, b d t r i d i e o ludi tam gide, khodng cdch gida hai b l e t h a m , S = 1.6 m. Sd d g n g io^i bde thdm MD 7407 cua Thdi Lan ed kfch thUdc 3.0 X

« B

(5)

100 m m . Khd n d n g thodt nudc, q ^ = 1300 m V ndm. Cde ehi tidu c o ly t i ^ g Idp ddt duoc t r i n h b d y t r o n g B d n g 5 [ 3 ] .

6J2 Qud trinh dip nin vd quan trie Qud t r i n h gia tdi tai v i tri nghidn edu t h e o Hlnh 14. V\ trf nghidn cUu dupe b d trf t h i e t bi do Idn tai tim n d n d u d n g SSI (Hlnh 13). K i t qud quan trde quan sdt trong 130 ngdy, bdt dau t d ngdy 25 t h d n g 5 ndm 1996 d i n ngdy 3 t h d n g 10 ndm 1996 vd dUpc t h i hidn d Hlnh 13 [3J.

63 Kit qui nghiin cdru

K i t q u d m d p h d n g tai k m 33 + 620 dupe t h i hidn d Hlnh 15. Dya vdo sd lidu quan trdc da t h i hidn d Hlnh 14, k i t q u d Idn bdng p h u o n g phap gidi tfch theo [2] vd 2 phUOng phdp FEM (Plaxis 2D v 8 3 ) t h e o [4,12] vdi gid t h i l t PVD Idm vide t:^ t u d n g .

6.4 Nhin xit

Ket qud eho t h i y t^ Id chdnh Ideh tUong d d l Idn nhdt gida d<i Idn t i n h todn vd quan trde Id:

11.8% khi gid tr| d p Idn dat 0 3 5 m vd kdt qud m d p h d n g FEM-1 vd FEM-2 tl$m cdn nhau.

7. T h i o l u f n c h u n g k i t q u d n g h i d n c i h i h i d n t n A m g n i m d i ^ d n

Qua phdn tieh t d edc d p dn cho thay, d p Idn tinh todn 1]^ t h u y l t dua vdo tidu chudn hidn hdnh 22 TCN 244-98, cho d d Idn t h i l t k l khdng didn ra nhU quan trdc thUc t l , ddn d i n Idn dU.

Khi d d lun n h d hon 0 3 m, t ? sd chdch lech tuong d l i gida gid tri tfnh todn vdi gid trj quan trdc t d 8 - 1 1 % . Chdnh Idch ndy cd t h i d o dnh hudng eda v d n g xdo t r d n . Khi d 9 Idn < = 0.5 m, khd ndng thodt nude eda bde t h i m Id 1^ t u d n g eho ddt d v d n g d d n g bdng sdng Cdu Long [10, 11]. Rixner et al. (1986) eho rdng gia tdi n h d ndn ehua ehju dnh h u d n g eda d p lye ngang. Cde hat sdt chua d d t h d i gian eung nhU dp lye ngang d l ed till chui vdo bde t h i m Idm tde nghen bSc t h d m 19]. K i t qud nghidn cdu trdn p h d hpp vdi nghidn c d u eua Indraratna & Chu (2005).

Khi d p idn trdn 0.5 m, t y Id chdnh Idch tuong ddl Idn nhdt t d 20-44%. B^ Idn tinh todn d giai do^n ndy, d o iJng sudt bdn thdn vd dng suat d o tdi t r p n g ngod) vUpt qua dp lUc tidn cd ket ndn dp lye nudc Ifi rdng tdng eao. VI v^y, giai d o ^ n ndy nude thodt ra ngodi n h i l u . Oudng Idn d o quan t r i e t h e o nghidn edu [10, 11] khi do Idn Idn h a n 0 3 m t h i khd ndng thodt nudc cua bde t h d m bdt diu bj dnh h u d n g bdi b i l n dang. Khi tdi trpng cdng Idn t h i dp lye ngang cdng Idn Idm eho bde t h i m b| gidm t i l t didn d o d p lye ddt xung quanh tdc d d n g , khi dp ipc ngang Idn hpn 200 kPa t h i khd ndng thodt nude eda b l e tiidm g i i m [20]. B l e t h i m bj edc h^t sdt d p n g lai d Idi Idm eho b l e t h d m bj tdc n g h d n , gidm khd ndng thodt nudc eda bde t h i m [1].Theo nghidn cUu eda Indraratna & Chu (2005) eho t h i y rdng, dng vdi d p Idn Idn h o n O.S m t h i giai d o ^ n ndy bde t h d m tdm vide ngodi dnh h u d n g bdt v d n g xdo t r d n cdn bj d n h h u d n g bdt cdc y i u t d Idm gidm khd n d n g t h o d t nudc eda b l e t h d m . Theo kdt

q u d nghidn c d u eda [13], ty' Id ehdnh Idch tUong d d i giiib gid tri tinh todn khi bae t h a m lam viec 1;^ t u d n g vdi gid trj quan trdc eda eong trinh d Malaysia Ia31.8%.

Sy khac biet gida d p Idn quan trde va m d p h d n g dat eye dai tai d p Idn t d 0.8 m den 1.75 m, t u o n g dng vdi c h i l u cao dat ddp t d 3 3 d e n 4.05 m. Sau giai doan nay, sy khdc bidt gidm dan cho d i n cudi qud trinh gia tdi. L;? d o cho dug x d ndy cd t h i d o d p lye nude dan dan tidu t a n , d d rfing t r o n g ddt gidm d a n lam cho dUdng t i n h todn va quan trdc cd d p ddc tUOng ddi bang nhau d cudi glai doan gia t d i . Giai doan nay, t y Id chdnh Ideh t u o n g ddi gida gid trj t i n h todn viH gid trj quan trdc eda cae edng trinh dao d d n g t d 9-14% p h d h p p vdi k i t qud eda [13] Id ddi vdi ddt d Malaysia Id 1 1 % .

TU n h d n g phan tieh trdn cho ta thdy sy lam vide eda bde t h d m gida tinh todn 1;^ t h u y l t theo tidu c h u I n hidn hdnh 22 TCN 244-98 vd t h y c t l id khdng tidm cdn nhau. Gla tri tfnh todn t h e o 1;? t h u y l t chua p h u hpp vcri gid tri thyc t l . Ndn khi sd lieu tfnh idn d cdc edng trinh dat gid trj lOn theo tieu e h u i n n h u t i i U c t l t h i gid trj quan trde khdng dat tiM gid trj ti'nh todn. Chlnh vl thd, nhidu c d n g trinh t h i edng x o n g vdn tdn tal Idn d u , gdy I n h h u d n g khdng n h d d i n ch^t lupng eda cdng t r i n h .

Theo k i t qud d ^ t dupe tU nghidn cdu khi ede cdng t r i n h cd d d Idn h i t t h d i gian gia tdi <

0.6 m th1 k i t qud phdn tich theo phUong phdp FEM-1 vd FEM-2 ludn tiem cdn vdi nhau. Khi cdng trinh ed d d Idn het t h d i gian gia tdi 0.6 m

< S < 2.0 m hai d u d n g trdn ludn song song vdi nhau. Khi cdng trinh ed d p Idn h i t t h d i gian gia tdi 5 > 2.0 m t h i hai dUdng trdn tdch ddn nhau ra. VI vdy, t h e o k i t qud nghidn cdu eho thay, khi edng trinh ed d p Idn h i t thdi gian gia tdi S <

0.6 m t h i ndn s d d u n g phuong phdp FEM-2 d l m d p h d n g vl p h u d n g phap ndy d o n gidn, de sd dgng. Khi edng t r i n h ed d p Idn h i t t h d i gian gla tdi S > 0.6 m ndn sCr d y n g phuong phdp FEM-1 vl nd cd d p t i n cdy cao h d n .

8. K i t l u a n

Nghien edu da phan tieh hidn t r ^ n g lam vide eda bae t h d m d m p t sd cdng trinh cd x d ly ddt yeu bdng bae t h d m kdt h p p vdi gia tdi.TU k i t qud phdn tfch md nghien ciai da tim ra m p t sd nguyen nhdn vi sao bae t h a m Idm vide khdng n h u m o n g m u d n cua nha t h i l t k l khi sd d u n g tieu chuan hidn hdnh 22 TCN 244-98. K i t qua nghidn edu cho ta thdy khi d p lun < 0.5 m khd ndng Idm vide eda b i c t h a m cd t h d dnh hudng bdi v d n g xdo t r d n , t ^ Id chdnh Ideh tUong ddi Idn n h l t dao d d n g trong khoang 8 - 1 1 % . Khi d p lun 0.8 m < S < 1.75 m, khd nang Idm vide eda bac t h d m ed t h e dnh h u d n g bdi vdng xdo trdn, khd ndng thodt nude bj dnh hudng bdi nhidu y i u t d : b i l n dang, tde nghen, d p lye ngang, chieu ddi bde t h d m , v.v. A n h hudng eda cdc y i u t d ndy theo nghidn edu tht t# Id chdnh Ideh idn nhat t u p n g d d i dao d d n g trong khodng 20-44%. VI

vdy, kha nang lam vide bac t h a m Idm vide p h u thudc vao rdt nhieu yeu t d ma tidu c h u I n hidn hdnh 22 TCN 244-98 da khdng xdt d i n vd gid thidt k>le t h a m Idm vide trong dieu kidn ly t u d n g Id ehua p h d h p p vdi t h y c t l .

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19. Saigon East - wst highway canstnxtai project coretniciion contraa padcage 2,'Repon fix SMfemen at new thu thiem road: