I I mill Mill M'I'li'I'li'l H T M
THi NGHIEM M 6 HINH DANH GIA BIEN DANG LUN CUA NEN DAT YEU DUOC GIA C 6 BANG CAC COT D A T TRON XI MANG
TS. Le Ba Vinh Trudng dgi Hoc Qudc Gia Thdnh Phd Hd Chi Minh
Tom tat: Khi tinh todn do liin ciia cdng trinh dap tren nen ddt yeu dugc gia co bdng cdt xj mdng ddt, mdt sd cdc phuang phdp vd tieu chudn Irong nuac cUng nhu mcdc ngodi deu dua tren nhieu gid Ihiet dan gidn hda. Dieu dd ddn den nhOng chenh lech giUa ket qud tinh todn do lun theo cdc phuang phdp ndy vd theo thitc te. Trong bdi bdo ndy, cdc Idc gid xdy dung md hinh thi nghiem de ddnh gid bien dgng lun cita nen ddt yeu duac gia cd bdng he thdng cdt ddt trdn xi mdng. Dua tren ket qud quan trdc do lun theo cdc cdp dp luc nen khac nhau, tien hdnh so sdnh vdi kel qud tinh todn theo cdc phuang phdp gidi tich de Idm ro dnh hudng ciia ma sdt giiia khdi gia cd vdi nen ddt xung quanh.
Summary: In the calculation of settlement of embankments on the soft soil improved with cement treated soil columns, many methods and standards are ba.fed on several simplifying assumptions. That leads to the difference between the results calculated according to these methods and measured settlements. In this paper, the authors carried out model experiments to evaluate the deformation of soft ground reinforced by soil cement columns. From comparison between the analytical analysis and test results under inclined loads, the effects of friction between the reinforcement block and surrounding soft soils can be analyzed.
I. BAT VAN DE
Giai phap dung he th6ng c^t dit trgn xi mang dS gia c6 n§n dSt ySu la mgt phuong phap pho biln 6 Viet Nam va tren thj gioi. Hien nay, vSn dk ve bien dang ciia nen dat dugc gia co bjng cgt ddt trgn xi mang van egn nhiju tranh luan. Trong nhiju phuong phap va tieu chuan, cong thilc tinh toan dg liin ciia khdi gia eg khong xet din ma sat ciia kh6i gia co vol nen djt xung quanh, khong xet den su giam irng sudt theo do sau va mo dun bien dang cua khoi gia c6 chi dugc tinh tnmg binh, khong xet den tuong tac giira tr\i va ddt. Cach tinh nhu the se chira sat v6i thvc tS, vi trong thirc te phan iing Ngucri phan bien: TS. Phiing Vinh An Ngiynhjn bail 02/4/2015 Ngay thong qua phan bien: 16/4/2015 Ngay duyet dSng: 24/4/2015
thuy hoa xi mang se lam mat nuoc trong nen, d6ng nghia voi vi$e ma sat giira tru va dat tang dang kl. Ngoai ra, anh huong cua tai trgng ngoai se giam dan theo do sau. Trong bai bao nay, tac gia xay dung mo hinh thi nghiem de danh gia bien dang lun cua nen dat yeu dugc gia c6 bdng he thong cgt dat trgn xi mang.
II. CAC PHirONG PHAP TINH TOAN SO LUN ON DINH CtJA NEN DAT YEU DUQC GIA C 6 BANG Hi; TH6NG CQT DAT TRON XI MANG
Nhin chimg, cac qui trinh tinh tgan ciia Vi?t Nam, Trung Qu6c, Chau Au, Thuy Dien diu phan do lun cua nen gia eo thanh 2 thanh phdn S=Si+S2 (Sl - do liin ciia khoi gia co, S2 - do Wn cua nen ddt duoi kh6i gia c6). Trong bai nay dg lun cua kh6i gia c6 dugc tap trung phan tich.
TAP CHl KHOA HOC VA CONG NGHE T H C Y LOI SO 2 6 - 2 0 1 5 9 5
I KHOAHOC ^ . J . I J I e l J I . ) ! ! ^
A. Tinh toin dg tin theo TCVN 9403-2012 [2]
Do lun cua ban than khdi gia cd dugc tinh theo cdng thiic:
r^qH^ qB (1) ' E„ oE^.+(!-«)£:
Trong do:
q - tai trgng cdng trinh truydn len khdi gia cd (kgf/cm^)
H - chieu sau cua khdi gia cd (cm) n.Ac a - ty sd di?n tich, a =
BX Ac - dien tich tidt didn tru (cm ), n- tdng sd tru.
B, L - kich thude khdi gia cd (cm) Ec - modulus dan hdi cua cdt dat trgn xi mSng (kgf/cm^)
Es - modulus bien dang ciia dat xung quanh cgt (kgfcm^)
B. Tinh todn dp lun theo tieu chuin DBJ 08- 40-94 (Trung Quoc) [I]
Dg liin cua khdi gia cd dugc xae dinh theo cdng thiic:
(PQ + Poz).H Sj =
2.Etb
(2) Trong do:
po - ap !uc trung binh tai dmh cdt (kgfi'cm^) Poz - ap luc tai mui cdt (kgf/cm^)
Yc - dung trgng ciia cdt xi mang dat (kgfi'cm"') Ys - dung trgng ciia ndn dat yeu trong hop md hinh (kgf/'cm^)
(3) (4)
IH. THI NGHIEM M 6 HINH DANH GIA BIEN DANG LUN CUA NEN DAT YEU DU'OC GIA CO BANG H? THONG CQT XI MANG DAT
A. Muc dich thi nghiem
Thi nghidm tren md hinh nhdm danh gia iing xir cua he cgt xi mang dat va nen dat yeu theo cac cap ap luc nen (d day chu ydu danh gia anh hudng cua ma sat giiia khdi dat gia cd va dat xung quanh den bidn dgng liin ciia khdi gia cd). Do ap l\rc nen, chuydn vi ciia he thdng cdt xi mang-dat trong md hinh d tung cap ap lire theo thdi gian. Tir kdt qua thi nghiem trdn md hinh, dung phuong phap Asaoka dd xae dinh do liin dn dinh cua nen gia cd. Tir do so sanh, danh gia kdt qua do liin trdn md hinh vdi cac phuong phap giai tich.
B. Npi dung thi nghiem
- Diic mau xi mang-dat vdi ham lugng xi mang 16% cd dudng kinh 20mm, dai 200mm - Thi cdng cdt xi mang-dat vao trong nen dat ydu bdn trong hop mo hinh
- Gia tai theo timg cap ap luc, do tri so ap luc nen, chuydn vi ciia he cgt xi mSng ddt va ndn dat yeu theo thdi gian, quan sat, chup hinh.
C. Cach tien hdnh
Mlu ddt ydu dugc ISy d phudng Binh Khanh - Quan 2 - TP Hd Chi Minh. Dimg may trdn chd bi lai mau dat, sau dd cho mau dit vao trong hop md hinh dS dugc quet mdt ldp diu nhdt de hgn chd tdi da ma sat giiia dat va thanh hop, dgy nap hop md hinh Igi dd dit cd kdt dudi trgng lugng ban than trong vdng 3 ngiy. Sau do, dgt mgt ldp vai dia ky thuat ldn tren nen dit ydu, rdi rai mgt ldp cat day 10mm len ttdn ldp vai dia ky thuat. Ldp vai dia ky thugt va ldp cat se dam bao cho nudc dugc thoat ra theo bien trdn. Dgt tim ciing tan luc ldn tren ldp cat va gia tai cd kdt dit d cac cap ap lyc nhu bang 1.
96 TAP CHf KHOA HOC VA C O N G N G H E T H O Y LOl S(5 26 - 2015
KHOA HOC Bang I: Cap ap lire d l co k i t I4p dat trong
mo hinh Cap ap luc (kgffcm^)
Thai gian (ngay) 0 3
0.20 4
0.43 4 Sau khi cd kdt xong, mang m l u dit di thi nghidm, kdt qua phan tich cac chi tidu co ly ciia dit sau khi chd hi dugc thd hidn hrong bang 2
Bang 2: Tinh chat ciia mau dat sau khi ehe bi
TT
1
2 3 4 5 6 7 8 9 10 11
Gia tri cff Iy
Cat: 0.05 - 2.0 (mm), % Bui: 0.005-0.05 (mm), % Set < 0.005 (mm), % Bglm tir nhien, W(%) Dung trgng ty nhi^n, yw (KN/m')
Ty trgng, Gs H? so rong ban dau, EO Dg rong, n (%) Dgbaohoa, Sr(%) Gioi han chay, LL (%) Gidi han deo, PL (%) Chis6deo,Pl(%) + ip (Do) + C(kPa)
Gia trj d^i dien ciia cac lop dat
5.1 53.6 41.3 73.2 148 2.66 2.093 67.7 93.0 71.2 35.6 35.6 03°39'
6.27
Hgp md hinh dugc Iam bang thep tim cudng dg cao day 2mm, c6 kich thude dai 900mm, rgng 130mm, cao 230mm.
Hinh I. Md hinh thi nghiem
1 jO 0 0 0 0
1 G O O
9
1
=
Hinh 2. Mat bdng bd tri cpt xi mdng ddt trong md hinh thi nghiem
He thdng gia tai sir diing bom thiiy luc va kich ep, he thdng do ap luc tac dung ISn tam ciing bang ddng hd didn tii. Ldp dat yeu trong md hinh day 230mm. He thdng ddng hd do chuydn vi cua cot dat trdn xi mang se ghi lgi gia trj chuyen vi theo tung cap ap luc nen theo thdi gian. Sau khi cd ket xong nen dSt ydu, do tai, cao ggt mat tren cua md hinh dd chieu day ldp dat yeu cdn lgi 200 mm. Diic mau xi mSng/dit vdi ham Iugng 16%, ham Iugng nudc/xi mang bang 1,5, dudng kinh 20mm, chieu dai 200mm.
Bang 3 : Mot so chi tieu cua mau xi mang-dat vdi ty If 16%
Tuoi bao dirong Ngay 7 14 28
at
%
16 q»
kgf/cm^
5.302 5593 6.691
E kgt/cm^
526.8 577.6 678.9
e
%
1.33 1.20 1.13
TAP CHl KHOA HOC VA CONG NGHE T H C Y LOI Sl3 26 - 2015 97
I KHOAHOC l . l t l J I c l J i a ! ! ^ Khoang each bd tri cac cgt dat trdn xi mang tu tam ddn tam la 50mm, bd tri cgt theo hinh tam giae. Mau diic dugc 7 ngay tudi se dugc thao ra khdi khudn va cam \ ao hop nro hinh, ke den trai mdt Idp vai dia ky thuat Idn phia trdn khdi gia cd, sau do rai thdm mdt ldp cat day 10mm len phia tren ldp vai dia ky thuat. Chd cgt xi
mang-dit dii 28 ngay tudi thi bit diu tidn hanh thi nghidm. Dgt tim ciing tan luc day 3mm, dai 140mm, rgng 127mm ldn trdn va tidn hanh gia tai theo tung cap ap luc, ddng thdi bim thdi gian va ghi lgi sd dgc ciia ddng hd chuydn vi ling vdi 1, 2, 4, 8, 15, 30, 60, 120, 240, 480, 720, 1440 phut.
9 8 TAP CHl KHOA HOC VA CONG NGHE THUY LOl S 6 26 - 2015
^OA HOC "1^BJS3!B!^B
Hinh 3. Cdc budc thuc hien trong md hinh thi nghiem
Tidn hanh gia tai theo tirng cip ap luc, (sd dgc da dugc hieu chinh trgng lugng sd dgc lire tren ddng hd tuong iing vdi ciia trgng lugng kich thuy luc va tim tling cap tai dugc tinh toan nhu bang 4 cung tan luc)
B^ng 4: So dgc dong ho tinrag img vdi ap luc nen Ap lyc nen
S6 dfc trSn dong ho kgfcm^
kN 0.5 0.7
1.0 1.6
1.5 2.5
2.0 3.3
2.5 4.2
3.0 5.1
4.0 6.8 Ap lire nen cua timg cap se dugc giii khdng ddi hinh theo thdi gian, viec phan tich dg liin dn cho ddn khi chuyen vi Iiin ciia ndn dat va he cdt xi diiih cua nen dat yeu gia cd bang cdt dat trdn mang dat dudi tam Cling dn dinh (khoang 24 gid). xi mang dugc thuc hien theo phuong phap D. Cac kit qua thi nghi?m ^^^°^^ t^l '^'^^ ^ 8 '^^P ^P ^^'^ ' ^ ^ ^^"•
Vdi mdi cip ap luc nen, tir cac dg lun cua md * "^^' ^^P ^P ^"^^ "^^ ^^ kgC'cm^
TltirliUiuiipltiili
0 200 400 &00 SOO 1000 1200 1400 1600 0 070
B 0.065
0 040 0 044 0 048 0 052 0 056 0 060 0 064 0 068 0 072
&f Mu tr d i M dlfm t-1 ( C H )
Hinh 4. Kit qud phdn tich dp lun dn dinh theo Asaoka a cdp dp luc 0.5 kgf/cm
TAP CHl KHOA HOC VA C O N G N G H t THUY LOI S6 26 - 2015 99
: KHOAHOC M I I ' l l i ' l l l M
* Vdi cdp dp luc nen LO kgf/cm^
0 107
0 1 0 » 1 1 * 11B-12D 1 2 1 1 1 2 » 1 3 » 13D-141) 1411 149 fifUnvttaMdlnn t - K a n )
Hinh 5. Kit qud phdn tich do lun on dinh theo Asaoka a cdp dp luc 1.0 kgf/cm
* Vdi cdp dp luc nen I.S kgf/cm
1 1
J
0 1 9 7 0 192 0 187 0 182 II 177
n 17i;ip 17411 1780 1820 1860 1900 1940 1980 202 tiq hin a HiM d l n n t-1 (cm)
Hinh 6. Kit qud phdn tich dp lun dn dinh theo Asaoka a cdp dp luc 1.5 kgf/cm '' Vdi cdp dp luc nen 2.0 kgf/cm^
0 0 215 0 220 J 0 225 1 D230 I 5 0/^". 4 1 0^4.. \
5 0 245 \ 0 I'.i) >
0 255 0 2 6 0
TIiDlKliUiiphni
500 1000 1500 2000
0 2 7 0
Z 0 2 6 0 ^ r
•1.1... y ^
•r,«n ^
J 0 245 > T ^ ^
* 0 2 4 0 ^ / ^ 0.2 J 5
0 - 2 3 5 D 2 S ' J l . ; 4 I i 2-1^1 i'.\t ^'.H>i';go 2 t , j j {>f M M * i h M M r a i i - 1 1 n n ,
Hinh 7. Kit qud phdn tich do lim on dinh theo Asaoka a cap dp luc 2.0 kgf/cm'
100 TAP CHl KHOA HOC VA CONG NGH£ THUY UOIS6 26 - 2015
' ^^ <^4P ip lu-c nin 2.5 kgf/cm'
Tlioieliuiipliuii 500 1000 1500
KHOA HOC ^ E S 3 ! B ! ^ B
0328 0-J26
£ ..J24 5 0 J22 I 0 JZO 1 "J18 .» 0 316 S 0 514 (= U J12 0 510 0 308
0.i0» 510 JIB 51* 310,51» 320 5211 52* 526 328 D9 ION a Ihdi dlcm t-1 ((ml
Hinh 8. Kit qud phdn tich dp lun on dinh theo Asaoka a cdp dp luc 2.5 kgf/cm
* Vdi cap dp It^c nen 3.0 kgf/cm^
ThsieiaD ipbafi
0 200 400 600 800 lOOO 1200 1400 1600
0 370
0 370 0 375 0 380 fl 385 0 590 0 395 f>mtmmmikki4itmt-Htm\
Hinh 9. Kit qud phdn tich dp lun dn dinh theo Asaofca a cap ap luc J. V tcgf/cm'
* V&i cap dp luc nen 4.0 kgf/cm^
0 ?3ir?*=*f*SH' 1500 2000 ']l[\
0 47» 47» 48« 4H» 49# 49» V»* 50* 61# 51* 'V4
^ BiHmmtkHMtmt-Hamt
Hinh 10. Kit qud phdn tich dp lun on dinh theo Asaoka a cdp dp luc 4.0 kgf/cm
TAPCHfKHOAHOCVACONGNGHeTHUYLOl 5(326-2015 101
KHOA HOC
Tong hgp cac ket qua phan tich do lun on de xae dinh do liin 6n dinh cua n^n gia co dinh duoi tung cap ap lire dugc the hien trong mo hinh, cac kh qua tinh liin dugc the trong bang 6. Men trong bang 6 [4]. Trong do Es % theo gl4
• Ki4m chtog do lun 5n dinh cua nSn gia cd "1 "™ <=* ''^' ''^^ "mg "^ap ap lgc. Tir thi theo cac phuong phap giai tich "S^'*"' °™''° ^^^ " ^ ^^ ^^u khi ehe bi ta co cac gia tri modulus bien dang cua khoi gia co Neu ap dung 2 phuong phap giai tich neu tren ,^g(, ((^g ^^p ^p ,„^ ^ „ ^ing 5.
Bang 5: Gia tri modulus bien dang cua khoi gia co theo tirng c^p ap lyc nen p
Etb kgCcm^
kgf/cm^
0.5 87.4
1.0 88.3
1.5 89.4
2.0 2.5 90.7 1 91.9
3.0 93.3
4.0 96.4 Bang 6: DO lun hn dinh tinh theo cac
phinmg ph^p CSpap
luc (kg/cm')
0.5 1.0 1.5 2.0 2.5 3.0 4.0
TCVN 9403-
2012 (cm) 0.075 0.150 0.219 0.299 0.359 0.426 0.598
DBJ 08 40 94
(cm) 0.077 0.152 0.221 0.302 0.361 0.428 0.600
DO lun quan trac (cm) 0.064 0.137 0.198 0.263 0.330 0.400
• 0.524
cip *pl*i BM (kfl am')
Hinh 11. So sdnh dp lun dn dinh tinh theo mpt sd phuang phdp
NH^N XET
Trong 2 quy trinh tinh toan dg Iiin ciia khoi gia CO bing cgt xi mang dat TCVN 9403- 2012 va tieu chuin Trung Qudc BDJ 08-40- 94 thi tinh toan theo quy trinh Trung Qudc cho kdt qua Idn hon tir (0.4^ 3.0) %, do BDJ 08-40-94 CO xet ddn aidi hudng cua ling suSt phu do trgng lugng ban than cgt.
Kdt qua quan trac Iiin trong md hinh cho kdt qua nhd hon so vdi phuong phap tinh cua 2 tieu chuan trdn, vdi chenh Idch ldn nhit la 20.3%. Nguyen nhan cua sir chdnh lech nay la vi:
Cac cdng thiic tinh trong cac tieu chuan thudng cd xu hudng thidn vd an toan.
Cdng thiic tinh Iiin theo tieu chuin tuong tu nhu dinh luat Hooke kha don gian. Khi tinh liin theo tieu chuan da khdng xdt ddn l\rc ma sat xung quanh khdi gia cd do dit ndn tao ndn. Do do tao ra su khac bi?t giiia kdt qua tinh Iiin theo tidu chuin va theo thi nghiem trong md hinh thge te.
Trong cdng thirc tinh Iiin theo tieu chuin, modulus dan hdi cua khdi gia cd liy theo phuong phap trung binh trgng sd la chua phu hgp, vi modulus bidn d ^ g phy thugc rit nhieu vao su tuong tac giira dit va tru, dan ddn nhihig sai lech so vdi kdt qua th\rc td trdn md hinh.
102 TAP CH( KHOA HOC VA C O N G N G H E T H O V LOI S<5 2 6 - 2015
KHOA HOC ^ E S g H g g S ^ B Tinh todn dg lun theo phuang phdp gidi tich
CO xet dnh hudng cua ma sdt giQa khdi gia cd vd nin ddt xung quanh.
Luc ma sat giua khdi gia co va ndn dit xxmg quanh tinh theo cdng thiic:
/, =(l-sinp)x(7^x/'g^+C Trong do:
rjf^ - ling suat hihi hieu giiia Idp dat trong khdi gia cd theo phuang thang diing
. _ / x f t _ 4,8x0,2
= 0,48 (kN/m^) - 4,8.10-'(kgfcmO
/,=(l-sin 3,65)x4,8xlO-'x/g3,65+0,0627=0,063 (kgfi'cm')
Tir do tinh liin vdi tai trong thuc tac dung len khdi gia cd la:
, q>iBxL-fx2xHxB q' = ^ ^
BxL
Hinh 12. So sdnh do liin dn dinh tinh theo mpt sd phuang phdp c6 xet dnh hudng cua ma sdt
giira khdi gia cd vd nen ddt xung quanh.
Khi xet ddn anh hudng cua ma sat giiia khdi gia cd va ndn dat ydu xung quanh, cac ket qua tmh lun dugc the hi$n nhu tren bieu do hinh 12. Tir day ta thay do Iiin xae dinh theo cac phuong phap chenh Idch khdng nhieu. Chenh lech giu'a do Iiin quan trac trong md hinh so vdi dd liin tinh theo phuong phap giai tich (tinh theo % dugc thd hien trong bang 7).
Bdng 7: Chenh Ifch giu-a dp Iiin tinh theo phurong phap giai tich va dg liin quan trac Cap dp luc n6ti
Theo TCVN 9403-2012 Theo BDJ 08 40 94
Kgf/cm^
%
%
1.5 6.7 5.7
2 0.5 1.3
2.5 1.7 1.1
3 1.8 1.3
• 7.3 7.7 IV. KETLU.^N
Trong 2 quy trinh tinh toan dp liin on dinh cua kh6i gia c5 bing cgt xi mSng-dit theo TCVN 9403-2012 va ti^u chuSn Trung Qu6c BDJ 084094 thi tinh toan theo quy trinh Trung Qu6c cho k6t qu4 Ion hem tvr (0.4+
3.0) %, do BDJ 08-40-94 co xet d6n anh hu6ng cua ling sudt phu do trpng lugng ban than cpt.
Cae kSt qua dp liin do dugc tir mo hinh thi nghi$m dSu nho hon cac kit qua tinh toan dp liin cia kh6i gia c6 theo TCVN 9403-2012 va theo tiSu ehuin Trung Qu6c BDJ 084094,
voi chenh lech Ion nhat la 20.3%, mpt trong nhQng nguyen nhan la vi khi tinh lun theo cac tieu chuan da chua xet den lire ma sat xung quanh kh6i gia co do dit nin tao nen.
- NIU khi tinh liin theo cac tieu ehuan co xet din luc ma sat xung quanh khoi gia co do dat nSn t?o nen thi chenh lech giua kSt qua tinh liin theo cac tieu chuin va dp liin do dugc tir mo hinh thi nghiem chi Ion nhit la 7,7%. Do do, ki6n nghi cin xem xet tinh iin lire ma sat ciia khdi gia co va nen dat xung quanh khi tinh toan dp liin on dinh cua khoi gia co bing cpt xi mang dSt.
TAP CHl KHOA HOC VA CONG NGHE T H O V LOl S<5 26 - 2015 103
I KHOA HOC ^ « ? « 1 J f c l J f c f f T ^ L6I CAM ON
Nghidn cuu nay dugc tai trg bdi Dai hgc Qudc gia Thanh phd H6 Chi Minh (VNU-HCM) trong khudn khd dd tai '"Nghien ciiu phucmg phap tinh toan do liin dn dinh va do liin theo thdi gian ciia ndn dit yeu dugc gia cd bing cgt dit xi mang", cap DHQG, ma sd: C2014-20-13. Tac gia ciia bai bao xin tran trgng cam on.
TAI LIEU TILWI KHAO
[1] Quy pham ky thuat xu ly ndn mdng cua Trung qudc (Shanghai- Standard: Ground treatment code, DBJ 08 40 94) do Truong Dai hgc Ddng td bien soan, nam 1995
[2] Tieu chuan xay dung Viet Nam TCXDVN 9403 : 2012 "Phuong phap gia cd ndn dit ydu bang tru dit xi mang", 2006.
[3] A. Asaoka, Observation procedure of settlement prediction. Soil & Foundation Vol.18, No.4, Septl978
[4] Dmh Hiru Dung, Phan tich tinh toan do liin ndn dip tren nen dit yeu dugc gia cd bing cgt dit trdn xi mang, Luan van Thac a trudng DH Bach khoa TP.HCM, 2014.
[5] K.Oinine & H.Ochiai "Homogenization method for numerical analysis of improved ground with cement treated soil columns".
104 TAPCH(KHOAHOCVAC0N6NGH£THUYLOtS<526-2015
