J T - . H S ^
'^\-li
Phan tich, xac dinh hap ly cac tinh chat CO* ly cua dat yeu khi gia co bang xi mang
Ngay nhan bai: 20/7/2014 Ngay sOft bai: 5/8/2014 Ngay chap nhan dang: 10/8/2014
Le Ba Vinh, Dinh Hu'U Dung
T O M TAT:
Xuf ly nen dat ylu bang try dat xi mang la giai phap ph6 bien, nhim n ^ g cao cUdng do, giim bien dang cua nen dit can xtl Iy. Vi vay, viec xic dinh mot each h<?p ly siJ bien d6i cua cic chi tifeu ve cii6ng dgi, biS^n dang, tinh thim cua tru dat xi mang la rat quan trpng trong viec thiet k<f, tinh toin xii ly nen dit yeu bang triji dat xi mang. Bii bao tip trung phin tich sif bi^n doi ve tinh nen liin, he so tham va cifdng dp cua tru dat xi ming theo him lilpng xi mang vi th6i gian bao diOng khac nhau bang cac thi nghiem trong phong.
Tii khoa: tru dat xi mang, m6 dun dan h6i, mo dun bien dang, he so tham
ABSTRACT
Soft soil reinforcement methods by using soil cement columns are very popular by enhancing the strength and deformation characteristics of the soft soils. Therefore, the reasonable determination of the strength, deformation, and permeability characteristic of soil cement columns is very important in the design and calculation of these methods. This paper analyse the compressibility, coefficient of permeability and shear strength of soft soils reinforced by cement with different cement contents and curing times.
Keywords: soil cement columns'. Young modulus, modulus of deformation, coefficient of permeability.
TS.LeBaVinh
Khoa Ky thuat Xiy diing, Trii6ng Dai Hoc Bich Khoa, Dai Hpc Quoc Gia Thanh Pho Ho Chi Minh
Email: [email protected] KS. Dinh Hflu Dung - Hoc vi^n cao hpc Tnfdng D ^ Hpc Bich Khoa Thanh Pho Ho Chi Minh
I.Gidlthifu
Hien nay, try dSt xi mang la m6t trong nhiJng gidi ph^p pfio bien de gia CO, xCr 1^ nen dat yeu. Khi tfnh toin 66 lOn on dinh va do lOn theo th6i gian cua nen d^t y^u co gia co bang tru dat xi mSng, can x^c ^ n h mdt each hop ly sif bien d^i cua cac chl tieu v l bien dang, cudng dp, vi tinh thIm cCia tru dat xi mang. Beii bao ndy tSp trung phSn tich sif bien d6i ve tinh n€n liin, h | s6 tham vh cudng do ciia tru d^t xi mang theo cac hdm lu'gng xi mang va thdi gian bSo du'dng Ichdc nhau bSng cdc tht nghiem trong phong. Qua d6, de xuit viec lira chpn mpt each hpp ly cac dac trifng ve bi€n dang, va tinh tham ciia tru dat xl mang Ichi tinh t o i n bi^n dang ctHa nen gia co.
2.1111 nghiem xic djnh cic ^ tntng ccf Ij^cOa <Kft trdn xi mang 2.1. Cdc vdt liia sif dung
IMau dat dUdc lay ddo sau -2.5m 6 phudng Binh Khanh - Quan 2 -TP.
Ho Chi IWinh. Dat nghien cilu thupc loai set it deo (CL) trang thai chiy (TCVN 5747-1993), ham luung nhdm hat bui chiem 39.6%, nhom hat set chi^m 50.5%, do am tu nhien 75.5%, gidi han chdy 71.2%, gidi han d^o 35.6%, hdm lu'png chat hCru CO tiiang do! cao (6.5%) goc ma sdt trong cp = 2=43'vd iLfc dinh C =10.3 ItPa.
Chat dinh ket difpc sii dung la xi mang Portland (xi mang Hoicim PCB40).
2.2. Chuin hi mau dat trdn ximdng
Mau dat dUdc trgn vdi xi mdng theo cdc t f le: 10%, 12%, 14%, 16%, 18%, va 20% (tinh theo trong lupng the tich dat khd), dd I m cOa hon hpp dUdc CO dinh d 75.5%. Hda xi mang vdo nu'dc theo hdm lu'png da tinh toan trifdc, rdi tUdi d^u dung dich nay vao trong dat Cho hon hpp vaomaytrpn, trpn trong vdng 5 phiit dexi mi'ing vd nddc dUpc phSn t i n
(a) (b) Hinh 1. May tron dat-xi mang (a), thiing bio dU^g mSu (b)
10.2014 B V I I i i B I l 171
Bdng 3: Chi sd nen Ham lu'png xi
mang
(%)
10 12 14 16 18 20
va chi so n d tif thi nghierr oedometer Cc
7 ngay
0.565 0.399 0.302 0.239 0.236 0.233
14 ngay
0.561 0.409 0.292 0.233 0.229 0.219
28 ngdy tuoi 0.555 0 3 9 5 0.282 0.199 0.189 0.173
Cs 7 ngdy
tuoi 0.033 0032 0.024 0.020 0.018 0,016
14 ngay tudi 0 031 0.029 0.02 0.016 0.015 0.014
28 ngay tudi 0.029 0.021 0.013 0.012 0.011 0.009
B^m tir^ne 11 mang/dll (%)
-^ ,„.., — i , N , . , -^M^ -^"^'^ -^'"^ ^ " " ^ Hinh 10 QuantiegiaaciilsSnenvahamluHngximang Kinhll.QuanliegiiJaclilsan&vahamlifflngximang Bdng 4: Md dun bien dang cCia mau dat trdn xi mang xac dinh til thi nghiem nen cd ket
d p ap lUc (kqf/cm^)
0 25 0.5
1 2 4 8 16
Cdp dp ldc (kqf/cm') 0.25
0.5 1 2 4 8 16
Ham lu'ong xl mang % 10
7 nqay 24.5 104.2 119,0 208.3 59.5 55.6 46.3
14 ngdy 26.0 92.6 119.0 277.8 64.1 55.6 49.0
28 ngay
26.0 75.8 83.3 138.9 75.8 59 5 46.3 16 7 ngdy 75.8 166.7 166.7 208.3 119.0 138.9 75 8
14 nqay 83.3 92 6 208.3 277.8 277.8 138.9 7S.8
28 ngdy 138.9 833.3 208.3 277.8 416.7 166.7 92.6
12 7 ngay
22.5 37.9 166.7 104.2 119.0 83 3 52.1 HamiL
14 nqay 59.5 99.2 160.3 189.4 231.5 189.4 173.6 onq XI m
28 ngay 28.7 49 0 64.1 92.6 104.2 83.3 69.4 a n g % 18 7 ngdy 138.9 138.9 166.7 277.8 208.3 138.9 69.4
14 ngay 138.9 166.7 166.7 277.8 208.3 138.9 69.4
28 ngay 138.9 208.3 138.9 277.8 277.8 166.7 92 6
14 7 ngdy 29.8 59.5 166.7 208.3 166.7 1042 55.6
14 ngdy 29.8 641 119.0 208.3 208.3 119.0 69.4
28 ngdy
36.2 69 4 166.7 208 3 277.8 119.0 75.8 20 7 nqay 104.2 138.9 277.8 208,3 208.3 138.9 69 4
14 nqay 138.9 104.2 277 8 208.3 208.3 166.7 69 4
28 ngdy 138.9 208.3 166.7 833.3 277.8 208.3 75.8
tii 10% den 16%, khi ham lupng xi mang t(n6%
den 20% chl sd nen co xu hu'dng gidm cham. fl 28 ngay t u o i , chl so nen cua ddt trdn xi mang v6i ham lu'png xi mang Id 20% gidm di (5-6) lan so vdi dat t u n h i ^ n , d o vdy dat trdn xi mang lun it hon so vdi dat t p nhien. Khi tang hdm luang xl mang vdo t r o n g dat, bd khung ket cau cCia dat dupc cdi t h i ^ n dang ke, ldm cho 6$t6n djnhvS t r d nen cOtig hem.
* Chl sd n d cua mau dat trdn xi mang Chl 56 n d cCia dat t p nhien Id 0.116, cdn mlti dat trdn xi mang vdi ham Idpng 10% d 7 ngSy tudi cd chl sd n d giam di 3.8 Idn so vdi chi s6 n d cCia mau dat t p nhien. Nhif d hinh 11,chi sfl n d cua mau dat trdn xi mang co xu hudng bi^n ddi gidng n h u sp thay ddi cua chl sd n^lfcQa dat trpn xi mdng: gidm manh khi ham liTflngxi mang tif 10% den 16%, cdn khi hdm lifUng xl mdng til 16% d^n 20% chl sd nd cd xu hi/cing gidm cham IWau dat-xi mang cd hdm lUang xi mang 20% va bdo d d d n g sau 28 ngay thi c6 chi sd n d gidm di 12.9 lan so vdi chl sd nd cQa Sk t u nhien. Dieu do chu'ng t d khi d d tdi dat trdnxi mang n d ra it hdn so vdi dat tU nhi&n.
N h u vay, khi thay doi ham lupng xi mang, vdi sp bi^n ddi cCia cUdng d p khdng nen mot true, md dun dan hdi cua mdu dat trdn ximSng trong cac t h i nghiem nen mdt true 6 tr^n, cung n h u sU bien doi cCia chl sd nen vd chl sd nfi cCia mau, cd the chpn ham lUpng xi mang tdi uU cho loai dat yeu tai khu vUc nghien ci3u la 16%.'"
* Md dun bien dang cCia mau dat trdn xi mang
Hinh 12 Suttiay doi ciia moflun bien dangtheoham lumg XI mang, then gian b ^ diiSng, va ^p life nen
TU cac ket qud t h i nghiem, su thay doi cila md dun bien dang ciia mau dat trdn xi mang khi thay ddi t y le xi mang/dat dUOc t h ^ hi^n nhi/
trong bdng 4 vd hinh 12. Ti^n hanh so sanh cSc dac trUng bi^n dang cua mdu dat trdn xi mang (xac dinh theo 2 phUOng phdp thi nghi§m neu tren) n h u bang 5. Co t h i nhdn thay md dun dan hdi t h u dupc t d p h u o n g phdp nen cd ket cho ket qud hau n h u nhd hdn nhieu so cdc gia trj thu dupc tif p h u a n g phdp n^n d d n , vdi sU ch&nh lech CO the len d^n 80%.
Theo m d t sd h u d n g ddn tinh toan 66 liin cua nen dat yeu dupc gia co bSng cac tru dat- ximang [1],[3], [4], ... thi m o dun ddn hoi cOa mau dat-xi mdng cd the t h u dUpc tif thi nghiem n^n d o n , ttfc Id coi n h u xung quanh tru d^wi mang Id khdng khi. Tuy nhien, vdi cdc nen dat
74BII!BIOai 10.2014
Bang 5: M d d u n ddn hdi va m d d u n bien dang cda mau dng vdi cdc hdm lUdng xi mdng
Ematn*.(61A(kgf/Cm') E5D,n«,an->(kgf/cm')
Chenh lech (%)
Hdm lupng xi mang % 10
138.9 265.1 47 6
12 104.2 522.1 80.0
14 277.78
624.6 55.5
16 833.3 689.9 -20.8
18 277 8 736.4 62.3
20 833.3 772.9 -7.8
thUc te t h i x u n g quanh m p t t r u dat-xi mang cdn cd rdt n h i l u t r u ddt-xi mang khdc, va d i l u kifin cda t h i nghiem nen d d n Id chUa that sU d u n g vdi d i l u kifin thuc t l ndy ' Do vdy, can cd cdch t h i nghiem phdn dnh d u n g ^ e u kien lam viec thPc t l cda n i n gia cd khi xac d m h m d d u n ddn hdi cda cdc tru dat-ximdng.
* He sd t h a m ciia mau dat trdn xi mang Su thay ddi cua h& sd t h a m cua mau theo cdc hdm lupng xi mang khdc nhau dUpc t h i hien n h u t r o n g bang 6.
3.3. Kit qud thi nghiem tiidm Nam Kinh Bdng 6: H f sd t h a m cCia mau xde dinh theo cdc t h i nghiem
Ham lupng x i mdng (%)
10 12 14 16 18 20
Nam Kinh Oedometer HesdthamKv.E-7 (cm/s)
0.370 0.260 0.161 0.088 0.051 0,033
0.151 0.200 0.180 0.038 0.031 0.046
Hinh 13. Quan \\i giiia M so tha'm va ty \i xi mang/ffSt NHAN xer
Thf nghiem t h a m bdng d u n g cu t h a m kieu Nam Kinh vd t h i nghiem nen cd k i t cho k i t qud h^ sd thSm gdn t u o n g dUong nhau, t r o n g d d thf nghiem n^n c6 k i t cho cdc gid tri n h d hdn. H&
s6 tham ciJa m i u ddt t r d n xi mdng gidm t h e o sU tdng cOa hdm Iddng xi mdng c6 t r o n g dat. V6i mdu dat trdn xi mang sau 28 ngdy bdo dUdng c6 hd sd t h i m n h o h o n so vcA hi sd t h a m cCia d i t t u n h i l n . Khi hdm l u p n g xi mang Id 10% t h i h& sd t h i m gidm di 3.1 Idn, con khi hdm lupng xi mdng t a n g l l n 20%, h6 sd t h i m gidm di 34.5 I i n .
4 . K^t l u | n
1- Khi thay d d i hdm lucmg xi mdng, vdi su
bien ddi cCia cudng d p khdng nen m d t true, m d d u n ddn hoi cua mau dat trdn xi mdng trong cdc t h i nghiem nen m d t true d tren, cung nhU sU b i l n ddi cua chi sd nen vd chi sd n d ciia mau, cd the chpn hdm lUong xl mang tdi Uu cho loai ddt y l u t?i khu vUc nghi§n cdu Id 16%,
2- Chl sd n^n cua dat trdn xi mdng gidm manh khi ham lupng xi mdng t i ^ 10% den 16%, khi hdm lUdng xi mdng t d 16% d i n 20% chi sd nen cd xu hUdng gidm cham, d 28 ngdy tudi, chi sd n i n cCia dat trdn xi mang vdi hdm lupng xi mang Id 20% gidm di (5-6) lan so vdi dat t p n h i e n . 3- Chi sd n d cda mau dat trdn xi mdng cd xu hudng bien ddi gidng nhU sU thay ddi cCia chl sd n^n cOa dat trdn xi mdng: giam manh khi hdm lupng xi mdng til 10% den 16%, cdn khi hdm lupng xi mang t d 16% d i n 20% chl sd nd cd xu hudng gidm cham Mau dat-xi mang cd hdm lupng xi mdng 20% vd bdo dudng sau 28 ngdy t h i cd chi sd n d gidm di 12.9 lan so vdi chl sd n d cua dat tU nhifin.
4- Khi t i n h toan d o lun cua nen ddt y l u dUdc gia cd bang cdc tru ddt-ximang, m d d u n dan hdi cua mau dat-xi mdng thu dUdc t d thf nghiem nen d o n can cd sU dieu chinh thich hdp, vl dieu kien cua th( nghiem n^n don Id chUa that sU dOng vdi d i l u kien thuc te cua nen dat yeu cd gia cd bang cac tru dat-ximdng. Vdi cac k i t qud t h i nghiem niu tren, m d d u n dan hdi t h u dupc t d t h i nghiem nen co ket cho ket qud hdu n h u n h d h o n n h i l u so cdc gid tri t h u dupc t U t h i nghiem nen d o n , vdi sU chenh lech cd t h i len den 80%.
5- Thi nghidm t h a m bSng d u n g cu t h a m kieu Nam Kinh vd t h i nghi&m nen cd k i t cho ket qud he sd t h a m gan t u o n g dUong nhau, trong d d t h i nghiem nen cd ket cho cdc gid tri n h d hdn. HesothdmcCia m l u dat trdn xi mdng gidm theo s U t d n g cda ham lupng xi mang cd t r o n g dat. Vdi mau dat trpn xi mang sau 28 ngay bdo d u d n g cd he sd thdm n h d han so vdi h§ so t h a m cua d d t t u nhien den 34.5 lan Do vay, can Idu y d i n dac diem nay khi t i n h toan d p lun cua nen d i t yeu cd gia cd bang cdc t r u dat-ximdng t h e o thdi gian.
LOI C A M O N
Nghien cuU nay ductc tai trp bdi Dai hgc Qudc gia Thdnh p h d Hd Chl Minh (VNU-HCM) trong khudn khd 6i tai "Nghien cuu phUdng phap tfnh toan d d liin dn djnh va dp lun t h e o t h d i gian cua nen dat yeu duoc gia cd bSng cdt dat XI m d n g " cap DHQG, ma so: C2014-20-13.
Cac t i c gid cda bdi bdo xin trdn t r p n g cdm On.
TAIUEU THAM KHAO
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3. Ouy pham ky thuSt xQ ly nen mong cija Tmng quoc (Shanghai- Standard: Ground treatment code, DBJ OS 40 94) do TnfcmgDai hocDfingte bien soan, nam 1995
4 Tieu chuSn xay diJng Vi^t Nam TODVN 9403:2012
"PhifOng phap gia co nen dat yeu b i n g t n i dat xi mang", 2006.
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637-640
6. K.Omine & H.Ochiai 'Homogeni^ation method for numerical analysis of improved ground w i t h cement treated soil columns"
