CAC DAC TRUNG BI^N DANG COA OAT VA Tl/ONG QUAN GIOA OAC TRUNG BÎ N DANG V6l DAC TRUNG VAT LY ThS Do Thj Thu Hien CN Pham Trgng Tinh Khoa XSy dt/ng Ciu dudng Trudng Dai hgc XSy dung Tdm tat TU kit qua[.]
Trang 1CAC D A C T R U N G BI^N D A N G C O A O A T V A Tl/ONG QUAN
GIOA OAC TRUNG BI^N DANG V6l D A C TRUNG VAT LY
ThS Do Thj Thu Hien
CN Pham Trgng Tinh
Khoa XSy dt/ng Ciu dudng Trudng Dai hgc XSy dung
Tdm tat: TU kit qua thi nghidm cho thay chi sd nen C^ cht phu thupe vao loai dit,
khdng phu thupc vao khoing img suit; he sd quS cd kit OCR cd thi eoi khdng dii ddi
vdi mpt loai dat, khdng phu vao dp sSu lay miu 'Vt vay, tSe gia klin nghj ndn sit dung
quan he e - Igo, cOng cSe dSc trung tuang itng C^, C, se thuan Igi hgn trong vide danh giS tinh biin dang ciia dit; ndn sit dung he sd quS ed kit OCR di dSnh giS trang thSi cd
kit cua dat
Summary: Results of an odometer test shows that compression index C^ depend
on the type of soil but not depends on increment of stress; over consolidation ratio OCR
is more or less a constant with the type of soil, doesnt depend on a depth of sample I
petition for using e-lga plot with correlative compression characteristics C^, C, because this form of plot is convenient for showing stress - strain behavior over a wide range of
stresses and such curve usually become more or less straight at large stresses; and
petition for using OCR to define the consolidated state of soil
I M d D A U
Biin dang cda da't xay ra rat phdc tap, gdm nhiiu dang vd phy thude vdo nhieu y i u td
khdc nhau, ehu yeu do sU thay ddi the tich Id rdng vd mdt phin la sU s i p x i p lai vj tri cac hat
d i t Do dac diem cda tai trpng edng trinh ldn n i n dat, biin dang eua dat chd y i u la biin dang
nen Vdi d i t tinh nen la kha Idn vd hdu qua la edng trinh cd the bj Idn qua mdc dan d i n khdng
the sddyng dupc binh thudng, thdm chi pha hoai edng trinh hoac mpt bd phan edng trinh
Du bao biin dang cda nen d i t Id mpt cdng vide khd khdn, do dd chung ta ein phai nghidn
cilu cin than tinh biin dang cda da't
2 CAC D A C T R U N G BIE'N DANG CCiA DAT
Oe nghien edu tinh biin dang cda daL ngudi ta tiin hanh thi nghidm bdn nen tai hidn
trudng Td k i t qua thi nghidm bdn nen, ngUdi ta xde djnh Mddun bien dang £ „ :
E„ = pblriio3 p: dp lue nen;
b; dudng kinh ban ndn trdn hoac canh ban nen vudng;
lo: he sd hinh dang bdn nen, ta = 0.79 vdi ban nen trdn, a> = 0.88 vdi bdn nen vudng;
S: dp Idn cda bdn nen tuong dng vdi ap luc nen p;
Trang 2Thi nghidm bdn nen tuy phan dnh tUong ddi tdt tinh hinh Idm vide eda n i n d i t dudi tde dung cua tai trpng nhung khd dp dung thi nghiem nay khi mudn nghidn ci!ru cdc Idp dd't d sau hon Vi vdy, ngudi ta thudng dung thi nghidm nen mpt ehiiu khdng nd ngang trong phdng thi nghidm d i thay t h i
K i t qua thi nghidm nen thudng dupe bieu dien bing dd thi quan he gida dng suit ndn vdi
hd sd rdng theo hai dang:
- Dang e = f(a)
- Dang e = f(lga)
2.1 Dudng cong ndn dang e = f(a)
a) Thi nghipm nen miu chi bj b) Thi nghidm nen - dd tii
Hinh 1 Dudng cong ndn dang e - f(o)
- H$ s6n4n liin a trong khoang thay ddi dng suit ndn tif a^ d i n oj:
Ae e - e ,
a = - = —^ —
ACT (72 - o " ,
Hd sd ndn lun a dupc sd dung Idm dai lupng ddc trung cho tinh biin dang eda dat Dat ed
hd sd ndn cdng Idn thi kha ndng Idn cua dd't edng Idn (tinh bien dang cdng eao) vd ngupc lai
Oo dudng cong ndn dang e - f(o) khdng phai Id mdt dudng thing, md cd dang mpt dudng
cong, ndn ddi vdi mdt lo^i dit hp s6 nin a khdng phai li hing so mi phu thupc vao khoang thay d6i Cmg suit Au, vio diem bat dau cua lirgng ting iiy,a = f (dUt, CT„ Aa)
- Mddun bien dang E„ xdc dmh theo cdng thdc: E„ = k E„
k: hd sd hidu chinh Id'y phu thudc he sd rong ban dau Oo;
E„: mddun ndn cda da't xdc ^ n h td thi nghiem nen mdt chiiu khdng nd ngang
m„ 1
-2MI
-fo
A
m
^ vdi p = 1
-m; hd sd biin dang ngang, \i^ phy thudc vdo loai d i t ; m,: he sd nen the tich;
TAP CHf KHOA HOC C O N G N G H $ XAY DUNG sd 02-12/2007 83
Trang 32.2 Oudng cong nen dang e = f(lga):
OUcing cong nen nguyen thdy
i g f ) Igbi) '9fe) Igfcj)
a) Thi nghiem ndn miu chi bj b) Thi nghidm ndn - đ tai
Hinh 2 Dudng eong ndn dang e=f (Igo)
oac trung biin dang eda đ't dupc bieu thj bang dp đe cda dudng cong ndn gpi Id chisd nin Cc xac djnh theo bieu thdc sau:
lg(CT,)-lg(CT,)
C^ khdng phu thudc vio khoang thay d6i iing suit mi chi phg thupc vio loai dit
Terzaghi vd Peck (1948) de nghj xdc djnh ehl sd nen C^:
+ Vdi m i u dat c h i bj: C^ = 0,007(W„h -10%)
+ Vdi mau d i t nguydn dang: C^ = 0,009(W„h -10%)
Trong đ: W^^ Id dp am gidi han nhao, tinh bing phin trdm
K i t qua nen lai khdi phuc dan trang thai trudc đ theo dudng cong ndn lai cd đ đc nhd
hon Cc rat nhiiu dupe gpi Id chis6nin lal C^
Vdi mlu dát d do sau h ndo đ trong dát
d trang thdi tu nhidn, phdn td dat tai dp sdu h chju tac dung cda trpng lupng ban thdn cac
Idp đ't d bdn trdn Ung suit ndn theo phuong dimg (dng suat Idp phd) a, = Y,t,h Trong đ, y^,:
trpng lupng ridng trung binh cua đ't trdn dp sdu h Khi mau dupe lay ra khdi đ't, img suit giam xud'ng bang 0, dat da trai qua qua trinh đ tai Idm cho mau bj nd rạ
Khi a < a „ dUdng eong nen Ide nay Id dUdng eong nen lai vdi dp đc C, Khi a > a „ dUdng
eong nen d i n trd lai dudng eong nen nguydn thdy vdi dp đc C^ (Hinh 3)
Oiim giao cda hai doan thing tuong dng vdi iimg suit nen tdi da trong qud khd md mau
ttmg trii qua gpi Id dng suit tiin ed k i t ộ Tuy vdo loai dat md iJfng suit ô cd t h i bing hode khac img suit a, Co hpe dát phdn bidt cdc trang thai cd k i t cua dat theo quan hd gida â vd a,: + a,, = o,; d i t cd k i t binh thudng (đ't NC: Normally - Consolidated)
+ Oj > a,: dat qud cd k i t (đ't OC: Over - Consolidated)
+ Ce < a,: dat chua cd k i t (dat UC: Under - Consolidated)
- Ode diim biin dang eda ttmg loai d i t ndi trdn khac nhau tuy thudc vdo trang thai cd k i t cda đ't, do đ đ ldn eua n i n khi chiu tai cQng khde nhaụ Vide xde djnh c^ Id c i n thiit
Trang 4Oudng cong nen sda đi
JK Oudng cong thi nghiem
igC)
Hinh 3 Dudng cong ndn dat thuc ti
Xdc djnh â: Trdn dUdng cong nen thi nghidm e = f(lgCT), keo đi hai doan thing gap nhau
tai diim F Ung vdi hoanh dp ậ
Nhan xdt: Ung suit tiin ed k i t ô vd dng suit Idp phd o, phu thudc vdo dp sdu Id'y mau,
do đ g i n đng cd the coi ty sd giiJfa â vdi o, khdng phu thudc vdo dp sdu liy mau, khdng đi cho mdt Idp đ't
cr OCR= —^
OCR: hd sd qud cd k i t (Over Consolidation Ratio) vd dupe dung Idm dac trUng cho trang
thdi cd k i t cda đ't O i t OC cd OCR >1 Dat NC ed OCR = 1 Dát UC cd OCR <1
3 THI/C NGHIEM VA PHAN TiCH KET QUA
3.1 Mau thi nghiem
- Mau thi nghidm Id mau c h i bj vd mau nguyen dang Id'y td hien trudng
- Vdi mau c h i bj: Chia mau thanh cdc td hpp de thi nghidm Mdi td hpp gdm 3 maụ
- Kich thudc m i u : dudng kinh: d = 6.18 em, chiiu cao h = 2.0 cm
3.2 Qui trinh thi nghiem
Vdl mau nguydn trang
T i i trpng tdc dung Idn mau theo tdng cap vd dupe duy tri cho den khi dat dn djnh bien
dang ndn thi mdi dugc tdng cap tiip theọ C i p dp luc nen lan lupt nhusau:
a, = 2 5 (kN/m^) 02 = 50 (kN/m') 03=100 (V.HIm')
04 = 200 (kN/m^) 05 = 400 (kN/m^) 06 = 800 (kN/m^)
Vdi miu chSbi: Moi td hpp mau dupe chia thdnh 3 m i u thi nghidm trong đ;
+ Mau 1: Tai trpng tdng dan theo ttmg c i p tuong tu nhuthi nghiem mau nguyen dang + Mau 2: Thi nghidm tai trpng tang d i n theo ttmg cap d i n 03 = 100(kN/m^), sau đ, tién
hdnh giam tai v i gid trj a = 0 Tiin hdnh tdng d i n t i i trpng theo ttmg cap td a, dén ộ
+ M i u 3: Thi nghidm tai trpng tdng d i n theo ttmg c i p d i n ô = 200(kN/m^), sau đ tiin hdnh g i i m tai v i gid tri a = 0 Tien hdnh tdng d i n t i i trpng theo tdng cap td c, d i n ậ
TAP CHf KHOA HOC C O N G N G H $ XAY DUNG sd 02-12/2007 85
Trang 5bang gia tri dng suit khi dd tai Oudng eong nen lai sau khi dd tai cd vai trd tuong tu dUdng cong thi nghidm cda mau dat d dp sdu h
3.3 K i t qua thi nghiem
a Miu nguyen dang
Oja diem liy mau: My Oinh, Me Tri - Td Liem - Ha Npi
Mdi Idp dat tae gia lua ehpn 2 mau dd't d cdc dp sdu khde nhau de thi nghidm
0.00 H K l
m
m
4 ^ "
4-m
I -9 'S0
g
i
^
'; Cat hat irung, xam ving, xam xanli
I -4S.3(
Set plia, nau h6ng, nSu viing, deo cting
W = 26.0 (%) W„h= 38.5 (%) Wj = 22.5 (%)
A = 16.0(%) B = 0.219
Y=1.97(g/2m ) A =2.68
c = 0.25(kCScm )(p=22''35'
c i ^
cat hat thd, xam ghi, xam xanh
Cu6i SOI lin cat hat th6
0.00 H K 5
Set pha, vang loang ghi, deo cumg
W = 27.5 (%) W ^ = 38.1 (%) Wd = 22.6 (%)
A = 1 5 5 ( % ) B = 0.316
, = 1.96(g/cm') A=2.69
0.24(kG/cm:!) p=22''32'
Cat pha, xam ghi, deo
W = 23.1 (%) W„h= 25.7 (%) Wd = 20.0 (%)
A = 5.7 (%) B = 0.544
, = 1.92(g/cm:') A = 2 6 8
c = 0.03 (kG/cm-) (p= 26°36'
mi
-24.40
|-34.5(
Set pha vang loang ghi, dec cumg
W = 27.3 (%) W„h= 38.3 (%) W,, = 22.2 (%)
A = 1 6 1 ( % ) 8 = 0.317 , = 1.97(g/cm3) A=2.68
c = 0.22 (kO/cm-) (p= 2 r 0 3 '
S6t pha, nau gu, deo cling
W = 29.4 (%) W„h= 37.2 (%) Wj = 22.4 (%)
A = 14.8 (%) B = 0.472
r = 1 8 7 ( g / c m ' ) A=2.66
c = 0.15(kG/cm2)p=n»2.5'
Sit pha nau h6ng, nau ving, deo cling
W = 26.0 (%) W„h= 39.1 (%)Wd = 22.3 (%)
A = 16.8 (%) B = 0.220 Y= 1.95 (g/cm3) A=2.69
c = 0.27 (kG/cm:!) ^ 23°02'
Cat hat trung, xam vang, xam xanh
Cat hat lh6, xim ghi, xam xanh
Cu6i soi l8n cat hat lh6
Hinh 5 Tru dia chat HK1 va HK5
HK
1
5
SH
1
2
3
4
5
6
7
8
9
10
11
z(m)
1.8
2.8
6.0
7.5
13.8
15.0
1.8
2.8
6.5
7.8
10.8
Bang 1
Vs em^
51.71 51.72 52.72 52.77 52.90 52.93 51.79 51.69 51.36 51.28 52.91
Bang kit qui eSc eh! tidu vSt ly mau nguydn dang
(%)
26.85 28.16 23.02 23.24 26.30 26.08 27.54 28.07 29.08 29.81 26.23
(%)
22.50 25.87 19.94 18.86 22.94 22.10 10.97 21.50 25.47 24.82 19.58
ytr
g/crrP
1.95 1.96 1.92 1.92 1.97 1.98 1.98 1.96 1.87 1.88 1.95
g/emP
2.18 2.24 2.13 2.10 2.18 2.17 2.17 2.16 2.12 2.11 2.10
A
2.69 2.69 2.68 2.68 2.69 2.69 2.68 2.68 2.66 2.66 2.69
e^
0.753 0.575 0.717 0.722 0.720 0.712 0.727 0.747 0.835 0.840 0.740
(%)
37.6 38.5 25.8 25.7 38.4 38.8 37.9 38.8 36.8 37.7 39.4
Cc theo Terzaghi
0.2484 0.2565 0.1422 0.1413 0.2556 0.2592 0.2511 0.2592 0.2412 0.2493 0.2592
Trang 6Bang 2a Bing kit qui hd so ndn lun cUa miu nguyen dang
SH
1
2
3
4
5
6
7
8
9
10
11
12
a„., (m'AN)
0.0012
0.0013
0.0016
0.0016
0.0007
0.0007
0.0011
0.0012
0.0017
0.0016
0.0006
0.0007
a , , (m'/kN)
0.0005 0.0004 0.0006 0.0005 0.0004 0.0004 0.0004 0.0004 0.0006 0.0007 0.0004 0.0004
a,., (nf/kN)
0.0004 0.0004 0.0005 0.0005 0.0003 0.0004 0.0004 0.0004 0.0006 0.0006 0.0004 0.0004
a,^ (nf/kN)
0.0004 0.0004 0.0004 0.0004 0.0003 0.0003 0.0004 0.0004 0.0004 0.0004 0.0003 0.0003
a « (ni'/kN)
0.0003 0.0003 0.0002 0.0002 0.0003 0.0002 0.0003 0.0003 0.0003 0.0003 0.0002 0.0003
a^ji (rri'/kN)
0.0002 0.0002 0.0001 0.0001 0.0002 0.0002 0.0002 0.0002 0.0002 0.0002 0.0002 0.0002
Bang 2b Bing kit qua eSe dSc tn/ng biin dang khSe cQa miu nguyen dang
SH
1
2
3
4
5
6
7
8
9
10
11
12
c
0.2437
0.2579
0.1429
0.1455
0.2506
0.2563
0.2407
0.2571
0.2362
0.2563
0.2566
0.2683
c,
0.0280 0.0318 0.0508 0.0392 0.0323 0.0310 0.0293 0.0334 0.0524 0.0519 0.0364 0.0356
a, kN/m^
105
148
67
93
143
161
102
146
103
118
155
174
a kN/m^
35.28 54.88
117 155.4 268.9 282.7 35.64 54.88 126.6 150.9 209.2 242.4
OCR 2.98 2.70 0.57 0.60 0.53 0.57 2.86 2.66 0.81 0.78 0.74 0.72
Oit
OC
OC
UC
UC
UC
UC
OC
oc
uc
uc
uc
uc
b Miu chSbl
To hpp 1: O i t sdt pha (A = 10.9%), trang thai deo cdng (B = 0.33) Od am tu nhidn
W = 17.9(%); dp i m gidi han d i o W^ - 14.3(%); dp am gidi han nhao W„h = 25.2(%)
Trpng IUpng rieng dd't tU nhidn YW = 2.00 (g/cm^); ty trpng A = 2.69
To' hop 2: Od't set pha (A = 10.2%), trang thai deo cdng (B = 0.441) Op am IU nhidn
W = 18.4(%); dp i m gidi han deo W^ = 13.9(%); dp i m gidi han nhao W„^ = 24.1(%)
Trpng lupng ridng d i t tu nhidn y* = 2.00 (g/cm'); ty trpng A = 2.69
Bang 3 Bang kit qui cac chi tidu vSt ly mau chi bj
TH
1
2
SH
1
2
3
1
2
3
V,cm^
53.10
52.88
55.74
52.31
52.18
54.94
W„(%)
17.69 17.94 17.81 18.57 18.98 18.31
W, (%)
15.07 15.10 14.88 12.96 16.92 15.44
Ttr g/cm^
1.98 1.99 2.01 1.97 2.00 2.01
Ts g/cmP
2.19 2.21 2.11 2.15 2.26 2.14
A
2.69 2.69 2.70 2.68 2.69 2.70
So 0.596 0.592 0.583 0.612 0.597 0.590
Cc theo Terzaghi
0.1094 0.1094 0.1094 0.0987 0.0987 0.0987
Trang 7Bang 4ạ Bang kit qua hd sd ndn lOn cQa miu chi bi
TH
1
2
SH
1
2
3
1
2
3
ag.,' (m'AN)
0.0014
0.0008
0.0009
0.0018
0.00068
0.00042
a 1-2
(m^/kN)
0.0012 0.00035 0.00027 0.0011 0.00043 0.00028
(ní/kN)
0.0007 0.00024 0.00022 0.00074 0.00041 0.00027
â^' (rrí/kN)
0.0003 0.0002 0.0002 0.00034 0.00028 0.00021
ấ(nf/kN)
0.0001 0.0002 0.00016 0.00016 0.00015 0.00013
ấ (rrí/kN}
0.00008 0.00008 0.00008 0.00008 0.00008 0.00008
Bang 4b Bing kit qui cSc dSc tn/ng bien dang khac cCia miu chi bj
TH
1
2
SH
1
2
3
1
3
Cc 0.1013
0.1084
0.1094
0.1047
0.1045
0.1014
Cr
0.0280 0.0293 0.0221 0.0286 0.0361 0.0235
OckN/m'
89
172
58
113
o„ kN/m'
100
200
100
200
OCR
0.89 0.86
0.58 0.57
Dát
UC
UC
UC
UC
Ghi chu: 0^: xde djnh td dudng cong ndn e = f(lga)
4 KET LUAN VA KIEN NGHj
4.1 Ket luan
Td k i t qua cac mau d i t md tac g i i tiin hdnh thi nghidm eho thay:
- Chi sd nen Cc khdng phy thudc vdo khoang thay đi cua iimg suit md phy thudc vao loai dit, ed the coi Cc ed gid trj khdng đi cho mdt loai đ't
- Ung suit tien cd k i t â thay đi theo dp sdu lay m i u , trong khi ty sd cd k i t OCR cd thi
coi Id khong phu thupc vao dp sdu lay maụ
Tac gia tim kiem tuong quan eda Cc eda mau thi nghidm vdi W„^:
Vdi mau nguydn dang: Cc = 0.0086W„h - 0.0783
Vdi mau e h i bj: Cc = 0.0054W„h - 0.0274
4.2 Kien nghj
Ndn dung cdch bieu dien dUdng cong nen e = f(lga), tuong img cd cdc đc trung biin dang Id ehl sd nen Cc, chi sd nen lai C^ vl Cc khdng phu thudc vdo khoang thay đi dng suit, cd
t h i eoi Id đc trung cho mdi mpt loai d i t
Trang 8Ndn dung hd sd qud cd k i t OCR de danh gia trang thai cd k i t cda d i t vi he sd ndy cd the
coi nhu khdng phu thudc vao dd sdu lay mau
Tdi lieu tham khao
1 GS.TS Vu Cdng NgU, PGS.TS Nguyen VSn Dung - Co hpe dd't Nxb Khoa hpc vd Ky thudt
Hd Npi, 2006
2 ThS Phan Hdng Quan - Co hpc dat Nxb Xdy dung Hd Ndi, 2006
3 TS DoSn Thi Tudng, KS Ld ThuSn DSng - Thi nghiem d i t vd n i n mdng cdng trinh Nxb
Giao thdng van tai Hd Ndi, 2002
4 T William Lambe vS Robert V.Whitman - Soil Mechanics, SI Version John Wiley and Sons,
New York, 1979
TAP CHf KHOA HOC CONG NGHE XAY DUNG Sd02 -12/2007 89