Abstract

In excavated earth structures (e.g., deep excavation, cut slope, and underground construction etc.) unloading is the most predominant factor that affects the behavior of soil mass. However in engineering practice, the influence of unloading factor has not been really considered. For example, the soil shear strength characteristics are often investigated from the conventional triaxial shear test, consequently it leads to some doubts when applying the shear strength properties under loading condition to analyze the stability and displacement problem of unloading cases. In this study, a comparison of soil shear deformation and strength between loading and unloading conditions was carried out, which was based on two series of tests for remoulded clay conducted on the Advanced Stress Path Triaxial Testing System. The test results showed that the unloading factor affects soil behaviour significantly. The differences in friction angle, collapsibility, excess pore-water pressure, and shear modulus during shear under unloading condition are remarkable from under loading condition.

References

1.
Bao
,
C. G.
and
Ng
,
C. W. W.
, “
Some Thoughts and Studies on the Prediction of Slope Stability in Expansive Soils
,”
The First Asian Conference on Unsaturated Soils
, Singapore, Balkema,
2000
, pp.
15
31
.
2.
Ng
,
C. W. W.
, “
Stress Paths in Relation to Deep Excavations
,”
J. Geotech. Geoenviron. Eng.
 1090-0241, Vol.
125
, No.
5
,
1999
, pp.
357
363
. https://doi.org/10.1061/(ASCE)1090-0241(1999)125:5(357)
3.
Chen
,
S. X.
,
Ling
,
P. P.
,
He
,
S. X.
, and
Yang
,
X. Q.
, “
Experimental Study on Deformation Behavior of Silty Clay Under Unloading
,”
Yantu Lixue/Rock Soil Mech.
, Vol.
28
, No.
12
,
2007
, pp.
2534
2538
.
4.
He
,
S. X.
,
Han
,
G. S.
,
Zhuang
,
X. S.
, and
Wu
,
X. G.
, “
Experimental Researches on Unloading Deformation of Clay in Excavation of Foundation Pit
,”
Yantu Lixue/Rock and Soil Mechanics
, Vol.
24
, No.
1
,
2003
, pp.
17
20
.
5.
Yang
,
X. Q.
,
Zhu
,
Z. Z.
,
Han
,
G. S.
, and
He
,
S. X.
, “
Deformation and Failure Characteristics of Soil Mass under Different Stress Paths
,”
Yantu Lixue/Rock Soil Mech.
, Vol.
27
, No.
12
,
2006
, pp.
2181
2185
.
6.
Zhang
,
M. X.
and
Sun
,
J.
, “
Unloading-Induced Deformation and Strength Properties of Loess During Construction
,”
Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering
, Vol.
24
, No.
13
,
2005
, pp.
2248
2254
.
7.
Wu
,
W.
and
Kolymbas
,
D.
, “
On Some Issues in Triaxial Extension Tests
,”
Geotech. Test. J.
 0149-6115, Vol.
14
, No.
3
,
1991
, pp.
276
287
. https://doi.org/10.1520/GTJ10572J
8.
Bishop
,
A. W.
, “
Shear Strength Parameters for Undisturbed and Remoulded Soil Specimens
,” Roscoe Memorial Symposium, Cambridge University,
1971
, pp.
3
58
.
9.
Atkinson
,
J. H.
,
Richardson
,
D.
, and
Robinson
,
P. J.
, “
Compression and Extension of K0 Normally Consolidated Kaolin Clay
,”
J. Geotech. Eng.
, Vol.
113
, No.
12
,
1987
, pp.
1468
1482
. https://doi.org/10.1061/(ASCE)0733-9410(1987)113:12(1468)
10.
Siddique
,
A.
and
Clayton
,
C. R. I.
, “
Mechanical Properties of Reconstituted Soft London Clay
,”
Journal of Civil Engineering—Bangladesh
, Vol.
27
, No.
1
,
1999
, pp.
81
98
.
11.
Ma
,
W.
and
Chang
,
X. X.
, “
Influence of Loading and Unloading on Strength and Deformation of Frozen Soil
,”
Yantu Gongcheng Xuebao/Chinese, J. Geotech. Eng.
, Vol.
23
, No.
5
,
2001
, pp.
563
563
.
12.
Barla
,
M.
, “
Numerical Simulation of the Swelling Behaviour around Tunnels based on Special Triaxial Tests
,”
Tunn. Undergr. Space Technol.
 0886-7798, Vol.
23
, No.
5
,
2008
, pp.
508
521
. https://doi.org/10.1016/j.tust.2007.09.002
13.
Fam
,
M. A.
and
Dusseault
,
M. B.
, “
Effect of Unloading Duration on Unconfined Compressive Strength
,”
Can. Geotech. J.
 0008-3674, Vol.
36
, No.
1
,
1999
, pp.
166
172
. https://doi.org/10.1139/t98-074
14.
Li
,
Y. Q.
,
Ying
,
H. W.
, and
Xie
,
K. H.
, “
Dissipation of Negative Excess Pore Water Pressure Induced by Excavation in Soft Soil
,”
J. Zhejiang Univ., Sci.
 1009-3095, Vol.
6A
, No.
3
,
2005
, pp.
188
193
. https://doi.org/10.1631/jzus.2005.A0188
15.
GB/T 50123-1999, “
Standard for Soil Test Method, Ministry of Construction of P.R. China
,” Beijing,
1999
.
16.
Balasubramiam
,
A. S.
and
Waheed
,
U.
, “
Deformation Characteristics of Weathered Bangkok Clay in Triaxial Extension
,”
Geotechnique
 0016-8505, Vol.
27
, No.
1
,
1977
, pp.
75
92
. https://doi.org/10.1680/geot.1977.27.1.75
17.
Wood
,
D. M.
,
Soil Behavior and Critical State Soil Mechanics
,
Cambridge University
,
New York
,
1990
.
18.
Bishop
,
A. W.
, “
Progressive Failure-with Special Reference to the Mechanism Causing it
,”
Proceedings of the Geotechnical Conference on Shear Strength Properties of Natural Soils and Rocks
, Vol.
2
, Oslo, Norwegian Geotechnical Institute,
1967
, pp.
142
150
.
19.
Zhai
,
Y.
, “
Fundamental Shear Behavior of Saturated Loose Fills of Completely Decomposed Rocks
,” Ph.D. thesis, Department of Civil Engineering,
University of Hong Kong
,
2000
.
This content is only available via PDF.
You do not currently have access to this content.