1116
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
As can be seen, the experimental data is nicely fitted by a
non-linear relationship between small-strain shear modulus and
the variables suction and confining pressure. The non-linearity
between shear modulus and net confining stress or soil suction
was also observed for sands by Nyunt et al. (2011) who used,
however, different fitting equations to represent these
relationships.
The hyperbolic fit suggests that
G
o
tends asymptotically to a
limit value, which for the range of suction tested, seems to be
close to the shear modulus associated to the suction of 100 kPa.
However, tests at larger suction should be performed to confirm
this behavior.
0
100
200
300
400
500
0
100 200 300 400 500
3
- u
w
;
3
-
u
a
(kPa)
Go
(MPa)
u
a
-
u
w
(kPa)
0
15
40
100
Figure 5. Variation of the small-strain shear modulus with confining
stress.
0
100
200
300
400
500
0
20
40
60
80 100
u
a
-
u
w
(kPa)
Go
(MPa)
10
50
100
300
500
σ
3
- u
w
; σ
3
-
u
a
(kPa)
Figure 6. Variation of the small-strain shear modulus with suction.
Table 1. Parameters of the potential fits.
Soil suction
a
b
r²
0 kPa (saturated)
29.7
0.406
0.99
15 kPa
43.6
0.369
0.99
40 kPa
96.2
0.247
0.98
100 kPa
116.9
0.227
0.98
Table 2. Parameters of the hyperbolic fits.
Net confining
stress (kPa)
G
o sat
(MPa)
m
n
r²
10
71.5
0.282
0.0054
0.90
50
142.8
0.251
0.0037
0.99
100
191.0
0.261
0.0044
0.99
300
293.8
0.098
0.0070
0.98
500
391.1
0.357
0.0097
0.99
4 CONCLUSIONS
Triaxial compression and bender element tests were performed
on saturated and unsaturated compacted sandy soil. Aiming at
reducing the time consumed on unsaturated tests, the specimens
went through suction imposition prior to testing and shear
strength was measured in multistage constant water content
tests.
A planar failure envelope, as suggested by Fredlund et al.
(1978), was able to represent shear strength of non-saturated
soil, as non-linearity was not evident in the experimental data.
This behavior was probably associated to the small range of soil
suction registered at failure, since some non-linearity has been
reported in the literature to affect the relationship between shear
strength and suction.
The wave path length to wavelength ratio was used to
evaluate the interference of near-field effects on the shear wave
velocities and resulting shear modulus. The small-strain shear
modulus tended to increase non-linearly with net confining
stress and soil suction. The increasing of shear modulus with net
confining stress was more significant as suction was reduced.
The shear modulus has increased with suction, seeming to
approach an asymptotic value.
5 ACKNOWLEDGEMENTS
The authors acknowledge CAPES, FAPESP and CNPq
(Brazilian Research Agencies) for the financial support given to
this research.
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