Environmental Engineering Reference
In-Depth Information
500
400
300
200
- u a
50 kPa
σ
=
σ
- u a
=
100 kPa
100
σ
200 kPa
σ - u a = 400 kPa
- u a
=
0
0
200
400
600
800
1000
Matric suction ( u a - u w ), kPa
Figure 12.23 Measured shear strength data in terms of apparent cohesion intercept versus soil
suction for various net confining pressures (after Cunningham et al., 2003). (Open diamonds have
confining pressure of 400 kPa.)
600
Oberg and Sallfors (1997)
500
Goh et al. (2010)
400
300
D. G. Fredlund et al. (1996)
200
Vanapalli et al. (1996b)
100
Data under 50 kPa net
confining pressure
0
0
400
800
1200
1600
2000
Matric suction ( u a - u w ), kPa
Figure 12.24 Comparison of estimations of shear strength from various proposed equations and
measured data for reconstituted silty clay for net confining pressure of 100 kPa.
Table 12.3 Estimation Soil Parameters
for Reconstituted Silty Clay
about 250 kPa and becomes more significant at a suction of
400 kPa. The air-entry value and the saturation suction are
assumed to be independent of the confining pressure.
The predictions of shear strength for the unsaturated silty
clay tend to separate and spread out over quite a wide
range once the inflection point on the SWCC is reached
(see Fig. 12.24). Oberg and Sallfors (1997) and Goh et al.,
(2010) gave the highest strength estimations. Vanapalli et al.,
(1996b) gave the lowest shear strength estimations. The
D.G. Fredlund et al., (1996) estimation of shear strength
was near the middle of the results. Other test results obtained
when using higher net confining pressures were quite con-
sistent with the estimation of unsaturated soil shear strength.
Equations
Soil Parameters
Oberg and Sallfors
(1997)
SWCC, S
D.G. Fredlund et al.
(1996)
κ
=
1 . 16, θ s =
0 . 6032, SWCC
Vanapalli et al. (1996b) θ s =
0 . 6032, θ r =
0 . 055 , SWCC
Goh et al. (2010)
n d =
1 . 44, ψ aev =
250 kPa, PI,
SWCC
12.2.5.2 Data on Compacted Kaolin Assuming No
Volume Change (Thu et al., 2007a)
Thu et al. (2007a) measured the shear strength of compacted
kaolin under different soil suctions using a modified triaxial
The estimated shear strengths are quite consistent with
the measurements in Cunningham et al., (2003), where it
was observed that desaturation commences at a suction of
 
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