Environmental Engineering Reference
In-Depth Information
100
Best-fit curve
Experimental data
80
a
= 5.706
n
= 0.606
m
= 2.617
60
40
Void ratio: 0.474
Preconsolidation pressure: 100 kPa
Initial water content: 16.3%
Total density: 1.80 mg/m
3
20
0
10
6
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
Figure 5.30
Best-fit SWCC for glacial till (Data from Vanapalli, 1994).
(i.e., Eq. 5.53) is shown in Fig. 5.31. It can be seen that
the application of the correction function improves the fit
of the SWCC equation to the measured data. The SWCC
curve is forced by the correction function
C(ψ)
to go to
zero at a suction of 10
6
kPa.
A graphical estimation of the four soil fitting parameters
a
f
,n
f
,m
f
, and
ψ
r
for a SWCC with the correction function
(i.e., Eq. 5.53) can be obtained as follows. The SWCC infor-
mation should be plotted on a semilog form. First, determine
the suction corresponding to the residual water content
ψ
r
by locating a point where the curve changes slope in the
high-suction range (Fig. 5.32). Numerical results show that,
in most cases, an approximation of residual suction,
ψ
r
,is
satisfactory in Eq. 5.53. The magnitude of the residual suc-
tion will generally be in the range 1500-3000 kPa for most
silt and clay soils. Sand soil can have residual suction val-
ues that are in the range of 10-100 kPa. Figure 5.32 uses a
residual suction value
ψ
r
equal to 3000 kPa for illustration
purposes. Next, locate the inflection point
(ψ
i
,θ
i
)
on the
semilog plot and draw a tangent line through this point
(Fig. 5.32). Let
s
denote the slope of the tangent line on
the semilog plot. Then, the fitting parameters
a
f
,n
f
, and
m
f
can be determined as follows:
a
f
=
ψ
i
(5.55)
3
.
67
/
ln
θ
s
C(ψ
i
)
θ
i
m
f
=
(5.56)
1
.
31
m
f
+
1
m
f
C(ψ
i
)
3
.
72
s
∗
n
f
=
(5.57)
where
s
θ
s
−
ψ
i
s
∗
=
(5.58)
1
.
31
m
(ψ
i
+
ψ
r
)
ln[1
+
(
10
6
/ψ
r
)
]
100
Best-fit curve
Experimental data
a
= 427.0
n
= 0.794
m
= 0.613
ψ
r
= 3000
80
60
40
Void ratio: 0.474
Preconsolidated load: 100 kPa
Initial water content: 16.3%
Total density: 1.80 mg/m
3
20
0
10
6
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
Figure 5.31
Best-fit SWCC for glacial till with correction factor
C(ψ)
applied (Data from
Vanapalli, 1994).
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