Environmental Engineering Reference
In-Depth Information
90
q
Impervious
X
80
30
°
70
Impervious
60
Head
50
Head
40
X
30
20
-30
-20
-10
0
10
20
30
40
50
60
70
80
90
100
110
Horizontal distance, m
Figure 8.77 Geometry and boundary conditions for analyzing moisture infiltration to a slope.
Various a f values for the Fredlund and Xing (1994) SWCC
were used (e.g., 1, 5, 10, 20, 50, 100, and 200 kPa) and fixed
values of n f ,m f and saturated coefficient of permeability
k s values (i.e., n f
0.40
0.30
10 5 m/s) were
used in the parametric study. The SWCCs and the corre-
sponding coefficient-of-permeability functions for the soils
are shown in Fig. 8.78. The effect of varying n f and k s was
also studied.
The results shown in Figs. 8.79a to 8.79f were obtained
for soils having the same saturated coefficient of permeabil-
ity of 10 5 m/s, with n f
=
2, m f
=
1, and k sat =
0.20
a f = 1, n f =2, m f = 1
a f = 5, n f =2, m f = 1
a f = 10, n f =2, m f = 1
a f = 20, n f =2, m f = 1
a f =50, n f =2, m f = 1
a f =100, n f =2, m f = 1
0.10
a f =200, n f =2, m f = 1
0.00
1. The pore-water
pressure profiles correspond to soils with a f equal to 5,
10, 20, 50, 100, and 200 kPa, respectively (Fredlund and
Xing, 1994). Different ratios of ground surface flux to satu-
rated coefficient of permeability (i.e., q/k s equal to 0.001,
0.01, 0.1, 0.2, 0.5) were applied to the ground surface of
the slope.
The results illustrate that matric suction at the surface of
the slope approaches zero as the rainfall flux approaches
the saturated coefficient of permeability of the soil.
There is essentially a vertical matric suction profile [i.e.
=
2 and m f
=
0.01
0.1
1
10
100
1000
Soil suction, kPa
(a)
10 5
10 7
10 9
a f = 1, n f =2, m f = 1
a f = 5, n f =2, m f = 1
a f = 10, n f =2, m f = 1
a f = 20, n f =2, m f = 1
a f =50, n f =2, m f = 1
a f =100, n f =2, m f = 1
10 11
d u w w g / dy is zero] established under steady-state
conditions as the ground surface flux is increased toward
the saturated coefficient of permeability. The depth to
which there is a constant-matric-suction profile decreases
with decreasing ratio of the steady-state rainfall flux to the
saturated coefficient of permeability q / k s .
Matric suction values along a vertical portion of the pres-
sure profiles decrease with decreasing a f values for SWCC.
The depth of the constant-matric-suction portion decreases
with an increasing a f value for the soil. The long-term
matric suction remains close to the hydrostatic profile when
the steady-state rainfall flux is two or more orders of mag-
nitude less than the saturated coefficient of permeability
and the a f value is greater than 100 kPa (Fig. 8.79f). The
reduction in matric suction is more significant when the a f
parameter is small.
10 13
a f =200, n f =2, m f = 1
10 15
0.01
0.1
1
10
100
1000
Soil suction, kPa
(b)
Figure 8.78 SWCCs and permeability functions for parametric
study with varying a f values: (a) SWCCs with various a f values;
(b) estimated permeability functions based on SWCCs (after Zhang
et al., 2004).
Figure 8.80 presents the pore-water pressure profiles for a
soil with the same SWCC (i.e., a f
1)
but different saturated coefficients of permeability (i.e.,
10 3 , 10 5 , and 10 7 m/s, respectively). These results
confirm the observations of Kasim et al., (1998a) which
=
10 ,n f
=
2 ,m f
=
 
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