Civil Engineering Reference
In-Depth Information
FIGURE 9.25
Cross section of the slope used for the example problem.
2.
Natural liquefiable soil:
Underlying the fill, there is a 5-ft-thick layer of loose nat-
ural sand having the following shear strength parameters:
30
and
c
0 lb/ft
2
.
The total unit weight of the sand
t
125 lb/ft
3
.
The results of the liquefaction analysis (Chap. 6) indicate that this layer has a fac-
tor of safety against liquefaction less than 1.0. When the correction factor for sloping
ground (i.e., Fig. 9.24) is applied, the factor of safety against liquefaction is further
reduced. It is thus anticipated that during the design earthquake, this 5-ft-thick layer
will liquefy.
3.
Natural:
Underlying the natural liquefiable soil layer, there is a denser natural soil that
has the following shear strength parameters:
40
and
c
0 lb/ft
2
. The total unit
weight of the soil
t
130 lb/ft
3
. This soil has a factor of safety against liquefaction that
is well in excess of 1.0, and thus this layer will not liquefy during the design earthquake.
●
Groundwater table:
The groundwater table is located at the top of the natural liquefi-
able soil layer. For the compacted fill layer, the pore water pressures
u
have been
assumed to be equal to zero.
The slope stability analyses for the example problem were performed by using the
SLOPE/W (Geo-Slope 1991) computer program. In particular, the slope stability analyses
for the cross section shown in Figure 9.25 were performed for three cases: (1) the static
case, (2) the weakening slope stability case using the pore water pressure (
r
u
) ratio, and (3)
