Civil Engineering Reference
In-Depth Information
FIGURE 9.26
Slope stability analysis for the weakening condition (
r
u
1.0) using the SLOPE/W com-
puter program (Geo-Slope 1991).
indicates the center of rotation of the circular arc slip surface with the lowest factor of safety
(i.e., lowest factor of safety
0.899). Since this factor of safety is less than 1.0, it is
expected that there will be a flow slide during the earthquake.
●
Normal stress:
Figure 9.27 shows the normal stress acting on the base of each slice.
The horizontal axis is the distance measured along the slip surface, starting at the upper-
most slice. Each data point in Fig. 9.27 represents the normal stress for an individual
slice. Notice in Fig. 9.27 that the highest normal stress occurs for those slices located near
the middle part of the failure mass (see Fig. 9.26). These slices have large depths and low
angles of inclination, hence high values of normal stress.
●
Pore water pressure:
Figure 9.28 shows the pore water pressure acting on the base of
each slice. As previously mentioned, the compacted fill is above the groundwater table,
and both the initial (
u
i
) and earthquake-induced pore water pressures (
u
e
) were assumed
to be equal to zero. Thus the first 10 slices and the final 3 slices, which are those slices
in the compacted fill, have zero pore water pressure.
All those slices within the natural liquefiable soil layer have pore water pressures.
These pore water pressures were calculated by the computer program, assuming (1) that
the groundwater table is located at the top of the natural liquefiable soil layer and (2) that
this layer has a pore water pressure ratio
r
u
equal to 1.0. In comparing Figs. 9.27 and 9.28,
it is evident that all the slices within the natural liquefiable soil layer have nearly identi-
cal values of normal stress
n
and pore water pressure
u.
