Civil Engineering Reference
In-Depth Information
FIGURE 9.27
Normal stress along the base of each slice for the weakening slope stability analysis (
r
u
1.0).
The SLOPE/W computer program was used to generate the plot (Geo-Slope 1991).
●
Shear strength and shear mobilized:
Figure 9.29 shows the shear strength and the
mobilized shear along the base of each slice. Notice in Fig. 9.29 that the first 10 slices
and the last 3 slices have both a shear strength and a mobilized shear value. This is to be
expected since all these slices are within the upper compacted fill layer. However, all the
slices within the natural liquefiable soil layer have essentially zero shear strength and
hence zero mobilized shear. The reason is that a pore water pressure ratio
r
u
equal to 1.0
was utilized for this soil layer. An
r
u
1.0 caused the normal stress
n
to be equal to the
pore water pressure
u,
which can be observed by comparing Figs. 9.27 and 9.28. If the
normal stress
n
acting on the slip surface is equal to the pore water pressure
u,
then the
effective normal stress
n
will be equal to zero (
n
n
u
). Using the Mohr-Coulomb
failure law (
f
c
n
tan
), with
c
0 and
n
0, the shear strength
f
is equal to
zero, as indicated in Fig. 9.29.
Example Problem, Weakening Slope Stability Analysis (Shear Strength
0)
. The third
slope stability analysis was for the weakening slope stability case using a shear strength of
zero for the liquefied soil layer. The analysis was identical to that in the previous case,
