Civil Engineering Reference
In-Depth Information
FIGURE 9.17
Seismic force for each slice in the pseudostatic slope stability analysis. The SLOPE/W com-
puter program was used to generate the plot (Geo-Slope 1991).
those accelerations that plot below the zero line are considered to be into-the-slope accelera-
tions. It is only the out-of-slope accelerations that cause downslope movement, and thus only
the acceleration that plots above the zero line is considered in the analysis. In Fig. 9.19
a,
a
dashed line has been drawn that corresponds to the horizontal yield acceleration, which is des-
ignated
a
y
.
This horizontal yield acceleration
a
y
is considered to be the horizontal earthquake
acceleration that results in a pseudostatic factor of safety that is exactly equal to 1.0. The por-
tions of the two acceleration pulses that plot above
a
y
have been darkened. According to the
Newmark (1965) method, it is these darkened portions of the acceleration pulses that will cause
lateral movement of the slope.
Figure 9.19
b
and
c
presents the corresponding horizontal velocity and slope displace-
ment that occur in response to the darkened portions of the two acceleration pulses. Note
that the slope displacement is incremental and occurs only when the horizontal acceleration
from the earthquake exceeds the horizontal yield acceleration
a
y
.
The magnitude of the
slope displacement depends on the following factors:
1.
Horizontal yield acceleration a
y
:
The higher the horizontal yield acceleration
a
y
,
the
more stable the slope is for any given earthquake.
