Civil Engineering Reference
In-Depth Information
FIGURE 3.54
Cracking of the Anchorage-Portage highway. The
small highway embankment experienced lateral movement during the
Prince William Sound earthquake in Alaska on March 27, 1964.
(
Photograph from the Steinbrugge Collection, EERC, University of
California, Berkeley.
)
There are two cases of weakening slope stability analyses involving the liquefaction
of soil:
a. Flow slide:
As discussed in Sec. 3.4.4, flow failures develop when the static driving
forces exceed the shear strength of the soil along the slip surface, and thus the factor of
safety is less than 1.0. Figures 3.38 to 3.40 show the flow slide of the Lower San
Fernando Dam caused by the San Fernando earthquake on February 9, 1971.
b. Lateral spreading:
As discussed in Sec. 3.4.5, there could be localized or large-
scale lateral spreading of retaining walls and slopes. Examples of large-scale lateral
spreading are shown in Figs. 3.41 and 3.42. The concept of cyclic mobility is used to
describe large-scale lateral spreading of slopes. In this case, the static driving forces
do not exceed the shear strength of the soil along the slip surface, and thus the ground
is not subjected to a flow slide. Instead, the driving forces only exceed the resisting
forces during those portions of the earthquake that impart net inertial forces in the
downslope direction. Each cycle of net inertial forces in the downslope direction
