Civil Engineering Reference
In-Depth Information
relatively intact during the earthquake-induced slope movement. Another example is a rock
avalanche, which by definition implies a large mass of displaced material. Figure 9.5 shows
a rock avalanche caused by the Hebgen Lake earthquake, in Montana, which blocked a
canyon and created a temporary lake.
As discussed in Sec. 3.5.3, the seismic evaluation of slope stability can be grouped into
two general categories: inertia slope stability analysis and weakening slope stability analy-
sis, as discussed in the following sections.
9.1.1
Inertia Slope Stability Analysis
The inertia slope stability analysis is preferred for those materials that retain their shear
strength during the earthquake. Examples of these types of soil and rock are as follows:
●
Massive crystalline bedrock and sedimentary rock that remain intact during the earth-
quake, such as earthquake-induced rock block slide (see Tables 3.1 and 9.1).
●
Soils that tend to dilate during the seismic shaking, or, for example, dense to very dense
granular soil and heavily overconsolidated cohesive soil such as very stiff to hard clays.
●
Soils that have a stress-strain curve that does not exhibit a significant reduction in shear
strength with strain. Earthquake-induced slope movement in these soils often takes the
form of soil slumps or soil block slides (see Tables 3.2 and 9.2).
●
Clay that has a low sensitivity.
●
Soils located above the groundwater table. These soils often have negative pore water
pressure due to capillary action.
●
Landslides that have a distinct rupture surface, and the shear strength along the rupture
surface is equal to the drained residual shear strength
r
.
FIGURE 9.5
Rock avalanche caused by the Hebgen Lake earthquake in Montana on August 17, 1959.
(
Photograph from the Steinbrugge Collection, EERC, University of California, Berkeley.
)
