Previous

Next

1. The simplest slope stability problem is a dry embankment as shown in Figure 6(a). The pore pressures are equal to zero and the effective stress strength parameters, c' and ', should be used. Consolidated-drained (CD) tests should be performed to determine c' and '.

2. A partially submerged slope is shown in Figure 6(b). In this case, the water table is static and the pore pressures are easily determined by taking the depth below phreatic surface and multiplying by the unit weight of water. Effective stress strength parameters should be used as determined by CD or consolidated-undrained (CU) tests with pore pressure measurements. This problem may be solved two ways:

   1. Use total unit weights throughout, apply the boundary water pressure and specify the pore pressures in the slope.

   2. Use buoyant unit weight below the water table and neglect the boundary water pressure and pore pressures. This type of analysis is demonstrated in Example 3i for TSLOPE.

   Note that if a pseudo-static seismic loading is subsequently applied, method (a) must be used because the correct inertia forces are obtained only by using total unit weights.

3. The classic long-term stability problem is the steady state seepage condition shown in Figure 6(c). This represents, for instance, the most critical condition for the downstream slope of a dam with a full pool and with steady seepage through the dam. Again, use c' and ' as determined by CD or CU tests. Pore pressures should be determined by drawing a flow net or by field measurement. Apply boundary water pressures on upstream and downstream slopes where applicable.

Figure 6 Long-term stability problems.

Top of Page

Previous

Next