Anomalies in Pseudostatic Seismic Stability Analysis

Slopes in soil and rock are often defined in terms of their static and pseudostatic factors of safety. For the case of sliding along a single plane, a simple equation relates the pseudostatic factor of safety to the static factor of safety, the slope of the failure plane, and the friction angle for the single plane model and gives remarkably accurate estimates for more complicated analyses. A further result is that the horizontal seismic coefficient necessary to bring the pseudostatic factor of safety to 1.0 increases as the slope of the failure plane increases. This result is counterintuitive, but it arises because of the complicated interactions among the parameters defining the factors of safety.