Application of Pseudo-Static Sliding Stability Analysis in Seismic Design and Safety Evaluation of Embankment Dams

Pseudostatic methods for the seismic analysis of concrete and embankment dams were introduced in the 1930s, in which the seismic hazard was represented by a seismic coefficient of 0.1for most dam sites. For the sliding stability analysis of dams, the pseudostatic method is still in use and corresponding safety factors are given for different load combinations in design guidelines and codes. Typically, a sliding safety factor of greater than 1 is requested for the ground motion caused by the safety evaluation earthquake. In order to show that a slope of an embankment dam is stable, seismic coefficients are used, which have nothing in common with the characteristics of the earthquake ground motion. Although results of reanalyses of dams after the 1971 San Fernando earthquake in California have shown that the pseudostatic analysis method is not suitable for the prediction of the seismic safety of embankment dams subjected to strong ground shaking, and despite of repeated calls for the use of more reliable methods of seismic analyses of embankment dams by the seismic committee of the International Commission on Large Dams (ICOLD), the pseudostatic method is still in use. The paper discusses the new seismic design and performance criteria of large dams published by ICOLD in 2016 and the simplified method of dynamic slope stability analysis to be used today for large dams. Today, the seismic safety of dams is assessed based on typical failure modes and inelastic deformations of dams due to ground shaking of the safety evaluation earthquake, and not on pseudostatic sliding safety factors.