SEISMIC RISK ANALYSIS FOR EARTH DAMS

There are many sources of uncertainty involved in seismic safety evaluation of an embankment or an earth dam. Even when conservative assumptions and selections of parameters are made, there will always be a probability that performance of the dam during its lifetime may not be as predicted. To evaluate seismic risk of damage or failure of earth dams, a seismic risk analysis procedure is presented. The future occurrence of earthquakes is probabilistically described in terms of both intensity and number of cycles of ground motion (seismic hazard analysis). Furthermore, a probabilistic procedure for the calculation of permanent deformation of earth dams (seismic performance analysis) is presented, characterizing the seismic event in terms of acceleration, number of cycles, and predominant period of motion. The results of seismic hazard and seismic performance analyses are combined to yield the risk of seismic damage or failure of a dam (seismic risk analysis). An example case study is presented, illustrating the application of the procedures. A risk-based seismic safety evaluation of an embankment or on earth dam can provide estimates of relative risks that are useful in design and decision analysis and can avoid compounding of conservatism.