Stochastic seismic stability analysis of dam slopes considering softening of rockfills

The rockfills of earth-rockfill dams gradually show softening characteristics subjected to earthquakes, especially strong ones, which will affect the safety of dam slopes. In order to evaluate the effect of rockfill softening on the stability of dam slopes, a probability analysis method of dam slope safety based on the equivalent extreme-value distribution and probability density evolution method is proposed considering the stochastic earthquake excitation and different earthquake levels. A 242-m CFRD is used to perform stochastic dynamic response analysis and probabilistic reliability analysis based on three physical parameters of dam slope stability, the minimum safety factor, cumulative time of safety factor (F_s)<1.0 and cumulative slippage. The results show that the difference between considering softening and without considering softening gradually increases with the increase of earthquake intensity, and the attributes to the softening characteristics of rockfills are gradually revealed during the earthquake. Meanwhile, the softening is a gradual process. Hence, it is of great significance to analyze the seismic performance of the high earth-rockfill dams considering softening of rockfills. Moreover, it is unreasonable to study the stability of earth-rockfill dams only from the point of the minimum safety factor, and it is necessary to combine the cumulative time of F_s<1.0 and cumulative slippage to fully evaluate the safety of dam slope. The proposed stochastic probabilistic analysis method can give a more accurate evaluation of the reliability of high earth-rockfill dam slopes.