EVALUATION OF EARTHQUAKE-INDUCED SLIDING IN ROCKFILL DAMS

Abstract

The relation between the factor of safety obtained from dynamic response analyses on arbitrary potential sliding surface of a rockfill dam and the one obtained from conventional method such as slice method has been made clear by introducing a concept of equivalent instantaneous seismic coefficient.Throughout many numerical experiments of dynamic response analyses conducted on a typical rockfill dam section with sinusoidal ground motions of various kinds of accelerations and periods, a simple expression for the sliding permanent displacements has been obtained as a function of maximum equivalent instantaneous seismic coefficient and duration of sliding which is independent of the scale and location of sliding surface, the period of ground motion and the amplitude of ground acceleration. This formula has been applied to the simplified evaluation for the sliding permanent displacements in the cases with the ground motions of recorded accelerograms.Acceleration response spectra of many recorded accelerograms have been calculated and the ratio of each maximum value to peak ground acceleration has been plotted against corresponding predominant period. With this diagram the amplitude of equivalent sinusoidal ground acceleration has been specified as 0.5 to 0.6 of peak ground acceleration in conservative side.Combining above formula with the magnification factors of the equivalent instantaneous seismic coefficients in the potential sliding circles near crest, an expression for the relationship between the amplitude of above equivalent sinusoidal ground acceleration and the earthquake-induced sliding displacement at near crest has been derived. Giving certain amount of allowable permanent displacement, an earthquake-resistant design diagram for rockfill dams concerning with the equivalent sinusoidal ground acceleration has been proposed.