PERMANENT DEFORMATION ON PREEXISTING SLIDING SURFACES IN DAMS

A finite-element model capable of computing permanent deformations alo ng preexisting sliding surfaces in darns and embankments is used to ev aluate the error in the current state-of-practice two-step procedures that are based on the simplifying assumption that the computation of d ynamic response and of the resulting sliding displacements can be deco upled. Both sinusoidal and real earthquake ground motions are used as excitation, and Coulomb's friction law governs sliding along any point of the rigid-plastic tensionless interface. It is found that only whe n the dominant excitation frequencies lie in the proximity of the fund amental dam frequency will the permanent deformation from the decoupli ng assumption exceed appreciably the ''single-step'' value. As a valid ation of the single-step procedure, an analysis is performed and shown to successfully explain the nonsymmetric response of La Villita Dam r ecorded in the 1985 Mexico Earthquake.