OBSERVED AND PREDICTED EARTHQUAKE RESPONSE OF LA VILLITA DAM

La Villita earth and rockfill dam in Mexico has been subjected to five major earthquakes during the period 1975-1985. The recorded time hist ories of crest acceleration and associated permanent displacements imp ly the occurrence of seismically induced localized stick-slip slope de formations. In this paper, the upstream-downstream seismic response of La Villita dam is investigated in detail. The dam vibration character istics are represented by a one-dimensional shear-wedge elasto-plastic numerical model. Available bedrock acceleration histories are employe d as input excitation and seismic response is calculated using a step- by-step time integration procedure. Crest acceleration histories are c omputed and further employed to predict the observed permanent displac ements, For that purpose, an elastic-perfectly plastic single-degree-o f-freedom (SDOF) model is used in a Newmark-type sliding mass analysis . The predicted SDOF permanent displacements are found to be similar t o their recorded counterparts. Moreover, this yielding SDOF model is f ound to capture the peculiar asymmetric response characteristics assoc iated with the evolution of stick-slip displacements, and observed in the recorded crest accelerations of La Villita Dam. Finally, the emplo yed numerical procedures are found to demonstrate the possible develop ment of additional permanent crest displacements during future seismic events.