SEISMIC PERFORMANCE EVALUATION OF POTENTIALLY LIQUEFIABLE EARTH DAMS

Seismic performance evaluations of earth dams are essential to characterize the geotechnical risk implied by slope stability failures. There are a large number of case histories compiled in the international technical literature, which report failures of these types of earthen structures caused by moderate to large magnitude earthquakes. The observed damage is more important when liquefaction occurs on the dam body and foundation, which often leads to cracking, settlements, tilting, and general distortion of the dam geometry. Analyses based on limit equilibrium are generally sufficient to establish hazard zones. However, numerical models with solution schemes formulated in the time domain, which are capable of taking into account the kinematics of the soil movement more realistically, are needed to quantify the geotechnical risk. This paper describes the application of a practice-oriented simplified constitutive model, which implemented in a lagragian finite difference platform, is capable of predicting the accumulation of pore pressure due to earthquake loading in finegrained saturated materials, the reduction of shear strength, and its effect on the development of permanent displacements. The model uses a bilinear Mohr-Coulomb type failure criterion coupled with an incremental pore pressure generation scheme. The pore pressure is accumulated as a function of the number of stress cycles. The tangent soil stiffness and hysteretic damping are modified with the loading history. The model capability to evaluate the seismic response of earth dams is illustrated through the analysis of a case history comparing the model predictions with actual field measures. The model is able to properly capture the kinematics of the slope failure and the observed damage. The measured permanent displacements after liquefaction and those computed with the model are in good agreement.