Endochronic-Based Approach to the Failure of the Lower San Fernando Dam in 1971

The Lower San Fernando dam failure, which took place in 1971, is one of the most reported cases of seismic liquefaction damage in the geotechnical literature. For this reason, it has been analyzed by almost all of the numerical models developed since that year. In this paper, a comparison between numerical simulations, using a new endochronic model, with measured response of this dam during the earthquake of 1971, as well as numerical results previously obtained by other researchers, is presented. The main particularity of this new constitutive law is a nonassociative flow rule, related to a parameter quantifying degradation with shaking duration, in terms of stiffness reduction. It is incorporated in the model to represent soil dilation. Furthermore, contractive, dilative, and collapse trends of soil behavior are jointly embodied into the new developed constitutive law, which has been implemented in a two-dimensional coupled finite-element model. By so doing, the failure mechanism and the critical locations of the dam are identified and compared with field observations, and the approximate time for the beginning of the upstream sand fill slide is determined.