Probabilistic Analysis of Deposit Liquefaction

A probabilistic methodology is presented for liquefaction analysis of horizontally layered sand deposits, subjected to vertically propagating seismic S waves. Three different deposit models are developed. The models are effectively one-dimensional and differ in that they include or neglect pore pressure diffusion and stiffness reduction due to pore pressure buildup. Conclusions are drawn about sensitivity of the results to different assumptions about the mechanical behavior of the deposit, the effect of vertical and horizontal variations of soil properties, and about the importance of statistical variability of the response spectrum at bedrock given peak acceleration. An approximate procedure is proposed for the calculation of the probability of almost complete layer liquefaction, for given input motion and given layer average SPT results. Predictions from the approximate procedure are in good agreement with historical data.