Liquefaction hazard evaluation under bidirectional seismic shearing: Optimal ground motion intensity measures

Conducting liquefaction hazard analysis in the framework of performance-based earthquake engineering requires an optimal characterization of ground motions, which reduces variability and uncertainty in the predicted response. Existing studies evaluating intensity measures rely only on unidirectional seismic shearing analysis, disregarding the multidirectional nature of ground motion excitations. In particular, the impact of bidirectional seismic shearing on the liquefaction potential of level ground sand deposits has been shown to be significant compared to unidirectional shearing. Consequently, selection of optimal intensity measures for bidirectional shearing should not be overlooked. This paper studies the results of a series of numerical simulations of sand deposits subjected to unidirectional and bidirectional seismic shearing to evaluate optimal intensity measures for liquefaction hazard. Depth-averaged peak excess pore water pressure ratios were chosen as index for liquefaction potential. The results suggest that CAV and CAV(5) are optimal ground motion intensity measures to assess the effect of bidirectional seismic shearing on the liquefaction potential of uniform sand deposits.