Evaluation of the Liquefaction Potential Index for Assessing Liquefaction Hazard in Christchurch, New Zealand

Abstract

While the liquefaction potential index (LPI) has been used to characterize liquefaction hazards worldwide, calibration of LPI to observed liquefaction severity is limited, and the efficacy of the LPI framework and accuracy of derivative liquefaction hazard maps are thus uncertain. Herein, utilizing cone penetration test soundings from nearly 1,200 sites, in conjunction with field observations following the Darfield and Christchurch, New Zealand, earthquakes, this study evaluates the performance of LPI in predicting the occurrence and severity of surficial liquefaction manifestations. It was found that LPI is generally effective in predicting moderate-to-severe liquefaction manifestations, but its utility diminishes for predicting less severe manifestations. Additionally, it was found that LPI should be used with caution in locations susceptible to lateral spreading, because LPI may inconsistently predict its occurrence. A relationship between overpredictions of liquefaction severity and profiles having soils with high inferred fines-content was also investigated. It was determined that the LPI procedure might be improved if it accounted for the characteristics of soils in the crust and interbedded nonliquefiable layers, as well as the characteristics of the soils predicted to liquefy. Further research is needed in this regard. Finally, it was found that for the in situ conditions in Christchurch, the computed LPI values were relatively sensitive to estimates of groundwater depth because of the proximity of liquefiable strata to the ground surface.