Probabilistic Seismic Loading Considerations for the Assessment of Liquefaction-Induced Volumetric Settlements in the Free Field

Abstract

Engineers have long integrated predicted volumetric strains in liquefied soils to predict free-field, postliquefaction settlements. These free-field settlements have commonly been used to define a lower bound estimate of settlements beneath structures or embankments. Semiempirical methods for predicting volumetric strains during liquefaction require characterization of the seismic loading impacting the soil. The way in which probabilistic estimates of seismic loading is characterized can significantly impact the predicted postliquefaction settlements. This study evaluates three potential approaches for characterizing probabilistic seismic loading and their impact on the computed free-field, postliquefaction volumetric settlement hazard. The pseudo-probabilistic approach, which is arguably the most common approach in engineering practice in the US, shows considerable bias in its predicted volumetric settlements, including an average underprediction of settlement equal to 38% when compared to a fully probabilistic approach at a return period of 2,475 years. A simple linear relationship to correct pseudo-probabilistic estimates of free-field, postliquefaction volumetric settlements at return periods of 475 and 2,475 years for two common semiempirical volumetric strain models is presented.