Probabilistic Liquefaction Triggering and Manifestation Models Based on Cumulative Absolute Velocity

Abstract

This study proposes the capacity cumulative absolute velocity (CAVc) as a novel measure for the resistance of granular soils to earthquake-induced liquefaction. The CAVc is defined as the cumulative absolute velocity (CAV) needed to generate a threshold excess pore pressure ratio (ru) value at a specified depth in a layer of liquefiable soil. A probabilistic model for predicting CAVc corresponding to ru values between 0.5 and 1.0 is developed using a database of over 280,000 estimates of CAVc from one-dimensional (1D), nonlinear, effective stress site-response analyses. These models provide CAVc as a function of depth, the presence and location of low-permeability interlayers in the soil profile, and soil stiffness (as reflected in the normalized cone tip resistance from cone penetration test results). The standard deviation around the model’s estimates of CAVc ranges from 0.59 natural log units for an ru threshold of 1.0 to 0.83 natural log units for an ru threshold of 0.5. Correlation models are provided for predicting CAVc throughout the depth of a soil profile, across multiple ru thresholds, or both. Finally, CAVc is implemented in a proposed modification of the liquefaction potential index (LPICAV). The new index is validated using data from three earthquakes in Canterbury, New Zealand, and has a slightly improved predictive capability compared to existing indices, while making use of a relatively predictable intensity measure (i.e., CAV of the outcropping rock motion); this intensity measure is also compatible with performance-based methods for predicting liquefaction consequences. Finally, a guide for model implementation and examples of various applications are provided.