UC Davis

Interlayered soil deposits with alternating and discontinuous beds of sands, silts, and clays underlie and interact with infrastructure worldwide. However, common simplified methods have been shown to typically over-predict earthquake ground deformations at interlayered sites, due to limitations in site characterization tools and methods, triggering and strain correlations, and analysis approaches. The most common of these simplified methods are one-dimensional liquefaction vulnerability indices (LVIs) that integrate strains and factors of safety against liquefaction triggering using empirical correlations with geotechnical site investigation data [e.g., cone penetration tests (CPTs) and borings]. Recent improvements of computational models for evaluating seismic soil responses have shown great value in resolving over-prediction biases.

This dissertation first provides a framework for site-specific CPT-based fines content (FC) correlations, which has posed significant uncertainty for both LVIs and nonlinear dynamic analysis (NDA) evaluations of liquefaction effects in interlayered deposits. Next, a system-level workflow that integrates detailed subsurface modeling with two-dimensional (2D) NDAs is utilized to evaluate the spatial extent and magnitude of ground deformation at three well-documented post-earthquake case history sites. These sites produced sediment ejecta, lateral spreading, and an extensional graben, within unique geologic environments in New Zealand, Taiwan, and California, respectively. Alternate geostatistical approaches for modeling subsurface spatial variability conditioned on available CPT data and geological details were considered, including deterministic, transition probability-based indicator simulation, kriging, and sequential Gaussian simulation (SGS) methods. The NDAs were performed with the Fast Lagrangian Analysis of Continua (FLAC) finite-difference program, with site-specific calibrations of the PM4Sand and PM4Silt constitutive models. The factors and neglected mechanisms that most contributed to prediction biases at each of these sites are explored, and improvements as well as limitations of the NDA workflow relative to LVIs and other simplified methods are discussed. This dissertation concludes with a holistic discussion of insights gained from a larger set of post-earthquake NDA case studies, and future research needs for evaluating interlayered deposits in practice.