Performance-Based Assessment and Design of Structures on Liquefiable Soils: From Triggering to Consequence and Mitigation

Abstract

AbstractEffective liquefaction mitigation requires an improved fundamental understanding of triggering in terms of excess pore pressures in realistically stratified deposits that experience cross-layer interactions as well as performance-based consequence procedures that account for 3D soil-structure interaction (SSI), all mechanisms of deformation, total uncertainty, and the impact of mitigation. In this paper, we first present a series of centrifuge experiments to evaluate site response and pore pressure generation in layered liquefiable deposits, soil-structure interaction (SSI), and the impact of ground densification as a mitigation strategy on SSI and building performance. Second, experimental results are used to validate 1D and 3D, fully-coupled, nonlinear, dynamic finite element analyses of layered sites and soil-foundation-structure systems with and without mitigation. Third, numerical parametric studies (exceeding 167,000 1D and 63,000 3D simulations) are used to identify the functional forms for predicting liquefaction triggering in the free-field based on the capacity cumulative absolute velocity (\(CA{V}_{c}\)) required to achieve a threshold excess pore pressure ratio (ru), settlement of unmitigated structures, and the relative impact of ground densification on foundation’s permanent settlement. And finally, a limited case history database is used validate the triggering and consequence models, accounting for field complexities not captured numerically or experimentally. This integrative approach yields a set of procedures that are the first to consider variations in soil layering and geometry, layer-to-layer cross interactions, foundation and structure properties (in 3D), contribution of all mechanisms of deformation below unmitigated structures, geometry and properties of densification, ground motion’s cumulative characteristics, total inherent model uncertainties, and the explicit conditionality of structural settlement on free-field triggering—which are necessary to realize the benefits of performance-based engineering in liquefaction assessment. KeywordsLiquefaction triggeringMitigationSoil-structure interaction