Development of an Improved and Internally-Consistent Framework for Evaluating Liquefaction Damage Potential

Soil liquefaction continues to be one of the leading causes of ground failure during earthquakes, resulting in significant damage to infrastructure around the world. The study presented herein aims to develop improved methodologies for predicting liquefaction triggering and the consequent damage potential such that the impacts of liquefaction on natural and built environment can be minimized. Towards this end, several research tasks are undertaken, with the primary focus being the development of a framework that consistently and sufficiently accounts for the mechanics of liquefaction triggering and surface manifestation. The four main contributions of this study include: (1) development of a framework for selecting an optimal factor of safety (FS) threshold for decision making based on project-specific costs of mispredicting liquefaction triggering, wherein the existing stress-based "simplified" model is used to predict liquefaction triggering; (2) rigorous investigation of manifestation severity index (MSI) thresholds for distinguishing cases with and without manifestation as a function of the average inferred soil-type within a soil profile, which may be employed to more accurately estimate liquefaction damage potential at sites having high fines-content, high plasticity soils; (3) development of a new manifestation model, termed Ishihara-inspired Liquefaction Severity Number (LSNish), that more fully accounts for the effects of non-liquefiable crust thickness and the effects of contractive/dilative tendencies of soil on the occurrence and severity of manifestation; and (4) development of a framework for deriving a "true" liquefaction triggering curve that is consistent with a defined manifestation model such that factors influential to triggering and manifestation are handled more rationally and consistently. While this study represents significant conceptual advance in how risk due to liquefaction is evaluated, additional work will be needed to further improve and validate the methodologies presented herein.