Dynamic properties of unsaturated soils and their role in prediction of seismic compression

John McCartney

UC San Diego, Department of Structural Engineering

Date & Time
Building 3, Rambo Auditorium
Jack Norbeck

This presentation will focus on the impact of unsaturated conditions on the dynamic response of unsaturated soil layers, with the goal of understanding the seismic compression of unsaturated soil layers during earthquakes. After an introduction to unsaturated soil mechanics, the first half of the presentation will focus on an experimental evaluation of the dynamic properties of unsaturated soils. This includes a summary of resonant column tests highlighting the roles of stress state, suction hardening, and hydraulic hysteresis on the small-strain shear modulus of unsaturated soils, and a summary of cyclic simple shear tests highlighting the modulus reduction and seismic compression of unsaturated soils. The second half of the presentation will focus on different effective stress-based methodologies that can be used to estimate the seismically-induced settlement of a free-field layer of unsaturated sand. This includes both an empirical methodology that synthesizes and extends available empirical methodologies for saturated and dry soils, and a semi-empirical methodology that extends the UBCSand constitutive model. The validation of both models as well as parametric evaluations will be presented to highlight model features and the path forward in future research.

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