Liquefaction of Level Ground Unsaturated Sand Deposits Using a Validated Fully Coupled Analysis Procedure

Abstract

Liquefaction of unsaturated sands has been observed in laboratory tests and in the field. A comprehensive investigation of unsaturated sand deposits subjected to seismic loading, especially using validated computational tools, is still lacking. This paper presents an analysis procedure to study the response of level ground unsaturated sand deposits subjected to seismic loading. The analysis procedure is a fully coupled flow–deformation finite element code with solid skeleton displacements, pore water pressure, and pore air pressure as nodal variables. The stress–strain behavior of unsaturated sands is described by a coupled hydro-mechanical elastoplastic constitutive model that includes the hysteretic model for soil water characteristic curves and the hydro-mechanical coupling mechanisms. The finite element code is first validated by comparing simulations with centrifuge test results. Reasonable comparisons of surface accelerations, ground settlements, and lateral deformations are obtained. A parametric study is then conducted to investigate the effects of initial degree of saturation, relative density, and effective overburden pressure on the seismic response of level ground unsaturated sand deposits. The results of the parametric study show that the thickness of the liquefied layer increases with an increase in degree of saturation. The potential for liquefaction reduced with increases in relative density and effective overburden stress. The results also reveal a drastic reduction in surface accelerations following liquefaction of a sand deposit.