Liquefaction Response of Partially Saturated Sands. II: Empirical Model

Abstract

Partial saturation in sands attributable to the presence of gas bubbles (not capillarity) can be encountered naturally in the field be- cause of the decomposition of organic matter, or it can be induced for liquefaction mitigation. An empirical model (RuPSS) was developed to predict the excess pore pressure ratio (ru) in partially saturated sands subjected to earthquake-induced shear strains. The model is based on experimental test results on partially saturated sands. Cyclic simple shear strain tests were performed on specimens prepared and tested in a special liquefaction box. Excess pore pressures were measured for a range of degrees of saturation 40%,S,90%, relative densities Dr 520267%, and cyclic shear strains g50:0120:2%. The test results demonstrated that partially saturated sands achieved a maximum excess pore pressure ratio (ru,max) when large enough cycles of shear strain were applied. The excess pore pressure ratio (ru) that partially saturated sand can achieve under a given earthquake-induced peak shear strain and the number of equivalent cycles of application can be significantly smaller than ru,max. Therefore, the empirical model was developed in two stages. In the first stage, ru,max was related to S, Dr, and shearstrain(g).In thesecondstage,amodelwasdevelopedrelatingru toru,max,shearstrainamplitude(g),effectivestress(s9),andearthquake magnitude(M).Thispaperpresentstheequationsthatdefinethepredictivemodelsforru,max andru.Throughtheseequations,plotsforru,max and ru are provided for ranges of soil and earthquake parameters for ease of use in engineering applications. To illustrate the implementation of the empirical model for predicting ru,max and ru, an example is presented in which a partially saturated sand layer experiencing a peak earthquake- induced shear strain was analyzed, and the pore pressure response of the sand was evaluated using both the predictive equations and the plots. DOI: 10.1061/(ASCE)GT.1943-5606.0000816. © 2013 American Society of Civil Engineers. CE Database subject headings: Soil liquefaction; Soil treatment; Saturated soils; Pore pressure; Empirical equations; Sand (soil type). Author keywords:Soil liquefaction; Soil treatment; Saturation; Pore pressure; Empirical equations; Induced partial saturation; Liquefaction mitigation; Empirical model; Soil model.