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Mechanical model for the analysis of liquefaction of horizontal soil deposits Lee, Kwok Wing

Abstract

During the development of liquefaction in a soil deposit subjected to vibration there are two processes which work in opposite directions. The volume compaction tendency under cyclic loading causes the pore water pressure to rise, and the dissipation of excess pore water pressure (consolidation) decreases it. Recently, Martin, Finn and Seed (l975) studied the mechanics of pore water pressure generation of a soil sample subjected to cyclic loading and a relation between shear strain cycles, volume compaction and pore water pressure increment was established. A material model based on this relationship is developed in this thesis for saturated granular soil under cyclic simple shear conditions. The model includes a hysteretic stress-strain relationship, volume compaction, pore water pressure rise and dissipation. Using this proposed comprehensive material model, a global mechanical model is constructed to simulate the liquefaction (including consolidation) behavior of a thick horizontal deposit when subjected to horizontal base motion. In this way the coupled problems of dynamic response, pore water pressure rise and consolidation of the deposit under seismic loading can be analysed. The numerical techniques used to solve such problems are discussed in detail. The response of a typical saturated sand deposit under earthquake loading is determined using the proposed model and the results show that the model can predict the various phenomena that saturated sand deposits exhibit during earthquakes. The global model also makes clear the influence of permeability on the liquefaction potential of the soil deposit.

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