EXPERIMENTAL AND NUMERICAL STUDIES ON THE CHANGE INGROUND STIFFNESS BEFORE AND AFTER LIQUEFACTION

摘要

It is possible, at present, to simulate liquefaction of ground due to earthquake with reasonable accuracyusing an effective stress analysis. One of the key issues in liquefaction analyses is how to make a modelthat can take into consideration ground stiffness reduction before liquefaction. Yet, the process of groundstiffness recovery after liquefaction is also important issue. The change of soil stiffness has been studiedwith undrained cyclic triaxial tests or shaking table tests [1]. Based on the experimental results, a numberof well-performed constitutive models have been proposed. Among those constitutive models, someelastoplastic models based on a nonlinear kinematical hardening rule have been well used in liquefactionanalyses, mainly for clean sands. Unfortunately, those models cannot predict the change in groundstiffness well for soils of fine grains and gravels. In this study, in order to clarify the ground stiffnesschange during liquefaction, shaking table tests, undrained cyclic triaxial tests and effective stress analysesare conducted for three kinds of geomaterials. Decomposed granite, clean sand called Kasumigaura-sandand crushed stone called gravel are used in the series of tests and simulations. The experimental resultsare compared with the results of effective stress analyses. It is found that the change in pore waterpressure during liquefaction is well simulated for Kasumigaura-sand and gravel. On the other hand, fordecomposed granite, simulation results of the change in excessive pore water pressure in liquefactionprocess cannot express the experimental results well. It is also found that from laboratory tests, the changein ground stiffness in the process of primary liquefaction is largely affected from the performance of theexcessive pore water pressure.