CIVIL ENGINEERING 365 ALL ABOUT CIVIL ENGINEERING



AbstractSite survey revealed that a liquefiable sand layer was often sandwiched by low-permeable layers with fine particles, which could hinder the dissipation of excess pore water pressure (EPWP) after earthquake excitation. However, the remaining EPWP within the liquefied sand layer may significantly reduce the reliquefaction resistance of the sand during an aftershock of the main earthquake. Many investigations on the liquefaction of stratified sand have been performed in model tests, e.g., 1 g shaking table tests and centrifuge tests as boundary value problems. However, few contributions on this topic from element tests are available in the literature. Investigations on the reliquefaction of sand sandwiched by low-permeable layers are even less available. Therefore, three groups of reliquefaction tests with different reconsolidation ratios, or different dissipation degrees of EPWP, were performed on Toyoura sand using a cyclic triaxial loading apparatus. In each group of tests, two key factors, stress-induced anisotropy formed in the first liquefaction process and the cyclic stress ratio in the second loading, were designed to investigate the reliquefaction resistance of incomplete reconsolidated sand that had already experienced liquefaction in the first loading. The test results indicated that the reliquefaction resistance decreased significantly if residual EPWP existed in the specimens. Furthermore, stress-induced anisotropy has a substantial influence on the reliquefaction resistance of both complete and incomplete reconsolidated sands. In an extreme case, even a small amplitude of aftershock could trigger reliquefaction of sand if the first liquefied sand maintains a high level of stress-induced anisotropy or has a large amount of residual EPWP. Finally, the relations among the cyclic stress ratio, stress-induced anisotropy, and reconsolidation ratio were proposed to predict the reliquefaction resistance of sand sandwiched by low-permeable layers.



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