Cyclic Behavior of Kaolin Clay under Undrained Conditions: Role of Microfabric

The role of microfabric in the undrained cyclic behavior of kaolin clay is a topic of considerable interest but is yet to be fully understood. This paper presents new experimental data and analysis to address the topic. An efficient method is suggested to prepare flocculated and dispersed samples of good uniformity and repeatability in the laboratory. The experiments consistently show that there exists a critical cyclic stress ratio (CSR)—when the applied CSR is less than or greater than it, the accumulation of plastic strain and of residual pore water pressure during cyclic loading can be markedly different. The microfabric of kaolin clay affects the critical CSR, and this effect appears to be coupled with the effective confining pressure. In general, the flocculated sample has a larger critical CSR than the dispersed one and it has stronger resistance when subjected to CSR that is greater than the critical CSR. When subjected to CSR that is less than the critical CSR, the dispersed sample, however, exhibits larger resistance than the flocculated sample. Furthermore, the possible microscopic mechanism for the macroscopic experimental findings is explored by means of quantitative analysis of microfabrics of the flocculated and dispersed samples at different loading stages.