NUMERICAL INVESTIGATION ON LIQUEFACTION MITIGATION OF LIQUEFIABLE SOIL IMPROVED BY STONE COLUMNS

Using a plasticity model for large post-liquefaction deformation of sand for liquefiable soil and an equivalent nonlinear incremental model for stone columns (SC), a centrifuge model test with a SC improved 19m liquefiable sand layer is simulated. The time histories of acceleration and excess pore water pressure (EPWP) at various locations both within and outside the improved area agreed with the experimental data. Upon validation, analysis is conducted on the densification and drainage effects of SC on the dynamic response of the improved ground under various shaking intensities. The build-up and dissipation process EPWP of the deformation process from small pre-liquefaction deformation to large post-liquefaction deformation, and the different response within and outside the improved areas are investigated. The results show that the installation of SCs can mitigate earthquake-induced liquefaction in saturated sand. For the case of 0.2 g shaking intensity in this study, no substantial liquefaction is observed in the SC improved area except small portions near the ground surface. The effective influence area of each column is about 2.5~3 times its diameter. For a group of SCs, the periphery SCs act as drainage barrier for the improved area and drainage path for the unimproved free field. Densification of soil due to SC installation increases the peak value of shear stress ratio in the soil.