碎石桩加固可液化场地数值模拟与分析

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

采用砂土液化大变形模型模拟饱和砂土及等效非线性增量模型模拟碎石桩,对碎石桩加固约19 m厚饱和砂土场地的动力离心模型试验进行数值模拟,在加固区与非加固区不同部位的加速度和超静孔隙水压响应时程与试验数据符合较好。在试验验证的基础上,对不同震动强度下碎石桩的排水与加密效应对加固可液化场地的动力响应影响进行了模拟研究,包括:超静孔压累积与消散,土体液化变形的发展,及加固区内部与外部响应差异等。结果表明:碎石桩加固可明显改善土体抗液化能力,在所分析的0.2 g震动强度工况,碎石桩加固区除桩间土浅层1 m^2 m少量部位外未出现土体液化,基本达到加固消除液化的目的。碎石桩抗液化的有效影响范围约为2.5倍~3倍桩径,在浅层小而随深度增加;外围桩发挥着加固区排水屏障和非加固区排水通道的作用;碎石桩加固加密土体时,会提高土体的剪应力比峰值。

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.