Shear wave velocity-based evaluation and design of stone column improved ground for liquefaction mitigation

The evaluation and design of stone column improvement ground for liquefaction mitigation is a challenging issue for the state of practice. In this paper, a shear wave velocity-based approach is proposed based on the well-defined correlations of liquefaction resistance（CRR）-shear wave velocity（Vs）-void ratio（e） of sandy soils, and the values of parameters in this approach are recommended for preliminary design purpose when site specific values are not available. The detailed procedures of pre-and post-improvement liquefaction evaluations and stone column design are given. According to this approach, the required level of ground improvement will be met once the target Vs of soil is raised high enough（i.e., no less than the critical velocity） to resist the given earthquake loading according to the CRR-Vs relationship, and then this requirement is transferred to the control of target void ratio（i.e., the critical e） according to the Vs-e relationship. As this approach relies on the densification of the surrounding soil instead of the whole improved ground and is conservative by nature, specific considerations of the densification mechanism and effect are given, and the effects of drainage and reinforcement of stone columns are also discussed. A case study of a thermal power plant in Indonesia is introduced, where the effectiveness of stone column improved ground was evaluated by the proposed Vs-based method and compared with the SPT-based evaluation. This improved ground performed well and experienced no liquefaction during subsequent strong earthquakes.