The use of permeable piles as an effective drainage method in liquefiable sites has become widely accepted. In this study, the seismic response of both the liquefiable soil and the pile was simulated using FLAC3D software to validate the anti-liquefaction performance of the permeable pile. A group of permeable piles designed according to the China foundation code were numerically modeled with various opening ratios (i.e. area of openings/total surficial area). The numerical results showed that the permeable pile is able to enhance liquefaction resistance by dissipating excess pore water through the drainage holes. The bending moments and axial force of the permeable pile decrease but the ultimate bearing capacity increases in the process of drainage. It is found that the excess pore water pressure ratio (EPWPR) of soil around permeable pile under seismic loading reduces rapidly with increasing opening ratio, but the excess pore water pressure tends to keep nearly a stable level once the opening ratio is beyond a critical value of 0.5%. As a result, the critical value of the opening ratio may be considered as the optimum parameter to design the permeable pile against liquefaction.

A semi-numerical approach is proposed to estimate the dissipation of excess pore water pressure and the development of negative skin friction at the normal impervious pile and the permeable pile after piling. An impeded drainage boundary associated with the opening ratio and opening size is introduced to simulate the drainage condition at the soil-permeable pile interface. In the proposed mathematical framework, analytical approaches are adopted to solve the linear equations, and numerical techniques are utilized to address the nonlinear problems so that the adaptivity and efficiency of the mathematical framework can be well balanced. Through comparisons with the field tests, the model tests, and the theoretical answers, the correctness and rationality of the proposed method are validated. Through a parametric study, the key design parameters of the permeable pile are investigated, and the following design tips are obtained: 1. The opening ratio plays the most important role in the drainage efficiency of the permeable pile; 2. Increasing the number of openings is preferred rather than increasing the size of openings, especially when the opening ratio is determined.