Numerical simulation of pore water pressure dissipation method based on a soil-water coupled analysis enhanced by macro element method

Abstract

In the excess pore water pressure dissipation method (referred to as EPWPD method hereafter), ground settlement occurs to some extent due to compaction, because vertical drains in the ground could prevent the pore water pressure from rising during earthquake. Therefore, in this method, it is particularly important to predict the amount of ground deformation under liquefaction as well as to discuss whether liquefaction could be prevented. In this study, the fundamental characteristics of this method were examined by a series of numerical simulations to quantitatively predict the ground deformations. The macro element method, which had been applied only to consolidation phenomena, was mounted on a soil-water coupled finite deformation analysis code GEOASIA which is capable of handling inertial forces and utilizes the SYS Cam-clay as the elasto-plastic constitutive model of the soil skeleton. The main conclusions obtained in this study are outlined next. 1) It was evident that the macro element method that had been only used for quasi-static problems has satisfactory approximation accuracy even in dynamic problems. 2) Basic characteristics of EPWPD method (i.e., liquefaction/compaction during earthquake and consolidation settlement after earthquake) can be adequately reproduced even when a comparatively rough finite element mesh without accounting the drains pitch is used in the macro element method mounted on the analysis code GEOASIA. 3) It is possible to efficiently design the effective drain spacing under the EPWPD method by conducting 1-dimentional mesh analysis prior to multi-dimensional mesh analysis.