Influence of encasement length and geosynthetic stiffness on the performance of stone column: 3D DEM-FDM coupled numerical investigation

Abstract

The design of geosynthetic encasement is the most important factor that controls the performance of the geosynthetic-encased stone column (GESC) improved ground, and encasement length (Lenc) and geosynthetic stiffness (J) are two basic design items. Numerous continuum-based numerical models have been proposed to investigate the influence of geosynthetic encasement on the behavior of GESC improved ground, however, the micro-mechanics of stone aggregates cannot be properly simulated due to its discrete nature. In this paper, a three-dimensional discrete element method (DEM) and the finite difference method (FDM) coupled numerical modeling scheme was proposed. Surrounding clay is modeled by the continuum method using FLAC3D and the stone column and geosynthetics are modeled by the discrete element method using PFC3D. The proposed numerical models are validated using laboratory observations. The influence of geosynthetic encasement is analyzed by predicting pressure-settlement behavior, lateral deformation of surrounding clay, stress distribution within the column, and microscopic characteristics of granular materials (i.e., porosity, coordination number and contact force distribution). Numerical results demonstrate that full length and high stiffness encasement will significantly improve the load-bearing capacity of GESCs. In practice, fully-encased stone columns are recommended for reducing the settlement.