Three-Dimensional DEM Analysis of Axially Loaded Geogrid-Encased Stone Column in Clay Bed

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Abstract
The discrete-element method (DEM) was employed in this study to analyze the micromechanical behavior of an axially loaded geogrid-encased stone column (GESC) installed in a clay bed. A three-dimensional DEM model was developed to simulate a partially encased stone column in the laboratory test under a plate loading condition. The aggregate, the geogrid encasement, and the surrounding soil were simulated using particles with different sizes and micromechanical properties. The load-displacement behavior of the DEM model closely matched the experimental result during the loading process. This study investigated the vertical and radial stresses in the column and its surrounding soil, the porosity change and particle movement in the column, and the contact force distributions before and after loading. The interaction and the interlocking effect between particles were different in the encased and unreinforced sections due to the existence of the geogrid encasement. The surrounding soil developed high vertical and radial stresses in the layers below the base of the geogrid encasement due to the strong interaction between the aggregate and the soil. The maximum coefficient of radial stress (2.4) in the encased column was approximately half the coefficient of passive earth pressure (4.6). The current design method overestimated the bearing capacity of the GESC based on the coefficient of passive earth pressure.

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