# A DEM Study on Bearing Behavior of Floating Geosynthetic-Encased Stone Column in Deep Soft Clays
## 2 Numerical Simulation: Discrete Element Modeling  
### PFC Modeling of a FGESC in Soft Clay  
The three-dimensional particle flow code (PFC3D, version 5.00.40) is a DEM software developed by Itasca, which was used to simulate the behavior of an FGESC installed in soft clay. The aggregates, the geogrid encasement, and the soft soil were simulated by spherical particles with different sizes and contact properties, and the mechanical behavior of spherical particles were updated according to [PERSON]'s law at each calculation cycle.  
The behavior of a group of FGESCs in deep soft clay was simplified to a single FGESC installed in the center of a cylinder of clay, as shown in Figure 1. In the unit cell idealization of FGESC, only vertical deformation was allowed, and the side and bottom boundaries were rigid and fixed. For PFC, the concept of unit cell idealization could control the number of particles within a certain range, which was helpful to improve the computational efficiency.  
Figure 2 shows the 3D DEM model for an FGESC in soft clay. The diameter of the FGESC was 90 mm, and the length was 360 mm. The diameter and height of the model were 250 mm and 540 mm, respectively. Therefore, the area replacement ratio was 12.96%. The linear model was applied to simulate the aggregates of the FGESC. The diameters of the aggregates ranged from 16 mm to 26 mm, of which 16 mm-20 mm accounted for 25%, and 20 mm-26 mm accounted for 75%. The aggregates were rigid. Due to the high tensile stiffness of geogrid, the linear parallel contact model was used to simulate the geogrid. The geogrid was composed of two rows of particles with a diameter of 2 mm, and the spacing between the two rows was 20 mm. The geogrid completely wrapped the stone column, with a length of 280 mm. The mechanical property of the soil particles was complicated in nature. The soil around the FGESC and the soil in the underlying layer were mainly subjected to vertical deformation. Therefore, this study focused on the compression characteristics of soil particles. The soil particles were simulated by the linear contact bond model. The soil particles were 6.8 to 7.2 mm in diameter and had an initial porosity of 0.4. For clear display, the soil particles were divided into two groups with different colors, and the height of the underlying stratum was 180 mm.  
A circular plate with a diameter of 90 mm was generated. It acted as a loading plate while moving down. When the particles of the model were generated, the loading plate moved downward to apply vertical load. The side boundary was a cylinder, and its friction coefficient was 0 to reduce the impact of the boundary on the soil. The bottom slab of the model was a rigid disk, which was fixed.  
In order to monitor the deformation and mechanical properties of aggregates and soil particles during loading, 37 measurement spheres were created. Figure 3 shows the positions of the measurement spheres in the model. The measurement spheres (No. 1 to 11) with a diameter of 88 mm were used to monitor the stress and deformation characteristics of the underlying soil and column body. The measurement spheres (No. 12 to 37) with a diameter of 40 mm were used to monitor the stress of the soil around the column and the soil of the underlying stratum.