# DEM Simulation of the Load Transfer Mechanism of a GRPS Embankment with a Fixed Geogrid Technique
## 2 Establishment and Calibration of DEM Model
### Numerical Simulation Procedure for the GRPS Embankments  
Based on the calibration tests, the calibrated micromechanical parameters of each material are shown in Table 1. The servo loading mechanism was defined for the top wall to control the surcharge load in stages on the embankment surface, with each load increment being 10 kPa. Figure 4: Comparison between the numerical and experimental results for the geogrid tensile tests. Figure 3: Comparison between the numerical and experimental results for the compression loading tests. Similar to the simplified numerical method used by [PERSON] et al. [9] and [PERSON] et al. [18], to balance the calculation efficiency and the number of particles, according to the symmetry of the GRPS embankment model, half of the laboratory model was considered for the numerical model, as shown in Figure 5. A model box with a width of 420 mm and a height of 850 mm was built using the walls. The height of the pile in the numerical model was 150 mm and the width was 50 mm (the half-width of the physical model). The clear spacing between piles was 320 mm. The model building process was as follows: \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Parameter Value** \\ \hline Normal stiffness of embankment fill, \(k_{\text{n,f}}\) & \(2.25\times 10^{7}\) N/m \\ Shear stiffness of embankment fill, \(k_{\text{s,f}}\) & \(1.50\times 10^{7}\) N/m \\ Friction coefficient of embankment fill, \(\mu_{\text{f}}\) & 0.7 \\ Density of embankment fill particles, \(\rho_{\text{f}}\) & 7600 kg/m\({}^{3}\) \\ \hline Normal stiffness of subsoil, \(k_{\text{n,s}}\) & \(4.50\times 10^{6}\) N/m \\ Shear stiffness of subsoil, \(k_{\text{s,s}}\) & \(3.00\times 10^{6}\) N/m \\ Friction coefficient of subsoil, \(\mu_{\text{s}}\) & 0.3 \\ Density of subsoil, \(\rho_{\text{s}}\) & 1800 kg/m\({}^{3}\) \\ \hline Normal stiffness of geogrid, \(k_{\text{n,g}}\) & \(1.00\times 10^{8}\) N/m \\ Shear stiffness of geogrid, \(k_{\text{s,g}}\) & \(1.00\times 10^{8}\) N/m \\ Friction coefficient of geogrid, \(\mu_{\text{g}}\) & 0.5 \\ Density of geogrid, \(\rho_{\text{g}}\) & \(1000\) kg/m\({}^{3}\) \\ Parallel bond normal strength of geogrid, \(\sigma_{\text{mp-g}}\) & \(1.00\times 10^{8}\) N/m\({}^{2}\) \\ Parallel bond shear strength of geogrid, \(\sigma_{\text{sp-g}}\) & \(1.00\times 10^{8}\) N/m\({}^{2}\) \\ Parallel bond normal stiffness of geogrid, \(k_{\text{mp-g}}\) & \(9.20\times 10^{10}\) N/m\({}^{3}\) \\ Parallel bond shear stiffness of geogrid, \(k_{\text{sp-g}}\) & \(9.20\times 10^{10}\) N/m\({}^{3}\) \\ Parallel bond radius multiplier of geogrid, \(r_{\text{pb}}\) & 1.00 \\ \hline Normal stiffness of wall, \(k_{\text{n,w}}\) & \(6.00\times 10^{10}\) N/m \\ Shear stiffness of wall, \(k_{\text{s,w}}\) & \(6.00\times 10^{10}\) N/m \\ Friction coefficient of wall, \(\mu_{\text{w}}\) & 0.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Micromechanical parameters for the DEM models (Part of the data was reported by [PERSON] et al. [18]). Figure 5: DEM models of the embankment arrangements (unit: mm). (1) The model boundary and piles were simulated using walls, and then the subsoil between the piles with an initial porosity of 0.14 was generated in three layers (each layer with a thickness of 50 mm) and auxiliary walls were created to compact the subsoil. Then, the calculation was performed until the unbalanced force dissipated to a tolerable level and the auxiliary wall could be removed. (2) The geogrid was generated and different bonding properties at the ends were set. In the fixed geogrid model, both ends of the reinforcement were fixed to the top of each pile to prevent horizontal and vertical displacements. In the unfixed geogrid model, a 20 mm thick cushion of granular material was created, and then the reinforcement was placed. The horizontal displacement of the ends of the geogrid was fixed but could move freely in the vertical direction. (3) Embankment backfill with an initial porosity of 0.14 was generated and compacted in layers.