# Calibration of Model Parameters for Soda Saline Soil-Subsoiling Component Interaction Based on DEM
## 3 Results and Discussion
### Discussion  
In this study, the contact parameters between soda saline-alkali and soil-subsoiling components in Northeast China were calibrated. Based on the DEM, the JKR model and HMB model were used as contact models, and the accuracy of the calibrated contact parameter combination was verified by the AoR test and DS test. Through the PB test results (Table A1), it can be found that both the soil intrinsic parameters and the contact parameters will affect the AoR. The contact parameters between the soils (soil-soil rolling friction coefficient, soil-soil static friction coefficient, and JKR surface energy of the soil) have a more significant effect on the AoR, and the JKR surface energy of the soil has a greater effect than the static friction coefficient and the rolling friction coefficient; the results are similar to those of [PERSON] et al. (2019). After that, the SA test and BB test were conducted on the parameters with significant influence, and the BB tests were analyzed by ANOVO (Table A2). The results showed a model \(p\)-value < 0.001; a coefficient of determination of R\({}^{2}\) = 0.9661; a coefficient of determination adjusted of R\({}^{2}\) = 0.9225, close to 1; and a coefficient of variation of C.V. = 1.02%, thus indicating a significant relationship between the response values and the parameters. Through the ANOVO analysis, it can be seen that the interaction of two significant parameters will also have a significant impact on the angle of repose. The interaction term containing soil JKR surface energy is more significant than other interaction terms. The results of this study are similar to those of [PERSON], [PERSON], et al. (2016, 2018). We speculate that because the soil moisture content cannot be characterized when the EDEM software (EDEM version: EDEM 2018, DEM Solutions, Edinburgh, UK, 2002) is used to simulate the soil particles, when the JKR model is used as the simulation contact model, the soil moisture content can only be simulated by \begin{table}
\begin{tabular}{c c} \hline \hline
**Simulation Test Parameters** & **Value** \\ \hline Density & 2650 kg/m\({}^{3}\) \\ Poisson’s ratio & 0.4 \\ shear modulus & \(3\times 10^{7}\) Pa \\ Soil–soil restitution coefficient & 0.2 \\ Soil–soil static friction coefficient & 0.734 \\ Soil–soil rolling friction coefficient & 0.151 \\ Soil–65 Mn steel restitution coefficient & 0.2 \\ Soil–65 Mn steel static friction coefficient & 0.6 \\ Soil–65 Mn steel rolling friction coefficient & 0.2 \\ JKR surface energy & \(0.33\) J/m\({}^{2}\) \\ Normal stiffness per unit area & \(1\times 10^{5}\) N/m\({}^{3}\) \\ Shear stiffness per unit area & \(1\times 10^{5}\) N/m\({}^{3}\) \\ Critical normal stress & \(8\times 10^{3}\) Pa \\ Critical shear stress & \(8\times 10^{3}\) Pa \\ Bonded disk radius & 5 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Soil simulation parameters table. Figure 19: Comparison of static AoR between simulation test and physical test after correction. changing the surface energy of the JKR, which also indicates that the soil water content has a large effect on its AoR and friction coefficient. When using EDEM to calibrate soil contact parameters, most scholars use the angle of reprose as the response value and use a single contact model as the contact model [6; 14; 17; 21; 23]. However, during the subsoiling process, the soil is sheared by the subsoiling components. Taking this into account, we conducted direct shear tests to verify the calibrated contact parameters. The results show that there is a certain error between the simulation results of the direct shear test and the physical test results when only using the JKR model as the contact parameter obtained by the contact model (Figure 16). This discrepancy can be attributed to the fact that the AoR test and DS test characterize the soil's flow and shear characteristics, respectively. A single model cannot precisely simulate both aspects of soil behavior.