## 4 Summary and Conclusions  
1. The particle parameters of southern orchard soil were experimentally measured, and modeling was conducted using the EDEM2021 discrete element software. The Hertz-Mindlin with the Johnson-Kendall-Roberts contact model was employed. Utilizing the Plackett-Burman Design, significant contact parameters and model parameters influencing the soil pile angle were selected. These parameters include soil JKR surface energy, soil-soil restitution coefficient, and soil-steel static friction coefficient. 2. The optimal value ranges for significant parameters were determined through steepest ascent experiments. Subsequently, a regression model for the soil pile angle and signif \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **n/(r\(\cdot\)min\({}^{-1}\))** & **v/(m/s)** & **M/(N\(\cdot\)m)** \\ \hline  
\hline \hline \end{tabular}
\end{table} 
Table 11: Experimental design and results. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source of** & **Mean Sum of** & **Degree of** & & & \\
**Variance** & **Squares** & **Freedom** & & & \\ \hline Model & 7405.73 & 11 & 673.25 & 361.57 & \textless{}0.0001 \\ n & 5894.95 & 3 & 1964.98 & 1055.31 & \textless{}0.0001 \\ v & 701.73 & 2 & 350.86 & 188.43 & \textless{}0.0001 \\ n v & 313.96 & 6 & 52.33 & 28.10 & 0.0011 \\ Pure Error & 9.31 & 5 & 1.86 & & \\ Cor Total & 7415.04 & 16 & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Analysis of variance. icant parameters was established and optimized using the Box-Behnken Design. The optimal values for the parameters were found to be 5.85 J\(\cdot\)m\({}^{-2}\) for the soil JKR surface energy, 0.65 for the soil-soil restitution coefficient, and 0.5 for the soil-steel static friction coefficient. Simulation experiments were conducted under these calibrated parameters, and the relative error between simulated and measured pile angles was determined to be 0.01%. 3. Torque comparative experiments for spiral earth auger were conducted in a soil trench, and the results indicate that the trends in simulated and experimental values align. The torque increased with higher rotational speeds, with a maximum relative error of 7%. The torque initially rose from 0 to a maximum value, then gradually decreased to a lower value, followed by a rapid increase to a higher value before declining again, repeating this pattern. The average total force at a feed rate of 0.05 m/s was found to be a minimum of 200 N. The simulation model effectively captures the variation patterns in drilling power consumption and accurately represents torque values, demonstrating a certain level of reliability. 4. Among the three forces, vertical resistance is the primary factor contributing to power consumption. As the rotational speed increased, the maximum value of vertical resistance was found to continue to rise, while horizontal and lateral resistances exhibited a declining trend. With an increase in feed rate, the maximum values of resistance in all three directions also increased. When the feed rate exceeded 0.05 m/s, there was a sharp increase in the maximum lateral resistance. 5. By analyzing the three-dimensional forces acting on the spiral blades and conducting a comparative analysis at different rotational speeds and feed rates, along with the results from optimal variance analysis experiments, the optimal rotational speed and feed rate were determined to be 100 r\(\cdot\)min\({}^{-1}\) and 0.05 m/s, respectively. According to the formula, the optimal power consumption is 0.314 kW. This study demonstrates the accuracy of the Discrete Element Method in analyzing the three-dimensional working resistance of helical cutting tools. The relevant experimental data can serve as a reference for the analysis of equipment energy consumption, machine vibration, and blade wear studies. However, soil is a complex composite with many influencing factors, and accurately describing the contact state of soil particles remains challenging.