## 3 Soil Parameter Discrete Element Calibration
### Discrete Element Parameter Calibration and Result Analysis
#### 3.3.2 Plackett-Burman Test  
The Plackett-Burman experimental design was used to analyze the significance of the simulation parameters with the rest angle as the response value and to screen the most significant factors. Through the preliminary experimental investigation, a total of seven discrete meta-parameters were determined for screening, which are denoted by \(x_{1}\)-\(x_{7}\). The range of values was determined by referring to previous studies [19; 20; 24] and in combination with physical tests, as shown in Table 5. The Plackett-Burman test design and results are shown in Table 6; a total of 15 sets of tests were required. To ensure the accuracy of the test and verify the test error, three sets of central level tests were added. The PB test results were analyzed, and the results are shown in Table 7. The order of significant factors is: JKR water content model coefficient \(X_{7}>\) soil-soil rolling friction coefficient \(X_{6}>\) soil-soil recovery coefficient \(X_{4}\), with influence rates of 42.87, 36.36, and 14.40%, respectively, and the rest of the factors are not significant. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multicolumn{5}{c}{**Factors**} & \multicolumn{5}{c}{**Rest Angle**} \\ \cline{2-7}  & \(X_{1}\) & \(X_{2}\) & \(X_{3}\) & \(X_{4}\) & \(X_{5}\) & \(X_{6}\) & \(X_{7}\) & (\({}^{\circ}\)) \\ \hline
1 & \(1\) & \(-1\) & \(1\) & \(-1\) & \(-1\) & \(1\) & 40.07 \\
2 & \(1\) & \(-1\) & \(1\) & \(1\) & \(-1\) & \(1\) & \(-1\) & 18.63 \\
3 & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & 32.47 \\
4 & \(-1\) & \(1\) & \(1\) & \(1\) & \(-1\) & \(1\) & \(1\) & 46.20 \\
5 & \(-1\) & \(1\) & \(1\) & \(-1\) & \(1\) & \(-1\) & \(14.00\) \\
6 & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & 36.37 \\
7 & \(1\) & \(1\) & \(1\) & \(-1\) & \(1\) & \(1\) & \(-1\) & 32.96 \\
8 & \(-1\) & \(-1\) & \(-1\) & \(1\) & \(1\) & \(1\) & \(-1\) & 25.97 \\
9 & \(-1\) & \(-1\) & \(1\) & \(1\) & \(1\) & \(-1\) & 1 & 22.16 \\
10 & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & \(0\) & 41.97 \\
11 & \(-1\) & \(-1\) & \(-1\) & \(1\) & \(1\) & \(1\) & 64.70 \\
12 & \(1\) & \(1\) & \(-1\) & \(1\) & \(-1\) & \(-1\) & \(-1\) & 4.69 \\
13 & \(-1\) & \(1\) & \(-1\) & \(-1\) & \(-1\) & \(1\) & 1 & 72.16 \\
14 & \(1\) & \(1\) & \(-1\) & \(1\) & \(1\) & \(-1\) & 1 & 21.72 \\
15 & \(-1\) & \(-1\) & \(-1\) & \(-1\) & \(-1\) & \(-1\) & 9.15 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Plackett–Burman experimental design and results. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{1}{c}{**Parameter**} & **Code** & **Low Level(\(-\)1)** & **High Level (+1)** & **Level Selection Source** \\ \hline Soil–65 Mn steel recovery factor & \(x_{1}\) & \(0.2\) & \(0.5\) & \([19]\) \\ Soil–65 Mn steel static friction coefficient & \(x_{2}\) & \(0.5\) & \(1.2\) & \([19]\) \\ Soil–65 Mn steel rolling friction coefficient & \(x_{3}\) & \(0.05\) & \(0.4\) & \([19]\) \\ Soil–soil recovery factor & \(x_{4}\) & \(0.15\) & \(0.75\) & \([20]\) \\ Soil–soil static friction coefficient & \(x_{5}\) & \(0.6\) & \(1.0\) & Friction coefficient determination \\ Soil–soil rolling friction coefficient & \(x_{6}\) & \(0.1\) & \(0.4\) & Friction coefficient determination \\ JKR water content model coefficient & \(x_{7}\) & \(0\) & \(0.75\) & \([24]\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Plackett–Burman test factor codes. Combined with the test principle, the analysis showed that in the process of rest angle determination, the soil only had contact with 65 Mn steel before the ring knife was spread; the rest of the time there was only collision and friction between soil and soil, and the rest angle after the soil overflow was more accurate, so the contact parameter between 65 Mn steel and soil was not the decisive parameter affecting the rest angle.