**3. Results and Discussion**

*3.1. Calibration of the DEM Parameters of Peat*

3.1.1. Plackett–Burman (PB) Test

The protocol and results of the PB test and the significant results of each parameter are listed in Tables 2 and 3, respectively. The total contribution of B, D, and J was 83%, and they all significantly affected the stacking angle and followed the order: J > B > D. As shown in the Pareto chart (Figure 3), the contribution values of those three parameters were all exceeded the Bonferroni limit, which also indicated that the parameters were significant for the response. The contribution value lower than the t-value limit usually meant there was no effect for the response [19]. The contribution value of E between the Bonferroni limit and t-value limit was considered E and also had some effect on the response. Additionally, the information provided by Pareto chart showed that J and B had a positive effect on the response, while D and E had negative effects. Therefore, those four parameters were identified as the key parameters for the substrate to be calibrated in the steepest climbing test and BBD test below.


**Table 2.** The protocol and results of PB test.

**Table 3.** Significance analysis of parameters in PB test.


Note: \* and \*\* represent the significance at the 0.05 and 0.01 probability level, respectively.

**Figure 3.** Pareto chart of parameters on response.
