## 3 Results and Discussion
### Simulations vs. Experiments for Single Shovels
#### 3.1.3 Soil Bin Experiments for Single Shovels  
It is obvious from Table 7 and Figure 11a that the variation trend of the draught force obtained from the soil bin experiments matches well with those in simulations, and the experimental values with a range of 1.51-3.61 kN are slightly lower than the simulated values, but the relative errors are within 15%; thus, the simulated results are reasonable and acceptable accordingly. For the soil rupture distance ratio (Figure 11b), the variation trend of the experimental results obtained from the soil bin test is generally consistent with that of the simulated results. However, great errors exceeding \(\pm\)40% are seen at deep digging depth \(D\) or high cutting speed \(v\). On the one hand, it is difficult to keep the soil conditions everywhere in each experiment perfectly identical, and the soil rupture presents high randomness under these extreme operation conditions. On the other hand, those small displacements which  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Run No. **} & \multicolumn{3}{c}{**Factors**} & \multicolumn{3}{c}{**Soil Bin Measured Values**} \\ \cline{2-9}  & \(v\) & \(D\) & \(\gamma\) & \multicolumn{2}{c}{\(F_{D}\) **(kN)**} & \multicolumn{2}{c}{**DR**} & \multicolumn{2}{c}{\(f\)} \\ \cline{3-9}  & \(v\) & \(D\) & \(\gamma\) & \multicolumn{2}{c}{**DZ**} & \multicolumn{1}{c}{**YS**} & \multicolumn{1}{c}{**(\%)**} & \multicolumn{1}{c}{**YS**} & \multicolumn{1}{c}{**DZ**} \\ \hline
1 & \(-1\) & \(-1\) & 0 & 1.56 & 1.51 & 3.16 & 2.64 & 2.52 \\
2 & \(1\) & \(-1\) & 0 & 1.82 & 2.05 &  
can be easily observed in simulations are hardly measurable in practical experiments [20]. In this regard, it is necessary to improve soil preparation technics, and the soil rupture properties under more other operation conditions also deserve further evaluation. Specifically, for the combinations No. 5, No. 6, No. 9, and No. 10 of YS, there are no valid test data in soil bin experiments, and the corresponding simulated values for the draught force are higher than those of DZ. For these circumstances, they can be explained based on the report of [PERSON] et al. [46], as shown in Figure 12. For YS, there is an angle of 23.25\({}^{\circ}\) between the plane of P-a and P-c. The soil mass applies resistance onto the obverse side when \(\gamma\) is larger than 23.25\({}^{\circ}\) (e.g., combination No. 8), which ensures that YS works at a steady depth like DZ. However, when \(\gamma\) is smaller than 23.25\({}^{\circ}\) (e.g., combination No. 6), the rake angle \(\alpha\) of YS exceeds 90\({}^{\circ}\), and then a newly formed soil wedge below the reverse side of YS produces a new interface, which applies large resistance forward and upward to the reverse side of YS. In simulations, potato diging shovels are constrained to move only along forward direction, which guarantees YS a steady working depth. However, in soil bin experiments, the three-point linkage of the soil bin test vehicle is floating in some range, and thus, YS is unable to work in the set depth and even cannot stick into soil, especially at a shallow depth or high speed. Therefore, it is essential to adopt \(\gamma\) more than 23.25\({}^{\circ}\) for YS to avoid the formation of a soil wedge. Compared with DZ, it also can be concluded from Tables 4 and 7 and Figure 11 that YS increases the draught force significantly at \(\gamma=16^{\circ}\) but decreases the draught force at \(\gamma=30^{\circ}\) (especially for combination No.12 where the draught force is reduced by more than 8% in both simulations and soil bin experiments), while the draught force for \(\gamma=23^{\circ}\) is not significantly different, which means that YS is suitable to be adopted on the 4U-110 potato harvester at a deep digging depth and great mounting angle. Soil failure can be defined as the permanent deformation of the soil, and thus, plastic strain can be used to evaluate the soil failure [31].