## 5 Results and Discussion
### Maximum Soil Thrust According to the Shape of the Grouser  
The shape ratio has a significant impact on the tractive performance of an off-road tracked vehicle [1,26]. In this study, the total soil thrust of continuous track on which the grousers with different shape ratio (1.5, 2.0, 2.5, 3.0, 4.0, 5.0, and 7.5) were attached was calculated to evaluate the effect of the grouser shape ratio on the total soil thrust. For quantitative analysis, the maximum soil thrust of the continuous track with grousers was normalized with the maximum soil thrust of the continuous track without grousers (i.e., the peak values of the soil thrust and slip displacement curves). Since the existing method did not consider the difference in soil thrust according to the grouser shape ratio, only the proposed method was used for the analysis. Also, the trend of the normalized maximum soil thrust and shape ratio was not affected by the shear strength parameters and shear deformation constants of soil. Therefore, the results of using the peak values of Figure 7, Figure 9, and Figure 11 are representatively presented.  
The normalized maximum soil thrusts according to the grouser shape ratio are shown in Figures 12 and 13. The soil thrust of the continuous track with grousers was always greater than that without grousers (approximately 1.44-1.71 times). Under the same conditions, the highest normalized maximum soil thrust (i.e., the rate of increase of soil thrust owing to grouser) was observed in the soil with hardening behavior and the smallest was observed in the soil with softening behavior. In general, hardening and softening behaviors occur mainly in loose and dense soils, respectively [25]. Hence, it was predicted that the increase in soil thrust realized by grousers would be more pronounced in loose soil.  
As mentioned above, in all three soil types, the total soil thrust increased as the shape ratio decreased under the same height. This is because the sizes of the soil blocks formed between the grousers decreased as the grouser spacing decreased; hence, even at a low slip ratio (that is, even if only a small slip displacement occurs), a large soil thrust is developed  
Figure 12: Normalized maximum soil thrust and shape ratio relationships of EC145E: (**a**) hardening behavior, (**b**) softening behavior and (**c**) hump behavior.  
Figure 13: Normalized maximum soil thrust and shape ratio relationships of EC380E: (**a**) hardening behavior, (**b**) softening behavior and (**c**) hump behavior.  
in each soil block. Also, the longer the grouser height, the greater the side thrust, which increases the total soil thrust. However, when the grouser shape ratio was 7.5, the increase in the total soil thrust with a longer grouser was smaller. This is because the grouser spacing increases when both shape ratio and height of the grouser increase. Consequently, the two opposing effects (an increase in soil thrust due to an increase in grouser height and a decrease in soil thrust due to an increase in grouser spacing) are offset.  
Additionally, the shape ratios of commonly used commercial grousers (approximately 2.3-3.9) are shown in Figures 12 and 13. For commercial grousers, as the grouser height increases and the shape ratio decreases (that is, the grouser spacing decreases), the total soil thrust of the off-road tracked vehicle significantly increases.