THE EFFECTS OF THE OFF-ROAD VEHICLE ON THE SOIL COHESION AND INTERNAL FRICTION

The movement of the off-road vehicle on a deformable track such as soil and grass modifies the soft soil profile and mechanical properties - cohesion and internal friction - of the soil. It is assumed there is a dynamic physical change in the tire-soil interface, the cohesion and internal friction soil properties being also not constant. In our paper we summarize the most important methods which can be applied to compute the towed force in tire-soil interface situations. We have carried out many in situ soil shearing tests with different soil moisture contents and in different soil depressions. We conducted the soil shearing test before and after the vehicle movement, which means there are different soil compactions. Based on our soil shearing tests we can say that the soil cohesion increase depends on the soil depth. The value of the increase depends on the soil compaction and the soil depth. The soil internal friction hardly decreases and its changing value is less than that of soil cohesion. The soil cohesion and shearing values decrease as a function of soil moisture content. The higher values of both soil cohesion and soil shearing are characteristics of compacted soil. The results of our tests were as follows: soil cohesion and soil shearing values are not constant with different types of soil. Both of them change as a function of the soil moisture content and soil depth. The equation for the towed force which occurs during the tire-soil interface is more precise if the soil cohesion would be a function of the soil moisture content and the soil depth in the equation. Soils are multifarious, hence our results are accurate for the above soil conditions and test methods.