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.