If Pressure-Sinkage is checked, contact parameters between the ground and track link shoe is changed as soil conditions. 6 parameters are used to describe soil conditions.
Figure 1 Contact parameter between soft ground and track link shoe
Pressure-sinkage (Bekker’s theory) relationship is described as the following equation proposed by Bekker:
Where, 
is pressure, 
is the smaller dimension of the
contact patch, that is, the width of a rectangular contact area, 
is sinkage, and 
, 
, and 
are pressure-sinkage parameters.
Repetitive normal load of a terrain can be considered as shown in the Figure 2 because a terrain element is subject to the repetitive loading of the wheels of a tracked vehicle. The range between unloading and reloading can be approximated by a linear function in the pressure-sinkage relationship.
where, and are the pressure and sinkage,
respectively, during unloading or reloading; 
and 
are the pressure and sinkage,
respectively, when unloading begins; and 
is the average slope of the
unloading-reloading line.
where, 
is sinkage ratio
Figure 2 Response to repetitive normal load
Shear stress-shear displacement relationship is described by an exponential function of the following form proposed by Janosi and Hanamoto:
where, 
is the shear stress,
is the shear
displacement, 
and 
are the cohesion and the
angle of internal shearing resistance of the terrain, respectively, and 
is referred to as the shear
deformation modulus.