When the user chooses Bekker’s theory at assembly information dialog, contact parameters between the ground and track link grouser are defined differently. RecurDyn uses seven parameters to describe soil conditions.
Figure 1 Contact parameter between soft ground and track link shoe
Pressure-sinkage relationship is described as the following equation proposed by Bekker:
where, p is pressure, b is the smaller dimension of the
contact patch, that is, the width of a rectangular contact area, z is sinkage,
and n, 
,
and 
are pressure-sinkage parameters.
Repetitive normal load of a terrain can be considered as shown in the Figure 1 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, p and z 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, j is the
shear displacement, c and 
are the cohesion and the angle
of internal shearing resistance of the terrain, respectively, and K is
referred to as the shear deformation modulus.