Custom foot-ground contact interactions

[yjvyas]

I would like to apply my own custom foot-ground interaction model.
I can see how to apply forces on the Articulated system bodies making contact with the ground using setExternalForce().
What I would like to know is whether there is a stiffness parameter for the ground, that I can relax for deeper penetration (for example, mimicking a granular substance). Based on that, I would like to calculate the nonlinear dynamic forces based on my model using the getPosition(), getDepth(), and getNormal() methods and apply them.
Please let me know if there are any other methods to achieve this (for example, creating a fake ground layer on top of the ground to make contact with?).
I'm aware of the paper "Learning quadrupedal locomotion on deformable terrain", however I am not aware whether the model used to produce those research has been made publicly available in the raisim code.