Greetings Maria Fernanda,

To learn about the M-C soil model, I suggest starting with the simplest soil model possible. Forget the rubber and the tubes. Make a container that has five surfaces (not solids) and make a solid block to fill it, but make the soil thickness less than the height of the container so that the container walls are above the top of the soil. The bottom of the container can be fixed and the only load is gravity.

Use frictional contact between the soil and the container. See if you can get this simple model to converge. When you do, you will know what is needed to have a working soil model.