Here, I am doing landslide simulation with Toe erosion (region 4, black circle). At the very begining I want to do geostatic step where I would like to see that my slope is stable and then next step, erosion step, where the toe region will be failed due to either creasing the strength completely of that region or something like this. And for the other parts the strength will be depending on the plastic shear strain. I am using Mohr- Cuolomb Material model. So here I would like to vary Angle of Internal Friction and Cohesion will be varied based on the plastic strain. The plastic shear strain will come from the toe erosion. I can write a vusdfld subroutine where it calculates the plastic shear strain and I can define as a field variable say,1. 

Now, can anybody tell me how can I initiate the failure of the toe and how to do others? Here is the geometry for your better understanding.  I am not so pro user. I just started my journey in abaqus few days back.