Model Behavior
The modified Mohr-Coulomb model is characterized by linear-elastic, ideal-plastic behavior. A corresponding stress-strain relation is illustrated in the following image.
A. Reversible, Elastic Stress States
The model shows elastic behavior within a range of allowable stresses enclosed by a boundary condition. Within this range, the yield area, there is an isotropic linear-elastic stress-strain relation according to Hooke's law.
B. Stiffness
The proportional relation of linear elastic behavior is described by the constant modulus of elasticity.
C. Irreversible, Plastic Stress States
If the stress fulfills the boundary condition and is located on the yield surface, the behavior transitions to a plastic state, which is defined by the yield law. The Mohr-Coulomb yield criterion is described by the following linear relation.
The resulting yield surface is shown in the 3D principal stress space in the following graphic.
Stress Failure Hypothesis
The Mohr-Coulomb failure criterion assumes that the material fails when the internal shear resistance is lower than the shear stresses resulting from external loads.
Input Parameters
The following five input parameters are required to define the material with the modified Mohr-Coulomb model.
- Modulus of elasticity E
- Poisson's ratio ν
- Cohesion c
- Friction angle φ
- Dilatation angle ψ
Suitability
The Mohr-Coulomb model can be regarded as a rough approximation of actual soil behavior, as it assumes linear elastic behavior and a constant modulus of elasticity.
This allows for a comparatively low effort in defining the material properties. The model is conditionally suitable for deformation analysis. It is recommended to approximate the increasing stiffness of a soil with depth by modeling several sublayers, each with constant stiffness but increasing with depth.
With the Mohr-Coulomb failure criterion, the material model is principally suitable for stability analysis.