Model Behavior
The modified Mohr-Coulomb model is characterized by linear-elastic, ideal-plastic behavior. The corresponding stress-strain relation is shown in the figure below.
A. Reversible, elastic stress states
The model shows elastic behavior within an allowable stress zone enclosed by a boundary condition. Within this area, the yield surface, there is an isotropic linear-elastic stress-strain relation according to Hooke's law.
B. Stiffness
The proportional relation of the linear-elastic behavior is described by the constant modulus of elasticity.
C. Irreversible, plastic stress states
If the stress fulfills the limit condition and is on the yield surface, the behavior is changed to plastic, which is defined by the yield rule. The yield criterion according to Mohr-Coulomb is described by the following linear relation.
The resulting yield surface is illustrated in the following graphic in the 3D principal stress space.
Stress Failure Hypothesis
The Mohr-Coulomb failure criterion assumes that the material fails when the internal shear resistance is less than the shear stresses resulting from the external loads.
Input Parameters
Es werden die folgenden fünf Eingabeparameter zur Definition des Materials mit dem modifizierten Mohr-Coulomb Modell benötigt.
- Modulus of Elasticity E
- Poisson's ratio ν
- cohesion c
- Friction angle φ
- Dilatation angle ψ
Suitability
The Mohr-Coulomb model can be seen as a rough approximation of the actual soil behavior, since linear-elastic behavior is assumed and the modulus of elasticity is assumed to be constant.
This allows for a comparatively low effort for the definition of the material properties. The model is partially suitable for the deformation analysis. It is recommended to approximate the stiffness that increases with the depth in a soil by modeling several partial layers with the respective constant stiffness that is, however, increased with the depth in some layers.
With the failure criterion according to Mohr-Coulomb, the material model is, in principle, suitable for stability calculations.