Mohr-Coulomb
The Mohr-Coulomb strength model: cohesion and friction angle.
Mohr-Coulomb is the default strength model. It describes the available shear strength along the slip surface as a linear function of effective normal stress.
Strength relation
The shear strength on the base of a slice is:
tau = c' + sigma'_n * tan(phi')where sigma'_n is the effective normal stress on the slice base (total normal
stress minus pore pressure), c' is the effective cohesion, and phi' is the
effective friction angle.
Parameters
| Parameter | Unit | Default | Description |
|---|---|---|---|
| Cohesion (c') | kPa | 1 | Effective cohesion intercept. |
| Phi (phi') | degrees | 35 | Effective angle of internal friction. |
Both parameters are edited on the LEM tab of the Define Material Properties modal once Mohr-Coulomb is selected as the failure criterion.
Optional tensile strength
A Use Tensile Strength checkbox enables a tensile-strength cutoff (in kPa, default 0). When enabled, the cutoff limits the negative normal stress the material can sustain before strength is reduced.
When to use
Use Mohr-Coulomb for the great majority of soils, where a linear effective-stress failure envelope is appropriate. For rock masses, a curved envelope, or direction-dependent strength, use one of the other criteria. The other models ultimately resolve to an equivalent Mohr-Coulomb cohesion and friction angle at each slice's normal stress, so Mohr-Coulomb is the common basis for all four.