Mohr-Coulomb Failure Criterion

The Mohr-Coulomb Failure Criterion calculator computes the shear strength based on the normal stress, slope of the failure envelope computed from the angle of internal friction and the intercept of the failure envelope.

INSTRUCTIONS: Choose units and enter the following;

• (σ) This is the normal stress
• (Φ) This is the angle of internal friction.
• (c) This is the intercept of the failure envelope (cohesion)

Failure Criterion(τ): The shear strength is returned in Newtons per square centimeter (N/cm²).  However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

The Mohr-Coulomb Failure Criterion represents the linear envelope that is obtained from a plot of the shear strength of a material versus the applied normal stress.  The formula for the shear strength is:

        τ = σ•tan(Φ) + c

where:

• τ = shear strength
• σ = normal stress
• Φ = angle of internal friction, where tan(Φ) is the slope of the failure envelope
• c = intercept of the failure envelope (cohesion)

References

Wikipedia (https://en.wikipedia.org/wiki/Mohr%E2%80%93Coulomb_theory#Mohr.E2.80.93Coulomb_failure_criterion)