Mohr–Coulomb Failure Criterion

A linear shear-failure criterion for cohesive-frictional materials stating that shear stress on a potential failure plane τ_f equals cohesion c plus the product of normal stress (often effective normal stress σ') and the tangent of the internal friction angle φ: τ_f = c + σ' tan φ.

An empirical engineering failure criterion for soils and rocks that represents shear strength as a linear envelope: shear stress at failure τf = c + σ'·tan(φ), where c is cohesion, φ is the internal friction angle, and σ' is the effective normal stress; failure is predicted when the stress state reaches this envelope under the assumed stress path and drainage conditions.