Linear failure criteria with three principal stresses

Any failure criterion can be represented as a surface in principal stress space σ1, σ2, σ3 (with no order implied), and the shape of the surface depends on the functional form of the criterion. For isotropic rock that exhibits a pressure dependence on strength, the simplest failure criterion is a linear function, and the failure surface is a hexagonal pyramid with a common vertex Vo on the tension side of the hydrostatic axis, where...