How should one-dimensional laboratory equations be cast into three-dimensional form?

An ever-present key question for rock mechanics analysts is: “How can one-dimensional laboratory equations be generalized such that they are valid for arbitrary, three-dimensional stress states?” Classical thermodynamics principles are used in this paper to derive a proper three-dimensional generalization consistent with laboratory stress and strain measures. The multiaxial form of the equation permits the natural separation of shear and volumetric material behavior without the assumption of a unique flow potential. Results of an underground room simulation show the importance of different generalizations which emphasizes the need for testing where the principal stresses are unique.