Strength evolution of geomaterials in the octahedral plane under non-isothermal and unsaturated conditions

Current geomechanical applications imply non-isothermal processes of unsaturated geomaterials, in most cases following stress paths different than the classical triaxial compression often used in laboratory testing. Though the effects of temperature, suction and stress path direction (Lode’s angle) on the strength of geomaterials have been investigated independently, the integrated analysis combining the three effects has not been performed yet. In this paper, we formulate a thermo-plastic constitutive model for unsaturated conditions that accounts for the Lode’s angle on the strength of geomaterials. The yield surface evolves shrinking for increasing temperature, expanding for increasing suction and has its maximum strength for triaxial compression and the minimum for triaxial extension. We highlight the importance of accounting for temperature, suction and Lode’s angle on the evolution of the strength through examples that can be related to geo-energy applications. Numerical results show that not considering these effects may give rise to misleading predictions of the strength of geomaterials.