Strength evolution of geomaterials in the octahedral plane under nonisothermal and unsaturated conditions

Current geomechanical applications imply nonisothermal processes of unsaturated geomaterials, in most cases following stress paths different from the classical triaxial compression often used in laboratory testing. Although the effects of temperature, suction, and stress-path direction (Lode's angle) on the strength of geomaterials have been investigated independently, an integrated analysis combining the three effects has not yet been performed. In this paper, a thermoplastic constitutive model for unsaturated conditions that accounts for the effect of Lode's angle on the strength of geomaterials is presented. The yield surface evolves-shrinking for increasing temperature and expanding for increasing suction-and has its maximum strength for triaxial compression and its minimum for triaxial extension. Examples that can be related to geoenergy applications highlight the importance of accounting for the effects of temperature, suction, and Lode's angle on the evolution of the strength of geomaterials. Numerical results show that not considering these effects may give rise to misleading predictions of the strength of geomaterials. © 2017 American Society of Civil Engineers.V.V. acknowledges support from the ‘EPFL Fellows’ fellowship programme co-funded by Marie Curie, FP7 Grant agreement no. 291771. We would also like to acknowledge financial support from NAGRA (Swiss National Cooperative for the Disposal of Radioactive Waste).Peer reviewe