Thermodynamically consistent modelling of viscoplasticity and damage coupling in saturated rocks

Viscoplastic damage behaviour of rocks has to be considered for the design of geostorage facilities such as oil and gas reservoirs or radioactive waste disposals. In underground structures, rocks might be saturated by groundwater, which would influence their time-dependent behaviour. This paper aims at developing a theoretical framework for modelling the time-dependent behaviour of saturated rocks. Viscoplasticity and isotropic damage are taken into consideration in the poromechanical framework by means of an effective stress. This framework represents a good compromise between different requirements in constitutive modelling: capability to reproduce the main features of the time-dependent behaviour of rocks, simplicity for practical applications and thermodynamic consistency. The applicability of this framework is illustrated by formulating a specific constitutive model. This model is then validated against experimental results obtained from a series of laboratory multi-step creep tests.