An Elasto-Damage Constitutive Model with Nonlinear Failure Criterion for Quasi-Brittle Intact Rocks

Intact rocks exhibit complex stress–strain behaviour that is controlled by its intrinsic characteristics such as mineralogical composition, damage evolution and the level of brittleness as well as the external factors including loading conditions. Conventional constitutive models often fail to predict such complex responses due to their lack of integration of intrinsic and external factors or shortcomings to capture the transition from brittle to ductile response and strength degradation. This paper introduces a novel elasto-damage constitutive framework for capturing the damage behaviour of quasi-brittle intact rocks across a range of loading conditions. The proposed model employs a nonlinear failure criterion and integrates it with a bounding surface framework and damage evolution, introducing a novel inelastic damage hardening concept, where the evolution of damage bounding surface is governed by a coupled influence of inelastic volumetric strain and inelastic shear strain, allowing a more accurate representation of stiffness degradation and strength reduction. Additionally, the radial mapping rule is employed to capture the interplay between shear and volumetric strains, improving predictions under various loading conditions. The model is validated against the laboratory data obtained from Vosges and Darley Dale sandstones under a range of confining pressures, exhibiting an acceptable agreement between the model predictions and the experimental results. The analyses also highlight the model's precision in simulating the complex nonlinear mechanical characteristics of quasi-brittle intact rocks applicable to rock engineering projects within civil, mining and geo-energy disciplines.