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Due to the existence of true three-dimensional high-geostress in deep underground engineering, rock shows different mechanical properties and brittle–ductile behaviours from conventional triaxial stress states, however, the different characteristics of rock are not clear. Therefore, a series of true triaxial tests were performed on deeply buried marble to investigate the effects of σ2 and σ3 on the characteristic strength (peak strength, yield strength and residual strength), post-peak deformation and brittle–ductile behaviour. Based on test results, a three-dimensional elastoplastic damage constitutive model that describes plastic hardening and damage softening of rock was established within the framework of irreversible thermodynamics, and a sensitivity analysis of key parameters ( η and ζ) was performed. A method that controls the brittle–ductile behaviour of rock through key parameters η and ζ was studied, and functions of these two parameters with σ2 and σ3 were proposed. The proposed model was implemented numerically with the cutting-plane algorithm in a finite element program. A series of numerical simulation experiments were performed, and numerical simulation and experimental results are consistent. In addition, brittle–ductile transition of marble under untested true triaxial stress levels were reasonably predicted.

After the excavation of underground engineering, the failure and instability of surrounding rock under hydro-mechanical coupling conditions is a common type of engineering disaster. However, the hydro-mechanical coupling mechanical characteristics of rock have not been fully revealed, and suitable models for the stability analysis of surrounding rock under hydro-mechanical coupling conditions are very scarce. Therefore, a series of triaxial compression and cyclic loading and unloading hydro-mechanical coupling tests were carried out to study the mechanical characteristics, deformation and mechanical parameters of rock under different confining pressures and pore pressures. Then, based on Biot’s effective stress principle, a hydro-mechanical coupling damage constitutive model within the framework of irreversible thermodynamics was proposed to describe the initial compaction effect, pre-peak hardening and post-peak softening behaviors. The functional relationships between the proposed model key parameters (η and ζ) and the effective stress were established to characterize the pre- and post-peak nonlinear behaviors of rock. A compaction function Ck for the evolution of the undamaged Young’s modulus in initial compaction stage was introduced to characterize the pre-peak compaction effect. A user-defined material subroutine (UMAT) was compiled in ABAQUS to numerically implemented the proposed model. The numerical simulation results are highly consistent with the test results, the proposed model can also predict the hydro-mechanical coupling characteristics of rock under untested stress levels. In addition, the yield function of the proposed model considers the influence of intermediate principal stress, which is also suitable for the simulation of hydro-mechanical coupling characteristics under true triaxial stress states. Graphical abstract