Strain-softening model for granite and sandstone based on experimental and discrete element methods

Abstract

Combing macroscopic experimental method and mesoscopic numerical method, this study analyses the strain-softening behaviours of granite and sandstone. From the macroscopic perspective, the stress–strain curves of granite and sandstone under different confining pressures are studied by laboratory triaxial compression test. Variations of post-peak reduction modulus and critical plastic shear strain versus confining stress are obtained. Evolution of strength parameters at peak, residual and strain-softening stage are proposed. Then a method to develop the strain-softening model of hard and soft rocks is presented. From the mesoscopic perspective, based on the laboratory test results, the parameters of discrete element method PFC for the samples of the granite and sandstone are calibrated. Comparing the basically consistent results of laboratory experiment and numerical simulation, the feasibility of discrete element method is verified. Evolutions of mesoscopic crack propagation and mesoscopic particle displacement field in the complete failure process are analysed. Typical stresses of granite sample and sandstone sample in the failure stage are investigated. Above combined macroscopic experimental method and mesoscopic numerical method systematically analyse the characteristics of hard rock and soft rock in the strain-softening stage. Failure process and mechanical property of hard rock and soft rock are revealed at the macroscopic and mesoscopic levels. The initiation and propagation process of micro-cracks in rock are thoroughly investigated. The research results provide a scientific foundation for the analyse of strain-softening behaviour of hard rock and soft rock. The result shows that both the mesoscopic numerical method and macroscopic experimental method indicate that the failure pattern of sandstone is influenced by both confining pressure and axial stress, while granite is mainly affected by axial stress.