Numerical and Experimental Investigation on the Role of Loading Condition to Granite Post-Peak Behaviour

Understanding brittle rock failure and the associated energy conversion is vital for investigating the rockburst mechanism and controlling rockburst damage. However, the influences of loading conditions on brittle rock failure, especially regarding post-peak deformation behaviour, remain unclear due to limitations in testing methods. In addition, although rock microstructure is closely related to its failure process, the quantitative microscopic assessment is still challenging in the laboratory. This study evaluates the effects of circumferential strain incremental rate and confinement on the post-peak behaviour of granite using the circumferential strain-controlled loading method. Comprehensive laboratory experiments are integrated with numerical modelling implemented using an extended loading algorithm. Results reveal that higher circumferential strain incremental rates increase the formation of intergranular and intragranular cracks throughout the test, resulting in greater energy dissipation and a consequent reduction in excess energy. Under confined conditions, elevated confining pressures preserve more energy at peak strength for post-peak deformation by suppressing microcrack formation. At confinements up to 15 MPa, post-peak behaviour changes, with the excess energy amount largely reduced because uneven fracture induces more intragranular cracks, requiring additional energy for their formation. In contrast, at higher confinements, a localised shear failure pattern develops, reducing intragranular crack formation and allowing more excess energy to be released. This study concludes that both the energy stored in the pre-peak region and the energy dissipated in the post-peak region affect the post-peak behaviour and associated excess energy of brittle rock. From a microscopic perspective, increased microcracking is crucial for reducing excess energy, with intragranular cracks playing a critical role under confined conditions.