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To investigate the influence of thermal treatment on the rockburst in granite caverns, true-triaxial compression tests were conducted on pre-heated granite cubic samples containing a circular through-hole using a true-triaxial test system, and the micro camera was used to monitor and record the rockburst process in realtime. Test results show that the uniaxial compressive strength and elastic modulus first increase and then decrease as the temperature increases, which reach the maximums at 200 °C and sharply decrease at temperatures from 400 to 600 °C. The density and P-wave velocity decrease and the peak strain increases with increasing temperature. The main failure mode is X-shaped shear-tension failure at 25 and 200 °C, and single-slope shear failure at 400 and 600 °C. Thermal treatment exhibits slight effect on the rockburst incubation process in granite caverns. The stress required for rockburst decreases when the temperature increases or decreases from 200 °C. The higher the temperature, the lower the required stress. At 25 and 200 °C, rockburst is violent, and fine particles and large slabs are mainly produced; at 400 and 600 °C, the intensity of rockburst is relatively weak, and fine particles are mainly generated. Thermal treatment exhibits double effects on rockburst. The mechanism of thermal treatment on granite rockburst is the strengthening effect caused by water loss and the weakening effect caused by thermal expansion cracking. This study can provide theoretical guidance for the stability analysis and rockburst prevention of temperature-affected granite caverns.

The shear behavior of backfill-rock composites is crucial for mine safety and the management of surface subsidence. For exposing the shear failure mechanism of backfill-rock composites, we conducted shear tests on backfill-rock composites under three constant normal loads, compared with the unfilled rock. To investigate the macro- and meso-failure characteristics of the samples in the shear tests, the cracking behavior of samples was recorded by a high-speed camera and acoustic emission monitoring. In parallel with the experimental test, the numerical models of backfill-rock composites and unfilled rock were established using the discrete element method to analyze the continuous-discontinuous shearing process. Based on the damage mechanics and statistics, a novel shear constitutive model was proposed to describe mechanical behavior. The results show that backfill-rock composites had a special bimodal phenomenon of shearing load-deformation curve, i.e. the first shearing peak corresponded to rock break and the second shearing peak induced by the broken of aeolian sand-cement/fly ash paste backfill. Moreover, the shearing characteristic curves of the backfill-rock composites could be roughly divided into four stages, i.e. the shear failure of the specimens experienced: stage I: stress concentration; stage II: crack propagation; stage III: crack coalescence; stage IV: shearing friction. The numerical simulation shows that the existence of aeolian sand-cement/fly ash paste backfill inevitably altered the coalescence type and failure mode of the specimens and had a strengthening effect on the shear strength of backfill-rock composites. Based on damage mechanics and statistics, a shear constitutive model was proposed to describe the shear fracture characteristics of specimens, especially the bimodal phenomenon. Finally, the micro- and meso-mechanisms of shear failure were discussed by combining the micro-test and numerical results. The research can advance the better understanding of the shear behavior of backfill-rock composites and contribute to the safety of mining engineering.