Mechanical properties of Beishan granite under complex dynamic loads after thermal treatment

A systemic understanding of the thermal effects on the dynamic behaviour of granite is significant to geological engineering safe applications such as nuclear waste disposal engineering. The experimental granite was taken from Beishan area of Gansu province, China, a preferable region for high-level radioactive waste repository. In order to carry out in-depth research, elevated temperature, confining pressure and impact velocity on the strength of Beishan granite were studied. The results show that above 600 degrees degrees C, the granite specimens produce a large number of obvious fine cracks, some of which have large cracks, volume expansion and density decrease, and their thermal conductivity decreases rapidly. The minerals change due to heat, resulting in an increase in initial damage, which determines the degree of macroscopic impact compression fracturing, which increases with the temperature under the same impact velocity of uniaxial impact. In triaxial impact compression, the circumferential confining pressure has a strong restraining effect on the radial deformation of the specimen, which effectively improves the mechanical strength of the specimen. Below 600 degrees degrees C, the peak stress change of granite specimens is relatively small, and the confining effect and impact velocity strengthening effect of confining pressure is stronger than thermal damage effect. Above 600 degrees C, the peak stress decreases significantly, and the thermal damage effect is stronger than the confining pressure strengthening effect.