Investigations of the Progressive Damage and Failure Behaviors of Thermally Treated Granite Under the Coupling Action of Biaxial Stress Constraint and High Strain Rate

The elevated temperature, high geostress environment, and strong dynamic loading are important factors that induce disasters in deep rock engineering work. The progressive damage and failure behaviors of granite under the coupling of elevated temperature, biaxial stress constraint, and high strain rate were studied by true triaxial split Hopkinson pressure bar (SHPB) tests. The results show that the P-wave velocity attenuation rate k(p) increases exponentially with temperature, and k(p) is closely related to the thermal damage of granite grain structures. Under the biaxial stress constraint, the dynamic strength and elastic modulus of granite both increase at first, then decrease with the increase of temperature and a thermal enhancement effect is observed at 150 degrees C. The threshold temperature for the transition of dynamic failure from brittleness to plasticity is 500 degrees C. The dynamic strength generated by axial compression and lateral expansion increases exponentially with the strain rate. The lateral stress sigma(2) enhances the dynamic strength of granite. Under true triaxial stress condition (sigma(1) > sigma(2) > sigma(3) not equal 0), the enhancement of the dynamic strength is further improved, and the lateral expansion of samples develops along the direction of the minimum principal stress. Under the same stress constraint, the number of impacts that can be borne by granite samples is linearly negatively correlated with heat treatment temperature. The samples are compacted apparently in the early stage of cyclic loading, and the maximum strain experiences three stages: a decrease, slow increase, and sharp increase. When the heat treatment temperature is 700 degrees C and above, the slow increase stage no longer occurs. Highlights 1. The progressive damage behaviors of thermally treated granite shows nonlinear growth under biaxial stress constraint and repeated impacts coupling. 2. The dynamic strength of granite under biaxial stress constraint has both the strengthening effect of strain rate and the hardening and weakening effects of temperature. 3. The lateral stress increases the dynamic strength of granite, and the lateral expansion develops along the direction of the minimum principal stress.