Mechanical Properties of Limestone After High-Temperature Treatment Under Triaxial Cyclic Loading and Unloading Conditions

High temperatures can cause deterioration of the physical-mechanical properties of rocks. In this study, the triaxial cyclic loading and unloading of rock specimens under different temperature conditions were investigated to reveal stress-strain curves, strength and deformation characteristics, failure forms, and peak stress dropping of the rock specimens at high temperatures. The deformation of treated rocks has an elastic after-effect, and the stress-strain curves formed a hysteresis loop. Under increasing confining pressures and temperatures, the increase in plastic deformation exacerbated the degree of damage in the rock specimens, and the stress-strain curves gradually transformed from brittle to ductile failure, thereby reducing its severity. With the rise of sigma(3), the bearing capacity, strength and deformation of the rock specimens increased, showing an enhancement effect of the confining pressure. With the rise of T, the effect of deterioration due to temperature was apparent. The brittleness index (B-s) of the stress rock specimens was established to quantitatively express the rules of influence from sigma(3) and T on the state of post-peak stress drop. Specifically, B-s increased with the rise of sigma(3), whilst the post-peak stress drop (N-s) decreased, then increased with the rise of T. These findings provide a theoretical basis for the analysis of surrounding rock stability, restoration and reinforcement, and the shoring design of underground works following exposure to high temperature such as those occurring after a fire.