Combined Effect of Joint Contact Area and Temperature on Stress Wave Propagation in Granite Rock Mass

To explore the effect of the joint contact area and temperature on the dynamic property of rock joints and wave propagation in granite rockmass, an impact test of a jointed granite specimen was conducted with a split-Hopkinson pressure bar. The jointed specimen was composed of an artificially grooved specimen and an intact specimen. The ratio of the joint contact area to the cross-sectional area of the intact specimen was defined as the joint matching coefficient (JMC). The specimens were heat-treated at temperatures of 25 degrees C, 200 degrees C, 400 degrees C, and 600 degrees C. The experimental results showed that with the decrease in the JMC, the nonlinear characteristic of the stress-strain curve for the initial loading segment was more evident for the heat-treated specimen at a constant temperature. Furthermore, the transmitted coefficient, secant modulus, and joint-specific stiffness gradually decreased. For a given JMC, the expansion of the mineral component in the specimen heat-treated at 200 degrees C caused the internal cracks to close, resulting in a larger transmitted coefficient and joint-specific stiffness. For the specimens heat-treated at 400 degrees C and 600 degrees C, the transmitted coefficient and joint-specific stiffness gradually decreased owing to thermal damage. In addition, the deformation of the jointed specimen at different temperatures was mainly caused by joint closure. A smaller JMC or more serious thermal damage led to an increase in the peak value of the joint closure.