Cross-Scale Characteristics of Damage Evolution in Granite under High-Confining Pressure Cyclic Loading

Abstract

The rock properties under periodic load are important to the stability of engineering works. It needs to analyze the mechanical properties and damage of deeply buried rock under periodic load. Taking granite in a mine as the research object, designed the experiment involving different cycles under different confining pressures and constant periodic upper and lower limit loads, carried out corresponding high-confining pressure cyclic loading experiment. The results show that a closed stress hysteresis loop is formed during loading and unloading cycles under different confining pressures. The hysteresis loop area of axial deformation decreases gradually with an increase of cycles. With the confining pressure increasing, the deformation modulus decreases gradually. However, under the same confining pressure, the deformation modulus remains almost unchanged as the number of loading–unloading cycles increase. As the number of cycles increase, the residual displacement shows an increasing trend whereas the axial and circumferential strains decrease. This can be explained by primary cracks gradually becoming compacted with the increase of cycles so that the proportion of axial elastic strain increases, the proportion of circumferential elastic strain increases. Fractal analysis of the T2 spectrum shows that the sample has fractal characteristics before and after cyclic loading.