Cyclic disturbances during the excavation of underground powerhouses in large hydropower stations can damage the surrounding rock mass

compromising its mechanical properties. To reveal the failure characteristics and damage process of deep-buried granite in the Yebatan underground powerhouse after cyclic disturbance

this study conducted pre-peak constant amplitude cyclic disturbance tests on granite samples with a confining pressure of 30 MPa. The tests used cyclic stresses of 12.5%–17.5% (low stress)

10.0%–37.5% (medium stress)

and 62.5%–72.5% (high stress) of their peak strengths. Subsequently

three types of graded unloading confining pressure tests were conducted

followed by an analysis of the evolution of characteristic parameters and the construction of damage variables for deep-buried granite under pre-peak cyclic disturbances. Under different graded unloading confining pressure paths

the deformation of rock specimens is primarily concentrated during the reduction of confining pressure in the final three stages

and their macroscopic failure mode is compression-shear failure. The elastic modulus shows a downward trend

while the Poisson’s ratio exhibits an upward trend; the maximum dilatancy angle remains largely consistent. After constant amplitude cyclic disturbance under high axial pressure

the rock specimen shows the highest cumulative strain energy in the graded unloading confining pressure test

indicating an increased tendency towards brittle failure. Furthermore

the strain energy of rock specimens under graded unloading confining pressure exceeds that under conventional triaxial compression. This serves as a threshold to identify if rock specimens under graded unloading confining pressure transition into the accelerated damage rupture stage. Using the lateral strain response method and crack volumetric strain method

the closure stress

crack initiation stress

and damage stress of deep-buried granite are found to be 17.9%

42.7%

and 73.8% of the peak strength

respectively. Based on these insights

a damage variable derived from crack volumetric strain is formulated

allowing the delineation of four distinct stages in the damage process of deep hard rock. The research results provide experimental and theoretical support for analyzing the failure process of high-stress granite.