Abstract: Stress-type brittle failure of hard rock poses a serious threat to the surrounding rock mass stability of underground structures under high geo-stress. In order to study the deformation and failure characteristics of deeply-buried granite under the condition of high confining pressure cyclic loading and unloading, MTS815 is used to perform conventional triaxial and cyclic loading and unloading tests on the granite from an underground powerhouse under confining pressures of 10, 30, 40, 50 MPa. The corresponding stress-strain curves and deformation and failure characteristics are obtained. The following observations are made from the results: 1) Under the two stress paths, granite specimens under various confining pressures show obvious brittle failure characteristics. 2) Under the two stress paths, the peak strength and crack damage stress of the specimens increase linearly with the confining pressure; elastic modulus and cracking initiation stress increase first and then decrease with confining pressure. Poisson's ratio increases first and then remains unchanged or decreases with confining pressure. 3) Under the same confining pressure, the peak strength, crack initiation stress, crack damage stress and the Poisson's ratio of the specimen in cyclic loading and unloading tests are generally larger than those in conventional triaxial tests, while the unloading elastic modulus is smaller than that in conventional triaxial tests. 4) Under the two stress paths, the macroscopic failure of the specimens is primary shear failure. The deformation and failure rules of granite specimens revealed have significant reference for the selection of rock mass mechanical model, the evolution rules of mechanical parameters with damage variables, and the formulation of support countermeasures for the surrounding rock mass stability of deeply-buried underground structures.

Key words: deeply-buried hard rock, triaxial cyclic loading and unloading, unloading elastic modulus, cracking initiation stress