Effect of principal stress direction interchange on the failure characteristics of hard rock

In the process of underground engineering excavation, the adjustment of the stress field includes not only the magnitude of stress but also the direction of stress. The failure characteristics of Portuguese granite caused by interchange of the 02 and 01 directions are studied using a true triaxial testing system to investigate the effects of the interchange of principal stress directions on the failure characteristics of rock. After the interchange of the 02 and 01 directions, the bearing capacity of the rock increases, the anisotropic characteristics of deformation and fracture are interchanged, the macroscopic failure surface is deflected, and the brittleness of the rock is enhanced. When the rock failure degree increases upon the interchange of the 02 and 01 directions, the amplitude of the rock bearing capacity increases, the deformation difference decreases, and the number of deflection failure surfaces decreases. Based on the anisotropic characteristics of true three-dimensional stress-induced fractures, the reason for the change in failure mode induced by the interchange between the 02 and 01 directions is explained. By measuring acoustic emission parameters and performing scanning electron microscopy (SEM) observations, the tensile and shear fracture mechanism and fracture mode with interchange of the 02 and 01 directions are investigated. The effect of stress rotation on the rock strength and the reason for the change in the failure mode of deep hard surrounding rock excavated in underground engineering projects are discussed.