Effect of disturbance on the progressive failure process of Eastern Himalayan Gneiss

Abstract

Disturbance induced by stress relief has a significant effect on the laboratory properties of rocks in high in situ stress regions. A better understanding of its mechanism can help evaluate rock properties in regions such as the Tibetan Plateau. In this study, the progressive failure process of gneiss with high disturbance in the eastern Himalayas was explored using triaxial tests, acoustic emission minoring, X-ray computerised tomography (CT), and three-dimensional reconstruction. We established a grading standard to evaluate the impact of disturbances on the mechanical properties of Eastern Himalayas gneiss. With an increase in the degree of disturbance, the compressive strength c and φ decreased. The disturbance exerted a greater influence on the frictional strength than cohesion. In addition, the frictional strength cannot be fully mobilised in gneiss with a high disturbance, which is supported by the unchanged normalised crack initiation stress and the reduction of shear cracks. The internal fracture network reconstructed by CT scanning indicates that the fracture modes of gneiss are determined by the disturbance. With the advancement of disturbance, the main failure mode of gneiss is transformed from shear sliding failure controlled by foliation into splitting failure controlled by microcracks.