Crack propagation mechanism in rock-like specimens containing intermittent flaws under shear loading

Abstract

The rock masses, especially with existing discontinuous joints, are prone to shear failure when subjected to constant changing stress in the direction perpendicular to the free face, which may result in tunnel collapse and slope slip instability in the processes of rock engineering construction. To better understand the effect of various joint geometries on the shear behavior of rocks, the mechanism of crack initiation, propagation, and coalescence in rock-like materials (a kind of cement mortar) with intermittent flaws under shear loading is investigated using both laboratory experiments and numerical simulations. The component of moment tensor is utilized to investigate the temporal and spatial evolution of acoustic emission events and determine the geometry state of the cracks. The major principal stress and velocity field are presented to distinguish crack types and study the stress evolution associated with crack propagation. The results reveal that for specimens with various flaw dip angles the propagation direction of all newly generated cracks is basically parallel to the shearing loading, and the failure patterns of specimens are mainly controlled by tensile fractures. When the flaw inclination angle reaches 45°, the evolution of the thickness of newly generated micro cracks is controlled by the type of stress field, and after peak strength its variation mainly occurs near the tips of the pre-existing flaws. The secondary cracks obtained from the velocity field analysis mainly include tensile, compressive-shear, tensile-shear and pure shear cracks rather than simple tensile cracks, and the secondary cracks appear instantly and abundantly on both sides of the specimen. The work may shed light on the mechanism of slope slip, and provide guidance to the safe construction of engineering projects.