Fracturing behaviour of sandstone specimens with a cavity formed by intersecting excavations under compression: Experimental study and numerical modelling

To investigate the mechanical properties, damage characteristics, and fracturing behaviour of specimens with a cavity formed by intersecting excavations, a series of uniaxial compression tests were conducted incorporating digital image correlation (DIC) and acoustic emission (AE) techniques. PFC2D modelling was conducted to further study the failure modes and crack evolution under biaxial loading. The results showed that the mechanical properties are significantly weakened by the cavity and influenced by its shape. The failure of the specimens containing a cavity under uniaxial compression can be considered as a progressive process of crack initiation, propagation, and coalescence of different cracks with each other, leading to forming macrofractures, which can be visually displayed by the DIC technique. A new method for determining the crack closure stress is proposed, and the crack initiation stress and the crack damage stress of specimens are also obtained by the AE measurements. The failure mode of the intact specimen changed from the tensile-shear failure mode under the uniaxial compression to the shear-dominated failure mode under the biaxial compression. Failure of the specimens with a cavity is dominated by shear cracks rather than tensile cracks. Under high confining stresses, almost no macrotensile cracks appeared on the roof or floor of the cavity; instead, several spalling fractures were visible on the two sides of the cavity. The fracturing mechanism is well explained by the evolution of the internal stresses in the specimens.