Investigation of cracking behavior and mechanism of sandstone specimens with a hole under compression

In this paper, the cracking behaviour of rocks with a hole loaded in compression was investigated both experimentally and theoretically. First, a series of uniaxial compression tests on prismatic red sandstone specimens containing a circular or a rectangular hole were performed using a rock mechanics testing system in conjunction with digital image correlation (DIC) and acoustic emission (AE) systems. Afterwards, the theoretical solutions of stress for a circular and a rectangular hole under different stress conditions were solved by combining the complex variable method and the Box's complex algorithm. Experimental results show that the mechanical properties of rock specimens are significantly degraded by the hole and influenced by its shape. Crack evolution proceeds from primary tensile cracks through secondary tensile cracks and slabbing fractures to shear cracks, which can be visually displayed by the real-time deformation fields. The failure of specimens containing a hole under uniaxial loading is induced by the coalescence of the shear cracks and slabbing fracturing zones. Besides, several critical stresses associated with cracking behaviour were estimated based on a proposed method and the AE measurement. Theoretical investigation indicates that both hole shape and lateral stress ratio are important factors influencing the stress distribution, and the initiation mechanisms of different cracks can be well revealed according to the stress states around the holes under uniaxial compressive loads.