A comprehensive study of fracture evolution of brittle rock containing an inverted U-shaped cavity under uniaxial compression

This paper aims to investigate the fracture evolution around an inverted U-shaped opening under compressive loads. Firstly, a series of uniaxial compression tests were conducted on sandstone specimens containing a cavity incorporating digital image correlation (DIC) and acoustic emission (AE) techniques. Next, the complex variable theory combined with an optimization algorithm was used to find the analytical stress solution for the inverted U-shaped cavity. The experimental results show that the shear dominated failure of the pre-holed specimen is a progressive process of "primary tensile cracks - secondary tensile cracks and slabbing fractures - shear cracks". The DIC results are consistent with the variation of AE signals, The crack closure stress, crack initiation stress and crack damage stress of the specimen containing an inverted U-shaped cavity are about 24%, 30% and 90% of the peak stress, respectively. Theoretical analysis indicates that the cavity shape and lateral stress ratio are prominent factors affecting the stress distribution. Based on the stress distribution around the inverted U-shaped cavity under uniaxial stress, the fracture evolution mechanisms are well revealed. Moreover, the propagation behavior of the primary tensile cracks is discussed in detail, and a method for determining the crack length is also proposed.