Experimental study on the acoustic emission and fracture propagation characteristics of sandstone with variable angle joints

Abstract

By studying the mechanical characteristics of sandstone, particularly its acoustic emission (AE) behaviour and fracture morphology, we can obtain insights into its deformation, stress, and fracture mechanisms, thus promoting knowledge in the field of geology. In this work, the mechanical properties of sandstone samples with different joint angles were investigated by applying shear force and observing the fracture propagation trend on a microscopic scale, using an AE-based technique. The experimental results demonstrated that the fracture expansion trend altered from a shearing fracture, which developed from the top to the lower areas of the samples, to a tensile fracture in the middle area of the samples and escalated in the angled joints; in particular, the severity of the fracture maximised at a joint angle of 60°. The energy released during the crack formation can be indicated by the decibels produced from the AE signal. While investigating the AE signals of the samples during shearing, it was determined that the decibels obeyed a Gaussian distribution centred at 50–69 dB. The surface fractures were macroscopically analysed through the self-defined fracture dispersion and fractal dimension, revealing that as the joint angle increased, the fracture dispersion initially increased and subsequently decreased, reaching its maximum at 60°, whereas the fractal dimension constantly increased. Through our investigation on the mechanical properties, main failure modes, AE characteristics, and microscopic features of sandstone, we aimed to elucidate the mechanisms responsible for fracture propagation both on a macroscopic and microscopic scale and provide theoretical insight in the field of geological disaster.