Fracture propagation characteristics and failure mechanisms of parallel-fractured sandstone

It is important to study the fracture mechanism of fractured rocks. Uniaxial compression tests and discrete element numerical simulations were conducted on sandstone specimens with fixed dip angles and parallel fractures. With the help of acoustic emission detection technology, the effects of different fracture spacings and number of fractures on the mechanical properties, fracture mechanism and acoustic emission full dynamic time-varying evolution of sandstone were investigated. The results show that: there is an obvious correlation between the number of fractures and elastic modulus and no obvious correlation with strength. There is no clear relationship between fracture spacing, elastic modulus, and peak strength. The fracture spacing determines the basic type of crack aggregation, and the number of cracks mainly affects the diversity of crack aggregation types. Spalling damage mainly occurs at the middle position of through-bridge shear cracks, and plate crack damage mainly occurs at the position on both sides of the specimen. Through-bridge shear cracks are a common type of crack in specimens containing parallel fractures, which influence the initiation location of the main shear crack and the damage mechanism of the specimen, and affect the overall strength of the specimen by changing the local narrowest width of the "column" structure. There is a mutual excitation between the tension and shear cracks, and each sudden increase in the shear-tension crack ratio corresponds to a macroscopic rupture of the specimen. The multifractal parameters of acoustic emission can provide a more detailed description of signal complexity. The abrupt changes in the time-varying multifractal parameters Δα and Δf(α) can serve as short-range prediction indicators for disaster occurrences.