Characteristics of crack extension and fracture mechanism of parallel-fissured sandstone

It is of great significance to study the fracture mechanism of defect-bearing rocks. Through the uniaxial compression test and discrete element numerical simulation on the fixed inclination parallel-fissured sandstone, the mechanical properties, fracture mechanism and acoustic emission full dynamic time-varying evolution law of sandstone with different fissure spacing and fissure number are investigated with the help of acoustic emission multi-signal characteristics. The results show that: There is an obvious correlation between the number of fissures and elastic modulus, and no obvious correlation with strength. There is no obvious correlation between the fissure spacing and elastic modulus and peak strength. The prefabricated fissure spacing determines the basic aggregation type of cracks, and the number of prefabricated fissures mainly affects the diversity of the aggregation type of cracks. 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 cracks in specimens containing parallel fissures, 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 acoustic emission multifractal dimension describes the complexity of the signals more finely, and the sudden increase and decrease of the time-varying multifractal parameters Δα and Δf(α) can be used as a short-range prediction signal for the occurrence of disasters.