Acoustic Emission Characteristics and Crack Types Evolution of Soft and Hard Interbedded Rock-Like Specimens under Uniaxial Compression

In order to further reveal the acoustic emission characteristics and crack propagation law of soft and hard interbedded rock with different bedding plane dip angles under uniaxial compression, the soft and hard interbedded rock-like samples were prepared by rock-like materials. Based on the RMT-150B rock mechanics test system equipped with DS-5 acoustic emission monitoring system, uniaxial compression experiments were carried out on soft and hard interbedded rock-like samples with different bedding plane dip angles (0°, 30°, 45°, 60°, and 90°). Accordingly, the influences of bedding plane dip angle on acoustic emission characteristics, damage evolution and crack propagation of rock samples were analyzed. The results show that the acoustic emission activity of the sample presents obvious stage characteristics, and its distribution characteristics are obviously different under different bedding plane dip angles. The acoustic emission characteristic parameters show obvious bedding effect, and the cumulative ringing count and cumulative energy of acoustic emission decrease first and then increase with the increase of bedding plane dip angle. The sudden appearance or increase in the proportion of low frequency-ultra high amplitude signals can be used as a precursor information for the failure of soft-hard interbedded rock samples. The failure of low-angle (0° and 30°) samples is the steady expansion of large-scale cracks. The failure of medium-angle (45° and 60°) samples is the sudden instability expansion of large-scale cracks. The failure of high-angle (90°) samples is the sudden instability expansion of small-scale cracks. The dip angle of 60° is the most unfavorable angle for sample failure. The damage accumulation process of the specimens also has obvious stage characteristics. Before the peak stress, the damage accumulation of the specimens is mainly concentrated in the high rate damage stage, and the medium angle (45° and 60°) bedding surfaces accelerate the damage accumulation process of the specimens. The influence of different bedding plane dip angles on the evolution of tensile-shear cracks in soft-hard interbedded rock-like samples is obviously different. The horizontal bedding plane promotes the generation of tensile-shear cracks, and the gradual increase of bedding plane inclination angle promotes the development of tensile-shear cracks in rock-like samples. Under the joint action of bedding plane and rock matrix, with the gradual increase of bedding plane dip angle, the proportion of shear cracks in rock-like samples increases first and then decreases, and the number of shear cracks is at a high level. The research results have certain reference value for the stability evaluation of surrounding rock structure in underground engineering.