On dynamic behaviors and failure of bedding coal rock subjected to cyclic impact

Dynamic triaxial cyclic impact experiments on the coal rock samples with the bedding angles of 0°, 30°, 45°, 60°, and 90°, respectively, were conducted using a 50-mm split Hopkinson pressure bar (SHPB) system to study the dynamic mechanical behaviors of the coal rock with characteristic bedding under complex ground conditions. A 3D profile scanner was utilized to quantify the fracture interface roughness and to investigate the bedding effect on the dynamic fracture process of the coal rock. The bedding angle effect and confining pressure effect on the dynamic properties of the coal rock were explored by combining dynamic parameters such as compressive strength, elastic modulus, energy distribution evolution with the fracture surface roughness variation. The research shows that when confining pressure is applied, the stress-strain curve of the coal rock has an elastic aftereffect. The dynamic compressive strength and failure strain of the bedding coal rock with confining pressure are respectively 3.9−4.2 and 2.59−3.05 times higher than those without confining pressure. As the bedding angle increases, the dynamic compressive strength, elastic modulus, and energy transmitted ratio of the coal rock display the U-shaped distribution, which decreases first and then increases, reaching the minimum at the bedding angle of 45°. Meanwhile, the energy absorbed ratio and fracture surface roughness show the ∩-shaped distribution, first increasing and then decreasing, and the damage variable shows the N-shaped distribution, reaching the maximum at the bedding angle of 45°. The failure of the coal rock with 45° bedding is the most serious, which is more prone to intergranular and spalling fractures. However, the 90° bedding coal rock is more likely to absorb energy and to form transgranular fractures, resulting in a large number of mesoscopic fractures. Variation of the damage characteristics of the coal rocks with bedding angle can be summarized as a tensile damage (0°)-shear damage (30°, 45°, 60°)-splitting damage (90°) evolution process. The relevant characteristic results obtained from the experiments can provide a theoretical support for the safe and efficient exploitation of coalbed methane resources in the complex environment under practical working conditions. © 2023 Explosion and Shock Waves. All rights reserved.