Mechanical and crack evolution characteristics of coal–rock under different fracture-hole conditions: a numerical study based on particle flow code

Coal–rock material contains many fractures and holes and it is of great significance to study their mechanical characteristics for understanding the instability mechanism of coal body. In this manuscript, considering fracture with different inclinations and hole with different positions, a variety of defective coal–rock specimens were established by PFC2D software, then characteristics of stress–strain and crack evolution law of coal–rock with different fracture-holes were discussed. The results show that mechanical properties, crack evolution characteristics, propagation forms of initial crack and final crack distribution form of coal–rock specimens with different fracture holes are different; the fracture angle has a larger influence than the hole position. Peak strength, peak strain, peak step and the total crack number show an increasing trend with the increase of fracture angle, while the crack initial propagation length becomes shorter and shorter.