Numerical investigation on crack development and energy evolution of stressed coal-rock combination

Abstract

To uncover the failure and instability mechanism of coal-rock combination under loading, it is very crucial to investigate crack development and energy evolution. In this work, the uniaxial compressive and Brazilian split tests of coal-rock combinations were first performed. Secondly, the corresponding numerical models were built using the UDEC-Trigon method. Based on numerical results, the number, length and macroscopic area of cracks during failure and instability were determined, and the crack development and energy evolution rules were analysed. The main conclusions were obtained as follows: 1) the stress thresholds of crack initiation and damage of coal-rock combination rose with the increasing height ratio of coal to rock. The maximum event count of acoustic emission (AE) appeared earlier than the peak strength; 2) the failure and instability of coal-rock combination occurred when crack propagation and connection in central coal exceeded the damage limit. The shear failure was dominant mechanical behaviour of coal with the ratio 9:1 of shear to tensile fractures. The cracks connection was presented as a shear failure surface with an inclination angle of 15°–30° in coal and a vertical tensile failure plane in rock; and 3) the energy evolution in coal-rock combination was described as follows: the larger the height ratio of coal to rock is, the higher the cumulative energy is, and the faster the speed of energy dissipation is, indicating the higher risk of rockburst triggered by failure and instability of coal-rock combination.