The strength characteristics and competitive failure mechanism of primary coal-rock combination considering interface damage quantity

The strength and failure characteristics of primary coal-rock combinations are essential in coal-rock dynamic hazards prevention and coalbed methane drainage. Current studies simplify the primary coal-rock interface as smooth, which is inconsistent with the fact that there is a complex structure at the actual primary coal-rock interface. To study the influence of actual primary coal-rock interfaces on the strength and failure characteristics of primary coal-rock combinations, large primary coal-rock combinations from the Shendong Baode coal mine were collected, processed into standard samples, and scanned by industrial CT to reconstruct the 3D model of the primary coal-rock combinations interface. The probability density function of interface microelement inclination angle was statistically obtained, and the progressive damage model of the interface was established based on the density function. Then, uniaxial compression tests with acoustic emission localization were conducted on primary coal-rock combinations with different interface inclination angles. Finally, the competitive failure mechanism was used to analyze the influence of interface damage quantity on the strength characteristics and failure mode of the primary coal-rock combination. The results show that the primary coal-rock combination interface has a complex microstructure, and the inclination of the interface microelements is right-skewed distributed between 0 and 90 degrees, with a plurality of 16 degrees, conforming to the Rayleigh-Beta joint distribution. The coal and interface competed for the damage quantity of the primary coal-rock combination under uniaxial compression. As the interface inclination increased, the interface damage quantity increased, but the strength and energy density decreased, and the main damage gradually changed from the coal to the interface.