Influence mechanism of contact surface mechanical properties on mechanical behavior of coal rock combination

The uniaxial compression test of coal and rock combination was carried out in order to clarify the influence mechanism of the contact surface mechanical properties on the rock-burst tendency of the coal rock combination, and the contact surfaces with four different mechanical properties were considered. The variation laws of strength, elastic modulus, strain softening phenomenon, acoustic emission characteristic signal, energy accumulation and dissipation characteristics, and impact tendency of coal rock combination were analyzed. The influence mechanism of end face effect caused by the bonding properties and failure of contact surface on local deformation characteristics and strength of coal and rock was studied. The results show that the mechanical properties of the contact surface have a certain influence on the mechanical properties of the coal rock combination. The complete contact surface enhances the strength and elastic modulus of the coal rock combination, improves the elastic energy accumulation ability, inhibits the sample fracture in the pre-peak stage, and weakens the strain softening stage after the peak. The failure of the contact surface reduces the influence of the end-face effect, improves the failure degree of the coal rock combination, prolongs the post-peak strain softening process, and the strain energy density in the pre-peak stage is mainly plastic dissipation. The mechanical indexes of unbonded coal rock combination samples are lower than that of others. The constitutive relationship of coal rock combination is established, and the strength estimation method considering the contact surface failure, and the determination method of contact surface fracture are proposed. The theoretical calculation results are consistent with the experimental results. With the improvement of mechanical properties of rock coal interface, the proportion of elastic energy of combined coal increases, and the proportion of plastic property decreases. The influence law of the mechanical properties of rock coal contact surface on the rock burst tendency of coal rock combination is clarified. It is considered that the relative mechanical properties between the contact surface and coal is an important factor which causes the conflict of various indexes of coal rock combination rock burst tendency.