Characteristics of Fracture Mechanism and Acoustic Emission of Rock-Coal Combined Body with Prefabricated Fissure

In order to analyze the mechanical characteristics of the composite rock sample, numerical simulations for the rock-coal combined body with a coal persistent joint are conducted using RFPA^2Dsoftware. Effect of the joint angle and height ratio on the uniaxial compressive strength (UCS) and acoustic emission (AE) characteristic in rock-coal combined body were analyzed. The results show the following. (1)With the increase of joint angle, the peak strength and peak strain first decrease and then increase, presenting ‘U-shape’ curves; With the increase of rock-coal height ratio, the peak stress increases gradually and the peak strain decreases gradually; (2)The different joint angle of prefabricated fissure affects the failure form of rock-coal combined body, but the height ratio of rock-coal has less influence on the failure form of the composite rock sample; (3)When the coal sample in the combination is near to failure, the AE energy accumulation curve will show a slow step shape curve and then a sudden increase. This phenomenon will occur in the combined samples with different combination modes, which can be used as a precursor to the failure of the rock-coal combined body.