Response characteristics and influence mechanism of uniaxial compression mechanics and AE of coal with different joint angles

The mechanical properties of coal and rock and the AE response law are very important for the moni-toring and early warning of rock burst. In order to study the influence of the angle (α) between the loading direction and the joint surface on the mechanical properties,crack propagation mode and acoustic emission (AE) response of coal sam- ples,some uniaxial compression tests were carried out on coal samples with different α,and the characteristic response laws of mechanical and AE signals were analyzed. The results show that the angle between the loading direction and the joint surface has a significant effect on the mechanical properties and AE signals. With the increase of α,the peak load and failure time both show a trend of decreasing first and then increasing,from 0° to 30°,the failure time after the peak tends to drop sharply. The stress-strain curve of coal samples with α≤45° fluctuates after the peak value or at peak value,and the uniaxial compressive strength and strain are less than that of coal samples with α> 45°. The stress-strain curve of coal sample with α>45° does not fluctuate after the peak value or at peak value. The coal samples with α ≤ 45° is mainly the stress component of the parallel joint surface,and it is more likely to slip along the joint sur- face. The accumulated sharp increase of AE pulse and the high-energy AE signal are mainly concentrated in the post- peak stage,and the AE signal has a high correlation with the stress drop. For the samples with α>45°,the stress com- ponent of the vertical joint surface is the main stress component,and the main failure mode is extrusion friction. The accumulated value of pulse increases steadily before the peak point,and the high-energy AE signals are mainly con- centrated in the pre-peak phase. With α increasing,the stronger the impact tendency of coal samples is,and the size of AE early warning parameters is different. Therefore,when identifying the coal impact tendency and using AE to monitor and warn the impact,it is necessary to take full account of the coal seam joint surface and the field stress.