Macro-meso damage characteristics of coal body under different pressure relief conditions

The mining of the protective coal seam usually produces different pressure relief effects on the different areas of protected coal seam, the reason is that the stress paths of protected seam coal body in different areas caused by mining effect are different. In order to explore the differential pressure relief damage effect of coal body under different pressure relief conditions, the stress evolution path of coal body in different areas of the protected coal seam is obtianed by using theoretical analysis and the macro-micro damage characteristics of coal body under different stress paths by using numerical simulation in this paper. The results show that: The damage characteristics of the sample models are basically the same in the in-situ stress recovery stage and the mining disturbance stage of the two stress paths. With ith the sequence of stress stages experienced by the sample model, the distribution of acoustic emission events concentrates in the high-intensity area and the porosity continues to decrease. The number of cracks increases slowly in the stage of in-situ stress recovery stage, most of which are tensile cracks, while the number of cracks increases sharply in the mining disturbance stage, most of which are shear cracks. The difference of the deformation and macro meso damage characteristics of the sample models under the two stress paths is mainly reflected in the post mining pressure relief stage. At the post mining pressure relief stage of path 1, the number of cracks in the sample has little growth, and most of them are small energy tensile cracks, and the porosity increases, which verifies its obvious pressure relief activation antireflection effect; At this stage of path 2, the crack growth of the sample is obvious, and most of them are high-energy shear cracks, and the porosity continues to decrease. Compared with path 1, the pressure relief expansion effect of the sample model is suppressed and the compression damage continues to develop in this stage of path 2.