INFLUENCING FACTORS OF DEFORMATION AND FAILURE OF POROUS COAL UNDER CONVENTIONAL LOADING

Coal exploration requires draining the gas from the coal seam. For this purpose, drill holes in the coal seam are required. Under the field conditions, the stress and strain states around a drill hole are not easy to determine and the same is valid for the material law defining their dependence. In this study, by arranging boreholes in coal samples, the effects of loading rate, borehole inclination, borehole diameter and other factors that influence the mechanical properties of porous coal are studied. The results show that the strength of porous coal increases with the increase of loading rate, which is consistent with the behavior of non-porous coal. The porous coal samples with certain inclination angles of the drill hole are easier to destroy compared to the porous coal samples with a horizontal drill hole. Furthermore, the failure surface is consistent with the inclination angle, and a specimen with an upward inclination angle of the drill hole is easier to destroy compared to a specimen with a downward inclination angle. Comparing the samples with the borehole diameters of 5 mm and 10 mm, the axial deformation and transverse deformation of the latter are 1.7 times and 1.63 times that of the former, respectively. Regarding the failure mode, it is shown that the borehole plays a leading role in the process of fracture propagation.