Experimental Study on Mechanical and Seepage Characteristics of Raw Coal Under Different Loading Conditions

Taking the coal sample from Lu’an Group Changcun Coal Mine as the research object, we researched the mechanical and permeability characteristics of coal containing gas by using WYS-800 microcomputer control electro-hydraulic servo triaxial test device under different loading conditions. The results show that the ultimate compressive strength and elastic modulus of compression of coal in three axial compression are larger than the corresponding value of uniaxial conditions; with the increasing of confining pressure, the compressive strength and elastic modulus of coal will also increase, and the elastic modulus shows good linearity; stress-strain curve under cyclic loading and unloading tests is subject to the corresponding curves of conventional triaxial compression tests in a certain extent, and the peak strength decreases; the stress body strain curve of coal rock showed expansion mechanism under low confining pressure; however, under higher confining pressure, the coal sample body is always in a compressed state in pre-peak and post-peak. The relation between the permeability of coal containing gas and the strain presents a trend of inclined letter “V” under triaxial compression. With the increase of loading and unloading times in cyclic loading and unloading axial compression test, the permeability of coal sample decreases, but the decreasing gradient decreases.