Study On Micro-damage Experiment Of Gas-Containing Coal Under Shear Load

Geostress and gas pressure also unceasingly increases with the depth of mining increasing, which trigger all kinds of problems at the same time, and coal and gas outburst is one of the main serious mine disasters. The more serious the coal and gas outburst, the more damage will be brought to coal mining workers and coal mining enterprises. From the comprehensive function hypothesis view, coal and gas outburst is essentially a dynamic disasters caused by the shear destruction under the influence of both external and internal powers. Studying the dynamic change processes of gas-containing coal during mining process, which can provide basis for further studying the mechanism of coal and gas outburst. This paper used independent developed microscopic shear device for gas-containing coal, had micro-shear experiments of gas-containing shape coal and raw coal with different gas pressure, different shear rates and different normal stress, aim to provide effective theoretical support for preventing coal and gas outburst. Adoption of this study, the following achievements have been obtained.1) Independent researched microscopic shear device for gas-containing coal, and this device can be used to have micro-shear experiments of gas-containing shape coal and raw coal with different gas pressure, different shear rates and different normal stress; micro-crack monitoring system can realize the real-time testing and recording about the crack on the face of coal. This experiment device has high reliability, flexible operation etc, and it can have gas-containing coal's shear experments under of solid-air coupling condition, to reveal gas-containing coal's micro-damage law during shearing, which is big value of using.2) The shear strength of gas-containing coal increases with the increase of gas pressure and normal stress, but decreases with the increase of shear rate. Analyzed from the angle of microstructure, micro-cracks initiate in the upper part of coal and descend flexurally with the increase of shear stress; When the shear stress increases to a certain stage, micro-cracks are created at the foot of coal and expand in word.3) Micro-cracks in gas-containing coal initiate at the upper end and lower end, and stretch achead with the increase of shear stress; the cracks of shape coal initiate, stretch and penetrate before reasched the peak pressure, the cracks of raw coal initiate before the peak preaaure while quick stretch and main crack's penetration are after reached the peak pressure. After reached the peak pressure, the shape coal almost lost bearing capacity while the raw coal still has bearing capacity.4) On the surface of Vertical bedding raw-coal, there is bedding face which will causes crack initiation at the junction of shear derection and bedding face with increasing shear stress; and the exist of bedding face will cause crack. Bit the bedding face on the surface of parallel bedding raw-coal layer is not obvious.