(1. State Key Laboratory of Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing 400044,China;
2. State and Local Joint Engineering Laboratory of Methane Drainage in Complex Coal Gas Seam,
Chongqing University,Chongqing 400044,China)
Abstract:Using self-developed meso-shear test equipment for coal and rock containing gas,tests of raw coal containing gas under compression-shear stress were carried out to study the meso-cracks? dynamic evolution. The formation of gas migration pathways is described;and the factors influencing meso-morphological characteristics of cracks are analyzed. The results show that the evolution of cracks provides pathways for gas migration in coal continuously. Coal surface crushes and then drop as the gas pressure and compression-shear stress on coal simultaneously. The fractured zone has more initiations of cracks conversely. Both the horizontal original cracks and hard granules have effects on the meso-cracks;cracks initiate more easily when encounter the original cracks;then the newly formed cracks and the original cracks together make the composition of an H-shaped one locally. There is also always a dislocation for newly formed cracks subjected to the original cracks. The evolution directions of cracks change because of the existence of hard granules which are always bypassed,the bifurcation angles range from 10°–100° which shows obvious discreteness and meso-cracks are formed by tension and shear together. There are more pathways for gas migration as the existence of original cracks and hard granules. Both the fracture distribution rate and coal crushing extent increase as the normal stress increases and the effect of initial damages and hard granules.