The initiation and evolution of the cracks around the hole in coal specimens with a central hole under different uniform loads are studied by the rock failure process analysis software RFPA2D. The results show that homogeneity not only has an influence on the peak strength of coal specimens, but also on the crack propagation directly. The lower homogeneity, the more extensive the stress concentration areas, the rougher the surface crack, and the more irregular the crack propagation path. However, homogeneity has a certain impact on acoustic emission (AE) number and instantaneous effective coalescence rate of cracks, but the influence degree is significantly lower than that under nonuniform load gradient and original cracks. Nonuniform load can cause the obvious stress concentration on the higher load area of the coal specimens (right side), which mainly reflects the micro-crack initiation in the area, and the greater the nonuniform load gradient, the more significant is this trend. The peak stress of models does not change with the change of load forms (the change from uniform load to nonuniform load), but nonuniform load will accelerate the effective coalescence of the surface crack, and the larger the nonuniform load, the shorter the time to achieve the effective coalescence of the surface crack. The original cracks with a certain inclination weaken the stress concentration around the hole. When the dip angle of original crack reaches a certain range (such as 45 degrees), this trend will be more obvious. But it is not closely related to the homogeneity of the coal and the size of the load gradient, and has a certain universal applicability. Finally, the stress around circular tunnel is analyzed based on the theory of elastic mechanics, and a criterion for judging the crack initiation around the laneway is proposed.

Taking red sandstone specimen as the research object, this paper makes a rather systematic research on the formation and morphology of the main control fracture surface of the red sandstone under restrictive shear creep based on the basis of fractal theory by using three major self-designed research devices, that are, shear creep experimental device for soft coal or rock material, three-dimensional automatic measure and control experimental device for microstructure evolution based on micro-analysis, and three-dimensional mesoscopic monitoring software for dynamic evolution of micro-structure on the surface of coal-rock. The results show that restrictive shear creep of red sandstone experiences three stages, from the initial, steady to accelerated creep stage. The mechanism of creep action is the crystal slip under shear creep load and the slip due to dislocation. The formation of the main crack on the surface of the red sandstone under restrictive shear creep consists of four kinds of crack propagation modes: merging propagation, tensile propagation, intergranular propagation, bypassing crystal propagation. The changes of the profile along the shear direction are great in the distribution of the fracture surface, which shows a double crest trend in the second half, but the profile along the vertical shear direction declines relatively gently, slightly lower in the middle; in addition, the complexity of the roughness in the main fracture surface of the red sandstone specimen along the shear direction is greater than that in the vertical shear direction. A new method is proposed to calculate the fractal dimension of the fracture surface, and based on this method, it is found that the fractal characteristics of the main fracture surface of the red sandstone specimen show that the fractal dimension along the shear direction increases first and then decrease, and appears maximum value in the middle. And the changes of fractal dimension of the vertical shear profile are smaller than that in the shear direction, so does the fractal dimension.

Based on a self-developed coal seam gas emission test device, taking briquette samples containing penetration partings as the research object, and taking gas emission speed and gas cumulative emission amount of coal sample as study parameters, the influences caused by penetration partings on coal seam were studied systematically, and the mechanism of gas emission of coal seam with penetration partings was discussed.The results show that the gas emission speed of all briquette specimens presents power-function decay over time, and the cumulative emission amount presents an upper limit monotone increase over time.Both gas emission initial speed and cumulative emission amount of coal samples increase with the increase of adsorption equilibrium pressure.Under the same adsorption equilibrium pressure, the gas emission speed of specimens containing penetration partings is faster than the ordinary specimens in the initial stage, but two emission speed curves appear intersection from 30 min to 90 min, while the cumulative emission amount of specimens containing penetration partings is more than that of the ordinary specimens in the former 120 min.Penetration partings can improve the permeability of coal seam, provide migrations path for gas emission of coal seam, and create favorable conditions for the gas emission, so the gas emission efficiency is improved.