Relationship between failure characteristics and fracture spacing of surrounding rock of short-distance coal seams group.

The fracture network of short-distance coal seams group in Liujia Coal Mine is well developed. In order to prevent water conduction caused by fracture in roof and coal seams, gas exceeding the limit in the working face that near goaf, and spontaneous combustion, based on fractal theory, Brazilian splitting test and borehole peeping statistical test, the impact of fragmentation scale and evenness of rock mass on fracture fractal characteristics were investigated. The study shows that the fractal dimension D of split fragmentation is closer to 2, the fragmentation scale becomes more even after fracture. It shows that there is a main crack that roughly divides the sample and the fissure-plane is relatively flat. The fractal dimension D of split fragmentation shows greater difference with 2, the fragmentation scale becomes more uneven and the fissure-plane is rougher. The fractal dimension D of split fragmentation and the fractal dimension D of cracks are in accordance with parabolic distribution. The fractal dimension D of split fragmentation is closer to 2, the bigger the fractal dimension D of cracks. This shows that the fragmentation scale gets more even, the less the number of cracks in the rocks, the more smooth the crack ring and the smaller the angle between the crack ring and interface of rock stratum. The fractal dimension D of split fragmentation shows greater difference with 2, the smaller the fractal dimension D of cracks. This shows that the fragmentation scale gets more uneven, the more the number of cracks in the rocks, the more rough the fissure-plane and the more irregular the crack azimuth. Crack distribution has nothing to do with the splitting fragmentation scale size, but is closely related with the homogeneity of fragmentation scale. [ABSTRACT FROM AUTHOR]