Fracture criterion of basic roof deformation in fully mechanized mining with large dip angle

To explore the structure evolution of overlying strata and pressure characteristics of coal mining with large dip angle, the basic roof mechanical model was established that based on the thin plate theory and the development characteristics of 1212 (3) working face of Panbei Mine. The formula was deduced that used for calculating the basic roof stress distribution in large dip angle coal seam. It revealed the mechanism evolution of mining stress and its influence on overburden deformation. Furthermore, it was also discussed that the effect of false roof on the failure of the basic roof. It showed that the false roof increases the differentiation of gangue’s filling rate in goaf and improves the evolution rate of basic roof fracture. It is the main influencing factor that the large dip angle leads to the “scoop” distribution of the stress and deformation in basic roof. It dominates the evolution of overburden fractures and the regional instability. The maximum deformation of the basic roof is located in the middle and upper part of the working face. This theoretical model is verified by means of numerical simulation and field monitoring

Three-dimensional reconstruction and growth factor model for rock cracks under uniaxial cyclic loading/unloading by X-ray CT

The spatial distribution and propagation of cracks are one of the key factors that can influence the initiation of rock failure. In this investigation, the technique of X-ray computed tomography (CT) scanning was used to survey the pattern of rock cracks during cyclic loading/unloading. The distribution and nonlinear development of rock cracks were explored by three-dimensional (3D) reconstruction for use to quantitatively describe their growth. An entropy model for rock mass and a crack growth factor model were established, which could help to reveal the relation between the crack propagation and the macroscopic destruction.The results showed that all disconnected cracks in two-dimensional (2D) images became connected with each other in 3D images. The fractal dimension of rock cracks was increasing first and then decreasing, which was the result of gradual transformation of rock cracks. The growth rate of cracks was decreased with the increase of the quantity of cracks, which was caused by the retardation. When the quantity of cracks grew to a maximal, the growth rate was reduced to zero.Published versio