Test study on the top cracking process of large coal sample

In this paper, the pressing crack effect of the top coal under the abutment pressure in Xinzhouyao Mine is simulated The characteristics of strength and deformation of top coal are analyzed It is found out there are six evolution stages during the process of pressing crack of top coal, that are crack compressing, density increasing, expanding, hardening, failure, softening. The changing regularities of pressing crack and lump diameter are given by method of the fractal dimension. According to the damage mechanics theory, the constitutive equations of the top coal pressing crack is obtained. This paper provides scientific foundations for the technical parameter selection and numeral analysis of the fonwall top-coal caving technology.