Mechanical model of lateral fracture for the overlying hard rock strata along coal mine goaf

Considering the continuous development of gob side entry driving technology, the influence of roof fracture on coal pillar is difficult to be accurately predicted. In order to explore the fracture structure characteristics of the overlying multi thick hard rock strata and its influence on coal pillars, the stress analysis tests of coal pillars under different roof fracture positions were designed. Different fracture positions of immediate roof and high-level thick hard rock were simulated by different corresponding positions of goaf, coal pillar edge line and rotary fixture line. According to four experimental design schemes, the strain distribution of coal mine goaf under different roof fracture combination positions was obtained. By analyzing the results of digital speckle pattern experiment, the distribution range and form of stress above coal pillar and low level thick hard rock are obtained, which provides theoretical basis for studying the whole process of coal pillar fracture.