Quantitative characterization of mining-induced cracks in overlying strata of grouting filling mining in caving area of fully mechanized mining face

To quantitatively characterize the influence of grouting filling in caving area on the degree of mining-induced damage of overlying strata, taking the 110903 working face of Renjiazhuang Coal Mine as the research background, the physical similarity simulation experiments before and after grouting filling mining by caving mining and caving area filling mining are carried out. The fractal theory is used to study the evolution characteristics of cracks of overlying strata , and the migration law of overlying strata is compared and analyzed. The results show that the change law of fractal dimension of mining-induced cracks after caving mining without grouting filling is rapid rise-slow decline-slow rise-rapid rise, and the change law after grouting filling mining is rapid rise-rapid decline-slow decline-slow rise. The mining-induced crack development network is divided into four areas: the separation crack area, the separation compaction area, the caving crack area and the vertical breaking crack area. Compared with the caving mining and the caving area filling mining before and after the filling, the cracks of overlying strata are not developed after the filling, and the separation compaction area is small, and the development height is only 21.96 m. After grouting filling mining, the subsidence of each key stratum decreases significantly. The maximum subsidence of key stratum 2 appears at the initial crack of roof. The maximum subsidence of key stratum 2 appears in the middle of goaf after caving mining before grouting mining. Grouting filling mining in caving area can effectively improve the crack damage of overburden rock, control the development of cracks of overlying strata and slow down the subsidence of overlying strata. The results can provide a theoretical basis for filling mining to control surface subsidence in Renjiazhuang Coal Mine.