Instability motion characteristics of overburden rock and the distribution pattern of fissures in shallow thick seam mining

This paper analyzes the instability movement characteristics of overburden in shallow thick coal seam mining and its influence on the development and distribution of fault fractures. The similarity simulation experiment and theoretical analysis were combined based on the classification of the occurrence characteristics of the key bearing layer in the overburden rock of shallow thick seam mining. This study investigated the fracture characteristics and the instability motion mode of the key bearing layer in shallow thick seam mining and their effects on the distribution of fissures in the overburden rock. The results indicated that according to the horizon of the key bearing layer, the occurrence of overburden rock could be classified into 2 categories, i.e., the horizon of the key bearing layer within the caving zone and within the fissure zone. The horizon of the key bearing layer has a significant effect on the fracture characteristics and the instability motion mode of the key bearing layer. When the horizon of the key bearing layer is in the overburden caving zone, a "step rock beam" develops after fracture, and the instability motion mode is sliding instability. When the horizon of the key bearing layer is in the overburden fissure zone, a "masonry-like beam" develops after fracture, and the instability motion mode is rotary instability. The fracture instability of the key bearing layer could control the development and distribution of fissures in the overburden rock, and the whole favorable zone for the development of fissures extends along the advancing direction of the working face in a form of "diagonal stripes" with the instability motion of the key bearing layer.