Mechanism and application of competitive fracture propagation in layered group fracturing of massive thick overburden strata.

The massive thick overburden strata (MTOS) above the coal seam can result in high mining pressure in the stope, with significant manifestations of mine pressure, potentially triggering safety issues such as mine pressure bursts. In this paper, the fracture and migration characteristics of layered fracturing in MTOS above the stope were analyzed. The competitive fracture propagation mechanism in closely distances group fractures was revealed. Moreover, the layered group fracturing (LGF) technology for MTOS above the stope was proposed. The results showed that: LGF technology can reduce the caving step distance in the MTOS, and the formation of a "V"-shaped masonry beam structure by the fractured blocks provides effective support for the working face. Smaller fracture spacing leads to shorter initiation time for competitive fracture propagation within groups, and this competition is more intense. The superposition of the internal stress fields in the rock caused by fracture expansion is the fundamental reason for the "backward" competitive fracture propagation among group fractures. The field application results showed that LGF of MTOS can effectively reduce the intensity of periodic pressure on the working face, decrease the cycle pressure step distance, and lower the resistance of supports on the working face.