Evolution mechanisms of mining-induced overlying strata structures: a case study in the Qinshui coalfield

The phenomenon of surface subsidence in mining areas is closely associated with the mechanical properties of rock movement, which are influenced by the complex diversity of mining geological factors and technical conditions. This study examines the overlying rock of a nearly horizontal coal seam as a case study to elucidate the evolutionary mechanism and fracture mechanics conditions of the overburden structure in goaf areas. The research findings reveal that the maximum principal stress value within the rock support beam is linearly related to the load (q) and Poisson's ratio (µ), approximately following a quadratic function with the beam length (l), and showing an inverse proportional relationship with the beam height (h). The magnitude and direction of the principal tensile stress depend on the ratio of normal stress to shear stress within the beam, thereby influencing the beam's failure mode. The span-to-height ratio of the beam impacts the final fracture mode of the rock mass, while the direction of the maximum principal stress within the beam and the internal friction angle of the rock mass are the primary factors influencing the fracture angle of the rock strata. Two types of "stacked beam" structural models are established, along with the corresponding mechanical conditions for failure.