Full-field stress evolution and fracture mechanisms in overburden rock strata during coal seam mining

Large-area collapse of overburden strata represents a major dynamic hazard in coal mining. Understanding the deformation characteristics and stress field evolution of these strata is essential for preventing roof failure disasters. Existing research on stress evolution and fracture behavior has largely been based on rock beam theory; however, the beam-arch structural model fails to fully capture the structural characteristics of overburden strata across an entire working face. To further investigate the movement behavior and mechanical responses of overburden strata above the working face, this study takes the 3105-coal seam in the Mataihao Coal Mine, Ordos, Inner Mongolia, as a case study. Using theoretical analysis and numerical simulations with ABAQUS software, a spatially statically indeterminate plate-shell mechanical model was established for different caving stages of the overburden strata and the advance disturbance zone. Analytical functions for the stress field during the elastic and elastic-plastic deformation stages were derived. The results show that during the initial caving stage, significant stress concentration occurs in the midspan region of the overburden, while the central part of the floor experiences tensile stress that intensifies with increasing overhang length. As the working face advances, stress at the coal wall and on the goaf side gradually transitions from tension to compression, with continuously increasing magnitude. During the periodic caving stage, owing to asymmetric boundary conditions (simply supported on the left and fixed on the right), normal stress changes from positive to negative along the mining direction, exhibiting an asymmetric distribution. The peak positions of tensile and compressive stresses shift and differ in magnitude, with compressive stress concentration occurring on the non-mining side. Furthermore, integrating field monitoring data of working conditions, this study analyzes the distribution characteristics of the stress field during both elastic and elastic-plastic deformation stages, as well as the dynamic evolution of advance abutment stress across the entire area. These analyses reveal the non-uniform fracture characteristics and mechanical mechanisms of the stope overburden: the fracture pattern is “O+X”-shaped during the initial caving stage and “X+U”-shaped during the periodic caving stage. These findings provide a scientific basis for predicting fracture locations and optimizing advance abutment strategies in subsequent coal seam mining.