Abstract:
To further reveal the evolution laws and disaster characteristics of the stress, displacement, and fracture fields during shallow buried coal seam mining in valley areas, this study takes the N1120 working face of Ningtiaota Coal Mine as the engineering background. Numerical simulation and comprehensive analysis methods are employed to investigate the overburden failure process and characteristics in shallow buried coal seam mining across ditches, clarify the dynamic evolution features of the overburden stress, displacement, and fracture fields, and uncover the dynamic variation of the water−conducting fracture zone (WCFZ) height. The disaster characteristics of mining in the N1120 working face are also analyzed. The research findings show that during the insufficient mining stage, overlying strata undergo vertical expansion via "layer−by−layer fracturing" and expansion along the mining direction through "rock block hinge rotation", respectively. In the sufficient mining stage, overlying strata evolve in a coordinated manner through overall fracturing. The mining−induced overlying strata "stress field" comprises stress concentration zones and stress release zones, expanding in an "arch" shape. The overlying strata displacement field during mining evolves in a "trapezoidal" pattern with delayed recovery, and subsidence gradually decreases from the coal seam floor to the surface. The surface subsidence curve gradually transitions from a "V" shape to a "U" shape, which is primarily controlled by key strata. The "fracture field" morphology in overlying rock evolves into a "semi−circular arch−trapezoid−hyperbolic shape" as mining proceeds. The fracture number (N) exhibits a strong positive linear correlation with mining distance (L), following a linear function. The measured WCFZ height ranges from 30.3 m to 50.1 m, and the ratio of the WCFZ height to the coal seam mining height is between 17.82 and 30.30. Based on the research results, roof cutting and channel collapse disasters are theoretically unlikely to occur during mining of the N1120 working face; however, landslide hazards are easily induced. Prior to mining the working face, it is necessary to further systematically analyze the working face’s geological conditions in accordance with the research findings, conduct a comprehensive investigation of potential landslide−prone areas and surface structures, and eliminate causative factors to prevent disasters.