Asymmetric Stress Evolution and Zoned Control of Gob-Side Entry Driving in Close-Distance Coal Seams Under the Influence of an Obliquely Intersecting Overlying Goaf Boundary

Gob-side entry driving (GSED) in close-distance coal seams (CDCSs) is subjected to complex loading paths when influenced by an obliquely intersecting overlying goaf boundary (OGB), making it difficult to determine an appropriate narrow coal-pillar width and limiting the adaptability of uniform support schemes. Taking the return-air roadway of the 100204 working face in the Baigou Coal Mine as the engineering background, a combined approach involving laboratory mechanical tests, theoretical analysis, UDEC numerical modelling, and field monitoring was employed to investigate cross-seam load transfer from the overlying goaf, the evolution of coal-pillar loading, and zoned surrounding-rock control. The test results showed that the roof sandy mudstone and floor mudstone had comparable compressive strengths, whereas the floor mudstone exhibited markedly lower stiffness and tensile resistance. Considering the spatial zoning of goaf-floor loads and their diffusion and attenuation through the interburden, a piecewise load model for the roof of the underlying coal seam was established. The cross-seam load attenuation coefficient was calculated as 0.480, and the peak load in the multi-stress superposition disturbance zone was 13.13 MPa. By combining the Bieniawski coal-pillar strength criterion with the internal and external stress-field theory, the reasonable coal-pillar width was determined to be 6.0 m. Numerical results showed that, after upper-seam extraction, the vertical stress in the floor was characterized by unloading beneath the central part of the goaf and stress concentration near its boundaries. When the distance between the coal pillar and the OGB decreased to 30 m, the stress-concentration zones associated with the upper and lower coal seams began to connect, and stress superposition intensified markedly within 15 m of the boundary. As the coal pillar approached the OGB, the pillar-side vertical and shear stresses increased markedly, reaching local peak values of 56.2 MPa and 15.62 MPa, respectively, at an offset of 15 m. After the pillar entered the projected extent of the goaf, these values decreased to 30.7 MPa and 8.71 MPa, respectively. Based on differences in loading conditions and roof structure, the roadway was divided into an under-goaf pressure-relief zone, a multi-stress superposition disturbance zone, and a unilateral stress-influence zone. Accordingly, a zoned asymmetric support (ZAS) scheme was adopted, with asymmetric cable reinforcement applied on the coal-pillar side within the boundary disturbance zone. Field monitoring showed that surrounding-rock deformation in all zones gradually stabilized and that deep roof separation was effectively controlled, demonstrating that the proposed ZAS scheme can satisfy the requirements for roadway stability and normal working-face operation.