Study on the influence of stress relief in close-distance coal seam Goaf and roadway excavation disturbance on surrounding rock

To investigate the influence of pressure relief in the close-distance coal seam goaf and roadway excavation disturbance on surrounding rock stability, this study focuses on the large-section open-off cut of Ⅱ8224 N. Methods employed include RQD rock mass quality evaluation, FLAC3D numerical simulation, similar material simulation experiments, and field borehole camera observation. The results show the following: The RQD evaluation indicates that the immediate roof siltstone (thickness: 3.8 m) and the fine sandstone in the lower part of the main roof are classified as medium-quality Grade III rock mass, while the fine sandstone in the upper part of the main roof and the mudstone at the floor of No. 73 coal seam are extremely poor Grade V rock mass. The goaf of No. 73 coal seam exerts a significant pressure relief effect on the surrounding rock of the Ⅱ8224 open-off cut, creating a pressure relief zone with a range of 2.5–5.0 MPa. A 3 m-wide non-plastic failure zone exists between the goaf floor and the open-off cut roof, with no plastic failure occurring within the 7.4 m anchorage range of the cable bolts. The roof rock bolt zone is a tensile stress zone, while the cable bolt zone experiences compressive stress. After excavation of the open-off cut, a new surrounding rock bearing layer forms between the open-off cut and the goaf. Stepwise excavation induces secondary stress disturbance in the roof surrounding rock, and after roadway formation, stress continues to increase, with the most concentrated tensile stress occurring in the middle part of the roadway. The similar material simulation experiment shows that the roof of No. 73 coal seam fully collapses when the load exceeds 6.60 kN, with caving angles of 65 ° and 60° respectively. The stress in the goaf floor shifts to tensile stress after 300 min and stabilizes after 1200 min. Field borehole camera observation reveals that the overall integrity of the roof surrounding rock is good, with only a small number of circumferential fractures. These findings provide a theoretical basis and technical support for surrounding rock control in large-section open-off cuts under close-distance goaf conditions.