Mechanized complete set of equipment and surrounding rock control technology for flexible formwork gob-side entry retaining in end area

Systematic theoretical guidance for the fracture characteristics, dimension calculation, and stability control of arc triangular suspended plates in the end area of flexible formwork gob-side entry retaining is lacking. As a result, equipment selection and support parameter design for gob-side entry retaining rely excessively on experience and cannot fully adapt to complex and variable underground conditions. To address these problems, the working face 42305 of Wanli No.1 Mine of CHN Energy Baotou Energy Co., Ltd. was taken as the engineering background. A mechanized complete set of equipment for flexible formwork gob-side entry retaining was developed, consisting of an end-area anchor-avoidance support, end-area transition support, gangue-retaining support, formwork-hanging device, and a new type of stirrup flexible formwork. The system achieved coordinated support integrating "advanced support – temporary protection – permanent bearing". The fracture characteristics of arc triangular suspended plates during working face advancement were revealed. The top coal arc triangular suspended plate, immediate roof arc triangular suspended plate, and main roof arc triangular suspended plate fractured successively. Regarding fracture periodicity, the top coal arc triangular suspended plate had the shortest fracture period, followed by the immediate roof arc triangular suspended plate, while the main roof arc triangular suspended plate had the longest fracture period. The size of the arc triangular suspended plates increased layer by layer from bottom to top. A calculation formula for the side length of the main roof arc triangular suspended plate was derived, and the side length was found to be mainly controlled by factors including the lithology and thickness of the main roof, the load of overlying strata, and its self-weight. The study found that the main roof arc triangular suspended plate spatially overlapped with the arc-shaped triangular block formed by "O-X" fracture, thereby forming a "large structure" of the arc triangular suspended plate, which, together with the "small structure" of support in the entry-retaining working space, formed a stable coordinated bearing mechanism. Numerical simulation results showed that the equipment in the end area caused the trajectory of the ultimate bending moment of the roof to shift toward the goaf at the intersection between the working face and roadway boundary. Its rigid supporting effect effectively limited roof deformation on the goaf side and achieved good roof control performance.