Mechanical behavior of the lateral gangue-retaining structure and roof cutting regulation in fully gob-side entry driving in a steep coal seam

Fully gob-side entry driving refers to the excavation of a roadway along the edge of the gob after the completion of mining in the adjacent panel. Since no coal pillar remains between the full gob-side entry side and the gob, the reliability of the gangue-retaining support is crucial and directly affects the control effectiveness and usable cross section of the roadway. In steep coal seam mining, the downward sliding of gob gangue influences the stress on the gangue-retaining support structure, which increases the difficulty of roadway maintenance. Focusing on the challenge of gangue retention in steep gob-side entries, a theoretical analysis method was adopted to establish a mechanical model of the gangue-retaining structure. The relationships between the required gangue-retaining force and factors such as the coal seam dip angle and roof cutting parameters were derived, revealing how the support force varies with geological conditions and mining parameters. The required gangue-retaining force is positively correlated with the coal seam dip angle and roof cutting height and negatively correlated with the roof cutting angle. Under steep mining conditions, the stress on the gangue-retaining structure can be effectively regulated by adjusting roof cutting parameters. Designing the gangue-retaining structure on the basis of the lateral thrust from the gangue after pressure relief by roof cutting can ensure close alignment with field engineering conditions. This conclusion was verified using numerical simulations. Finally, construction convenience was considered; a roof cutting angle of 10° and mine-supplied U36 steel (with a yield strength of approximately 400 MPa) were adopted for gangue retention under known conditions; and the applicable roof cutting height for fully gob-side entry driving in the Baogushan Mine was determined as 10 m through the use of the back-calculation method. An industrial field trial was conducted that combined conventional bolt–mesh–cable supports with unit supports for active and passive support purposes. The rib deformation was approximately 320 mm, the roof-to-floor convergence reached approximately 380 mm, the maximum roof separation was less than 60 mm, and the residual roadway cross-sectional ratio was 82%. No significant large deformation or overall inward movement occurred of the gangue-retaining structure on the side of the gob, which satisfies mine production requirements. On the basis of limit equilibrium theory, a method for calculating the required gangue-retaining support force in steep gob-side entry was developed. A synergistic control concept involving gangue retention and roof cutting was proposed. Controlled roof cutting was employed to precisely regulate the gangue-retaining force and prevent instability of the rib on the exposed side due to insufficient support capacity. A new perspective on the engineering application of roof cutting and pressure relief technology was offered for fully gob-side entry driving in steep coal seams.