Numerical simulation research on roadway section shapes selection for horizontal slicing mining of steeply dipping extra thick coal seams

Roadways for horizontal slicing mining in steeply inclined extra thick coal seams are subjected to three adverse factors including uneven vertical roof pressure, intense unilateral horizontal pressure and coal seam dip slip, which leads to prominent hazard risks. Different section shapes produce distinct mechanical responses of roadway surrounding rock. Nevertheless, no consensus has been reached regarding which section shape delivers the best comprehensive control capacity and what corresponding response characteristics will occur. This situation restricts the selection of roadway section shapes and the formulation of support schemes at Yimen Coal Mine. Taking this mine as the engineering background, this study adopts numerical simulation methods to compare and analyze surrounding rock mechanical response characteristics of right trapezoid roadway, isosceles trapezoid roadway and semicircle arch roadway. The semicircle arch roadway is selected for the mine, and an asymmetric support scheme is formulated with denser supports arranged on the surrounding rock at the right side of Roof extraction roadway and the left side of floor extraction roadway. The research results indicate that surrounding rock of roof and floor extraction roadways exhibit common mechanical response characteristics detailed below. Plastic failure of roadways is dominated by shear failure, and the floor presents the highest plastic development degree due to slip effect. Roadway stress shows an inverse distribution pattern. Vertical loads induce tensile stress concentration on the roof and floor as well as compressive stress concentration on two sidewalls, while horizontal loads follow the opposite rule. Vertical and horizontal displacements of roadway surrounding rock form bidirectional zoned convergence features along the section. Differentiated mechanical response characteristics can also be observed. For roof extraction roadway, eccentric load is mainly reflected in increased vertical compressive stress on the left sidewall and elevated horizontal compressive stress on the roof, whereas deformation is characterized by right sidewall extrusion and floor heave. For floor extraction roadway, eccentric load mainly contributes to higher vertical compressive stress on the right sidewall and increased horizontal compressive stress on the floor, whereas deformation is dominated by left sidewall extrusion and roof subsidence. Under the effect of eccentric load moment, greater surrounding rock deformation emerges on the opposite side of high stress zones. Roadway section shapes exert similar influence laws on roof extraction roadway and floor extraction roadway. The semicircle arch converts high horizontal tensile stress into low compressive stress, markedly restrains stress concentration and surrounding rock deformation, and reduces the development of plastic zones, yielding the optimal comprehensive control performance. The right trapezoid roadway can only effectively reduce horizontal tensile stress in roof extraction roadway and presents the poorest overall control effect. The isosceles trapezoid roadway achieves moderate control performance and can serve as an alternative section shape to the semicircle arch roadway. Field monitoring results demonstrate favorable support performance. The proposed scheme effectively guarantees safe mine production and can provide references for the formulation of engineering schemes under similar geological conditions.