When a tunnel traverses an inclined coal seam, the coal-tunnel angle α of the seam significantly alters the stress distribution in the surrounding rock, its failure mode, and the loading conditions on the support structure. This study investigates the influence of coal-tunnel angle α on surrounding rock stability and support structure loads, with the No. 1 Meijiaxiang Tunnel on the Wengma Railway in Guizhou Province serving as the engineering case. An integrated approach combining laboratory tests, numerical simulations, and engineering verification is employed. Laboratory tests were conducted to determine the basic mechanical properties of the limestone and coal. A refined 3D finite element model was developed in MIDAS GTS NX to analyze the effects of coal-tunnel angle α (α = 30°, 45°, 60°, 75°, 90°) and different construction methods on surrounding rock deformation, plastic zone development, and the stress state of the initial support. The results indicate that the coal-tunnel angle α significantly influences tunnel stability. Both crown settlement and the plastic zone extent decrease notably as α increases. Among the construction methods, the reserved core soil method most effectively controls surrounding rock deformation, but induces greater stress concentration in the initial support. Furthermore, for the most unfavorable case (α = 30°), an optimization analysis of the cyclic advanced length for the reserved core soil method was conducted. It is shown that using an 8 m advanced length can effectively control settlement while significantly reducing support stress and bolt axial forces. With its integrated methodology and detailed parameter analysis, this study provides a valuable theoretical and practical reference for optimizing the design and ensuring the safe construction of similar tunnels traversing inclined coal seams in complex soft–hard interbedded strata.
Chen et al. (2026) studied this question.