Staged and geometry-adapted support for coal mine roadways under weak rock conditions: a numerical study

Controlling large deformation and instability of roadways in weak coal seams remains a critical challenge for safe and efficient mining operations. This study carried out an engineering filed observation firstly, and by setting three main roadways as research targets, it then proposed a series of supporting strategies for each of them. Numerical model was established using RockScience Phase2 finite element software to simulate the roadway's mechanical response across all stages. Results indicated that the staged supporting strategy sequentially mitigated excavation-induced instability, roadway widening increased rib convergence, roadway heightening triggered additional roof sag. Supplementary grouting and rib bolts were testified as effective. Stress redistribution analysis revealed that grouting and bolts transferred concentrated stress from the weak coal seam to the stiff sandy mudstone. Additionally, a comparative analysis of a trapezoidal roadway variant validated the universality of the hybrid 'liner + grouting' support, which reduced yielded elements compared to unsupported conditions. This study demonstrates that phased support, tailored to excavation sequence and geological weakness, is an effective solution for roadway stability control, providing theoretical and technical references for similar weak rock mining projects.