Mechanical response mechanism and temporary support for unsupported roof area in coal roadway excavation

This study investigates the mechanical response mechanism and temporary support method of surrounding rock in coal mines under varying unsupported roof distances, with 9103 transportation roadway of Wangzhuang coal mine taken as a case study. We established a mechanical model of shallow surrounding rock in the unsupported roof area of coal mines by drawing on the thin slabs and universal falling arch theories, where an expression of the maximum unsupported roof distance was derived. Numerical simulation was conducted using FLAC 3D software to simulate the spatiotemporal evolution of deformation, stress, and plastic zone of surrounding rock in roadway with varying top spacing. Results show that: identified roadway width, the tensile strength of the roof, the load on the roof, and the thickness of the shallow separated rock mass as main controlling factors affecting the empty roof distance. As the unsupported roof distance increases from 0.5 m to 1.0 m, 1.5 m, and 2.0 m, the increments in roof subsidence are 4.82 mm, 3.67 mm, and 8.31 mm, respectively, showing an initial steady subsidence followed by an accelerated trend. The minimum vertical stress at the center of the cross-section along the excavation direction decreases from 7.85 MPa to 1.24 MPa. When the unsupported roof distance increases to 2.5 m and 3.0 m, internal damage in the surrounding rock intensifies, leading to surface deformation instability. The critical value for a reasonable unsupported roof distance is determined to be 2.0 m. To address the limitations of the temporary support device of the coal roadway, we proposed a new type of machine-mounted temporary support device, and its sufficient supporting capacity is verified using Ansys software. The 9103 transportation roadway adopts this support device, the excavation speed is increased by 33.3 % by increasing the cyclic feed of the roadheader and through the parallel operation of knocking on the top and temporary support.