Surrounding Rock Stability in Unsupported Roof Area and Rapid Heading Technique for Deep Arch Coal Roadways under Goaf

Abstract

In order to achieve rapid heading of deep arch coal roadways under goaf, the maximum unsupported roof distance (URD), surrounding rock stability of unsupported roof area and influencing factors, and rapid heading equipment and processes for these roadways are investigated in the context of the working face geology and mining conditions of Coal #9 of a certain coal mine, through theoretical analysis, numerical simulation, equipment modification, and construction process optimization. The following work is carried out: (1) Based on the thin shell theory, a mechanical model of a top cover cylindrical shell for roadways with an arch section is built. The formula for calculating the maximum URD of arch roadways is developed. The influences of roadway width, tensile strength, buried depth, and arch height on the maximum URD are analyzed. The theoretical maximum URD is worked out to be 2.4 m. (2) Numerical simulation reveals that when the URD is around 2 m, the arch roadway is free of tensile failure and the surrounding rock is well stable; when the URD is greater than 4 m, tensile failure occurs on the roadway sides, and the surrounding rock becomes less stable. Therefore, the maximum URD for numerical computation is set to 2–3 m. No additional failure occurs on the arch roof with the increase in URD, suggesting that an arch roof has the best stability. Properly increasing URD can help U-steel to gain support strength more quickly. In the shallow part of a roadway surrounding rock under goaf, failures are primarily determined by vertical stresses, whereas in the deep part, failures are determined by horizontal stresses. (3) A combined onboard standing platform + onboard beam lift device and a new onboard temporary support device for long excavation are developed as a solution to the low shed and temporary support efficiency and safety of roadways with a URD of 2.4 m and used on-site in conjunction with the optimized construction process. The result shows an average footage of over 550 m per month with a peak footage of 846.4 m and 16 supports totaling 14.1 m per shift. Additionally, the forming quality of a shed roadway is good enough to accommodate normal mining of the working face, consequently the rapid heading of the roadway.