Stability of roadway in upper seam of deep multiple rich gas coal seams through ascending stress-relief mining

The first mining of a protective coal seam through ascending stress-relief mining is one of the most effective techniques for eliminating the risk of coal and gas outburst during the exploitation of multiple coal seams containing high rich gas. However, the difficulty of controlling roadway stability in the upper protected coal seam above the goaf increases greatly after ascending mining. Based on the geological conditions in Guqiao Coal Mine in China, a numerical simulation model is established by means of Itasca’s Fast Lagrangian Analysis of Continua (FLAC) software in order to analyze the influence of the ascending mining on the stress distribution of the overlying rock strata and the stability of the roadway with different support parameters in the upper protected coal seam. The results show the impact scopes of stress relief and concentration zones in the overlying rock strata are up to approximately 100m and 90m above the goaf. The vertical stress, plastic zone and displacements in one sidewall of the roadway in the upper protected coal seam are bigger than that of the other sidewall close to the underlying goaf side. However, the stability of the roadways can be improved efficiently by using the appropriate support scheme including high strength and pre-stressed thread steel bolt support combined with pre-stressed cables. Field measurements indicate that the displacements of the surrounding rock could be controlled efficiently in 41 days when the roadway is excavated in the upper protected coal seam above the goaf with a compaction duration of 150 days.