Mechanism and Safety Mining Technology of Overall Instability-Induced Rockbursts of Multi-Coal Seam Spatially Isolated Working Face

The isolated working face has always been the hardest hit area for the occurrence of rockburst, and the spatially isolated working face with multiple coal seams is often easily overlooked due to its hidden nature, which leads to the occurrence of rockburst accidents. This paper takes the Liuhuanggou coal mine (9–15) 08 isolated working face as the engineering background, used field research, theoretical analysis, numerical simulation, and field monitoring, investigated the coal body stress evolution law during mining, and revealed the overall instability rockburst mechanism of the working face and deduced the limit advance distance when the working face was in a state of boundary instability. The research results show the following: (1) with the increase of advancement, the overlying strata on the working face are dynamically transformed from the “C†spatial structure with hollowing on both sides to the “θ†spatial structure with coal body support in the middle; (2) when the dynamic load stress on the coal body of the working face exceeds 1.5 times its integrated compressive strength, there is a risk of overall instability rockburst; (3) when the working face advances to 430 m from the open cutting, the superimposed stress on the coal body exceeds its comprehensive compressive strength and reaches a critical instability state, which is verified by numerical simulation. Based on the analysis of the mechanics and mechanism of the overall instability rockburst of the working face, this paper proposes a set of targeted safe mining solutions: (1) The joint monitoring system of microseism-stress-drilling cutting is adopted to monitor and warn the dangerous rockburst areas. (2) The “rockburst-gas†drilling technique is used to unload the pressure on both sides of the working face and the coal wall. (3) The mining speed shall not exceed 3.2 m/d when the working face is mined before 350 m, and shall not exceed 2.4 m/d when the working face enters the influence area of mined-out LW(4-5)02 (350∼550 m). The microseismic monitoring results and field practice confirmed the reasonableness and effectiveness of the safe mining technology plan.