Overlying Strata Structure Evolution and Engineering Practice Based on the Mining of Lower Liberating Seam in Deep Bursting Coal Seam Group

Abstract

Suncun coal mine in Xinwen mining area is a typical deep rockburst mine. And the main mining seams are the No.2 and No.4 coal seams. The No.2 coal seam is with the weak bursting liability, and its roof and floor with the strong bursting liability; the No.4 coal seam and its roof and floor are with the weak bursting liability. In order to ensure the safe production of mine, the No.4 coal seam should be chosen as the liberating seam and firstly mined. Therefore, first of all, the upward mining feasibility of coal seam group is studied by theoretical analysis method, and then the structural evolution, fracture development and stress distribution characteristics of overlying strata in stope after mining of No.4 coal seam are studied by numerical simulation method. The research results show that the mining of No.4 coal seam do not destroy the mining condition of No.2 coal seam, instead, it can effectively reduce or even eliminate the bursting risk in the process of No.2 coal seam mining. Based on the above research results, the No.4 coal seam was mined by the following prevention and control rockburst measures, namely: the large-diameter borehole for pressure relief of coal mass, and the drilling cutting method for effect test and evaluation. Besides, the borehole stress sensors are used to monitor and analyze the pressure relief effect of No.2 coal seam after mining of No.4 coal seam. The in-situ monitoring results show that the implementation of large-diameter pressure relief borehole in the front of working face can effectively ensure the safe production in coal seam with weak bursting liability; and the mining of liberating seam is an effective measure for safe production in coal seam with strong bursting liability.