Evaluation of a coal seam roof water inrush: case study in the Wangjialing coal mine, China

The Wangjialing Mine in southern Shanxi Province is seriously threatened by roof water and is infamous for a water inrush disaster that happened there in 2010. A root-cause-analysis was conducted. Three key issues, the height of the mining-induced fractured zone in formations overlying the coal seam, the water yield of aquifers overlying the coal seam, and working face water inflows before and after pretreatment of roof water-bearing aquifers, were studied based on the “three maps–two predictions” approach. According to the multi-source information composite principle, abundance zoning maps of the roof aquifer were made using the overlapping function of geographic information system (GIS) for five controlling factors: aquifer thickness, total core recovery, drilling fluid quantity, permeability, and thickness of brittle and plastic strata. Borehole-specific data from in-situ pumping tests were used to verify the water abundance results. For areas that did not meet the verification requirements, the weights of the controlling factors were calibrated by reestablishing the analytic hierarchy process judgment matrix. The total height of the fractured zone within the #2 coal seam roof was calculated using an empirical formula. An established roof crack safety zoning map was used to evaluate that aspect. A three-dimensional numerical simulation of the groundwater flow system was established based on the site conceptual model of the roof aquifer and was used to predict the working face inflows. The results indicated that the 20,518 working face of the 205 panel had the greatest abundance of water.