Construction of evaluation index system for water abundance of karst aquifers and risk assessment of water inrush on coal seam roof in Southwest China

Southwestern China is the largest contiguous bare carbonate distribution area in the world. Due to long⁃term karst process in this area，many forms of karst such as karst caves，depressions，sinkholes and disappearing streams are widely distributed in the carbonate strata of Wujiaping formation，Changxing Formation and Yulongshan section of Yelang formation on Permian coal seam roof. The water abundance of karst aquifers above coal seam roof has its own features such as spatial heterogeneity and anisotropy. During the process of coal mining，once the water⁃flowing fractured zone reaches the area of abundant water，it is easy to cause water inrush disasters. According to the occur⁃ rence characteristics of karst groundwater in Southwest China and based on the effects of factors on the water abun⁃ dance of aquifers， 12 evaluation indexes were determined from five aspects in this study， which are the degree of karst development，the lithology association of aquifers，geological structures，the hydrogeological parameters of aqui⁃ fers，and topography and landform. A comprehensive evaluation index system for the water abundance of karst aquifers above coal seam roof in southwest China was established. On the basis of this，an evaluation model of water abundance of karst aquifers above coal seam roof was constructed based on GIS and network analytic hierarchy process (ANP)， and the subdivision of water abundance of karst aquifers above coal seam roof of a typical coal mine was achieved. Be⁃ sides，according to the spatial distribution differences of mining thickness，mining depth and lithologic combination，a figure of calculation of subdivision of water⁃flowing fractured zone was made. By carrying out the numerical simula⁃ tion calculation of coal seam mining process under different geological conditions，the calculation results of the heights of water⁃flowing fractured zone in different subdivisions in the typical coal mine were obtained. The possibility of water inrush can be assessed by comparing the height of water⁃flowing fractured zone with the floor elevation of target aquifer. Specifically，when the water flowing fractured zone reaches the aquifer，the risk of water inrush can be deter⁃ mined according to the water abundance of the aquifer. Based on this principle，the risk of water inrush at coal seam roof of typical coal mine was subdivided and evaluated，and the accuracy of the evaluation results was verified by com⁃ bining with previous water inrush cases. The evaluation method of water abundance of karst aquifers and risk of water inrush at coal seam roof in southwest China proposed in this study can provide certain reference for the research in the related fields.