Method for evaluating the possibility of water inrush from coal seam roof aquifer

In order to develop the method for evaluating the possibility of water inrush from coal seam roof aquifer in China, combined with the geological and hydrogeological conditions of typical mines in Huanglong coalfield, this paper defines the coefficient of water inrush and proposes the standards and method of "the coefficient of water inrush method" to evaluating degree of water inrush from roof aquifer, and also gives the typical map of water inrush type such as "R-H grid map" and "R-H triangle map". In addition, this paper defines the "coefficient of water inrush" as "the product of ratio of thickness of aquiclude between coal seam and main aquifer and ratio between thickness from the height of water flowing fractured zone to the bottom of the main aquifer and distance from the coal seam to the main aquifer", and also gives the calculation formula. There are three types and five forms of water inflow from roof aquifer in Huanglong coalfield. Three types of water inflow include continuous water inflow from roof aquifer, water inflow from coal seam roof separation space, and water inflow with sand/mud from roof aquifer. Five forms of water inflow include small water inflow from roof aquifer, huge water inflow from roof aquifer, occasional water inflow from coal seam roof separation space, frequent water inflow from coal seam roof separation space, water inflow with sand/mud from roof aquifer. The research results show that: According to the value of "coefficient of water inrush", the water inrush from coal seam roof aquifer can be divided into four grades. At first level (D>0.2), the water inflow is small and its influence is also small. At second level (-0.25<D≤0.2), the water inflow and its influence are all moderate. At third level (-0.5<D≤-0.25), the water inflow influence is great and threatening. At fourth level (D≤-0.5), the water inflow influence is extremely great and extremely threatening. The criteria of water inrush from roof aquifer in Huanglong coal field consist of small water inflow from roof aquifer, ranging 120 m<H<190 m and 0.41<R<0.54 and -0.50<D<0.12; huge water inflow from roof aquifer, ranging 60 m<H≤120 m and 0.24<R≤0.54 and D≤-2.0; frequent water inflow from coal seam roof separation space, ranging 190 m≤H<250 m and 0.54≤R<0.80; occasional water inflow from coal seam roof separation space, ranging 250 m≤H<320 m and 0.54≤R<0.80; and water inflow with sand/mud from roof aquifer, ranging H≤60 m and R≥0.80. 3) This paper also gives the typical map of water inrush type of Huanglong coal field, such as "R-H grid map" and "R-H triangle map". When using these two maps, firstly the values of R and H of the mine are calculated, secondly, the area of the mine is drawn in the maps, then, it is easy to find the water inrush type of the mine. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.