Impact of mining-induced bed separation spaces on a cretaceous aquifer: a case study of the Yingpanhao coal mine, Ordos Basin, China

During coal mining, the unsynchronized flexures of the overlying burdens that have different hardnesses and thicknesses can cause the formation of bed separation spaces in which a large amount of water can accumulate from the surrounding aquifers; this water can be stored. The impact of mining-induced bed separation spaces on a Cretaceous aquifer over water-conducting fractured zones was studied at the Yinpanhao coal mine in the Ordos Basin, China. In situ tests of the hydraulic variation were conducted using four fiber Bragg grating sensors and the strata movement was measured using 60 magnetic loops anchored at different horizons in two boreholes drilled over an active mining panel. Three bed separation spaces in the Cretaceous strata were identified at depths of about 285, 401, and 435 m, respectively. Controlled by the development of the bed separation spaces, the hydraulic variation in the Cretaceous aquifer was divided into four stages. With the approach of the mining face, the bed separation spaces extended horizontally to the vicinity of the monitoring holes which resulted in a rapid decrease of the hydraulic head. Due to the long suspending distance of the upper strata, the sudden fracture of the strata caused the closure of the lower bed separation space and an increase in the volume of the upper bed separation space, inducing an abrupt and dramatic drop of the hydraulic head of the upper aquifers in the Cretaceous strata. These test results were verified with long-term monitoring data on the hydraulic variation in different aquifers.