Three step-drawdown dewatering test in unsteady flow condition: a case study of the Siwan coal mine in North China Coalfield

A dewatering test is a common tool to estimate the physical properties of water-bearing layers in coal mines. The three step-drawdown dewatering test of unsteady flow, which combines both steady and unsteady flows, is designed in this study. The test design involves the identification of hydrogeological conditions, calculation of hydrogeological parameters, and prediction of mine water yields, particularly those of the Siwan coal mine in the coal mining district of Hebi. The results show that the water storage and the abundance of the second limestone aquifer in Taiyuan formation (L 2 ) is limited and easy to drain, while the Ordovician system aquifer (O 2 ) lateral recharges the L 2 by the F 8 fault. The correlation curve method, the cone balance method, and the analytical method are conducted in this study. Results show that the average water yield was 1436.1 m 3 /h when the water level of L 2 decreased from + 127 m to + 17 m. The three step-drawdown dewatering test not only provides ways to enrich the experimental data and reveal hydrogeological conditions, but it can also be adopted in several approaches to predict mine water yields.