Physical simulation of strata failure and its impact on overlying unconsolidated aquifer at various mining depths

Abstract

Underground mining severely lowers the water table and worsens the ecological environment. To determine the mechanism influencing drawdown in unconsolidated aquifers induced by deep mining combined with overburden movement, with a view to environmental protection, physical simulations for three different depths were designed to investigate and contrast deformation and fracture distribution characteristics at diverse depths after mining. The impacts on overlying unconsolidated aquifers were then analyzed by monitoring overburden movement and ground water level data, and the deformation limit was estimated. Modeling results indicated that coal mining had different impacts on the overlying unconsolidated aquifer via various mechanisms of groundwater level reduction. The aquifer outside the fractured water-conducting zone could be affected by coal mining, and the water tables dropped rapidly. The failure and the deformation features of the aquitard floor were the key to revealing the mechanism of groundwater depletion in deep mining. The effects on aquitard decreased as the distance from the working face increased. A relationship between the strata deformation and the drawdown rate was established; that is, the rate of decline of the groundwater level did not accelerate until the maximum subsidence of the aquitard floor exceeded approximately 0.9 m, or the subsidence-bending area of the aquitard floor exceeded approximately 156 m2.