Numerical simulation of the surface subsidence evolution caused by the flooding of the longwall goaf during excavation of thin coal seams

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Underground mining has a significant influence on ground movement, which induces serious environmental disturbances on land. Movements of the rock strata can be the cause of changes in the hydrogeological regimes of groundwater. As a result, the risk of flooding of the longwalls goaf increases. The specific phenomenon of the Ukrainian Donbas is the flooding of the underground roadway system at the result of the closure of the mines. Water saturation of rocks leads to a decrease in its strength. The result is repeated subsidence. The activation of the ground movement processes over the longwall goaf due to their flooding has not been studied enough. In this paper, for the geological conditions of thin coal seams typical for the Ukrainian Donbas, ground movement evolution caused by flooding of longwalls goaf was studied. Ansys code was used to analyze the evolution of surface displacement in different hydrogeological conditions. As a result of numerical simulation, it was found that full flooding of the longwall goaf leads to an increase in surface subsidence by 22.4%, while the length of the trough increase by 1.3%. Maximal inclination increases by 34.4%, and maximal curvature – by 74%. This contributes to a significant increase in hazards for surface infrastructure located on the edges of the subsidence trough. The control of the negative impact on surface infrastructure objects, water and agro-industrial objects can be ensured by a timely prediction of ground movement and the implementation of surface controlling methods to prevent critical surface deformations.