Evolution mechanism of water-flowing zones and control technology for longwall mining in shallow coal seams beneath gully topography

The height and evolution mechanism of fractured water-flowing zones are of great importance for prevention of water inrush disasters and protection of immediate environments, particularly in ecological vulnerable areas. In this paper, comparative approaches including empirical formula calculation, physical simulation, numerical simulation and PROTEM transient electromagnetic analysis are employed to identify the development of the fracture zones caused by water-flowing so as to ensure mining safety and protection of groundwater in shallow coal seams beneath gully topography. An empirical formula was used to calculate the height of the water-flowing fracture zone, and an experimental study utilizing a model based on a similar material was adopted to analyze the movement and fracture development of the overlying strata. Results provide a reasonable basis from which a rational mining height may be determined. The PROTEM transient electromagnetic apparatus was employed to detect the water-flowing structure conductivity of the overlying strata induced by mining beneath gully topography in the field. The water-flowing fracture of the overlying strata can be estimated according to comprehensive analysis of the apparent resistivity changes of the field, gully surface crack development and aquifer water level. Accordingly, the control technologies in the field were implemented and discussed regarding preventing gully water from rushing into underground mining spaces through water-flowing fracture zones. Results indicate that safe and efficient mining of shallow seams beneath gully topography can be achieved by prevention of gully accidents and protecting the surface water resources of the ecological environment.