Using the Magnetotelluric Method for Detecting Aquifer Failure Characteristics under High-Intensity Mining of Thick Coal Seams

In the ecologically fragile mining area of northwest China, high-intensity mining has seriously affected the aquifer and surface eco-environment. In order to better implement water-preserved mining in ecologically fragile areas, the aquifer failure characteristics should be first detected accurately; therefore, it is necessary to find a convenient and fast detection method. Based on the analysis of the basic principles and influencing factors of the magnetotelluric (MT) method, the feasibility of using the MT method to detect aquifer failure is verified by testing the mined area with MT detection and field borehole measurement. Subsequently, the failure characteristics of overburden and unconsolidated aquifers under high-intensity mining are studied by MT detection and physical simulation. By comparing the physical simulation with the field measurement from the aspects of the maximum surface subsidence, interval of periodic weighting and step cracks, the reliability of the height of the water flowing fracture zone and caving zone obtained from physical simulation is verified. The analysis from MT detection and physical simulation shows that the results of the two methods are in accord with each other, which further confirms that the MT method can be used to detect the failure of overburdened structures and aquifers. The penetrating fractures are the main channel for the downward seepage of water resources, which is caused by the "two-zone" of overburden model and located in the "dimple" shape in the apparent resistivity (AR) isogram. It can provide a reference and technical support for the corresponding new water-preserved mining technology and the construction of digital mines.