Optimization of transient electromagnetic method for detection of water accumulation in coal mine goaf

Mine transient electromagnetic method (MTEM) is a great method to detect abnormal water body, but it is easy to be disturbed by the complex engineering geological conditions of the roadway and the equipment environment. Therefore, targeted optimization is necessary to enhance the data acquisition quality and interpretation accuracy. Based on the “smoke ring” diffusion theory, the detection principle of transient electromagnetic method and the vertical differential interpretation method of apparent resistivity are expounded. The influence of the main acquisition parameters on the electric field response characteristics of TEM is analyzed and compared through the transient electromagnetic detection test of known water accumulation in goaf; combined with the vertical differential interpretation method of apparent resistivity, a data acquisition and processing optimization scheme of mine mined-out water detection by transient electromagnetic method is proposed and its effect is evaluated. The results show that the closer the distance between the coil and the roadway surrounding rock, the higher the coupling degree between them, and there is a reasonable range of the distance, beyond which the voltage response received by the coil is too low, which does not meet the requirements of the data on the signal-to-noise ratio. Increasing the stacking times can improve the signal-to-noise ratio and effectively suppress the distortion of the tail branch of the voltage attenuation curve. The reasonable distance range applicable to Gaojialiang Coal Mine is 0-0.5 m, and the stacking times are 64 times.