Research and application of response characteristics of mine transient electromagnetic perspective detection technology

Aiming at the difficulty in detecting concealed geological isomers using conventional geophysical method in ultra-wide coal working face, the electromagnetic response mechanism of mine transient electromagnetic (TEM) perspective detection with opposite side emission and reception is revealed in this study. The electromagnetic field diffusion characteristics, data influence mechanism and detection capability of transient electromagnetic perspective detection technology are studied in detail by means of theoretical research, numerical simulation and analysis of measured data. The results show that the transient electromagnetic field diffusion of the full-space elongated emission loop is different from that of the half-space electromagnetic field diffusion due to the boundary between ground and air. In the full-space state, the extreme value of the induced electromotive force (EMF) is located in the center of the emission coil for a long time, which cannot be interpreted directly by using the ground ‘smoke ring effect’. The early transient electromagnetic perspective data transmitted and received on the opposite side are mainly affected by the primary magnetic field and have high resolution and detection ability of left and right low resistance anomalies. The late data and the same-side transmitting and receiving data have the same generation mechanism, both them are formed by mutual induction and diffusion of secondary fields generated near the transmitting loop, and their resolution and detection ability are relatively weak. Compared with the transient electromagnetic method, this technology can distinguish the spatial position of the low-resistance anomaly relative to the transmitting loop and the receiving point by combining early and late data. The closer the low resistivity anomaly body is to the transmitter loop, the greater the impact on the early data received at the opposite side, and the impact time period of the late data increases, but the degree of influence is smaller. On the contrary, the closer it is to the receiving point in the roadway, the opposite the impact characteristics are. Therefore, the approximate position of the low-resistance anomaly body along the working face can be roughly determined. The transient electromagnetic perspective detection technology, which combines early and late data, can more accurately interpret the spatial information of hidden water inrush geological isomers which are inside and near the working face.