A Review of Electrical and Electromagnetic Methods for Coal Mine Exploration in China

During the past 20 years, due to the rapid development of China's economy, the amount of coal mining activities has rapidly increased, which has led to a large increase in the number of mined-out areas. Therefore, the role of geophysical exploration in coal fields has changed from the detection of coal resources to engineering geological environmental investigation. The safety, efficiency, and green production of coal mines require more advanced geophysical detection technologies. In particular, the accurate detections of the locations of water-rich mined-out areas, as well as concealed water diversion channels, have become the main focuses of coal electrical methods in recent years. Therefore, electromagnetic methods have become the main means of hydrogeological investigations and deep explorations in mine-out coal areas. In this study, a common DC method was briefly introduced, along with an induced polarization method. Then, three representative electromagnetic sounding methods, including a surface frequency-domain electromagnetic method, time-domain electromagnetic method, surface to air electromagnetic method, and mine electromagnetic method, were respectively introduced.