Abstract: Three-dimensional numerical simulation has been carried out to test the theoretical models and high-resistance gob area models in coal mine based on the geophysical model established according to the actual geological conditions of the opencast mine in Hailaer. The response characteristic and distribution law of transient electromagnetic field have been discussed and the parameter of time-depth conversion has been determined. The numerical results show that Transient electromagnetic method can clearly reflect the shallowly-buried and extremely thick high-resistance objective underground. The level curve of the apparent resistivity has a drastic lateral variation, with a camber and concave line, which indicates that it is the high resistivity anomaly area. And numerical method has similar conclusions with physical experiment for the geologic model. For a given geoelectric model when choosing time-depth conversion parameter γ=1.1 or 1.2, the error is small. The applied result shows that: for the inter-mining coal pit, with the buried depth less than 100 meters, as long as a reasonable parameter is chosen, TEM can find out the small mine gob area with over 5 meters in diameter and its distribution range and depth.

Key words: small mine gob area, transient electromagnetic method, numerical simulation, time-depth conversion