Analysis of grounded Transient Electromagnetic with surface-tunnel configuration in mining

In order to avoid the strong metal interference and gas explosion of Transient Electromagnetic (TEM) detec- tion in mines,a new configuration,which put the transmitting line source on the surface and the receiver in the under- ground mining roadways,was investigated. Its modeling algorithm was developed using finite difference time domain ( FDTD) method in three dimensions. The characteristics of this configuration was studied with numerical experiments. Homogeneous half space and layered models were used to study the curve style and its sensitivity to the earth resistivity changes. The influences from the distance between the transmitter and receiver,the receiver azimuth angle were both compared. Five lines were designed along different positions. Many useful phenomenon were obtained according to the comparison as follows:(1)The TEM responses amplitude from the broadside are quite larger than that of the inline.(2) The valid investigation depth can reach about 1. 5 km using a line source of 1 km in length. (3) The high resis- tivity coalbed has little influences to the simulated acquired data. Then,models including roof and bottom water are simulated. The receiver decay curve has obvious difference which can be used to identify the acquirer. Finally,a com- plex model including dipping fault was used in the simulation. The best azimuth angle is broadside angle. This configu- ration can identify roof and bottom water in mines,and can generally identify dipping fault. This configuration is easy for intrinsically safe design in instruments manufacturing.