All-time data analysis of transient electromagnetic method for tunnels and investigation on 1∶1 water model

Considering the transition of receiving system and the turn-off time of currents, the expressions for impulse response function, primary electromotive force and secondary all-time induced electromotive force are derived. On this basis, the all-time response signals received by receiving coil are restored. The comparative analysis of the receiving and theoretical all-time data shows that the turn-off time of currents and the transition of receiving system distort the early and middle window time data, resulting in undistinguishable electrical information obtained by data processing in short range ahead of tunnels. To assess the impact of aberration data on the advanced water detection in a tunnel, a 1:1 quantitative sump model ahead of the tunnel is established. Through the continuous observation and analysis of the transient field data in different water less than 100 m³, the transient exception response characteristics of water are obtained. It is shown that the response time of the water model is within the time range of the aberration data, and it is further indicated that the technology of advanced water detection must be improved to increase the advanced forecast accuracy.