Three Dimensional Parallel Simulation Of Transient Electromagnetic Response Of Tunnel Boring Machine And The Elimination Of Its Response

TBM (Tunnel Boring Machine) will cause heavy influence on the TEM prediction ofhazardous targets in front of a tunnel face. The TEM response of TBM and the relationship ofTBM and hazardous targets are simulated using three dimensional finite difference timedomain method. Different models with water-filled faults in front of a tunnel face togetherwith the existence of TBM in the tunnel cavity are simulated. In order to make a fine mesh ofTBM, a grid with a size of0.2m is used in the forward modeling. Optimized GPU parallelalgorithm is developed for the purpose of speeding up the computational process.The air in the tunnel cavity is approximated with high resistivity media in the forwardmodeling process, thereafter, the empirical formula which is used in the stability condition isno more satisfactory in this case since it will produce an extremely small time step. A newempirical formula of stability condition is proposed in this paper based on a large amount ofsimulation results.The response of TBM is slightly influenced by the water-filled anomalous target judgingfrom the decay curves, and the response of TBM is restricted into the very early time period.The response of the anomalous body in front of a tunnel face can be easily distinguished fromthe decay curves containing the response of TBM when the distance between the anomalousbody and the tunnel face is long enough. However, the response of anomalous targets in frontof a tunnel face can be no longer distinguished if the size of which is very small or thedistance mentioned above is short, and as a result of which the influence of TBM must beeliminated before any kinds of processing procedure with the measured data. An eliminatingmethod of the TBM disturbance is proposed in this paper: first of all, the response caused bythe TBM is derived through the modeling, then minus this response from the measured data.At last, the remaining data can be considered as the approximate response caused by theanomalous body in front of a tunnel face.