科创中国

Transient electromagnetic responses in tunnels with strong interferences and the correcting method: A TBM example

• 摘要：

  © 2016, Science Press. All right reserved. The transient electromagnetic method is widely used in prediction of water-bearing structures in front of a tunnel face. But its decay curves are easily polluted in the environment with strong interferences, which can cause false abnormal bodies in determination. We take the Tunnel Boring Machine (TBM) as an example to analyze the influence and response characteristics of such a large metal body in tunneling to TEM detection. We obtain the TBM influences on the TEM decay curves. In addition, we establish a method to remove these influences. We use a three-dimensional finite difference time domain modeling algorithm to simulate the complex environment in tunnels. A vertical water-filled fault is designed in front of a tunnel face as the basic model. Models considering different distances between the fault and tunnel face, different resistivity values between the fault and the background, different fault sizes or thicknesses, etc. are calculated and compared with the normal model without the fault and TBM. By analyzing the simulated results, we propose a method to remove the influences from TBM according to superposition principle. The response of TBM is obtained by subtracting an only tunnel model response from a model containing tunnel and TBM responses. We consider this as the TBM influence background. In modeling or potential future field surveys, the TBM influence background can be subtracted from the total decay curves. Then, the TBM influence is removed. We design 8 groups of numerical models to test the efficiency of our method. The method is tested by comparing the decay curves and apparent resistivity between the removed data and the modeling data without TBM inside. By analyzing the modeling results of TBM, we find the following two significant results: (1) The response of TBM in a decay curve is likely a low resistivity target which will of course be a false abnormal body if not corrected in the result. Its influence is mainly in the early time. And (2) the response from the fault is focusing at relatively late time. By this, the responses of the fault and the TBM can be identified for some models with enough size or resistivity differences. We simulate the TEM responses of TBM in tunneling and analyze its characteristics in tunneling. Although the TBM responses pollute the decay curves, the abnormal body responses have different characteristics and can be distinguished from the receiver data. We show a simple method to remove the TBM influences from the total curves by subtracting the simulated responses. The method can be used to remove strong interferences of TEM detection not only in tunneling but also in other application environments including ground, airborne, semi-airborne and marine TEM.

• 作者：

  Sun Huai-Feng;Li Shu-Cai;Li Xiu;Lu Xu-Shan;Ren Bao-Hong

• 刊名：

  Acta Geophysica Sinica

• 在线出版时间：

  2016