Research On Media Materials And Electromagnetic Propagation Characteristics In Front Of Shield Machine

It is very important to discover the geology in front of the tunnel in advance in the process of the shield machine excavation because it can provide quite accurate geology data for the construction, adjust the construction craft in time, reduce and prevent the occurrence of the engineering accidents. This paper mainly studies two methods of the geological detected situation: Direct current resistivity and alternate current induced polarization method. And to study the chances of electromagnetic propagation in the two methods when media materials abnormal depth, resistivity changes. At present, most of us use the direct current resistivity in China, which uses the existing direct current resistance equipment plus a "control panel" will be able to achieve wild field observation. Difficult work of the current polarization in the electrical method is not easy to guarantee stabilities to the voltage between measuring electrodes and natural potential differences. But because DC induced polarization method simulation result to be possible to carry on compared to rightly with its corresponding value analytic theory formula, this article also carries on the related introduction and the simulation to it. The AC induced polarization method in the frequency domain for observation. The AC electrical method to be possible to use the small supply current, thus reduces the equipment to AC induced polarization. In recent years, the AC electrical method more and more places to bring to the domestic physical prospecting attention.In order to explain the influences of the different media materials on electromagnetic propagation characteristics correctly, this article applies the ANSYS finite element to carry on the massive numerical simulations of the DC resistivity and AC Induced polarization methods. Before this article first reviewed the research present situation which in the electrical prospecting the shield machine, tunnel forecasts in advance, summarized existing induced polarization methods of the numerical simulation, introduced the ANSYS finite element software's major function simply also the main steps and the attention key questions during the process of the induced polarization method to numerical simulation .It introduced the potential electric value and the variation question nearby the point source field, and prepared for corresponding computational procedure with APDL language which is provided to practical ANSYS itself, also to analog computation result and theoretical value comparison. Then introduction of the AC induced methods to the electric principle, which carries on the related simulation in the frequency domain.Summarizes the full text finally, It shows that the importance of different materials on the electromagnetic propagation characteristics, it can infer the abnormal situation in front of shield machine correctly.