Zhipeng Qi

Multi-component and multi-array TEM detection in karst tunnels

Emerging applications of transient electromagnetic methods (TEM) in tunnelling require higher resolution on the distributions and shapes of low resistivity bodies, such as karst water and karst pipes, using multi-component and multi-array receivers. However, there are no apparent resistivity definitions for both vertical and horizontal components with offsets inside the loop. Although the raw field can show the differences of the earth electric structure, it is not straightforward. Apparent resistivity is very convenient and easy for engineers. We have developed a method for multi-component and multi-array TEM which can be applied in tunnelling and defined the expressions of apparent resistivity. This method takes advantage of the difference in resolution among components. A homogeneous half-space model and four typical three-layered models are used to test the effectiveness of the new definition. A field case history is carried out and analysed to demonstrate the viability of this technique. The results suggest that it is feasible to use the technique in tunnelling, especially for identifying the spatial distribution of karst water and karst pipes.

Practice of TEM tunnel prediction in Tsingtao subsea tunnel

Summary Introduce the TEM tunnel prediction and its application in Tsingtao subsea tunnel. Give an introduction about the apparent longitudinal quadratic differential conductance imaging method. It has the characteristic of more sensitivity to geological surfaces. Finally, give a field test case of TEM prediction in Tsingtao subsea tunnel. The result forecast two water bearing structure ahead of the tunnel face successfully.

Technology of transient electromagnetic synthetic aperture method in tunnel prediction

Summary As an electromagnetic induction method, TEM (transient electromagnetic method) is sensitive to low resistivity water-filled fracture zone, and has made some achievements in the advanced prediction. However, as the geological and hydro geological conditions encountered in the excavation of buried long tunnel become more and more complicated, it is difficult to forecast the water hazard problems in the construction process of complex geological conditions, so new interpretation methods that fit to such conditions is in urgent need. In this paper, the principle of transient electromagnetic synthetic aperture method is introduced. Firstly, we get longitudinal conductivities with equivalent conductive plane method. Then, by borrowing ideas from synthetic aperture radar, correlation superposition can be used in the processing of differential conductance signals. Lastly, draw profiles with synthesized signals and give a joint interpretation combined with apparent resistivity sections. The results of imaging and interpretation for measured data have shown that this method is sensitive to geological disasters in front of the tunnel face, and compared with previous methods, the resolution has improved greatly.