Development of a New Electromagnetic Tool for Evaluation of Ground-water Environment

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The Electromagnatic (EM) method is presently applied in civil engineering surverys to compliment the seismic method. With the EM method, we can measure the conductivity of base rock without electrical contact at the surface. Theoretical and exprimental studies of EM tools for in-situ resistivity measurement have not been well covered in available literature.This study explains the principles of focusing techniques, which have been applied in the method, and shows the effectiveness of a new EM tool with double transmitter loops for focussing. Focussing techniques were originally developed for induction logging where the measurements have to be carried out in a high conductive environment and the detective of the surroundings are less sensitive by the water and mud filled around the sensor. With the usage of two or more coil technique this situation can be greatly improved.Now, this technique has found its application in the surveys not only under borehole but also on the surface, especially in the surveys for civil construction.Several numerical experiments were carried out to examine the main features of the relation between the response and the underground conductivity. The results of several numerical experiments have shown the effect of near surface inhomogeneity can be canceled by using this new tool.And the scale modeling system for resistivity measurement has been developed. The results of physical modeling proved the truth of numerical experiments.Furthermore, the test system for in-situ resistivity measurement has been developed, and used for in-situ resistivity measurements. The results show that the measurements are in their resonable range compared to the simulation results. But problems still remain due to imperfect system's construction and further improvement is expected.