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Abstract Practices show that the unfavorable geological body with water or mud in front of the tunnel face is great dangerous to the tunnel construction. If these unfavorable geologic bodies can not be detected，which will effect the tunnel construction progress；moreover，some engineering accidents and casualties may happen. As the transient electromagnetic method(TEM) is sensitive to the low resistivity body，and the unfavorable geological bodies usually can be equal to a low resistivity interbed，the study of the detection of the low resistivity interbed in front of the tunnel face becomes very meaningful. The TEM-equivalent conductive plane method based on the whole space theory and the apparent longitudinal conductance and its differential coefficient imaging will be used to have a forward modeling and application research on the detection of the low resistivity interbed in front of the tunnel face. Besides，a discussion on the electricity interface response character of the apparent longitudinal conductance is presented with differential coefficient imaging and the interpretation combined with apparent resistivity section contours. At last，some characteristics and laws of the detection are summed up so as to guide the actual TEM tunnel geological forecast and improve TEM detection accuracy and precision.
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Received: 03 December 2008
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