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Abstract Aiming the limit of traditional transient electromagnetic method(TEM) detection in tunnels only depending mainly on 2D apparent resistivity，a method of transient electromagnetic multipoint array detection in tunnels is presented learning from the fixed-loop survey method when detecting on the ground. The calculation method of high oscillation dual Bessel integration in frequency domain TEM response of non-central vertical component is studied. Taking the polynomial of center component in frequency domain as a basis function，a polynomial of non-central vertical component in frequency domain is defined；and the polynomial coefficients are obtained by least square fitting. The formula of non-central vertical component in time domain is derived. The late-time apparent resistivity of non-central vertical component is also derived according to the late-time approximate conditions of transient electromagnetic field. Transform of non-central vertical component of TEM detection in tunnels into apparent resistivity image is realized. It is the basic theory for transient electromagnetic multipoint array detection method in tunnel. The interpretation method using three-dimensional(3D) apparent resistivity images combining the multipoint response is also proposed. On the basis of the theory studies，transient electromagnetic multipoint array detection method is studied combining the field test in one tunnel. The transient electromagnetic multipoint array detection method for water bearing structure under the tunnel floor are carried out；and the comparison and interpretation are also given about the detection results. A 3D apparent resistivity image is formed；and the 3D space distribution law is obtained by analyzing the 3D apparent resistivity image.
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Received: 30 March 2011
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2011, Vol. 30 
