Study On The Mine Tunnel-drilling Transient Electromagnetic Method And Its Application

Transient Electromagnetic Method(TEM) has been widely used in prediction of coal mine disasters. Tunnel-drilling Transient Electromagnetic Method(TDTEM) is a drilling-inside detection method based on the traditional TEM, which uses underground tunnel space and several kinds of drilling on exploration. The Tunnel-drilling Transient Electromagnetic Method includes the mode of Drilling-Transmitting-Drilling-Receiving(In-Transmitting-Receiving, ITR) and the mode of Tunnel-Transmitting-Drilling-Receiving(Out-Transmitting-In-Receiving, OTIR), they work alternately for response signal feature extraction of water bearing structure of surrounding rock of the drilling and the change of surrounding rock in the drilling process, and determine the situation of water bearing structure and the change of surrounding rock's lithology.The research of Tunnel-drilling Transient Electromagnetic Method plays an important role in coal mine safety production and cost-saving, so this paper will determine the effectiveness of this method by theoretical formula derivation, physical simulation and field practice of the two modes of Tunnel-drilling Transient Electromagnetic Method. The contents and results of each part of the paper are as follows.(1) The paper introduces detection principle of the mode of ITR and the mode of OTIR in Tunnel-drilling Transient Electromagnetic Method, derive the receiving signal response formula of the mode of ITR by using the whole space response formula of the oblique step field source; derive the logarithm geometric distance theorem by using response signal feature of the mode of OTIR and image feature of double logarithmic coordinate system; derive receiving response signal feature of the mode of OTIR by using the response values of horizontal component and vertical component of magnetic field.The receiving probe of TDTEM is composed of two transmitting loop lines that transmit the same size opposite direction of magnetic field and six receiving loop lines that without using radial probing direction. Therefore, its working principle and signal response characteristics have a great difference from the traditional TEM. We can grasp the characteristics of the response curve better by analyzing of the response principle. Because of the response can get lots of "negative" information, and general double logarithmic coordinate system cannot meet the requirements of its image display, therefore, through deriving logarithm geometric distance formula conducive to the display of images and standardize the specifications of the size of signal response.(2) By utilizing indoor conditions and according to TDTEM response mechanism, the author designed physical simulation experiment with different work mode to detect low resistivity anomaly bodies with different angle and distance, and anomaly bodies with different lithology and angle. The following conclusions are obtained through physical simulation:(1)TDTEM has the ability to distinguish the electric interface, and it has a high resolution accuracy;(2)TDTEM has the ability to judge the distance between the electrical interface and the borehole;(3)TDTEM has the ability to distinguish strata with great difference in geoelectric characteristics;(4) TDTEM has the ability to judge the development of electrical interface; at the same time, The logarithm geometric distance formula does contribute to the analysis of the "negative" response signal, and provide the judgment standard for the response value.(3) A field test is conducted with TDTEM to prove the practicality and effectiveness of TDTEM by actual exploration in tunnel and drilling of a mine. Through the analysis of the data of the detection signal and the image of visual equipment, we can obtain the relationship between the response signal, the change of lithology, and the rock fragmentation degree. Therefore, TDTEM can reduce the cost of drilling effectively, and obtain more abundant geological data.