Study On Transient Electromagnetic Response Characteristics Of Borehole And Water Body Positioning

TEM has the advantage of being sensitive to low resistivity targets,so it is often used to detect water bodies in ground and tunnel engineering.In the transient electromagnetic detection on the ground,a rectangular loop is usually laid on the ground as the emission source,and the secondary field is collected in the loop;in the advanced detection of the tunnel,the loop source is laid on the tunnel face.However,due to the launch magnetic moment,detection depth,size and other factors,conventional TEM detection can not meet the requirements of large depth and small target detection.In view of the fact that advance drilling is often arranged in the engineering investigation and tunnel advance detection,this paper studies the method of transient electromagnetic detection of drilling which is transmitted from the ground(or tunnel face)and received in the drilling.Compared with the conventional method,the borehole TEM detection method has the following advantages:the existence of the borehole makes the receiving probe closer to the detection target,and the observed response signal will be stronger,which is conducive to the detection and identification of small targets.At the same time,the detection depth of the method depends on the depth of the borehole,and large depth detection can be achieved by increasing the magnetic moment of the transmitting coil.However,the response characteristic of different types of abnormal targets to borehole transient electromagnetic is not clear,and the method of abnormal location is lack of applicability.In view of the above problems,based on the finite-difference time-domain method,this paper studies the response law of the detection method of borehole transient electromagnetic.In the study of the three-component response characteristics of borehole transient electromagnetic on the ground and tunnel face,a water positioning method based on the total field is proposed.Combined with the characteristics of typical geological disasters,a series of three-dimensional geoelectric models containing anomalous bodies were designed and forward simulated,and the three-component time-channel response curve of borehole transient electromagnetics was drawn to verify that the borehole transient electromagnetic response to different horizontal and vertical orientations Azimuth targets are sensitive.After that,the tunnel model was designed and the three-dimensional transient electromagnetic response of the tunnel face was further studied.Based on the analysis and research of the transient electromagnetic response characteristics of the borehole,the models of different spatial position parameters are further studied and compared,and the three-component response characteristics of the borehole transient electromagnetic total field are analyzed and interpreted,and the positioning based on the total field is proposed.Method,thereby optimizing the data processing process and maximizing the retention of the effective information of the original data.The research content in this article has reference significance for the follow-up research and practical engineering application of borehole transient electromagnetics.It also provides a method and theoretical basis for water positioning for ground transient electromagnetic detection and advanced prediction of tunnel face.