Tunnel Lead Based On TEM Forward Inversion Study Of Prediction

Transient Electromagnetic Method,also known as time-domain electromagnetic method,is a pulsed magnetic field formed in the front geological body by inputting a rectangular pulse current into the ungrounded loop or the grounded electric dipole.After the sending current is shut off,the geological body will be excited to spread forward and outward due to the changes of magnetic field.By observing the secondary field generated by the induced eddy with the change of time,The secondary field with rich geological body information is extracted and analyzed.At last,the data is processed and interpreted.There are many types of transient electromagnetic method prospecting equipment,and the center of transient electromagnetic loop device is one of most widely used prospecting equipment due to its close observation location and observation is only the secondary field,with high work efficiency,strong layering ability,high exploration precision,TEM is widely used in mining,water conservancy,railways,traffic engineering and other fields.Based on the field working environment of advanced prediction of road tunnel,and the water-logged stratum being forecasting object,the central loop transient electromagnetic device can not only effectively cope with the relatively narrow working environment,but also has sensitive response to the low resistivity anomaly body.There for the center of transient electromagnetic loop device can be used as a common and reliable method for a tunnel advanced prediction.This thesis first introduces the present situation of several methods which are appliedin tunnel geological prediction in China,and analyzes the advantages and disadvantag es of these approaches as well as their development trends.Then the working mechanis m of TEM is explained,and the exploration principle and methods of TEM center loop device in tunnel are also described in detail.In the prospective of theory,theoretical res earch is first conducted and then the solutions of transient electromagnetic response in homogeneous half space and multi-layer homogeneous medium are studied and derive d.Finally the solutions of time domain of transient electromagnetic response in central loop are obtained.On this basis,the matlab language is adopted to write the forward pr ogram,and the transient electromagnetic response characteristics under different parame ters are analyzed and discussed by combining the homogeneous half space model.Furt hermore,the typical two and three-layer geoelectric models are calculated forward.By analyzing the characteristic changes of electromagnetic response of the above models,t he corresponding conclusions are gained and the central loop transient electromagneticmethod is further understood.For the definition of the total apparent resistivity of the center loop transient electromagnetic,the conventional method is used to acquire the definition formula of the early and the later apparent resistivity by magnetic field intensity or induced electromotive force and based on that,the total apparent resistivity is to be calculated.The smoke ring inversion is carried out by using the whole-period apparent resistivity calculation model,and the typical two-layer and three-layer geoelectric models are selected for the smoke ring,and the results of detecting low-resistance and high-resistance anomalies in the whole-period central loop transient electromagnetic by changing the thickness of the middle low-resistance and high-resistance anomalies in the k-type and h-type geoelectric models are studied and verified.Finally,by combining with on-site application examples of transient electromagnetic loop device,collecting data of different treatment on the spot,and drawing the pseudosection of apparent resistivity of late-time and all-time apparent resistivity and analyzing the results of different approaches,it fully proved that the central loop transient electromagnetic whole period of the apparent resistivity method can obtain more accurate stratigraphic information and more obvious low resistivity anomalies reaction according to the results of the subsequent tunnel operation,which can provide more accurate advanced forecasting for the tunnel construction.