Research Of Launching System In Tunnel Geological Exploration Based On The Transient Electromagnetic Method

The construction of underground engineeringis always extremely difficultdue to theconcealment and complexity of the geological environment underground engineering, aswell as the uncontrollability of the influencing factors from the surrounding environment.In order to ensure the healthy and harmonious construction of the subway and provide astrongscientific basis of decision-making for the design and construction department, it isparticularly necessary to conduct a deep research for the advance geology predictiontechnologyof thetunnel construction, andmore widelyapply it tothe practical field.Basedon the principle of detection of the transient electromagneticmethod,this papermakes a comprehensive analysis for the exploring ability that applied to the advancegeology prediction technology, and complete the formula deduction for the receivinginduced electromotive force when applying the overlapping loop-line launcher and centerloop-line launcher. The article has given a detailed description for the three devices oftransient electromagnetic method, analyzed the application scope and performance of thevarious devices, planned to accept center loop-line device as transmitting and receivingdevices of transient electromagnetic method. As the center loop-line method has the bestcouplingwith the target layer and littleinfluenced by lateral tilteffects and layer bit small,moreaccurate geologicalinformation can be gained from themeasuring.For the more widely application of transient electromagnetic method into the tunneladvance geology prediction, this paper conducts a research for the model of transientelectromagnetic transmitter coil. First, the formula of the magnetic induction is deduced,whichinducted by the rectangular transmitting coil within any spot of space.AccordingtotheBiot-Savart law,magneticfield distribution has been analyzed and calculated in detail,which is generated by launching rectangular coil for the central loop method.While at thesame time,Matlab is adopted for the numerical simulation of magneticfield strengthof thecalculated rectangular coil and the results obtained are consistent with the theoreticalcalculation. Apart from this, HFSS is used for finite element simulation. After the establishing of the finite element model of the transmitter coil, the magnetic field distribution within a certain space is analyzed. The final HFSS simulation results are in accordance with the numerical simulation of the MATLAB. The field strength of the coil at four corners is strong when Z=0and the rest of which are strong in the middle apart and weak around. After completing the analysis of the effect of the parameters of the emission source on the transient electromagnetic response, it is concluded that the induced electromotive force of the receiving coil is proportional to the emission current of the transmitter coil but not always proportional to the transmitter coil area, with whatever transient electromagnetic emission device. Compared with the deep geological exploration, the emission frequency of shallow geological exploration should be larger, while the turn-off time off should be shorter.This paper provides a theoretical basis for the practical analysis for the launch part of the transient electromagnetic method, which is useful to the structure design and optimization of the transient electromagnetic launchers.