Study On Multi-turn Loop Magnetic Resonance Sounding (MRS) Technique For Underground Water

MRS (Magnetic Resonance Sounding) is an effective and direct method for undergroundwater detecting. It has wide Happlication prospectHs in solving the problem of global waterresources shortage. The maximum exploration depth is about 150m (NUMIS system using150m side length loop, single turn). As the developing of the technique and extendingapplication fields for underground water detecting, new technical requirements areHcontinuouslyH proposed for MRS itself. For some new application fields such as Hwater inrushHprospecting of tunnel as well as mine and Hdam leakageH inspecting, loop size is often limitedwhich will cause am obvious exploration depth decreasing. Low exploration resolution causeby that also limited MRS application in fields such as HfissureH, karst cave and faultunderground water detecting. New techniques are required for these new application fields.The study of multi-turn loop MRS technique is conducted in the paper corresponding tothe problem above. The study is based on the enhancement of MRS exciting power andreceiving signal of multi-turn loop. In the paper, underground water with depth more than 2-3times of multi-turn loop side length is effectively detected. The paper receives Hfinancial aidHsfrom Key Projects in the National Science & Technology Pillar Program during the EleventhFive-Year Plan Period, the Hministry of educationH and the Department of Science &Technology of Jilin province.The major work of this paper is as follows:(1) Numerical simulation of multi-turn loop MRS signal for different undergroundwater is provided. MRS signal calculation method with one TX/RX loop is given based onHsuperposition Hand reciprocal principle. The calculation method of MRS exciting magneticfield and tipping angel is also discussed in passing series. With the established undergroundwater model, the initial amplitude-exciting pulse moment curve can be calculated. Thenumerical simulation result of the paper provides the Htheoretical basisH and numericalfoundataions for multi-turn loop and prototype designing as well as MRS exploration.(2) MRS multi-turn loop features are studied. As the variable impedance causes problems for multi-turn loop MRS exploration, the relations between loop inductance contains loop size,loop turn and loop paving are studied. The effective exploration depth of loops with differentsize and turn is calculated based on previous studies according to different explorationconditions. The results of effective exploration depth calculation for different loops to 6mthick with 20% water content layered underground water are provided in the paper. Thedesigning and fabrication of MRS multi-turn loop are also given.(3) The key technique of multi-turn loop MRS TX/RX apparatus is studied based onstudy basis of Jilin University. In the paper, the transmitting waveform quality, the receivingresonance matching method, very low MRS signal conditioning and dead time controlinfluenced by variable loop impedance is discussed and the corresponding solution methodsare given. Related simulation work is carried out to inspect the effect for instrumentationoperating parameters configuration.(4) The multi-turn loop MRS acquisition data processing method is studied from aspectssuch as acquisition data evaluation, acquisition data pretreatment and the acquisition datainversion. The MRS signal back-stepping and exciting pulse moment calibration methodcorresponding to MRS hardware system is mainly introduced.(5) Detailed inspection of multi-turn loop MRS hardware system key parameters iscarried out in the lab. Inspection platform is introduced and the inspecting method is alsogiven. The testing result of the improved MRS system is in consistent with the simulationresult of chapter 4.(6) According to the studies above, field experiments are carried out in Wanxingwoputest site in Jilin province. The Hgeographical positionH, natural and cultural conditions and theEM noise of the test site are analized. Relative outdoor tests are carried out to verify thesimulation result of multi-turn loop influencing experiment effect and determine theexperimental MRS parameters configuration. The testing results of 50m side length withsingle turn, 25m side length with 2 turn, 12.5m side length with 4 turn and 6.25m side lengthwith 8 turn are given. The experimental results indicate that the smaller size, multi-turn loopcan effectively detect the underground water as deep as 2-3 times of its side length. It is alsoverified that the smaller size multi-turn loop exploration achieves higher resolution forshallow underground water exploration.The key Hinnovative pointsH are as follows:(1) A more HflexibleH and practical multi-turn loop MRS exploration method is proposed.Multi-turn loop with certain side length realizes underground water as deep as 2-3 times of itsside length. The method is based on transmitting EM field and receiving signal enhancement of multi-turn loop. Series of experiments are carried out using a group of multi-turn loops inWanxingwopu testing site in Jilin province. The feasibility and effect of multi-turn loopdetecting is verified by the field experiments in the testing site.(2) A method of effective exploration depth for different multi-turn loop withdifferent size and turn calculation is proposed. The environmental noise, sensivity of MRSsystem, information of underground water (obtrained from existing Hgeological dataH) and loopimpedance are integrated in the method. The MRS exploration experience and numericalsimulation results are also considered. Effective exploration depth of different loops is thencalculated based on the conditions listed above. The method supplies a practical guidings formulti-turn loop MRS exploration for underground water.(3) The matching method of variable multi-turn loop and MRS hardware system isproposed. The method analyzes and calculates the influencing effects on transmittingwaveform quality control, receiving resonance matching, the very low MRS signalconditioning and dead time configuration. Solution method is supplied for variable testingloop and MRS hardware system. Experimental result verifies the simulation calculation andmetching method.(4) An exciting pulse moment calibration method based on transmitting waveformquality inconsistency caused by variable loops impedance is proposed. The method makes useof transmitting waveform quality calculation result and calculates the ratio (exciting pulsemoment calibration factor) of the integral of actural transmitting current and ideal transmittingcurrent. The factor is used for inversion result calibration. The method is used for multi-turnloop MRS exploration data calibration. Calibrated result is in consistent with the acturalunderground water conditions.Field experimental results verify the inference of the paper. The using of 12.5m sidelength with 4 turn loop achieves effective underground water detecting with depth of37.5-39m with about 5% water content. Also the use of 6.25m side length and 8 turnmulti-turn loop achieves 13-25m depth underground water detecting about 10% water content.The study of the paper supplies an effective and feasible way of MRS application for newapplication fields such as Hmine and tunnel water inrushH detecting, Hdam leakageH detecting,Hgeological disaster forecastHing.