| China has extremely high density of underground construction, many kinds ofgeological engineering, and faces complex geological conditions and serious disasters,particularly the risk of water-induced disaster.Currently, the detection methods ofunderground water are all based on the rock structure or electrical parameters of theformation to indirectly determine the location and size of the sudden and gushingwater body, which belong to the indirect detection method. Magnetic ResonanceSounding method for direct detection of groundwater is the most effective method inthe world, which is capable of direct detection ofthe hydrogeological parameters, likewater content, porosity and aquifer location of sudden and gushing water body.However, due to the influence by the confined space in the underground,MRSmeasurementmust reducethe antenna size. Furthermore, the small size of the antennacauses very weak signal, poor excitation energy output and high detection systemperformance and other difficult technology problems. Therefore, this method has notbeen applied successfully to the underground project all around world.This paper focuses on taking MRS technology to apply for solving thesetechnical problems in the underground engineering. I have calculated the whole spaceresonance response, designed the small size of separated antenna, developed the keyparameters of the instrument, simulated the field experiments, and applied in theactual project sites. The main research results obtained are as follows:1. As for the special underground engineering environment in the applications,this paper gives the calculation formulas for the separated multi-turn antenna withsmall size, which is suitable for the whole-space environment, and calculates themagnetic resonance sounding signal response based on the actual target water bodymodel,which provide the theoretical basis of the magnetic resonance soundingmeasurement in the underground engineering.2. As for the problem that the obtained signal is very weak because of the smallsize of the magnetic resonance sounding antenna, this paper models the receivingantenna system, proposes a method for evaluating the performance of the receivingantenna. I propose the receiving antenna optimized design process, and identify thekey parameters of the6-m,4-m and2-m side of rectangular receiving antenna. Thereceiving antenna has been improved by a factor of4.8,which can be applied in thetunnels and mines.3. As for the problem that the limitation of excitation energy transmitting antennawhich is caused by the narrow underground space, this paperanalyses the factorsaffecting the performance of the transmitting antenna system and give the most optimized design process of the transmitting antenna and identify theparameters.While ensuring the depths, the antenna energy efficiency is improved by65%.Combining with the actual situation, I discuss the effect of the emission currentwith metal supporting structure in the underground engineering and propose thecontrol method based on the distance parameters of the transmitting current.4. As for the problem that long dead time for multi-turn antenna, this papercarries out a dual inhibition from the transmitting system and the receiving system toaccelerate the turn-off time. Meanwhile, according to the variable Q principle, I usethe switching unit to eliminate the step response. This method shorts the dead time inthe small detection antennas from60ms to18ms, and improvesthe accuracy of thedetection SNR and hydrological parameters.5. As for the problem that weak signal and high threshold entering the detectionsystem, this paper proposes a method to match the front-end circuit. Throughcontinuous design of the discrete capacitor, I improve the stability of the frequencycenter of the high inductance-receiving antenna. The maximum transfer coefficientdeviation is less than2.8%. At the same time, the matching resistance influence onantenna transmission system is analyzed. Further improve transfer coefficient of themeter-antenna system,to ensure the effective extraction of very weak magneticresonance signals on nanovolt scale.6. As for the problem that measuring efficiency in the underground engineeringenvironment, this paper presents a fast charging method that uses combination ofcharging way to increase the charging system speed and accuracy. On the basis oferror of less than1%, the guaranteed maximum charge is fasterby5times. Meanwhile,I design a sweep method to quickly determine the inductance parameter. Antennaparameters can be determined rapidly in complex electromagnetic environment,which improve the work efficiency of the system. The accuracy of the antennainductance is determined of±0.01mH.7. Based on the known hydrogeological parameters field, I have carried outthemagnetic resonance soundingmeasurement with the small size antennas and obtaineda high quality magnetic resonance sounding signalwith more than4.5signal to noiseratio by using6m,4m,2m antenna,respectively. I have effective proved thefeasibility of the meter scale the antenna in the underground engineering.This paper has made the innovative research results as following:1. This paperaims at that the traditional method in the underground engineeringcan’t obtain the hydrogeological parametersof disaster-induced groundwater and hasdifficult to quantify. For the first time, I propose a totally new method that detects directly the hidden water hazards using MRS technology with the meter scale antennatoachieve a quantitative detection of hydrogeological parameters of disaster-inducedwaterin the underground engineering.2. I propose anevaluation methodfor the performanceof meter scale detectionantenna.Through establishing the constraint relations of the characteristic parameters,the transfer coefficient and the antenna performance, I complete the antenna designwith the optimal parameters.For the first time,I have used the developed antenna (6-m,4-m, and2m) to obtain the high quality of magnetic resonance sounding signalwiththe signal to noise ratio of more than4.5in the earth’s magnetic field environments,which fills the blank in magnetic resonance technology area.3. This paper aims at the problems thatit is difficult to get the weak signal and theresolution is too low to detect,proposes a front circuit conditioning method for themeterscalereceivingantenna. The method applies theprecision matchingof multi-turnreceiving antenna, short dead-time control, broadband phase-locked filtering andother key technologies to achieve very weak magnetic resonance soundingsignalsextraction of nanovolt.4. This paperaims at the problem thatthe long turn-off time of the multi-turnantenna, proposes amethod to control the high inductance antennastep response.Thismethod uses fast turn-off, residual energy absorption technique and shock suppressiontechnique based on the change Q principleto reduce the impact of energy release andringing effect on the initial signal, whichreduce the dead time from60ms to18ms,and provide effective protection of the result of the data inversion.This paper firstly uses the developed meter scale antenna and magneticresonance sounding system in Guizhou section of Shanghai-Kunming high-speedrailway， Wenzhou section of Jinhua-Wenzhou high-speed railway and Jinpinghydropower station phase II and other tunnels to detect hidden water hazards andachieved good engineering application results. These results confirm the effectivenessof the magnetic resonance sounding method for the disaster-inducedwater detection inunderground engineering. Through the research in this paper, I expand the scope ofapplication of magnetic resonance sounding area, solve directly and effectively thewater hazard problems in the underground engineering and provide the technicalsupport for basic research. |
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