| Conventional geophysical methods use the difference of physical parameters to find water,which can not realize the direct quantitative prediction of water content.Nuclear magnetic resonance water detection technology is the only geophysical method that can directly detect groundwater,but its detection depth is shallow and its antiinterference ability is weak.The author ’s research group has improved the Surfacetunnel nuclear magnetic resonance(STNMR)method,and proposed to lay a large-size launch wire frame on the ground and lay a multi-turn small loop receiving underground to improve its detection depth.The purpose and significance of this thesis are to study the response characteristics of STNMR signals under different conditions,improve the STNMR technology,improve the detection depth and enhance the detection effect of hidden water bodies.In this thesis,three-dimensional numerical simulation is used to analyze and study some factors affecting the STNMR signal response.The STNMR array detection method technology is discussed.The NMR signal response characteristics of typical coal mine disaster water body are analyzed and summarized.The main achievements are as follows :(1)The detection ability of STNMR in different positions of three-dimensional space is studied.By simulating the detection process of NMR detection of water bodies at different positions in the tunnel,the law of the response signal changing with the position of the water body is discussed,and the simulation results after the normalization of the power supply current are determined with 0.1 n V as the boundary.The approximate detection range of the STNMR device is determined.As a whole,for the emission wire frame with a side length of 150 m,the device can still detect the effective signal when the horizontal direction deviates from the center position within 60 m,and the detection range in the horizontal direction fluctuates greatly with depth.(2)The variation law of the response signal after changing the layout of the transmitting wire frame and the receiving wire frame under the STNMR device is studied.Increase the transmission line block area,will lead to the received NMR signal is the initial amplitude of the Maxima decreases,and reaches a maximum value of the desired pulse torque is also reduced.Under the premise of not changing the area of the receiving wireframe,it is impossible to increase the detection range in the horizontal direction by changing its side length.When only one side of the transmitting wireframe is changed,when the water body is located in a deeper position,the longer the long side of the transmitting wireframe,the stronger the detected NMR signal is.The water body deviates from the center position in the horizontal direction,and the maximum value of the corresponding NMR signal is reduced by the long side length of the transmitting wireframe.Only increase the receive Line Block one side of the side length,in response to the signal amplitude increases,and increases the magnification and the side length is increased magnification close,the water content of the body the greater the deviation from the center position,the signal amplitude increases the magnification and the side length is increased magnification closer.When the depth of the aqueous body to be detected is 120m～180m,the angle between the receiving wireframe and the horizontal plane changes from 0° to 90°,and the initial amplitude of the detected signal increases significantly,but the growth rate gradually decreases.(3)The influence of water-bearing resistivity on the STNMR detection and the signal response characteristics of water-bearing with multiple water contents and different relaxation time are studied.When the resistivity of the water body above the receiving frame and away from the transmitting source decreases,the maximum value of the response signal increases.When the resistivity of the water below the receiving frame decreases,the maximum value of the response signal decreases.It is difficult to distinguish the change of resistivity by nuclear magnetic resonance signal when the resistivity of water is high(50 Ω·m ～ 1000 Ω·m),while the imaginary part of E0 corresponding to low resistivity water(5 Ω·m ～ 10 Ω·m)can more sensitively reflect the change of resistivity.(4)The feasibility of STNMR array device and its signal response characteristics for detecting different water disasters were studied.In order to improve the efficiency and resolution of nuclear magnetic resonance water detection,this thesis further analyzes the feasibility of detecting hidden water bodies by STNMR array devices by studying the differences in the distribution characteristics of underground space kernel functions corresponding to different receiving wire frames in the roadway.After measuring the signal response characteristics of the water-bearing body at different positions with an array device,it is found that when the measurement line is long enough,the maximum value of the initial amplitude of the detected signal is an ’’M’’ type of ’’increase-decrease-increasedecrease’’ trend,and the corresponding frame position at the depression is closer to the water-bearing body.Finally,through the array device to detect groundwater damage,it is found that the NMR signals received by different wire frames are significantly different in the width of the signal peak and the maximum and maximum values of the initial amplitude.Therefore,by Array device can be more intuitive,more accurately determine the complex aqueous body shape and boundary. |
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