| The rapid development of China’s economic construction predestines to generate more tunnels and underground works in transportation, water conservancy, hydropower engineering and mining industries. During the tunnel construction period, various types of aqueous structure, such as fault fracture zone, caves and underground river, weak interlayer, joint development area, fissure water, will cause a great risk to construction security. It is of great importance in forecasting the geological conditions in front of tunnel face scientifically and effectively. Nowadays there are many geological prediction method, and some of them are relatively mature. By using these method we can make reliable judgments on the existence of geological hazards in front of tunnel face. But on the issue of forecasting spatial orientation of aqueous structure and the amount of water, for now we can only do qualitative judgment. There has not been a forecasting method which can forecast water condition directly and accurately and quantitatively. Compared with other geophysical methods, the biggest advantage of nuclear magnetic resonance technology is that the detected signal amplitude response is directly related to the content of water, and it can directly show the actual situation of the aquifer. At present, the research of using nuclear magnetic resonance technology in tunnel forecast has just started, and it’s a new field of advanced geological forecast research.On the shortage of existing geological prediction technology in forecasting water content, this article discussed the various types of tunnel geological prediction method and research status of nuclear magnetic resonance, used theoretical analysis, numerical simulation, laboratory test, field test methods to carried out research on the application of NMR in the tunnel geological prediction. The main results and conclusions are as follows:(1) The current tunnel geological prediction methods can not make identification and location and calculation of water contant. NMR is the only way in directly detecting water contant. But the research in tunnel advanced NMR forecast is still very little. There is no NMR instrument designed for tunnel geological prediction.(2) The principle of NMR in water probing was introducted. Working methods and calculation method of tunnel aquifer forecast using NMR were optimized. And advice on tunnel advanced NMR forecast was carried out.(3) Numerical calculation of tunnel NMR water probing was made. Increase the transmit power and the received signal sensitivity can distinguish the available aquifer information. Particle swarm algorithm and wavelet transform in NMR data inversion can reduce noise and improve the signal to noise ratio.(4) By the method of laboratory tests, discussion on the application of NMR methods in tunnel was made, and study on the laws of NMR response to water contant was carried out.(5) Experimental research was conducted. Geological prediction implementation method and influential factors and noise reduction methods using nuclear magnetic resonance under construction site conditions was discussed. It is found that the trends of surrounding rock water content forecasted by NMR method were very close to engineering practice, but the water content of surrounding rock has a large gap between the actual. The calculation theoretical needs further study and improvement. |
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