| In the 40 years since the reform and opening up,the number of infrastructure construction in China has been increased to a great extent,including the construction of water conservancy facilities.Hydraulic tunnel is becoming more and more complicated construction conditions,tunnel site area of the engineering geological condition is complex,with some constraints geophysical methods to detect geological conditions of surrounding rock in front of the necessary,can accurate proved the bad geological period ahead,fault fracture zone,hollow,dense joints and fissures belt,etc.)of the location and size,so that we can reduce the construction accidents,reduce economic loss.The geological advance prediction method has been developed over the years.At present,it is more advanced to produce the electromagnetic wave method based on GPR and transient electromagnetic method and the seismic wave method based on TGP and TSP,as well as the traditional method of recording the palm surface and the advanced drilling method.In these geophysical techniques,GPR and TGP have better development prospects.GPR features high resolution,small interference,simple operation and accurate forecast.The TGP detection method has the characteristics of long forecast distance,small disturbance to construction and accurate prediction of bad geological section.GPR and TGP is commonly used in underground engineering geological forecast method,but the single underground engineering geological forecast method,and the complicated geological conditions at the same time the scene exist some interference factors,the forecast is not accurate,part of the economic losses directly.GPR and TGP interpretation standard is not clear,the data interpretation mostly interpret people’s personal experience,so the study of GPR and TGP application in hydraulic tunnel advance geological forecast,put forward the common data interpretation methods,reduce the interference factors,to improve the forecast results of tunnel right is of great significance.Relying on jiangxi provincial department of science research project,this paper advance geological forecast under construction of hydraulic tunnel construction based on project,adopted the advanced geological forecast related literature at home and abroad were reviewed and summarized,the tunnel advance geological forecast field test,and combining with theoretical analysis,numerical simulation and other research methods,the main research content: the GPR data sensitivity analysis;Using GPRMax2.0 software to perform forward analysis of several typical bad geological bodies,the reflection electromagnetic wave waveform image is obtained in theory.The application of GPR and TGP in the advanced geological prediction of bad geological bodies,and the later excavation and verification,obtained the reflection wave patterns of GPR and TGP detection technology in poor geological bodies.In the end,two kinds of detection techniques of GPR and TGP are proposed.Through analysis and research,the following conclusions are drawn:(1)Engineering geological conditions of the study: to actual engineering for the project,in combination with related literature at home and abroad,the system analysis of the tunnel site area topography and geomorphology,geological structure,hydrogeological conditions,formation lithology,analysis the potential adverse geological body,and adverse geological effects on tunnel advance geological forecast work.(2)the study of GPR detection technology,which is based on the actual field test,using GPR in the tunnel advance geological forecast,through the control variable method,the conclusion summarizes some scene detection work:(1)including in front of the field test detection instruments and equipment debugging,selection of parameters,has a certain impact on forecast results,(2)Sensitivity to electromagnetic reflection wave analysis,the influence of the parameter selection is obtained(window size,length,dielectric constant,gain digital filter)effect on the detection results,so the correct selection of related parameters on the accuracy of geological prediction plays an important role;And methods for post-processing of raw data.(3)Through the analysis of the results of GPR’s different detection of the water content of surrounding rock,it is concluded that the greater the moisture content,the faster the attenuation of electromagnetic wave in the propagation process,and the detection effect is not obvious.(4)It is concluded that the difference of moisture content has certain influence on the dielectric constant of surrounding rock,and the dielectric constant can be selected correctly to determine the size and position of the bad geological body.(3)Of GPR advance geological forecast analyzing numerical simulations of electromagnetic wave propagation,a few farm electric model is established,including the karst cave,mezzanine(unconformable surface),different Angle of the fault fracture zone,complex model electric model,in theory,it is concluded that the GPR in several adverse geological body electromagnetic reflection waveform figure;In the later stage,GPR was applied to the prediction and excavation verification of several undesirable geological bodies,and the rapid identification of the reflected waveform of the bad geological body was obtained.(4)The study of the TGP detection technology: based on the actual field test,the use of the TGP system advance geological forecast in tunnel,combining with related theory analysis are separated by the longitudinal wave velocity of rock mass,as well as the bad geological body recognition(hard and soft rock changes with the discriminant,fault fracture zone,karst development zone,and identification of aquifer,etc.),preliminary established the TGP data interpretation method;Finally,the accuracy of TGP detection technique in advance geological prediction of tunnel is proposed. |
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