| As expressways in southwest karst areas are in the rapid development stage at present,many tunnels need to be built under the complicated and changeable geological conditions.However,the tunnel engineering is a concealed project,which will be faced with a variety of different geological disasters in the process of construction.The ground penetrating radar(GPR)has some features such as fast sampling,non-destructive,easy operation and high resolution and so on.As an effective method for short distance geological prediction,it is widely used in tunnel defective geological detection.In this thesis,physical model tests and numerical analysis were used to study the attribute extraction technology and analyze the attribute character of GPR of defective geology of typical karst based on the collection of a large amount of relevant information and investigation in field.Results of research contribute to improve the methodology of interpretation of GPR in karst tunnel geological prediction.Research results are as follows:(1)Based on extensive collections of geological data of karst tunnel that has been excavated,analysis and summary of the morphological characteristics and types of fillers of common karst defective geological bodies,indoor model experiments are designed.Through the physical model test,the typical karst defective geological body which is often encountered in tunnel construction at karst zone is simulated.The GPR data of different depths,different sizes,different shapes,and different filling materials are obtained.(2)The GPR signal interpreting technology based on attribute analysis is introduced.Based on the physical model test data,three instantaneous attributes and reflectance spectral properties of GPR sounding profile of different abnormal filling materials are respectively analyzed.The result shows that the resolution of the instantaneous phase is the highest,the instantaneous phase profile would be shown as in-phase discontinuous event in abnormal locations,especially when the abnormal body is water,the phase reversion is 180 degrees.Instantaneous amplitude characteristics vary with the difference of the relative dielectric constant of the abnormal filling material and the model itself.The larger difference the relative dielectric constant is,the more obvious performances they will display.The instantaneous frequency characteristic is not obvious,but it can assist the instantaneous amplitude feature to recognize the target;The amplitude spectrum can reflect the peak characteristics of reflected wave,and the difference between these characteristics and the dominant frequency of the GPR antenna.The average phase value of the-3dB bandwidth helps to identify whether the abnormal target is rich in water.(3)In order to describe the local features of the GPR signal better,time-frequency analysis method of GPR signal based on generalized S-transform is introduced.This method can adjust the factor value of k and p by changing the time domain and frequency domain to obtain the time-frequency transform results of different time domain and frequency domain resolution,and provide a new way for the analysis of GPR signal characteristics of the defective karst geology.(4)Relying on the Nali second tunnel engineering of Laima high way in Guangxi province,the method of this paper is used to analyze the data of the field detection and achieves a better effect.The extracted attributes include three instantaneous attributes,spectral attributes and time-frequency attributes. |
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