| Ground penetrating radar(GPR),as a new geophysical exploration equipment,is becoming more and more mature,and has the advantages of high detection efficiency,non-destructive detection,detection of high precision,strong anti-jamming capability and convenient use,which makes the theoretical research and practical application of radar technology more in-depth and extensive.At present,GPR is widely applied in tunnel detection,road surface detection,advanced prediction and bridge detection,but its application in geological survey has many limitations.The main reason is that underground geological body is an unknown and complex medium,and the response characteristics of the electromagnetic wave to underground media are complex.This complexity is mainly reflected in the variation of wave velocity and image reconstruction.Therefore,the study of these response characteristics has important theoretical significance and application value.Based on this background,the propagation velocity of electromagnetic wave in debris flow deposits and debris flow remodeling cylinders is studied through model experiments,and the in-situ measurement of wave velocity in landslide deposits is carried out.At the same time,the image characteristics of electromagnetic wave in different media are analyzed in detail.Finally,the above research results are applied to three landslide cases and one karst foundation.The specific application of GPR in geological survey is comprehensively analyzed.This paper mainly studies from the following aspects:(1)The propagation law of electromagnetic wave in underground media and the size effect of GPR detection are analyzed and summarized.The working methods of GPR detection and the interpretation methods of data images are given,which lays a theoretical foundation for the interpretation of radar images.(2)Based on the known depth method,an experimental model is established to investigate the wave velocity variation of electromagnetic wave in different media by summarizing the existing wave velocity calculation methods.For two indoor model experiments and two in-situ velocity measurements,the influence factors of this change are found,and the wave velocity is calculated by other means to approximate the real propagation velocity of electromagnetic wave in the medium infinitely.(3)Based on the propagation principle of electromagnetic wave in media,the image recognition characteristics of electromagnetic wave in different media and the interference signal characteristics caused by surrounding obstacles are analyzed and summarized.(4)Field exploration is carried out at four detection sites to explore the specific application of GPR in geological investigation.Through the study of the above contents,the following conclusions can be drawn:(1)The propagation law of electromagnetic wave in underground media is mainly affected by the dielectric properties of underground media.The size effect of GPR in detection is mainly used in three aspects: detection distance,detection direction(line layout)and target size(resolution).The effective interpretation of radar images requires dual quality assurance of data acquisition in the early stage and image processing in the later stage.(2)Through the establishment of model experiments,the velocity of debris flow deposit indoor model,debris flow remodeling column model.The field test model of Zhaizicun landslide dam in Yongsheng,Lijiang and the field test model of Touzhaigou landslide deposit in Zhaotong are carried out.The measured wave velocities are 0.168m/ns and 0.117m/ns,respectively.(3)The propagation of electromagnetic wave in underground medium is mainly affected by dielectric properties of the medium.Water has a strong absorption effect on the electromagnetic wave,which will affect the propagation speed of the electromagnetic wave in the medium.In addition,the velocity of electromagnetic wave is related to the material,composition and structure of the medium,as well as the shaping of the medium model.The propagation speed of electromagnetic wave in the medium is restricted by many factors.(4)Radar image features are mainly reflected in the kinematics,dynamics and abnormal characteristics of electromagnetic wave propagating in media.It can be simply attributed to the waveform characteristics of the image and the change of three phases.(5)GPR is used to conduct geological survey in three landslide hazards.The image characteristics of various geological defects in geological hazard areas are comprehensively analyzed,which provides a reference for the application of follow-up geophysical exploration equipment in geological survey.(6)In the investigation and study of the karst area of Dabanqiao,the anomalous area has obvious characteristics.There are karst caves in the depth range of 21.6-23.8 meters,which are consistent with the exposure of borehole profiles near the area.Based on the results of geophysical prospecting and field geological data,the reasonable treatment method of the karst foundation is given. |
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