Research On Vehicle-borne Transient Electromagnetic Response Characteristics For Internal Diseases Of High-speed Railway Tunnel Structure

With the rapid construction of high-speed railway tunnels,various tunnel diseases continue to appear in the operating tunnels,and the tunnel operation service period has gradually entered the stage of repair and maintenance.Especially,there will be more and more high-speed railway lines with high tunnel ratios in the mountainous areas of western China,and the maintenance of tunnel engineering will be exploding.Taking the requirements of rapid detection,repair and maintenance of internal diseases in high-speed railway tunnel structure as research background,the vehicle-borne transient electromagnetic method has been proposed to be applied to the detection of internal diseases of tunnel structures,and its purpose is to meet the development demand of rapid detection of high-speed railway tunnel diseases.The spatial transformation,electromagnetic response,position state evaluation,threedimensional inversion of the water-bearing body,and electromagnetic characteristics of tunnel interference sources are investigated in the application of vehicle-borne transient electromagnetic method detection through data investigation,theoretical analysis,numerical simulation,and indoor model test.The main research results and conclusions are as follows:1.Based on the principle and application of transient electromagnetic method,the vehicle-borne transient electromagnetic method and principle applied in the field of internal disease detection of high-speed railway tunnel structure are proposed,and the spatial transformation problem in the moving process of vehicle-borne transient electromagnetic detection system is put forward.Compared with electromagnetic diffusion in the half-space and whole-full space,the diffusion ring of the induced current in the three-fourths space exhibits a certain angle deflection due to the spatial asymmetry.Under the condition of uniform medium and medium containing a water-bearing body,the correction of different space states in the moving process of vehicle-borne transient electromagnetic spatial transformation can refer to the correction method of tunnel transient electromagnetic space.2.Combined with the transient electromagnetic response characteristics of the waterbearing body behind the tunnel lining structure,the vehicle-borne transient electromagnetic method has the feasibility of detecting low-resistance body and the inapplicability of detecting high-resistance body in the surrounding rock.Based on the sensitivity analysis of the physical parameters of the water-bearing body,different parameters have different influences on the uplift time,maximum value,maximum time,and regression time of the transient electromagnetic response curve,and the change law representing the transient electromagnetic response curve is also obtained.The numerical characteristic parameters provide important ideas for the subsequent three-dimensional inversion research.3.Aiming at the operating position of the vehicle detection system,the spatial correction method of different positions is proposed,and the critical distance that the space transformation does not affect is determined to be 300 m.Based on the numerical characteristic parameters,the correction principle of the tunnel background field related to the location of the vehicle-borne detection system is proposed,that is,the tunnel section does not need to be corrected,and the surrounding rock resistivity is inversely corrected according to the magnitude of the resistivity.Through the analysis of multi-components of transient electromagnetic response,the vehicle-borne detection system can only effectively identify the water-bearing body within a certain range of the size of the water-bearing body,and the transient electromagnetic response in different directions is dominated at different positions of the water-bearing body.At the same time,the Z-direction and X-direction transient electromagnetic response components are determined as the most important basis for evaluating the positional state of the water-bearing body,which provides an important theoretical basis for the design of vehicle-borne transient electromagnetic coils.4.Through correlation analysis,the Pearson correlation coefficients between different characteristic parameters and physical parameters of the water-bearing body are investigated,the correlation between inversion parameters and targets is determined,and a threedimensional iterative inversion method based on the numerical characteristic parameters is also proposed.Based on three different inversion methods,different inversion methods can obtain the inversion results of the inversion target of the water-bearing body,but each inversion method has advantages and disadvantages.Any single inversion method cannot quickly,effectively,and intelligently realize the three-dimensional inversion of the inversion parameters of the water-bearing body,which provides a theoretical basis for the subsequent selection of vehicle-borne transient electromagnetic multi-method joint inversion.5.Through the inversion of single-point and multi-point measurement data,both inversion methods can qualitatively determine the position of the water-bearing body in the moving process of the vehicle-borne detection system,and the inversion results of the indoor model test also verify the theoretical analysis and numerical simulation of vehicle-borne transient electromagnetic method.Combined with the single acquisition control time of the instrument and the running speed of the vehicle-borne equipment,it is considered that the two inversion methods have advantages and disadvantages.Besides,two inversion methods have their respective application scopes for different detection purposes,which provides an important technical reference for the functional positioning of vehicle-borne equipment.6.Based on the research of the transient electromagnetic response of the fixed interference source of the metal reinforcement network,there is a significant difference between the transient electromagnetic response of the fixed interference source of the metal reinforcement network and the transient electromagnetic response of the uniform medium.The response curve of the metal reinforcement network is mainly manifested in the lifting phenomenon of the response curve in the middle and late period,and there is no regression phenomenon in the response curve,which is obviously different from the variation law of the water-bearing body.Through the theoretical analysis and numerical simulation of multi-field transient electromagnetic response,the characteristic function forms of each interference source of the vehicle-borne transient electromagnetic detection system are analyzed,and the mathematical separation method of the total interference source electromagnetic field is proposed.The transient electromagnetic response curve of the total field source presents the response law of different subfield sources in different periods.The theoretical mathematical superposition method is basically consistent with the transient electromagnetic response obtained by the numerical simulation method,and the feasibility of the mathematical separation method of multi-field source is verified,which provides a significant foundation for the identification and determination of subsequent vehicle-borne transient electromagnetic response signals.