Underground Pipeline Detection And Forward Simulation Calculation Based On GPR System

The underground pipeline network is an indispensable and important part in the operation and development of a modern city.In the process of urban construction or construction,the lack of underground pipeline distribution map in the construction area will affect the safety and progress of the project.Therefore,how to use fast and accurate pipeline detection means to obtain the pipeline information in the detection area is a subject worthy of study.Compared with the traditional geophysical detection methods,ground penetrating radar technology has the advantages of high resolution,fast detection efficiency,strong anti-interference ability,non-destructive detection and non-metallic detection,which has been successfully applied to pipeline detection.Based on this,this paper combines the finite difference time domain(FDTD)numerical simulation and field measurement to study the pipeline map features and pipeline information extraction methods measured by GPR in different situations.Firstly,the hyperbolic mathematical model of underground pipeline echo is constructed and the hyperbolic characteristics of pipeline imaging under different conditions are analyzed;secondly,the urban underground pipeline model under different conditions is constructed by the finite-difference time-domain method,and the image feature library of common underground objects is established;secondly,the 3D underground pipeline model is created,and the 3D imaging characteristics of 2D radar detection image are studied and the underground image is calculated Finally,the hyperbola of pipeline echo is extracted by the relationship between single channel data,and the position and diameter of pipeline are calculated.The main contents and research results of this paper are as follows:(1)The mathematical relationship among the position,propagation time and propagation speed of the imaging pipeline is established,and the characteristics of the imaging hyperbola are analyzed.Through forward simulation,it is found that the top travel time of the imaging hyperbola is different under different filling media,and the opening and closing degree of the hyperbola are different.The larger the dielectric constant of the filling media is,the smaller the semi axis of the hyperbola is,and the smaller the opening of the hyperbola is.Under different burial depth,The shallower the buried depth of the pipeline,the shallower the position of the hyperbolic apex,the sharper the imaging will be,but the location of the asymptote intersection of the imaging hyperbola is the same;under different pipe diameters,the asymptote intersection of the imaging hyperbola is different,and the size of the hyperbola opening is different,but the angle of each hyperbola asymptote is the same.(2)Based on FDTD method,gprmax software is used to carry out GPR forward simulation experiment.The influence of different pipeline materials,shapes and filling materials on GPR imaging profile in complex environment is studied.The corresponding image database is established to improve the efficiency and accuracy of underground pipeline interpretation.(3)Through the simulation of 3D underground pipeline,using the way of survey line to distinguish,two-dimensional B-scan data are obtained and three-dimensional imaging is carried out to calculate the angle between the underground pipeline trend and survey line.The results show that the three-dimensional imaging method can calculate the included angle of the pipeline trend,and the error of the experimental results is 2.99%.The three-dimensional simulation has an unparalleled advantage in the recognition of the underground detection target.(4)According to the hyperbolic feature of the pipeline target signal in B-scan data,after the direct wave processing of the measured data by means method,the imaging hyperbola is extracted based on the relationship between the single channel data,and the pipeline target position is obtained by fitting calculation,then the detection and location of the underground pipeline are completed.The results show that the method can detect the underground target accurately and the calculation is small.(5)The hyperbolic parameter fitting method,three-point circle determination method and multiple wave method are used to calculate the pipe diameter and verify the calculation accuracy.The results show that the three-point circle determination method has the highest accuracy,the error is less than 8%,but the requirements for selecting points are high;the hyperbolic parameter fitting method has an error of less than 13%,and the influence of human factors is small;the multiple wave method is limited to nonmetal pipeline,and the error is similar to hyperbolic parameter fitting method.