Forward Simulation For Ground Penetrating Radar And Its Application For The Engineering Field

In recent years, tunnel and underground engineering develops more and more quickly, and the terrain, geological conditions and monitoring environment are more and more complex. It is difficult for GPR detection and results interpretation. To solve these problems, the writer carried out theoretical research and physical experiments about the geological radar detection simulation. The main research in this paper work is as follows:(1)Using the software MATLAB, developed a forward simulation software for GPR detection of 2D TM wave. Based on the three elements of FDTD of two order accuracy (the difference format, stability, absorbing boundary conditions), the software directly uses central difference approximation to transform the differential operator in Maxwell curl equations into differential form and gets the finite difference time domain equation of the GPR forward simulation. At the same time, based on the numerical stability conditions and ideal dispersion relation, the writer calculated the reasonable sampling interval and space interval, using two-dimensional Yee cell division set the mesh of the forward model and set electrical parameters of the corresponding forward model to each grid. Due to the limitation of computer storage space, the size of the calculation model of FDTD is fixed and limited, so that computer in the calculation of FDTD can’t simulate an infinite computational domain. Therefore, in order to simulate the spreading process of emission of electromagnetic waves in a infinite field in the GPR detection better, the perfectly matched layer (PML) absorbing boundary condition is added.(2)Using the software C# to develop a modeling software of GPR detection based on image recognition technology. The software has functions of reading the image of simulation modeling, assigning medium parameters and conversing and outputting modeling data. It can read any image of simulation modeling drew by any drawing software, assign medium parameters by different colors of the images and convert data into the forward simulation model data file for forward simulation software. The software can effectively simplify the forward modeling process.(3)Using the dynamic display module of the GPR forward simulation software, the software can simulate the spreading process of emission of electromagnetic waves in underground medium by dynamically outputting continuous time field value distribution image. It can help us understand and analysis the electromagnetic waves propagation process and law in GPR detection.(4)Using the GPR simulation software, the writer simulated the typical harmful geological body in tunnel and underground engineering (cave, fault), typical structures (steel, steel arch) and typical interface (layered, ladder shaped, ditched) models, got the corresponding GPR detection results and compared and analyzed them.(5) According to the typical harmful geology structure and typical structure in tunnel and underground engineering, the writer designed the corresponding physical experiments to carry the GPR detection, and find that the results of physical experiment are almost similar with the results of forward simulation. They mutually verify with each other and provide reliable basis for GPR detection.(6)Summarized the judging criterion of the typical target body in tunnel and underground engineering, and applicated into actual construction, to prove its reliability.