Forward Simulation Of Ground Penetrating Radar For The Tunnel Fore Geological Forecast

Ground penetrating radar(GPR) is a geophysical exploration method, using high-frequency electromagnetic pulse to detect underground media distribution, with the advantage of high-resolution, anti-electromagnetic interference, non-destructive, light and fast. It is widely used in the tunnel fore geological forecast.First of this paper, the development of GPR technology and theoretical research situation are introduced briefly. The contents and significance of simulation of GPR for the tunnel prediction was put forward. For one thing the basic operating principle are summarized, for another thing, the electromagnetic theory was made a detailed study starting from the Maxwell’s equations.The simulation of GPR was detailed study centering on the finite difference time domain method(FDTD) and emphasizing the Maxwell’s equations. First, the FDTD was summarized, which laid the foundation for this study. Second, the Maxwell equations of FDTD format were got by using the FDTD method in the approximate development starting from the Maxwell’s equations. The perfectly matching layer(PML) was set in truncated borders. The Ricker-wave which approximates the real antenna wave was selected as the excitation source to simulate the electromagnetic wave propagating.Last of this paper, the forward simulation of GPR was run using the software of GprMax based on the FDTD. First, the GPR was simulated in an isotropic homogeneous geological model. In this section, the propagation of radar signal in the medium was studied, based on this, the layered models, circular object, rectangular target, stepped models were built to simulate the diminutive ill geologic bodies of fault fracture zones, rich water zones, karst cave etc. second, the Debye dispersion geological model was simulated. In this part, models were built to simulate the fault fracture zones, rich water zones based on the study of propagation of radar signal in the medium. In addition, some interference factors of tunnel construction such as grid, anchor, vehicles were simulated. The results of simulation can play a substantive role in tunnel fore geological forecast.