Research On GPR Identification Of Tunnel Lining Hazards And Application

There are always hazards in operating tunnel, such as tunnel lining cavity, continual cavity, pervasive water, lining crack etc., which reduce the security of the tunnel. Detecting of these hazards is important to evaluate and enhance the tunnel. Ground penetrating radar (GPR) is a method that uses electromagnetic pulse and its reflected wave to identify the object character under the ground. It has many advantages. Because of the complexity medium in hazards, the identification of lining hazards is depending on experiences and not precision enough. Thus, it is necessary to study on radar identification of tunnel lining hazards through GPR forward simulation and model test methods. An instance of tunnel engineering is used to discuss the application of GPR detection method in this research.First of all, it was introduced the theory and technical parameter of GPR. Aimed at principle and application condition, the regular data processing method was concluded. And explaining method of GPR map was illustrated.Then,2D finite difference time domain (2D-FDTD) method was used to do forward simulation for tunnel lining. Deduce the2D-FDTD equations of TE wave based on Maxwell theories. Choose Mur method as absorbing boundary condition, and Ricker wavelet as source. So use Matlab programming to build numerical models of cavity, water, continual cavity, steel bar and cavity behind steel bar. Through GPR forward simulation, hazards’response maps were analyzed.In order to contrast with forward simulation results, model test of lining cavity and water had carried out. Made models in laboratory and applied radar in test. Matlab was also used to analyze the testing maps. At the same time, model test results were contrasted with forward simulation.Finally, took an operating tunnel as example, applied GPR in detecting lining quality. Based on the detecting results, tunnel lining security status was evaluated.Some conclusions are summed up from this research. FDTD is an efficient method for GPR forward simulation. Varied hazards’radar maps were acquired in this method. And they were improved the precision of radar data explanation. Results shown that model test was similar to forward simulation. The distribution of hazards was clear when radar detecting maps had analyzed. And it provided evidence for tunnel security status evaluating and structure enhancing.