Layer recognition and thickness evaluation of tunnel lining based on ground penetrating radar measurements

Ground penetrating radar (GPR) is a time-dependent geophysical technique for measuring the thickness of second lining, which is one of the most important tunnel quality targets. As the wave transmits from air (or the second lining) to the second lining (or the first lining), the Fresnel reflective coefficient is negative, i.e., the phase of reflective wave is reverse to the incident In the one dimension time-waveform diagram (A-Scan) of GPR, the lining layers are located on the inflexions which are decided by Fresnel reflection coefficients and the attenuation coefficients of electromagnetic wave in the transmission medium. By towing the antenna over the tunnel surface, two dimension scanning data (B-Scan) is constituted by multiple A-Scan channels, where the grey scale is applied to the amplitude values. In the process of exploration, the lining interfaces are separately plotted by connecting each maximum peak point or second maximum peak point of A-Scan. In the Long Hai Tunnel, the artificial recognition provides 15 sampling values on the exploration line from D9 + 015.195 to D9 + 065.195. However, the automatic recognition can provide more information, such as average thicknesses, standard errors of lining thickness and the qualification rates of lining thickness, etc. (C) 2010 Elsevier B.V. All rights reserved.