The Experimental Reaseach On Non-destructive Testing For Highway Tunnel Lining By Ground Penetrating Radar

The use of ground penetrating radar (GPR) has become widespread in highway tunnel inspection with the development of highway engineering. As an efficient and advanced non-destructive detection method, GPR can scan the tunnel lining successively, and obtain objective and accurate plots. However, the application of GPR has just commenced in China, accompanied with many problems, such as the inspection precision of GPR and the judging principles of the probing plots, which affects the reliability of the results probed by GPR.The development and maturation of the ground penetrating radar technology depend on the electromagnetic theory. The ground penetrating radar technology is based on the electromagnetic wave theory and the electromagnetic wave transmission theory. So, knowing well the basic electromagnetic theory and the operating principles of the radar could afford a theoretical guide to the analysis of the experimental data. Setting the radar test parameter reasonably is to make preparations for the rational collection of the experimental data. On the other hand, the analysis and the process of the experimental data rely on the digital filtering technology and the wave characteristics of the radar imagines. The thesis will introduce the above contents briefly.At the present, the selection of the radar wave speed which depends on the relative dielectric constant of the lining is directly related to the test accuracy of the lining thickness in the course of the non-destructive radar test about the road tunnel lining. An experiment is made in this paper in order to simulate a road tunnel lining with some steel bar embedded in the different height of the sample. The sample is layered by the embedded bar according to the total reflection theory of the radar wave from steel bars. The test steel bars embedded at different height in the lining can be located with the use of the RAMAC/GPR ground penetrating radar. At the same time, the thesis also discusses the problem about the influence of an age of the concrete on the speed of radar wave. At last, a qualitative analysis of the relationship between the relative dielectric constant and the thickness of the sample is made. After many experiments, several conclusions can be drawn as follows: the radar wave speed will be increased with the increase of the age of the concrete; within the same age, the radar wave speed will decrease with the increase of the thickness of the sample; the relative dielectric constant will appear increase approximately linearly as the thickness of the sample become large; which gives the explanation of the decrease of the radar wave as the height of the sample at the same age is increased. Accordingly, the thesis suggests that the radar wave speed should be classified according to the thickness of the lining to increase the degree of accuracy of the lining thickness under present radar test conditions.It has always been the most difficult problem for radar non-destructive test to locate the separation of the tunnel lining and to detect the size and shape of the cavity. The thesis approaches these problems by setting the unequal separation of tunnel lining and two other cavities, one of which is cylinder and the other is cube. Through radar detection experiments, the potential ability of radar used for the separation detection in tunnel lining is investigated. Besides, by experimental analysis, the following conclusions can be obtained: The GPR with 800MHz radar antenna can distinguish accurately the interface between the lining and shot-concrete, but not for detection of the PVC waterproof layer; The GPR with 800MHz radar antenna can get an ideal detection about the boundary between upper and lower lining when the height of the lining separation is larger than 5cm; The test result of the horizontal size of the cavity is also very good. However, for the vertical size of the cavity the result is not so good as the horizontal size; Meanwhile, the section shape of the cylindric and cubic cavity can be distinguished according the above information.