터널 라이닝 콘크리트 배면공동 두께에 따른 400MHz GPR 신호 변화에 관한 수치해석 연구

초록

This study proposes a practical method for evaluating the thickness of an air cavity (Hcavity) using low-frequency GPR. The interaction between low-frequency GPR signals with a center frequency of 400 MHz and air cavities with various thicknesses, which are formed behind tunnel concrete linings, is investigated using numerical analyses. The following three steps are performed: First, a numerical simulation model is developed to simulate transient electromagnetic wave propagations in an air cavity behind a tunnel concrete lining using open source software (gprMax). Second, based on the analytical results, a practical equation that relates the apparent time difference of EM reflections in the an air cavity and its thickness (Hcavity) is established. The results indicate that the ？？？ ？Hcavity relation is effective for evaluating the thickness of the air cavity Hcavity) with an error margin of 20% even for air cavities that are relatively thinner than the wavelength of primary GPR signals, λGPR (Hcavity /λGPR~1/8). Finally, the obtained analytical results are validated through comparison with the experimental results of previously reported studies.

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