지표투과레이더(GPR)을 활용한 터널 라이닝 콘크리트 배면공동의 두께 평가를 위한 실용식 제안

초록

This study proposes a GPR signal interpretation method to evaluate the thickness of cavities underneath tunnel lining concrete using low-frequency ground penetrating radar (GPR). The use of a low-frequency GPR antenna of 1,000 MHz or less, widely used in the GPR survey on tunnel structures, usually results in the overlap of the GPR reflection signals from the surface and the bottom of the cavity. In this study, a theoretical formula that relates thickness of cavity and apparent period of overlapped signals is proposed, and the validity of the formula is confirmed by comparison with the experimental results. The model specimen fabricated in this study includes a concrete layer with various thicknesses (100 mm, 200 mm, 300 mm, and 400 mm) and cavities with various thicknesses (0 mm, 30 mm, 100 mm, 200 mm, and 300 mm) in a shotcrete layer underneath the concrete layer. Three types of ground-coupled GPR with antenna frequencies of 400 MHz, 900 MHz, and 1600 MHz are used to measure GPR reflection signals from the various cavities in the concrete specimen. The results of this study can be used to quantitatively evaluate the cavity thickness information as well as the cavity location obtained using low-frequency GPR.

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