Applicability of non-contact inspection using laser ablation-induced vibration in a reinforced concrete tunnel lining

This paper considers the applicability of remote laser sensing to reinforced concrete tunnel linings with suspected corrosion of the reinforced steel. As an alternative to the hammering test, this approach represents a non-contact inspection method that provides quantitative evaluation. Remote laser sensing uses two types of lasers: an impact laser to induce vibrations in the measurement target by laser ablation and a detection laser to measure these induced vibrations. The validity of the method is verified by comparison with the results of a hammering test. It is shown that remote laser sensing can be successfully applied to a reinforced concrete tunnel lining, although the induced vibrations decay faster and the noise level are higher in the field than in the laboratory. Changes in natural frequency are occasionally observed; these are believed to be a results of changes in temperature and nonlinear vibrations. Based on the results of on-site laser measurements, the estimated frequency of the lowest mode is found to be the most useful index for the quantitative evaluation of defects.

Automated summary

This study confirms the feasibility of using remote laser sensing for reinforced concrete tunnel linings, although environmental factors in the field may affect the results, it still provides an effective quantitative evaluation.