2021 Volume 77 Issue 1 Pages 32-43
We considered the index for evaluating soundness against lining concrete spalling toward streamlining and mechanization of the hammering test. From the laboratory test, the following facts were found: the frequencies of the low-order vibration modes of the defect, which may be on the verge of destruction, become considerably low, and it is difficult to hear the vibration sound of the low-order modes from hammering sound. Besides, the following facts were found from the on-site measurements in Shinkansen tunnel: there was a considerable variation in the frequency of the lowest-order mode of the defects, and many of the defects are safe enough for spalling. The inspection criteria of the hammering test are vague, and the evaluation is on the safe side. Therefore, the frequency of the lowest order mode of the defect can be used as an index for evaluation, and it can contribute sufficiently to the efficiency of the inspection.