Vibration characteristics of spalling defects in concrete lining

Abstract

The mechanization of the hammering test, which checks the delamination or damage of concrete using a hammer, is required to improve the efficiency of inspections. To realize mechanization, the characteristics of defects with high risk of spalling must be quantified. The objective of this study was to investigate the vibration characteristics. To this end, concrete specimens with inclined detachment were prepared and the vibration measurement, detachment process, and loading were repeated until spalling occurred. In the loading process, it was assumed that the defect existed at the tunnel crown, and the self-weight was considered. The natural frequencies, damping ratios, and response amplitudes for each state are presented in this paper. Additionally, numerical analysis results are presented to supplement the experimental results. The experimental results reveal that spalling did not occur until the adhesion area and frequency of the lowest mode significantly decreased. The frequency of the lowest mode just before spalling is expected to be less than 100 Hz. Based on the simulation results obtained for an actual severe concrete spalling accident in Fukuoka Tunnel, it is concluded that the ability to detect defects with the response amplitude of 1 mm/s/N is required to mechanize the hammering test.