Study on the Variation of Vibration Characteristics in Rock Tunnels Depending on Ground Conditions and Tunnel Structures Using Ambient Vibration Measurements

Summary

Abstract

This study investigates the vibration characteristics of rock tunnels using ambient vibration measurements, focusing on the effects of ground conditions and structural configurations. Although ambient vibration techniques have been widely applied to soil deposits, their application to rock tunnels remains limited due to small vibration amplitudes and the complex interaction between ground and structures.Measurements were conducted in two tunnels in Japan under different geological and structural conditions. One tunnel was excavated but remained without lining and invert structures, while the other included sections with support, lining, and invert, allowing comparison of different construction stages. Fourier spectra and H/V spectral ratios were used to evaluate frequency characteristics.The results indicate that vibration amplitudes inside the tunnel are significantly smaller than those outside, suggesting limited amplification within tunnels. In the excavated tunnel without structural components, dominant frequency peaks were not clearly identified, and spectral characteristics varied depending on location. In contrast, in the tunnel with structural installations, vibration amplitudes decreased and spectral distributions became more stable. Repeated measurements at the same locations confirmed that invert installation reduces vibration amplitude and stabilizes spectral characteristics.These findings demonstrate that the predominant frequency is primarily governed by ground stiffness, whereas vibration amplitude and spectral stability are strongly influenced by structural conditions. The results highlight the importance of distinguishing between ground and structural effects when interpreting ambient vibration data in rock tunnels.