The nature frequency identification of tunnel lining based on the microtremor method

Many tunnels all over the world have been in service for several decades, which require effective inspection methods to assess their health conditions. Microtremor, as a type of ambient vibration originating from natural or artificial oscillations without specific sources, has attracted more and more attentions in the recent study of the microtremor dynamic properties of concrete structures. In this study, the microtremors of the tunnel lining were simulated numerically based on the Distinct Element Method (DEM). The Power Spectra Density (PSD) of signals obtained from numerical simulations were calculated and the nature frequencies were identified using the peak-picking method. The influences of the rock-concrete joint, the rock type and the concrete type on the nature frequencies were also evaluated. The results of a comprehensive numerical analysis show that the nature frequencies lower than 100 Hz can be identified. As the bonding condition becomes worse, the nature frequencies decrease. The nature frequencies change proportionally with the normal stiffness of the rock-concrete joint. As the concrete grade decreases, the third mode of frequency also decreases gradually while the variation of the first two modes of frequencies can hardly be identified. Additionally, the field microtremor measurements of tunnel lining were also carried out to verify the numerical results.