Abstract
A large number of tunnels in the world have been in service for several decades, and their health conditions deteriorate with the increasing service ages. Therefore, effective inspection methods are essential to accurately assess the health conditions of tunnels. Visual inspection method has been commonly utilized to investigate the integrity of lining concrete, however, this method is incapable of providing sufficient information about the inner state of the lining concrete, such as the existence of cracks and cavities. Since the microtremor characteristics of a concrete structure are significantly affected by its damage degree, this feature may serve as an effective method to investigate the health condition of a lining concrete. In this study, in-situ microtremor measurements were conducted on three spans of a road tunnel with varying damage degrees, and the power spectra density of the microtremors were analyzed. Then the microtremor behavior of the tunnel lining was simulated by using the two-dimensional finite difference code of FLAC. The results of both field measurements and numerical simulations indicate that the ratio of power spectrum density(RPSD) in the range of 0-110 Hz, can be used as a indicator for the damage location, type and degree. For the damaged lining where voids exist, the RPSD values are smaller than 0; for the circumferential cracks, the RPSD values are larger than 0. Therefore, as an initial step, this study gives clear evidence that the microtremor intensity characteristics have strong relation with the health conditions of lining concrete, which has the potential to be used in engineering practices.
