Voids delineation behind tunnel lining based on the vibration intensity of microtremors. (January 2016) - Gao, Yang
Highlights: A new inspection method for voids behind lining based on microtremor is proposed. Influences of voids and their geometrical parameters on RPSD were studied. Vibration intensity characteristics of microtremor have strong correlation with voids. The proposed method can be used in health condition assessment of tunnel linings. Abstract: In-situ microtremor measurements and numerical simulations were carried out to study the microtremor characteristics of tunnel linings. Power spectrum density (PSD) of microtremor signals measured from three spans of a tunnel lining with or without defects (cracks and voids) was calculated and analyzed. The results revealed that the normalized ratio of comparative power spectrum density ( NRPSD ) obtained by calculating the ratios RPSD, which is the ratio of PSD between different orientations (axial, radial and circumferential), of damaged spans to that of the healthy span, can be used as an indicator for the void delineation. For a damaged lining where voids exist, the vibration intensity is enlarged greatly in the radial direction, resulting in a pronounced value of NRPSD by comparing the NRPSD of the radial orientation to that of other orientations. Influences of properties of rock–concrete interfaces, geometric properties (location, arc length, and depth) of voids, and mechanical properties of rocks and concrete on the values of NRPSD were estimated via numerical simulations. As a preliminary study, these results provide clear evidence that the vibration intensity characteristics of microtremors have a strong correlation with the existence of voids located between lining concrete and surrounding rock masses, which has high potential to be developed to an effective approach for health assessment of tunnel linings in the future.