An optical-electrical co-sensing tape for cross-sectional deformation monitoring of shield tunnels

Abstract

Cross-sectional deformation is a crucial index for evaluating the stability and safety of shield tunnels. Monitoring the cross-sectional deformation has been an important content in assessing the health condition of tunnels. For this reason, an optical-electrical co-sensing tape (OECST) by embedding distributed optical fiber sensor (DOFS) and coaxial cable F-P interferometer sensors (CCFPI) into a high elastic polyurethane tape has been proposed in this paper. It can simultaneously measure the low-strain area of structure with high accuracy by DOFS and large-strain area with relatively lower accuracy by CCFPI. The conceptual and geometric design, fabrication method, and sensing mechanism have been discussed. A laboratory test has also been conducted to validate that the OECST can provide reliable strain measurement. Subsequently, an algorithm has been proposed to measure the cross-sectional deformation of shield tunnels by using OECST strain measurements. The cross-sectional deformation has discontinuous features with large deformation of joints (dislocation, opening, closing, etc.) and small deformation of segments. The former can be obtained by performing geometrical analysis on rough strain measurements of the CCFPI in OECST. The latter can be derived by implementing the strain–displacement conversion on the accurate distributed strain measured by the DOFS-S in OECST. The method has been investigated experimentally. The findings from the study have demonstrated that the proposed OECST can measure the cross-sectional deformation of shield tunnels with a satisfactory accuracy, which can be used to assess the health condition of tunnels.