Abstract: Based on the monitoring strains of distributed fiber optic sensors (DFOSs), an inversion method has been developed to predict the deformation behavior of shield tunnels. A curved Winkler beam-hinge model, which takes into account the joint rotational effect ignored in the existing related studies, is properly established and solved using the finite difference method (FDM). The inversed lining responses, including the deformation, internal force, external load and joint stiffness, are derived. Two types of lining damage, namely the voids behind the lining and stiffness reduction of joint, are identified in terms of the denoised strain increment and curvature profiles. The inversion accuracy is demonstrated to be hardly affected by the resistance of surrounding rock and noise interference. The assumption of dv/dφ=0 at the position of maximum strain yields high inversion precision, especially for a large lining deformation, where v represents the radial displacement, and φ represents the central angle of the node. An available inversion approach by fitting the bending moment of lining combining with few strain gauges is proposed for the case of single-sided layout of DFOSs. The influence of joint rotational stiffness on the deformation consistently lies within a range that remains almost unchanged for different surrounding stiffnesses, lining elastic modulus, and burial depths.

Key words: distributed fiber optic sensing, shield tunnel, segment joints, deformation inversion, damage identification