Distributed Settlement and Lateral Displacement Monitoring for Shield Tunnel Based on an Improved Conjugated Beam Method

Because of several unforeseen actions such as the deep excavation and long-term consolidation of ground, the settlement and lateral displacement have become important parameters for shield tunnel. Due to lack of distributed characteristic, the traditional monitoring methods based on manual observation on some preset uniformly spaced points, probably ignore some local settlements or lateral displacements which may occur anywhere along a shield tunnel. According to an improved conjugated beam method (ICBM) which uses the distributed fiber optic sensors to monitor the deflection of statically indeterminate structure with a finite number of supports, this paper first extends the ICBM to monitor distributed deflection of statically indeterminate structure with infinite number of supports. Then a settlement and lateral displacement monitoring method for shield tunnels is proposed. Two experiments including a scale-down longitudinal concrete model and a long steel tube model are carried out to verify the monitoring accuracy of the proposed method.