Monitoring the behavior of segment joints in a shield tunnel using distributed fiber optic sensors

Shield tunneling is a popular tunnel construction technique for its efficiency and speed. However, uncertainties associated with site soil conditions, past loading histories and analytical modeling, can result in performance issues. To monitor shield tunnels and ensure performance and safety, fiber optic sensing technique is proposed. Based on Brillouin optical frequency domain analysis, the technique can monitor the opening and closing of segmental joints in shield tunnels with high sensitivity. To determine tunnel lining segment displacement, different fixed-point spacings have been tested in the lab. The test results show that the difference in fixed-point distances had no impact on the test accuracy and the sensing cable with 0.9-mm polyurethane sheath coater has the best performance. For demonstration, the Brillouin optical frequency domain analysis-based monitoring technique is applied to the Suzhou Metro Line 1 tunnel for tunnel lining segment joint monitoring. The technique detected minor deformation of the segment joints in tunnels in operation and located leakages within the tunnel. The technique further identified that the minor deformations of the segment joints and track bed expansion were closely associated with temperature variations.