Performance monitoring of a curved shield tunnel during adjacent excavations using a fiber optic nervous sensing system

• Published in: Tunnelling and underground space technology Vol. 124; p. 104483
• Main Authors: Zhu, Hong-Hu, Wang, De-Yang, Shi, Bin, Wang, Xing, Wei, Guang-Qing
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.2022; Elsevier BV
• Subjects: Adjacent excavation; Cables; Clay soils; Compressive properties; Deformation; Distributed strain sensing; Excavation; Fiber optic sensor; Fiber optics; Frequency analysis; Frequency domain analysis; Geotechnical monitoring; Ground motion; Monitoring; Optical frequency; Performance indices; Population growth; Soils; Strain; Subway tunnels; Technology assessment; Tunnel construction; Tunnel lining; Tunnel linings; Tunneling shields; Tunnels; Underground construction; Urbanization; China; Suzhou China; Adjacent excavation; Geotechnical monitoring; Distributed strain sensing; Tunnel lining; Fiber optic sensor
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2022.104483

•A fiber optic nervous sensing system captured strain distributions of tunnel linings.•Two kinematic models are used to interpret longitudinal movements of the tunnel.•The strain measurements are converted to radial displacements of the tunnel lining.•A tunnel risk assessment method is proposed to evaluate the tunnel health conditions. With the accelerated urbanization and population growth in the Yangtze River Delta of China, numerous metro tunnels are in operation or under construction, and adjacent deep excavation activities are frequently encountered. For curved shield tunnels, the impact of excavation-induced ground movements is more complicated due to their asymmetric shape. This paper presents the monitoring results of a curved shield tunnel in clayey soil in Suzhou, China, which were captured by a fiber optic nervous sensing system. This system utilized Brillouin optical frequency domain analysis technology to monitor the distribution of longitudinal and circumferential strains of tunnel linings induced by adjacent excavation. The results show that the tunnel linings were mainly subjected to bending deformations along the tunnel alignment. Maximum compressive strains were observed below the tunnel springline, and their absolute values were higher than those of maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into a rotated oval/ellipsoid. Based on the monitoring results, two kinematic models reflecting the spatial relationship between movements of tunnel segments and measurements of strain sensing cables are proposed. Furthermore, a mechanical method is proposed to convert strain measurements into radial displacements of tunnel linings and the structural health condition of the tunnel is evaluated using longitudinal and circumferential risk indexes. The conclusions drawn in this study provide improved insight into the deformation pattern and health condition of curved shield tunnels subjected to adjacent excavations.