Application of structural health monitoring in Hangzhou Qiantang River tunnel

The Qiantang River originates in the borders of Anhui and Jiangxi provinces and passes through Hangzhou, the capital of Zhejiang province, before flowing into the East China Sea through Hangzhou Bay. It is known for the world's largest tidal bore, which is up to 9 meters high, and travels at up to 40 km per hour and has since ancient times been considered a spectacular sight. The Qiantang River tunnel, which was planned in 1996 and completed in 2010, is the first slurry shield tunnelling in Hangzhou soft ground, and also the first tunnel under Qiantang River. Whether the long-term impact of the surging tide will influence the normal service and structural safety of the under-river tunnel is concerned. In order to monitor the condition of the tunnel and study the impact of the tide on it, a structural health monitoring system was planed and applied in construction of the tunnel. Items of monitoring include the earth pressure acting on the shield tunnel lining, stain in the reinforcing steel bars of the segments, convergence of cross-section and long-term settlement in the longitudinal direction. Both traditional monitoring methods, such as the vibrating wire strain gauges, and the advanced fibre optic technology, such as distributed optical fibre strain sensing, were applied in this monitoring system. This paper describes the application of the structural health monitoring system in detail, including arrangement of monitoring sections, the installation of the instruments, and anticipated research achievements.