Monitoring the effects of tunnelling under an existing tunnel-fibre optics

摘要

Underground tunnel networks are at the heart of United Kingdom’s infrastructure, carrying morernthan 1,100 million passengers each year along its 249 miles long network via 11 underground lines, serving 270rnstations.With a complex existing underground rail network already in place; it is inevitable that new tunnels willrnbe constructed within close proximity to existing tunnels. At London Liverpool Street Station, the new eastboundrnCrossrail platformtunnel was constructed underneath the existing Royal MailTunnel at a parallel alignment overrna length of over 100m with a clear distance of less than 2m separating the two. Fibre optic strain sensing systemrnbased on Brillouin Optical Time Domain Reflectometry (BOTDR) was installed to measure continuous strainrnprofiles of the cast iron linings of Royal Mail Tunnel. This has provided valuable insights to the deformationrnmechanisms both during the pilot and final tunnel enlargement.