Tunnelling close beneath an existing tunnel in clay – perpendicular undercrossing

Abstract

A series of centrifuge model tests in clay were carried out to investigate the response of an existing tunnel at different clear distances to new tunnelling. A three-dimensional staged tunnelling model was adopted to simulate a wide range of tail-void volume losses for the new tunnel construction whilst monitoring detailed three-dimensional soil surface settlements and tunnelling induced strains in the existing tunnel lining. The paper also presents a detailed case study of a similar scenario in the London Underground redevelopment of Bond Street Station; various state-of-the-art instrumentation including fibre optic Brillouin Optical Time Domain Reflectometry, instrumented tunnel bolts and photogrammetry were deployed to monitor the response of the existing Royal Mail tunnel due to the new tunnelling works close beneath. The combination of field and centrifuge modelling data provides important new insights into the deformation mechanisms encountered in such complex tunnelling scenarios.