Distributed fibre optic sensing of a deep excavation adjacent to pre-existing tunnels

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Li, Zili
Soga, Kenichi
Kechavarzi, Cedric
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ICE Publishing
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This research study investigated diaphragm wall (D-wall) behaviour due to deep excavation at Paddington tunnel station site in London Clay. The Paddington site was the only train station in the Crossrail project constructed using a top-down excavation, and it provided the opportunity to evaluate the effect of a pre-existing tunnel on D-wall behaviour using distributed fibre optic sensing (DFOS) for the first time. Distributed fibre optic cables were embedded in the D-wall panels to monitor the changes in strain conditions during three key stages of construction; tunnel passage, concourse excavation and base excavation. After station construction, relevant finite element (FE) analysis was conducted to evaluate the D-wall performance during excavation, and the computed results were compared against the field measurements recorded by embedded DFOS in the D-wall as well as the ground inclinometers. The DFOS measurements depicted the D-wall behaviour in agreement with the conventional inclinometer method and FE results, demonstrating its feasibility in monitoring underground earth retaining infrastructure. A comparison between the D-wall behaviour with pre-existing tunnels at Paddington site and that of the same wall without tunnels allows providing some guidance for the design and construction of retaining structures adjacent to pre-existing tunnels.
Field instrumentation , Tunnels , Tunnelling , Wall-tunnel interaction , Top-down excavation , Pre-existing tunnel , Distributed fibre optic sensing , Diaphragm wall
Li, Z., Soga, K. and Kechavarzi, C. (2018) 'Distributed fibre optic sensing of a deep excavation adjacent to pre-existing tunnels', Géotechnique Letters, 8(3), pp. 171-177. doi: 10.1680/jgele.18.00031
© 2018, ICE Publishing. All rights reserved. This document is the Accepted Manuscript version of a Published Work that appeared in final form in Géotechnique Letters 8(3), pp. 171-177. To access the final edited and published work see https://doi.org/10.1680/jgele.18.00031