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Field monitoring of ground response to EPBM tunnelling close to existing tunnels in London Clay

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Title: Field monitoring of ground response to EPBM tunnelling close to existing tunnels in London Clay
Authors: Wan, Siu Pong
Item Type: Thesis or dissertation
Abstract: Field monitoring research was performed by Imperial College London, as part of an Engineering and Physical Sciences Research Council (EPSRC) funded research project, in collaboration with Crossrail urban railway project, to investigate how tunnelling affects adjacent existing tunnels. This field research aims to establish a high-quality case history involving comprehensive instrumentation and monitoring around earth pressure balance tunnel boring machine (EPBM) tunnelling in London Clay. Surface and subsurface instruments were installed in Hyde Park and bordering Bayswater Road, beneath which the new Crossrail twin-bore tunnels were constructed by EPBMs in London Clay below the existing London Underground Central Line tunnels. Responses to tunnel construction of the ‘greenfield’ ground and the ground near the existing tunnels were measured. Sufficient resolution and accuracy of the monitoring systems were established through pre-construction measurements to ensure that reliable data were obtained. The Hyde Park monitoring data are analysed and interpreted to characterise the surface and subsurface ground displacements and stress changes which are compared with similar results from other case histories of tunnelling in cohesive soils. They are also studied together with the Crossrail contractor’s measurements from instruments within the existing tunnels and in Hyde Park. It is demonstrated from the monitoring results during the construction of the first tunnel that the surface and subsurface settlement troughs were wider in the ground near the existing tunnels, compared with the troughs in the ‘greenfield’ ground, indicating the influence of the presence of the old tunnels. The form of the surface and subsurface settlement troughs induced by the second tunnel construction is found to be dictated by the more recent construction of the first tunnel, with larger settlements and wider trough widths on the side of the first tunnel, indicating the strain-softening effect of the ground by the tunnel construction. The measured ground displacement field in near vicinity of the EPBM tunnelling, determined from the subsurface vertical and horizontal displacement measurements, is found to be directed towards the tunnel construction (i.e. ‘inward’ displacement field), as opposed to the ‘outward’ displacement field observed in an instrumented site at Dagenham for a similar EPBM tunnelling for the Channel Tunnel Rail Link project (Standing and Selemetas, 2013). It is believed that the nature of the ground displacement field in close proximity of an EPBM tunnelling (i.e. ‘inwards’ or ‘outwards’) depends largely on the relative magnitudes of the machine face pressure and tail grout pressure compared with the in-situ overburden pressure. The mechanisms of ground displacements in the near vicinity of EPBM tunnelling are established by analysing key EPBM operation variables in conjunction with the measured surface and subsurface ground response.
Content Version: Open Access
Issue Date: Sep-2014
Date Awarded: Nov-2014
URI: http://hdl.handle.net/10044/1/42249
DOI: https://doi.org/10.25560/42249
Supervisor: Standing, Jamie
Potts, David
Burland, John
Sponsor/Funder: Engineering and Physical Sciences Research Council
Cross London Rail Links Ltd
Department: Civil and Environmental Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Civil and Environmental Engineering PhD theses

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