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Wan M.S.P.,Crossrail Ltd | Wan M.S.P.,Imperial College London | Standing J.R.,Imperial College London
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2014

Subsurface instrumentation was installed at a field monitoring site in Hyde Park and bordering Bayswater Road for measuring the ground responses to Crossrail tunnelling near Lancaster Gate. Prior to tunnel construction, porewater pressures were measured, both in the ‘greenfield’ ground and the ground in the vicinity of existing London Underground running tunnels, by three multi-level vibrating-wire piezometer boreholes fully backfilled with cement-bentonite grout. The pore-water pressures in the ‘greenfield’ ground were at the same time measured by conventional standpipe piezometers and pushed-in spade cells with built-in vibrating-wire piezometers. This paper investigates the performance of the multi-level vibrating-wire piezometers by comparing their post-installation and steady-state pore-water pressure measurements with those from the other piezometer types. Generally they performed well, providing an efficient means of determining pore-water pressures at several depths within one borehole. One of the ‘greenfield’ multi-level vibrating-wire piezometers indicated underdrainage within the London Clay while the other was influenced by inter-connectivity between individual piezometers within the borehole and also the presence of a claystone horizon. One borehole close to the existing tunnel indicated drainage of groundwater into it; this effect is compared with predictions made using a simplistic finite-difference model. © 2014, Thomas Telford Services Ltd. All rights reserved. Source

Wan M.S.P.,Crossrail Ltd | Wan M.S.P.,Imperial College London | Standing J.R.,Imperial College London
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2014

Imperial College in London, UK, as part of an Engineering and Physical Sciences Research Council (EPSRC) funded research project and in collaboration with Crossrail urban railway project, is performing field monitoring research to investigate how tunnelling affects existing tunnels. Comprehensive instrumentation was installed in Hyde Park and bordering Bayswater Road, beneath which the new Crossrail tunnels were constructed in London Clay below the existing London Underground Central Line tunnels. Surface and subsurface instruments were installed around the Crossrail tunnel alignments to monitor the ground response to the tunnel construction. Monitoring systems of sufficient resolution and accuracy were adopted to achieve high-quality data for assessing the tunnelling-induced ground response and mechanisms of movement from earth-pressure-balance machine tunnelling. The installation of surface and subsurface instrumentation took place in the summer of 2011. This paper describes and discusses the installation of rod extensometers, in-place inclinometers and multi-level vibrating-wire borehole piezometers. Selection of the appropriate cement-bentonite grout mixes for backfilling these borehole instruments is discussed, as this is critical for representative measurements of ground response. Some practical challenges arising during the installation process and how they were overcome are also described. Confidence in the instrument performance is demonstrated using example monitoring results from the piezometer and extensometer installations. © ICE Publishing: All rights reserved. Source

Yeow H.-C.,Flint and Neill Ltd | Nicholson D.,Arup | Ringer A.,Kier Engineering | Glass P.,BFK JV | Black M.,Crossrail Ltd
Proceedings of the Institution of Civil Engineers: Geotechnical Engineering | Year: 2014

Excavation of the western ticket hall box at Tottenham Court Road station represented a critical path activity of the Crossrail railway project in London, UK. Base slab construction and preparatory sprayed concrete lining works needed to be completed before the arrival of the two tunnel boring machines. A full observational method (OM) design was implemented to eliminate the lowest level of temporary propping, resulting in a 13 m prop-free excavation at the bottom of the 30 m deep diaphragm wall station box. This paper describes the design and successful implementation of the OM, which eliminated the need to fabricate, install and remove the fifth level of temporary propping. It covers the comprehensive review of the original design input parameters, back analysis of the most probable geotechnical design parameters and comparison of wall deflection and forces in the temporary props from early stages of the construction works. The robust strategy formulated as part of the observational method design to control the subsequent excavation is described: this included trigger criteria, a review process and predetermined contingency measures to ensure safe execution of the excavation works. A genuinely collaborative effort between client, permanent and temporary works designers, independent design checker and the contractor is elaborated. Cost and programme savings achieved by implementation of the observational method approach are outlined. © ICE Publishing: All rights reserved. Source

Mortimore R.,University of Brighton | Newman T.G.,Thames Water Utilities | Royse K.,British Geological Survey | Scholes H.,Geotechnical Consulting Group GCG | Lawrence U.,Crossrail Ltd
Quarterly Journal of Engineering Geology and Hydrogeology | Year: 2011

The geology of the Chalk beneath east London and the Thames Gateway is reviewed and key features affecting engineering geology are summarized. In particular, the variable stratigraphy preserved beneath the sub-Palaeogene erosion surface, the evidence for syndepositional tectonics in the Chalk, and the recognition of tectonic fractures and strata-bound fracture systems are emphasized. The contrasting physical properties of chalk and flint are discussed and the depth of weathering in the subcrop and outcrop are compared and contrasted. The information gained from separate ground investigations is combined to suggest that there are regions in east London where better quality chalk and less permeable ground are present between regions of poorer quality chalk with higher permeability, closely related to zones of faulting. © 2011 The Geological Society of London. Source

Dulake C.,Crossrail Ltd
Geomechanik und Tunnelbau | Year: 2011

Crossrail is a new railway currently being constructed in London and is the largest construction project in Europe. Linking existing surface railways to the east and west of the capital via 21 km of new twin bore tunnels it will run 118 km from end to end. This paper briefly summarises the benefits of the scheme and its sustainability strategy and goes on to describe the design of the sprayed concrete and bored tunnels, management and mitigation of ground movements. It finishes by outlining the contractual framework for the procurement of the main construction contracts. © 2011 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. Source

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