Channel Tunnel rail links

Enabling construction of Channel Tunnel Rail Links CTRL 240 and CTRL105

LBAs experience was drafted in on the construction of international rail links in hundred-million pound developments

(Channel Tunnel Rail Link) CTRL 240

A £130M contract for Rail Link Engineering Ltd. involved the construction of a 5km length of the dual Channel Tunnel Rail Link London Running Tunnels and supporting infrastructure, East of the Stratford International Station Box, London, between 2001 and 2005

International Rail Travel Tunnel

This contract involved the construction of a 5km length of the dual Channel Tunnel Rail Link (CTRL) London Running Tunnels and supporting infrastructure located east of the Stratford International Station Box beneath in a densely populated urban area. The contract formed one of the 200 Series contracts for constructing the CTRL London Tunnels between Kings Cross and the Ripple Lane Portal at Dagenham.

Fluctuating Geology

The contract involved the construction of dual 8.15m diameter running tunnels using fibre reinforced concrete segments placed by Tunnel Boring Machines (TBMs) with Earth Pressure Balance capabilities. The tunnels were driven along a fluctuating vertical geological section, largely through extensively dewatered and depressurised Thanet Sands but occasionally cutting into the overlying Upnor Formation materials or the underlying interface with the Chalk.

Surface Dewatering

The infrastructure constructed from surface included two permanent rectangular diaphragm-walled shafts built for ventilation, access and drainage and a temporary sprayed concrete lined shaft built to remove an obstruction and for TBM retrievals at the contract boundary. In addition to the main tunnels, 8 cross-passages had to be built by traditional timber supported methods using Spheroidal Graphite Iron (SGI) Segments. The cross-passages were the principal drivers behind the need for surface dewatering measures which lowered pressures sufficiently to permit their construction with some additional in-tunnel vacuum dewatering.

LBA Role

London Bridge Associates (LBA) provided a number of senior personnel who, working for the Costain Skanska Bachy JV, both planned and priced the successful tender and subsequently managed the execution of the work with personnel drawn from all the JV companies. The secret of the success of this project lay in the formation of a capable fully integrated team who were focused on building the contracted project on time and to budget.

Senior Project Personnel

The LBA personnel included Project Director, Chief Engineer, Tunnels Manager, Tunnels Agent, Chief Surveyor, Chief Geotechnical Engineer and a number of other specialists who were directly involved in all aspects of the daily management of the contract throughout its history, from the initial tendering to final closeout.

CTRL 240 Project Highlights

  • The enabling works incorporated the modelling, design, installation, monitoring, running and maintenance of a deep dewatering scheme involving abstraction and monitoring boreholes emplaced across the contract complete with a 5km discharge pipeline network placed through the residential streets. Costing in excess of £9m, this work ultimately ensured the safe and timely delivery of the contract by providing a draw-down of the lower aquifer of over 25m, pumping in excess of 10 million cubic metres of water during the contract period.
  • Within 40m of their point of launch from the Stratford Box the tunnels passed within 4m of the underside of the LU Central Line Tunnels. To achieve this, extensive enabling works were necessary in the LU tunnels involving condition surveys, a ground investigation, structural analyses and the provision and maintenance of extensive manual and real-time monitoring systems, which were all designed, procured and managed by the CSB JV contract team to the satisfaction of the client and LU.
  • In excess of 1000 properties and 2km of surface railways were within the zone of predicted settlement from the tunnels included in the contract. These structures and assets were inspected in advance of tunnelling and monitoring provisions devised and maintained in conjunction with precautionary temporary works provisions which were instigated where and when necessary.
  • The TBM design and specification was tailored to incorporate features to minimise settlement, these included double articulation of the shield body, body and tail-skin grouting facilities, compressed air provision for face interventions, and foam injection for spoil handling.
  • TBM spoil handling was done entirely by in tunnel conveyor systems.
  • Monitoring of ground and structure movements arising due to tunnelling was undertaken by surveying methods across the area of contract with the results processed daily and reported in terms of ground loss figures to the TBM management. In places this was augmented by deep datums and remotely controlled real-time theodolite monitoring systems, reporting in e-mail and SMS text formats.
  • Strain monitoring of sections of a pair of major buried gas mains and the critical areas of a major electrical sub-station was successfully undertaken to satisfy the concerns of utility providers during critical periods of tunnelling.
  • The contract also incorporated the creation of the temporary segment casting facilities used to supply all the segments used by the running tunnels driven from the Stratford Box.

(Channel Tunnel Rail Link) CTRL 105

Synopsis

Tender planning and preparation for the award of Contract 105, St Pancras Station

Planning Experience

In 2002 LBA assisted with the smooth start up of this project by providing expertise to assist with tender planning, preparation and presentation through to Contract award and the preconstruction phase for the Costain-Bachy-O’Rourke Joint Venture bidding for Union Railways Channel Tunnel Rail Link Phase 2 – St Pancras Station Contract C105, London, UK.

Critical Initial Submission

Key elements were the development of the programme critical initial submission and the definition and implementation of management processes to set the project on its way

 

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