Channel Tunnel Rail Link Contract 240
Costain Skanska Bachy JV
2001 – 2005
Construction Management & Supervision
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 and amongst 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.
The contract involved the construction of dual
7.15m 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.
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.
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. 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.
- The enabling works incorporated the modeling, design, installation, monitoring, running and maintenance of a deep dewatering scheme involving abstraction and monitoring boreholes.
- The TBM design and specification was tailored to incorporate features to minimise settlement.
- TBM spoil handling was done entirely by in tunnel conveyor systems.
- 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.
- 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.
- 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.
- 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.
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