Over 700 instruments were installed to monitor the performance of the cut and cover tunnels that carry the Channel Tunnel Rail Link through Ashford. Careful monitoring confirmed design assumptions and provided a sound basis for changes to the construction sequence that accelerated the works. This paper highlights key features of the monitoring system. It describes the instruments that were installed, reviews their performance, and identifies practical issues that were addressed during the contract. The results help to quantify toe movements of embedded retaining walls. They identify variations in temporary prop loads that are explained by reference to the method of excavation and changes in prop stiffness during initial loading. Prompt reporting and open access to the monitoring data developed confidence and trust between the project partners, and led to closer interaction and greater efficiency.
This paper describes the interaction of the Crossrail project to deliver London's new Elizabeth line in the UK with a building situated directly over the machine-bored tunnels, close to Paddington station. The initial scheme called for the demolition of the existing building at 4–18 Bishop's Bridge Road, including extraction of existing piles, which would have had a considerable impact on the local area. Changes in the design of the Elizabeth line station at Paddington allowed a revised strategy to be considered, whereby the building could be kept, reducing construction costs to the project considerably. A combination of desk study and ground investigation works was used to identify the likely extent of the piling under the building, and to predict the risk of clashes with the tunnels. The results of analyses considering the impact of construction works on the building, and associated monitoring results are presented. The decision not to demolish produced numerous benefits aside from the reduction in cost, including a considerably reduced impact on those using the building and adjacent areas.
Section 2 of the Channel Tunnel Rail Link – now known as High Speed 1 – included the construction of a new station for the existing Thameslink rail service under St Pancras International station. This paper describes the construction of the Thameslink box on the route of the existing tunnel along with a direct passenger interchange with the new international station. Two new tunnels were also constructed forming a potential connection to the existing East Coast main-line route.
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