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.
A most interesting paper expanding our knowledge on this subject. Perhaps I can add a little from my experience of ascertaining strut temperatures, which is even more difficult than it appears in the paper. The surface temperature of the steel exposed to direct sunlight varies rapidly in the event of clouds passing across the sun. The temperature gradient between sun and shade occurs over approximately 50 mm, and where the temperatures were measured on the topside and underside of the top flange of an I section, the underside was at shade temperature. It would be useful to know the temperatures on the inside of a tubular section. It is possible that we may in fact be overestimating the average temperature rise. Could the authors advise us of the type of analysis and soil parameters used to arrive at the design loads, and of the cost of the monitoring operation (including or excluding staff time in analysing the results).
This is the accepted version of the paper.This version of the publication may differ from the final published version. that support Moorhouse and the presence of these foundations placed tight constraints on acceptable ground movements associated with construction of the shaft. The depth of the shaft is such that it penetrates through stiff London Clay and is founded at the bottom of the Lambeth Group. The paper describes the contingency measures to deal with potentially difficult ground conditions including the water bearing layers of the Lambeth
Permanent repository linkGroup. The construction processes included a complex temporary works dewatering system around the shaft with the option to carry out additional dewatering from within the shaft during excavation. Provision was also made for radial grouting to "restress" the ground, to prevent long-term settlement of the Moorhouse piles, should the need arise. The success of the project was due, in no small part, to the detailed planning and consideration of contingency measures to deal with perceived risk.
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