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The largest railway tunnel ever built in the UK, at 3.2 km long and 6.53 m in internal radius, the tunnel through the chalk of the North Downs is also the first major NATM tunnel to be designed and built in the UK since 1994. Significant savings have been achieved through value engineering of the tunnel lining and the optimising ability of an on-site design team. Integration of the project manager's and contractor's designers has allowed fast-track evaluation and assessment of design verification data. The three main areas of the design with potential for a significant effect on costs were the geotechnical parameters, a revised waterproofing philosophy and a contribution to long-term support by the primary lining. The results of settlement monitoring and geotechnical investigation are presented., The largest railway tunnel ever built in the UK, at 3.2 km long and 6.53 m in internal radius, the tunnel through the chalk of the North Downs is also the first major NATM tunnel to be designed and built in the UK since 1994. Significant savings have been achieved through value engineering of the tunnel lining and the optimising ability of an on-site design team. Integration of the project manager's and contractor's designers has allowed fast-track evaluation and assessment of design verification data. The three main areas of the design with potential for a significant effect on costs were the geotechnical parameters, a revised waterproofing philosophy and a contribution to long-term support by the primary lining. The results of settlement monitoring and geotechnical investigation are presented.

The UK's largest railway tunnel is on target to be completed five months early and more than #10 000 000 below budget, a success achieved through innovation, value engineering, integrated design and construction, and effective project management. The construction process and logistics are described, including tunnel excavation, primary and secondary lining, tunnel waterproofing, construction of walkway supports, back grouting and completion of the portal canopies. The management of the project is examined and the process of contractor self-certification discussed., The UK's largest railway tunnel is on target to be completed five months early and more than #10 000 000 below budget, a success achieved through innovation, value engineering, integrated design and construction, and effective project management. The construction process and logistics are described, including tunnel excavation, primary and secondary lining, tunnel waterproofing, construction of walkway supports, back grouting and completion of the portal canopies. The management of the project is examined and the process of contractor self-certification discussed.

The 3.2 km twin-track tunnel, on the UK's Channel Tunnel Rail Link (CTRL), has an excavated face area in excess of 166 m2 and will pass through the Upper and Middle Chalk. The chalk contains solution features, which extend down to 40 m, and is faulted with throws of up to 10 m in the Kit's Coty area, where there are associated perched water tables. Failure of the Lewes Chalk is governed by the weak character of the mass fabric but failure of the other units depends on the nature and disposition of joints relative to the tunnel. The index properties, strength, and creep and hydrofracturing characteristics of the strata have been determined. The tunnel will have a conventional shotcrete primary lining, with local reinforcement, and an in situ secondary lining. The portals, which are both in areas designated as of outstanding natural beauty, are to be in a 50 m cut-and-cover section and will have parabolic leading edges extending 8 m from the backfilled slopes., The 3.2 km twin-track tunnel, on the UK's Channel Tunnel Rail Link (CTRL), has an excavated face area in excess of 166 m2 and will pass through the Upper and Middle Chalk. The chalk contains solution features, which extend down to 40 m, and is faulted with throws of up to 10 m in the Kit's Coty area, where there are associated perched water tables. Failure of the Lewes Chalk is governed by the weak character of the mass fabric but failure of the other units depends on the nature and disposition of joints relative to the tunnel. The index properties, strength, and creep and hydrofracturing characteristics of the strata have been determined. The tunnel will have a conventional shotcrete primary lining, with local reinforcement, and an in situ secondary lining. The portals, which are both in areas designated as of outstanding natural beauty, are to be in a 50 m cut-and-cover section and will have parabolic leading edges extending 8 m from the backfilled slopes.