DESIGN OF THE LIMEHOUSE BASIN TUNNEL

Access to the heart of London's fast-moving Docklands redevelopment has been much hampered by traffic congestion; virtually the only way into Canary Wharf lies in negotiating the overloaded A13. The London Docklands Development Corporation has attacked this problem by appointing a joint venture between Balfour Beatty Ltd and Fairclough Civil Engineering Ltd to build a tunnel, allowing easier access to the Isle of Dogs from the West. Highways and Transportation talks to Brian Bell of the design consultants Robert Benaim and Associates who have been awarded the contract to design the Limehouse Basin section of the tunnel. Although the rest of the tunnel is built by the top down method, in the basin area the tunnel is to be excavated in a cofferdam, with a conventional concrete cut and cover tunnel built by the bottom up method. The tunnel at this point will be 24 metres wide, including the walls. The base slab has a toe extending 1 metre thick and a 600 mm thick centre wall. Across the width of the tunnel the roof and base slabs taper from 1.4 metres at the centre to 1 metre at the outside, the base having a further 750 mm of integral concrete road construction on it with services in trenches to either side. The method of construction of the tunnel is briefly described, together with the role of the 3D surface modelling system, MOSS, which has enabled the production of drawings of cross sections, elevations, plans and perspectives at any scale, and throughout the design process. (TRRL)