Thames Reach Airport Consortium
|infrastructure||THAMES REACH AIRPORT|
|multi-modal Lower Thames Tunnel at Benfleet|
The airport development is led by the construction of a Lower Thames Tunnel that transforms the historic, radial infrastructure north and south of the Thames into an orbital and circulatory system, providing 24-hour access to the new airport from central London while also serving the whole Thames Gateway region.
The Lower Thames Tunnel combines road, rail and emergency access with utilities and services to form a multi-modal north-south infrastructure corridor that connects Canvey Island in Essex with the Hoo Peninsula in Kent, while passing directly under the airport site.
The tunnel consists of two sections, each similar to those of the Øresund Tunnel, that together accommodate a 2-track rail link, an 8-lane highway and two service roads with utilities. The utilities include high-power lines linking the national grid north and south of the Thames, pipelines for mains water, gas and aviation fuel, and conduits for telecommunications.
The north tunnel portal is located on OS gridline 83 to the north of Hole Haven near the Canvey Island shoreline. The tunnel advances south by the cut and cover method for 0.5 kilometres to just above the low-water line of Hole Haven. This length includes a casting basin where 20 No. 200m lengths of tunnel sections are cast, towed into position and sunk into a dredged trench to form 2 kilometres of immersed-tube twin-section tunnel across Thames Sea Reach to the low-water line of Blyth Sands. From here the tunnel proceeds 1.5 kilometres by the cut and cover method to the airport terminal excavation. The infrastructure corridor crosses the floor of this excavation for some 0.5 kilometres and continues as a cut-andcover tunnel from the south side of the terminal box for 2.0 kilometres, passing between Bromhey and Eastborough Farms to emerge beside Lipwell Hill. The 1.5 kilometres from the airport perimeter to the south portal is constructed as a semi-cut-and-cover tunnel to create a flood bund across the marshes. Each of the immersed tube tunnel sections is similar in length and cross-section to the 4.0 kilometre Øresund immersed-tube, road and rail tunnel in Denmark, which sets a technical precedent for the proposed Lower Thames Tunnel under Thames Sea Reach.
From the north portal the low-level, open road/rail route crosses the Canvey Island Safeway site, passes under Northwick Road and rises onto a causeway across Bowers Marshes to bridge East Haven Creek and reach higher ground north of the Fenchurch Street Line. The low-level lengths of this north route are protected by 6m high flood bunds. An area for tollgates is provided on the causeway north of Northwick Road.
Preparation of the airport site is led by construction of the road/rail tunnel, which provides spoil for raising the airport site, access for the airport construction and generates road tolls and rail tariffs ahead of the airport completion. Sheet piling of the Thames frontage and the airport terminal excavation, together with a dyke cut in the marshes and soil embanked around the perimeter, creates the airport site for distributing and settling spoil from the tunnel and from the airport terminal excavation.
Symonds: Øresund Tunnel
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