Tunnel units begin their journey to the bottom of the Tyne

A historic moment in North East history is taking place on the Tyne as the tunnel units for the New Tyne Crossing are floated to their final destination beneath the river.

image of Tunnel section being floated out of the dry dock

10,000 tonnes of pre-fabricated concrete make up each of the four 90 metre long tunnel units. One unit at a time is being floated out of the dry dock at Walker during January and February, to coincide with high tides and each one must be carefully navigated out of the narrow dock before beginning its 3km journey downstream to the site of the second vehicle tunnel.

Three tug boats are used to transport the tunnel unit to its temporary mooring at Howdon Basin, where it waits for a week as preparations are made for it to be lowered into place within the pre-dredged trench in the river bed between East Howdon and Jarrow.

Specialist contractor VolkerStevin Marine was appointed by New Tyne Crossing design and build contractor, Bouygues Travaux Publics, to construct, transport and immerse the four concrete tunnel segments at Walker Dry Dock.

VolkerStevin Marine’s project manager, Gerrit Smit, said: “This is an extremely precise procedure which we have been preparing for, for many months; we have a very short window of time when the water levels and currents are exactly right to transport the tunnel section downstream.  It will be docked in Howdon Basin during Sunday night and then we prepare it for immersion.  As well as connecting to the various winches, this will also include the installation of two 25m high towers, one which will provide access to the tunnel section when it lies on the river bed and a survey tower which will be vital during the immersion to ensure we know, with millimeter accuracy, exactly where the structure is when it is underwater.”

Nicolas Caille, Project Managing Director for Bouygues Travaux Publics, said: “This is a complicated and challenging part of the project, especially at this time of the year when the weather can be very harsh and the daylight hours are limited. We have permission to close the Tyne to other ships for up to 48 hours while we immerse each unit and we have highly specialised equipment and skilled divers in the river to make sure things go smoothly within this limited window.”

Trevor Jackson, Managing Director for Concessionaire TT2, said: “By mid-February we will have a tunnel across the Tyne. This is a historic achievement for the North East and one which I am very proud to be associated with. The flotation and immersion of each unit takes patience and a great deal of skill and I’m looking forward to watching this piece of history playing out on the Tyne over the next few weeks.”

Paul Fenwick, Project Director for New Tyne Crossing promoter, the Tyne and Wear Integrated Transport Authority, said: "The floating and immersion of the tunnel units are major highlights in the project overall and represent a great technical achievement. The completion of the river works means we are on schedule to open the new vehicle tunnel in February 2011."

image of Tunnel section being floated down river

The first unit to be immersed is located adjacent to Jarrow riverside and will connect to a transition structure built on the river bank which will link the river tunnel to the cut-and-cover tunnel beneath the land.

Once all the tunnel units have been positioned beneath the Tyne, rock armour will be placed above them to protect the tunnel from potential damage. The temporary internal bulk head walls and ballast tanks will be removed so that by spring 2010 there will be clear passage from one side of the river to the other.

The new vehicle tunnel is due to open to traffic in February 2011, at which point the existing tunnel will close for major refurbishment. Both tunnels will be operational by the beginning of 2012.