25 June 2009
Press release
Bachy Soletanche has Tyne (Tunnel) on its hands
The £38 million diaphragm walling package for the tunnel portals of the Second Tyne Tunnel is nearing completion thanks to leading geotechnical specialist, Bachy Soletanche Limited. The specialist contractor is conducting the cut and cover tunnelling works on behalf of TT2 and Tyne & Wear Passenger Transport Authority, using a variation of diaphragm walling techniques and continuous flight auger (CFA) piling.
The Bachy Soletanche team is working on both the north and south sides of the River Tyne to install 51,500m2 of diaphragm wall and 5,300m2 of contiguous piled wall. These works largely cover the construction of retaining walls for approximately 1,100m of cut and cover tunnel sections - 700m long on the south bank and 400m on the northern side.
Bachy Soletanche is also working on the transfer structures which link the submerged tube tunnel elements that form the tunnel under the River Tyne to the cut and cover tunnels on shore. These two transition structures are 18m wide by 8m long reinforced concrete boxes - 21m and 27m deep - constructed using the diaphragm wall technique.
Several different diaphragm wall techniques are been utilised on this project including hydrofraise, hydraulic and rope operated equipment. Although each of these are designed to do the same job, it is their processes which differ. The hydrofraise system grinds down rock found in the ground stratum and sucks this up to form the trench. The hydraulic and rope systems are both grab operated, but the hydraulic system can ensure better verticality and more power and is therefore used for the deeper trenches.
The walls vary in depth from 17m to 33m which provides sufficient toe beneath the level of road formation. The ground stratum is also varied - another reason for using different diaphragm walling applications - consisting mainly of glacial deposits and coal measures. Sections of the cut and cover tunnel at the approach on the south side have used an alternative walling technique which are constructed using CFA piling. 317no. 1050mm diameter piles are being installed to form contiguous piled walls.
Additional rigs from Soletanche Bachy's France and Spain operations have been sent across to ensure a full fleet is up and running at all times. With this backing from Bachy Soletanche's international sister company, the project is progressing well, on programme and in a safe and efficient manner. But with so many rigs appointed to this project, the long and narrow site can become crowded at times. As Project Manager, Claire Doby explained:
"Forward planning and a strict programme is essential to the success of this project, especially as the site itself is logistically challenging, even the reinforcement cages have to be constructed off site. What's more, the variety of ground engineering techniques being used on this site and in such large quantities makes it a very complex and exciting project. Despite the challenge, Bachy Soletanche is working safely and on programme to complete the works by the end of July 2009."
Bachy Soletanche started working on site in October 2008 after an extensive four year period of design and value engineering. With the retained wall structures near completion, excavation down to the road formation between the contagious and diaphragm walls has started and will continue in earnest to remove 230,000m3 of soil when Bachy Soletanche does finish on site.
The construction of the second vehicle crossing under the River Tyne is part of the New Tyne Crossing project and will be a welcomed addition to the strategic A19 route. When up and running, it will allow the existing 40 year old tunnel to be refurbished, a new interchange will replace the existing junction at the southern end of the Tyne Tunnel and a new toll plaza will be installed on the north side of the crossing. By December 2011 both vehicle tunnels are expected to be fully open to traffic.
The £260 million contract is one of the largest infrastructure projects in the UK.
For more information on this story, please contact Fiona Shackleton at Manifest
Communications on 01484 469601, or email fiona@manifestcomms.co.uk