Tyne crossing benefits from Sirius experience

The Sirius Group has employed a range of engineering services to help with one of Britain’s biggest transport infrastructure projects: construction of the new Tyne Crossing, the second vehicle tunnel under Newcastle’s River Tyne.

Sirius was directly employed by Bouygues Travaux Publics (UK Branch), the main design and build contractor appointed by Concessionaire TT2 consortium which is part-financing, and overseeing the design and build of the £260 million project.

The Sirius work originally entailed enabling earthworks along the line of proposed diaphragm walls/haul roads which covered an area of approximately 20,000m2. Sirius was then tasked with defining the extent of gas works contamination present within riverbed sediments on the line of the new tunnel. The contract has now been expanded to include the main excavation of the south cut-and-cover section of the tunnel, which represents one of the largest and most technically demanding engineered earthworks packages available on the project.

From Soil Testing to Soil Excavation
In determining the extent of contamination, Sirius outperformed expectations, reducing the scheduled over-water drilling works to obtain samples for chemical analysis from two weeks to four days, the client benefiting from a significant cost saving as well as a job well done. The excavation work has been a more challenging project: first, Sirius prepared the south platform, including large-scale excavation and re-profiling of soils in preparation for the bentonite batching plant. Then, to enable geotechnical specialist contractor Bachy Soletanche to excavate the diaphragm walls, it was necessary for Sirius to improve the ground by cement stabilisation in order to prepare an appropriate platform for their cranes and heavy excavating equipment.

Cut-and-Cover Excavation
Works to create the new tunnel, on the southern bank of the River Tyne, extend over a distance of around 1 km in length, reaching depths of up to 30 metres in places.

In order to gain a complete understanding of the main cut-and-cover excavation works, Sirius prepared a scale-model of the new tunnel for the south section of the site, demonstrating how equipment could access between a tight network of tailor-made props, which are being used to brace the diaphragm walls. The model assisted Sirius in understanding the project, but also benefited the client by providing a pragmatic and cost-effective approach to dealing with the project challenges.

At its deepest point the cut-and-cover section of the tunnel is being excavated to 30 metres below the existing ground level, and will involve excavation of approximately 400,000 tonnes of soil, working carefully around the plethora of existing services. Other key areas for consideration include dealing with the ingress of water, weak and difficult soils and an old gas works site on the river edge which in itself required contamination clean-up as part of the preparation of the south platform. Sirius has purchased and hired specialist equipment unique to this project, such as a telescopic grabber and 50-tonne excavator, along with specialist skips to recover soils from the tightest and deepest areas of the excavation.

Given the very tight working corridor on the site, space for stockpiling is very limited. Sirius identified a number of potential sites for receiving and storing the soils. Ultimately, a nearby former colliery site was selected as the most suitable option, and Sirius was granted the relevant Environment Agency permit for a waste transfer station.

It was the well thought through preparation and effective application of combined contracting and consultancy work that Sirius carried out on site at the new Tyne Tunnel which enabled the company to dramatically expand the scope of its original work and become an inherent part of the team creating this well-engineered project.

The new tunnel, which will ultimately carry southbound traffic, is due for completion in February 2011. The existing tunnel will then close for refurbishment, with both tunnels expected to be open to traffic in December 2011.

In addition to engineered earthworks, the Sirius Group provides an extensive range of services for the investigation and reclamation of brownfield and contaminated land. As a consultant and contractor, it deals with all risks in the ground, from desk study stage through to delivering a reclaimed brownfield site to the final levels required. All of this comes with full project management, regulatory approvals and transparent validation. For more details contact Sirius on 0191 378 9972 or see www.thesiriusgroup.com

ENDS