The Silvertown Tunnel linking Silvertown to the Greenwich Peninsula in east London showcases role of precast concrete in sustainable infrastructure, low carbon delivery and the use of calcined-clays.
Precast concrete is the offsite solution of choice when delivering large infrastructure projects, especially those that take us underground. There have been a string of notable projects coming to fruition over the past few years all of which have utilised the intrinsic benefits of precast concrete. Some of the more prominent examples include: Silvertown, Thames Tideway, Elizabeth Line and HS2 Green Tunnels.
Precast concrete is a popular choice for tunnel construction due to several advantageous properties and practical benefits. The big one being quality control. Precast concrete elements are designed to meet specific structural requirements and can be manufactured to exact specifications. This precision leads to improved fit and finish, enhancing the overall structural performance of the tunnel. Precast elements are manufactured in a controlled factory environment, ensuring consistent quality and strength. This controlled setting allows for better monitoring of concrete mix, curing conditions, and overall manufacturing processes compared to on-site casting. Factory production has other benefits on efficiency, programme and cost savings as well as health and safety risk reduction with fewer site-based activities and weather-related delays.
Precast concrete can be customised to meet the unique requirements of a tunnel project. This includes special shapes, sizes, and reinforcement configurations. The flexibility in design allows for innovative engineering solutions tailored to the specific needs of the tunnel, something Banagher Precast Concrete used to deliver a UK first on the Silvertown Tunnel project. The predictability of precast concrete elements in terms of dimensions, strength, and performance ensures fewer surprises during construction. This consistency helps in better planning and execution of the project.
These advantages make precast concrete an efficient, reliable, and cost-effective solution for tunnel construction. The Silvertown Tunnel project in London showcases just some of what can be achieved using precast concrete as the construction method.
Silvertown Tunnel
The Silvertown Tunnel in London is the largest diameter tunnel project undertaken in the UK to date. The twin-bore tunnel sits beneath the Thames linking Silvertown to the Greenwich Peninsula in east London. The aim of the project, due to open in 2025, is to help reduce the congestion through the Blackwall Tunnel as well as support public transport links. Infrastructure projects like this are vital to increase the sustainability of major cities like London, here tackling the huge social and environmental issues linked to poor air quality.
The main contractor, Riverlinx JV (Ferrovial, BAM Nuttall, SK Ecoplant), commissioned precast manufacturer, Banagher Precast Concrete, to supply 10,260 segments for the 2.2km of tunnels. Banagher worked closely with the client and consulting engineers to deliver the redesigned and intricate precast cross-passage segments, a critical element for the project to remove the requirement for propping during the construction of the cross passages – a UK first.
Banagher also managed to deliver impressive carbon savings of 1,480 tonnes of CO2 on the project. The carbon savings were achieved through incorporating 39% ground granulated blast furnace slag (GGBS) into the concrete mix design and use of steel fibres reduced the impact associated with traditional reinforcement.
Calcined-clay a new light at the end of the tunnel
Using waste clay in cement production could reduce the material’s embodied carbon by up to 30% and boost UK construction’s circular economy, according to a new report. A two-year study led by the Mineral Products Association (MPA) with funding from Innovate UK has demonstrated that UK reclaimed clays and finely ground brick powder can be used as calcined clays in cement and concrete manufacturing to deliver lower emissions compared to the market-leading CEM I cement.
The findings confirmed that calcined clays from these sources have the potential to divert 1.4 million tonnes of material from potential waste streams if the materials were adopted by the UK construction industry.
Clay is a naturally abundant material in the UK and can offer an alternative to industrial by-products such as GGBS and fly-ash which have been used in projects like Silvertown to lower embodied carbon. UK production of both materials is reducing as the power and steel industries decarbonise, so innovating new approaches is important as the concrete sector moves towards a net zero future.
An interesting application of this material is being pioneered by the HS2 rail project, which is working on a circular process that involves taking the material excavated by its tunnel-boring machines, calcining it on site and then using it as a binder on new infrastructure elements.
By their nature tunnelling and deep excavations generate large volumes of spoil that need to be transported and disposed of creating carbon emissions. By opening up possibilities for re-purposing some of this material into a circular process the future of large infrastructure projects could include calcined-clay based supplementary cementitious materials.
For more information visit: www.mpaprecast.org
Key features of the Silvertown Tunnel
Owner: Transport for London
Client: Riverlinx JV (Ferrovial / BAM UK & Ireland / SK ecoplant)
Consultants: COWI and Gall Zeidler Consultants
10,242 Tunnel Segments
Innovative steel-fibre reinforcement
Concrete mix 39% GGBS
1,480 tonnes of CO2 saved
1,000 trees planted by Banagher
ISO 17025 accreditation.
Image: London’s Silvertown Tunnel is the largest diameter tunnel project undertaken in the UK to date. The twin-bore tunnel sits beneath the Thames linking Silvertown to the Greenwich Peninsula
Source: Offsite Magazine – Issue 44
