A bespoke combined kerb drainage solution from ACO is playing a key safety role at the new Silvertown Tunnel, which runs beneath the Thames.
The tunnel is designed to ease congestion and reduce journey times in central London. Commissioned as a Nationally Significant Infrastructure Project (NSIP), ACO Technologies was tasked with crafting a solution to address the risk of fires and floods, including sprinkler-induced flooding and of vehicle fires spreading through the drainage system.
Brought on board by principal engineering consultancy COWI, part of the Riverlinx construction JV, ACO’s water management and building drainage divisions developed a solution to mitigate these risks, featuring a dual-purpose pipe connection that functions as a flame trap.
ACO began by performing hydraulic analyses using its QuAD software, modelling flow rates over the tunnel’s gradients and geometry. This, the firm explained, confirmed that the splayed KerbDrain SP480 units could manage the volume of water released by the sprinkler system.
Forming 2.8km of combined kerb drainage along one side of each tunnel, a total of 5,600 units of ACO’s KerbDrain SP480 were installed, with KerbDrain Gully outlets every 15m. This system meets Transport for London’s specification of 50mm inlet diameters or less, while preventing blockages from debris.
The KerbDrain system also features a flame trap system. To reduce the dangers involved with fuel spills entering the drainage network and alighting and spreading, ACO engineered a u-bend between the KerbDrain Gullies and the carrier pipe. This aims to ensure the pipes are always partially filled with water, which means fire is prevented from spreading through the downstream network.
The flame trap is constructed from stainless-steel components by ACO Building Drainage and uses a custom spigot to join 170mm ductile iron pipes with 160mm stainless-steel pipes.
ACO revealed that by April 2024, with many KerbDrain units already installed, it became apparent that expansion joints were necessary at tunnel interfaces to accommodate movement without disrupting drainage. The firm designed an accessory to link the SP480 units while allowing for this movement.
Faced with a two month deadline, ACO’s research and development team designed and tested a new channel expansion joint capable of accommodating 20mm of horizontal and 16mm of vertical movement, all while withstanding the force of a ten tonne lorry.
The end product was a stainless-steel unit anchored on each side of the KerbDrain SP480s. It features ribbed reinforcement and has been tested to EN1433 standards. ACO also specified two flexible 100mm polypropylene pipes, positioned behind the stainless-steel cover, to ensure water is carried across the joint effectively.
Mathais Hansen of COWI said, “We recognised the need for ACO’s specialist expertise, given their proven track record with projects like the Hindhead Tunnel in Surrey and their strong reputation for tunnel projects in Germany.
“Tunnel vehicle fires, which risk trapping people and hindering emergency response, necessitate controlled fire suppression despite associated flooding risks. ACO’s solution expertly mitigates both hazards while complying with specifications.”
Terry Wilkinson, specialist design & application engineer at ACO, added, “It isn’t every day that you get to work on a project with such significance as Silvertown Tunnel and we’re proud to have our solutions specified. By combining all of our experience across our divisions and working meticulously with Riverlinx, we’ve come up with a drainage system that satisfied all the necessary requirements from TfL and make the tunnel safer for users and the tunnel infrastructure itself.”
