The Silvertown Tunnel beneath the River Thames opened in April 2025, cutting journey times by up to 20 minutes and easing congestion in central London. The 1.4km twin-bore crossing links Silvertown to the Greenwich Peninsula and was delivered as a Nationally Significant Infrastructure Project.
The tunnel required a drainage system designed to manage two potentially conflicting risks: fire suppression and flooding. ACO Technologies developed a solution that addressed both challenges together rather than separately, offering useful insights for highways engineers working on similar UK projects.
Designing for fire and flood as one risk
Typical tunnel fire suppression uses sprinklers that release large volumes of water. This water, if not drained correctly, can cause surface flooding or spread spilled fuel. Silvertown’s drainage strategy had to prevent these additional hazards while allowing effective fire control.
Engineers used ACO’s QuAD hydraulic modelling software to study how sprinkler water would behave and whether a combined kerb and drainage system could cope with the expected flow rates. The analysis showed that the KerbDrain SP480 units, with splayed design, were suitable for the task.
The final installation included 2.8km of KerbDrain along one edge of each tunnel bore. A total of 5,600 units were installed with gully outlets spaced every 15 metres. Inlet diameters were kept at 50mm or less to reduce the risk of blockages while maintaining capacity, meeting Transport for London’s safety requirements.
Flame traps to prevent fire spread in drainage
Spilled fuel entering drainage systems can ignite, potentially spreading fire downstream and increasing danger. To manage this, ACO designed a bespoke flame trap featuring a U-bend between the KerbDrain gullies and the main carrier pipe. This ensured that pipes remained partially filled with water, creating a barrier to fire propagation through the drainage network.
This bespoke design confirms that standard drainage components may be insufficient in high-risk tunnel environments, requiring tailored solutions for safety and compliance.
Expansion joints that absorb movement without leaks
Tunnels experience structural movement, especially at transition points. Drainage systems must accommodate horizontal and vertical shifts without leaking or misalignment. At Silvertown, expansion joints were designed to allow 20mm horizontal and 16mm vertical movement while withstanding a ten-tonne wheel load.
ACO supplied stainless-steel expansion joint units anchored on both sides of the KerbDrain SP480 system. These units passed rigorous testing under the Design Manual for Roads and Bridges for accidental wheel loading. Two flexible 100mm polypropylene pipes behind stainless steel covers maintained flow continuity across the joints, ensuring drainage performance despite movement.
A fully integrated drainage system
The Silvertown Tunnel exemplifies a systems-based drainage approach. Kerb, drainage channels, flame traps and expansion joints were designed and installed as one coordinated solution rather than separate parts. This integration simplified installation, improved reliability and met stringent safety standards crucial for large infrastructure.
This approach and the lessons learned offer valuable guidance for delivery of tunnels across the UK. Early-stage hydraulic modelling, thorough planning and bespoke engineering help deliver drainage systems that are both resilient and compliant.
Applying these principles equips contractors and authorities to manage the demands of modern tunnel programmes, ensuring drainage performance and safety for decades.
