The new concrete infrastructure safeguarding the Thames.
After ten years of construction, London’s £5 billion Thames Tideway Tunnel is now fully connected and operational, marking it as one of the UK’s most ambitious civil engineering projects of the 21st century. The 16 miles of concrete tunnel runs beneath the River Thames, capturing and diverting combined sewage overflows to protect the capital’s waterway whilst significantly improving the health of the river environment.
At its core, the tunnel’s precast concrete segments form a watertight, durable lining capable of withstanding immense hydrostatic pressures and aggressive ground conditions. Its geometry, large enough for three London buses to fit side by side, provides the long-term capacity required to meet the needs of a growing city. Concrete’s inherent durability and resistance to corrosion made it the material of choice, ensuring a 100 year design life for this critical piece of infrastructure. Advanced mix designs were also used to enhance strength, reduce permeability and minimise maintenance requirements, ensuring that the structure will continue to perform effectively for generations to come.
In May 2024, the new super sewer was connected to the Lee Tunnel, which has been in operation since 2016, completing the full London Tideway Tunnel network. Together, the tunnels have a combined capacity of 1.6 million cubic metres, roughly equivalent to 600 Olympic sized swimming pools, protecting the entire tidal Thames from pollution.
Once captured, sewage follows through the 7.2 metre diameter tunnel towards the treatment facilities downstream. The tunnel begins at Acton in West London, 31 metres below ground level and gradually descends to a depth of 66 metres at Abbey Mills Pumping Station in East London, following the natural gradient of the river.
Construction of the main tunnel was carried out using four giant tunnel boring machines (TBMs) each named after inspirational women connected to the local area. Two smaller tunnelling machines were used to create connection tunnels in Greenwich and Wandsworth, including TBM Selina, named after Dr Selina Fox, who founded the Bermondsey Medical Mission in 1904. Across the project twenty one shafts were constructed, some to launch the tunnelling machines and others to channel sewage flows into the tunnel network.
Before the Tideway project, London’s Victorian sewer system, designed for a population less than half its current size and frequently discharged millions of tonnes of untreated wastewater into the River Thames. The new system is expected to eliminate 95% of these sewage spills, preventing over half a million tonnes of pollution each year. With heavy construction now complete, the system’s commissioning phase is under way and the tunnel is already intercepting and transferring waste away from the river.
FP McCann Precast Concrete Shafts Installed at Heathwall Pumping Station
As a member of the supply chain, FP McCann played a vital role in the delivery of two precast concrete segmental shafts, both of which have been sunk at the tunnel’s central London site at Heathwall Pumping Station.
Working in a highly constrained urban site presented multiple challenges to the contractors in charge of sinking the shafts, including proximity to the River Thames and neighbouring residential areas.
The smaller of the shafts at 11.4m ID was sunk to a depth of 28 metres below ground, while the second shaft, which is larger at 17.5m ID and at 54m deep, links to the base of the small shaft by a 2.4m ID 42 metres long culvert tunnel. Both shafts were sunk using the jacked caisson method to a depth of 16m followed by the underpinning method of construction to a depth of 33m and utilised Spray Concrete Lined (SCL) to 54m BGL. The smaller shaft was constructed using the same methodology.
Images, FP McCann and Tideway