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Underground construction completed on Thames Tideway tunnel

London’s super sewer project, formally known as the Thames Tideway Tunnel reached a significant milestone on March 27 when a 1.2 kt (1,320 t) concrete lid was lifted on top of a deep shaft in Stratford, signifying the completion of underground civil engineering on the project.

The 25-km (15-mile) long sewage tunnel designed to dramatically reduce sewage pollution in the central London River Thames.  In a typical year, tens of millions of tonnes of storm sewage spill into the River Thames. Once fully operational, the new infrastructure will reduce those spills almost completely, Tideway reported.

Tideway, the company building the super sewer, has now built the full 25 km (15 miles), 7.2-m (24-ft) wide main tunnel, a 4.5 km (2.8 mile) connection tunnel in south-east London, and a 1.1 km (0.7 mile) tunnel in south-west London.  

“This is the moment we’ve all been waiting for,” said CEO Andy Mitchell. “The underground civil engineering on the Tideway project is now complete following eight years of dedicated hard work from all our teams working in the capital.  

“There is still work to do – we need to finish some above-ground structures and, crucially, test the system – but this nonetheless marks an absolutely critical milestone for the Tideway project and for London.” 

Following the successful delivery of this final milestone, Tideway will begin the process of ‘commissioning’ the system – ensuring the new infrastructure functions as designed – before looking ahead to bringing it into full operation in 2025.  

The final major construction work on the project involved lifting a giant, 24-m (78-ft) wide circular concrete ‘lid’ over the shaft at Abbey Mills Pumping Station in Stratford.  

Using a purpose-built gantry crane and other maneuvering equipment, the lid was lifted into place over the course of around five hours.  

The maneuver represents the heaviest lift on the super sewer project – even surpassing the lifting of Tideway’s six tunnel boring machines early in the program.  

The shaft at Abbey Mills is the deepest on the project at 70 m (230 ft) – and is the point at which the super sewer connects to the Lee Tunnel, which was completed in 2016.  

Robert Ricketts, Tideway’s Project Manager at Abbey Mills Pumping Station said: “This maneuver was a complex operation, and required careful collaboration between various teams working on this project.  

“I’m absolutely delighted that the lid is now in place, and would like to thank everyone involved in getting us to this stage.” 

Commissioning of the tunnel will likely begin over the summer, when live storm sewage flows will be diverted into the new infrastructure – essentially protecting the River Thames for the first time.  

And with the cap now on the shaft at Abbey Mills, Tideway is also continuing its architecture and landscaping works at various sites along the route of the tunnel, including Blackfriars, Victoria and Chelsea.  

These sites will soon be home to completely new areas of public realm, reclaimed from the Thames, offering an entirely new vantage point of the city.  

The Eastern section of the Tideway project is being delivered in partnership with a joint venture of Costain, Vinci Construction Grands Projets and Bachy Soletanche. 

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