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Mayor opens London's first super sewer

The Mayor of London yesterday officially opened the Lee Tunnel, the first of two super sewers which will dramatically improve the health and cleanliness of the Rivers Lee and Thames in the capital.

London has outgrown its Victorian sewage system network, which captures both rainfall and sewage and was designed to be used by up to two million people, but is now used by more than six million. In a typical year, 39 million tonnes of untreated sewage mixed with rainwater has been discharged into the River Thames from overloaded treatment works and combined sewer outfalls. These discharges have prevented flooding of homes and streets after heavy rainfall, but at the cost of serious pollution to the river. The biggest of these outfalls, at Abbey Mills pumping station, has been discharging 16 million tonnes of sewage to the River Lee in a typical year. The Lee Tunnel will capture the polluting sewage and keep it out of the river, which will become much cleaner.

By increasing capacity in the sewer network the tunnel will carry the excess sewage, which has previously been discharged to the River Lee, to Thames Water’s Beckton sewage works in Newham for treatment, with renewable energy being generated from the bi products known as sludge.

The Lee Tunnel is the largest single project in the history of the privatised water industry in England and Wales and is the deepest ever bored under the capital at around 75 metres deep. It is the width of three double decker buses and is the most significant development of London’s Victorian sewers since Sir Joseph Bazalgette originally built the network in the 1860s. The tunnel was completed in January 2014. The five associated shafts are the deepest constructed in the London Basin. The project also includes 6 mega pumps of 3MW each. At its peak, MVB employed 750 people at the same time on this project.

The project’s success was made possible thanks to constant innovations, such as replacing traditional concrete with steel fibre reinforced concrete. This innovative SmartShell™ secondary lining technique, designed by UnPS, the Tunnel and Shafts designer of the Lee Tunnel, was first developed on the deep shafts of this project. The steel fibre reinforced concrete was applied as a secondary lining to the tunnel and brought a multitude of design, cost and efficiency benefits, including the elimination of 15,000 tonnes of steel rebar, £13.5 million saved on material costs, and a significant saving on construction time. Thanks to this method, a maximum productivity of 300 linear metres per week, which equals two concreting operations a day, 10 operations per week was achieved.

MVB and UnPS successfully developed this workable and pumpable concrete mix with Cemex and the newly developed Dramix 5DTM fibre (by Bekaert) to fulfill the high performance criteria.

The Lee Tunnel project has already received a number of industry accolades, including the ICE’s “Infrastructure Award” and the “Greatest Contribution to London Award” for the tunnel’s diaphragm walls; it also got several Gold Awards from the Considerate Constructors, as well as the “Project of the Year” at the Ground Engineering Awards. UnPS, the Tunnel and Shafts designer of the Lee Tunnel, was presented with the “Design Innovation of the Year Award” at the 2015 NCE Tunnelling & Underground Space Awards in recognition of the innovative SmartShell™ tunnel lining system it developed.

Alongside major upgrades already completed by Thames Water at its five main sewage works along the tidal River Thames, the Lee Tunnel will transform the quality of the River Thames and River Lee for river users, wildlife and those who live and work in the capital for generations. Construction on the Thames Tideway Tunnel, which will connect to the Lee Tunnel, will start later this year. Morgan Sindall is involved in the delivery of Tideway West and VINCI Construction Grands Projets and Bachy Soletanche in Tideway East.

The Mayor Boris Johnson, in partnership with Thames Water, the Environment Agency and London Councils recently launched the first London Sustainable Drainage Action Plan, identifying potential flooding hotspots across the city and proposing innovative ways of diverting rain back from the sewers into the soil with rain gardens or green roofs.

The Mayor of London Boris Johnson MP said: “This amazing new super sewer is providing the bold infrastructure needed to support the movements of our rapidly growing city. For years our historic Victorian systems have heaved at the seams, muddling along, battling to cope with the increasing rainfall and waste of a modern population. Now the River Thames will benefit from vast improvements to its water quality with less pollution and overflow. Alongside my sustainable drainage work to reduce flooding, the investment in the Lee and the forthcoming Thames Tideway Tunnel are set to benefit Londoners for generations to come.”

Thames Water chief executive Martin Baggs added: “We are honoured that the Mayor of London, Boris Johnson, was here to celebrate the opening of the ground-breaking Lee Tunnel, which is a crucial part of our ongoing work to clean up the River Thames.

“While the Victorian system still works very well, it needs additional capacity to cope with 21st century London. The Lee Tunnel and, when completed and connected, Thames Tideway Tunnel, will together capture the tens of millions of tonnes of sewage that currently overflow untreated into the tidal Thames every year. This will protect the future of the iconic river and capital for future generations.”
François Pogu, MVB Project Director declared: “This Franco-British success will leave a great legacy for generations to come. We are all very proud at MVB to have contributed to such a project.”

The £678 million Lee Tunnel runs 6.9km from Thames Water’s Abbey Mills pumping station, the biggest in Europe, and will act as a collection and storage tank before transferring the flows to Beckton sewage works, which Thames Water has expanded by a further 60 per cent to manage the increased volumes.