Management / Tunnel Vision: Inside London's £4.2 billion super sewer
Tunnel Vision: Inside London's £4.2 billion super sewer
28 April 2015 |
Clumping along in my heavy boots, dressed in orange hi-vis overalls, hardhat and with breathing equipment belted to my waist, I feel like an astronaut as I step into the lift. Except that instead of going up to a rocket, I am plunged 75 metres down into the deepest shaft in London.
There is a faint tang of sewage in the air, which is hardly surprising considering I am at Beckton, the biggest sewage treatment works in Britain, that deals with waste from 3.5million Thames Water customers.
The 75-metre deep Beckton overflow shaft is the entry point for the Lee Tunnel, a £635million project just as ambitious as the more highly-publicised Crossrail. Over the past five years, engineers have built a 6km tunnel stretching from Beckton up to Abbey Mills pumping station in Stratford, east London. The Lee Tunnel will help prevent more than 16 million tons of sewage from overflowing into the River Lee each year by capturing it and taking it down to Beckton. The sewage treatment works itself is being upgraded and expanded by 60 per cent to enable it to deal with the increased volume.
And the Lee Tunnel is just the first phase of the even more ambitious Thames Tideway Tunnel, a 25km tunnel that will handle sewage from Acton in west London through toAbbey Mills in the east. The Thames Tideway Tunnel will deal with the 34 most polluting overflow points along the Thames. Work on the £4.2billion project, known popularly as the London super sewer, starts in earnest in 2017 with engineers pulling the chain, so to speak, in 2023.
Separately, Thames Water is investing £675million into improving London’s five principal sewage treatment works.
Without the Thames Tideway and Lee Tunnel, London risks being overwhelmed by the amount of sewage pouring straight into the Thames, Thames Water tells me.
The volume of untreated sewage that spills into the tidal River Thames in an average year is 39 million tons – the equivalent of eight billion toilets flushing straight into the river. If nothing was done about it, this would reach 70 million tons by 2020.
The push to address London’s overwhelmed sewerage system has mainly come from Britain having to comply with the EU’s Urban Waste Water Treatment directive.
Overall, the three-pronged approach of the Lee Tunnel, the Thames Tideway and upgrading London’s sewage treatment centres will reduce the amount of untreated sewage flowing into the Thames by 40 per cent.
That 39 million tons currently being flushed into the Thames is around one third of the amount that was poured into the river back in the 1850s. With around 150 million tons then being flushed into the Thames, the river was biologically “dead” and the stench was overpowering. In summer 1858, Parliament had to be suspended because of the so-called “Great Stink”. As a result, Parliament passed an enabling act to raise £3million to build a network of giant intercepting sewers, pumping stations and treatment works.
In the 1860s, visionary engineer Sir Joseph Bazalgette had the foresight to build the sewerage system that Londoners still use today.
When Bazalgette started work, most of London’s rivers and streams were carrying both sewage and rainwater. Separating the two at the time was practically impossible, and so Bazalgette harnessed the north/south flows of London’s smaller rivers to feed into the Thames. To prevent the system backing up and flooding people’s homes, he designed it to overflow into the river, with 57 combined sewer overflows situated along the river’s banks from Hammersmith to Greenwich. Bazalgette built 100 miles of intercepting sewers in London using 318 million bricks.
Though built to last and still in excellent condition, today London’s Victorian sewerage system is struggling to cope with the demands of the 21st century.
At the time, the capital had a population of only two and a half million, but Bazalgette had the foresight to build in capacity for four million individuals. Today, London’s population is eight million, and set to rise to 10 million by 2030.
Standing inside the 7.2m diameter tunnel, you are overwhelmed by the scale of the project. The tunnel is the width of three double-decker buses and resembles nothing so much as a sepulchral cathedral.
The project has been managed by CH2M Hill, working with joint venture MVB – Morgan Sindall, VINCI Construction Grands Projets and Bachy Soletanches.
Andy Sefton, Lee Tunnel construction manager, tells me: “A project of this scale is mind-blowing, everything is so much bigger.”
Sefton, a down-to-earth Brummie, is visibly proud of what he and his team have achieved. The Lee Tunnel has been 10 years in the planning. The site took two years to excavate.
The next stage was to send down a 120m-long £15m tunnel boring machine (TBM), named Busy Lizzie by a local primary school. Busy Lizzie crunched her way along, blending more than 100 tons of excavated chalk with water for every metre of tunnel advance, forming a white slurry with a similar consistency to single cream, before transporting it through a pipe the length of the tunnel, so that it could be processed above ground.
In its first year, only 1km of tunnelling was completed as engineers came up against unexpected geological formations. The second year saw 6km of tunnelling completed, with engineers completing a 250-metre push in a record week.
Sefton says: “The biggest challenge for the tunnelling was getting the TBM launched. That took two years of planning alone.”
The tunnel itself has been created piece by piece, locking more than 30,000 concrete segments together to form 4,072 concrete rings. The last concrete ring was completed on January 24. An inner smooth concrete sleeve, 5.6km wide, has been inserted throughout the Lee Tunnel to prevent any seepage. A cement injection system, travelling on a flatbed railway and looking like a Soviet rocket, runs up and down the tunnel 24 hours a day. Engineers are 80 per cent of the way through completing this.
The big moment will come when the Thames Tideway connects to the Lee Tunnel. The original plan called for the Lee Tunnel to be shut down for three months during connection. Good project management has cut that downtime to between four to six weeks.
For Geoff Loader, head of stakeholder engagement, the biggest challenge has been to get public support for the project. Unlike Crossrail, which is fairly accessible for public visits and will have a visible impact on people’s lives – increasing house prices in some areas for one thing – the Thames Tideway has less tangible benefits.
Loader says: “One of the biggest challenges is to be seen as successful, and success will depend on everything we do over and above just being an engineering project. That means having a positive impact on the local community in terms of jobs and training. The difference between us and Crossrail is that people don’t get that direct a benefit. All they see is disruption, and, understandably, not wanting construction where they live.”
Towards the end of this year, engineers will pull up the railway track, switch off the lights and flood the tunnel. Nobody will come down here for another decade.