Before Sir Joseph Bazalgette’s sewer network, during the hot, dry summer of 1858, the smell from the Thames was so appalling that the curtains in the Houses of Parliament were soaked in chloride of lime in a vain attempt to protect the sensitivities of politicians. As a direct result, a bill was rushed through Parliament allowing civil engineer Bazalgette to construct a massive new sewer scheme for London.
150 years later, Bazalgette’s interceptor sewers are still the backbone of London’s sewer network today. His design centred around using the city's natural drainage system of 'lost rivers', such as the Fleet and the Tyburn, which had already been built over before Victorian times, to fl ow into his new interceptor sewers and transfer to balancing tanks in east London.
Bazalgette was a great visionary for London. “The interceptor sewers were the largest civil engineering project in the UK in the 19th Century,” says Phil Stride, director of external affairs at Tideway. “When he designed them in the late 1850s there were two million people in London, he had the vision and foresight to deliver to four million people, and now there are eight million people. So while they are in excellent condition, it doesn’t take a lot to imagine that they struggle in terms of capacity.”
When Bazalgette’s sewer network was being designed, there was no reason to believe London’s population would rise exponentially to its current levels, or how much water and solid waste would be dispersed. In times of severe storms, the system was designed to overfl ow through discharge points on the banks of the river into the River Thames, rather than fl ooding streets and homes.
When designed, this would have happened once or twice a year. It now happens every week, on average. “In a typical year 39Mt of sewage is discharged into the tidal River Thames and fi gures for 2014 show 62Mt of sewage was discharged into the Thames, which is a big problem,” says Stride.
The proposed solution is the super sewer – also known as the Thames Tideway Tunnel. “The Thames Tideway tunnel is the only solution that can be delivered to meet the standards set by the Environment Agency and within the timescale set by Government,” he explains.
Work begins
Construction work for the Central 25km interception, storage and transfer tunnel running up to 65m below the river, starts this year. The Thames Tideway Tunnel will be built from three main construction drive sites, under three separate contacts, in Fulham, Battersea and Southwark and will require the use of 24 construction sites, 11 of which are located along the river bank.
A joint venture between Laing O’Rourke and Ferrovial Agroman has landed the largest central section drive worth GBP 600M to 900M. The eastern section of the tunnel has been bagged by a Costain, Vinci and Bachy JV and is expected to cost GBP 500M to 800M (USD 734M to 1.174bn). While the consortium consisting of Balfour Beatty, BAM Nuttall and Morgan Sindall has picked up the shorter western tunnel drive, which is expected to be worth around GBP 300M to 500M.
“The tunnel will run from Acton in the west of London down to Hammersmith, and from Hammersmith it follows from west to east the route of the River Thames, all the way through west London and central London to a site called King Edward Memorial Park in the London borough of Tower Hamlets. From there it goes up to Abbey Mills Pumping Station. There are also two connection tunnels – one from Greenwich Pumping Station to Southwark and the smaller Frogmore connection tunnel,” says Stride.
A joint venture between Laing O’Rourke and Ferrovial Agroman has landed the largest Central section drive. The Eastern section of the tunnel has been awarded to a Costain, Vinci and Bachy joint venture, while Balfour Beatty, BAM Nuttall and Morgan Sindall has picked up the shorter western tunnel drive.
Site selection
The Thames Tideway Tunnel has not been without controversy. Since its initial proposal, questions were raised on the cost – the project is expected to cost GBP 4.2bn (USD 6.16bn) – the location of construction sites and duration and associated disruption of the works.
“As we are tunnelling through a built up area, there was always going to be some controversy or debate on the sites we ultimately selected,” notes Stride.
“We thought with that being the case it was really important that we agreed on the method we would use, so we could just debate how the method was going to be used. Otherwise we would have people tell us that they didn’t agree with the site we had chosen and they don’t agree with the method we’ve chosen to select the site. So that’s what we did and we originally considered more than 1,100 sites.”
These potential sites were then further evaluated against more detailed planning, engineering, environmental, property and community considerations resulting in a shortlist of sites.
“It is no good from a design point of view if we think it would be really good to have a site in a certain area but all that is there is residential buildings, or even areas of land where people are currently developing,” explains Stride. “Since one of the criteria of the site selection methodology was to not knock down residential property, so it’s a very iterative process of looking at the design, looking at what was available, seeing what was available and feeding it back into the design. So that led to our original scheme, which we then put out for consultation in September 2010.”
Consultation inundation
Stride said that through the process more than 9,000 pieces of feedback were received. In response to the comments received, changes and improvements to some of the sites were made.
“In all that feedback we received there were two key messages that could be summarised; where you can build on brownfield instead of greenfield, and where you can use the river for transporting materials rather than the road.
“So we changed our plans significantly. Some of the main drive sites changed for instance. One in the West, was originally in a place called Barn Elms, which is in a playing field, is a good example of where we went from a greenfield site to a brownfield site.”
The second consultation took place during November 2011, and the planning application was submitted in February 2013. This was the largest planning application ever submitted in the UK.
“The key challenge in any built up area is that we will do everything we can to be a considerate neighbour,” explains Stride. “We committed to do everything we could to limit noise, dust and light from the construction sites, and also initially addressing the development consent order process we did everything we could to move materials by river rather than road – for example, we committed to moving a minimum of 90 per cent of the material from the main drive excavations by river.”
Michael Francis, tunnels practice leader, Mott MacDonald, adds that most of the sites have unique challenges. “At Greenwich Pumping Station the shaft is constructed close to a Grade 2 listed building and the DLR viaduct; at Earl Pumping Station the site is contaminated and there is limited space due to the configuration of existing structures; King Edward Memorial Park and Deptford Church Street Sites are in the context of public open space park areas.
“Breaking into the existing Victorian sewers is challenging in all cases. We are using comprehensive BIM models to ensure we have a multidisciplinary design which is totally integrated. We are developing a sustainable design that builds on experience gained on the Lee Tunnel Project and challenges the conventional approach with innovation wherever possible.”
The project also includes makeovers of local areas; for example, at Barn Elms, Tideway will be providing modern changing rooms and a cafe for people using the sport pitches, there will be more viewing platforms along the River Thames, and at Deptford Park Street – where the tunnel will connect to the sewer under the park – the park will be regenerated through landscaping with the local community.
After more than five years of consultation, planning and the awarding of contracts, the first visible signs of construction activity were apparent late in 2015 in central London. “Having worked on the project for many years it is quite an exciting landmark that we are actually out on these sites getting them ready for the main construction,” says Stride.
At Chambers Wharf – which will be used to drive the main tunnel to Abbey Mills Pumping Station and receive the main tunnel from Kirtling Street, to the west – the site is being prepared for the main construction works. The works include the demolition of structures including a substation and removal of stockpile. “Thames Water are removing massive amount of rubble that was left on the site when it was purchased by the firm in 2011. So there is a big operation on clearing the site by river.”
At Blackfriars Bridge work has begun, this time by Tideway, to prepare the site for the main construction to start. Work includes construction of the new Millennium Pier, to replace the existing Blackfriars pier, which is being moved to make way for work under and around the road and rail bridges, a new public lift and staircase to access Blackfriars Road Bridge while the existing pier is taken out.
Adjacent to the pier was moored the ex-HMS President, the 98-year-old WW1 veteran Q ship, which has now been tugged down to the Medway for restoration.
Geological investigations
In order to begin the main works, Tideway undertook the biggest linear geotechincal investigation to take place in London. “We’ve done over 300 boreholes – either land based ones or ones in the river over the line of the tunnel,” says Stride. “It’s a very extensive geotechnical investigation.”
Now that most of the London Clay formation has been used up by tunnelling projects, new tunnels are being forced to go deeper and penetrate the Lambeth Group deposits more and more. Thames Tideway Tunnel goes through all of London’s geology including London Clay, Lambeth Group, Thanet Sands and Chalk.
“The geology in the west is London Clay; so the shaft at Carnwath Road Riverside is roughly at the point where the geology changes from clay at the tunnelling horizon to mixed sands and gravel,” explains Stride. “Then there’s mixed sands and gravel generally all the way through Central London both sides of Kirtling Street all the way through to Chambers Wharf.
“There we’ve got Thanet Sands and Lambeth beds. On the eastern section we have chalk, which is similar to where Thames Water worked on the Lee Tunnel, the link between Abbey Mills Pumping Station and Beckton and the tunnel the Thames Tideway Tunnel will connect into.”
In the west, Tideway is anticipating the use of an EPBM, while it is expected that a slurry machine will be used for the eastern sections, since a slurry machine was used for excavating the Lee Tunnel.
Stride says: “One of the best understood tunnelling mediums is through London Clay, which is what we have in the west. In the centre, as we get deeper we have more water pressure to deal with – it will go up to seven or eight bar when you get to Abbey Mills Pumping Station.
In the central section, another challenge is that we have mixed sands and gravels. The TBM needs to be designed to deal with the water pressure and the mixed sands and gravels it will encounter.
“In the east, where the water pressure is greatest of the three sections because it’s deepest, we’ve got chalk. Although chalk is a good tunnelling medium, the key challenge there is the flints within it. So a slurry machine that is capable of dealing with flints – some of the flints we are anticipating are 1m across – and the TBM needs to cut these without getting damaged.”
In addition, Francis says that they expect to encounter contamination during shaft excavation in the historic industrial areas on some sites. “This will require special measures including ground treatment to minimise risk to construction personnel and the public. The shafts lined with diaphragm wall and internal linings are designed to minimise risks in construction.
The TBM is designed to reduce risks associated with a high proportion of flints and the possibility of a dip in the top level of the chalk. Linings of shafts and tunnels are designed as composite structures to provide structural capacity.”
Lining and production
The main tunnel will be lined with a primary steel fibre reinforced segmental lining. Inside the segmental lining it will have a secondary cast in-situ lining, and Tideway is currently looking at how that will be reinforced.
Both sprayed concrete lining and pipe jacking are being considered for the primary lining for the connection tunnels, and have a cast in-situ secondary lining.
The project timeline has shifted, and the completion date has been brought forward from 2024 to 2022, Stride notes. “Our CEO, Andy Mitchell, challenged the main works contracts to see how they could reduce the programme, while not in any way compromising health and safety.”
Stride adds: “When we’re in full production we are going to employ some 400 to 450 people at the main drive site. We’re getting on and setting up. What’s going to be starting towards the end of this year, beginning of 2017, is we’re going to be constructing the main drive site shafts. Towards the end of 2017 after that’s completed we’ll start the main tunnelling.
We’ve just agreed our Strategic Target Schedule and we’re working towards completion in 2022.”
Stride says that Tideway is creating “more than just a tunnel". Tideway is hoping the project will impact the city’s economy – 90 per cent of the expenditure will take place in the UK and the company has challenging targets around local employment and using small enterprises – plus improve the aquatic environment.
“Furthermore, our vision for the project is to reconnect London and Londoners with the River Thames,” says Stride. “Over the years, the Thames has been less clean than it is now, there are good examples of people building along the Thames where they’ve actually faced the building away from the Thames as opposed to towards the river.
“We are keen to create a legacy that everybody can be proud of; we want Londoners and ultimately Thames Water customers who pay for the project to get the best value from the project”
