“The Thames Tideway Tunnel is the biggest construction project ever undertaken in the UK water industry,” says Mark Sneesby, Thames Tideway Tunnel chief operating officer.
The £4.2bn Thames Tideway Tunnel, also known as the ‘Super Sewer’, is part of the London Tideway Improvements Scheme, which is expected to clean the River Thames by 2023.
The 25km interception, storage and transfer tunnel will start in West London, and follow the route of the River Thames to Limehouse, where it will continue north-east to Abbey Mills Pumping Station near Stratford. Here, it will be connected to the Lee Tunnel, which will transfer the sewage to Beckton Sewage Treatment Works.
The tunnel project, according to Sneesby, will prevent the pollution of the River Thames by the discharge and overflow of the existing sewerage network.
London’s sewerage network was built by Sir Joseph Bazalgette in 1860, and even though it is still in good condition, it can’t cope with the city’s current volume of sewage — it was first built to serve 4M people, when at the time there were 2M people living in London.
Sneesby says: “When the network was built it used to overflow once or twice a year. Now, with a population of 8M plus, it overflows 50 to 60 times a year, which means that we are seeing on average about 39M tonnes of sewage being discharged into the Thames every year.
“Our project will capture those overflows, and transfer that flow down to a treatment works in the east of London where it can be either treated or it can overflow further east.”
Preparatory works started in 2016 on the three main construction sites: Chambers Wharf (East Section), Kirtling Street (Central Section) and Carnwath Road Riverside (West Section).
“We are building the shafts on those sites that will then put the tunnel boring machines (TBMs) in. I think we made a really good start, we are 3 to 5 months ahead of where we said we were going to be,” says Sneesby.
He adds: “At Chambers Wharf, the site is very small and we are putting a cofferdam into the river to give extra space. The cofferdam is now in and we are filling it with soil to create a bigger site, and allow us to start building the shaft.
“At Kirtling Street, we started the diaphragm walling for the shafts, so we are building the shaft itself.
“On Carnwath Road in the west, our first piece of work there is to reinforce the river wall. We are piling the river wall to strengthen it before we start the main shaft construction.”
Chambers Wharf construction site.
The BMB joint venture (JV), comprising Bam Nuttall, Morgan Sindall and Balfour Beatty, is responsible for the West Section of the tunnel, while the Ferrovial Agroman and Laing O’Rourke JV (FLO), for the Central Section. A JV of Vinci Construction, Bahy Soletanche and Costain (CVB), are carrying out the works in the East Section.
Amey is serving as the system integrator and CH2M as the programme manager. The special purpose company Bazalgette Tunnel Limited, which owns Tideway, owns, finances and is responsible for the delivery of the tunnel project.
Key aspects of the construction include the techniques being used to build the shafts and proceed with the tunneling work.
“For the shafts that are 50 to 60m deep we are using diaphragm walling techniques and we are building sheet piles to build the cofferdams. And then we will use TBMs to tunnel the main tunnel.”
The TBMs have already been ordered — the first one is expected to be delivered in the middle of 2017, as tunneling is anticipated to start in early 2018.
The construction strategy was also determined by the underlying geology of London. In the West Section, the soil is composed of London clay, in the East of chalk, and in the Central Section, it crosses boundaries between clay, sands and gravels and chalk.
Sneesby says: “We did about 350 boreholes [depths up to 90m] along the river and there is a database of over 5000 boreholes in London, so it’s a very well-known geology. We benefited from previous projects of the likes of Crossrail, Lee Tunnel and cable tunnels that have been tunneled in the last five to ten years in London.
“There are always challenges in tunneling, but we know what is in front of us. The machines we will be using are very sophisticated and we are confident in the way that we are going to tunnel.”
The 7.2m-diameter tunnel will feature a pre-cast concrete segmental lining: “There is a primary lining [to be installed by] the TBM. It is composed of precast segments that make up rings, so there are about seven or eight segments to make a ring as we go along and then behind that we will build a secondary lining.”
Sneesby adds: “The secondary lining is there to ensure that we don’t get infiltration and probably more important exfiltration. It’s a 300mm concrete lining.”
The ‘super sewer’, to be a gradient one, will fall 1m for every 790m it travels at a depth up to 65m below the river.
In 2016, the first piece of construction for the project was completed. The Millennium Pier at Blackfriars was moved to facilitate the access to the sewer overflow next to it.
Sneesby says: “We needed to access that overflow and connect it into our tunnel, and we couldn’t do that with an operational pier right next to it.”
A new pier, manufactured in the Netherlands and floated to London, was put in place to the east side of the existing one. Sneesby adds: “All of that was done early, commissioned at the end of October and now handed over.”
Barge with crane used in the new Blackfriars pier.
The ‘super sewer’ is expected to be complete in 2022, according to the targets set by the project’s team.
The project, to have a capacity of 1.2M cb m, will create 4,000 jobs. Sneesby adds: “we are committed to have 1 in 50 apprentices and 1 in 100 ex-offenders working on the scheme.”
The Thames Tideway Tunnel is expected to bring great benefits to the city of London by cleaning up the river, but for Sneesby the most important one is that “it will reconnect London with the Thames and make people appreciate what is on their doorstep”.
The London Tideway Improvements Scheme comprises two other construction projects: the upgrade of five major sewage treatment works on the River Thames, and the Lee Tunnel — both of which have already been completed.
Named the deepest tunnel ever constructed beneath London at an average of 75m below ground, the Lee Tunnel was completed in 2015 and officially opened in January 2016 by the acting mayor of London at the time Boris Johnson.
“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,” said Boris Johnson at the time.
He added: “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.”
The 6.9km tunnel in the London Borough of Newham will help prevent more than 16M tonnes of sewage mixed with stormwater from overflowing into the River Lee.
Construction work on the £678M tunnel started in September 2010 with the construction of the 80m deep shaft at Beckton. The design and build contract was awarded to MVB, a joint venture of Morgan Sindall, Vinci Construction Grands Projets and Bachy Soletanche.
The tunneling of the 7.2m-diameter Lee Tunnel started in 2012, and was completed in 2014.
The Busy Lizzie TBM, named by a local primary school pupil for good luck, was custom made to bore on the soil composed of chalk and flint.
Busy Lizzie at the bottom of Lee Tunnel's shaft.
Similar to the Thames Tideway Tunnel, the Lee Tunnel benefits from a 300mm thick secondary inner-lining against leakages.
Challenges were faced when boring the tunnel, as the TBM went through high groundwater pressures and 6.4km of highly abrasive ground.
The Tideway Pumping Station, an 87m-deep, 38m-diameter pumping shaft, was also constructed as part of the project. It will transfer the Lee Tunnel and the future Thames Tideway Tunnel flows to Beckton for treatment.
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