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Thames Tideway Tunnel

Thames Tideway
Written by Roma Publications

Thames Tideway Tunnel

The biggest infrastructure project ever undertaken by the UK water industry, the construction of the 25km Thames Tideway tunnel under the River Thames will deliver massive environmental benefits for London.

Starting in Acton, West London, the tunnel will travel through the heart of London at depths of between 30 and 60 metres, using gravity to transfer waste eastwards. In addition to the tunnel preventing tens of millions of tonnes of pollution previously poured into the river every year, the removal of spoil from its construction is being undertaken through an ingenious sustainable approach known as ‘More by River’.

The tunnel is needed because London’s Victorian sewers, designed by Sir Joseph Bazalgette, while still in excellent condition, now lack the capacity to meet the demands of modern-day living. In the mid-nineteenth century, more than two million people lived in London. Bazalgette had the foresight to design his system to serve four million, but today the city’s population is nearing nine million – and continues to grow.

The construction of the tunnel is due for completion in 2024, and is happening across 24 sites in London. These span from Acton in West London to Beckton in the East, and many are located on the river edge in the centre of the city.

Tideway (Bazalgette Tunnel Limited) is the company financing, building, maintaining and operating the Thames Tideway Tunnel. Tideway employs more than 400 highly experienced professionals to deliver the project, together with its four main delivery partners.

The construction in the west region is being delivered by a joint venture of BAM Nuttall Ltd, Morgan Sindall Plc and Balfour Beatty Group Limited. This contract is known as Tideway West, with work taking place from Acton to Fulham.

The construction in the central region is being delivered by a joint venture of Ferrovial Agroman UK Ltd and Laing O’Rourke Construction. This contract is known as Tideway Central, with work taking place from Fulham to Blackfriars.

Works within the east region are being delivered by a joint venture of Costain Ltd., Vinci Construction Grands Projets and Bachy Soletanche. This contract is known as Tideway East, with work taking place from Bermondsey to Stratford.

Finally, the System Integration contract was awarded to infrastructure support service provider, Amey. Amey is responsible for providing process control, communication equipment and software systems for operation, maintenance and reporting across the Thames Tideway Tunnel system.

More By River

Tideway have made a £54m investment into the ‘More by River’ transport scheme using huge barges to transport the tunnel project’s spoil, construction materials and equipment by water – avoiding hundreds of HGV movements every day.

Darren White, Head of Sustainability for Tideway said: “We are halfway through construction of the tunnel.

“The strategy behind ‘More by River’ is to increase the transport of spoil and construction materials, plant and equipment by river barge – cutting down road transport of these by around 72% to around 140,000 road vehicle movements. For example, each one of our 1,600 tonne barges can carry the equivalent of 93 HGV movements in one trip.”

He added that Thames Tideway have invested in new infrastructure, barges and tugs, jetties and dredging to achieve this objective. Additional benefits of using river transport include neither causing, nor being caught in traffic congestion, avoiding collisions and reducing annoyance to local residents.

In terms of moving materials by even a Euro VI HGV, the scheme is achieving savings of approximately 90% carbon dioxide and 54% NOx (nitrogen oxide) emissions. Air emissions are responsible for around 9,000 people dying prematurely in London every year.

Darren White said: “This scheme has taken a great deal of planning and our contractors and suppliers have been brilliant in getting things organised. We have had to build a considerable number of extra jetties on the river and have also had to train a large number of new apprentices to operate the boats. We have also had to implement new navigational safety systems geared to avoiding accidents due to the huge number of additional vessels we are operating on the river.

“Much additional work has been required for this scheme, but it is definitely winning over the hearts and minds of the public. We are primarily a privately financed organisation and our shareholders fully support this ethos.”

Speaking of the challenges of construction he added that 11 of the tunnel’s construction sites (all of which are operating 24/7) are on the river – including at sensitive, high-profile locations such as outside the Houses of Parliament, alongside the Secret Service HQ in Vauxhall, close to the London Eye, and adjacent to the ‘legal’ community area of Blackfriars. So far, all is going well and minimal disruption has been caused.

The Thames Tideway tunnel itself is a major piece of engineering, involving a team of world-class contractors to build this key infrastructure in the most sustainable and cost-effective way possible for one of the world’s greatest cities.


Six giant tunnel boring machines (TBMs) are being used to build the tunnel (and its two smaller connection tunnels).

These machines excavate using a rotating disc-shaped cutterhead, simultaneously creating the tunnel walls with pre-made concrete segments and removing the thousands of tonnes of spoil via a conveyor. Spoil is then transported up the deep shafts to ground level to be removed by barge. The machines work around the clock, excavating up to eight metres per day.

Ursula, one of the TBMs, recently completed half of her stretch of the main tunnel, passing Waterloo Bridge in the process. In March 2019, Ursula became the second giant tunnelling machine to be launched from a 45m deep shaft at Tideway’s Kirtling Street site in Battersea. Since then, the TBM has travelled 3.8km eastbound following a subterranean route below the River Thames. Her journey so far has seen her pass by famous landmarks including the London Eye and the Houses of Parliament.

The TBM has also journeyed beyond Tideway sites at Heathwall Pumping Station, Albert Embankment and Victoria Embankment. Upon arrival beneath the site at Blackfriars Bridge Foreshore, Ursula will undergo a 6–8 week pit stop to prepare for the final part of her drive to Chambers Wharf in Bermondsey.

To date, Ursula has installed over 2000 concrete segment rings used as the primary lining for the tunnel. Each ring is made up of eight segments including a key stone, and weigh in excess of 30 tonnes.

Over half a million tonnes of excavated material has already been removed from this stretch of tunnel, all of which was removed from site by barge.

Millicent, the westbound TBM launched from Kirtling Street, completed her 5km journey to Tideway’s Carnwath Road site in Fulham late last year, becoming the first tunnelling machine on the project to complete her section of the main tunnel.


More than a dozen shafts have been sunk as part of the work – some to a depth exceeding 60 metres – and some using a hydrofraise cylindrical cutter.

This has been used to create the walls of some of these shafts, using a suspended rotating cylindrical cutterhead that drops through the ground, churning and excavating. A special material is then pumped into the void to stop the walls falling in before beginning pumping concrete, from bottom to top, in one long continuous operation, until the shaft wall is complete.

Thames Tideway

Engineering Challenges

A key project such as this presents many engineering challenges – some of which are outlined by Barry Donnelly, Marine Project Manager for the scheme.

“Primarily my focus at the beginning of the scheme was on temporary works creating marine infrastructure to allow all of the construction sites on the Thames to be built – as well as infrastructure enabling the TBMs to operate out of Kirtling Street South in Battersea.”

Kirtling Street is the central point of the sewer and is the largest site on the entire project. Located next door to Battersea Power Station, the site is the point from which tunnelling both east and west takes place to connect the other sites along the route.

Other marine infrastructure works include the construction of cofferdams to create new land along the river, and for the construction of spoil handling facilities at East Tilbury.

Barry Donnelly said: “Works to facilitate these operations commenced with unexploded ordinance surveys to locate any WW2 bombs along the river. The surveys were carried out using a variety of methods including ground scanning to detect objects on the riverbed, and magnetometers to locate metal.

“Our engineering teams then started to design and build seven separate cofferdams on five high-profile central London sites. These are located at: Victoria Embankment, opposite The London Eye; Blackfriars; the Albert Embankment, opposite the MI6 building (three sites); Battersea (two sites) situated near a new apartment development and Battersea Power Station, and at Chelsea, near the venue of the Chelsea Flower Show.”

Cofferdam construction involves piles being sunk into the river. These thin, interlocking, metal sheets are driven into the riverbed, one by one until the perimeter is watertight.

Water is then drained from the new enclosed area, and sections of the cofferdam are filled with material, until it reaches the height of the river bank.

Six cofferdams have been installed and and the seventh is under construction. A further challenge is that the piles for these cofferdams need to be driven into London Clay, which is extremely hard.

Barry Donnelly commented: “This element of the works has required a great deal of stakeholder engagement in the neighbourhood of each of these five sensitive sites, where we had to operate within noise and working time restrictions. It is an immense undertaking and we have to work as considerately as possible in order to ensure minimal disruption. One of the ways of achieving this was to deliver all of our materials by river from a service centre which we set up at Northfleet.”

Additional challenges of the project included correctly outsourcing specific designs required for ease of construction of the cofferdams in various locations. All of the cofferdams were constructed at the same time across the five sites – which required an immense fleet of barges and cranes to transport materials. These works included the simultaneous operation of six jack up barges, 20 flat top barges, three tugs and six safety boats. All of the required materials and specific marine craft needed for each task were sourced by Barry Donnelly. Currently Tideway have purchased two jack up barges and six flat top barges for this purpose, with the remainder being hired.

Further construction elements include a new berth for the barges at Cremorne-Wharf, the consolidation centre at Northfleet, where three separate barge berths were also built for the project, and a spoil facility for offloading TBM excavated material at East Tilbury. The spoil facility construction included sinking piles and building a jetty out into the river. To form a quay, a huge sea barge was permanently grounded on the foreshore.

Reclaimed Land

Once the Thames Tideway Tunnel is complete, London will also be left with new pieces of public space, reclaimed from the River Thames – the first new land in London for generations.

This includes three acres of new public realm along the route of the River Thames at seven different locations. Parts of the new spaces at Victoria and Chelsea Embankments and at King Edward Memorial Park will be ‘floodable’ at high tides, giving Londoners the first opportunity of its kind to dip their toe in what will be a cleaner River Thames.

These new pieces of land are required to connect existing sewers (which spill directly into the river), to the new tunnel.

Edge of Pipeline Visible

The outer edge of the sewer pipeline became visible for the first time after a connection tunnel to the main tunnel was recently completed.

The 10m tunnel was built between Tideway’s site along Albert Embankment using a sprayed concrete lining method from within the site’s 50m deep shaft.

The exterior of the segments being used to line the main tunnel are now visible; however the team will not break through into the main tunnel until Ursula, the tunnel boring machine being used to dig the main tunnel, has completed her journey to Tideway’s Chambers Wharf site in Bermondsey.

The Albert Embankment site is the first site to connect to the main tunnel through its own permanent structures.

River Environment

The Thames Tideway Tunnel will clean up the river for London, its inhabitants and its wildlife and allow the city to sustain a rich, diverse ecology.

Tideway will greatly reduce the quantity of sewage-related litter in the Thames and, in turn, the amount ingested by wildlife. Over the last 30 years, there has been a dramatic clean-up of the Thames, making it a prime example of a recovering ecosystem.

But the millions of tonnes of raw sewage that still overspills into the river each year represents its last major source of pollution. The visual appearance of the river will improve, and the new structures in the river will provide new habitats for aquatic wildlife.

But Tideway want an environmental legacy that goes beyond the physical structures they leave behind. Working with academics and ecologists, Tideway want to improve understanding of the river and provide a broader knowledge of habitats and aquatic ecology.

Sustainable Financing

A further benefit of this privately financed project is the use of sustainable financing to provide funding. This involves a Sustainable Finance Framework under which Thames

Tideway can raise debt to support the financing and/or refinancing of assets and expenditures of a sustainable nature across its activities. The framework follows with the ICMA Green Bond Principles (GBP) and the Loan Market Association Green Loan Principles (GLP).

According to Tideway: “The scale of the project and its place at the heart of one of the world’s greatest cities, means we have an historic opportunity to leave a positive, lasting legacy for London.

“We’re raising the bar for health, safety and wellbeing in the construction industry and bringing jobs and recreation back to the river.

“Beyond that our investment in local communities, education, training and the supply chain will ensure that the legacy of the Tideway project will be profound and long-lasting, far outliving the construction of the super sewer.”


Tideway is owned by a consortium of investors that comprises Allianz, Amber Infrastructure, Dalmore Capital and DIF. The company’s investors have extensive experience of investing in and managing a wide range of infrastructure assets in the UK and overseas.

More than two million UK pensioners have an indirect investment in Tideway through UK pension funds managed by investors. The consortium’s backing fulfils a key component of the HM Treasury’s National Infrastructure Plan, designed to finance the development of UK infrastructure with the support of highly experienced private investors.

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