Locale : North America (English)
Northern Line Extension Nine Elms to Battersea
Our work focused on finding ultra-low carbon alternatives to Portland cement, which is traditionally used in concrete.
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Going further on London’s Northern Line

Some 130 years after our founders Basil Mott and David Hay designed the first deep underground railway lines in London, our engineers delivered a extension of the Northern Line two miles (three kilometers) long, with new stations at Nine Elms and Battersea. The Northern Line Extension (NLE) opened in September 2021.

FLO, a joint venture of Ferrovial Construction (UK) and Laing O’Rourke
Civil, structural, mechanical, electrical, public health, and rail systems and integration services; architectural design was by our design partner Grimshaw
2 miles
of twin-running tunnels
tunnel boring machines, called Helen and Amy
precast concrete segments forming 4,000 rings lining the tunnels
metric tons tunnel excavation waste removed by more than 26 barges a week
metric tons material excavated overall
forecast jobs
new homes


The area just south of the River Thames and to the west of Vauxhall was dominated by the vast, derelict, Battersea Power Station and rail yards, and was poorly served by public transportation. The NLE was needed to initiate regeneration, unlock investment, and breathe new life into the area.

The two-mile (three-kilometer) route was packed with challenges. It passes beneath countless homes and other buildings, including more than 130 listed structures, and crosses below mainline railway tracks and viaducts between Clapham Junction and Victoria, and Waterloo stations.

Underground, the tunnels run very close to the existing Victoria and Northern lines, water and gas mains, and electricity and communications cables.


We were lead designer for FLO, the joint venture between Ferrovial Construction (UK) and Laing O’Rourke that delivered the line. We provided multidisciplinary services that included the following:

  • Alignment design
  • Civil, structural, fire, traction power, and tunnel ventilation engineering
  • Systems integration
  • Environmental and planning advice

We brought architect Grimshaw onboard to provide architectural design.

Along with the two new subterranean stations at Nine Elms and Battersea, the project included two major ventilation shafts at Kennington, twin bored tunnels with sprayed concrete lining, complex step plate junctions to connect to the existing Northern line, and the provision of all associated rail systems. The junction between the NLE and existing Northern Line tunnel was geometrically, structurally, and logistically complex.

Meanwhile, both new stations support significant over-site development. Complex structural support had to be provided within the station boxes, while providing attractive, passenger-friendly spaces and architectural excellence.

We used Building Information Modeling (BIM), possibly more so than on any other transportation project to date, to coordinate the complex design, achieving safe clearances, avoiding clashes, and planning the sequence of construction works.

We linked the BIM models to visualization tools such as virtual reality (VR) and augmented reality (AR) to enable the client, contractor, user groups, and emergency services to explore and examine the design, leading to improvements. Design for manufacture and assembly (DfMA) was used extensively to speed and simplify construction.


The new station boxes sit 66 to 82 feet (20 25 meters) below ground. To speed construction and avoid extensive temporary works, top-down construction was employed to build them. This enabled the foundations and superstructure to be built simultaneously.

Noise limits for the NLE are particularly strict. We used our in-house ReVERB software to model train vibrations and noise levels to predict their peak and cumulative impacts in residential areas. We validated our predictive models by measuring noise on the nearby Victoria Line, setting a new benchmark for ground-borne noise and vibration modeling.

To ensure the two tunnel boring machines could excavate the twin tunnels without causing damage to nearby utilities and structures, we compiled a database of underground assets, representing them in BIM. A virtual construction model of the tunnels, generated from BIM, enabled FLO to hold detailed weekly briefings with stakeholders including Thames Water, Network Rail, and London Underground.

We fine-tuned the design, reducing the thickness of the tunnel linings by 1.2 inches (30mm). This saved about 95,350 cubic feet (2,700 cubic meters) of concrete and 1,500 metric tons of carbon.

We also worked with FLO to design a concrete mix, replacing ordinary Portland cement with ground-granulated blast furnace slag from steel manufacturing. This reduced embodied carbon by 80%.

Introducing LED lighting for the tunnels and stations produced significant whole-life cost and carbon savings compared with conventional lighting: $2.9 million (£2.4 million) in energy savings and 23,400 metric tons of carbon.


Construction took six years. The new stations have been catalysts for economic and social transformation.

Three towers, from 243 to 292 feet (74 to 89 meters) tall, above the station box at Nine Elms, contain 479 “build to rent” homes with associated amenity space. A fourth building alongside the station provides commercial and retail spaces.

Oversite development above the Battersea NLE station forms part of a mixed-use precinct of residential, retail, and commercial units. A new park. Nine Elms, and Battersea are new destinations. The NLE also provides the area’s new residents with swift and easy access to the rest of London.

Overall, the extension is forecast to boost London’s economy by up to $9.6 billion (£7.9 billion), with about 25,000 jobs and 20,000 homes created in the area. Better accessibility and quicker journeys alone will contribute about $1.8 billion (£1.5 billion).

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