Laing O’Rourke joint venture, FLO, completes Northern Line Extension

First expansion of the London Underground this century opens to passengers

Laing O’Rourke, working in joint venture with Ferrovial Construction (FLO), has completed the Northern Line Extension (NLE), with the first passengers travelling on the new line today.

The project is the first major expansion of the London Underground this century and is the principal infrastructure upgrade for the Nine Elms South Bank re-development, Europe’s largest regeneration project, which will support thousands of new homes as well as new businesses and attractions.

The NLE involved the design and construction of two spacious new stations, Nine Elms and Battersea Power Station, and the tunnels, rail and connections to the existing Northern Line railway. There were operations on two complex shaft sites at Kennington, (Kennington Green and in Kennington Park) which enabled the construction of four new cross passages between platforms. The Kennington sites also house an extensive array of tunnel ventilation and power supply equipment and provide emergency evacuation and maintenance access.

Major construction works started on the project in November 2015, with excavation and construction of the 3km twin rail tunnels starting in March 2017. To excavate and line the tunnels, FLO used two 304-tonne tunnel boring machines and installed more than 20,000 precast concrete tunnel lining segments.

In total, 850,000 tonnes of excavated spoil were transported away by barge on the river from Battersea. The spoil was deposited near Tilbury where it was repurposed to create arable land. Using the river kept 47,000 lorry movements off the roads and avoided 2,600 tonnes of C0² emissions.

The two Kennington shaft sites were vital in the construction of the project. The tunnel boring machines, on completing their tunnel drives from Battersea to the shafts, were removed through them.

To connect the extension into the existing railway, we had to expand the underground space available where the tracks merge. We achieved this with the construction of two step plate junctions, encircling the old rail tunnel in a wider one before demolishing it. New junction trackwork was installed during the 2017-18 Christmas/New Year holiday season. This was a significant feat of engineering and construction. The FLO team then self-delivered the remaining track infrastructure through to Battersea. 6.4km of low vibration track (LVT) was installed between June 2018 and August 2019. Rail was delivered into the tunnels in 90-metre lengths, minimising on-site welding and rail joints. London Underground engineering trains delivered the rails via the available network.

The building and architectural fit-out works required wide-ranging co-ordination between different work packages, trades, and subcontractors. The mechanical and electrical works included the sub-systems of high voltage and low voltage electrical services, tunnel ventilation, mechanical ventilation and the building management system, fire prevention and detection, the communications systems, lifts and escalators, pumps and drainage and the integration of the sub systems, along with other TfL sub systems including signalling and ticketing facilities.

The project owes a large part of its programme compliance, safety performance and quality assurance to its approach to offsite manufacture and digital engineering. The project was built once in virtual reality where snags and safety issues could be detected early and rectified.

The project has also been a force for good in London and further afield, having employed 79 apprentices and 159 previously unemployed people. The team also engaged with local communities, including 115 engagements with local schools, reaching over 3,000 young people, and providing 1,629 days of work experience.