Tunnelling has been completed on the London Underground’s Northern Line extension.

UK: Tunnelling on the London Underground’s Northern Line extension was completed on November 8, when tunnel boring machine Amy broke through at Kennington.

Amy began tunnelling in May, following sister machine Helen the previous month. Helen broke through into a shaft at Kennington Park at the end of October. Both TBMs had been supplied by NFM Technologies from its Le Creusot factory in France.

The twin 5·2 m diameter tunnels have been bored at a depth of up to 26 m, and are lined with nearly 20 000 precast concrete segments. More than 300 000 tonnes of excavated earth was transported on the River Thames to Goshems Farm in East Tilbury, where it has been used to create arable farmland. The project has a target for 92% of the estimated 680 000 tonnes of spoil to be carried away by river.

The 3·3 km extension from Kennington to Battersea will have one intermediate station at Nine Elms. Construction is being undertaken by Ferrovial Agroman Laing O’Rourke under a six-year design-build contract awarded in 2014, with opening due in 2020.

Most of the estimated £1·2bn project cost is coming from the private sector through a package agreed between the government, the Mayor of London, Wandsworth and Lambeth councils, and Battersea Power Station. This includes the creation of a 25-year Enterprise Zone covering the Vauxhall, Nine Elms and Battersea areas which came into force in 2016.