Breakthrough on the Northern Line Extension

23 November 2017

Great Britain - The two TBMs mining the Northern Line Extension project in London have broken through. Launched in February 2017, the two 6m-diameter EPBMs bored twin 3.2km tunnels running from Battersea to Kennington, with the second breakthrough taking place on 8 November.

The main contractor, Ferrovial Agroman, launched the TBMs from shove frames housed in two 75m SCL launch tunnels, excavated by a Schaeff tunnel excavator. At the conclusion of the drives, the machines broke into 26m-deep secant-piled shafts, which ran into the Lambeth group at its base and the potential of running water. Some thirteen wells were employed for dewatering operations.

Regarding the main drive, one full ring consisted of five full concrete segments with arc length of 3,063mm and one key with arc length of 1,021mm. Segments were bolted together using Grade 8.8 M24 bolts. The rings were designed for the project by Mott MacDonald and fabricated by Morgan Sindall at the Ridham facility in Kent.

The cutter head of both machines will now be lifted by crane out of the shafts at Kennington while the rest of the machines will travel back to Battersea and be lifted, in parts, out of the ground there. The extension is due to open in 2020.

For more information, please read the feature on the Tunnels and Tunnelling website: