Underground waterproofing longevity: How will the Northern Line Underground extension be achieved?


The Northern Line Extension (NLE) will provide improved transport links and assist in the transformation of Vauxhall, Nine Elms and Battersea. Potentially creating up to 25,000 jobs and 20,000 new homes, the journey time into the West End or the City will in some cases be reduced to under 15 minutes. This vast underground construction project will consist of brand new twin bore running tunnels of approximately 5200mm internal diameter and will cover a distance of approximately 3300 metres with new stations being built at Battersea and Nine Elms. This exciting project is supported by the Mayor of London, Wandsworth, Lambeth and Southwark Councils.

How will the NLE be achieved?

2015 – NLE preparation works began in the spring.

2017 – The main tunnelling works were underway by spring.

2019 – Station fit out will take place

2020 – Testing and commissioning of the NLE will take place and the line will become operational.

How will this vast project be waterproofed for future longevity?

For the underground waterproofing project, SOPREMA’s Flagon Tunnel Waterproofing System has been selected to ensure the water tightness of this underground structure, the system exceeds the level of water resistance required and achieves Grade 4 of BS8102.

Junctions between systems and other construction components were detailed at design stage to ensure precautions are included to avoid any leakage. The waterproofing system selected incorporates protection geotextile, waterproofing membrane, water stops, attachment rondels and a number of specialist accessories to ensure a watertight structure.

The tunnel waterproofing system is designed to allow for long term ground movements and effects of ground water levels and seasonal variation. Water bars are included as part of the system to compartmentalise, and injection pipes incorporated to further increase confidence and assist with long term maintenance by facilitating future repair possibilities.