The Northern line extension is a project to extend the London Underground Northern line from Kennington to Battersea in South West London, terminating at the redeveloped Battersea Power Station. The extension will form a continuation of the Charing Cross branch of the line. Two new underground stations will be built at Battersea Power Station and Nine Elms. Construction began in 2015, and the extension is due to open by 2020.

To undertake a project such as this in central London, it is inevitable that the tunnelling will have to pass in close proximity to existing underground assets, potentially damaging them.

The tunnelling for the Northern Line extension brings it within approximately 1.5 meters of an existing Thames Water Asset in the Nine Elms area. There was some concern that as it passes the Tunnel Boring Machine (TBM) could cause movement in the ground and potentially damage the Sewer. As a result of this plans were made to reinforce the existing Tunnel and segment it to allow articulation if necessary.

Clear Route Involvement

Clear Route had several objectives to achieve during their involvement in their project:

• Determine the exact location of the asset and its route
  
• Find and record the location of the existing tunnel rings
• Create a 3D model of the Sewer and the access shafts
  

Method

To gain accurate data on the route of the tunnel and the location of the existing tunnel rings a Total Station was used to conduct a line and level survey along the route. Once this was complete then Clear Route used a Leica P40 Laser Scanner to scan the access shafts and the tunnel itself to produce the 3D model required.

All areas of the Sewer were designated as a Confined Space, meaning that all operatives had to be appropriately trained.