Overview

Started in Spring 2020, the London Power Tunnels is an immense 7-year, £1billion project by the National Grid to rewire South London via deep underground tunnels.

Most of the electricity supply in South London is currently transmitted through underground cables, traditionally found just below the road surface. However, work to maintain them is carried out at street level and can be disruptive.

By housing new, high-voltage cables in deep underground tunnels, the benefits include:

  • Less disruption during construction as the majority of works will take place deep underground

  • Future repairs and maintenance work can be carried out without disrupting traffic, residents and businesses

  • Additional cables can be installed in the tunnels to meet future demand

The new tunnels will upgrade the network’s capability to ensure it is ready for London’s future energy needs.

Project

Designed by engineers AECOM the 32.5km of 3m-diameter tunnels are being constructed deep below the roads, rivers, canals and tube lines between Wimbledon and Crayford.

At a depth varying between 10 and 63m below street level, the tunnel also required the construction of multiple vertical access shafts along the route. These ranged from 9m to 15m in diameter and up to 55m deep, allowing the specialist team from ASF Waterproofing to safely access the tunnels and carry out the resin injection waterproofing.

The tunnels are constructed using a tunnel boring machine (TBM) that places precast and interlocking concrete segments against the tunnel walls. The segments are fitted with a rubber gasket to seal the joints, however this is sometimes dislodged, damaged or not seated properly, resulting in seepage of ground water under considerable hydrostatic pressure.

ASF Waterproofing Specialists were appointed by the Hochtief Murphy Joint Venture to undertake resin injection of these joints to seal them against water ingress.

Solution

As experts in below-ground injection resin waterproofing, ASF Waterproofing was able to bring its considerable experience to bear on this project too. Utilising a variety of products, such as Newton's exclusive range of advanced acrylic injection resins from TRADECC, ASF was able to waterproof the joints, providing a Type B solution in line with Section 11 of British Standard 8102:2022 for waterproofing.

Result

ASF Waterproofing was engaged in Phase 2 of the London Power Tunnels project for 3 years, ensuring that all joints in the tunnel and access shafts were fully sealed against water.