Project outline

Construction of major underground tunnel, 3km in length to link substations between South East London, the City and East London.

The construction of the 3.5km underground tunnel was completed on programme and through improved innovation, provided cost savings of c. £4m to the project. Despite the tight urban environment and sensitive nature of works, we were able to deliver the project safely and with minimal disruption to the public and other key stakeholders, TfL and Network Rail. The project was a major milestone in UKPN’s continuous capital programme to develop and meet the capital’s increasing energy needs and to improve resilience across the network.

Key challenges

• Managing logistics of complex underground works in an urban environment
• Highly constrained working areas
• Tunnelling under major infrastructure assets belonging to Network Rail and TfL (Jubilee Line)
• Challenging ground conditions and tight horizontal alignment leading to inundation of silt in Tunnel
• Adhering to Section 61 obligations – with many residents living close to the shaft, innovative solutions were important in managing noise pollution
• Avoiding roadwork excavation and minimising the impact to the public and other affected stakeholders.

Innovations

Despite challenging geological conditions, the tunnel was constructed successfully through a refurbished Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM). Further challenges presented due to the small size of the site (70m x 20m) and the close proximity to private housing.

We developed a bespoke methodology where the cable reeler stand was lowered into shaft and placed on the bottom. The cable drum was then lowered and positioned onto the cable reeler and was electrically power fed from a local power point via leads. The cable end was attached to steel arm fixed to a battery operated tunnel tug vehicle to pull the cable. It was then fed through a series of rollers from the bottom of the shaft through to the chamber and into the tunnel. To ensure that the pulling of the cable was never exceeded during the installation process, a tension meter was used to monitor force. This achieved benefits to project through increased productivity and a safer, more controlled installation.

Awards

Project of the Year (up to £50M) and ITA Tunnelling Awards 2017.