NEC used for award-winning power tunnel under London, UK

NEC has been used to deliver a new 32.5 km award winning electricity tunnel under south London, UK. NEC Users’ Group gold member National Grid let the phase 2 tunnel and shafts package to Hochtief-Murphy joint venture under an NEC4 Engineering and Construction Contract (ECC) Option C (target contract with activity schedule) in December 2019. Despite the challenges of Covid-19 and unexpected ground conditions, the £506 million works were completed to the agreed programme and budget in July 2024, with contract completion in November 2024.

The contract was part of the £1 billion London power tunnels phase 2 project to rewire south London via a 3 m diameter tunnel up to 55 m deep – the UK’s longest single tunnel contract. Running from Wimbledon in the west to Crayford in the east, it will replace three existing life-expired transmission circuits when 400 kV and 132 kV cables, substations and shaft headhouses have been installed and commissioned in 2027. The 32 km phase 1 tunnel, from Wimbledon to Hackney in northeast London, was completed in 2018.

The concrete-lined phase 2 tunnel was driven by three Herrenknecht earth-pressure-balance tunnel boring machines (TBM) and a refurbished openmode Lovat TBM supplied by Murphy Plant. There were five TBM drives from three of the eight 9–15m diameter shafts, with ground conditions ranging from chalk to sand, including some contaminated by hydrocarbons.

Project 13 Delivery Model

Phase 2 is being delivered under the industry-led Project 13 enterprise delivery model, with National Grid’s Infrastructure Development and Delivery department acting as integrator and NEC project manager for each package. The integrator and project manager is supported by Mott MacDonald, WSP, Gardiner & Theobald, Mace and Arcadis, each of which is engaged under an NEC4 Professional Service Contract (PSC) Option E (cost reimbursable contract).

The tunnel and shafts contract won the Utility Project of the Year in the 2024 British Construction Industry Awards. 

Contract of Choice

National Grid Electricity Distribution team manager Ben Davis says NEC was chosen as it is the organisation’s contract suite of choice. ‘This was reinforced by early market engagement, which informed us it was also the suppliers’ preference. In this case ECC Option C was the sensible choice for a risk-based contract, with a fair apportionment of risk for the geotechnical works.’

He says National Grid is an early adopter of the Project 13 infrastructure delivery model. ‘We developed an enterprise to collaborate and deliver the overall project using NEC secondary option X12 on multiparty collaboration. The project manager’s team undertook early engagement with the contractor across various disciplines to ensure focus and alignment on project outcomes from outset.’

Davis says in line with the NEC requirement to act in a ‘spirit of mutual trust and co-operation’, there was regular engagement between both teams throughout the contract to manage the works according to the conditions and scope. ‘This was underpinned by robust assurance processes that were applied and followed to validate NEC defined costs and the evaluation of NEC compensation events.’

He says including a programme in the NEC contract data part two enabled a baseline for the project manager’s team to measure progress and change. ‘The schedule of partners contained in option X12 included incentives for the contractor to increase its share percentage by outperforming across a wide variety of key performance indicators.’

Despite the challenges of the Covid-19 pandemic, Brexit and unexpected ground conditions, Davis says the tunnel and shafts were successfully delivered to the agreed programme and budget in July 2024, and the contract was completed in November 2024. 'Following completion, both teams undertook a joint exercise to identify lessons learnt and capture the positive outputs and opportunities for improvement on future contracts.’ 

Benefits Of Using NEC

• NEC was the client’s and supply chain’s preferred contract suite and ECC Option C provided a fair apportionment of geotechnical risk.
• NEC requirement to act in a ‘spirit of mutual trust and co-operation’ ensured regular engagement between both teams to manage the works according to the conditions and scope.
• NEC secondary option X12 on multiparty collaboration enabled a Project 13 enterprise delivery model, with a strong focus and alignment on project outcomes.