Rewiring London

In February 2011, National Grid embarked on a seven-year project to rewire London using deep underground tunnels. Project investigates how the firm is working to keep the lights on the capital.

It is seen as a vital project. The £1bn London Power Tunnels will meet increasing electricity demand and help the capital access the renewable energy supplies of the future.

To deliver this mega-project, National Grid has created an experienced project team supplemented by consultancy support from Arup, Gardner and Theobold, and Mott MacDonald.

“London is home to more than eight million people and is a leading global business hub with a growing hunger for energy,” explains David Luetchford, head of Cable Tunnels for National Grid.

“This project will create a thoroughly modern electricity superhighway for the capital, transporting energy from both traditional and renewable energy sources as efficiently as possible.”

London Power Tunnels will replace the ageing electrical transmission cables buried a few metres below London’s streets by the Central Electricity Generating Board (CEGB) in the 1950s. These cables are reaching the end of their service life and must be replaced to ensure that new supply and demand patterns can be met.

In place of the old infrastructure, three tunnels deep below the road network will be constructed to carry high-voltage electricity cables. In total, 32km of tunnels up to four metres in diameter are being constructed between 20 and 60 metres deep. The tunnels will carry high-voltage (400kV) electricity cables and connect to existing substations at Hackney, St John’s Wood, Willesden and Wimbledon.

“Housing the cables in deep underground tunnels will significantly reduce disruption for people who live or work in the local area,” explains David. “We’ll be able to lay the cables and carry out future maintenance work without digging up the road network.”

Two new substations will also be constructed as part of the project – one at Kensal Green will provide traction supplies for the new Crossrail line and another in the Islington area will provide additional capacity for the capital’s distribution network.

Tunnel Boring

Construction involves sinking shafts deep below ground at 14 sites across London. Located at key points along the tunnel route, these intermediate shafts and headhouses ensure the safety of people working underground during construction. They also provide access to the tunnel for maintenance work, and store the ventilation equipment to cool the cables and regulate the temperature inside the tunnel.

Three of the shafts also act as drive sites for the tunnel boring machines (TBMs), named Evelyn and Cleopatra, used to construct the tunnels. Costain is the contractor responsible for this part of the project. The 100m-long machines are lowered down the shaft in pieces and assembled underground. Once up and running they move forward at a speed of up to 200mm/min, laying the concrete segments of the tunnel behind them as they go and conveying the excavated soil along their gantries and out of the tunnels. It is a similar system to that being deployed by the Crossrail project team.

Operated by electronic control systems, these state-of-the-art tunnelling machines give their operators fine-tuned control, which they can use to minimise any surface settlement as the machines bore through the London clay. The TBMs also use a process called earth pressure balance (EPB), where the face of the tunnel is stabilised by putting pressure on it behind an airlock, where the ground is weaker.

Waste soil from the tunnelling is being put to good use in the reclamation of former gas-holder sites which are being cleared by National Grid and prepared for future development. London clay is ideal for the task and using it in this way also reduces hauling distances. 

A mega project approach

Delivering this project meant finding the right people to work together as innovatively as possible. David says: “We created a strong in-house management team supplemented by consultancy support and we have grouped multiple sub-projects into a mega-project.

“This has allowed us to use the skills of our existing supply chain, trial some new procurement options and put the specialist tunnelling work out to competitive tender, while keeping responsibility for the relationships and overall delivery management. We’ve achieved buying gains by ordering cable directly and running a mini-competition between substation framework contractors where we’d normally allocate the work geographically.”

Acting as part of the client’s team, Arup is providing National Grid with integration support to ensure the management team is aware of change, schedule, risk and interfaces across all elements of the supply chain. This role has also included management, health and safety and information management support.

Mark Neller, Arup’s programme management office leader for the London Power Tunnels, explains why he thinks the approach is the right one. “Managing the programme in-house means that National Grid can take direct control of the risk management and associated planning. This recognises that it is best placed to manage the majority of high risks, rather than those in the supply chain.

“National Grid has designed its procurement strategy to allocate risks to the part of the supply chain best able to manage them, enabling more focussed delivery by suppliers, and delivering all round better value for money.”

Mark acknowledges that the programme management approach can be challenging. “The main area of client risk is in the interactions between the different contractors, and the 30 packages of work they are delivering.

“To manage this we’ve put together an overall integrated schedule of key activities. This has helped us work out where the main interactions and interdependencies are. Tracking and mapping them all has been a major challenge.”

Creating a culture

Mark says that it is also important that the team understands who the stakeholders are for each component. “We’re working hard to create a consistent culture between all the stakeholders – contractors – maintenance people and network operators. This ensures that everyone understands that it’s the overall aims and objectives of the programme that are most important.”

Mark and his team are making use of information management to ensure the right information gets to the right people at the right time. Data is presented using a Geospatial Information System (GIS) and the team is sharing CAD models to aid design coordination between suppliers. An extranet tool has also been deployed to share information easily.

There are seven tier one suppliers, whose activities must be coordinated to ensure the successful delivery of the project. “We are spending a lot of time getting buy-in from all tier one suppliers,” adds Mark. “To ensure everyone delivers what’s required, we have implemented a system of multi-party review meetings. Project managers have been allocated to cross-functional packages based on geography. They then bring all the supply chain partners together regularly to review progress in design, risk and construction to keep the job on track.”

Arup has a team of six people co-located with the client, with another 10 supporting them when needed. Mark says: “As a consultant, I find being fully integrated with clients in this way very rewarding. You can see everyone pulling together to deliver a successful project.”

Meeting challenges

The smooth running of the project perhaps belies the enormity of the task. Although most of the route is through London clay, other areas are more of a challenge for the TBMs. The route has to weave between London Underground lines, between water mains, around Crossrail tunnels, and avoid the route of the planned Thames Water super-sewer.

Despite this, the tunnelling is expected to be complete in less than three years – and to set world-record drive rates along the way. With the tunnels complete, cables will be laid by a specially designed machine, rather than manually, to speed up the process, and make it safer. Manufacture of these machines is part of Balfour Beatty’s work package and builds on the technology they have developed on two smaller National Grid cable tunnel projects.

Innovation doesn’t only take place in the tunnels. Above ground, with land at a premium, National Grid has had to squeeze the substations into tight locations – designing layouts for the transformers that can be accommodated in constrained sites. The tunnel headhouses are designed to blend in with surrounding buildings.

Away from the physical infrastructure, the project is aiming to build even more of a legacy. National Grid – with support from public relations consultants Grayling – has created the Energy Education Centre.

Based near Willesden Junction, the centre is a free facility to help youngsters understand energy and to strengthen their interest in science. Visiting groups learn more about the vital role of energy, how it's made and delivered, the problems with fossil fuels and the importance of renewable energy.

Since opening in June, 500 schoolchildren have already visited the centre and National Grid hopes to see a further 100 schools visit before the end of 2013.

National Grid has been rewarded for its attention to detail in managing this mega-project with good progress in construction. In September 2012, TBM Evelyn completed the first 3.5km of her 19km journey, arriving at the Kensal Green shaft. The second TBM, Cleopatra, which is digging the other 13km of the route, is currently around 2.5km from her launch site in Haringey.

National Grid expects the tunnelling work to be completed in 2014, with the London Power Tunnels providing energy to the capital from 2018. Designed to last 100 years, the tunnels will provide London with a safe and reliable electricity supply long into the future.

In numbers...

32km of tunnels up to four metres in diameter are being constructed between 20m and 60m deep

400kV the voltage that will surge trough the tunnels

500 schoolchildren have to date have visited the Energy Education Centre. National Grid hopes to see a further 100 schools visit before the end of 2013

 

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