In the summer of 2005, London won the right to host the 2012 Olympics. Preparations for the construction of the Olympic facilities in East London began in earnest with the undergrounding of the transmission lines that traverses across the site.

The two high voltage transmission lines snake up the Lea Valley from Hackney to West Ham: 25 towers carrying 275kV cables owned by National Grid, who operates high voltage electricity transmission systems for England and Wales; and 22 towers carrying 132kV cables owned by EDF Energy, who operates, manage, maintain, design, construct and control a range of electricity systems in London and the South East of England.

In order to replace the overhead lines (OHL) with systems of equivalent capacity in the tunnel, two circuits, each with three 275kV cables were required for National Grid and six circuits, each with three 132kV cables were required for EDF Energy

There are a large number of stakeholders for the project. In the planning stage the London Development Agency (LDA) engaged in discussion with National Grid and EDF Energy. This is when the feasibility study was carried out by KBR, who also undertook a reference design and prepared contract documents. Soon after the 2012 announcement was made, the project came under the directive of the Olympics Delivery Authority (ODA). The Project Steering Group consists of National Grid, EDF Energy, the Project Director and representatives from the Department for Culture, Media and Sports (DCMS). Their purpose is to discuss matters relating to the progress, major procurement issues, and interface issues. The Project Delivery Team includes Arup who are involved with project management, the Contractors, J Murphy & Sons (JMS), and Detailed Designers, Faber Maunsell. The ODA retained the responsibility of gaining planning consents, land acquisition, and had the support of their in-house legal team. National Grid with Parsons Brinckerhoff (PB) and EDF Energy are part of the team involved in the cable installation and substation upgrades.

Programme

The commencement of the engineering works for the cable tunnel project preceded the award of the 2012 Olympics. Feasibility studies were completed for National Grid and EDF Energy by April 2004. A year later, the reference design and tender documents were completed. This paved the way for the contractor to be appointed two weeks after the award of Olympics to London on the 6 July 2005. The start date on site less than three months after that was remarkable, especially considering the planning permission and land acquisition that needed to be achieved.

It was the programme imperative that drove a lot of the decisions on the designs and methodology for the Lower Lea Valley Cable Tunnels Project. These new cables need to be installed, tested and commissioned prior to any dismantling of the Overhead Lines. When JMS got a letter of intent in September 2005, Charcon, the segment fabricators, and Faber Maunsell were immediately carrying out design of the tunnel and shaft segments as well as the manufacture of moulds. By late 2005 they were producing segments in line with the specification of the project.

Project options

Due to the concern about the high cost of cables in tunnels, there was a need for an exhaustive consideration to determine cost effectiveness. Several options were considered including a multi-utility shared tunnel where National Grid and EDF Energy would have shared a tunnel with other utility companies and diversion of the overhead lines using new towers.

The chosen solution called for a 4.15m i.d. tunnel for National Grid and a 2.82m i.d. tunnel for EDF Energy, respectively. The greatest advantage was that it gave maximum programme security with independent construction programmes which was compatible with the overall Olympics development. Furthermore, cable installation can be carried out from separate work sites at the same time. It also gave National Grid and EDF Energy independence during operation and when maintaining the infrastructure.

Alignment

The two tunnels, 6km each, more or less run parallel to each other. Both National Grid and EDF Energy have Statutory Powers to lay cables under the Highway so the alignment follows public land or the Highway where possible. Central drive shafts for both tunnels were established at Carpenters Road. TBM’s were driven in both directions on both tunnels at the same time because of programme constraints. Four shafts in total were required on EDF tunnel for safe access. Longer distance between shafts on National Grid tunnel was possible based on emergency egress using a monorail vehicle. Hence there are only three main shafts for the National Grid tunnel.

Numerous historical borehole records were used, particularly the CTRL Ground Investigation results. The programme did not permit completion of specific site investigation before tender. As a result, the tender documents were produced with a Geotechnical Report based on historic information. Eleven project specific boreholes were carried out and the results were issued to the contractors at a later stage after the tender period.

The two tunnels were driven more or less at the same level in the Thanet Sands for the majority of the drive and transition up to the Lambeth Group at the West Ham end. The vertical alignment was confined between the Bullhead Beds just above the Chalk and the foundations for the third party structures like the CTRL Station Box. The deepest point was at the Carpenters Road drive shaft at 45m deep below ground level.

Approvals and consents

At the preliminary stage, there was a consensus between the LDA, National Grid and EDF Energy concerning the arrangement of the scheme. There were many other parties that needed to be consulted and informed.

The scheme was one of 21 options formulated to connect the West Ham and Hackney sub-stations. DCMS have conducted an independent audit and the Treasury carried out a Green Book Appraisal.

An Infrastructure Development Agreement was set up directly between the LDA and the two companies, National Grid and EDF Energy. The shafts, tunnels, head houses, and M&E services were undertaken by a design and construct contract – IChemE Target Cost Contract (Burgundy Book). The target cost with pain and gain share was the means for the Client, ODA, to share financial risk with the Contractor, J Murphy & Sons.

Planning applications were made to the Boroughs of Newham and Hackney before the announcement of the 2012 Olympics. In contrast, Statutory Authorities and Land Owners were only approached after the 2012 announcement was made. A Land Tracker was developed to monitor the advance of the TBM and the status of the acquisition of land permissions. As a result, no delays were experienced due to the lack of consents.

In an urban environment, it is inevitable that the space below ground will be occupied as much as the space above ground. Assets affected by the scheme included:

• Thames Water has the historic Northern Outfall Sewer built by Joseph Bazalgette as well as numerous other assets including old 48” diameter cast iron mains crossing Hackney Marsh

• National Grid: Cast iron gas mains one of which needed diversion

• Network Rail crossings, including tracks adjacent to the Carpenters Road shaft site

• London Underground above ground tracks for the Central and District Line

• National Grid Sub-station

• EDF Energy Sub-station

• CTRL Station Box

It was the responsibility of the Project Manager to gain access and settlement criteria consents with the aforementioned third parties. Standard contractor’s consents like discharge consents remained with the contractor.

Shafts

The two drive shafts at Carpenters Road, 15m i.d. for National Grid and 12.5m i.d. for EDF Energy, were constructed through Thames Gravels overlaying the Lambeth Group and the Thanet Sands. There was around 7m of head in the Thanet Sands with intermediate aquifer in the Lambeth Group and upper aquifer in the gravels. Dry caisson technique was used initially with underpinning down to the Thanet Sands. Needless to say, the use of dewatering was crucial during the construction of the shafts. WJ Groundwater, a specialist dewatering sub-contractors was brought in for the task.

In the variable intermediate aquifer in the Lambeth Group, ejector wells were installed before shaft sinking to permit a rapid start. Deep wells were also established penetrating into the chalk to underdrain the Thanet Sands, however there the programme did not permit long term use of these wells. Local vacuum well points was considered to be a contingency for dewatering the Thanet Sands.

Despite all of the above dewatering systems being in place, JMS started shaft sinking without ground water control. A railway embankment is adjacent to the shaft site and Network Rail had not given permission to switch on the dewatering. As the excavation reached the Lambeth Group, there was an inflow of water. To keep on track with the tight programme, JMS proceeded sinking the shaft by wet caisson. However, the silt in the Lambeth Group slowed the shaft sinking process. Finally when the consents were gained from Network Rail, the ejector wells, together with the deep wells were activated with some effect, however the delayed groundwater control was not enough to alleviate the problems.

In comparable conditions at Canary Wharf and on the CTRL project, they had a year to lower the water level in the Thanet Sands by deep wells. The Lower Lea Valley team had just ten days. JMS and WJ Groundwater jointly developed an integrated approach to groundwater control so that shafts could be built plate by plate by underpinning and the local well points can be installed progressively. A ring main was attached to the well points cast into the segments. Using this method, the shaft was successfully sunk through the Thanet Sands.

It was a different story for EDF Energy’s Quarter Mile Lane Shaft. The water level could not be lowered to the designed formation level even with the array of vacuum well points. Although the horizontal alignment of the tunnel was fixed, the vertical alignment was not. This was used to the advantage by saving programme damaging delays by raising the formation level of the shaft to eliminate the need to lower the groundwater level to such a level.

The construction of EDF Energy’s reception shaft at Hackney is also worth mentioning. The shaft was constructed as a wet caisson but soon hit difficulty in dense gravels. The clock was ticking as the EPBM was rapidly approaching the shaft. A secant pile wall was constructed inside the shaft to enable the construction of the shaft to the required depth. Within 36 hours of the solution being agreed, specialist sub-contractors were called in and secant piles were installed. Consequently, this has reduced the shaft i.d. from the original 10.5m to 7.5m, enough to accommodate the extraction of the EPBM. In the end, there was a slight delay for the EPBM breakthrough but with no adverse effect on the overall programme.

Tunnel

EPBM was the best machine for the job with its proven record of tunnelling in the ground condition expected in the East London area on CTRL and projects for Thames Water. TBMs for the 2.82m i.d. EDF Energy tunnels, Fionnula and Helen were refurbished and fitted with new heads by J Murphy. The other two TBM’s, Lucille and Sonia, for the 4.15m i.d. National Grid tunnels, had been used in Los Angeles and were refurbished in Canada by Lovat. An 8.2MVa power supply was installed to power these machines. The four cable extensions a week allowed high voltage switching manoeuvres.

The push for the programme meant that after the initial steep learning curve, JMS had to keep the TBM’s constantly working at their optimum. The muck was transported away form the face of the tunnel using rail trains. Vertical conveyors were used at the drive shaft. This reduced the number of windings in the shaft and provided quicker turnaround of the muck wagons. Overhead conveyors extended to a muck holding area across Warton Road. This layout kept the yard free from vehicle movements.

A year after London winning the 2012 Olympics total excavation advance on the four faces was in excess of 600m on a consistent basis. This was a great achievement. All four EPBM’s performed magnificently in the Thanet Sand and the Lambeth Group.

The civil aspects of the shaft and the tunnel are now complete. Currently, the brackets are being mounted in the tunnels for the preparation of the cable installation.

Summary

The Lower Lea Valley Cable Tunnels Project was exposed to the programme pressure from the early planning stage. The flexible and committed approach from the stakeholders, together with the implementation of active risk management, has benefited the project immensely.

The construction of the tunnels and the shafts are on time and on budget. The successful completion of the cable tunnels will pave the way for the construction of the Olympic facilities and ultimately, for the successful running of the 2012 London Olympic Games.


Lower Lea Valley Cable Tunnels project Lower Lea Valley Cable Tunnels project Members of the crew celebrate breakthrough Members of the crew celebrate breakthrough The vertical conveyor The vertical conveyor Figure 2. Longitudinal section of the tunnel geology Fig 2 – Longitudinal section of the tunnel geology Figure 1. Layout of the two tunnels Fig 1 – Layout of the two tunnels Shaft construction well underway Shaft construction well underway Aerial shot of the construction site Aerial shot of the construction site Questions from the floor

Tony Gee (Mott MacDonald) asked what volume loss was achieved for the tunnel drives and also how well the vertical conveyors performed. Kevin McManus responded that an average volume loss of 0.7% was achieved. The vertical conveyor, overall, performed very well. There was a concern that the conveyors were able to tackle everything that was offered to them.
Tony Swain (UCL) asked why IChemE, Burgundy was used for the Civil Works Contract instead of NEC. Michael Francis responded that since the early stages, the IChemE contract was seen as the one that National Grid and EDF Energy were comfortable with.
Tim Hughes asked how the Civil Works Contract worked in practice. Kevin McManus responded that there were no problems on the commercial side for JMS.
John Murphy (Tubelines) asked whether the availability of labour impacted on the project. Kevin McManus said it was a very intensive job. Once the TBMs were ready to go, there was a ramping up of labour but there was enough skilled labour around. In the summer of 2006, the TBMs in the Lower Lea Valley Cable Tunnels Project represented 80% of the large diameter UK TBM market.
Rapporteur: Nao Otsubo