At first sight, a project that involves rerouting power lines may seem insignificant or even described as a bit boring. However, the complex and challenging project to move two sets of existing power lines from pylons into tunnels was fundamental to the Olympic Park site. Without the removal of these power lines that went through the centre of the planned Olympic park the development of the rest of the venues could literally not get off the ground.
The bare bones of the project included the creation of 10 shafts, 13 km of tunnels, over 200km of cabling and the removal of 52 existing overhead pylons adding up to a project cost of £250 million. Significant hurdles had to be overcome from the outset: difficult ground conditions, approval from a plethora of landowners, river crossings and utility approvals, and a very challenging deadline of three and a half years (half the industry norm). Extensive offsite trials were conducted in tunnel mock-up environments to develop both cable installation and jointing techniques.
The tunnelling and shaft work were completed by August 2007 – 13km in 13 months. Laying of the cables proved to be just as challenging. the innovative design of cable rollers and use of bespoke tunnel vehicles for plant and materials transportation allowed up to three cable lengths totalling 2400m to be pulled through the tunnel at any one time. Cable lengths for the 400 kV cables were such that the joint bays were spaced at 800m centres. Hundreds of metres of galvanized cable support systems have been used throughout the tunnels to ensure that no costly maintenance is needed for these systems.
The power was switched underground during August 2008, allowing work to remove the overhead pylons and overhead lines to begin in September 2008. The careful planning, collaboration and innovation used by the project team set a benchmark for world-class delivery of high-voltage cable tunnels.
Image: London 2012