The less interesting lower half of Britain’s capital city witnessed at the weekend an end to boring to aid flows of backbone electricity – for the time being at least.
Digging activity on National Grid’s £1 billion London Power Tunnels project ceased in south London on Saturday, as a 140,000-tonne boring machine optimistically named “Grace” poked out its nose mole-like above ground close to Eltham’s sub-station.
Grace had been on a journey across 11 kilometres from New Cross substation in the borough of Southwark, a journey completed as much as 60 metres below the city’s streets.
Her breakthrough, pictured, rounds off the full massive 32.5 kilometres of the project across seven London boroughs, linking substations extending from Wimbledon to Crayford.
Grace and her three gargantuan sisters Christine, Caroline & Edith began in 2020 shifting south London’s sand, soil and rock, taking the first steps towards obliterating bottlenecks on the capital’s 132 kV transmission grid.
Work now begins in laying 200 kilometres of cable through the new tunnels, notionally enough to run from London to Cardiff. Operational plug-in for the amp-toting liquorice is timetabled for 2026, in time to meet increased power demand for the capital.
In total the drilling project has shifted 900,000 tonnes of earth – equivalent in volume to half of Wembley Stadium – with 99.98% of that material diverted away from landfill.
HOCHTIEF-Murphy Joint Venture have been the National Grid’s tunnelling contractors on its £400 million, six-year hole punch.
HMJV project director Santiago Daniele commented: “It’s been an incredible journey so far, from taking over our tunnel drive sites a week after the covid lockdown, to sinking eight shafts and undertaking five tunnel drives with four tunnel boring machines over the past three and half years.
“With our final drive breaking through at Eltham ahead of (schedule), it’s testament to the collaboration, ingenuity and fantastic joint culture of all involved, despite all the challenges we faced.
President of National Grid Electricity Transmission Alice Delahunty said:
“Our London Power Tunnels project has achieved a lot since it kicked off in 2020, but the final tunnelling breakthrough at Eltham is a particularly remarkable moment.
“This complex engineering endeavour is now really taking shape, with completion of tunnelling now physically linking our sites across South London for the first time and meaning we can move on to the next chapter to progress our vital cabling work.
“The outstanding effort by our project teams and suppliers is strengthening London’s electricity network and making sure it safely, reliably and efficiently powers homes and businesses in the capital for years to come.”
Tunnelling was completed in three sections between existing National Grid substations. First from Wimbledon to New Cross over 12km; then the 18km from New Cross to Hurst, and finally the 2.5km from Hurst to Crayford.
Vertical shafts ranging between 9 and 15 metres in diameter and up to 55m in depth were constructed along the route, serving as waypoints for the drilling sister machines, enabling project teams safely to access the tunnels for maintenance now and during future operations. Structures called headhouses will be built to cover the shafts for safe future use.
The Hurst substation site recently saw a world record-breaking pour of cement-free concrete to fill the base of its 55 metre deep shaft following Christine’s two tunnel drives to Eltham and Crayford.
As well as reinforcing the capital’s electricity network for the future, NG’s London Power Tunnels project also supports community organisations and charities across south London, as part of National Grid’s Community Grant Programme (CGP). To date twelve organisations serving community needs near LPT sites have been awarded grants of up to £20,000, enabling them to drive remarkable initiatives which enhance their localities.
In another first for the LPT, National Grid’s new Bengeworth Road substation on the tunnel route between Loughborough Junction and Denmark Hill railway stations is being built free of the greenhouse gas sulphur hexaflouride (SF6) – the only substation of its kind to date in Britain, and part of National Grid’s ambition for its infrastructure to be SF6-free by 2050.