Engineers at National Grid Gas Distribution are kicking off the new year with their biggest project yet. Starting at the Royal Hospital Chelsea, the team will sink a shaft 30m down into London’s sticky clay. Three hundred metres away in Battersea Park, another landmark site, a sister hole will mirror the first. The final stage of the plan will see engineers tunnel under the River Thames to join the two shafts together.
The ambitious project is part of National Grid’s £1 billion master plan to future-proof London’s ageing gas infrastructure. Once complete, the tunnel will be home to a brand new mains gas pipe, delivering energy to homes across the city.
Shaft number one will measure 7.5m across and will drop down through the Chelsea Pensioners’ back garden. The dig will take place in the first quarter of 2017, then the pressure will be on to clean up the site in time for a busy summer season. With big events like the RHS Chelsea Flower Show and art fair ‘Masterpiece’ in the calendar, there is little room for delay.
With the vertical tunnel dug, engineers will move to Battersea Park and start all over again. A smaller tunnel, this one just 6m across, will sink beneath London between April and August 2017. Only when both of the wells on land are dug will the laborious process to cross the river begin.
The team will dig the 330m long stretch using a micro tunnel boring machine, or TBM. Usually measuring around 0.5 to 1.5m wide, these are scaled-down versions of the subterranean giants used to dig out Crossrail’s tunnels. Because of their tiny size, the digging machines don’t have space for an on-board pilot. They will instead be remotely controlled from above ground.
A spinning disc at the front chews through the clay, inching the machine forwards under the river to the other side. The team estimate that the dig will finish in 2018, allowing the installation of the new gas pipe.
Project Manager, Andrew Heidner, described the dig as the company’s ‘flagship’ civil engineering project between 2013 and 2021. “Designing a tunnel 330m long that runs 30m under the River Thames is fairly straightforward in tunnelling terms,” he said. “However, to secure so many permissions, and factor in Thames Tideway’s works, in such a short space of time is an impressive undertaking.”
To get the project to this stage has taken an enormous effort and almost a year of intense planning. The team had to consult 15 organisations and secure almost 20 different permissions before getting the go-ahead for the work. It was also crucial to work closely with Thames Tideway and their nearby Chelsea Foreshore project to ensure success.
Speaking of the project, engineering manager Stuart Donaldson said: “This is quite a bit different to the average gas mains replacement scheme, to say the least! However, the purpose of the project is the same- keeping people connected to safe and reliable gas supplies for cooking and heating. The project is going to leave a great legacy and help London maintain its status as a leading 21st-century city.”
The project will be delivered by National Grid Gas Distribution’s strategic partner tRIIO, which also includes contractors Mott Macdonald and Skanska.