Picture caption: Tilbury, near the site of the project’s first shaft
The largest-diameter vertical shaft sinking machine in Europe has begun working on a 48.7-metre deep shaft, kicking off the Grain to Tilbury power tunnel project. This £230-million civil engineering project is part of National Grid’s Great Grid Upgrade, and this particular work involves building a new 2.2km tunnel under the Thames, parallel to the old one.
The tunnel will run from Tilbury in Essex to Gravesend in Kent, close to the Isle of Grain. The current tunnel has been in operation since the 1960s and has two problems. Firstly, it is no longer suitable in terms of capacity, and secondly it lets in more water than is ideal.
The machine, known as Verena, will sink a 15m-diameter shaft on the Tilbury site, before being moved to the Gravesend site to sink a corresponding shaft to 46.3m on the other side of the Thames. The German-built machine is machine-maker Herrenknecht’s biggest VSM in Europe.
The machine can be operated entirely from the surface, meaning no people will be in the shaft during the initial excavation, which eliminates a great deal of risk from the project. The work is done in a water-filled environment, and each shaft will be lined with segmental concrete rings, which are added to the top at ground level.
This method is novel in the UK and has only been used once before, on the Woodsmith Mine in Yorkshire. When the shaft reaches the intended depth, the vertical shaft sinking machine (VSM) will be lifted out by crane.
The tunnel boring machine (TBM) will not initially fit into the shaft at full size, so sections will be added one step at a time. Each time another 12m is excavated, at roughly 2m per day, another section of the TBM can be attached. It’s estimated that it will take around six months for the TBM to be at its full 100m length. At that point the machine will be able to bore around 23.3m per day.
All tunnelling is expected to be completed by the end of the year, followed by another two years to get the project over the finishing line. Additional work includes building the headhouses on top of each shaft and replacing the existing overhead lines between Kingsnorth, Grain and Tilbury.
Power cables are expected to be installed in the tunnel between April 2027 and January 2028, with full completion set for March 2029.
Carl Trowell, National Grid’s president of strategic infrastructure, has said this project is “an important part of the overall upgrade because a lot of power is coming into East Anglia and as it comes down you end up with a bottleneck around the South East if you’re not careful. So this reinforces the network by not having to send all of the power through the London circuits.”
Speaking to the press towards the end of 2024, Keith Anderson, ScottishPower’s chief executive, said the UK had been a victim of its own success by adding renewables faster than other countries, putting a strain on the grid. “It’s creaking at the seams,” he said. “We need to play catch-up. For every pound we invest in renewable energy we should be investing at least £1 in the grid. We need to increase the overall investment in the grid, and evolve our methodology for new grid connections.”
It’s clear that the Grain to Tilbury project is much needed but is potentially a drop in the ocean of the work that’s necessary to get the right infrastructure in place. You can add as much solar and wind power as you like, but if you can’t get it into our homes and businesses then the UK will not be able to hit the decarbonisation targets already agreed by the government.
National Grid says their Great Grid Upgrade is “the largest overhaul of the electricity grid in generations”. Let’s hope that there are many more impressive feats of engineering to come.
In the meantime, if you need any assistance with the structural elements of an upcoming project, please do get in touch.
