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UK first for shaft sinking innovation at £4.2bn potash mine

The new £4.2bn potash mine in the North York Moors is using a raft of new technologies to excavate its two 1.5km deep shafts and 37km of tunnels.  

These include the UK’s first use of an innovative vertical shaft sinking machine (VSM) and the longest ever conveyor belt.

The project will also be the first time in the world the VSMs will be used to a depth of 120m. To construct the lower depths of the shaft, the project will use a new shaft boring roadheader (SBR), used only once before in Canada. The conveyor belt in the tunnel will be the longest single belt in the world and be used to transport the polyhalite to the processing plant.

“One of the things I take pride in being part of this project is that we are an innovative project, we’re not afraid to make decisions and take risks, hence the optimisation of the new technology on the project,” said Sirius minerals project civil engineer Mark Pooleman.

“My personal view is that we should embrace new technology and never be afraid to take those risks.”

The massive project will involve building the two vertical shafts down to the mine site in the North York Moors at Woodsmith, an intermediate shaft at Lockwood Beck, and three, 6m external diameter, 12.5km long tunnels costing £1.5bn.

The tunnels are being dug to carry the mined polyhalite – a fertiliser – to a processing plant at Wilton near Teesside Harbour, after transporting the material at ground level through the moors was not deemed an acceptable solution.

The construction of a cut and cover pipeline was put forward as an alternative to tunnelling, but dismissed due to it being not very environmentally friendly, potential complications over the lifetime of the mine and high maintenance costs.

In total, three tunnel boring machines (TBMs), each starting from different locations, will excavate simultaneously at a rate of approximately 17m per day. 

Contractor Strabag started the first drive, launched from ground level from Wilton to Lockwood Beck in in June this year after winning the design and build contract in April. However, the TBMs launched from Woodsmith and Lockwood Beck will be constructed underground from a launch cavern at approximately 360m below ground level.

Pooleman said tunnelling has been chosen to go through the Redcarr Mudstone strata as it is soft enough to tunnel through and would avoid the water bearing rock and abandoned mine workings above.

To avoid transporting the 1M.m3 of material excavated from the tunnel and the shafts through the park, it will be used on the Woodsmith mine site to build up bunds around the buildings, hiding the mining site from view.

In all but one of the areas, the bunds will have a natural looking slope at around 1:7 to reflect the surrounding landscape. In the area where the bund is too steep, mechanical stabilisation will be used.

“The area will be landscaped to fit in with its surroundings,” he said. “This was a key part of getting permission to build the mine, and rightly so.”

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