One of the most challenging parts of accessing Saskatchewan’s potash reserves deep underground comes in the form of a wet, sandy layer of earth located between 400 and 600 meters below surface.
This is where the Blairmore Formation is found. It’s a 100-meter thick zone that has threatened the success of potash mining in Saskatchewan since the first shaft was sunk in the mid-1950s.
Arnfinn Prugger, PotashCorp’s Senior Director, Earth Science and Mining, explains that during the excavation of a mining shaft, the layer of sand will immediately collapse into the hole if it’s not frozen and walled-off to prevent it from moving.
Unfortunately for Saskatchewan’s potash pioneers, they discovered the Blairmore Formation the hard way. The first potash shaft sunk near Unity around 1955 failed as a result of the sand flooding the project and making the potash layer, located about 1,000 meters underground, inaccessible.
“The first shaft sinking operation failed at that Blairmore level. The subsequent mines, almost all of them, decided ‘ok, we’re going to have to freeze this ground, that way we’re excavating through solid rock’,” Prugger said.
Since then, potash engineers have been using what’s known as a Blairmore Ring to hold back the temperamental layer. After freezing the zone, concrete is used to wall off the wet sand, then a series of iron rings – Blairmore Rings – are fixed to the concrete, making a barrier strong enough to prevent the earth from moving in on the shaft.
As the first company to sink a potash shaft in Saskatchewan in decades, PotashCorp is using new technology to improve the Blairmore Ring solution, Prugger explained. Crews are currently working in this zone at the new Scissors Creek shaft at the Rocanville operation.
Higher-strength concrete, improved calculations and 3D imaging are all helping the project come along safely and efficiently. While the idea is the same, Blairmore innovation has evolved since the last shaft was sunk at PotashCorp’s Lanigan operation in 1980.
“We’re building on what people did in the past, and trying to learn from any mistakes that they made,” he said.
Out of 114 Blairmore Rings to be installed in the shaft at Scissors Creek, some 33 had been fitted to the concrete barrier by in early May, 2012. The rings will be covered by concrete again, essentially making a “concrete and steel sandwich” 623 meters underground.
The new shaft at Scissors Creek is expected to be complete in 2013 and the project is expected to be fully ramped up by 2015.