One of the world’s largest potash producers, Potash Corporation of Saskatchewan (PotashCorp) has teamed up with joint venture partners, Redpath and Thyssen Mining in the newly formed Associated Mining Construction (AMC) for the first new potash mine shaft in Saskatchewan to have been built in over forty years – Scissors Creek. Due to the nature of the deposit, the Scissors Creek shaft must be sunk through layers of unconsolidated water bearing strata. Therefore, specialised ground freezing techniques are utilised, along with complex high pressure shaft liners.Back in the 1960s and 1970s, Thyssen Schachtbau and Redpath’s parent company, Deilmann Haniel were among four German companies that formed the original joint venture, AMC, which became one of the forerunning companies that provided expertise and shaft sinking services to the Saskatchewan potash industry. It was this initial relationship and the knowledge of shaft liners and ground freezing techniques that led to the reformation of the AMC venture between Redpath and Thyssen Mining. AMC draws upon the experience of both parent companies and their subsidiaries to provide solutions to what have proven to be some of the most complex shaft sinking projects in the world. Scissors Creek is located near the town of Rocanville, Saskatchewan and requires a 6 m diameter composite lined shaft that will be sunk to an ultimate depth of 1,123 m including a 600 m deep section of frozen ground. Traditionally, temporary headframes are used for the sinking portions, and only when sinking is complete and the ground thaws, is the permanent headframe construction started. For Scissors Creek, an alternative methodology was developed, whereby the freeze circle is “bridged” by the headframe, which is supported on piles spanned by massive concrete reinforced beams below grade and external to the ground freeze circle.
This method precludes the requirement for temporary and permanent headframe construction; therefore eliminating excessive costs and scheduling to PotashCorp. The freeze holes and final liner designs (varied by depth and geology) were completed early in 2010. Actual freeze plant operations and ground freezing has progressed sufficiently to allow sinking in the upper portions of the shaft to begin, with the freeze the wall thickness already stable down to 400 m below the collar. AMC also completed the freeze hole drilling for BHP’s Jansen project in the summer of 2010.