Stability of excavations and design of mining layouts in a deep level potash mine
The shafts at Boulby Potash Mine were sunk between 1969 and 1974 and the first potash was put through the processing plant in 1973. The decision to mine the deposit was based on the results obtained from fifteen exploration boreholes put down from surface. Since the first potash was mined, the mine has been faced with a number of problems. Many of these result from the seam and near seam geology which has turned out to be far more variable over short distances than was at first anticipated. Not only has the thickness and strength of the ore itself varied considerably, but also the proximity to, and thickness of, the overlying shale and marl formations. These latter two play a vital role in the stability or otherwise of the immediate roof of the rooms and roadways. The combination of the above factors has made it very difficult to maintain long term roadways in potash. Due to the cost and other short term disadvantages of driving development roadways in halite beneath the potash seam, alternatives in the form of "stress relief" and high extraction development in potash have been implemented.