When mining depths increase, so do the challenges. This week at the virtual Euro Mine Expo, Dr. Matthias Wimmer, mining engineering manager for LKAB’s Kiruna mine in Sweden, presented a new method for underground mining, raise caving. “This is a major groundbreaking step toward a safer, more efficient mine,” Wimmer said. “Raise caving has been developed for efficient mining at great depth.”
Rock stresses increase at depth and the challenges associated with rock mechanics will require innovative solutions for the mines of the future. While discussing the evolution of mining methods, Wimmer compared it to flying an airliner and, as the pilots encounter different conditions, they have to adjust. LKAB is making a similar adjustment that will extend the life of the Kiruna mine to 2060 and beyond.
LKAB developed the raise caving concept working with Montanuniversität Leoben in Austria (Austrian School of Mines). LKAB is well-known for its use of large-scale sublevel caving underground, but there are concerns surrounding its continued use at greater depths. Raise caving would mine the orebody from bottom to top, as opposed to the tradition top-down methods. The sequence is reversed where the raiseborer would be used to develop the drawbell and then it would be drawn upward through the slice, creating a large slot raise. A cylindrical drilling platform with a rotating drilling boom on the bottom would be lowered into the raise. The manless drilling system would then drill holes downward radially along the circumference of the raise. The blast would slab the material off toward the drawpoint at the bottom. The automated drilling machine at the base of the platform would both drill and load the holes.
Ordinarily, caving operations require significant initial investment with the development of sublevels and a network of drawbells, which will become difficult at depth. In this case, raises are bored and that is the starting point for mining in slices and the caving begins from the bottom to top. Mining starts in the raises as opposed to conventional, horizontal methods that use long-hole drills in the drifts. Since the infrastructure and drifting will be reduced significantly, Wimmer believes mining efficiency could be improved by as much as 50%.
“What started as an idea has developed into something much more, thanks to our many committed and innovative co-workers and colleagues. Together, we have developed raise caving based on existing mining methods, well-established de-stressing principles used in deep mines, and combined the best,” Wimmer said. “We have several incredibly exciting years of tests and analyses ahead of us.”
Large-scale testing will begin next year at the Kiruna mine. “We still have a huge amount of work ahead of us,” he said. “Two test areas will be developed: one for the machine concept and one for the mining method. Initially, individual components will be tested step-wise. Thereafter, the complete system will be tested.”
