Closure monitoring in Potash Mines using LiDAR

Underground soft rock mines are constantly deforming - this is a normal rock response to mining excavation. Once a mine opening has been excavated or cut, the opening begins to deform into the excavation. This rock displacement, or room closure, could occur quickly or much more slowly depending on the stress changes caused by mining pattern, rock mechanical properties and in-situ rock pressure. Of particular importance to Mining Engineers and Rock Mechanics specialists is the rate of this closure and where it is occuring within the mine. Room closure is traditionally measured using simple displacement transducers; these instruments give readings only at the points where they are installed. This paper proposes the use of Laser Range Finders (LRF) in generating 3D models of the mine areas where closure needs to be monitored. With this approach, closure can be measured at many points in the room, not just at individual instrumented stations. A procedure is presented using automatic scan registration to obtain a 3D model of an area using an inexpensive 3D LRF. Test results are presented from the Allan Potash Mine. It is shown that this procedure produces results consistent with a standard closure meter in a real mine environment. The difference between the average closure measured with LRF and the closure rod ranged from 3 millimetres to 13 millimetres (4% to 14% of total displacement change).