Mining Publication: Coal Bumps and Odd Dynamic Phenomena - A Numerical Investigation
The Crandall Canyon accident investigation included an interesting and unexplained observation by rescuers that the "barrier rib had shifted northward as a unit, as much as 10 feet." This is not the first mention of such a movement, although such reports are rare. Historical accounts describe unusual movement and displacement of intact coal, cribs and timbers. Two movements of particular interest are the creation of gaps above coal pillars and falling of standing support elements without apparent damage. A dynamic boundary element program was used to explore movements induced by slip on geologic features removed from the affected panel. While the resulting models are much too simple to fully replicate these observations, they do show that the types of phenomena observed are possible. They can also provide insight into the types of motions that ground support elements are subjected to during large bump events. This was demonstrated for the case of a large bump in a Book Cliffs coal mine. Seismic information suggested the source mechanism to be normal slip on a fault. A model of that source showed initial dilation of the panel followed by dynamic compression and rebound - consistent with underground observations. The initial dilation is important as it may allow slender standing support to shift or fall.