Presented at the 2017 Mining Health and Safety Conference
Introduction of MD bolts as part of dynamic support system in rock-burst damaged areas at Copper Cliff Mine - A case study
D.R. Chinnasane, A. Forsythe, and M. Yao, Vale Sudbury
This is a presentation about a case study which outlines the performance of the MD Bolt installed in the damaged areas while mining the stopes that were located in the vicinity of seismically active ground conditions. Mining under the sill pillar region in the 100/900 ore bodies at Copper Cliff Mine has always been associated with significant seismic activity. A seismic event that occurred following a crown blast in a vertical retreat mining (VRM) stope on the 3710 Level had caused considerable damage to the walls/shoulders of adjacent top sills (9550 and 9510 Sills), even though these sills were supported with the current dynamic ground support system. The recommended ground support to recondition the top sills comprised of 1.8 m (6 ft.) long FS-46 Split Set bolts with #4 Gauge screen (primary support system) and 20 mm 2.4 m (8 ft.) long D-Bolts with #0 Gauge mesh straps on 1.5 m x 1.5 m (5 ft. x 5 ft.) pattern (secondary support system). There were no problems encountered when installing the Split Set bolts with #4 gauge screen, but installation of the D-Bolts was unsuccessful due to the heavily fractured and damaged ground. Since the primary support system alone was considered to be inadequate to withstand the seismicity associated with the future mining in the area, the Mechanical Dynamic (MD) Bolt from Sandvik was introduced as a substitute for D-Bolt to complete the dynamic ground support system. The bolts were installed in conjunction with #0 gauge mesh straps without any major installation issues in the damaged areas. The MD-Bolt is essentially a 47 mm friction stabilizer bolt reinforced with a 20 mm bar with a wedge arrangement at the toe of the bolt. Once the bolt is fully driven into the hole (similar to a friction bolt), the bolt nut at the collar is rotated to activate the wedge to firmly anchor the bolt into the drift walls.