Engineering & Mining Journal

NOV 2018

Engineering and Mining Journal - Whether the market is copper, gold, nickel, iron ore, lead/zinc, PGM, diamonds or other commodities, E&MJ takes the lead in projecting trends, following development and reporting on the most efficient operating pr

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ROCK BOLTING NOVEMBER 2018 • E&MJ 65 www.e-mj.com systems for detection and early warning of rock movement. The company's D-FOG System is a Fall Of Ground detection system consisting of a chain of D-FOG lights fixed into drilled holes in the hanging wall. They are wired in series and linked to a control box which in turn is linked to one or more ro- bot heads and a PC link. The individual D-FOG Units can be installed up to 16 m apart and monitor movement in the hanging wall continuously. If the system is healthy and the D-FOG Units are not triggered, the lights in the units and in the robot heads flash green. Should po- tentially unsafe movement in the hanging wall or a fall of ground occur, the trig- gered D-FOG Unit will flash red and send a signal to the control box which in turn illuminates the appropriate warning lights on the robot heads. The control box also alerts a remote PC of the status. In some deeper mines, the reality is the ground support will likely sustain multiple seismic events and should be designed accordingly. A whitepaper on the company's website (www.ncm.co.za), Relationship between energy per impulse and dynamic capacity of a rockbolt, demonstrates the NCM's knowledge of rock mechanics at depth. NCM's research concludes that the dynamic capacity of a rock bolt is not a constant value. They discuss the importance of developing a better understanding of how rock bolts are loaded during rockbursts. NCM suggests that suppliers quote the energy capacity of a rock bolt when test- ed in a large number of low input energy impacts rather than a single large ener- gy impact. To do this, the industry would have to adopt a stricter definition of the quantification of the dynamic capacity of a rock bolt. They offered the following definition, "The true dynamic capacity of a rock bolt is the amount of energy a rock bolt will absorb (at a given impact velocity) such that the rock bolt slows the impact mass down to zero velocity at the point that the rockbolt breaks." Discussion are still on- going in the rock mechanics community. A green light on NCM's D-FOG System indicates safe working conditions.

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