Modern Quarrying July-August 2015

TECHNICAL FEATURE SAFETY BERMS

Bench crests – the risks and remedies

Surface mines are becoming increasingly popular as a form of mineral extraction around the world, partly as they are inherently safer than underground mining methods, with a much reduced rock-related risk. This does not mean that they are without risk. One of the highest risk areas lies at the crest of production benches, where persons/machines could fall off the edge or the weak crest could fail, leading to potentially fatal consequences. This paper by Applied Rock Engineering’s Dave Fenn looks at some of the risks associated with crests and suggests actions to minimise them.

M any industr y lead- ers and notably the Department of Mineral Resources (DMR) are pushing for crest pro- tection measures. Along haul roads and especially inclined ramps, this is largely an industry standard and widely accepted, but there is a need to define safety berms. • Safety berms are mostly used to describe a continuous wall of loose material emplaced close to a crest edge to warn, discourage or prevent pedestrians/vehicles from falling off the crest edge. • Haul road berms are safety berms that are used along haul roads and espe- cially inclined ramps. These berms are often large and are generally long- term or permanent installations. • Rock traps or toe berms describe a

wall of loose material emplaced close to the toe of a slope, primarily to pre- vent rock rolling into the workplace from the adjacent highwall ( Figure 1 ). They also act as a barricade and moni- toring device, trapping fallen rock. • Perimeter berms are placed around a quarry to negate the effects of noise, visual and dust pollution, and can help to prevent inadvertent and non- authorised access. These can be very high and placed a safe distance from the crest edge, anticipating post-clo- sure instability. There is little standardisation in the materi- als tobe used in the construction. Examples include waste overburden or aggregate sand to boulders and are often a combi- nation of material types and sizes. There is also no standardisation in their con- struction method required, compaction,

Consultant rock engineer Dave Fenn (Photo: Dale Kelly).

drainage and future maintenance. High berms would have to be laid in lifts which adds to the safety risk. The dimension of safety berms is another area where many standards have been adopted: • They are often not constructed to a particular standard of height or width, being bigger where copious quanti- ties of convenient waste materials of various sizes exists. • Guidelines in international literature normally quote the berm height as half the height of the largest TMM wheel.

Figure 1: Sandy rock trap designed to stop the rolling rock threat from above and act as a barricade and even a monitoring device, if rock is trapped.

Figure 2: Size of berm to halt a heavy truck.

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MODERN QUARRYING July - August 2015