Highwall Monitoring to Combat Rockfall Accidents at Opencast Collieries

Following its introduction on underground collieries, the mandatory Code of Practice to Combat Rockfall Accidents (CoP) was applied to all opencast operations of lngwe Collieries (the South African division of BHP Billiton Energy Coal). The CoP includes, but is not limited to, requirements to assess hazards, manage them and monitor compliance. Information on methods to measure highwall conditions and compliance with control measures on opencast strip mines, as opposed to open pit mines, was found to be anything but freely available. However, on the Ingwe underground mines, a system of rating physical conditions in each section and how well production personnel were managing the situation, has been used with success for some time. It was decided that a similar approach would be taken, and, as with the underground rating system, the resultant rating forms should not be aimed at rock engineering specialists only but should be able to be used by production personnel as well. This paper discusses the highwall risk rating method as evolved over a couple of years and highlights that it is a flexible tool that can easily be changed to suit an individual mine's requirements. It also shows how operational aspects are being measured to determine how well the identified hazards are being managed. Allied to the method is a relatively easy, and certainly "low capex," mapping technique which allows between 500 and 1000m of highwall to be covered in a day. Features generally recorded include lithology, bench height, work still to be completed, coal losses or "toes", presence of water, dolerite intrusions, existing and potential failures, prominent joints, declared special and cautionary areas, cracks on upper benches and condition of spoil piles. Highwall mapping and photography as well as basic geological data collection, enable highwall risk and operational ratings to be determined. The same rating sheets may also be completed by production personnel, but without detailed mapping.