Maintaining haul road or overburden tip berms (or bunds) at the correct height has become a safety critical operation at mines and dumps around the globe. Berm maintenance has in the past been a minor operational task, requiring occasional grader or dozer attention of secondary importance. Perhaps not so any more.
Since 1990 there has been an average of one fatality per year due to inadequate safety berms at dumping points (Giacomini and Theoni, 2015) which were completely preventable had sufficient attention been paid to the issue. Indeed, it is thought that dump-point related accidents are rather more severe than other surface mine accidents and consequent lost productivity.
Any area within a mine which has heavy traffic flows, and in particular with reversing operations, can end up being an accident ‘hot-spot’. Research by the U.S. Bureau of Mines (May 1990) found that dump-point accidents over a 4-year period in the industry lead to thousands of lost workdays and several fatalities, the majority of the incidents being related to haul trucks.
Even with damaging statistics like these, the design, construction and most importantly, the maintenance of berms have, aside from some recent government industry oversight departments’ intervention, been traditionally determined by ‘rule of thumb’ experience. The inclusion of minimum berm heights related to the axle height of the largest vehicles operating in the area, along with guidelines for the thickness and firmness of the berm, should have solved the problem. This is particularly so as more recent studies (Giacomini and Theoni, 2015) indicated the importance of berms as a safety barrier for reversing haul trucks as a ‘tactile’ feedback mechanism to drivers, assisting them in identifying when they should stop and where the edge of the dump was.
The height of the berms in any mine is vitally important and is a critical safety mechanism which contributes to the overall safety of haul truck drivers.
Further considerations relating to the berms are material and geometry, which can be summarized as:
- Material type used to construct the berm. This is normally re-mined material that can contain various sizes and types of material. This also has an impact on the angle of repose that the material can achieve, which relates indirectly to its effectiveness.
- Berm height. Various berm heights are present on a mine however, the rule of thumb still applies to the berm being at least half the diameter of the largest truck in operation,
- Geometry of the berm. Recent studies showed that where possible, trapezoidal shape should be applied to berms at the dump-point, as they are efficient in keeping their shape after various impacts from trucks at dumping.
- Maintenance of the berm. Without constant and efficient maintenance of the berms, the likelihood of berm failure increases after each impact from dumping trucks
- Angle of approach. Haul truck drivers should be adequately trained to ensure that 90° angle is used at dumping sites. 75° angle of approach has a dramatic and negative effect on the stability, shape and effectiveness of berms. This will allow higher wheel climb and possibly lead to the haul truck going over the berm.
If the berm height, and to some extent the geometry, are crucial factors for safety, then the knowledge of when corrective maintenance on them is required is critical to operations. A completely automated berm height measuring system based on laser scanning clearly has the potential to remove not only ‘rule of thumb’ based decision making, but also allow a fully integrated alerting system to be provided over a mine communication network. Once deficient berms are identified and located, relevant mine staff can be informed and tasking for grader or dozer operators created, either manually or automatically. If synchronized into a fleet management system, haul trucks can be re-routed to alternate dumps or haul routes in real time maintaining operational efficiency.
With global demand for commodities rising and mining activities increasing, pressure on mining companies to stay competitive through productivity enhancements while keeping employees safe, is a major focus and an undisputed imperative. Having safety berms in place, and in accordance with safety guidelines, is an essential part of the goal of ensuring accident and fatality free mines, whilst improving efficiency by reducing lost workdays and maintaining production.