Friction: the key to safe and competent haul road operations
By Eric Tomicek
Friday, 30 June, 2017
When the lifeblood of a mine is an ever-changing and potentially hazardous network of unsealed haul roads, how do you provide a safe working environment and maintain an efficient and prosperous haul road circuit operation? Here are my thoughts on why friction is important to a mining operation from safety and operating cost perspectives.
A mine’s network of haul roads can either be its greatest asset or its greatest liability. The path to safe and efficient haul road operations begins with understanding what friction is, being able to measure it and knowing how to manage it. A haul road that is dusty when it is dry can become extremely slippery and dangerous due to rain or when sprayed with water to suppress the fugitive dust.
Two independent friction concepts are required to effectively manage haul road safety and maintain competent haul road operations:
- Friction supply is the available friction where vehicle tyres meet the haul road surface. Typically, when water is applied to haul roads (by rain or by water cart to suppress fugitive dust) the friction supply value will decrease by varying amounts. Quality coarse haul road sheeting material, such as basalt, will exhibit a high friction supply value when dry and wet. In contrast, a haul road with considerable clay content will have high friction supply when dry, but have hazardously low friction when wet.
- Friction demand is the required friction to operate the vehicle for a given circumstance on mine haul roads. Broadly speaking, this is a sum of how the vehicle is driven (braking, acceleration and steering) combined with the specific geometry of the haul road design. Critical locations where friction demand needs to be considered include ramps, particularly those at the upper range of gradient specifications, vehicle conflict points such as intersections and geometrically demanding road layouts such as those with curves.
If the friction demand at a section of haul road is higher than the friction supply, the vehicle operator will be unable to safely negotiate that specific geometry of haul road. The outcome will most likely be an uncontrolled/unplanned movement causing damage, injury or, in the worst instance, death. By managing the haul road’s friction supply to be always in excess of the friction demand a safety margin is maintained.
Friction supply and demand is measured using an instrumented portable accelerometer attached to a light vehicle with an anti-lock braking system. An easy-to-use, plug-and-play haul road friction measurement tool that is simply mounted to the window of a vehicle, in combination with a proven methodology, is now available for mine operators to measure and manage their haul road conditions. A driver can easily perform friction demand and friction supply testing for which the tool will output a simple friction number.
The friction measurement process and methodology can be used for the following applications:
- To provide a friction supply measuring procedure and risk management model for the road network by friction profiling of a selection of haul road surfaces for friction analysis and comparison under a consistent water application rate process.
- To provide commentary and recommendations on mine road design, watering and maintenance practices.
- To assess surface friction after rain to inform decisions to return to work.
- Operational road watering audit for proactive vehicle safety management practice.
- Road surface material evaluation for measuring before and after road sheeting friction benefit.
- Friction-related vehicle incident investigation for friction supply/demand safety margin analysis.
Understanding friction is important to a mining operation from safety and operating cost perspectives, especially with the unpredictability of uncontrolled movements occurring on mine haul roads. Water trucks which allow for a quantitative level water output, used in conjunction with road profiling technology, should be implemented across mining operations to advise a safe level of water to apply to a haul road to maintain an adequate level of friction.
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