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 and friction demand.
Friction supply is the available friction where vehicle tyres meet the haul road surface. Typically, when water is applied to haul roads (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.
At Australian Diversified Engineering, we are at the forefront of bespoke product design aimed at providing solutions to commonly faced challenges by the mining and construction industries.
We pioneer the development of the next generation water truck control system that manages both dust and safety, giving mining and earthmoving companies confidence that their vehicle operators are driving on safe haul roads. We will continue to grow our line of innovative products to ensure mining and construction companies can operate safely and efficiently.
Eric Tomicek is sales manager at Australian Diversified Engineering. This article also appears in the July edition of Australian Mining.