Q&A series #34 : Interview with Roger Thompson

Topic of Discussion: Understanding Mine Haul Road Design and Construction 

Understanding the overall concepts and principles of Mine Haul Road Design is important for mining operators, mine planners, civil engineering practitioners, consulting engineers, mine consultants, contractors, truck fleet operators, and personnel involved with the design, construction, and day-to-day operations and maintenance of mine roads. 

Principles of mine haul road design and the philosophy of provision, road building material selection and characterization, road-user (truck and traffic) requirements, fundamental geometric design concepts, structural (layerworks) design, sheeting (wearing course) selection, and improvement are available in this Haul Road Design Workshop (Online). 

Mining Haul Roads – Theory and Practice is the first comprehensive treatise on mining haul road design, construction, operation, and management. The book presents an authoritative compendium of worldwide experience and state-of-the-art practices developed and applied over the last 25 years by the three authors, over three continents, and many of the world’s leading surface mining operations. 

Global Road Technology had the privilege of speaking to one of the world’s leading mine haul design and construction gurus, Roger Thompson. He is currently the Principal Consultant at Mineravia Consulting and is based in Perth, WA, Australia. 

Q1) Welcome to the GRT Q&A Series Roger, it is really an honor and pleasure to have you with us. Seldom do we get to speak to a contributing author in Mine Haul Road Design and co-author of ‘Mining Haul Roads – Theory and Practice’ amongst the many hats you wear over an illustrious career that has transitioned in industry, academia, and now consultancy. Can you kindly tell us more about your journey to date leading to your role as Principal Consultant at Mineravia Consulting?

I’ve been fortunate in that my career spans both mining production and academia. Following graduation, I worked for Anglo American for a few years – which provided me with a really solid foundation in the day-to-day realities of mining operations. This sparked an interest in mining technology and research was, and still is, a vibrant and innovative field and so I then embarked on academic research and teaching path. This led to my Ph.D. in mine haul road design and the development of novel and improved mine road design and construction techniques that meet the demands of today’s mines and haulage vehicles.

Q2) Let us borrow your principal consultant hat for a moment there. What goes into mine road design and operation. What are the key areas of focus when it comes to the provision, rehabilitation, or improved design and management of mine haul roads?

Haulage represents one of the largest mining cost elements, especially for deep, large open-pit operations. Today, more than 50% of mining costs can be associated with loading and hauling material out of such pits. That translates into a significant opportunity to realize cost savings through improved haul road performance. The mine haul road is an asset and should, in conjunction with the haul trucks using the road, be designed to deliver a specific level of performance and its design, operation, routine, and longer-term maintenance requirements managed accordingly. If not, a critical production asset becomes a significant operating liability. 

They say a picture paints a thousand words, so let’s start with this diagram which shows the integrated approach to mine road design – and the key focus areas. It’s obvious but critical to recognize that the design decisions made when a road is built ultimately impact the operational safety and efficiency of the road.

We can make further improvements to the road during the latter stages of the design, or during operations, if required, but geometric or structural design problems are more difficult to address, being both costly and extremely disruptive – it’s estimated that the cost to repair or rebuild a poor road can be up to 5x the original unit-construction cost. So the value proposition for fit-for-purpose design or improvement lies in the increased safety, durability, trafficability, and productivity of mine haul roads, through the design, build, or rehabilitation to minimize rolling resistance and deterioration, contributing to reducing truck cycle times, improved tire life and fuel efficiency, reduced road maintenance activities, together with enhanced 24x7x365 trafficability and safety.

Q3) To what extent have autonomous haulage systems changed the way in which mine haul roads are designed? What really goes into conceptualizing the best mine haul road for autonomous mining trucks?

With autonomous haulage systems (AHS), the mine haul road remains a critical component in the production process – the truck itself has not fundamentally changed, only the control systems. The operating performance of the haul road is central to the overall success of autonomy since the rapid deterioration of haul roads will trigger truck speed reductions and stoppages. To remediate will be costly, requiring human intervention and significant (albeit temporary) changes to operating procedures when road performance is compromised. Hitherto, we’ve had a well-developed understanding of how a road deteriorates over the short term, using this knowledge as a basis for planning and optimizing our routine road maintenance interventions. However, with AHS, we’d like to minimize routine maintenance, through more informed sheeting selection in the first instance, together with stabilization or palliation, etc. if indicated. AHS has also put the spotlight on longer-term performance trends and the need to predict when, for instance, a sheet would be required, again based on the design parameters of the road itself, traffic volumes hauled, season and even material types carried. All of these variables exert an influence on-road and truck performance and the ideal would be to design and build the road to match the production life of the block.

Truck operators do a lot more than just ‘drive’ – when faced with road defects, hazards, or obstacles, drivers judge and compensate, and when transitioning to AHS, it’s easy to lose that additional level of road performance feedback. With road defects and large trucks, you need to catch them early or they’ll quickly ‘grow’ to the point where AHS will perceive it as a hazard. With AHS, we’ve seen much richer data coming off the trucks themselves, and this leads to a much more mature picture of the road conditions and the trucks’ response to those conditions. However, it’s important to remember that while we’re ‘detecting’ these conditions, obstacles, or hazards, it’s nevertheless just as important to diagnose the root cause of these issues so that when a road goes down, the repairs we undertake are sure to address the true causation, not just ‘hide’ them for a while.

Q4) How would you achieve the best road maintenance in autonomous operating zones to minimize autonomous haul trucks’ slow or stop events? What methods can be used to effectively deal with the loss of traction, rutting, and dust generated on the haul roads?

‘Best’ road maintenance practice will vary from site to site, depending on the impact of the deterioration – often assessed in terms of rolling resistance. I couldn’t pass up this opportunity (as a former academic) to present a graphic to help explain some concepts here.

Using truck speed-rimpull-gradeability data gives us a useful insight into where on a network of roads the impact of deterioration (measured as an increase in rolling resistance) is greatest. In the above graphic, you can see that the flatter hauls, where trucks operate at a higher speed, are more susceptible to the effects of deterioration, than are the steeper hauls on-ramp. Of course, we also need to factor in traffic volume, lengths of roads, etc., to fully evaluate the cost-benefit of maintenance intervention.

Common defects on a road such as you mention, loss of traction, rutting, dust generation can be traced back to the design methodology we discussed. Rutting is a typical example of a structural design issue – not enough or poor quality cover over the weaker sub-grade or in-situ, or for new builds, often poor layerworks compaction too. In this case, simply blading the road will not correct the problem as they’ll reoccur again as the layerworks and sub-grade continue to deform. Rutting is a common problem, especially with AHS, related to the wheel path channelization of the trucks on the road which concentrates wheel loads to these specific areas of the road, more than is the case with conventional trucks. The other two defects can be traced back to sheeting (or wearing course) material selection, deterioration, and/or spillage on the road. Even the best sheeting will deteriorate over time, often exhibiting an increase in fine clay fractions, which leads to dustiness when dry and slipperiness when wet. So, the first step if these problems persist would be to check the upper 50mm of your sheeting, how does it compare to the selection criteria? It’s often only the upper 50mm or so of the sheeting that is regularly bladed and in contact with the truck tyres (and often contaminated with tyre carry-over), sheeting material below that is still in a good condition and, assuming your sheeting was well selected in the first instance, a deep rip and remix will bring the fresh sheeting back to surface and address the problem in the short-term. In the longer term though, eventually, a resheet will be required.

Q5) What are the common challenges experienced by haul road practitioners around the world? In dealing with these challenges, what are the basic steps of achieving fit-for-purpose solutions that consider the most important factors and seek to preserve the haul road as an asset to the mine?

Most often we see the competing requirements for production and construction resources limiting what a crew could actually achieve in terms of materials and build quality. Mining is dynamic and we often need to make short-term tactical decisions to maintain production and fleet utilisations. It’s when these short-term ‘fixes’ become a long term that the road problems increase – you can’t ‘undamage’ a haul truck once it’s been run on a poor road for a few shifts. . All too often we see sites chasing their tails; poor roads require frequent maintenance blading, often at the expense of the better roads, which eventually results in an overall decrease in road conditions across the site.

Mines are constrained too by the materials, time, and cost of construction. It’s critical that a site firstly recognises good quality road building materials that it can source from its own waste rock and flag these at the planning stage so they’re not lost as waste, but rather earmarked for removal to a stockpile of road construction materials. It takes time to build a road, both a good road and also a bad one. Your construction crew should be able to eyeball construction material quality and importantly too, have the ability to recognize when either the material or the building process is not to standard. Most often this is seen as no- or poor compaction, which is a critical aspect in road building – especially when we’re dealing with the wheel loads of large mine trucks.

Finally, here, we often see some roads enjoying priority over others when in fact, a quick assessment will show that often the ‘poor cousins’ are really cost and performance critical to the operation. Typical here would be the waste haul roads – waste doesn’t produce and income right, so why expend much effort there? When stripping ratios are high, these roads move lots of tonnes and small improvements are multiplied both by the number of trucks using the road and by the stripping ratio contribution to overall mining production cost. After all, you need to move the waste to get at the ore in the first instance.

Q6) How has wet haul road dust suppression evolved in your career? Which products have you commonly come across in the industry and what can we learn from the different best practices from around the world?

Dust suppression has certainly matured over the years – gone are the days of a product being sold to site with a promise of a magic fix to all their road problems. Suppression and stabilisation, although having two different performance goals, often have shared benefits, especially when applied to the uppermost layer (sheeting or wearing course) to increase density, strength, fines retention, etc. Given the variation in road-building materials from site to site, there’s no ‘one size fits all’ approach, each solution must be tailored to the specific materials and site constraint encountered, and this is where the supplier plays a crucial role. Polymer-based products have been used with good success at many sites – simply by virtue of their formulation flexibility which means there are many variant options that can be tailored to a client’s specific requirements. 24x7x365 trafficability is becoming a more realistic goal too with these additional treatments, reducing the susceptibility of a road to wet-weather closure, quicker remobilisation times, and also eliminating conventional road maintenance needs entirely. Whilst that sounds great – it’s important to remember that this comes at an investment cost and a mine must satisfy itself of the value proposition. 

Generally, longer-term high traffic roads, trolley-assist, etc. may qualify in this respect, but it’s important to remember that any road selected for treatment must be well designed in the first place – you don’t want structural failures (rutting etc) triggering maintenance of the road since this would, in itself, destroy the treatment and all benefit is lost. Similarly, we need to look closely at our road management philosophy too – do these products suit how we manage our roads? You wouldn’t clean your kitchen floor tiles with a spade and likewise, with a treated road surface, blading would damage the surface, so brooming to removes fines, spillage and tyre carry-over, can be more appropriate. This illustrates the extent to which a decision to treat a road has implications that extend well beyond simply the value-proposition, and into the broader road design, management, and mine planning aspects too – all of which need careful consideration if treatments are to deliver the scale of benefits of which they’re capable.

Q7) Can we expect another co-authored book from you? Or perhaps the second edition to ‘Mining Haul Roads – Theory and Practice’? What does the future hold for Roger Thompson?

Well, we’re waiting for the book to chart in the NYTimes best-sellers list…may be a while yet. It’s been a useful exercise to combine our experiences in road design and management from different regions, into a single reference. Reading a book though isn’t the be all and end all, it’s the practical application of the knowledge that ultimately counts, and this has led us to develop training courses tailored to various audiences to help with upskilling. This is where we’re heading at the moment – and it’s very gratifying because in addition to facilitating better mine roads, participants share a wealth of experience and knowledge which greatly improves the global best practice.

Find out more about mine haul road design and construction: http://www.mininghaulroads.com