Haul roads – overlooked in your mine productivity improvement plan?
The relationship between haul road quality, productivity and unit cost is undoubtedly complex and different for every mine. However, in all cases, it does exist. A full analysis requires many factors to be considered including:
Expected haulage (quantified) for each segment
Haulage units (ie size, gross weight, rimpull and retardation)
Availability of material to build subgrade, pavement and wearing courses
Climactic variations in rainfall and temperature
Construction and maintenance resources and technical skills
Legislation or codes of practice
CEA’s team has been working on and around haul roads for many years. While we know the importance of all of the above, there are a few issues that always come to the fore…
The king – drainage
If a mine has limited resources, there are three haul road components that should receive attention:
Drainage
Drainage
Drainage
Well-drained roads are always safer, stiffer and easier to maintain than the alternative. Here are some key areas to cover in a site check for drainage:
Is there ponding in the table drains after rain, or worse, are there no table drains? Ensure water can escape from shoulders at all times.
Do soft spots keep appearing in the same locations? Remember, soft spots are generally due to groundwater making its way to the surface. This source can and should be cut off, so take the time to find the source of water as soon as possible.
Is there a clear cross fall or superelevation? Flat roads in the transverse and longitudinal direction should be avoided. It only takes a few per cent grade to make all the difference.
Does haulage stop for even the smallest of rainfall events? It is possible to make roads that perform in all weather events. It comes down to a question of return on investment.
Are tyre wear rates below target during the wet season? If so, it’s likely the roads are ponding water, which is a proven catalyst for tyre damage.
The Princess and the Pea – the subgrade
In Hans Christian Andersen’s fairy tale, the princess endures a sleepless night due to a pea being hidden below a stack of mattresses. Trucks and haul roads are similar. It doesn’t matter how good the running surface might be (aka the mattress)…if there is a pea below (read ‘poor subgrade’), the truck will feel it and the impact will be real. Good running surfaces initially mask poor subgrades but they are always found out and, when they are, the running surface itself will be well on its way to destruction.
Good subgrades are made of robust material that has been moisture conditioned and evenly compacted. There is generally no easy fix for a poor subgrade. If the subgrade fails, it’s either a case of removing the pavement and wearing course to access the subgrade, or trying to bridge over the failures with more pavement. The good news is that it’s generally pretty cheap to get a quality subgrade to start with. A little effort when selecting good waste rock, some controls around the thickness of dumping and basic compaction are typically all that is required. A small investment up front will generally give great returns in the long run.
No jack of all trades – ‘good’ roads aren’t created equal
The best mines have a very clear view of what standard haul roads should be – and that’s not to say that all roads across a mine should be the same. Professionally-run mines understand that primary, secondary and tertiary roads all have different roles and, as such, should be designed and constructed to different standards. It’s a common mistake to insist on a blanket standard, pouring money into roads where the return on investment is low. Plan your roads, be clear on their purpose and then, as they say, work your plan!
We know all too well that haul roads are generally low on the priority list when it comes to operating mines. Our team finds that clients not only value our expertise in this space – they also value our independence and the fact that when they contract us, they are contracting a guaranteed outcome in a guaranteed timeframe. For more on our haul road inspections and end-to-end haul road improvement programs, please get in touch with our team.
