Eltirus

Eltirus founder Steve Franklin examines why smooth roads are so important and, in many cases, so overlooked.

As a young shift supervisor in the mining industry, one of my most important functions was to ensure the loading tool operators were “digging to grade”. By this was meant that rather than “digging to hard” i.e. to the bottom of the blast, we used laser levels to ensure that the operators dug to “design floor” or “grade”. This matter was not taken lightly.

Many of the mining contracts that we worked to had extremely strict tolerances for floor levels and adherence to them was non-negotiable.

At the time I used to think that this was “over the top” but with a few more years (and some more experience) under my belt I began to realise that it was a vital discipline and one that was needed not only to reduce the incidence of being yelled at (in the bad old days of “it’s my way or the highway”), but was in reality, just sound operational practice.

Why is it important?
The simplicity is this: Smooth roads do make more loads. A smooth level floor enables higher truck travel speed across the floor and with it less wear and tear on both truck and operator.

It also makes it much easier to drill and blast the next shot, as a constant bench height can help ensure more even breakage of material towards the top of the bench because of consistent blast pattern geometry.

Lastly, it also ensures that loading tool operators (particularly face loader operators) are not subjected to the stress and impact of digging “toe”. Unless you have been on a large wheel loader digging out of a face or on a dozer ripping rock, you really can’t comprehend just how uncomfortable it is to go from full throttle in first gear to a complete stop instantly – it is very hard on your body.

In most quarries, operators dig to level as best they can. Image: Eltirus

Why do we get toe?

Firstly, let’s look at the blasting process. When a blast pattern is designed, one of the key parameters to consider is the sub-drill depth. That is, the depth below the design floor level. So, if for example the correct design level for the bench is 100mRL, the drill and blast designer will always design the holes to go deeper than this level to ensure that there is additional depth to cover any fall back of material into the hole and also to ensure that when the blast is fired, that all the material below the design level is completely broken. Realise that the subdrill needs to be enough to ensure that consistent breakage, but not so much that it breaks too much material on the next bench which would be wasteful from a cost perspective but will also make it harder for the driller to get through next time.

My training as a drill and blast supervisor (in addition to shift supervisor) was such that we always worked to ensure good breakage in the subdrill zone through taking care to drill holes to the correct depth, dip them and correct them as needed. Likewise, as a shift supervisor, I was rigorous in ensuring that we didn’t dig below the design RL.

When I moved into the quarry industry, I was very surprised to find out that these concepts were not universally practiced.

I famously remember working on a site where there was a tremendous moaning about “toe” and continual complaints about the blasting contractor. Out of curiosity, I went across the bench with a laser level and found that every single instance of “toe” was below the design RL. In essence, the drill and blast contractor had done their job and was falsely maligned.

In this instance, the blame fell entirely on the loading tool operator who consistently dug out the sub-drill zone. By way of example, take a look at the bench cross section shown in Figure 2. In this example you can see that while much of the material in the sub-drill zone has been broken (and indeed loaded out) there is an area of what many operators would call “toe” on this floor. The reality however is that in the example shown, the “toe” is actually below the design floor level and if the operator was digging to grade, it would not have been hit.

Figure 2 – Digging to design floor level vs. below it. Image: Eltirus

What does it cost?

In most quarries, operators dig to level as best they can. This inevitably means that they either dig too deep (into the sub-drill zone) and experience “toe” or they leave anything from 0.5-1.5m of blasted material on the bench (which means you are paying your drill and blast contractor to shoot the same material twice). Where the sub-drill zone is dug out, the site generally compensates for the poor floor condition by bringing dust back into the quarry to level up the floor, resulting in a better running surface, but also in the drill and blast contractor being paid to blast the volume of the backfill on each bench.

I did some rough back of envelope calculations on a quarry moving one mtpa and a bench height of 12 metres. Just leaving half a metre of material above design floor level means that you would be paying your drill and blast contractor to shoot some fifteen thousand additional cubic meters of material a year – what does that cost your site?

What to do about it?
The key to resolving this issue is two-fold. First, you must have an appropriate quarry design and your drill and blast contractor must be drilling to the design RL’s and with sufficient depth of sub-drill.

Take the time to make sure that you have a good quarry design that is realistic, takes into account the site geological and geotechnical structures and has been created by a competent, qualified, Chartered Professional mining engineer.

Note that in Queensland, any engineering work must be conducted (or closely supervised) by a Registered Professional Engineer of Queensland (RPEQ) and that this also goes for work that a Queensland based company does for a quarry in another state.

A draftsperson with a CAD licence might seem like a cost-effective way to create your pit design, but it should be realised that that person (in Queensland and increasingly other states) is committing an offence and is liable for prosecution. If there is any doubt about whether the person you have engaged to work for you (if Queensland based) is appropriately qualified, take the time to check the RPEQ directory online. In other states, at the very least, you should expect the person to be a Chartered Professional mining engineer.

Likewise, select a drill and blast contractor who can take the pit designs and create blast designs in accordance with them. It is of no use whatsoever having a good pit design if the drill and blast contractor cannot accurately blast to it. The days of just throwing a tape over the face or shooting to the level of the floor in front of the face are past.

A reputable, competent drill and blast contractor can shoot to design, will run GPS equipped rigs and give you the confidence that they won’t inadvertently blow out berms and ramps in the process. This may appear to cost more in the short term but will save you a lot of heartache in the long run.

Secondly, you must have a way of indicating to the operator whether they are digging to grade or not. There are several ways that this can be achieved, from the simple (using a laser level) to the more complicated (and expensive) which is to use 3D machine guidance systems.

Example of 3D machine guidance system on a face loader. Image: Eltirus

While 3D machine guidance is extremely common in the civil construction and mining industries, it is much less common in the construction materials space. Part of this is due to expense ($50-100k), part due to unfamiliarity on behalf of quarry operators and also as a result of a lack of understanding by the suppliers of what it takes to implement such a system in our industry.

Having been involved with the implementation of 3D machine guidance on face loaders, large excavators and dozers, I can tell you that it is worth the cost.

If you don’t think this is the case, do a quick exercise to determine what it costs to re-blast the material that is left on each bench blast to blast, but also more importantly, take the time to think through the impact (no pun intended) on your face loader operator who hits an unexpected piece of toe (through digging too deep) and damages their back.

Whether you go simple with a laser level, use a GPS rover for bench checks or go the whole hog and implement 3D machine guidance, there are solutions to this issue.

Figure 1: The purpose of sub-drill. Image: Eltirus

As a side note, we have seen some tremendous low-cost GPS rovers (approx. $4k) come on the market recently and trials have shown them to be an excellent fit in the quarry space. If 3D machine guidance is a bridge too far, take the time to explore the GPS rover route and regular supervisor checks of bench level.

You might be aware that to get high accuracy (± 2cm) you need not just a GPS receiver and a view of the sky, you also need a correction service, either by 4G/5G (NTRIP correction over the internet) or from a base station on site (via radio signal).

We generally favour NTRIP solutions and when combined with the free AUSCORS NTRIP service, part of the National Positioning Infrastructure Capability (NPIC) network, these can supplement or replace commercial services costing thousands of dollars a year. In essence, if you have mobile data coverage, you can have a free correction service and achieve high GPS accuracy.

If you would like to know more about this subject or have any questions, please feel free to reach out to me and I will be only too glad to give you a briefing on the concept and pass on some of our learnings to you.

As an aside, if Microsoft Copilot is to be believed, American journalist, Doug Larson is responsible for the quote “smooth roads make more loads’ and apparently was not originally intended for the extractive industries.

This article was originally published in Quarry Magazine – click here to view original article.

To find out more, contact Steve Franklin on +61 474 183 939 or steve.franklin@eltirus.com