Top Initiation: A Different Approach to Blasting

Most blasting theory courses teach that bottom initiating blast holes is the best and sometimes only way to detonate blast holes.  This is true in cases with open free faces when we don’t mind a bit of throw.  But what about all of the other times?  What about in a typical non-ideal mining environment where there is no free face, there is mud in the holes, and there are vibration/fume issues?
 

Top initiating (aka delaying the bottom primer rather the top primer) can be a generic risk mitigation tool when blasting conditions are less than ideal.  Picture a typical single 20m hole with 4m of stemming and a booster at the top and bottom of the hole.  Consider the following,

Where is the least contaminated explosives product in the hole?  Top or Bottom?

Which booster is more likely to fire?  Top or Bottom?
With no free face, where is the best relief point for the hole?
Which initiation location will cause the least vibration?

TOP!  If there is mud, water, or left over drill cuttings in the bottom of the hole, it is likely that the bottom meter or two or explosives is contaminated in some way.  It is also difficult to ensure that the booster is placed in an ideal location at the bottom of the hole.  Detonating into bad product can slow run up times for the explosive.  This can waste energy and cause fume.  At the top of the hole, there is little to no contamination and it is very easy to place a booster exactly where you want in the top of the hole.  A clean top initiation means ideal run up time for the explosives column.  This also means that any contaminated product at the bottom of the hole has a higher chance of detonating properly since the detonation front is at full speed when it hits muddy or wet product.

The Bottom booster also has more weight on it which increases the risk, although still low, for line failure.

The top of the hole is the best free face for confined blasts.  Top priming takes advantage of this free face in the same way as firing face holes first in a throw blast.  Top initiating encourages material to move upward and can lead to better heave. 

Better heave, and more relief leads to less vibration.

Top initiating can also help with cap rock.  Blast energy always moves towards the initiation point.  If the hard rock is at the top, shouldn’t we encourage the energy to go to the top?  With that said, top initiating will do very little for a hard toe so please use wisely.

As was once told to me… Top Initiating:  “If you can find an excuse to use it, use it”

(4) Inventory Management – This is what it’s all about!

Now to the crux of the matter, scheduling is primarily an inventory management process. While every mine is different and they all have their idiosyncrasies or complexities, the reality is the scheduling methodology doesn’t necessarily have to be any different. In fact who says it needs to be any different to a factory production line or any other scheduling process? Scheduling is about what resources you have, what are their production rates and what are your schedule targets – regardless of the activity being carried out. Resources and production rates are topics for another blog, this blog will discuss schedule targets.

So what should you target (focus on) in your scheduling so as to be most effective? I believe the key targets for an activity, should be around providing adequate inventories for the following activity. Don’t get me wrong, still schedule the equipment, such as drills, excavators and draglines, processing plants, etc. You need to do this to ensure that production targets are being met, the right quality ore is going to be mined, etc. And in fact you need to schedule equipment, as it generates the inventory for the following activity and also depletes inventory from the preceding activity.

What I am saying, is consider what the outputs of the schedule are and what you actually focus on when carrying out the schedule, i.e. the schedule target. So while you are scheduling the drill, keep an eye on the drilled inventory and schedule the drill accordingly, so as to maintain inventories within the target bands. Going back to Blog (1), schedule the drill with an eye primarily on what quantity and quality of broken stocks will result. But you still need to schedule the excavation equipment, as it will deplete the broken stocks and so this is required to calculate resulting inventories. Carry out a similar process with all scheduled mining activities on site.

Now of course if you’re scheduling to target inventory bands, then a key question becomes what should those bands be? Stay tuned for Blog (5).

So does anyone agree? Does anyone disagree? Would love to hear some feedback.

Where are the camp sites? - Life in the Hunter Valley as a FIFO Mining Engineer from Brisbane

The first thing that I asked when I started working in the Hunter Valley was ‘Where are the camp sites?’ Previously I have only worked in Central Queensland mines and lived in dongas that felt like a fridge at night. When I started working in the Hunter Valley and was living in a warm serviced apartment, it felt like I had stepped up in the world.

Every Monday morning I would get up before the sun and catch the first flight to Newcastle, Williamtown Airport. With the domestic flights sharing the runway with the RAAF jets, you would occasionally see them take off and hear them roar away into the clouds. We’d then jump in our hire car and drive a couple hours out to site. We’d stop halfway in Maitland to grab the Monday lunch orders from Blakeney’s Pie. These pies are the bee’s knees and after loading up about 15 of them we’d continue on our way. Several others in the Tech Services team would eagerly await the arrivals of their pies.

After finishing up at work we’d travel back to Singleton and check into our apartment, then go to the local Woolies and stock up for the week. We made some good friends down there, so most days after work we’d have something on. Tuesdays was trivia night at the local RSL where we rivalled against a team of senior citizens every week. What we lacked in age and experience we made up for in numbers. On occasion the 10 of us were better than 4 of them and we’d take home the 1st prize of $50, which we would use on beers for the following week. Wednesday was indoor soccer night, where we’d play a social game of 5v5. This was my exercise for the week. Then on every second Thursday or so, we’d go out to one of the famous Hunter Valley vineyards for dinner. This is a must if you’re going to spend time in the region. Flying back on Friday during daylight savings time, meant taking off and landing at the same time. This also meant no time was lost for weekend beers. Having spent some time working in Central Queensland and the Hunter Valley, there was a clear winner if I had to choose between the two. Work is work, but it’s what you do outside of work that makes you happy to live where you live.

Dig Plan Standards… or lack thereof

I know each site is different, and there’s no one right way to create a dig plan; but should there be? All designs have a toe, a crest, access, volumes and they follow geotechnical approved bench and batter profiles. This ensures that each design is accurate, useful and can be implemented by others. Where are the standards when it comes to conveying these designs to operators? I‘ve seen dig plans that consist of a photo with a square drawn on it, all the way through to an 18-page pass by pass 3d-dig presentation. Which is more useful? Which helped the operator understand? 

Dig plans can vary on technical content and method of delivery depending on who the audience is. In a Tech Services weekly planning meeting a few Vulcan or Minescape screen shots will be understood by most, but give this to a digger driver and he’ll think it’s the matrix. The purpose of a dig plan is to help the operators, therefore why does every site have a similar hole in the ground, a similar workforce but completely different dig plans??

In my opinion there are some must-haves; dig limits, cross section, long section, waste volumes, coal volumes, access point, the number of passes required for the scheduled machine (including pass heights) and an associated dump plan. Each dig plan can then be tailored for each dig; pointing out unusual aspects or steps that the particular dig may have, highlighting critical tasks.

It doesn’t stop there…. A good dig plan is useless if it’s not being followed. Communication is king! Make sure you talk to the supervisors or operators often, get survey control pegs placed before the dig starts and check the progress frequently. It’s also a good idea to make sure digger operators have a copy of the plan in the machine at all times, they are the ones who will actually dig the dig plan! 

If some sort of dig plan standards were accepted by the industry then new engineers would be taught how to create a useful tool and less people would waste their time creating documents that get thrown onto the dash of the dozer cab and never glanced at once. 

What do you think makes a good dig plan? How does your site convey the plan to operators?

Electronic Detonators: Should they come with training wheels?

My opinion of electronic detonators has changed greatly over the last few years. As a relatively young engineer, I love anything that is digital and new. Why would anyone fax something when they can email. Why use non-electric systems when there are electronics? And det cord? What is that? Electronic dets can be a highly specialized tool and can be used to improve many aspects of a drill and blast program. However, just as email allows us to accidentally and sometimes catastrophically “reply all”, electronics can make it very easy to deliver unwanted results in blast. The high reward that is promised with electronics comes with high risk.

Please consider the following worst case scenario:

A site fully switches to electronic timing and therefore sells back all non-electric systems. A full conversion offers a lower price per det and can be more attractive. Training and mentoring is then supplied to the drill and blast team on site. Once things begin to run smoothly, mentoring is no longer needed and the site runs sufficiently. Before long, it is time to rotate engineers and therefore time to bring in a new, and typically inexperienced, drill and blast engineer. A short handover is given and the new engineer is free to use any of the infinite timings available with the system. About 99% of these timing options should never be used. The new engineer will now get creative and apply a timing that sends all of the energy in the wrong direction, is too fast, too slow, or just plain wrong. The senior engineer reviews the timing but doesn’t fully understand the system and approves. A non-ideal timing is now issued to the shot firers who are now used to the system and comfortable with the engineering support. There is no indication of a problem in the field since the shot firer only sees copper wire and a list of holes and their delay times. It can be difficult to get an idea of how the timing behaves without an animation or timing contour map. The shot firer does not receive either. When it is time to fire, the shot firer goes through all of the necessary safety checks with the system and is cleared to fire. Upon firing vibration is exceeded, fragmentation is poor, there is back break into the highwall, and flyrock is thrown out of the exclusion zone. Worst case indeed. This case assumes all holes are labeled adequately and receive the correct det sequencing which can be another issue.

The case above is one that happens too often with electronics. The cost of such incidents can easily offset any savings that the system may bring once (or should I say if) it is optimized. With that said, very few sites have been able to effectively measure the cost savings after switching. I am not saying they don’t exist, I am simply saying they are hard to measure and compare with confidence.

With all of that said, electronics can be quite brilliant for the experienced user. The question is how do we create an experienced user in a safe an controlled manner i.e. without incident. Is there a way to offer electronics with limited timing options? Is it worth keeping non-electric dets for training purposes and shallow, less complex shots? Can site specific electronic timing intervals be offered in a way similar to non-electrics? Should the design software have locked features for beginners?

(3) What do you have most schedule control over?

For me this is one of the thought provoking concepts to come from this event. Although in theory Short Term Planning Department was responsible for planning from 0-3 months, in reality the Grade Controllers (even though they sat in Mine Production department) were really the VERY short term planners. They were in control of mining equipment on each shift as they were tasked with producing spec quality stockpiles. I would note that this is really is all that everyone is at the mine site for – to produce the required quantity of saleable product!

So the Grade Controller dictated where all mining equipment worked and the Shift Supervisor was charged with maximising equipment productivity, given the equipment working locations. Consequently, as Mine Planning Department, why even try and schedule where the shovels would dig on a short term basis?? The fact is that you are never going to dictate that, as the Grade Controller always will, as they carry responsibility for hitting the mine quality and quantity targets.

Ah, but there is a way you as the mine planner can lead the Grade Controllers where you want them to go (i.e. follow your 3 month plan) and therefore indirectly have the shovels working where you want them to. That is by focussing on the scheduling of the mining activity that is prior to excavation in the mining sequence, which is normally drilling and blasting the material. So if you focus on the scheduling of drill and blast, incorporating the management of broken stocks as per the discussion in Blog (2), the shovels are sure to follow. They have to as they have no choice, if it is not broken they can’t dig it!!

Short Term Planning Department continually fed back to us about how we (Grade Control) were digging the wrong pits and weren’t conforming with the Annual Plan pit quantities, but we had to as it was constantly a struggle to achieve target quality stockpiles (noting that we had 8 quality targets). We had little flexibility and so would dig wherever we had to, in reality following the Annual Plan was very low in priority compared to the heat that came from Marketing as a result of sending out off spec boats. But if Short Term Planning Department concentrated on drilling in the right place, then they could follow the Annual Plan pit quantities, as long as it maintained target broken stocks. If you can’t follow Annual Plan and manage broken stocks to within target, then either this reflects on the fact that Annual Planning is a high level and granular schedule which is typically a monthly time period and so may hide weekly variability (and there is another learning in itself), or that it was a bad Annual Plan in the first place!

And the most ironic issue from all of this? The reality is the drills are probably one of the easiest pieces of equipment for Mine Planning/Tech Services Departments to actually have some control over. The D&B Superintendent or Supervisor generally don’t care too much where they are drilling, as long as they are productive because you’re not constantly moving drills or firing very small shots. So set a workable plan for the drills and blasting crews and there is a high probability it will be followed. Shovel Superintendents and Supervisors on the other hand are often much more particular about where they will dig and I would suggest at many mine sites, much more difficult for Planning Department to have some control over.

So, at your mine site, what equipment on site are you most likely to have some control over as a planner? And if you want to indirectly control an activity, think about focussing on the activity prior to this in the mining sequence. Good luck!!

(2) Broken Stocks Management

Follows on from (1) The Broken Stocks Saga.

The first learning for me related to the broken stocks. The importance of these in achieving target qualities for each stockpile construction can not be understated. If you provide the grade controllers with a set of broken stocks that are close to quality specs, you make it relatively easy for them to hit their target. On the other hand, provide them with a set which has one or more qualities a long way off spec and you make it extremely difficult. Similarly, provide a large quantity of broken stocks and you provide more choice, provide a small quantity and even though they might be at average spec, the lack of choice (and therefore scheduling flexibility) may make it difficult to achieve target.

So whereas the short term planning group were planning the shovel excavation for the next month, I believe a much better solution would be for them to manage the broken stocks instead. The precursor to planning is to determine the quantity and quality target bands that will provide sufficient capability to meet necessary targets. The planning process then involves determining what the starting broken stocks (quantity and quality) are and then assessing which blocks need to be added to this, to either maintain it within target bands, or restore it to within target bands.

In this way, scheduling is effectively an inventory management process, which is both a key part of mine scheduling and also one that is underutilised. Inventory management will be discussed in further detail in a later blog to come.

Kick-starting my Career

When starting my career as a mining engineer, there were many things I wanted to gain in the first few years; experience, experience and experience! The on-site consulting world has offered me this in spades! Throughout university we were often told of the benefits and diversity of skills we would gain while undergoing a graduate program with a well-established mining company, so when I was faced with the decision of continuing my job as a Graduate Consultant or applying for the much sort after graduate rotation positions I felt as though they had it all. I loved my job and the culture of the company I worked for, Echelon, so I threw caution to the wind and didn’t apply for any of the roles I had been prepping for over the previous four years. It turned out to be one of the best decisions I’ve ever made! Especially when they took us to Aria for Christmas lunch!

Over the last two years with Echelon (who became Xstract) I have had the opportunity to work on many different mine sites, learning best practices across the industry and seeing how different people and teams tackle the same issues every mine faces. It’s been great to be able to apply my skills to different situations, introduce new ideas to a technical services team and also rack up my frequent flyer points. Across these different sites and the Brisbane office I have worked in various roles; short term design, medium term design, life of mine scheduling, and pre-feasibility and feasibility studies. To have had exposure to all aspects of the mining cycle has been great, work is never boring and I’m constantly learning new things and looking at mining projects from different perspectives. It has also been a good way to learn where my passions lie and decide what career path I want to take in the future.

From day one I was given real responsibilities and accountabilities and I quickly learnt superior time management skills, making sure that I am always producing quality work in a timely manner for clients. Working with a close-knit team of consultants means my colleagues are always eager to help me learn new skills and various software packages, sharing their combined experiences with me on a daily basis. The faster I mastered a new skill, the sooner I could contribute to client jobs or take ownership of onsite roles.

One of the best parts of my job is the unmatched opportunity I have to network. Building up relationships with accomplished engineers across the coal industry and making friends in new places, predominately small mining towns, will no doubt benefit me time and time again.

I have found a job where I am part of a family, I am expected to “hit the ground running” and own each job I am tasked with, and I love it!


Caitlin McCarthy

(1) The Broken Stocks Saga

Many years ago in an iron ore mine I was the Grade Control Superintendent, leading a team charged with producing weekly stockpiles of lump and fines ore. This position was located in Mine Production Dept rather than Mine Planning Dept. Between the two ore stockpiles, there were a total of 8 target qualities with very tight target bands - so quality was "king".

Mine Planning Department were responsible for short term schedules of all mining equipment over a 3 month time frame, the primary schedule driver being that of the excavators mining "specification product" on a weekly basis.

Now broken stocks (material already blasted) are extremely critical in weekly ore stockpile construction, as they’re pretty much all there is available to mine from within that time frame. We came into a situation where we had very high phosphorus in our broken stocks, which made it near impossible to build stockpiles to our quality targets.

Our problem was that Mine Planning Dept produced plans that effectively continued to add target quality material at one end, while we attempted to take target quality material off the other end. Consequently the high phos broken stocks weren't being remedied. So for a sustained period of nearly 2 months, the broken stocks continued at high phos levels and during this entire period we really struggled to produce "on spec" weekly stockpiles. And yes this was very much a saga for me with the heat we drew from sending out "off spec" product!!

This situation was a catalyst for many learnings for me personally and these will be discussed in my following posts.