Paper on the issues surrounding selection of a haul truck tray or body. Covers Technical and organisational matters.

1. 177- Selecting Haul Truck Bodies
Increasing Mine Productivity
with an Appropriate Mine Truck Body
By: Richard Lang
Date: October 2010
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2. Increasing Mine Productivity with an Appropriate Mine Truck Body
Introduction
Achieving Mine Productivity requires input from all levels of management, Innovative
thought, a detailed understanding of the mine application, working with the supplier to
get the right result including providing correct information, correct application of what is
quite simple maths and an understanding of the pitfalls of using SAE volumes.
A truck body needs to suit the purpose rather than be a general purpose device. It
needs to be selected to match the particular environment of the mine. The first part of
that selection is matching the technical environment and the second part is making sure
that the supplier and the mine have a common understanding.
But first, look at who in the organisation should understand this process and the concept
of the calculation. This paper is intended for a wide range of personnel.
The main points covered are:
• The importance for all levels of management to have an understanding
• The huge financial payoffs possible
• Traps for the unwary in angles of repose and loose bulk density as they effect
achievable tray payload.
Organisation
Take a typical organisation structure as depicted below.
Managing Director
General Manager General Manager General Manager
Commercial Technical Operations or Mine
Manager
Specialist Supt Mobile Supt Mining
Mining Equip
Services Maintenance
Figure 1: Typical Organisation Structure
Initiative, analysis and recommendations on equipment like truck bodies tend to happen
at the Superintendant level. Is this a good idea? The short answer is yes but.........
These people have to be heavily involved as they live with the consequences of the
decision for years afterwards.
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3. However, I believe that people up the line need to understand the concepts in order for
the organisation to achieve Mine Productivity. Mine haulage is a substantial cost in the
scheme of things as shown in Table 1 below.
TYPICAL OPEN CUT MINING COSTS
Haulage 32%
Drill & Blast 25%
Loading 17%
Other 26%
Table 1: Mining Costs
Given the substance of the issue, the top levels of management should understand the
basics of haulage. Furthermore if you look at the responsibilities of the management
levels in Table 2 below, there is an argument that because haulage decisions impact
over many years, there is a need for senior management to take an interest.
Level Time Horizon & Thinking Patterns
V - Managing Director 5-10 Yrs & Conceptual Thinking – Creative,
positioning the business as it sits in the industry.
IV - General Manager 2-5 Yrs Reviewing recurring Issues, undertaking
investigations and generally directing traffic.
III - Superintendant 1-2 Yrs Action Focused on issues in front of them
Table 2: Management Levels and their Focus
The Company’s Board of Directors has delegated responsibilities for taking care of the
shareholders money to the Managing Director and in turn the General Manager. So it is
incumbent upon them to consider innovation especially when there are significant
shareholder benefits to the decision.
The level IV and V people in large organisations don’t need to be involved in the detail
but they should understand enough to raise issues and make critical assessments on
analysis presented. They also have a critical role in communicating the organisations
appetite for risk and in which areas the company needs to move ahead to be in the
lower quartile of the cost to revenue ratio curve for the industry. The average
Superintendant left to their own devices will deal competently with the issues that
present themselves for action in the 1-2 year time frame. The leadership task for the
level IV and V people is to encourage the Level III people out of their comfort zone. In
order to perceive the opportunities in mine haulage as well as to promote some critical
thinking, the level IV and V people need to understand the basics of haulage analysis.
Going straight to an example; a mine had been running for many years with the
following empty truck weights which are driven by the tray weight.
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4. Reduction in
Tray Weight
Truck Empty Truck Possible -
Number Weight Tonnes Tonnes
400 171 21
401 180 30
403 172 22
404 181 31
405 180 30
406 179 29
407 180 30
408 181 31
409 182 32
411 172 22
412 177 27
413 177 27
414 150 0
415 178 28
417 177 27
418 179 29
419 180 30
420 174 24
421 176 26
422 180 30
423 178 28
424 172 22
425 175 25
426 172 22
427 179 29
428 173 23
429 178 28
430 177 27
431 178 28
432 175 25
433 180 30
472 150 0
Average 27
Table3: Potential Reduction in Tray weight = Payload increase
Can you imagine the financial implications if you carried 27 tonnes more or even just
half of that every load on every truck.
Truck Operating Hours per annum 5,500
Cycle time 40 mins
Loads per annum per truck 8,250
Extra Tonnes carried per load 27 or say 20 to be conservative
Extra Tonnes per annum per truck 165,000 - This is about 9% increase
but potential is around 13%
Number of trucks 30
Extra Tonnes per annum for the mine 4,950,000 OR park 3 trucks
Imagine the extra revenue associated with that!!
or Imagine the cost and capital savings of parking up between 2 and 4 haul trucks!!
Table 4: Calculation of Savings
So who in the organisation is going to come up with the creative thought to look at
replacing the 30 odd trays with one that weighed less and lasted without increased
maintenance?
For years the people at the lower levels kept maintaining what was in front of them until
a creative Superintendant / Manager came along and asked the question and started
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5. the assessment process. Soon the profits will be flowing to the shareholders as a
result. So the point is that while the maths is very simple, it takes someone with a
capacity for level IV or V thought processes to make it happen. That person may be
someone on the rise through the ranks from Superintendant level or a level IV – V
incumbent. So to achieve Mine Productivity everyone in the organisation needs to be
paying attention to haulage at an appropriate level of detail commensurate with their
position and the capacity of the people around them.
Technical Assessment
The designer has to make the body suitable for the impact loading, the abrasive
environment and the nature of the material being loaded. Very large loading tools filling
the body in a small number of passes will impart more “damage” than a smaller tool.
Dropping the load from further away will also increase the “damage”.1
So in environments where the loading will be rugged, we suggest a 25mm floor for the
DT truck body. We have not seen damage in the loading impact area with this policy.
For less arduous environments we suggest a 19mm floor. The trade off is weight and
longevity.
With material having a Bond Abrasiveness Index of 0.34 (eg hard rock – gold mine) ,
we expect that over the rear 2-3M of the floor, all but the last 100mm of the body will
wear at 0.85mm/1,000 Hrs. The treatment here is to let the body wear and then add
wear tiles in the worn areas to bring the body back to the original weight.
In less abrasive environments, the wear process will take longer but the tile solution is
the same. In coal, the body may only ever get three rows of tiles at the rear over its life.
In aggressive environments where the material is sharp and harder than the material
with Bond Abrasive Index 0.34; then specific tile packages can be provided.
DT HiLoad offers canopy protection plates and rear support rails for tough
environments. In addition, the body comes with 19mm or 25mm thick floors. The tray
manufacturer can’t do much about haul road condition, even though it does impact on
body life. As the truck twists and slides over rough and slippery haul roads enormous
forces are applied to the body and the chassis of the truck. Where all other factors are
pointing in the direction of specifying a 19mm floor, poor haul roads may cause the mine
to choose a 25mm floor to help cope with the higher stressed environment. Abrasive
material will also push the body selection towards a 25mm floor model.
For optimum Mine Productivity, the body needs to be rugged enough. Options selection
is important for matching the application.
1
Damage is a term used in fatigue analysis whereby the number of stress cycles undergone by the material
expressed as a fraction of the total number to cause failure allows “rainflow diagrams” to be drawn which relate
the stress level and the frequency to the damage created during the loading. This allows the designer to see
whether a large number of low stresses or a few large impacts are source of the “damage” which is consuming the
body life.
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6. The sizing of the body is mathematically simple.
Gross Vehicle Mass set by 384,000Kg
the manufacturer:
Less: Chassis Weight 118,000Kg
Less: Weight of the body 30,000Kg
Equals: Payload Allowable 236,000Kg
Loose Bulk Density of 1.6
material:
Volume of body required for 147M3
material
Fill Factor 0.9
Volume of body required 163M3
Body size to order 170M3
Table 5: Body Volume calculation
Two questions arise from this calculation, firstly the loose bulk density number and the
volume. What volume and what density?
Loose Bulk Density
If the mine supplies the supplier with a loose bulk density number from the feasibility
study done for the original mine development analysis – that can be risky because
today’s reality may be different. An error of 10% in the bulk density will result in a
matching error in the target truck body size.
The build up from Bank Density (the density in the unfired material) to the density in the
truck is shown in Table 6 below.
Bank Density 2.2 T/M3
Swell Factor 1.30 (say)
Bulk Density as fired 1.69
Swell Factor 1.05
Loose Bulk Density in the truck 1.61
Table 6: Example of relationship of Bulk Densities
Accurate numbers can be obtained using a scanner in conjunction with a set of truck
scales. The trucks are scanned and weighed empty and again when full. The increase
in weight and the volume difference yields the material density. If the mine is
processing different materials, the density needs to be calculated for each material eg
overburden and ore. Reconciliations between surveyed volumes and weightometer
readings at the plant will calculate bank Density. Knowing the number of truckloads will
allow calculation of Bank M3 per truck load but don’t be confused as using that density
will result in the wrong sized tray. Note also that there will be a small density difference
between material in a shovel dipper and the truck or as shot. Furthermore, you need to
measure the moisture content at the time of calculation as if done in summer at 2%
moisture, there will be a difference in payload in winter at say 6% moisture. The
moisture will not usually increase the volume measurably but it will add to the weight.
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7. Figure2: Scanning and weighing of empty and Full Trucks by Transcale of Queensland
Australia Ph +61732170311
Unless the mine wants dedicated haulage fleets for each material, then the body should
be sized to the lightest material. This yields the biggest body so there needs to be
loading control when the most dense material is carried. If the amount of light material
is relatively small, it may be decided that the optimum solution is for a smaller body.
This illustrates how managing Mine Productivity involves some tradeoffs and the
importance of getting the loose Bulk Density right. Readers should be aware that
mistakes have been observed in practice associated with the above points – otherwise
how does a mine get a body that is too small for the task?
Body Volume
The 147M3 body volume calculated in Table 5 above, is not enough as we can’t have
the load spilling over the sides, leaving rocks at the loading area. Also when the truck
climbs a 10% grade on the haulroad, there needs to be some free space at the tail so
that rocks don’t roll off onto the haulroad. The 90% fill factor allows for this and
variations in density in order to target the allowable payload of the truck. Depending on
the expected variations in loading and material density it is quite important to think
about what size of body to order. The loading tool operator needs to be able to get the
+10% and the +20% loads in the tray in order that the truck will average the design
payload. The OEM loading rule is generally that 10% of the loads can be 10% over the
target payload while no load should be more than 20% over and the average of all loads
should be the Allowable payload or less.
At one mine site, we looked at 22,000 truck loads from 11 loading tools and the
Standard Deviation of each load overall was 9.8%. That means that it is impossible to
achieve the average without a policy of tipping off the +20% loads. Overloads would
be 2.5% of the total according to the theory of normal distributions where the band
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8. within two standard deviations (ie +2*9.8 = 20%) is covering all but 2.5% at the end of
the distribution. In fact, this set of data had 89 loads =0.4% of loads over the +20%
target. This indicates that the loading tool operator was taking some care not to
overload, making the distribution not a classical normal distribution. To manage the
situation, the policy of tipping off the +20% load needs to be adhered to or the loading
tool operator is given a lower target payload so that the natural variation in loads does
not drift over the +20% target.
The data also illustrates that if the body is merely sized to the target payload, then how
will your average achieve that target? When the truck has the +10% load on board,
assuming that it is sized to 90% fill factor, the material will be spilling over the edges.
Fragmentation can help reduce the variation and increase fill factor in the dipper. In
statistical terms, this means that if you reduce the standard deviation of the dipper
passes, the standard deviation of the truck payloads will tighten up and that means the
chance of overload is less. Improved fragmentation can sometimes be achieved by
more careful placing of the explosives and managing the timing rather than using more
explosives.
The next thing effecting body volume is the angle of repose. Different materials will
stack at different angles depending on the way the particles interlock and rill. Moisture
content can affect this angle as well.
When calculating the volume of a body you need to assume this angle. So there is a
point of difference possible from different suppliers.
There is a standard which is widely used in the industry called SAE J1363.
That calculates haul Truck Tray Volume by the following means:
It takes the “Struck volume” which is conceptually a water holding capacity and then
you add a volume of a pyramid shape with sides sloping at 2:1 (if that is the standard
complied with).
So it looks like Figure 3 below.
Figure 3 : SAE 2:1 Volume representation
We all know that material doesn’t stack like that. You might think that it doesn’t matter
because all trays being considered having the same “error”. But that is not true. Trays
with different shapes will have different actual carrying volume ratios to their SAE 2:1
heaped volume. Then to add confusion there is a thing called SAE Field Heap.
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9. Furthermore, not everyone is “tight” in their use of the standard. One contractor we deal
with filled truck bodies to overflowing and measured the volume showing that the actual
was 15% less than SAE. We had one mine site that was confused by suppliers claiming
tray volumes which made no relative sense to each other. The reason was that one
supplier had used an inappropriate angle of repose.
Figures 4 and 5 below show the extent of the volume difference. The angles in Figure 4
are actual from a field example! The 38degrees was the angle that a competitor tray
volume was calculated at. The 26 degree line represents 2:1 stacking angle .
Figure 4: Representation of Volume Difference with variation of Angle of Repose
Repose angle vs. Load cone volume
(m3)
210 210.2
Body Capacity (m3)
200
194.4
190
180 180.2
170 170.9
25 30 35 40
Repose angle (deg)
Figure 5: Impact on Stated Volume of Change in Angle of Repose
What you really want to know is how much will the tray hold. We all have computers at
our disposal now so we don’t need techniques rooted in the days when we added up
squares on graph paper to calculate the volume of things.
Figure 6: A representation of how Material Stacks – DT Volume
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10. Given the volume, if you assume 90% fill factor and multiply by the loose bulk density,
you will get the payload mass. We find that theory matches reality pretty well as
depicted in Figure 7 below.
Figure:7: 244Tonne in a body with a target payload of 240Tonnes
Just in case the argument is not convincing enough just yet. Below is a table that
shows the stacking angles or Angles of Repose of various materials. Note that the SAE
1:1 and 2:1 slopes used in the calculations can give answers a long way from reali reality.
The angle used should be the angle that the material sits at in the truck after being
agitated or shaken as that may be flatter than the angle it will freely sit at when carefully
piled on the ground.
Angle of
Repose θ
Distance
along Typical Range of Angle of Repose for Materials
horizontal
To 1 up
Degrees tan
20.0 0.36 2.7
22.5 0.41 2.4
25.0 0.47 2.1
SAE angle for
26.6 0.50 2.0 wet sand Top heap
soil & clay
27.5 0.52
2 1.9
30.0 0.58
8 1.7
32.5 0.64 1.6
soils
35.0 0.70
0 1.4
coal
37.5 0.77 1.3 Gravel
40.0 0.84
4 1.2 & small
Crushed SAE angle for bottom
42.5 0.92 1.1 material section (struck Vol)
45.0 1.00 1.0
47.5 1.09 0.9
50.0 1.19 0.8
Table 7: Angles of Repose
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11. So to achieve Mine Productivity care needs to be taken when interpreting the volume
of a tray. What you really want to know is how much material it will carry given the loose
bulk density and angle of repose settings. Now that we have computers, the industry
shouldn’t be using approximations like the SAE method.
Some Other Things
Under sized bodies can be selected by merely looking at the payload calculation as
depicted in the Table 5 ie 236,000Kg. Yes the truck will carry it but if the body can’t fit
the volume in, then you won’t be averaging that payload. It seems straight forward but
this error has been seen in the field.
As suppliers, we get concerned when confronted by assessment spreadsheets built by
customers like the one below in Table 8
The concerns of this, from a supplier viewpoint are:
• What is the customer interpreting from the SAE volume? Do they think that the
truck will be carrying this amount? You can bet the level IV and V managers who
don’t have a detailed background in this area, think it will be.
• The payload is calculated without options and wear pack. So how is that number
relevant in comparing suppliers? The analyst says they will take it into account
later – but will they recalculate the payloads? The weight of the wear pack and
accessories are part of the Empty Vehicle weight and are significant.
Unit of Detail for Company
measure XYZ
Supplied Information
Gross Vehicle Weight tonnes 384.0
Chassis Weight tonnes 138.1
Unit of Tray
Tray Volume measure
Supplier XYZ Co
Make & Model of Tray text *****-150-19
3
Volume of Payload SAE m 160.0
Payload tonnes 221.0
Tray Weight (before options/wear
pack) tonnes 24.5
Check - Payload Must = 0 0
Table 8: Worrying Assessment by a Customer
The point is that to get good decisions and achieve Mine Productivity, attention to detail
is vital and not always easy when information comes from numerous sources.
Secondly, this is not a process which is undertaken every year so people forget.
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12. Economic Evaluation
In some organisations this is where the investment decision that has the potential to
increase Mine Productivity can go astray. It is the part of the process where commercial
people are dealt into the team. If they do not understand the issues, the spreadsheets
will not bring out the salient points. Focus on capital cost; unless the company is
artificially constrained, is rarely going to maximise the shareholders position. One mine
we know has been analysing the issue for over eighteen months. If they had bought the
trays, six months after they started the analysis, they would be paid for by now through
cost savings. So how your company goes about managing change and analysing
projects also impacts the potential for improving Mine Productivity.
Floor thickness
If a body with lots of buttressing or bolsters is the same weight as a body without them,
you need to ask how that can be so.
Figure 8: Butressing consumes weight that has to be saved elsewhere
Usually it will be found that the floor thicknesses are quite different in bodies like those
illustrated in Figure 8. With a thinner floor, there is less wear allowance. That can only
mean less life or more maintenance cost unless the body is carrying benign material
which never wears the body.
Implimentation
Change is a process which needs to be managed and if you are looking to buy
something other than the stock standard repeat of what you have been using, there will
be people to be managed as depicted in Figure 8 below.
Figure 8: The Change Bus Source: Strategic Partnering by Tony Lendrum
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13. Percentage of people in a Typical Organisation
Terrorists Followers Early Adaptors Innovators
16% 68% 13% 3%
Table 9: Seating Arrangements on the Change Bus
So spare a thought for the innovative person who is trying to manage this change. If it
is the level V manager, it is easier as their position has a significant degree of power but
if it is an innovative Superintendant, it is much harder and they need help from top level.
That help just needs to be taking an interest in the project to nudge the innovation and
the naval gazing along, so that the terrorists in the organisation don’t derail the
improvements that will increase Shareholder returns.
To do this, the level IV and V managers need to understand the basics contained in this
paper. One of our customers achieved this change process from the Superintendant
level by building a multi disciplinary team who worked on the project. This produced a
strong coalition of knowledgeable people to drive the project forward. The amount of
such firepower required depends on where the organisation sits on the scale of
moribund to agile and innovative.
Conclusion
The selection of haul truck bodies to achieve Mine Productivity with an Appropriate Mine
Truck Body requires:
• Attention from all levels of the management,
• Innovative thought,
• A detailed understanding of the mine application,
• Working with the supplier to get the right result. This includes providing correct
information,
• Correct application of what is quite simple maths
• An understanding of the organisations inner workings and who the innovative
free thinkers are,
• An understanding of the pitfalls of using SAE volumes and
• An ability to conduct economic analysis and technical evaluation to ensure that
the best value for shareholders is purchased rather than just the cheapest.
i
i
Richard Lang is Chief Executive Officer of DT HiLoad Australia Pty Ltd. The company manufactures haul
truck bodies in Australia and there is an operation in South America. They have sold some 1000 bodies
in the world with over 150 in Australia. He is a graduate of the University of Queensland Engineering
School and holds a Master of Administration from Monash University. Richard is also a Graduate
Member of The Australian Institute of Company Directors. He has managed a Shipping business for
Patricks and was Managing Director of a manufacturing and maintenance business servicing the mining
industry. Prior to that, he was Sales & Marketing Manager for Argyle Diamonds.
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