177 Selecting Haul Truck Bodies

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177- Selecting Haul Truck Bodies

Increasing Mine Productivity

with an Appropriate Mine Truck Body

By: Richard Lang

Date: October 2010

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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.

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.

Managing Director

General Manager

Commercial

General Manager

Technical

General Manager

Operations or Mine

Manager

Supt Mobile

Equip

Maintenance

Supt Mining Specialist

Mining

Services

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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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Truck Number

Empty Truck Weight Tonnes

Reduction in Tray Weight Possible -

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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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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The sizing of the body is mathematically simple.

Gross Vehicle Mass set by the manufacturer:

384,000Kg

Less: Chassis Weight 118,000Kg Less: Weight of the body 30,000Kg Equals: Payload Allowable 236,000Kg Loose Bulk Density of material:

1.6

Volume of body required for material

147M3

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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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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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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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

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

170.9

180.2

194.4

210.2

170

180

190

200

210

25 30 35 40Bo

dy

Ca

pa

city

(m

3)

Repose angle (deg)

Repose angle vs. Load cone volume

(m3)

Given the volume, if you assume 90% fill factor you will get the payload mass. We 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

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

Degrees tan

20.0 0.36

22.5 0.41

25.0 0.47

26.6 0.50

27.5 0.52

30.0 0.58

32.5 0.64

35.0 0.70

37.5 0.77

40.0 0.84

42.5 0.92

45.0 1.00

47.5 1.09

50.0 1.19

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 welldepicted in Figure 7 below.

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

slopes used in the calculations can give answers a long way from reali

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

θ

Distance

along

horizontal

To 1 up

Typical Range of Angle of Repose for Materials

0.36 2.7

0.41 2.4

0.47 2.1

soils

wet

soil

0.50 2.0

2 1.9

8 1.7

Gravel

& small

Crushed

material

0.64 1.6

0 1.4 coal

0.77 1.3

4 1.2

0.92 1.1

1.00 1.0

1.09 0.9

1.19 0.8

Table 7: Angles of Repose

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and multiply by the loose bulk density, find that theory matches reality pretty well as

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

slopes used in the calculations can give answers a long way from 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

Typical Range of Angle of Repose for Materials

sand

& clay

SAE angle for

Top heap

small

Crushed

material

SAE angle for bottom

section (struck Vol)

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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

measure

Detail for Company XYZ

Supplied Information

Gross Vehicle Weight tonnes 384.0

Chassis Weight tonnes 138.1

Tray Volume

Unit of

measure

Tray

Supplier XYZ Co

Make & Model of Tray text *****-150-19

Volume of Payload SAE m3 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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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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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.