TSV Mining’s presentation on factors that affect an overburden fleet’s rate. Reviewing the processes that make up the system and how process improvement benefits are usually overestimated. Demonstrating that when we do not have detailed analysis, and have a lack of exposure to how a system actually works in reality, the more we rely on our statistical intuition which is usually wrong.

1. Presented by:
Christopher Braund
Director
TSV Mining Pty Ltd
M: +61 438 886 473
cbraund@tsvmining.com.au
www.tsvmining.com.au
Total System Value

2. Typical project states 10%
overburden fleet improvement
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A project to improve the dig rate of an excavator by 10% has
been initiated and is justified based on a 10% increase in
production for the fleet

Is the assumption of a 10% improvement in the fleet production
correct?
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3. Overburden removal fleets
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Lets break down the rate of material movement for a fleet into 3
main areas:
1. At the excavation (digging)
2. On the haul (hauling)
3. At the dump (dumping)
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Each of these areas can be influenced in different ways
So what are some of the variables that influence the rate of each
of these areas (leaving availability and utilisation out for now)?
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4. At the excavation

Some factors that can determine the excavation rate:
 Equipment used
 Diggability of the material
 Floor conditions
 Highwall conditions
 Face height
 Swing angle
 Bucket fill factor
 Passes per truck load
 Operator skills
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5. On the haul

Some factors that can determine the haulage rate:
 Haul distance
 Change in elevation
 Trucks required
 Truck type
 Consistency of haul
 Haul road surface conditions (roughness, dust, grip, road maintenance)
 Haul road grades
 Corner design
 Intersections
 Turning room at face and dump (spot times)
 Visibility (eg dusty conditions)
 Spotting techniques at excavation and at the dump
 Breaks and breakdowns that disturb the steady state flow
 Operator skills
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6. At the dump
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Some factors that will determine the dumping rate:
 Dump surface conditions
 Dump stability conditions
 Operator skills, both with operating the dozer and controlling the dump
 Dump progression rate
 Rate at which material is coming into the dump
 Dump dozer capacity
 Alternative dump options
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7. The dig rate of the fleet
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So when determining the dig rate of an overburden fleet, you
cannot just compare the digging units with each other – the
whole system needs to be taken into consideration
At any stage any three of the areas that make up the fleet can
be constraining the system
So how does the 10% improvement in excavator dig rate look
like for a 10% fleet production improvement?
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8. A 10% improvement in production?
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For a 10% improvement in an excavator dig rate equating to a
10% production improvement, the excavator must be the system
constraint all of the time
For this to be true, the excavator must never wait for a truck. This
means that:
1. The circuit cannot be under trucked at any time, ever
2. There cannot be any part of the process stopping the excavator from
loading, ie there cannot be any spot time occurring

Lets run through an example of each of the two points above to
see what impact there is on the proposed 10% production
increase:
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9. 1. The circuit can never be under
trucked
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Lets look at the effects of having a circuit that is under trucked
When a circuit is always under trucked, the truck cycle time is the
constraint in the system. This means that the improvement will only
benefit the system the proportion the load time is improved in the cycle
time. A calculated example of this can be:
 120 sec truck load time (before improvement)
 30 sec spot time
 570 sec total travel time
 40 sec dump time
 TOTAL = 760 sec truck cycle time (just under 13 minutes, very reasonable)
 The 10% improvement is only on the truck load time: 10% improvement of
120 sec = 120 - (120/1.1) = 10.9 sec
 Therefore the improvement in this example is: 760/(760-10.9) - 1 = 1.5%

So the 10% excavator improvement is now a 1.5% system improvement
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10. 2. There can be no spot time

If spot time is occurring in the system, then the 10% improvement on
the dig unit will deteriorate, as the constraint will move off the dig unit
when spotting is occurring. A calculated example of this can be:
 120 sec truck load time (before improvement)
 30 sec spot time
 Assumed fully trucked (there is always a truck in the queue for the
excavator)
 TOTAL = 150 sec (ie trucks are rolling out loaded every 150 seconds)
 Again the 10% improvement is only on the truck load time: 10%
improvement of 120 sec = 10.9 sec
 Therefore the improvement is: 150/(150 – 10.9) - 1 = 7.8%
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11. The 10% improvement does not
look likely

The 10% performance improvement of the system is very unlikely.
For the calculated examples in the previous slides you will be
looking at between 1.5% to 7.8% improvement (these will be
different depending on site/equipment specific load, spot and cycle
times)

Why would most people in the mining industry link a 10%
improvement in excavator productivity to a 10% improvement to the
fleet performance?

First a quick exercise to help explain it:
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12. The cost of a bat and ball
QUESTION: If a bat and ball costs $1.10, and
the bat costs $1.00 more than the ball, how
much does the ball cost?
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13. The cost of a bat and ball
ANSWER: Most people who do not think through the
problem answer with: the ball costs $0.10
This is wrong as: $1.00 - $0.10 = $0.90 which is not
$1.00 more
The correct answer is the ball costs $0.05, as:
$1.05 - $0.05 = $1.00
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14. We are bad intuitive statisticians

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We have very good instincts in certain areas. Eg distance yourself
from big things with sharp teeth (try introducing an small child that has
had almost no interactions with dogs to a friendly 60kg Rottweiler that
you know. Not only will the child scramble back into arms, they will
also try to position themselves so that you are between them and the
dog)
However, the fact is that humans are very poor intuitive statisticians.
Work in this area over the past 40 years has proven this to be the
case (see work by Amos Tversky and Daniel Kahneman)
The less data that we have and the less exposure someone has to an
operating system, the more likely we are to rely on our intuition, and
statistically it will most likely be wrong. Most people in the mining
industry link the dig unit (an excavator in this case) to the production
of an entire overburden fleet
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15. This was basic analysis on one
overburden fleet
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One simple example analysing a change in excavator rate, for one
fleet. Imagine the statistical intuition being used for an entire mine
plan
A typical operation can contain: overburden drills, blast crews,
excavators, shovels, dozers, draglines, continuous haulage
systems, lots of trucks, loaders, graders, water trucks, grade
control processes, dozers used for preparation, pumps,
processing plant, etc
On top of these processes we also have other factors impacting
the system: layout of the resource, pit design, equipment access,
policies, inventories etc
All of these things make up the system, and changes to any of
them will most likely impact the system
It is little wonder why a majority of improvement projects do not
deliver expected value, or the value is not sustained
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16. How could you look for improvement
opportunities in a overburden fleet?
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Following on from the improvement initiative for the overburden fleet:
The first step would be to find the parts of the circuit that are mainly
constraining the circuit* most of the time
Drill down to the cause – Ensure that the detail is covered. Eg a circuit
may appear to be under trucked, but the cause may be contained
within: design, scheduling, road maintenance, operator skills, circuit
management etc. The devil still sits in the detail where it always has
Use, but never trust automatically generated data or opinions
Improving any part of these may need to be discounted as a system
improvement. As in the 10% increase in excavator rate; fixing one part
of the system does not necessarily equate to a system improvement of
the same magnitude (some do, most don’t)
*Mainly constraining the circuit, as you will find that just about everything will have a turn constraining
the circuit during a shift
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17. Summary
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An overburden fleet is not just the dig unit
Unless the process is the only constraint in the system all of the
time, any improvement to it will not equate to the same benefit
flowing through to the system
We are bad intuitive statisticians. The less exposure we have to
the detail of what actually happens in a system, the poorer this
intuition will perform
Never ignore the detail
All variables will not be captured by any system. Automatically
generated data can easily be misinterpreted
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18. Always customised – no two sites are
the same
Thank you
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