mine engineering project

Mine Engineering Practice PROJECT 2015

Inefficiency of the load and haul process at Dorstfontein mine which impacts the production outputs and profitability

Lawrence Tjale

Scope and Objectives

Project Justification and Background:Eqstra is an integrated leasing and capital equipment group, which also offers value-added services

to their customers through their three divisions - Fleet Management and Logistics, Industrial

Equipment and Contract Mining( MCC) and Plant Rental.

The mining process consists of:

Drilling

o The process of sinking a hole into the earth to place the explosive material in.

Blasting

o The process of placing the explosive material into the drilled hole and igniting it

Loading

o The process of collecting the raw ore and placing it into the load bin of a dump truck

by using an excavator

Hauling

o The process of transferring the raw ore from blast site to dump site

Dumping

o The process of unloading the raw ore from the dump truck

From a capital expenditure and labour perspective, the load and haul require the greatest capital

investment; hence, the project will focus on this area.

Dorstfontein is currently one of three soft rock mine sites the MCC group is mining in. Currently there

are other initiatives to improve the other two sites, hence the reason I chose Dorstfontein.

Project Objectives:

Define Dorstfontein tender and industry standards

Identify actual production output

Determine the difference between the standards and actual

Identify reasons for the difference between the standards and actual

Determine impact of difference between the standards and actual

Identify possible solutions and recommendations

Exclusions from the project scope The actual implementation of these recommendations and the timeline process will be

excluded from this Project.

Mine Engineering Practice PROJECT 2015 Lawrence tjale 36927678

Project Process:

Deliverable Deadline

Final Scope Completed 04 May 2015

Research Defined 13 May 2015

Research Complete 08 June 2015

Results 10 June 2015

Analysis of results & Recommendations 11 August

Draft Report 21 September 2015

Final Report Hand in 28 September 2015


Coal Mining within South Africa

Mining is one of the most lucrative—and destructive—industries on earth.

China and the United States the greatest contributors globally with respect to coal production and coal

consumption with the likes of Russia, Australia Indonesia and Colombia competing with regard to

global export volumes.

South Africa is also viewed as being a significant contributor to the global coal market due to its

relatively low cost of production; it has the world’s largest coal export terminal and is positioned

conveniently between Atlantic and Pacific coal markets. It is a potential swing producer, able to export

competitively to either Europe or the East. (Eberhard, 2011)

The BP Statistical Review Of World Energy 2015 (BP, 2015) stated that South Africa held 30,156

million tonnes of total proven coal reserves by the end of the 2014 - 2015 period, of which 147.7

million tonnes was mined making South Africa the sixth largest holder of coal in the world (Coal,

2014).

89.4 million Tonnes of coal was consumed by South African Industry over this same period.

The coal reserves held in South Africa constitute more than a third of all coal reserves found within

the Southern Hemisphere and are the main source of energy supply to South Africa (Schmidt, 2010)

Fifty one percent of South African coal mining is done underground, the remaining 49 percent being

produced by open-cast methods (Energy, 2015)

As the country’s second largest earner in terms of the value of total sales after gold, coal provides

6.1% of the country’s total merchandise exports. By international standards, South Africa's coal

deposits are relatively shallow with thick seams, which make them easier and, usually, cheaper to

mine.

The Figure below supplies an overview of South Africa’s coal deposits in relation to the globe

Figure 1


Challenges experienced within the South African context

Open-cast mining operations utilise haul trucks to transport the excavated cubic dirt or ore (cubes)

from one area to the next and are therefore designed to carry significant loads during each trip.

Figure 2 A CAT 785 Dump Truck and a Liebherr 9350 Excavator

This may seem to be a simple task. However there are numerous challenges that need to be

overcome to ensure that the haul process proceeds as smoothly and efficiently as possible. By

overcoming these challenges the mine operation will experience a significant increase in revenue as

either volume of cubes transported per hour will be increased or fewer machines would be utilised to

achieve the necessary outcomes.


Challenges

The following challenges will be focussed on within the open cast mining sphere due to their impact on the case scope:

Weight Distribution and Transporto Load placement in the dump truck bin

Haul Road Traffic and Designo The dump trucks operating surface

Benches and Blastingo The operating surface of the Excavator and the preparation thereof

Challenge 1: Weight Distribution and Transport

Whilst the haul trucks are designed to carry a predetermined amount of mass and volume, the cubes

of dirt or raw ore that are dumped into each truck will differ with each load cycle of the excavator. Elliot

Duff (Duff, 2004) explains how mining operations could leverage from various technologies to improve

the estimated tonnages and volumes within the load bin of the haul trucks. Density scanning lasers

(Cezary Toś, 2007) `mounted 5 m above the truck can measure the weight and volume of the load

and the data stored to be processed at a later time.

This data may range from: distribution, profile and fragmentations of the ores from each of the load’s

blast processes. This type of production monitoring will afford the mining operation an additional tool

of analysis to determine each truck’s load with a net result in increasing productivity.

Duff again advises that there are two ways in which productivity is to be improved:

Reschedule haul trucks

Re-evaluation of tray (load bin) designs

“Reschedule trucks”

Mining operations utilise a variety of mining equipment and it is critical that the equipment utilised is of

the best fit for the job on hand for each operation.

By rescheduling the best-fit haul truck to the type of material it will be transporting, the tonnage and

cubic volume transported per vehicle trip can be increased. This would furthermore result in the haul

vehicles requiring less maintenance per operational hour and decreasing the operational expenditure

per load cycle.


“Comparison of tray (load bin) designs”

Raw ores mined within each mining operation vary in structure, volume and weight and it is critical

that the correct tray or load bin be utilised, fitting not only the mining operation but also the raw ore

composition.

As load bins of each haul truck are designed to carry specific material compositions the mining

operation should monitor the effects on the load bins which have been used by the haul truck, as an

incorrect fit would shorten the life span of the tray.

Challenge 2: Haul Road Traffic and Road Haul Design

A study by Andrew Chapman from the Queens University (Chapman, 2012) showed how haul road

traffic is increasingly becoming an area of concern for mine operators. Due to the time spent by mine

operators in traffic the mining operation suffers a considerable decrease in cubic output as

productivity is slowed.

Furthermore, each haul truck is generally filled to its maximum haul capacity and this raw ore

becomes stationary in the haul process should haul traffic not be managed. Due to differing materials

having varying densities, shape and volume the number of units each haul truck can transport is

variable and this affects the operation.

During the haul phase there is a great emphasis placed on the completion of the haul cycle as fast

and efficiently as possible. Any decrease in the time taken for each haul truck to complete its haul

cycle will have a significant impact on the productivity of the mining operation and ultimately on the

revenue of the operation.

The mine haul road network and infrastructure is a vital and highly critical component of the

production process and a poorly designed network and surface carry a significant portion of costs on

a mine’s productivity. The provision for and creation of a well maintained haul road enables the

machinery to operate more efficiently and in a safer environment.


RJ Thompson (Thompson, 2011) confirms this requirement of an integrated design approach.

This approach is referenced to:

Reduce traffic hazards and provide for safer driving conditions

Reduce operational costs

Improve cycle times

Less maintenance costs

Improvement on rim and tyre life, drive trains and suspensions

Thompson confirms that many concepts from general highway engineering can be adapted from and

applied when implementing this approach on the design, construction and maintenance phases. It

should however be noted that there are significant differences between the two design approaches

due to applied loads, traffic volumes and costs. As such the design is basically flawed should all

factors not be accounted for within the integrated design approach.

Impacts to be expected are amongst others:

Rolling resistance increases, translating into

Equipment downtime

Increased maintenance costs (machinery and the road itself)

Challenge 3: Bench creation and Bench heights

Blasting actions result in the addition of air molecules into the compacted earth resulting in the earth

taking up more volume. This addition creates what is referred to as heave, resulting in additional ore

and ground required to be moved which is not accounted for within the initial surveying analysis.

This heave creates an area of operation not suitable for the excavators to operate on due to it’s

unstable nature and should firstly be levelled to facilitate the operation of the excavators.

Bench heights (A in Figure 4) (the vertical distance between the each horizontal level of the pit

(Kennedy, 1990) are determined by taking into account the excavators stick length (C in Figure 4). If

the stick is 5 meters the bench should also be approximately 5 meters. This will enable the bucket to

be filled more easily as the backhoe is designed to have maximum force in a digging motion when

using the boom cylinders to assist with the lift and breakout force (stick cylinders).


Figure 3 will assist in explanation of the various excavator components:

Figure 3

If the bench is too low the operator tries to fill but cannot use the boom function as desired or the

bucket will be only 50% full. The excavator operator must reload and reposition himself in the time

frame of the truck exchange. Time frame for exchange is approximately 40 seconds and should not

be exceeded. The excavator must be ready to load as soon as the truck is in place.

The following photos will explain digging better:

Figure 4


Legend:

A – Correct/good bench height (A = B = C)

D – Good flat operating surface

Legend:

A – Boom

B - Stick

C – Boom cylinders

Hossein, Marteza et al (Selection of practical bench height in open pit mining using a culti-criteria

decision making solution, 2010) showed that if there were two options for bench heights - a 10 meter

bench or a 12.5 meter bench - for an open pit mine, the calculations showed that the time used for the

load and haul process for the 12.5 meter bench was 33.33% faster than the 10m bench. This shows

that the optimum bench height used by a mine should be calculated based on the equipment

operating at that mine.


MCC Tender

MCC was awarded the Dorstfontein tender in February 2011. The Tender employs on average 29

persons who manage the following kit:

1 x Liebherr 974 excavator

1 x Liebherr 9350 excavator

2 x Liebherr 984 excavators

13 x CAT 777 dump trucks

4 x CAT 785 dump trucks

Assortment of support equipment including road graders, water trucks and dump trucks

The Net Book value of the equipment is R 359 million Rands as of August 2015

The team conducted a site visit to Dorstfontein mine in Mpumalanga to determine the current process

and identify the gaps that exist.

The below highlights the various items focussed on as detailed in the project objectives, weighing up

the industry norms to site actuals:

Item Industry Standards

Actual Practices Variance between Standard and Practices

Bench preparation Flat surface Uneven, unstable 7.5min delay for Excavator to

prepare its work bench

Bench height 5m 5m Meets standards

Haul road quality Smooth surface Marked with

numerous

potholes

Vehicles unable to maintain a

constant speed and travel in a

straight line

Haul road gradient Smooth

constant grade,

not undulating

Uneven and

lacking

consistency. 13

degree incline

3 degree increase in incline, sudden

increase around corner from gradual

to steep requiring downshift and

decrease in average rolling speed

Truck fill factor 40bcm 36bcm 4bcm per load lost due to inefficient

loading


Recommendations

The Practices as detailed above support the research provided highlighting the critical nature that the

haul roads play in the effective operation of the mine.

Based on the variances found between the Industry Standards and actual outputs from Dorstfontein,

the team have found that the most sustainable route to achieve our predetermined scope objectives

would be a focus on two key items:

1. The upgrade of the current road infrastructure, the future design and maintenance thereof

going forward

2. The view to ensure dump trucks are filled to their maximum capacity with each load cycle

Each project will be implemented as per the below structure:

1. Road haul upgrade

The team propose the upgrade of the current road infrastructure by focusing on the incline

and gradient increase found at turn 1 (refer to attached Dorstfontein schematic) leading from

West to the incline moving South.

Loads transported will be dumped systematically at this point rather than at the dumping

ground at section 1 (refer to attached Dorstfontein schematic – Appendix 1)

Each load will be levelled out with a CAT D10 Dozer already being utilised on site for this

same function at section 1.

Once levelled, a CAT 14M Grader will be utilised to smooth the surface level to an acceptable

operating surface.

Both additional machinery items will carry a zero running cost addition as they are already

accounted for in the monthly budgeting for the very roles they will be required for.

Once completed all current haul roads will be upgraded with the CAT D10 grader, ensuring all

potholes are filled and the surface is kept at a constantly smooth surface.

The implementation of this recommendation would result in an efficiency increase of 15%

based on discussions held by senior MCC Plant and Engineering Managers.


2. Load capacity management

Each excavator is to be allocated a dedicated supervisor

Their role is to ensure each dump truck is loaded to an optimal level rather than the current

80% capacity as highlighted in the site visit Practices.

Each supervisor will further be managed by a Senior Supervisor monitoring each load from

the central view point. This will ensure the optimal load of each dump truck, increasing that

the cubic transport per load be increased by 15%, allowing for a 5% variable to 100%

capacity


Business Case

The financial information provided herewith has been supplied courtesy of MCC Finance Department

It should be noted that all values quoted are subject to both the Engineering and Production

Departments of MCC Dorstfontein remaining within their allotted budgets and parameters

All costs are determined as a multiplier of an hourly rate

The below table highlights briefly the following, all supporting figures are supplied as Appendix 2

Current monthly Operational Expenditure

Proposal 1 - Impact on profitability when the haul road upgrade is actioned

Proposal 2 - Impact on profitability when the load capacity optimisation is implemented

Combination - Impact on profitability when both Proposal 1 and Proposal 2 are implemented


Current Proposal 1

Engineering R5.8m R4.9m

Current Proposal 1

Engineering R5.8m R4.9m

Bibliography

A REVIEW ON EXISTING OPENCAST COAL MINING METHODS. Scott, B, et al. 2010. 2010, Journal of Mining Science, Vol. 46, No. 3, 2010, p. 280.

BP. 2015. BP Statistical Review of World Energy 2015. London : Platts, 2015.

Cezary Toś, Bogdan Wolski, Leszek Zielina. 2007. OPTIMIZATION OF LASER SCANNING TECHNOLOGY IN MONITORING OF ROCK AND NATURAL GROUND SURFACE. Cracow : Polish Ministry of Science and Higher Education, 2007.

Chapman, Andrew. 2012. A Field Study on Haul Time Variability in Open Pit Mines. Qspace. [Online] 2012. https://qspace.library.queensu.ca/handle/1974/7410.

Coal, Universal. 2014. Universal Coal PLC. Universal Coal PLC. [Online] 2014. [Cited: June 10, 2015.] http://www.universalcoal.com/our-projects/coal-mining-in-south-africa/~.

Duff, Elliot. 2004. Automated Volume Estimation of Haul-Truck Loads. CSIRO Manufacturing Science and Technology. 2004, Vol. 2.

Eberhard, Anton. 2011. The Future of South African Coal:. Stanford : Stanford University, 2011.

Energy, Republic of South Africa Department of. 2015. Coal Resources. Republic of South Africa Department of Energy. [Online] 2015. http://www.energy.gov.za/files/coal_frame.html.

Jai, Shreya. 2015. Economy and Policy. Business Standard. [Online] August 27, 2015. http://www.business-standard.com/article/economy-policy/global-coal-price-on-the-downslide-115082700011_1.html.

Kennedy, Bruce A. 1990. Surface Mining, Second Edition. Surface Mining, Second Edition. s.l. : SME, 1990, 1990.

Mitra, R and Saydam, S. 2012. Surface coal mining methods in Australia. 2012.

Schmidt, Stephan. 2010. Coal deposits of South Africa - the future of coal. Freiberg : Institute for Geology, Technische Universität Bergakademie, 2010.

Selection of practical bench height in open pit mining using a culti-criteria decision making solution. Soltanmohammadi, Hossein, et al. 2010. June 2010, Geology and Mining Research Vol.2, p. 55.

Thompson, Roger. 2011. Mine haul road design, construction and maintenance management. [book auth.] Peter Darling. SME Mining Engineering Handbook. Lyettleton, Colorado : s.n., 2011.


Annexures

Annexure 1: Schematic representation of MCC Dorstfontein Mine

Annexure 2: Financial documentation as support to Business Case


Annexure 1

Current operational expense figures from MCC Dorstfontein

The operational variable costing matrix is supplied as per the below rate card:

Variable costs

Type Model Unit

RDT CAT 777 Hour 282.57

Depreciation rate

The operational fixed costing matrix is supplied as per the below rate card:

Model Fleet Unit Interest rate Interest Insurance rate InsuranceCAT 777 14 Month 47,267.02 661,738.29 928.51 12,999.14 CAT 785 10 Month 76,305.96 763,059.57 1,563.66 15,636.57 CAT 773 Month 23,434.99 - 463.55 -

Total monthly expenses - R 9,210,429.12


Annexu

Truck

CAT 785 5.8 38

Loads per hour

bcm per load

Tender bcm per hour

CAT 777 13 4110 R 282.57

Proposal 1: Road haul upgrade

By improving the haul roads, the team propose a 15% improvement in the total loads per hour.

The below outputs will be achieved:

The net result amounts to the removal of 2 CAT 785’s and 1 CAT 777’s from the fleet.

The financial impact is a net cost savings of R 1,063,338.56 per month


TruckLoads per

hourbcm per

load

Tender bcm per

hour

Forecast bcm per hour

Units Availability Utilisation Hours worked TOTAL bcm for

month

CAT 785 6.7 38 254 8 80% 70% 2 724 691 694 CAT 777 4.7 35 165 13 80% 65% 4 110 678 266 CAT 773 4.4 13 57 - 85% 0% - -

1 369 960

D785 3405 R 221.48777 4426 R 282.57

Proposal 2: Load capacity management

By improving the load volumes by 10%, the below outputs will be achieved

The net result amounts to the removal of 1 CAT 785’s and 1 CAT 777 from the fleet

The financial impact is a net cost savings of R 793,793.29 per month


Truck

CAT 785 5.8 42

Loads per hour

bcm per load

Tender bcm per hour

Truck Total Units

CAT 785 8 2724 R 221.48CAT 777 13 4110 R 282.57

Hours Operation

Depreciation Rate

Combination - By implementing both recommendations, the below outputs will be achieved

By combing both proposed changes, the below outputs will be achieved

The net result amounts to the removal of 3 CAT 785’s and 2 CAT 777’s from the fleet




Trucks

Truck

CAT 785 6.7 42

Loads per hour

bcm per load

Tender bcm per hour

777 4426 R 282.57

mine engineering project

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