The Development of a Diggability Index for Bucket

THE DEVELOPMENT OF A DIGGABILITY INDEX

FOR BUCKET WHEEL EXCAVATORS

A thesis submitted for the degree of

Master of Science

A. INAL

The University of New South Wales

School of Mining Engineering

Faculty of Applied Science

December, 1984 SR.P.T10

CERTIFICATE OF ORIGINALITY

I hereby declare that this thesis is my own work and that, to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree or diploma of a university or other institute of higher learning, except where due acknowledgement is made in the text of the thesis.

(Signed)

I hereby certify that the work containel in this thesis has not teen submittal for a higher legrae to any r)g^nni^ensit/ or xn^titi -ion.

Sign ature• UNIVERSITY OF N.S.W.

-3 DEC 1985

LIBRARY ABSTRACT

Bucket wheel excavators are widely used in open-cut mining

operations. While in the past they have excavated unconsolidated

material and only the softest rock and mineral deposits, their

role is currently being extended to include harder overburden,

which may or may not be pre-blasted. Machine manufacturers have

developed a simple wedge penetration test to assess ground

conditions, to provide input data for machine specification and

to predict excavation rates.

This thesis discusses the role of bucket wheel excavators

and describes seme typical designs and methods of operation.

Thereafter, the design of a portable but rigid wedge test

apparatus is discussed. The experimental work presented in this

thesis relates to the use of the wedge test apparatus to

determine the diggability index for overburden material

recovered frcm the bucket wheel excavator site at Goonyella

Mine in Central Queensland. Tests, involving the use of a

linear rock cutting rig were also undertaken, as was sane additional work involving samples cast fran sand/cement mortars.

In conclusion the thesis correlates wedge test results with

standard physical and mechanical properties of the samples

and discusses whether the wedge test provides an adequate measure of diggability. ii

CONTENTS Page No.

ABSTRACT i

CONTENTS ii

LIST OF ILLUSTRATIONS vi

LIST OF TABLES X

LIST OF MAPS xii

ACKNOWLEDGEMENTS xiii

CHAPTER 1 INTRODUCTION 1

CHAPTER 2 ORIGIN AND DEVELOPMENT OF THE BUCKET WHEEL

EXCAVATOR 5

2.1 Introduction 5

2.2 Wheel Excavators Operation Methods 9

2.2.1 Terrace and Dropping Cuts 12

2.2.2 Terrace Cut 12

2.2.3 Dropping Cut 12

2.3 Systems of Bucket Wheel Operation 16

2.3.1 Full Block Working 16

2.3.2 Face or Front Working 16

2.3.3 Face Block or Side Block Working 17

2.4 Bucket Wheel Excavators Design 17

2.5 The Bucket Wheel 19

2.5.1 Cell Type Wheel 20

2.5.2 Cell-less Type Wheel 20

2.5.3, Semi-cell Type 24

2.5.4 Bucket and Bucket Knives 24

2.5.5 Pre-Cutters 2 7

2.5.6 Ripping Teeth 27 iii

Page No.

2.6 Slewing Mechanism 30

2.6.1 Slewing Gear 32

2.6.2 Turntables 32

2.6.3 Ball Races 34

2.7 Steel Structure 34

2.7.1 Bucket Wheel Excavator Design

Based on Spare Frames 34

2.7.2 Bucket Wheel Excavator Structures 37

2.8 Crawlers 40

2.9 Lubrication 42

2.9.1 Lubricating Techniques 42

2.10 Material Transport 44

2.10.1 Conveyor Belts on Bucket Wheel Excavators 44

2.10.2 Analysis of Belt Conveyor Requirements

at Transfer Points 46

2.10.3 Conveying Path in Bucket Wheel Excavator 48

2.10.4 Truck Loading 51

2.10.5 Train Loading 51

2.11 Electrical Equipment 53

CHAPTER 3 AUSTRALIAN EXPERIENCE 57

3.1 Brown Coal 57

3.1.1 Development of Mining Equipment for

Latrobe Valley 57

3.2 Black Coal 61

3.2.1 The Goonyella Mine 61

3.2.2 Mine Operation 63 iv

Page No.

3.2.3 Nature of the Goonyella Overburden 65

3.2.4 Bucket Wheel Excavator Selection 66

CHAPTER 4 EXPERIMENTAL PROGRAMME AND TEST MATERIALS 68

4.1 Physical and Mechanical Properties of

the Test Material 71

4.2 Test Samples 72

4.2.1 Test Samples from Goonyella

4.2.2 Artificial Rock Samples 73

4.3 Compressive Strength 74

4.4 Tensile Strength 78

4.5 Bulk Density 81

4.6 Shore Hardness 83

4.7 Cone Indenter Test 87

CHAPTER 5 DEVELOPMENT OF THE WEDGE TEST 91

5.1 Determination of Digging Resistance 91

5.2 Ground Diggability Determination 94

5.3 Detailed Design of UNSW Wedge Test Apparatus 95

5.3.1 Design Parameters 97

5.3.2 Manufacture of the Apparatus 99

5.4 Wedge Test Results 99

5.5 Effect of Specimen Size and Shape on

Test Results 111 V

Page No.

CHAPTER 6 ROCK CUTTING TESTS 122

6.1 Cutting Results 127

6.2 Disscussion of Cutting Programme Results 140

6.3 Comparison of the Cuttability of the

Three Rock Types 143

CHAPTER 7 CONCLUSIONS 146

REFERENCES 157

BIBLIOGRAPHY 159 vi

LIST OF ILLUSTRATIONS Page No.

FIGURE NO.

2.1 Details of an 1881 Patent for a B.W.E. 6

2.2 First Rail Mounted Bucket Wheel Excavator 7

2.3 Bucket Wheel Excavator at the Cuba Mine, Illinois 8

2.4 The Bucket Wheel Excavator Sch Rs-^—^- - 25 10

2.5 A Large Bucket Wheel Excavator 11

2.6 Alternative Excavation Methods for Bucket

Wheel Excavators 11

2.7 .a A Crowd-type B.W.E. Undertaking a Terrace Cut 13

2.7. b Crowdless-type B.W.E. in Terrace Cut 13

2.7 .c A Crowd-type B.W.E. in a Dropping Cut 14

2.7. d A Crowdless-type B.W.E. in a Dropping Cut 14

2.8 Block Working System of Bucket Wheel Excavator 15

2.9 Face Working, Rail Mounted Bucket Wheel Excavator 15

2.10 Face or Side Block Working B.W.E., Used in

Conjunction With a Shovel 18

2.11 Cell Type Bucket Wheel 21

2.12 Cell-less Type Bucket Wheel 21

2.13 Bucket Discharge Types 22

2.14 Bucket Discharge Types Photos 23

2.15 Semi-Cell Type Bucket Wheel 25

2.16 Comparison of Bucket Wheel Types for

Bucket Filling Process 25

2.17 Cover Plate of the Wheel Body 26

2.18 Chain-back Type Bucket 28 vii

FIGURE NO. Page No.

2.19 Pre-cutters (Inter cutters) 29

2.20 Buckets and Bucket Teeth 31

2.21 Position and Shape of Teeth 31

2.22 Turntable on the B.W.E. SchRs--^-- - 35 - 11 33

2.23 Ball Race Section 33

2.24 Control and Lighting Current Slip Rings 35

2.25 Drum Shaped Membrane Structure 38

2.26 B.W.E. Framework in Balanced and Unbalanced

Conditions 39

2.27 Various Crawler Designs 41

2.28 Alternative Lubrication Systans 43

2.29 B.W.E. with Shiftable Conveyor Systan 45

2.30 Transfer Point 47

2.31 Possible Transfer Point Configurations 47

2.32 Reduction of Conveyor Path in B.W.E. 49

2.33 Catenery Idler Sets 49

2.34 Typical Bucket Wheel Boon Cross Section 50

2.35 Truck Loading 52

2.36 Train Loading 54

2.37 B.W.E. Cable Reel Car 56

3.1 Coal Resources of Australia 58

3.2 Development of Equipment for Victorian Open-Cut

Mines 60

3.3 Intermediate Cutters 62

3.4 Typical Application of a B.W.E. 62

3.5 Detailed Plan of Goonyella Open-Cut 64 viii

FIGURE NO. Page No.

3.6 Continuous Pre-Stripping at Goonyella Mine 64

3.7 0 & K 1367 B.W.E. for Goonyella Mine 67

4.1 Plan Showing Location of Boreholes Relative

to B.W.E. Zone 70

4.2 Shore Scleroscope 84

4.3 Cone Indenter Test Equipment 88

5.1 General Plan of Wedge Test Apparatus 96

5.2 Detail of Top Plate 100

5.3 Detail of Wedge and Connecting Systems 101

5.4 Detail of Sandbox 102

5.5 Detail of Bottom Plate 103

5.6 General View of Wedge Test Apparatus 104

5.7 Avery Test Machine with Wedge 106

5.8 Ideal Breakage of Sample 112

5.9 Shear Failure in Strong Specimens 113

5.10 Wedge Test Results for Mix 5 117

5.11 Wedge Test Results for Mix 6 118

5.12 Wedge Test Results for Mix 7 119

5.13 Comparison of Cubic and Cylindrical Specimens

after Testing 120

6.1 Linear Rock Cutting Rig and Pick Dynamometer 123

6.2 Isometric Drawing of Dynamometer 126

6.3 Chisel Pick 126

6.4 (A) Effect of Depth of Cut on Forces for Block B2 130

6.4 (B) Effect of Depth of Cut on Yield and Specific

Energy in Block B2 131 IX

FIGURE NO. Page No.

6.5 (A) Effect of Depth of Cut on Forces for Block B3 134

6.5 (B) Effect of Depth of Cut on Yield and Specific

Energy in Block B3 135

6.6 (A) Effect of Depth of Cut on Forces for Block B4 138

6.6 (B) Effect of Depth of Cut on Yield and Specific

Energy in Block B4 139

6.7 Shape of Excavated Groove 141

6.8 Ccmparison of Mean Cutting Forces in the Three

Goonyella Block Samples 144

6.9 Ccmparison of Specific Energies for the Three

Goonyella Block Samples 144

7.1 Relationship Between Ccmpressive Strength

and Wedge Strength 148

7.2 Relationship Between Tensile Strength and

Wedge Strength 148

7.3 Ccmparison of Shore Hardness and Wedge Strength 149

7.4 Ccmparison of Cone Indenter Hardness and

Wedge Strength 149

7.5 Relationship Between Cutting Forces and

Ccmpressive Strength 151

7.6 Relationship Between Cutting Forces and Cone

Indenter Hardness 151

7.7 Overburden Cuttability as a Function of

Wedge Strength 152

7.8 Specific Energy of Cutting as a Function of

Wedge Strength 152

7.9 Variation of the Correlation Factor f With Actual Material Strength 155 X

LIST OF TABLES

TABLE NO. Page No. 4500 2.1 Streel Structure for B.W.E. SchRs -yy-- 44 36

3.1 Victoria Brcwn Coal Resources 59

3.2 Comparison Between Three Heavy Duty Bucket

Wheel Excavators 67

4.1 Composition of Artificial Material Samples 72

4.2 Core Samples Received from Goonyella 73

4.3 Block Samples from Goonyella 73

4.4 Uniaxial Compressive Strengths of Goonyella

Block Samples 75

4.5 Uniaxial Compressive Strengths for Artificial

Samples 76

4.6 Uniaxial Tensile Strength-Brazilian Disc Test

of Goonyella Block Samples 78

4.7 Uniaxial Tensile Strength-Brazilian Disc Test

of Artificial Samples 79

4.8 Bulk Density of Goonyella Block Samples 81

4.9 Bulk Density of Artificial Samples 82

4.10 Shore Hardness Results of Goonyella Core Samples 85

4.11 Shore Hardness Results of Goonyella Block Samples 86

4.12 Shore Hardness Results of Artificial Samples 86

4.13 Cone Indenter Test of Goonyella Core Samples 89

4.14 Cone Indenter Test of Goonyella Block Samples 89

4.15 Cone Indenter Test of Artificial Samples 90

5.1 Wedge Test Results for Goonyella Core 107

5.2 Wedge Test Results for Goonyella Blocks 108

5.3 Wedge Test Result for Simulated Overburden Material 109 XI

TABLE NO. Page No.

5.4 Effect of Specimen Size on Wedge Test Results 115

5.5 Wedge Test Results for Rectangular Prism and

Cubic Samples 116

6.1 (A) Results of Cutting Test in Block B2 (Forces) 128

6.1 (B) Results of Cutting Test in Block B2 (Yield,

Specific Energy and Coarseness Index) 129

6.2 (A) Results of Cutting Tests in Block B3 (Forces) 132

6.2 (B) Results of Cutting Tests in Block B3 (Yield,

Specific Energy, Coarseness Index) 133

6.3 (A) Results of Cutting Tests in Block B4 (Forces) 136

6.3 (B) Results of Cutting Tests in Block B4 (Yield,

Specific Energy, Coarseness Index) 137

6.4 Breakout Angles 142

6.5 Summary of Mechanical and Physical Properties

of the Goonyella Block Samples 143

7.1 Effect of Height/Diagonal Ratio for Rectangular

Prisms of Artificial Material 154 xii

LIST OF MAPS

MAP NO. Page No.

3.1 Brown Coal Deposits in Victoria 59

3.2 Goonyella Mine in Central Queensland 64 ACKNOWLEDGEMENTS

The work described in this thesis was undertaken at The School of Mining Engineering, The University of New South Wales and

funded by Australian Coal Industry Research Laboratories Limited.

The support of both organisations is gratefully acknowledged.

The author wishes to thank the project director, Dr. H.R.

Phillips for his guidance and supervision.

Special thanks are due to Mr. Dam Truong of ACIRL who organised field visits and collection of samples and was always ready to discuss the project.

The assistance and encouragenent received frcm all the staff of the School of Mining Engineering is much appreciated, particularly the efforts of Mrs. Fisher and Mrs. Kwan who typed this thesis.

Finally, my thanks to ray wife Aydan who constantly supported and encouraged me throughout this period of study. CHAPTER 1

INTRODUCTION

Man has always had to contend with the problem of earth

excavation. Civilisation and his future will depend on his ability

to dig, whether for mining or other purposes, so that it can be

considered a prime human activity.

Mining plays an important role in supplying the world

economy with the necessary raw materials and these must continue

to be produced at similar prices to those of today, if the standard

of living for an increasing population is to be improved or even maintained.

The world wide trend of recovering more of these materials

frcm open cuts may be expected to continue due to the advancement of open-cut technologies. Twenty years ago the main problem for open-cut mining engineers was the high and increasing ratio of overburden to mineral. This has, in many cases, been solved by exploiting economies of scale, so that today machines of giant proportions, almost unimaginable a generation ago, are common place in huge, highly productive mines. However, the potential

for exploiting economies of scale has been largely exhausted, as

so very often, have the higher grades of ore.

Today's mining engineer is being faced with the problems of developing and mining deposits of lower grade and with 2.

higher overburden ratios than is the current experience.

The requirement for movement of materials will be of significantly greater importance.

Open-cut mines of up to five hundred metres depth are now being developed. Present and future open-pit mining technology becomes primarily a matter of overburden stripping, while extraction of the paymineral is of secondary consideration.

It must, therefore, become a basic aim to strip overburden at the lowest possible cost. In consequence, the principles of continuous digging and handling have gained predominance.

In this regard the Bucket Wheel Excavator has emerged as one of the principal means of continuously excavating orebodies.

Bucket Wheel Excavators have established themselves firmly as effective digging machines and have proved themselves capable of the economy intended of continuous methods of excavation, in a variety of soils. For example: The overburden of the Neyveli mine in India has a very abrasive effect on all digging elements and is, on account of its density, very difficult to cut. Generally, however, the overburden has no rock or inclusions of other material which cannot be cut at all. 3.

Versatility in actual application has also been proved

under variable and extreme conditions, such as the Athabasca

oil sand deposits, where the nature of the oil sand itself makes mining difficult, especially in the winter months, when the water film around the sand particles causes the mined oil sands to freeze into solid lumps. The oil sands themselves

are also very tough and abrasive. Examples also abound of

applications in both thick and inclined deposits. These machines (BWEs) have also shown themselves capable of maintaining purity of material mined fran thin seams, irrespective of

type and hardness of material. The structure of material and

its diggability in spite of stickiness, plasticity and moisture

contents does not seriously Impair its work. For example,

in the Latrobe Valley Lignite Mine in Victoria the overburden consists of clayey silts and silty sand and is regarded as very sticky and difficult to handle. Also the inter seam materials are composed of a mixture of fine sands, silty sand,

silty clays and clays.

The applicability of the machine has also been shown to be

successful to a limited extent in hard slatey shales, friable

sandstones, and types of overburden similar to that found at

Goonyella. Applications in hard material are sometimes adopted

in conjunction with pre-blasting of the overburden. 4.

For the bucket wheel excavator, the first consideration is the design of the wheel and its drive to ensure it will be able to excavate the material frcm the operating face at a steady rate of output, with high reliability and without undue wear and tear. For this the designer needs to know the digging resistance. Several measure of this parameter are used; one of those tests, developed by bucket wheel manufacturers, is the wedge test. This procedure simulates the entry of an excavator tooth into the soil and measures seme information in respect of the impression made and split resistance encountered.

In this thesis the history, specification and use of bucket wheel excavators is discussed, as is the design of a portable wedge test machine. Results obtained frcm testing Goonyella mine samples are also presented. Other, important rock parameters such as unconfined compressive and tensile strength were determined.

These results have been compared with those obtained using the wedge test apparatus and correlations made between two sets of data. 5.

CHAPTER 2

ORIGIN AND DEVELOPMENT OF THE BUCKET WHEEL EXCAVATOR

2.1 Introduction

About two-hundred years ago, international canal building created

the need for the development of land operated, bucket chain excavators.

In 1827 and again in 1859, bucket chain dredgers very similar to their modem counterparts were patented (1) .

In 1881 a patent taken out by Charles A. Smith of New Carlisle,

Indiana, on an earth excavator gave sufficient data for construction of a workable bucket wheel excavator (2). (see Figure 2.1)

The oldest European patent, (Germany, 1906) was granted to S.J. Loyd and A.R. Grossmith (2) . This patent provided for a cutting wheel to be arranged in front of a bucket chain transporting the excavated material.

In 1916 the lignite mines of Bergwitz in the Bitterfield lignite field put into service the first rail mounted bucket wheel excavator for the digging of overburden (1)(2). (see Figure 2.2)

In-the early 40's United States Midwestern coal producers sought cheaper mining methods and began using bucket wheel excavators which were put into operation at the Cuba Mine, Illinois, of the United Electric Coal

Co. (1)(2) (3) (4). (see Figure 2.3) 6. Rasper).

(After

ii iiii !■ B.W.E.

for 11 -V Patent

V" 1881

GvI an

£ Details

2.1

FIGURE 7 Excavator.

Wheel

Bucket

Mounted

Rail

First

2.2

FIGURE 8. . Kolbe)

(After

Illinois

Mine,

Cuba

The

Excavator

Wheel

Bucket

2.3

FIGURE 9.

West. German manufacturers, however, also delivered strip mining equipment to the U.S.A.. In 1964, the machine Sch Rs - 25, designed by DEMAG Lauchhammer and built primarily in the U.S.A. by McDowell

Wellman Engineering Co. was put into service for overbuden removal in the lignite opencast mine of the Truax Traer Coal Co. in North Dakota (2) , as shown in Figure 2.4. At the same time, in the U.S.S.R., East Germany and

Czechoslovakia, bucket wheel excavators were being developed. East Germany, today has a range of machines 0 to 5 designated, which are built for small to medium digging height ranges. The smallest machine has two crawler tracks, and the largest which is already in service has up to eight crawler tracks.

2.2 Wheel Excavators Operation Methods

Similar working procedures apply to machines of all sizes, although in this section they are described on the basis of large excavators in large opencut mines. A typical machine of this size is shown in Figure

2.5.

The working methods ccmmonly adopted can be classified as,

1. Face or front working

2. Full block working

3. Face block or side block working

Each of these methods can make use of terrace cuts, dropping cuts, or a combination of both, as shown in Figure 2.6. 10. . Rasper) (After (After 1.0 N 25 --- ~ — Rs Rs

Sch

Excavator

Wheel

Bucket

The

N 2.4

FIGURE 11.

FIGURE 2.5 A Large Bucket Wheel Excavator (After Krumrey).

Terrace Cut Dropping Cut

FIGURE 2.6 Alternative Excavation Methods for Bucket Wheel Excavators (After Aiken and Rasper). 12.

2.2.1 Terrace and Dropping Cuts

When undertaking terrace cuts the buckets on the front side of the wheel do the cutting, while in the dropping cut the buckets on the under side of the wheel cut the material.

2.2.2 Terrace Cut

Figure 2.1.a. shows a crowd-type bucket wheel excavator in a terrace cut operation. The block is excavated in a number of layers (terraces) of equal height, with between 40 and 70 per cent of the wheel diameter being actively involved in the cutting process, depending on the ratio of face height to diameter and the nature of the material excavated. At the start of the top terrace the wheel is in the retracted position, and at the end of each pass it is extended by the slice thickness.

Figure 2.7.b shows a crowdless excavator. After each segment is finished the thickness of the next slice is set by moving the excavator forward by a distance equal to the slice thickness. The slice thickness varies across the face and depends on the angle of slew.

2.2.3 Dropping Cut

The dropping cut is often employed where the nature of the deposit causes surging or excessive lump size.

At the start of the block the wheel is lifted to a height sufficient to clear the face, see Figure 2.7c and 2.7d. The wheel is then set at the segment ends by lowering it an amount equal to the slice thickness and retracting the wheel to give the batter angle. Slewing to 90° is 13. thrust retracted THRUST extended

FIGURE 2.7.a A Crowd-type B.W.E. Undertaking a Terrace Cut (After Rodgers).

FIGURE 2.7.b Crowdless-type B.W.E. in Terrace Cut (After Rodgers). 14.

thrum ^CNOt°

FIGURE 2.7.C A Crowd-type B.W.E. in a Dropping Cut (After Rodgers).

FIGURE 2.7.d A Crowdless-type B.W.E. in a Dropping Cut (After Rodgers). 15.

FIGURE 2.8 Block Working System of Bucket Wheel Excavator (After Scott).

FIGURE 2.9 Face Working, Rail Mounted Bucket Wheel Excavator (After Rasper) . 16.

common, so that the front and slide batter have the same slope. In the dropping cut the slice thickness remains constant but the segment slope height gradually decreases to zero at a slew angle of 90°. When the wheel reaches the bench level a small toe ridge is left between it and the crawlers, which is often cleared by a bulldozer.

Material handling on shiftable conveyors and the excavation of "hard digging" conditions are more efficient with the dropping cut, because it controls lump size better and allows the high speed conveyors to operate without the tendency to overload or clog the transfer points.

2.3 Systans of Bucket Wheel Operation

2.3.1 Full Block Working

Full block working represents something close to the optimum operating method.

A full block is excavated in several bench cuts by raising, lowering and continuously slewing the bucket wheel, while at the same time the bucket wheel excavator is driven straight along the face length, as shown in Figure 2.8. The best results are obtained if the block is as wide as possible. The full block operation method can be undertaken by excavators of all sizes.

2.3.2 Face or Front Working

In the face working method the excavator travels along the working face. 17.

Face working can only be applied in good conditions where the bench

slope angle gives good slope stability. Figure 2.9 shows a rail mounted

excavator when operating a face working system.

2.3.3 Face Block or Side Block Working

Face block or side block working is the method most camionly adopted

in the U.S.A. black coal mines, where a bucket wheel excavator operates

in tandem with a shovel.

The bucket wheel excavator removes the top layers and overcasts

directly to the spoil pile, as illustrated in Figure 2.10. The bucket wheel excavator travels on top of the coal seam and often has a boon crowd

action because of the need to reach over the lower overburden layers.

In addition, the discharge boon must be long enough to clear the shovel

spoil.

Travelling distance for the machine is longer in face block operations

than for the full block method but much shorter than for front face working.

Face block operations are generally used for the selective mining of minerals occurring in several thin seams.

2.4 Bucket Wheel Excavator Design

Bucket wheel excavator designs are as numerous and various as the tasks which they have to perform. However, they are substantially influenced by the desired excavation rate, selected method, slope angle, cutting resistance, temperature and ground bearing pressure. The excavated material 18.

STRIPPING SHOVEL

WHEEL EXC.

47'-50'

FIGURE 2.10 Face or Side Block Working B.W.E., Used in Conjunction With a Shovel. 19.

can be loaded into trucks, onto trains or directly onto shiftable face

conveyor belts which usually stack directly onto spoil piles. Finally, maintenance plays an important role in determining the design of the machine. This is particularly important for the quick removal and re-installation of mechanical and other parts subject to wear and tear.

The various aspects mentioned above show how difficult it is to achieve a genuine comparison of quality and performance using different machines.

The most meaningful criteria for evaluating performance is the cost per cubic metre for excavating and removing the material.

2.5 The Bucket Wheel

In the U.S.A. and Germany a large number of bucket wheel designs have been developed and tested, in which improvements to the wheel design have led to better performance and, perhaps more importantly, a reduction in wheel weight. Reducing wheel weight is important because a reduction of one tonne in weight leads to a corresponding decrease of between four and five tonnes in the overall weight of the machine.

The shape of the wheel is influenced by the properties and consistency of the soils, the strength of the soil, and the output volume to be excavated. For these reasons, an optimum shape for each individual operating condition must be pursued as far as possible. The three most common wheel configurations are the cell, cell-less and semi-cell types. 20.

2.5.1 Cell Type Wheel

With the cell type wheel, as shown in Figure 2.11, the wheel continues into the appropriately shaped cell wall without a break.

The individual cell walls are joined to the cone shell of the wheel body where they are rounded. The cell contours are mostly arranged at a tangent to the rotating axis of the wheel.

The interior cell itself takes excavated materials to the point of transfer to the primary haulage system, i.e. next to the open-side of cell there are two vertical chutes down which the material is tipped and which prevents a lateral emptying of the material during the cutting and filling processes.

A cell type wheel requires a longer wheel boom for deep excavation but gives the best results, especially when operating in coarse and lumpy material. However, this design is not suitable for sticky material.

2.5.2 Cell-less Type Wheel

In the cell-less type bucket wheel, there is only a short continuation of each bucket into the wheel body, as shown in Figure 2.12, and this increases the capacity of the buckets.

The advantage of the cell-less wheel, compared to the cell type, is the very short distance covered by material in the buckets before it leaves the rotating ring space, and the almost free discharge. Thus a higher wheel speed and a consequently higher output can be achieved. 21.

FIGURE 2.11 Cell-type Bucket Wheel (After Rodgers).

FIGURE 2.12 Cellless-type Bucket Wheel (After Rodgers). 22.

... ['■//•

Slope Sheet

Bant Feeder Disc Feeder

FIGURE 2.13 Bucket Wheel Discharge Types (After Drust, Rasper, Rodgers). 23.

FIGURE 22.14 .14 Bucket Wheel Discharge ~jpesTypes Photos (After Rasper)Rasper). • 24.

The empyting process is mainly influenced by the soil properties,

i.e. grain size and shape, water content, adhesion and cohesion; the wheel

speed; wheel design; i.e. wheel diameter, chute angle, bucket shape; and

the cutting conditions, i.e. lump size and swell.

Discharge can be aided by a slope sheet, roll feeder, disc feeder,

canted wheel and a belt feeder, as illustrated in Figures 2.13 and 2.14.

2.5.3 Semi-Cell Type Wheel

The semi-cell type wheel is a compromise between the cell type and

the cell-less type wheel.

The ring space is enlarged by a semi-cell, thus reducing the load

pressure of material on the ring chute and also the wear on the ring chute.

The buckets empty onto a slope sheet fitted in front of an extra

large hub, as shown in Figure 2.15.

Compared to the other two forms of the wheel design, the semi-cell wheel has the highest degree bucket fill (Figure 2.16) , with the best

anptying characteristics, even for sticky soils.

2.5.4 Buckets and Bucket Knives

When digging sticky material, a large opening in the cylindrical

coverplate of the wheel body immediately in front of each bucket is

necessary, as shown in Figure 2.17. Thus it permits material which has

remained in the bucket after passing its highest position to drop down onto the discharge cell. 25.

FIGURE 2.15 Semi-cell Type Bucket Wheel (After Rasper).

FIGURE 2.16 Comparison of Bucket Wheel Types for Bucket Filling Process (After Rasper). 26.

FIGURE 2.17 Cover Plate of the Wheel Body (After Strzodka). 27.

Bucket edge plates are usually formed on-site using a cutting torch.

In very abrasive soils, good results can be obtained using the following

materials to reduce wear; line tax, a soft kind of rubber, plastic material

and teflon.

For sticky soils, the chain-back type bucket is now in general use.

The chain mats hanging freely in the cut-out back of the buckets are pulled

inwards by gravity and thus help to discharge the material which tends to

adhere to the bucket, as shown in Figure 2.18.,

2.5.5 Pre-Cutters

Pre-cutters (inter-cutters) are used when hard material has to be broken down into smaller fragments by a cutting process. Pre-cutters are

similar to buckets but are without backs and are spaced between the buckets.

The pre-cutters improve the running of the wheel, especially when the bucket operates in a full cutting mode when using the dropping cut method.

With these advanatages, the requirement for a larger wheel is not considered to be significant. The weight of pre-cutters (Figure 2.19) is often as high as that of buckets.

2.5.6 Ripping Teeth

The bucket teeth are useful in every type of soil, except for loose sand. They break up the cutting face material with their wedge action and thus decrease the wear on the bucket knives. It is important that teeth are easily and quickly exchangeable. 28.

FIGURE 2.18 Chain-back Type Bucket (After Rasper & Roman). 29.

BUCKET/vO

INTER

8W RADII

HORIZONTAL „0*

INTER CUT TER

BUCKET

VIEW 'A'

FIGURE 2.19 Pre-cutters (Inter-cutters) (After Rasper & Rodgers). 30.

The following features must be considered when designing bucket teeth

for excavating in hard soils; cutting geometry; long life, rigid mounting,

see Figure 2.20.

The life of bucket teeth is dependent on shape, abrasion resistance of the tooth material and the properties of soil being excavated. The bucket teeth cutting edges are generally protected against wear by means of abrasion resistant hard-face welding or hard metal tipping (tungsten carbide inserts).

In hard but homogeneous soil, moderate blasting with low energy explosives prior to digging has considerably extended the lifetime of the bucket teeth.

The position and shape of the teeth must be chosen to take into account the cutting process, e.g. specially designed strong cornered teeth, at least two side teeth and centre teeth for starting the cut, as shown in Figure 2.21.

2.6 Slewing Mechanisms

When a bucket wheel excavator is employed in a block cutting operation, the excavation process requires a continuous slewing of the superstructure.

In full block operation, the slewing mechanism provides the necessary motion for cutting the sickle-shaped segments, ensuring a constant output. In face or front operations the travel mechanism is used for this task. 31.

BUCKET

Comer Teeth

FIGURE 2.21 Position and Shape of Teeth (After Mani.) 32.

The main slewing mechanism consists of two components, the slewing

gear for rotating the superstructure and the turntable for transmitting

the loads.

The slewing drives are needed not only to slew the superstructure

during operation, but also to hold the superstructure during non-

operational periods. To achieve this, slewing gears are provided with

an infinitely variable DC motor, and three brakes (wind, service and overload brakes) . The slewing gear motor must be rated so that the

superstructure can be slewed with certainty under any operational loads,

such as inclination, wind, and a lateral force at the wheel circumference.

2.6.1 Slewing Gear

For giant and medium size machines only, load independent, infinitely variable DC motors with adjustable voltage armature control provide the optimum slewing drive.

The American bucket wheel excavators use a roller race mounted in the superstructure to transmit the vertical loads to a circular track attached to the portal. The German bucket wheel excavators use a ball race, which has become a standard component of excavator turntables, as it can transmit vertical and horizontal loads, thus eliminating the need for guides.

2.6.2 Turntables

The largest examples of this type are probably the two concentricaly arranged roller turntables on the bucket wheel excavator Sch Rs - 35-11.

Included in this design was an intermediate structure for an independently slewable discharge belt, as seen in Figure 2.22. 33.

2100 FIGURE 2.22 Turntable on the BWE Sch Rs 35 11 4 (After Rasper)

FIGURE 2.23 Ball Race Section (After Rasper) 34.

2.6.3 Ball Races

As far as can be determined, the first slewing mechanism was based

on a ball race, as illustrated in Figure 2.23.

As ball races are able to transmit both vertical and horizontal loads,

no guides are necessary for the transmission of lateral loads. The entire

inner portion of the race is available for the conveying system and the

material flow stream can be conducted through this area. At the same time,

slip rings for power and control circuits can be accommodated, see Figure

2.24.

2.7 Steel Structure

It is difficult to decide at what point structural parts should be

considered as steel structure or machine elements. It can be said that

50% of total machine weight is steel structure. The stress analysts continue their effort to achieve a reduction in the dead weight of the

structural members by using steels with higher yield strength to achieve

smaller counterweights and crawler loads. This trend is shown in Table 2.1.

2.7.1 Bucket Wheel Excavator Design Based on Spare Frames

The structure of bucket wheel excavators must be in the form of three dimensional frameworks. Horizontal forces are transmitted by horizontal braces and perpendicular forces by the main trusses to end braced frames or to the supports. 35. Rasper)

(After

Rings

Slip

Current

Lighting

and

Control

2.24

FIGURE 36.

A. Breakdown of Operating Weight

Operating Weight 8011 mt Payload and Build up 385 mt Service Weight 7 626 mt Counterweight 325 mt Vendor Components (Electrical motors, converters, conveyor belts) 48 mt Total Construction Weight 7 253 mt Construction Weight Loading Station 815 mt Construction Weight Intermediate Bridge 493 mt Construction Weight BWE 5 945 mt

B. Breakdown of BWE Construction Weight

Crawlers 1 763 mt Chassis 1 601 mt Turntable 293 mt Superstructure 1 296 mt Wheel Boom 992 mt Total Construction Weight 5945 mt

C. Breakdown of BWE Structural Weight

Supporting Structure 2511 mt Additional Structures 619 mt Machine Components 1 827 mt Electrical Components 350 mt Crawler Treads 233 mt Counterweight, belts, oil etc 405 mt Construction Weight BWE 5 945 mt

D Breakdown of Steel Structure on Intermediate Bridge and Loading Station 472 mt

Total Steel Structure of the BWE Unit 3 602 mt

i.e. 49.6% of Construction Weight of the BWE Unit

4500 TABLE 2.1 Steel Structure Weight for BVtfE Sch Rs 12 (After Rasper) 37.

All the planes in a space framework are of equal importance, and in constraint-free movement the supports must be statically determinate, i.e three supporting points with six constraints, with not more than three constraints passing through one point of intersection and not more than three constraints in one plane.

2.7.2 Bucket Wheel Excavator Structures

The bucket wheel excavator structure is composed of the substructure which carries the main slewing mechanism and is supported by two or three crawler groups and a revolving upper platform with supporting frames for the bucket wheel and discharge boons. The bucket wheel bocm and dumping boon are moved by a cable and spindle hoist respectively.

The most practical and frequently used design for the substructure is a drum-shaped membrane structure, as shown in Figure 2.25. The upper framework consists of two rigid space trusses, i.e. the bucket wheel boon and counterweight boon. Small to medium excavators are often built with

C-frame design for the upper structure, while for giant excavators a central enclosed tower is designed to transmit all the forces directly to the centre of the excavator and substructure. The centre of gravity for the excavator should remain within the ball race core circle diameter under all operational load conditions.

Figure 2.26 shows an excavator framework in both the balanced and unbalanced situations. 38.

FIGURE 2.25 Drum Shaped Membrane Structure (After Rasper and Rodgers) 39.

FIGURE 2.26 BWE Framework in Balanced and Unbalanced Conditions (After Rasper) 40.

2.8 Crawlers

Seme of the various crawler designs developed for bucket wheel excavators are shown in Figure 2.27. All these designs may be categorised in five groups, ranging frem two crawler units to twelve crawler track units per machine.

Category 1. Two crawlers of the various design possibilities, type 1-c

is preferred to 1-b, while type 1-d is considered unsuitable

for bucket wheel excavators.

Category 2. Of the three crawler type, layout 2-a, with asymmetrical

arrangement of steering crawlers, is known as the "piechsel"

(tempo) arrangement. Type 2-b shows the symmetrical

arrangement of steerable crawlers, one after the other, and

a self aligning crawler which is often driveless.

Category 3. Steerable crawler, still used for bucket wheel excavators

with six crawler tracks.

Category 4. Large units with six double crawlers.

Category 5. A four crawler unit which is steered by a speed difference

method.

All crawler units (except the two crawler type) are steered through spindles with the crawler being controlled by one or even two spindles. Sometimes hydraulic jacks are used instead of spindles.

The travel drives are reversible so that the excavator can be moved in both a forward and reverse direction. Crawlers also have to be capable of 41

4 jifh-1

HHii

FIGURE 2.27 Various Crawler Designs (After Benecke, Hillesheim and Rasper) 42.

safely transferring the load to the ground, with not only vertical loads but also a number of other dynamic effects having to be allowed for.

Design of the larger excavators usually includes three point crawler suspension. Track frames are triangularly placed and the crawlers, independently driven, are mounted in single or bogie units at the comers.

Equalizing devices in the crawlers allow uniform weight distribution.

During operation, the drives have only to be switched on for a short time period as the excavator has to travel only short distances. Special care has to be taken, therefore, that all gear elements are well lubricated.

2.9 Lubrication

Giant bucket wheel excavators can have up to 90 reduction gear boxes, with about 3000 lubricating points, yet should require only one mechanic.

Continuous research in petrochemicals has created products with good lubrication properties, such as high thin-film, pressure resistant, and a resistance to ageing. Also, both oils and greases are of such a chemical composition so as to give almost equally good lubricity and penetration in summer and in winter avoiding time-consuming oil and grease changes.

2.9.1 Lubricating Techniques

Bucket wheel excavators are generally equipped with controlled grease lubrication systems. One system is installed in the excavator substructure and lubricates the mechanical parts of the travel gear and the main roller bearing slewing rim of the supersturcture. The other system is arranged on the excavator turntable and supplies the upper hinges of the excavator. 43.

P=250mt(f) | A = 1980 cm2 p=250000/1980~125 kg(f)/cm2

oil level

drain cock

P= 2000mt(f), A = 10 £00cm2 p = 2000000/10£00 = 190 kg {11/cm2 gauge cock gauge cock

lubricated surface

FIGURE 2.28 Alternative Lubrication Systens Above - stand-oil lubrication system Below - pressurised grease lubrication system (After Rasper) 44.

For the bucket wheel gear boxes, and also for the gear boxes of belt conveyors and hoisting winches, force feed lubrication is used. For many of the excavator drives, especially for the slow-running gear stages of the crawler drives, as well as sane conveyor drives, splash lubrication is used. At ball supporting points, such as for the crawlers, stand-oil lubrication is used. The ball cap can be filled with stand-oil which will creep into supporting spherical surfaces, as illustrated in Figure 2.28.

If the ball centre is below the edge of the spherical cap, pressurised grease lubrication is preferred.

Lubrication systems operate with tuning mechanism and are interlocked with the assanbly groups. They are set to transmit air pressure generated by an on-board compressor to each of the respective grease lubrication pumps.

2.10 Material Transport

If direct spoil dumping is not carried out, sane form of transport must be used to take material away frcm the bucket wheel excavator; conveyors, trains or trucks could be used.

2.10.1 Conveyor Belts on Bucket Wheel Excavators

A bucket wheel excavator and conveyor system is best employed when removing flat-bedded homogeneous materials which can be transported to a fixed point. The drives of conveyor equipment must be so interlocked they can only start up in a specified sequence (starting at the discharge belt). When one belt fails, the drives of the previous belts must 45.

,--40' DEEP CUT °f 0R£ B00Y

HOPPER CAR EXCAVATOR

FIXED CONVEYOR

I SHIFTABLE CONV, DECK SECTION

LATERAL BRACING PLANE shifting rail Details of Shiftable .timber tie IlfCTT. -.—7 I «---- ggg Conveyor

SECTION Thru module

FIGURE 2.29 ESWE with Shiftable Conveyor System (After Griffin and Smith) 46.

automatically be switched off. For repair purposes, each belt must be capable of being operated in the unlocked state.

To achieve the lowest operating costs, the conveyors should be closely matched to the bucket wheel excavator output. In practice, this is seldom ahcieved without expensive oversizing of the conveyor system. Most conmonly a design multiplication factor of 1.3 to 1.5 of the true average hourly bucket wheel excavator output is used for proper sizing of belt.

In order to minimise the number of conveyor shifts for the main bench conveyor, it is advantageous for the bucket wheel excavator to dig two or three blocks before shifting the conveyor. This is achieved by using shiftable conveyor sections normal to the direction of advance in parallel mining, as shown in Figure 2.29. Belt shifting is effected by a bulldozer with a special arm and head attachment. The distance between the centre of the excavator and the bench conveyor must be bridged with either a short discharge bocm in combination with a separate belt wagon, or with an’ extendable bridge connected to the excavator and supported on a side crawler unit.

2.10.2 Analysis of Belt Conveyor Requirements at Transfer Points

In the excavator conveyor system, transfer points are necessary to transfer the material frcm one belt to another on the same axis, but at different speeds or inclinations. Care must be taken at these points that the flow of material drops verticaly in free fall onto the next conveyor down line, as shown in Figure 2.30. 47.

FIGJRE 2.30 Transfer Point (After Drust).

Schn.A-8 . '\J ~

Schn. C-0

FIGURE 22.31 .. 31 Possible Transfer Point Configurations (After Scharf) . 48.

Maximum inclination should, as far as possible, be not more than

Illustrated below are several solutions to transfer point problem

(Figure 2.31) , in which the receiving belt is protected by interposing a baffle band (a) or a roller gate (c). In order to eliminate the influence of the wear on rubber strips, small rubber belts can be made to circulate at the same speed as the belt (b).

In the course of the development of bucket wheel excavators, the number of belts on one unit has been reduced, thereby eliminating transfer points and short belts. Modem units have only four conveyors from the bucket wheel to the loading point; bucket wheel bocm belt, a centre belt loading to the bridge, extendable bridge belt, and the loading belt.

Good design of the transfer point in the slewing centre of the equipment is of prime importance, as the conveying direction of the feeding belt continually changes at this point in relation to the conveying direction of the belt taking the material away. This is due to the belt in the bucket wheel boon being continually slewed.

2.10.3 Conveying Path in Bucket Wheel Excavator

The present day trend in designing the conveyor path of bucket wheel excavators is characterised by the following; reduction in the number of belts, elimination of acceleration belts, and elimination of roller gratings, see Figure 2.32. This development has been made possible by the design of catenery idler as shown in Figure 2.33. Impactrollers 1 Belt 1 Belt 2 Belt 4 Belt 3 Baffle drum Impact rollers Belt 6

Belt 1 Belt 3

Reduction of Conveyor Path in BWE (After Lubrich)

FIGURE 2.33 Catenery Idler Sets (After Reman) 50.

FIGURE 2.34 Typical Bucket Wheel Boon Cross Section 51.

The short acceleration belts have to be specially manufactured. They

are made complete with sides, as an aid to straight running, and can only be put on as endless belts in the workshop.

Figure 2.34 shows a typical bucket wheel boon cross-section with arrangement of the conveyor belt. For trouble-free operation, good belt training characteristics are absolutely essential, even when transverse inclinations are present and belt is loaded off centre.

2.10.4 Truck Loading

Truck transport used in conjmotion with bucket wheel excavators is attractive for irregular excavations, selective mining and short hauls, see Figure 2.35.

In fact, operating costs for trucks can be shown to be compatible with conveyors, provided that production is not too large and the haul length does not increase beyond some fixed value.

Variable excavating rates and haul distances can be handled easily by providing sufficient spares in the truck fleet.

2.10.5 Train Loading

A strong trend has developed in Germany away from rail transport and towards conveyors.

Train loading for large outputs is achieved by using two or three rail tracks with the ccmbination of a slewing belt with two adjacent loading 52.

FIGURE 2.35 Truck Loading (After Joachim) 53.

belts running in opposite directions and bridged by a saddle chute, as

shown in Figure 2.26.

Seme advantages of rail transport which offset its high initial cost

are: good availability, low labour costs (automated), better flexibility

and built-in surge capacity in the cars.

2.11 Electrical Equipment

The continuous progress in bucket wheel excavator design makes

increasingly heavy demands on electrical technology.

The size and rating of excavator drive motors depends upon the load condition, performance specification, supply system conditions, and special consideration such as multi-motor drive operation.

Individual drives must be independently controlled. The operator does not physically operate each, as remote control and automatic sequences are more common.

The incoming supply for all giant bucket wheel excavators is at high voltage, three phase current. An important factor in the selection of the voltage to be used, however, is not only voltage available at the open-pit mine, but also the power to be transmitted.

Excavator transformers are generally of the heavy-duty oil-cooled type, and are often used as part of the bucket wheel counterweight. 54.

FIGURE 2.36 Train Loading (After Rasper) 55.

Power is fed to the machines by trailing cable frcm a fixed supply point, which is normally a switch or transformer substation. The latter

supplies the reduced voltage to the bucket wheel excavator.

The power fed to the bucket wheel excavator is by way of a slip-ring assembly mounted on the reel, as seen in Figure 2.37.

The start-up process is then initiated frcm the discharge end, the last drive to be started being that of the bucket wheel.

Automatic sequential electric interlocking of drives is necessary to prevent overfilling and damage to the conveyors. If a unit fails, all drives delivering to that point are brought to a standstill.

Emergency step switches are arranged at accessible points through the machine. Warning systems, such as wind warning for large machines, buzzers, bells, sirens, and light switches are also located throughout the excavator. 56. ^

FIGURE 2.37 BWE Cable Reel Car (After Rasper & Joachim) 57.

CHAPTER 3

AUSTRALIAN EXPERIENCE

3.1 Brown Coal

Australian brown coal deposits are primarily located in the Latrobe

Valley in Victoria and were first discovered in 1857 ( 5) , approximately one hundred and fifty kilometers east of Melbourne. The extent of these deposits is illustrated in Figure 3.1 and by Table 3.1. Coal mining by the State Electricity Ccmnission of Victoria has been largely confined

to the Yalloum and Morwell coal fields, however, development of the Loy

Yang coal field has already started (Map 3.1) .

Victoria's electricity is produced in lignite fired power stations and plans for future power generation are also based on the utilization of the lignite reserves.

3.1.1 Development of Mining Equipment for Latrobe Valley

The development of equipment for the SECV open cut mines, as shown in Figure 3.2 has been carried out in several ways. Older machines have been modified and now ones designed from experience gained in operation to give each machine optimum performance in the specialised digging conditions it encounters. In general the overburden material consists of clayey silts and silty sands and is regarded as very sticky and difficult to handle. For this reason the buckets and wheel ring space are lined with linatex, a soft rubber which prevents clogging of the bucket because of the flexibility (Figure 3.3) . 58.

ROCkhauPTon

Cl_AOSTO*£

a; co

3 s^own zo*l

VICTORIAN BROWN COAL

FIGURE 3.1 Coal Resources of Australia (After Rodgers). 59.

\ YALLOURN NORTVl Rintouls Creek Yalloum*sr YALLOURN EXTENSIONTgk4*~Bh OPEN CUT ___ \( nEWBOROUGH *g^00ff&i$b ? *Z.innS Vat Latrobe River f ^YALLOURN .*ri Railway g a/ Morwell f \ H!iliHH::H!ll|i«4llfr( POWER STATIONS / v\ river diversion \7 LEGEND I x / ^ W \ / ^MORWELL \\ ' \j ^OPEN CUT Cities 4 townships £2 {&::{»..*<§&»• N^V ! V Boundary ot main ___ L 1=3 ;It. MORWELL< )r\AA coal reserves S i{jjO^^urdenits NARRACAN1 \ Areas of coal PTH \ ,':::::::p;j dump FIELD ^YV reserves investigated1^ Traralgon Hazelwood/Zt Existing power station □ ^ Creek ^ cooling Existing open cuts m| Morwell , P000* v\//////77////////A ___ Kilometers River ^^\J^///////////J P^ned open cut [—-| r-r~A v/ffi////'//////f extensions ?! 2 3 4 5 Z/?yinnar ^/^churchill //^ Plan ol the existing open cut mines and the Loy Yang protect in the Latrobe Valley

MAP 3.1 Brown Coal Deposits in Victoria (After Darling) .

COAL TO SEAM RESOURCES OVERBURDEN THICKNE COALFIELD (million metric tons; RATIO (metre: Anglesea 400 160 1:1 30 Bacchus March 100 20 1.5:1 25 Gelliondale 1,000 200 3:1 50 Gormandale 2,400 600 1:1 200 Holey-Plains- Coolungoolun 250 Loy Yang 12,500 4,700 4:1 250 Morwell 6,700 3,300 4:1 100 Rosedale 1,400 Stradbroke 500 Yalloum 9,500 2,800 3.5:1 60

TABLE 3.1 Victoria Brown Coal Resources (After Bowen) 0

0'\ 60 .

3·8"'1

1953

1945

SHOVEL

BUCYRUS

DIPPER 1942- 1947-

120B

~?g

DREDGER)

SchRs

1977-

Rodgers)

U2_Q_

N°

1320

2·7ml

N°

1944

BUCYRUS

SHOVEL

E.C.V

(After

(

~4m

DIPPER

KRUPP

100RB

1942

RUSTON

Mines

fi1

8·8

CUt

·~em

~~~

som.

'f0

Open

<~~·9m

1953

DREDGER

~',

WOLf

208

1928

N°·

'd·l\~

Victorian

BUCKAU

for

o 19·8-

Equipnent

~.~0

DREDGER)

1976

tom

7 -

2·7

1933

1942

SchRs

N°

SHOVEL

1958

PPER

BUCYRUS

1923

1940

LCV

N°

175B

Developrent

KRUPP

:.Q_~m

FIGURE

~~,

1928

~\!

1·9

650

12-15

SHOVEL

1926

DREDGER)

1963

BUCYRUS

4 Jrr•Jm

DIPPER

1508

1922

1951

:._

.:PP

.<.R

~ 61.

Brown coal consists of partially preserved plant remains intimately

mixed and impregnated with humic substances. Brown coal hardens and its

strength increases with depth within each seam. Because of that the

gearing of the bucket wheels can be changed so that the wheel can turn at

two different speeds. The low speed is for operations in the overburden

and the higher speed for mining the coal. The design also allows for

the number of intermediate cutters to be arranged between buckets as shown

in Figure 3.3.

Each machine is responsible for the excavation of one or two levels

and follows the progress of the machine above it. The bucket wheel

excavator digs a block of coal loading it directly onto parallel face

conveyors or waiting trains, as shown in Figure 3.4. The coal is

conveyed directly to power stations located within the coal field.

3.2 Black Coal

The only application of a bucket wheel excavation for black coal

mining in Australia is at the Goonyella Mine in central Queensland.

(see Map 3.2) .

3.2.1 The Goonyella Mine

The Goonyella open pit currently operates at the greatest overburden

depth in the Bowen Basin Coalfields of central Queensland and mines

seams ranging from six to ten metres in thickness. The mine strike length

is about eighteen kilometers with the seams dipping at about five degrees.

Rehandling of the overburden becomes necessary at overburden depths »of

over forty five meters. Therefore overburden stripping at Goonyella mine has already reached the stage where draglines alone cannot operate 62.

iMTc*Mtou'f cum* CAPACITY

/ LINATEX LINING ING SPACE / capacity L return back of bucket

FIGURE 3.3 Intermediate Cutters (After Tweedley) .

FIGURE 3.4 Typical Application of a B.W.E. (After Rodgers). 63.

without very expensive rehandling of material and the mine could not

achieve the production targets required without the aid of additional

pre-stripping equipment.

Investigations of options available for this pre-stripping shewed

a continuous systan to be the best solution. Victorian and overseas

systans tend to operate in deposits much less consolidated than those

at Goonyella. Soil investigations suggested a continuous system would meet seme of the most arduous conditions yet encountered by this type

of plant. Subsequently extensive investigations have been made to

judge whether a suitably designed bucket wheel excavator could be obtained for Goonyella and in this case for drawing up the specification of the machine and associated transport and disposal units.

3.2.2 Mine Operation

At Goonyella coal is excavated by heavy duty shovel and loaded directly into trucks. The overburden, which is generally excavated by draglines, contains seme material likely to be too hard for direct excavation by a bucket wheel excavator. It could, hewever, be blasted to a lump size suitable for handling by conveyor. The majority of the overburden appears suitable for bucket wheel excavator operation but its occasional high stickiness poses severe design and operating problems. Therefore, seme extensive digging resistance tests had to be undertaken to confirm the suitability for bucket wheel excavator application. The results of these and other opinions suggested that a suitably designed bucket wheel excavator could be applied and the 64.

OPERATING MINE - OPEN CUT • • - UNDERGROUND NON-OPERATING MINE PROSPECT UNOER INVESTIGATION COAL WASHING PLANT fk. COLLINSVILLE PROJECT UNDER CONSTRUCTION RAILWAY *-*• EXPORT PORT \ BOWEN CD COAL BASIN I BASIN newlan\s® ' lance wodo e x .

WAR03 ) CREE' WELL k O e'DEE CREEK \ KEMMS V GOONYELLA tJAWALKERWSCyjH WALKER| vUy-err POITREl\ 9® DAUnU x \ ^ BASINB'AS‘N ^ BLAIR ATHOL V WJRWICH PARK V ' e GERMAN CREEK iSXKY CREEK 9 \\ j --Ol. af$EGORYV_^ CAPELUA WEST [ S'YARRABEE

-^^'^Yb^ckw^r nli^iCH^Seor— J \ J I souTH-J^siRius'l^et^ /GLADSTONt^X^

~'-V I \T\ /^LU«\\ ------^ WEST® V\.vy x BASIN \ R0LLEST0N 1 MOURaO* ^ y k,an°\T/

Kilometres MAP 3.2 Goonyella Mine in Central FIGURE 3.5 Detailed Plan of Goonyella Queensland (After Boyd). Open-Cut (After Maher).

FIGURE 3.6 Continuous Pre-stripping at Goonyella Mine (After Rodgers). 65.

decision was taken to proceed on the basis of a continuous system

However, the dragline system will remain the main stripping method

for the time being and hence the new system will have to integrate

satisfactorily with the existing one.

At present, a pilot pre-stripping operation using a bucket wheel

excavator in conjunction with a belt conveyor system and spreader is

being used at Goonyella. The bucket wheel excavator has been installed

at the northern end of the mine (Figure 3.5) and overburden has been

pre-stripped to within forty five metres of the top of the middle coal

seam and conveyed to the existing dragline spoil area for stacking.

The disposition of the existing dragline system and the new continuous system is shown diagrammatically in Figure 3.6.

3.2.3 Nature of the Goonyella Overburden

The overburden at Goonyella consists of tertiary sands and clays and minor gravels, with occasional boulder beds between five to

fifteen metres deep conformably overlying Permian sandstone. The

Permian sandstone often exhibits a well developed bedding structure with widely spaced joints as well as containing siltstone, claystone and occasionally thin coal beds with associated carbonaceous material.

The Tertiary sediments consist of high plasticity clays, poorly sorted sandy clays, clayey sands, quartzeous sands and lithic gravels.

The clays are sensitive to moisture loss which occurs rapidly upon exposure to air. This increases their initially low strengths on exposed surface. 66.

3.2.4 Bucket Wheel Excavator Selection

The first consideration in choosing a bucket wheel excavator is

the design of the wheel and its drive, to ensure it will be able to

separate the hardest of materials frcm operating face, a steady rate

of output, high reliability and without undue wear and tear. To enable

this design to proceed the most important input parameter is the digging

resistance of the overburden.

The most canmon methods of measuring digging resistances are the

0 & K wedge penetration test and compressive strength. The design of

the drive power and geometry of the wheel is based on those test

results. In addition, comparisons were made between the Goonyella deposit and other sites where bucket wheel excavators have been

successfully and unsuccessfully applied.

After all these considerations, an 0 & K 1367 Bucket Wheel Excavator was chosen for Goonyella. Table 3.2 shows the comparison between the

0 & K 1367 and other heavy duty bucket wheel excavators. A general view of the 0 & K machine operating at Goonyella is shown in Figure 3.7. 67

0 & K O & K O & K 1340 1355 1367

Athabasca Neyveli Goonyella

BW Diameter m 12.5 10.5 12.25 Bucket Capacity /, 1900 1400 1300 Ring Space Capacity l2 550 800 1000 Number of Buckets S 14 10 10 Number of Pre-cutters 0 10 10 Discharge Range buckets/min HIGH 53 65 48 LOW 26.5 65 16 Cutting Speed Range m/s HIGH 2.48 3.57 3 LOW 1.24 3.57 1 Bucket Wheel Drive kW 2 x 500 2 x 750 2 x 600 Basic Digging Force tonnes 35.0 36.4 34.7 Belt Width mm 2200 2000 1800 Belt Speeds m/s 4.7 4.5 2.5/4.2 Ground Pressure kPa 160 131 127 a. BW outreach m 21 31.3 36 b. Discharge boom outreach m 35 30 40 A. Max. height to centre of BW m 17 26 25 T Max. range below transport level m 10 8 11 Ballast tonnes 220 270 270 Mass Ready for Service tonnes 1725 2170 2230 Total Installed Power kW 3000 3750 3200

TABLE 3.2 Canparison Between Three Heavy Duty Bucket Wheel Excavators (After Rodgers).

FIGURE 3.7 0 & K 1367 B.W.E. for Goonyella Mine (After Rodgers). 68.

CHAPTER 4

EXPERIMENTAL PROGRAMME AMD TEST MATERIALS

The principal objective of this research was to compare the

results of wedge tests with other meausures of the cutability

of typical overburden rocks. In this way it was hoped that

the validity of tests conducted by bucket wheel excavator manufacturers could be established and that other tests,

involving less costly exploration drilling (150 mm diameter cores)

could be developed.

The programme of work involved firstly the design and manufacture of a wedge test apparatus of sufficient capacity and stiffness to allow the hardest samples of overburden from the

Goonyella mine to be tested. Thereafter, cores from the exploratory drilling programme at Goonyella, together with block samples recovered during the bucket wheel operations were transported to the laboratory, specimens prepared and tested in the apparatus.

Details of this work will be presented in Chapter 5.

The rock recovered from Goonyella proved insufficient in quantity and in variability to establish wide ranging relationships between the different parameters of rock strength. An additional programme of work involving mortar samples (of different mixes) was also undertaken and the physical and mechanical properties of these, together with those of the rock recovered from Goonyella, are presented later in this Chapter. 69.

The effects of specimen shape and size on the wedge test were also investigated. The standard cylinder with height equal

to diameter was examined, as were rectangular prisms and cubic

samples. The results of these tests are also recorded in Chapter 5.

The experimental programme devised to investigate these effects required sane 160 wedge tests to be conducted.

The cutability of the overburden frcm Goonyella was examined using a laboratory linear cutting rig. A simple chisel pick was chosen for these tests and cutting depths of 5, 10 and 15 mm were taken in a controlled fashion. The results of this programme will be presented in Chapter 6.

The main thrust of all this work has, however, been directed towards a correlation between the diggability of rock and the results of various test methods. In designing the experimental programmes it has been necessary to know the strength, mechanical and physical properties of the material being tested. In addition, as already stated, it was necessary to artificially produce test specimens using various mixes of sand, cement, lime and water content.

The specimens were subjected to standard and well kncwn tests such as the determination of uniaxial compressive and tensile strengths.

In addition, indirect rock testing was conducted using commercially available instruments which are designed to provide a measure of rock hardness or strength, involving the use of probes or an impact mechanism. ----J 0 70 .

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I-' ~ rt ~ h:j () ~ b N 5" t-0 ~ Hl 0 ~ 0 I-' PJ 1-'· f& ti:J ~ en }D 1--' 8 8" ttl ~ 1-'· :8 § Ul . . . . FIGURE 4.1 Plan Showing Location of Boreholes Relative to B.W.E.. Zone

lQ 71.

4.1 Physical and Mechanical Properties of the Test Material

Tests have been conducted using cores and blocks of rock and also artificial material. The cores were recovered from

Goonyella mine overburden while the block samples were taken from the face exposed by the bucket wheel excavator. Artificial samples were prepared in the laboratory using different mixes of sand, cement, lime and water. (Table 4.1).

The blocks were plastic wrapped at the time of collection and were presumed to be still at their original moisture content when they arrived at the laboratory. Samples were, therefore, kept wrapped for the majority of the time with specimens for testing being obtained from the blocks using a rotary diamond drill and air-flushing. This prevented any appreciable change in moisture content. Artificial samples were, in all cases, left to cure for eight days. On the eighth day all tests were undertaken and the average moisture content of the artificial samples was 6.99 percent. This compared favourably with the moisture contents of the block samples which were measured as 3.0, 4.05, 12.88 and 6.27 percent respectively when delivered. 72.

Table 4.1 Composition of Artificial Material Samples

Mix No. Sand (£t) Cement (£t) Water (lt) Lime (£t)

1 16 32 11 -

2 24 24 11 -

3 32 16 8 - 4 16 16 8 16 5 24 12 8 12 6 28 7 8 14 7 21 6 8 21

4.2 Test Samples

4.2.1 Test Samples from Goonyella

Rock samples from Goonyella mine have been provided in both core and block form. In all thirteen lengths of core and five block samples were received.

The core samples were all nominally 140 rrm in diameter and came from seven holes drilled in the area stripped by the

B.W.E. in 1983. The identification for each of the core samples is given in Table 4.2.

The location of each borehole with respect to the fourth strip excavated by the B.W.E. is given in Figure 4.1.

In addition to the cores, five block samples have been received.

One was fragmented during transport but the other four have been cored and also used for laboratory cutting tests. Details of the four blocks are given in Table 4.3. 73.

Table 4.2 Core Samples Received frcm Goonyella

Sample Hole Depth Rock Type Weathering No. No. (m)

C 1 21177 12.30 - 12.48 Clayey Sandstone Extreme C 2 21178 14.32 - 14.48 Caliche Soil C 3 21178 19.90 - 20.05 Claystone Extreme C 4 21175 7.02 - 7.16 Sandstone Highly C 5 21175 13.36 - 13.50 Pink Sandstone Moderate C 6 21324 16.25 - 16.42 Clayey Sandstone Extreme C 7 21325 13.06 - 13.23 Clayey Sandstone Extreme C 8 21325 18.75 - 18.91 Pink Sandstone Moderate C 9 21325 23.03 - 23.22 Sandstone Fresh CIO 21327 14.92 - 15.09 Sandstone Moderate Cll 21327 19.66 - 19.81 Sandstone Slight C12 21327 9.51 - 9.70 Sandstone Highly C13 21838 15.80 - 16.09 Sandstone Moderate

Table 4.3 Block Samples from Goonyella

Block No. Identification Location Obtained

Bl None Strip 4, Chainage 1917 m

B2 None Strip 4, Chainage 2090 m

B3 Yellow Sandstone Strip 4, Chainage 2129 m

B4 Pink Sandstone Strip 4, Chainage 2000 m

4.2.2 Artificial Rock Samples

Compressive, tensile and wedge test samples were all poured from a single batch of each mix. After allowing the specimens to cure for eight days all tests were undertaken within few hours. 74.

4.3 Compressive Strength

The strength of a specimen cannot be defined by a single

appropriately dimensioned numerical value. Heterogeneity always

exists in small or large measure and therefore a strength value

must be statistically qualified. Furthermore the strength of a

specimen is greatly influenced by the size and to a lesser extent

the shape of the test specimen. Test procedures should also be

defined since the testing machine platens and the rate of

applying the load can have a major influence on measured strength.

It is necessary therefore to undertake a number of tests

under standardised conditions to provide a statistically reliable

result. The widely accepted standard is to use cylinders

having a length to diameter ratio of 2.5, to use dry steel platens,

and to apply the stress at the nominal rate of 100 p.s.i. 2 (0.69 MN/m ) per second. These standards of procedure were adopted.

Specimens nominally 57 mm in diameter and 140 mm long were

prepared by drilling the blocks and sawing the cylinders to

length or by pouring the artificial material and finally

grinding the specimen ends to provide a fine finish. Because

of the need to conserve the limited amount of rock available

from Goonyella only three compressive test specimens were prepared from each block. Where structure was apparent the

coring took place perpendicular to the bedding plane.

For the artificial samples ten compressive specimens were prepared.

The results of all compressive tests are given in Tables 4.4 and 4.5. 75.

Table 4.4 Uniaxial Conpressive Strengths of Goonyella Block Samples

Specimen Dimensions Block Specimen Failure Compressive Load Strength No. No. Diameter Length kN MPa mm irm

Bl Bl/1 141 57.4 5.47 2.11 Bl/2 140 57.5 6.67 2.57 Bl/3 142 57.4 4.44 1.71 Mean 5.53 2.13

B2 B2/1 145 57.5 53.8 20.7 B2/2 143 57.5 46.5 17.9 Mean 50.2 19.3 1

B3 B3/1 126 56.7 2.3 0.91 B3/2 140 56.9 4.3 1.69 B3/3 130 56.8 3.7 1.46 Mean 3.4 1.35

B4 B4/1 145 57.5 44.5 17.1 B4/2 145 57.5 43.5 16.8 B4/3 146 57.5 35.4 13.6 Mean 41.1 15.8 ______76.

Table 4.5 Uniaxial Compressive Strengths for Artificial Samples

f Mix Specimen Specimen Dimensions | Failure Compressive No. No. Load (KN) Strength Length Diameter MPa

1 1 140 55 56 23.58 2 139 55 55 23.16 3 139 55 76 32.00 4 138.5 55 78 32.80 5 139 55 69 29.00 6 139.7 55 68 28.63 7 139 55 63.5 26.74 8 139 55 60 25.24 9 139 55 75 31.58 10 139.5 55 61.7 25.98 Mean 66.2 27.87

2 1 141 55 44.2 18.61 2 140 55 58.2 24.51 3 140 55 57.5 24.14 4 140.5 55 48.8 20.55 5 140 55 43.3 18.23 6 139 55 71 29.90 7 138.8 55 73.3 30.87 8 140 55 44 18.53 9 139.3 55 43 18.10 10 137.6 55 58.5 26.63 Mean 54.18 23.00

3 1 139 55 42.4 17.85 2 138.7 55 43.9 18.48 3 139 55 53 22.32 4 139.5 55 42 17.68 5 139 55 42.4 17.85 6 139 55 47.4 19.96 7 140 55 34 14.31 8 139 55 41.9 17.64 9 140 55 39.9 16.80 10 140 55 41 17.26 Mean 42.89 18.01

4 1 139 55 48 20.21 2 139.2 55 53.6 22.57 3 140 55 49.3 20.76 4 140 55 46.2 19.45 5 138.5 55 50.3 21.18 6 139.3 55 46.2 19.45 7 139.7 55 55.2 23.24 8 139.3 55 46.7 19.66 9 139 55 48.1 20.25 10 140 55 40 16.84 Mean 48.36 20.36 , — / ______l 77

Table .5 Cont'd.

Mix Specimen Specimen Dimensions Failure Compressive No. No. Load (KN) Strength Length Diameter MPa

5 1 139 55 34.2 14.40 2 139.5 55 27.4 11.54 3 140 55 25 10.52 4 140 55 22.7 9.56 5 140.5 55 28.2 11.87 6 140.4 55 23.1 9.73 7 138.5 55 31 13.05 8 140.1 55 29.5 12.42 9 139 55 33.8 14.23 10 139.2 55 31.5 13.26 Mean 28.64 12.05

6 1 139 55 17.2 7.24 2 138.9 55 17.8 7.49 3 138.5 55 15 6.32 4 140 55 14.4 6.06 5 138.5 55 ‘ 16.3 6.86 6 138.7 55 16.9 7.12 7 139.1 55 17 7.15 8 138 55 20.3 8.55 9 139.6 55 14.2 5.98 10 139.7 55 13.8 5.81 Mean 16.29 6.85

7 1 138.5 55 11.8 4.97 | 2 139.2 55 10.8 4.55 3 140 55 11.1 4.67 4 140 55 11 4.63 5 139.8 55 12.1 5.09 6 140 55 12 5.05 7 140.2 55 10.2 4.29 8 139.2 55 11.5 4.84 9 139.5 55 12.6 5.30 10 139.1 55 11.2 4.71 Mean 11.43 4.81 ______1 78.

4.4 Tensile Strength

The most canmon and convenient method of determining the tensile strength of specimens is the Brazilian Disc Method.

Discs 57 mm in diameter and approximately 30 mm thick were prepared. The tensile test results are given in Tables 4.6 and 4.7.

Table 4.6 Uniaxial Tensile Strengths - Brazilian Disc Test of Goonyella Block Samples

Specimen Dimensions Block Specimen Failure Tensile No. No. Load Strength Thickness Diameter KN MPa mm mm

Bl Bi/4 30.5 57.1 0.34 0.12 Bl/5 28.5 57.4 1.35 0.52 Bl/6 26.3 57.2 0.62 0.26 Mean 0.77 0.30

B2 B2/3 30.0 57.5 5.2 1.92 B2/4 31.0 57.5 5.3 1.89 B2/5 30.0 57.5 5.4 1.99 B2/6 30.5 57.5 4.4 1.60 B2/7 31.1 57.5 6.1 2.18 Mean 5.3 1.92

B3 B3/4 27.2 57.0 0.9 0.37 B3/5 28.4 57.2 0.4 0.16 B3/6 30.9 56.9 1.09 0.40 B3/7 30.0 57.0 0.86 0.30 B3/8 30.0 57.0 0.90 0.34 Mean 0.83 0.31

B4 B4/4 30.3 57.5 5.7 2.08 B4/5 30.9 57.5 6.7 2.41 B4/6 32.1 57.2 7.4 2.57 B4/7 29.9 57.5 5.9 2.19 B4/8 28.7 57.4 5.2 2.01 Mean 6.2 2.25 ______1 ■ 79

Table 4.7 Uniaxial Tensile Strength - Brazilian Disc Test of Artificial Samples

Mix Specimen Specimen Dimensions Failure Tensile No. No. Load Strength Thickness Diameter KN MPa mm mm

1 1 28 55 7.3 3.01 2 30 55 7.35 2.80 3 32 55 8.8 3.18 4 33 55 9.8 3.44 5 32.5 55 8.8 3.15 i 6 33.5 55 8.5 2.94 7 30.5 55 7.35 2.79 8 30.5 55 6.3 2.39 | 9 31.5 55 8.4 3.08 10 33 55 9.2 3.23 Mean 8.18 3.00 1 . 2 1 31.2 55 7.2 2.67 2 34 55 6.8 2.31 3 32 55 6.4 2.31 4 33 55 6.8 2.38 5 29.5 55 5 1.90 6 32 55 5.8 2.09 7 34 55 5.8 1.97 8 34.5 55 7 2.34 9 34 55 5.8 1.97 10 33 55 6.8 2.23 Mean 6.41 2.23 r" 3 1 29 55 5.2 2.07 2 29.5 55 5.4 2.12 i 3 34 55 6.8 2.30 4 31 55 5.3 1.98 5 36 55 5.2 1.67 6 30 55 5.5 2.12 7 33 55 6.5 2.28 8 39.2 55 7 2.07 9 33.5 55 6.6 2.28 10 32.5 55 5.6 1.99 Mean 5.91 2.08

4 1 32.5 55 8.7 3.10 2 32.5 55 8 2.85 3 34 55 9.5 3.23 4 32 55 6 2.17 5 28.5 55 6.1 2.48 6 32.8 55 8 2.85 7 33 55 8.75 3 8 34.5 55 8.95 3 9 32 55 7.15 2.59 10 31 55 8.8 3.28 Mean 7.99 2.94 7 • • •/ _ 80

Table 4.7 Cont'd.

Mix Specimen Specimen IDimensions Failure Tensile No. No. Load Strength Thickness Diameter KN MPa mm mm

5 1 33 55 5.3 1.86 2 30.5 55 4.6 1.75 3 33.1 55 5.5 1.92 4 32.5 55 4.65 1.67 5 29.3 55 4.4 1.74 6 29.2 55 4.1 1.63 7 34 55 5.1 1.70 8 31 55 4.7 1.75 9 31.7 55 4.9 1.79 10 32.5 55 4.95 1.76 Mean 4.82 1.757

6 1 30.3 55 3.45 1.32 2 32.5 55 4.45 1.58 3 32.6 55 3.50 1.24 4 34.4 55 3.95 1.33 5 33.2 55 4.4 1.53 6 33.9 55 4.4 1.50 7 35.8 55 4.35 1.41 8 34.2 55 4.10 1.14 9 30.5 55 3.7 1.4 10 31.5 55 3.55 1.3 Mean 3.98 1.39

7 1 30.6 55 3.2 1.03 2 34.3 55 3.32 1.12 3 36.25 55 3.5 1.10 4 33.3 55 3.05 1.06 5 34 55 3.25 1.11 6 32 55 3.275 1.19 7 29 55 3.425 1.36 8 32 55 2.8 1.01 9 30 55 3.2 1.23 Mean 3.224 81.

4.5 Bulk Density

The bulk density of the four rock types and the artificial material was determined by weighing cylinders of each rock and calculating the volume from their dimensions. Results are presented in Tables 4.8 and 4.9.

Table 4.8 Bulk Density of Goonyella Block Samples

Block Specimen Specimen Dimensions Weight Density No. No. Length Diameter g t/m3 mm mm

Bl Bl/7 35.0 57.5 178.3 1.96 Bl/8 25.0 54.3 112.7 1.95 Bl/9 31.0 55.0 133.8 1.82 Mean 1.91 ! * B2 B2/8 31.5 57.5 186.3 2.28 B2/9 30.0 57.5 185.3 2.37 Mean 2.33

B3 B3/9 24.3 57 120.2 1.94 B3/10 23.0 57 112.8 1.92 B3/11 22.8 57 111.8 1.93 Mean 1.93 -.. B4 B4/9 28.0 57.5 166.6 2.29 B4/10 27.0 57.5 162.0 2.31 B4/11 35.5 57.5 210.3 2.28 B4/12 26.25 57.5 159.0 2.33 Mean 2.31 82.

Table 4.9 Bulk Density of Artificial Samples

Mix Specimen Specimen dimensions No. No. Weight Density 1 • Length Diameter g 1 t/m3 mm mm

1 1 32 55 151.3 1.99 2 30.5 55 144.1 1.99 3 30.5 55 144 1.99 Mean 1.99

2 1 34 55 : 160.3 1.98 2 34 55 ! 157.8 1.95 3 34.8 55 166.1 2.01 Mean 1.98

3 1 29.5 55 134.9 1.93 2 31 55 143.9 1.95 3 30 55 138.3 1.94 Mean 1.94

4 1 28.5 55 133.9 1.98 2 32 55 148.1 1.95 3 31 55 145.7 1.98 Mean 1.97

5 1 29.3 55 136.0 1.95 2 29.2 55 136.1 1.96 3 31 55 142.9 1.94 Mean 1.95

6 1 34.4 55 141.2 1.73 2 33.9 55 142.6 1.77 3 32 55 137.6 1.81 - Mean 1.71

7 1 34.3 55 151.9 1.86 2 36.8 55 162.3 1.86 3 34 55 152.5 1.89 Mean 1.87 .______83.

4.6 Shore Hardness

This test is sometimes quoted as a measure, albeit incomplete, of rock cutability. The instrument used is the Shore Scleroscope which is illustrated in Figure 4.2.

Its action depends on dropping a small mass onto 2 prepared rock surface from a fixed height and measuring its rebound.

A tentative correlation is claimed between Shore Hardness (H) and Unconfined Compressive Strength (C.S.) thus

C.S. = 20,000 log H - 18,000 where compressive strength is in p.s.i. units.

The value of this test is at best a cursory indicator of rock strength with the attendant benefits of simplicity and speed of use. The Shore Hardness was obtained by testing three specimens from each block and mixture. The specimen were 57 mm in diameter and approximately 30 mm thick with one plane surface prepared by grinding to a smooth finish. A minimum of 25 replications were undertaken on each surface.

Samples prepared from Block 3 and some core samples could not be used, however, since the clay content was such that the dropping mass penetrated the rock surface and failed to rebound.

No results could, therefore, be obtained for Block 3. The remainder of the results are presented in Tables 4.10, 4.11 and 4.12. .84.

FIGURE] 4.2 Shore Scleroscope. Table 4.10 Shore Hardness Results of Goonyella Core Samples

Sample No. Hole No. Depth (m) Average Shore Hardness

Cl 21177 12.30-12.48 _1 C2 21178 14.32-14.48

C3 21178 19.90-20.05 _1

C4 7.02- 8.16 j 21175 -1 C5 21175 13.36-13.50 40.1

C6 21324 16.25-16.42 -1 _1 C7 21325 13.06-13.23

C8 21325 18.75-18.91 33.0

C9 21325 23.03-23.22 33.9 _1 CIO 21327 14.92-15.09

Cll 21327 19.66-19.81 42.6 _1 C12 21327 9.51- 9.70 _1 C13 21838 15.80-16.09

1 - Too soft for shore hardness test. 86.

Table 4.11 Shore Hardness Results of Goonyella Block Samples

Block No. Specimen No. Average Shore Hardness

Bl Bl/10 26.3 Bl/11 25.3 Bl/12 26.7 Mean 26.1

B2 B2/10 36.6 B2/11 35.1 B2/12 39.5 Mean 37.1

B4 B4/13 33.4 B4/14 33.1 B4/15 35.4 Mean 33.7

Table 4.12 Shore Hardness Results of Artificial Samples

Mix No. Specimen No. Average Shore Hardness

1 1 68.7 2 67.8 Mean 68.2

2 1 63.3 2 67.3 Mean 65.3

3 1 58.4 2 60.2 Mean 59.3

4 1 54.4 2 54.1 Mean 54.2

5 . 1 49.1 ^ 2 49.6 Mean 49.3

6 1 36.6 2 39.0 Mean 37.8

7 1 28.4 2 28.8 Mean 28.6 87.

4.7 Cone Indenter Test

This pocket instrument was developed for making rapid cursory assessments of rock hardness. It uses a pointed tungsten carbide probe which is forced into a small specimen under a load which is gradually increased up to affixed level. The load is provided by a spring leaf, the measured deflection of which determines the ultimate applied load.

(Figure 4.3).

Cone Indenter Hardness is defined as: Penetration

The scope of the test is enhanced by the use of two standard levels of load. The deflection for soft rocks is specified as 0.015 in. and for hard rocks as 0.025 in.

Tables 4.13 to 4.15 show cone indenter test results for core, block and artificial samples respectively. 88.

FIGURE 4.3 Cone Indsnter Test Equipment. 89.

Table 4.13 Cone Indenter Test of Goonyella Core Samples

Sample Depth Deflection Penetration Average Code No. mm in. in. Indenter No. _1 Cl (21177) 12.30-12.48 - - _1 C2 (21178) 14.32-14.48 - - _1 C3 (21178) 19.9 -20.05 - - _1 C4 (21175) 7.02- 8.16 - - C5 (21175) 13.36-13.50 25 59.5 0.420 _1 C6 (21324) 16.25-16.42 - - _1 Cl (21325) 13.06-13.23 - - C8 (21325) 18.75-18.91 15 36.8 0.407 C9 (21325) 23.03-23.22 25 67.2 0.372 _1 CIO (21327) 14.92-15.09 - - Cll (21327) 19.66-19.81 25 38.66 0.646 _1 C12 (21327) 9.51- 9.70 - - _1 C13 (21838) 15.8-16.09 —

- Too soft for cone indenter test.

Table 4.14 Cone Indenter Test of Goonyella Block Samples

Block No. Deflection Penetration Average Cone 1 in. in. Indenter No. ! B2 25 53 0.47 B3 81.5 0.18 15 - B4 25 52.1 0.48 1______Table 4.15 Cone Indenter Test of Artificial Samples

Mix No. Deflection Penetration Average Cone in. in. Indenter No.

1 25 36.16 0.69 2 25 37 0.67 3 25 37.8 0.66 4 25 39.2 0.64 5 25 52.4 0.48 6 25 58.7 0.43 7 25 59 0.42 91.

CHAPTER 5

DEVELOPMENT OF THE WEDGE TEST

Manufacturers of bucket wheel excavators have developed, and now place reliance in, several indirect methods of assessing the resistance of any ground to excavation by their machines.

The principal method now used is a wedge penetration test.

5.1 Determination of Digging Resistance

The digging force exerted by the cutting teeth of a bucket has three orthogonal components -

a. The tangential force, acting on the tooth in-line with

its instantaneous direction of travel. b. The lateral force, normal to the connecting line between

bucket wheel axis and the excavator slewing axis. c. The forward thrust force, acting radially to the tooth

or cutting circle.

The tangential force determines the torque requirements of a bucket wheel drive. Therefore, this force is the most important factor for the determination of the digging power and is generally known as the cutting or digging force. 92.

Garbotz (2) in 1927 was the first to publish the calculation of digging pcwer requirements for bucket chain excavators, in which he postulated the equation:

Qeff X* Ndig _ iQ2 [kW]

Ndig digging power

Qeff the effective hourly output of material "in situ"

X* = a resistance coefficient which

characterizes the kind of soil

Wagon (2) in 1939 designated the power required for digging one bank m^/h of soil as the "specific bucket wheel power requirement". After subtraction of the specific lifting power requirement (required to lift the material in the wheel), the "

"specific digging power" can be obtained.

Wimtzki (2) stated in 1963 that the effective output, Qeff can be determined fran the following equation

= n. Qth [bank m~Vh] et£ 1 + te/ta t

when te = sum of all setting up and downtimes

t = actual excavating times cl f = swell 93.

n = reciprocal of 1 + t /t S cl 3 Qth = theoretical output (= 60 js) [m /h loose

material]

J = nominal capacity of bucket [m ] = I = X ^

S = number of bucket discharges per minute

I = geometrical volume of single bucket [m ]

Ii = filling space of annular ring of cell-less

bucket [m^]

X = ring fill coefficient

On the other hand, Rasper (2) calculated the minimum digging

power of the bucket wheel, as follows

k Qth S nf 0.00584 % R [kW] dig, Min

where n overall efficiency referred to the

bucket wheel shaft

Qth theoretical output [m^/h lox>se material]

nf bucketfill %

f amount of swell

nf/f leading to the effective output in [bank m^]

S number of bucket discharges per minute

R radius of cutting circle of the bucket wheel [m]

k specific digging resistance [kg(f)/CM]

The last equation suggests that the relationship between digging power and hourly output is not linear, but a parabolic function (2). 94.

Since then there have been considerable differences of opinion

among researchers as to the best reference unit for the

tangential or digging force acting at the cutting circle of a

bucket wheel. The following parameters could be used:

A - The specific digging force referred to 1 an of

the mean cutting tooth length of the sickle cut.

This parameter is usually expressed in units of

kg(f) /cm.

B - The specific force fA referred to 1 cm^ of the

mean slice cross-section of the sickle cut and

expressed as kg(f)/on2,

and

C - The specific digging force f^L for 1 cm^ of the mean

excavated slice section referred to 1 cm of the

cutting tooth length, by the following relationship

fAL = tkg(f)/an3]

5.2 Ground Diggability Determination

The bucket wheel designer has to provide machines for digging

overburden and minerals whose digging characteristics may be

considerably different frcm those in which previous experience

has been obtained. This problen increases for bucket wheel 95.

excavator applications in areas where specific or detailed

information on ground conditions does not exist. Very often

the auxiliary methods used in classifying overburden digging

strength, such as measurements with a cylinder strength meter

and pocket penetrometer (plasticity needle and spring wedge

balance) no longer suffice or only give inconclusive

information on the cutting resistance to be expected. For this reason, the Lubeck Works of Orenstein and Koppel developed a method of determining cutting resistance of the bucket tooth in the laboratory. This test relies on the penetration of a simple wedge into a block or core of the material to be excavated.

Orenstein and Koppel make use of a 75 mm wedge, having a 5 mm flat machined at this apex. The wedge is attached to the upper head of a tensionmeter and is inserted into the material (test sample). The splitting force is read-off from the test machine gauge.

5.3 Detailed Design of UNSW Wedge Test Apparatus

A similar wedge test apparatus was designed at the School of Mining Engineering at The University of New South Wales.

The load required to split a 150 mm diameter sample of a strength typical of overburden capable of being excavated by a bucket wheel excavator was estimated to be in the region of

30 kN. A design based on a maximum loading of 50 kN was therefore adopted. The basic design and components of apparatus are shown in Figure 5.1. 96..

ITEM PART NAME QTY MAT ITEM part name QTY MAT T>Lfc»AwC£ SCALE 1:3 * ^ mm O* 1 HYDRAULIC RAM 1 5 WEDGE 1 VVCLLAJU 1 C.O 1 2 TOP PLATE 1 MS 6 ROD 4 MS SCHOOL OF MA( 3 NUTS 16 M S 7 SAND BOX 1 GSM MINING FNG ^HINt UNS W 4 THREAD COUPLING 1 MS 8 BOTTOM PLAT E 1 MS DRAWN A. INAL

FIGURE 5.1 General Plan of Wedge Test Apparatus 97.

5.3.1 Design Parameters

The apparatus consists of a framework capable of containing

the force exerted on the test sample by a hydraulic ram and wedge.

Adjustment for different heights of specimen is provided

by the screwed rods (itan 6, Figure 5.1) which were 19 mm in

diameter to provide seme lateral stability. The wedge force is

provided by an Enerpac RC53 ram which has a 5 tonne capacity

and stroke length of 90 mm. At maximum loading each rod will,

therefore, have a tensile load of 12.5 kN and since the material

used was mild steel with a maximum allowable stress in tension

and bending of 140 MPa, the factor of safety for the apparatus

can be calculated as follows.

Load _ 12.5x4 Stress in each rod Area TT 19 -

= 44.1 N/nm^

= 44.1 MPa

140 Factor of Safety 3.17 44.1

The other critical component in the design, which has to withstand the imposed stresses, is the baseplate and this

is likely to bend. Making assumptions that

1) The baseplate is loaded by a concentrated

load of 50 kN on the centreline. 98.

2) The wedge can rotate, therefore the loading

can occur in any direction.

3) Pure bending is assumed, rather than plate

behaviour (i.e. a conservative design).

4) The neutral axis is a distance y above the

base

k------300 ------H

then

(2 x 13 x 50 + 300 x 13)y = 13 x 50 x 25 + 300 x 13 x 56.5

16250 + 220350

236600 45.5 mm y 5200

2nd mcment of area about NA, Im is given by

o 13 X 50J l.io = 2\—tt:---- > + 13 x 50 x 20. 52

300 x 13- 2 + + 300 x 13 x 11

1343 983 mm

The bending moment 2500 kN mm

BM.y _ 2500 x 45.5 x 1000 .*. Bending Stress Im 1343 983

= 84.6 MPa

This gives a safety factor of 1.65 99.

The final aspect of the design was to check that the rods would not pull through the base plate. The cross-flat distance of 19 mn nuts was measured at 36 mm.

shear area is approximate tt.36. thickness of baseplate

= tt x 36 x 13

= 1470 rnn2

Load = 12.5 kN

Shear stress = = 8.5 MPa

This is very much smaller than the shear strength of mild steel (approximately 110 MPa).

5.3.2 Manufacture of the Apparatus

The detailed drawings of the wedge test apparatus are, for the sake of canpleteness, included as Figure 5.2 to 5.5.

The apparatus was constructed by the Applied Science Workshop and is photographed in its finished form in Figure 5.6.

5.4 Wedge Test Results

Wedge tests were undertaken on specimens cored frcm the block samples as well as on the core received frcm Goonyella.

After sawing the core ends square and to a length approximately 100

ff 1 —1—1—f— Vi/

-4>-

ITEM PaPTT name OTY MAT tO l£ s amCE SCALE • Q5C ON 1:3 2 1 TOP PLATE 1 MS □HfNSJONS wedge "test SCXXX OF MACHINE MINING FNG UNSW DRAWN A. INAL

FIGURE] 5.2 Detail of Top Plate 101

1 ®

ITEW cfcRT FART NAME QTY MAT TOlEHHNCE scale 1:3 ;050 oh 3 16 NUT 1 M S DJMEMSIoa WEDGE TEST 4 2 THREAD COUPLING 1 M S soooc or 5 1 WEDGE 1 MACHINE 6 4 ROD 1 MS UNSW DRAWN A. INAL

FIGURE 5.3 Detail of Wedge and Connecting System. 102

ITEM f*RT PART NAME DTY MAT 'OlEKanCE SCALE 1:3 *• 0.50 0 N 7 1 SAND BOX 1 SSM vfSi 0*5 YV Q UUC 1 a o SCHOOL OF MACHINE MINIMS FHT. ______UNS W DRAWN A. INAL

FIGURE 5.4 Detail of Sandbox 103

part name SCALE BOTTOM PLATE '.OB » DIMENSIONS WEDGE TEST MACHINE

UNSW A. INAL

FIGURE 5.5 Detail of Bottcm Plate 104.

• I ·:' .'1 ' . ~ ... . ~, · ~ \ ..

~~:-~: ~~~. ~ ~ ~ ~~ · ~ - ~ ~~ ------··~ -- ·-- .=---... :::. . . \ ..

:.. • -~ .d ... ,. ~·;,_ J~ · . -.~ ...... , ;,.. ___ ~ _:.;a._ -- -~

.:~

FIGURE 5.6 General Vie.NView of Wedge Test Apparatus. 105.

equal to the diameter, the cores were placed in the sand tray

on the lower platen of the apparatus. When the height of the

specimen was found to be insufficient to allow the wedge to

penetrate within its 90 mm stroke, the position of the top

platen was altered using the screwed rods to reposition it.

The simulated overburden material cast frcm mixtures of

sand, conent and lime, as detailed in Chapter 4, was also tested.

The stronger mixes proved too hard for testing using the wedge,

while the intermediate strength samples required the use of an

Avery 50 tonne Universal Test Machine to supply the required

load as shown in Figure 5.7. The weaker mixes, being more

representative of the overburden strengths commonly excavated by

bucket wheels were tested using the wedge apparatus, in the same

as for Goonyella samples.

After initial contact between the wedge and the top of the

specimen, pressure on the wedge was slowly increased using

the hand hydraulic pump. Pressure in the hydraulic system was monitored by a recording gauge, giving a reading of the maximum pressure achieved at the time of specimen failure. The area over which the specimen failed was obtained by tracing the shape of the fracture plane onto paper and using a planimeter.

Results of the wedge tests are given in Tables- 5.1, 5-2:and 5.3^ 106

FIGURE 5.7 Avery Test Machine with Wedge 107.

Table 5.1 Wedge Test Results for Goonyella Core

Specimen Dimensions Specimen Failure Failed Rock No. Load Area Strength Length Diameter kN cm2 N/an2 mm mm

Cl 138 143 7.5 98 76.5

C2 - - - - _ *

C3 - - • - _ * C4 125 145 6.5 36.3 179.3 ** C5 110 145 48.8 143.0 316.88 C6 140 138 1.2 144 8.3

C7 - - — - - ** C8 110 140 13.3 167 77.84 C9 150 140 31.7 140 226.1 ~ CIO 150 140 6.5 224 29.0 Cll 145 142 19.0 208 91.3 Cl 2 150 140 1.5 127 27.6 Cl 3 130 140 14.0 189 74.0

Insufficient rock to conduct test Pink sandstone - strength beyond capability of wedge apparatus therefore Avery Canpressive test machine was used Table 5.2 Wedge Test Results for Goonyella Blocks

Specimen Dimensions Failure Failed Rock Block Specimen Load Area Strength No. No. Length Diameter kN arr2 N/cm^ mm mm

B2 B2/13 150 144 31.9 154 207

B3 B3/12 154 144 4.0 214 19.0 B3/13 151 144 4.4 219 19.0 Mean 4.2 217 19.5

B4 B4/16 149 144 28.5 214 133 B4/17 149 144 26.1 207 126 Mean 27.3 211 130 109

Table 5.3 Wedge Test Results for Simulated Overburden Material

Block Specimen Specimen Dimensions Failure Failed Rock No. "no. -LKJdU. Area Strength Length Diameter kN cm2 N/crn^ mm mm

3 1 152 154 48.5 240 202.08 2 150 154 51 235 217.02 3 150 154 55.5 233 238.19 4 150.5 154 50 236 211.86 5 150 154 56 237.5 235.78 6 151 154 52 240 216.66 7 150 154 56 231 242.42 8 145.5 153.2 54.5 230 236.95 9 149 154 57 246 231.70 10 150 154 54.25 245 221.42 Mean 53.47 237.35 225.41

4 1 150 154 62.4 233 267.81 2 150 154 60.3 240 251.25 3 148 154 61.9 239.5 258.45 4 152 154 60.0 240 250 5 149 154 64.6 237.5 272 6 152 154 64.9 239.5 270.9 7 149 154 64.8 230.5 281.12 8 151 156 67.7 249.5 271.13 9 150 154 61.5 232.5 221.52 10 150 154 48 233.5 205.56 Mean 61.61 237.55 255.0

5 1 150 153.8 48.8 240 203.3 2 152 154 43.8 236.5 185.2 3 150 154 49 239 205 4 150 154 45.7 236.5 193.23 5 149 154 44.9 233.5 192.29 6 147 154 46.5 230 202 7 150 154 47.1 240 196.2 8 150 154 49.5 241 205.3 Mean 46.91 237.06 197.81

/ Table 5.3 cont

Block Specimen Specimen Dimensions Failure Failed Rock No. No. Load Area Strength Length Diameter kN cm9 N/cm^ mm nm

6 1 150 154 22.5 241 93.36 2 149 153.8 23 233 96.64 3 148 154 22.1 227.5 97.14 4 150 150 23.2 222 104.50 5 148 154 21.7 237.5 90.91 6 150 154 23.5 234.5 100.21 7 148 154 21.1 227 92.95 8 150 154 22.58 231 87.45 9 150 154 21.4 231.5 92.44 Mean 22.34 232.23 96.18

7 1 150 153.9 16.3 233.5 69.81 2 146 154 17.6 227 77.53 3 150 154 17 236 72.03 4 150 153.6 20.3 228 89.05 5 150 154 19.4 229 84.71 6 150 154 17.5 243 72.01 7 150 153.7 19 233.5 81.37 8 150 154 18.2 225 80.89 9 151 154 19 234.5 81.02 10 150 154 18.2 235.5 77.28 Mean 18.25 232.5 78.57 111.

It can be seen frcm these results that the failed area

can vary considerably. Two distinct failure mechanism occurred

provided the specimen was intact and without inherent planes of

weakness. In the ideal test the cylindrical specimen should

split along its axis, as shown in Figure 5.8. However in strong

specimens the characteristic ccmpressive test shear failure,

as shewn in Figure 5.9, was sometimes recorded.

5.5 Effect of Specimen Size and Shape on Test Results

Althouth the majority of bucket wheel excavator manufacturers

have adopted 150 mm diameter cores as the standard wedge test

specimen, there are advantages in considering other sizes and

shapes. Large diameter (150 mm) holes are expensive to drill and

tend to have a poor recovery rate for intact cores. Smaller

diameter holes could be spaced at closer intervals without

increasing the overall cost of the exploration operation. At sane

sites where the overburden is exposed and where wedge tests are undertaken to log the strata being excavated, it has become common practice to saw cubic samples frcm the exposed face.

However, there is very little mention in the literature of comparisons between tests conducted on different size or shape specimens.

A programme of tests has been conducted to investigate size and shape effects on wedge test results. Artificial material 112. Sample.

Breakage Ideal

5.8

FIGURE 113.

FIGURE 5.9 Shear Failure in Strong Specimens 114.

was used for this work and the mixes chosen were number 5,

6 and 7. Those three mixes gave wedge strengths in the same

range as the natural overburden material obtained from Goonyella,

i.e. the yellow and pink sandstones were also weak enough to

be tested in the wedge test apparatus, without recourse to

the Avery test machine. The results obtained fran tests using

different diameter cylinders, each with a diameter to height

ratio of one, are presented in Table 5.4.

Rectangular prism specimens were also prepared to give

diagonal dimensions on the test face equal to the specimen height.

In addition, seme fourteen true cubes having side dimentions of

150 mm were prepared to compare with 150 mm diagonal prisms and

the 150 mm diameter cylindrical cores. The full test results are presented in Table 5.5. These results are also presented graphically in Figures 5.10, 5.11 and 5.12.

Typical samples showing the failure plane are shown in

Figure 5.13. Table 5.4 Effect of Specimen Size on Wedge Test Results

Area of Specimen Dimensions Load at Material Sample Failure Failure Strength No. Diameter Length Plane mm mm kN (cm2) N/cm2 1 50.05 51.5 6.97 27.45 253.91 2 50.05 49.5 6.82 24.72 275.89 M 3 50.06 52.5 7.26 26.8 270.89 4 50.05 51 7.40 27.03 271.06 I 5 75.07 76.5 13.64 60.26 226.35 6 75.05 76.22 11.15 51.83 215.13 X 7 75.08 77.2 14.92 60.26 247.59 8 75.07 76.5 13.24 58.96 224.56 5 9 103.2 101.5 23.11 107.28 214.28 10 103.5 103 24.79 118.27 209.6 11 103.3 102.6 16.55 94.66 174.84 12 103.3 102.5 24.39 105.1 232.06 13 124.6 125.5 29.03 161.26 180.02 14 124.8 127 30.19 162.4 185.9 15 124.5 127.2 30.48 162.96 187.04 16 123.8 128 25.84 161.14 160.36

1 50.5 51.7 4.18 27.6 151.45 2 50.8 52 3.72 24.4 152.46 M 3 50.5 50.6 4.93 25.5 193.33 4 50.8 51.2 5.05 26.3 192.01 I 5 75.5 76.2 8.24 59.1 139.42 6 75.6 77 7.84 59.7 131.32 X 7 75.5 75.8 7.37 56.3 130.90 8 75.6 76 6.97 58.3 119.55 6 9 103.7 104 13.0 110 118.18 10 104.3 102.7 12.6 108.55 116.07 11 103.6 101.6 12.31 106.85 115.21 12 103.8 102.5 12.19 106.35 114.62 13 124.1 126 15.39 160.45 95.91 14 123.7 126.5 14.52 159.95 90.78 15 124.3 127 14.81 159.3 92.97 16 123.6 127.5 14.69 163.8 89.68

1 50.2 50.4 5.22 26.15 199.62 2 50.5 50.3 4.06 25 162.4 M 3 50.7 50.8 4.64 26.56 174.7 4 50.6 49.8 4.35 25 174 I 5 75.2 74.6 7.55 58.05 130.06 6 75.7 75.8 7.54 56.75 132.86 X 7 75 76 7.66 58.4 131.16 8 75.3 75.7 7.78 59.4 130.97 7 9 104.3 102.8 10.6 109.3 96.98 10 104.5 103.3 11.5 109.8 104.73 11 104.55 102.9 10.45 110.33 94.72 12 104 103.6 10.33 108.2 95.47 13 124.2 126 13.59 162.85 83.45 14 124 126 13.93 161 86.52 15 124.1 126 13.47 161.85 83.23 16 124 125.8 13.70 159.3 86 Table 5.5 Wedge Test Results for Rectangular Prism and Cubic Samples

Specimen Dimensions Area of Sample Diagonal Load at Material Failure No. Width x Width x Height Dimensions Failure Strength Plane mm mm mm mm kN N/cm^ (cm2) 1 34.4 35 51 48.4 7.26 19.36 375 M 2 36 34.6 51.5 48.15 5.57 19.13 291.16 3 52.2 52.8 77 73.5 11.32 42 269.52 I 4 52.8 53 75.6 73.65 8.13 39.4 206.34 5 73.1 73 102 101.6 14.22 79.26 179.41 X 6 72.5 72.8 103 101.5 17.13 81.7 209.67 7 82.7 83 126.2 126.4 20.32 112.7 180.3 5 8 82.3 82.8 126.4 126.85 20.26 110.93 182.64 9 109.2 109.3 151.2 151.72 22.93 171.85 133.43 10 108 108.4 153 151.65 20.9 168.85 123.78 11 149 151.7 151.5 212.63 30.77 235.52 130.65 12 149.7 146.5 149.2 209.46 46.6 223.83 163.51 13 152 150 151 213.55 25.8 232.5 110.97 14 149.7 147.5 152.5 210.16 21 230 91.3

1 36.5 35 52 48.75 3.66 15.6 234.61 M 2 52.5 52.2 78 72.75 6.68 40.46 165.1 3 52.5 53.5 76.2 73.65 5.52 41.33 133.56 I 4 72 73.5 102.8 103 9.58 71.85 133.33 5 72 73.4 105.3 99.7 90 77.9 115.53 X 6 86.5 87 126 121.75 11.9 109.05 109.12 7 86 88 127.3 120.5 11.15 111.7 ~ 99.82 6 8 103 109 152 150.75 15.5 168.4 92.04 9 108.7 109 152.5 151 15.1 167.6 90.09 10 149 151 151.5 212.14 17.13 226.35 75.68 11 150.5 150 151 212.48 16.37 231.85 70.6 12 148.5 149.5 151.2 210.72 17.71 231.85 76.38 13 149.3 151.2 150.2 212.49 15.8 237.7 66.47 14 148 148 149 209.3 15.45 224.45 68.83

1 35.7 34.5 50.7 48.2 3.6 19.4 185.57 M 2 34.5 35.2 50 48.8 3.54 18.6 150.32 3 53 53.1 75.3 73.9 5.23 41.65 125.57 I 4 52.3 53.2 74.2 73.5 6.50 38.25 169.93 5 71.8 72.2 101 100.75 8.82 77.05 114.47 X 6 72 73.2 100.7 101.2 8.71 75.6 115.21 7 87.2 86 125.2 121.75 10.57 113 93.54 7 8 86.8 87.5 125.3 121.75 10.51 115.8 90.78 9 107 108.8 151 151.9 14.4 170.85 84.28 10 110 108 150.5 152.2 14.51 168.6 86.06 11 150.5 150 151.2 212.48 17.42 233.25 74.68 12 146.8 151.5 151 210.95 16.72 236.9 70.58 13 151 147 151.5 210.74 17.71 235.15 75.31 14 152.3 147.4 152 211.95 17.71 236.46 74.27 15 150 148 152 210.72 17.30 237.9 72.72 Ui 5 O O Ui CO h* UJ £E z O H x O u. K iZ o -I < QC < 2 H < Ui cc < _i

ARTIFICIAL MATERIAL 3 o

1 220 200 1 2 280- 260-

1 140- 100 1 120 200 2 6 3 2 2

220 340

3 8 4 80- 60-

40-

0 0 6 8

DIAGONAL 2 0 0-

0- - 0 - 0 - 0- r — - - -

- - - -

DIAMETER 25 2'5 FIGURE

DIMENSIONS 50 ?0

5.10

75 OF

CYLINDRICAL 100 lio Wedge

125 1^5

SQUARE Test

1^0 150 Results ______

SAMPLES

1 AND 1 5

2b (mm) RECTANGULAR for

Mi_x (mm) 2^5

PRISM

SAMPLES £ UJ o O UJ co H X UJ z o I- X O U. < DC H IZ O -l < 2 < H UJ QC WEDGE STRENGTH OF ARTIFICIAL MATERIAL < CM z E 100 1 140- 200 1 1 1 1 100 140-

180- 80- 2

200 240- 60- 2 6 20 30-

0 0

- 0 - - - - - DIAGONAL - - FIGURE DIAMETER 2's

5.11 H

DIMENSIONS OF

Wedge Test

CYLINDRICAL 7io (mm)

1^5

OF 118.

Results

SQUARE 1

£o SAMPLES for

AND

Mix

RECTANGULAR

(mm) 6.

PRISM

SAMPLES

£ UJ F- Q 0 UJ CO QC Ui z o H- X o u. _j H ui iZ O < < a < WEDGE STRENGTH OF ARTIFICIAL MATERIAL < cc CM CVI o E z E o 100 16 1 140- 200- 120 200

8 80-

0 0 - - - - - DIAGONAL DIAMETER FIGURE 25 26

50 50 5.12 DIMENSIONS

OF ^5 7

1 5

Wedge CYLINDRICAL uTo 1 6 o

Test (mm)

TVs 1^5 OF 119.

Results

SQUARE 1

1 4o

j 5

SAMPLES 0

175

AND for

2t)0

Mix RECTANGULAR (mm)

225 7.

PRISM

SAMPLES 120.120.

FIGURE 55.13 .13 CarparisonComparison of CUbicCubic and Cylindrical Specimens after Testing. 121.

As expected, there is a significant reduction in wedge strength as the dimensions of sample increase. This parallels the well known phenomenon observed when conducting compressive tests on cubes of varying size. Figures 5.10, 5.11 and 5.12 show that the same effect is observed for cylinders, cubes and rectangular prisms and for all three materials tested.

The compressive strength of Mix 5, 6 and 7 have been reported as

12.05, 6.85 and 4.81 MPa respectively (Table 4.5) and, in general, the wedge tests results reflect these differences, with the highest values being observed for Mix 5 and the lowest for Mix 7. Taking

Mix 7 as a base value then the ratio of compressive strengths was

2.5:1.4:1 while the mean wedge test results (calculated from

Table 5.5) were in the ratio 1.8:1.04:1 for the three mixes.

The results also give some indication of the effect of specimen height to width ratios. The 150 mm high specimens formed two groups. One had diagonal dimensions of 150 mm i.e. a rectangular prism and the second group comprised cubes with 150 mm sides and diagonal dimensions of 212 mm. Table 5.5 and Figures 5.10, 5.11 and 5.12 show that the wedge test strengths of cubes were lower than the equivalent prisms, despite their lower height to diagonal dimension ratio. This phenomenon is considered further in Chapter 7. 122.

CHAPTER 6

ROCK CUTTING TESTS

The action of bucket wheel excavators is similar, although at a much larger scale, to that of other machines which use the mechanical action of dag bits to excavate rock. It is likely, therefore, that laboratory scale cutting tests can provide a useful link in the correlation of overburden physical properties with the performance of B.W.E.

These cutting tests have been undertaken on three of the block samples recovered from the Goonyella mine (B2, B3 and B4) using 250 mm cube specimens sawn from the original block. The single pick linear cutting rig used was a modified

Invicta type 6M shaping machine, the basic specification for which was:

Power 5.36 kw

Stroke 50 - 800 mm (adjustable)

Speed range 105 - 960 mm/s (adjustable)

Max. cutting force 50 kN (at 105 mm/s)

The principal modification included the provision of a cutting force dynamometer fixed rigidly to the backing plate of the shapers' tool holder assembly at the front end of the sliding head. This dynamometer, with appropriately designed pick holders, could accept any normal size and shape of cutter pick and dispose it at the required angles to the rock. The cutting rig and dynamometer are shown in Figure 6.1. 123.123

FimREFIGURE 66.1 .1 Linear Rock Cutting Rig and Pick Dynarnaneter.Dynamometer 124.

The machine's table is capable of accommodating a block

of rack measuring 400 x 400 x 300 mm high. Prior to mounting,

blocks are usually dressed square using a large rock saw.

Samples of highly competent rack can be given a flat base and

glued firmly to a base plate which is then bolted onto the

table. Less competent samples (such as coal and the Goonyella

overburden) , which run the risk of disintegrating during cutting,

are encased in a surrounding cement matrix before mounting.

This was then progressively reraved to expose the rock surface

as the cutting tests proceeded.

Prior to undertaking a cutting test, the surface of the

block was trimmed with a special pick to provide a flat level

surface. The depth of cut to be taken during a test was

thereafter accurately set by raising the table the required distance and locking it in position. Likewise parallel cuts,

at the same depth could be made at any required spacing by

shifting the table laterally.

After each cut had been completed the rock debris was

carefully collected, weighed and size analysed and the depth of cut checked by dial gauge at intervals along its length.

The generalised force acting on the pick during cutting was resolved into its three mutually orthogonal components

(cutting, normal and lateral) by a solid plate dynamometer. 125.

This instrument, which is shown in Figure 6.2, was

equipped with twenty four strain gauges (120 ohm foil gauges,

with nominal gauge factor of two) disposed at precise positions

on its four strain sensitive beams. To provide the appropriate

level of sensitivity, important when cutting weaker rocks,

the dynamometer used for these tests was machined from a solid

block of aluminium (manganese-magnesium 5000 series alloy).

The dynamometer, designed originally at the National

Coal Board's Research Establishment in Britain, provides good

linear response in each of the three directions and with

interaction between the circuits of less than 5 per cent.

The instrument was regularly calibrated and checked by

applying known forces in each of the three directions and also at known intermediate directions to test the accuracy of force resolution. The natural frequency of the dynamometer

is approximately 4 kHz, well in excess of that required to record the full magnitude of the transient peak forces generated when cutting.

A stabilised A.C. supply powers the dynamometer and strain gauge amplifiers to provide an output signal of 3 volts from each of the three channels. These signals were transmitted to a data was digitised and filed. Software has been produced to process the data and provide hard copy of relevant force values, specific energies and other information. 126.

FIGURE 6.2 Isanetric Drawing of Dynamometer.

Width of Pick = 30irm

FIGURE 6.3 Chisel Pick. 127.

6.1 Cutting Results

The cutting programme involved using a 30 mm wide chisel pick with a rake angle of +30° and a back clearance angle of

10°, as defined in Figure 6.3. Depths of cut of 5, 10 and

15 mm were taken, with a number of replications at each depth in order to produce statistically acceptable data.

The results for the block sample (B2), yellow sandstone (B3) and pink sandstone (B4) are given in Tables 6.1, 6.2 and 6.3 and presented graphically in Figures 6.4, 6.5 and 6.6. The results obtained conform with those found by other research workers (6) (7) (8) . 128.

Table 6.1 Results of Cutting Tests in Block B2

A) Forces

Depth of Cutting Force (KN) Normal Force (KN) Cut (mm) Mean Mean Peak Mean Mean Peak

5 1.73 2.85 1.22 1.47 5 1.90 3.26 1.18 1.84 5 2.20 3.73 1.84 2.28 5 1.87 3.00 1.15 1.79 5 1.86 3.11 1.04 1.85 5 1.86 2.97 1.21 1.88 Mean 1.90 3.15 1.27 1.85

10 2.40 4.64 1.11 1.80 10 2.87 4.70 1.24 1.74 10 3.17 5.32 1.66 2.51 10 2.14 4.25 1.29 1.70 10 2.49 4.56 1.34 1.71 10 2.17 4.19 1.43 1.69 Mean 2.54 4.61 1.34 1.86 -

15 4.06 7.14 1.70 2.28 15 3.25 8.37 1.19 1.79 15 3.68 6.78 1.45 1.96 15 4.10 7.04 1.39 1.99 15 3.44 6.29 1.37 2.04 15 2.91 5.48 1.21 1.67 Mean 3.57 6.85 1.39 1.95 129.

Table 6.1 Results of Cutting Tests in Block B2

B) Yield, specific energy and coarseness index

Depth of Yield Specific Energy Coarseness Cut Index m^/km rrvJ/m^ (mm) ]------5 0.16 10.76 509 5 0.17 10.95 538 5 0.19 11.47 522 5 0.13 14.29 528 5 0.18 10.16 542 5 0.17 10.69 515 Mean 0.17 11.38 525

10 0.48 4.95 628 10 0.55 5.17 674 10 0.41 7.62 589 10 0.51 4.20 635 10 0.51 4.84 623 i 10 0.51 4.28 637 Mean 0.50 5.17 631

15 0.89 4.54 564 15 0.97 3.35 652 15 1.04 3.52 666 15 0.85 4.84 633 1.14 3.01 669 15 15 0.86 3.38 639 Mean 0.96 3.77 637 o z DC < _J u. o QC o UJ co CUTTING FORCES (KN) ¥ z FIGURE] 8 3- 4- 8 1 5- 7- 2 2 3-1 1

------

6.4(A)

Effect i 5 T 5 ------

DEPTH of DEPTH

130.

Depth OF

CUT OF

10 1 ------of 1

CUT Cut on (mm)

Forces (mm) ------15 1 r-

5 for PEAK MEAN PEAK MEAN

Block

B2. SPECIFIC ENERGY (MJ/m3 FIGURE 0 0 0 0 0 0 0 1 1 1 1 0 1

. . . . . 4 8 . . 6 4 . . 2 0 . 2 3 5 2 9 6 4 0 7 1 8 ------

- - - - - _ - - - - 6.4(B)

Effect i 5

DEPTH DEPTH Depth

OF of CUT

10 ] ------CUT Cut

on (mm) (mm)

Yield

15 and r-

Specific

Energy -250 -300 ------600 -650

350 400 7 500 200 450 550

00 in

Block INDEX S 3 E N S R A O C

B2 132.

Table 6.2 Results of Catting Tests in Block B3

A) Forces (Normal force levels too low to be accurately determined)

Depth of Cutting Forces (kN) Cut (mm) Mean Mean Peak

5 0.43 0.89 5 0.37 0.84 5 0.41 0.86 5 0.32 0.92 5 0.38 0.84 Mean 0.39 0.87

10 0.67 1.34 10 0.66 1.23 j 10 0.66 1.36 10 0.88 1.61 10 0.80 1.44 10 0.65 1.28 10 0.67 1.33 | 10 0.65 1.33 Mean 0.70 1.36

15 1.42 2.66 15 1.32 2.40 15 1.23 1.96 15 0.97 1.78 15 1.06 1.84 15 1.08 2.02 15 1.15 2.02 15 1.05 1.86 15 1.01 1.84 Mean 1.14 2.04 133.

Table 6.2 Results of Cutting Tests in Block B3

B) Yield, specific energy and coarseness index

Depth of Yield Specific Energy Coarseness Cut (mm) Index m3/km MJ/m3

5 0.175 2.48 486 5 0.182 2.01 487

5 0.205 2.00 502 5 0.179 2.28 487 5 0.188 1.71 529 5 0.179 2.09 524 Mean 0.185 2.09 503

10 0.468 1.44 594 10 0.500 1.32 620 10 0.493 1.33 609 10 0.461 1.90 597 10 0.437 1.84 602 10 0.470 1.37 591 10 0.498 1.34 607 10 0.510 1.28 611 Mean 0.480 1.48 604

15 0.759 1.88 576 15 0.919 1.43 588 15 0.828 1.48 606 15 1.166 0.83 702 15 0.806 1.31 644 15 0.879 1.23 659 15 0.788 1.46 602 15 0.896 1.17 625 15 0.935 1.08 637 Mean 0.782 1.32 626 1 PEAK CUTING FORCE MEAN CUTTING FORCE FIGURE

6.5(A)

Effect

DEPTH of DEPTH

Depth

134. OF

OF of

CUT

CUT Cut

on (mm) (mm)

Forces for Block

B3. 135.

1.2- -7 00

1.1- -650

1.0- -600

0.9- -550 S S E N S R A O C 0.8- - 500

0.7- - 450

0.6- -400 NDEX E D IN

0.5- - 350

. - 0 4 - 300

0.3- - 250

0.2- -200

DEPTH OF CUT (mm)

> (3

DEPTH OF CUT (mm)

FIGURE 6.5(B) Effect of Depth of Cut on Yield and Specific Energy in Block B3. 136.

Table 6.3 Results of Cutting Tests in Block B4

A) Forces

Depth of Cutting Forces (kN) Normal Forces (kN) Cut (nm) Mean Mean Peak Mean Mean Peak

5 1.66 3.92 1.07 1.56 5 1.92 3.43 1.28 2.02 5 1.87 3.60 1.20 1.81 5 1.56 3.48 0.84 1.43 5 1.73 3.64 0.88 1.39 5 1.74 3.56 0.86 1.53 5 1.97 3.81 1.01 1.89 Mean 1.71 3.42 1.01 1.62

10 2.73 4.99 1.25 1.88 10 2.23 5.45 1.24 1.87 10 2.63 5.31 1.18 2.02 10 2.44 5.12 1.01 1.73 10 2.56 4.88 0.78 1.63 10 2.55 5.52 0.59 1.38 " 10 2.64 6.85 1.11 1.93 Mean 2.54 5.45 1.02 1.78

15 4.56 7.55 1.22 1.75 15 3.47 6.44 0.99 1.68 15 4.06 7.45 1.07 1.73 15 3.22 5.81 0.73 1.19 15 4.68 8.60 0.96 1.88 15 4.38 8.02 2.65 3.74 15 3.73 8.63 1.18 2.14 Mean 4.01 7.50 1.26 2.01 137.

Table 6.3 Results of Cutting Tests in Block B4

B) Yield, specific energy and coarseness index

Depth of Yield Specific Energy Coarseness Cut Index m3/km m/m3 (nm)

5 0.207 8.05 592 5 0.197 9.74 596 5 0.195 9.56 566 5 0.232 6.74 614 5 0.215 8.08 599 5 0.216 8.02 597 5 0.173 11.40 565 Mean 0.205 8.80 590

10 0.673 4.06 667 10 0.720 3.10 679 10 0.712 3.69 704 10 0.525 4.64 648 10 0.552 4.64 645 10 0.687 3.71 581 10 0.486 7.99 619 Mean 0.622 4.55 649

15 1.019 4.47 652 15 1.087 3.19 675 15 0.861 4.71 639 15 0.943 3.42 622 15 0.873 5.36 639 15 0.886 4.94 638 15 1.066 3.50 713 Mean 0.962 4.23 654 CUTTING FORCES (KN) FIGURE 1 4 2 5 3

8 8 7 9 ------6.6(A)

Effect T 5 of

Depth ------DEPTH of 138.

OF Cut 10 , ------

CUT on

Forces (mm) for 15 r-

Block

B4. SPECIFIC ENERGY ( M J /n f FIGURE 0 0 0 0 0 0 0 0 1 1 1 1 . . .

. . .6 . .

. 4 3 . 2 0 5 4 6 8 2 8 2

0 7 9

1 ------

6.6(B)

Effect in

5 Block

DEPTH DEPTH Depth B4

139 1 OF OF of

I 0

Cut CUT CUT

Yield (mm) (mm) 1

and

Specific

- -600 -6 -700 - - Energy -200 - - - -

500 550 300 450 350

400 250

INDEX COARSNESS 140.

6.2 Discussion of Cutting Programme Results

The results presented graphically in Figures 6.4, 6.5 and

6.6 are for the three main types of overburden excavated during

Strip 4 by the Goonyella bucket wheel excavator. The trends established are similar for each of the rock types, with only the magnitudes varying.

All cutting forces increased proportionately to the depth of cut. This is in agreement with a wealth of experimental data produced by other researchers. The normal force in this very weak (by machine excavation standards) material was very low and could not be measured accurately. In fact for the yellow sandstone, Block B3 the force levels recorded by the dynamcmeter were so low the signal could not be distinguished fran background noise and so no normal force results are available.

The relationship between yield and depth of cut has also been established. Yield is defined as the volume of rock produced by the tool per unit distance cut. Since in most brittle rocks the cross-section of the groove exceeds the area swept by the tool (see Figure 6.7) , yield will depend on how cracks propagate on either side of the tool. Frcm the definition of yield and the geometry of the groove, as shewn in Figure 6.7, it can be seen that

Yield = Wd + d2 tan 8 . . (1) 141.

K— W -X

Figure 6.7 Shape of Excavated Groove.

Since 0 is regarded as a parameter that remains fairly constant for any particular rock type, it can be seen that for a given width of tool yield will be a function of (depth of cut)2. Figures 6.4(B), 6.5(B) and 6.6(B) show this to be the case, with yield increasing rapidly as depth of cut increases using the values of yield and the face that pick width remained constant throughout, the average breakout angle has been calculated i.e.

0 = tan-'*' Yield (mm2) - Wd d2

The values of 0 for each experiment are given in

Table 6-. 4. 142.

Table 6.4 Breakout Angles

Rock Type Depth of Cut Breakout Angle (mm) (°)

B2 5 51 10 63 15 66

B3 5 54 (Yellow Sst) 10 60 15 55

B4 5 65 (Pink Sst) 10 72 15 66

It can be seen that there is no clear trend of breakout

angle varying with depth of cut. The three individual rock types do, however, exhibit scrne variation in average breakout angle with B2, B3 and B4 giving values of 60°, 56° and 68° respectively.

The most important measure of cutting performance is

Specific Energy, which is defined as the work done per unit volume of rock cut. This is a direct measure of cutting efficiency

and the curves for all three rocks show that specific energy

decreases with increasing depth of cut. In general, shallow

cuts are seen to be highly inefficient and considerable

improvement is gained by increasing the depth of cut. The benefits in this direction are not, however, unlimited since

specific energy appears to be approaching an asymptotic value. 143.

Coarseness Index, on the other hand, appears to increase with depth of cut, showing that the average size of product has also

increased. In fact, coarseness index for all three rocks appears

as a trend which is the inverse for that of Specific Energy,

thereby supporting the assumption that high efficiency and large product size go hand in hand.

6.3 Comparison of the Cuttability of the Three Rock Types

Variations in the mechanical and physical properties of the three block samples used for the cutting tests have been reported in Chapter 4. A summary of these results is new presented in Table 6.5

Table 6.5 Summary of Mechanical and Physical Properties of the Goonyella Block Samples

Test B2 B3 B4

Compressive Strength (MPa) 19.3 1.35 15.8 Tensile Strength (MPa) 1.92 0.31 2.25 Bulk Density (t/m3) 2.33 1.93 2.31 Shore Hardness 37.1 33.7 Cone Indenter 0.47 0.18 0.48

The results of cutting tests in the three blocks have been discussed and it has been noted that the trends are similar.

This work does, however, provide the apportunity to compare the magnitude of force and energy requirements in the individual rocks.

Curves for mean cutting force and specific energy have been

abstracted from Figures 6.4, 6.5 and 6.6 and are presented for

comparison in Figures 6.8 and 6.9. CO CL UJ O U. o z LU O UJ cc > 2 MEAN CUTTING FORCES (KN) Figure Figure

6.9 6.8

Three Comparison Three Comparison DEPTH DEPTH

Goonyella

OF of of

CUT CUT Specific

Mean Block 144.

Block (mm)

Cutting Samples.

Samples. Energies (mm)

Forces

for

in the

the

145.

The results show that despite the considerable mineralogical

differences between the B2 and B4 samples, the comparable mechanical strength is reflected in the close agreement between

forces and energies in the two rocks. On the other hand the

soft, yellow sandstone B3, with a high clay content and a silty

nature, is very much easier to cut, requiring only between one

third and a quarter of the force used in cutting pink sandstone

to the same depth. A similar ratio between specific energies

can also be observed in Figure 6.9. 146.

CHAPTER 7

CONCLUSIONS

The four principal objectives of this research were:-

Firstly to design and build a small, portable wedge test

apparatus capable of being used in the field, while at the

same time having the rigidity to test samples of hard overburden

such as that found at Goonyella.

The second objective was to correlate wedge test results with other more canmon indexes of the mechanical and physical

strength of the samples as well as to investigate their cuttability.

Thirdly it was intended to investigate whether specimen

shape and size significatnly affects wedge test results, while

finally it was hoped to investigate whether wedge test results gave any correlation with bucket wheel excavator performance, as monitored by ACIRL at Goonyella.

The first objective has been met in full. The wedge test apparatus, as described in section 5.3 has been manufactured and used to test overburden frcm Goonyella and samples of several sand/cement/lime mixes. Wedge loads of up to 50 kN can be applied, which for typical breakage of 150 nm diameter core, give wedge test results of approximately 325 N/cm2. It is unlikely that a bucket wheel excavator would operate in overburden of above this strength, even if it were pre-blasted. 147.

The four methods adopted for measuring the mechanical

and physical properties of Goonyella overburden were, uniaxial

ccmpressive and tensile strength, Shore Hardness and Cone

Indenter Hardness. The relationships between these parameters

and wedge test results are illustrated in Figures 7.1 to 7.4.

Both ccmpressive and tensile strengths appear to increase

linearly with the wedge strength, with no significant variations

between overburden and "artificial" material. The graphs have

all been drawn with wedge strength as the independent variable

and with standard deviations placed on the dependent variable

alone. This is because for the Goonyella block samples only

a very limited quantity of rock was transported to the laboratory

and so only one specimen was wedge tested fran Block 2 and three

specimens frcm both Blocks 3 and 4. Figures 7.1 and 7.2 do, however, allow estimates of wedge strengths to be made if

either the ccmpressive or tensile strength of the material

is known.

Figure 7.3 indicates that there is very poor correlation between Shore Hardness and the wedge strength results. This is not surprising since this test relies on the rebound of a pointed pellet frcm the surface of the rock. In fact no results could be obtained for Block B3 because, with it' s high clay content, the pellet penetrated the surface and failed to rebound. Since this test relies so heavily on the exact point of contact on the rock surface, variations in quartz content, t- ui a o o * < z o

ARTIFICIAL MATERIAL ARTIFICIAL MATERIAL FIGURE FIGURE

7.2

7.1

Wedge Relationship

R e l a t i o n s h i p and WEDGE WEDGE ARTIFICIAL ARTIFICIAL

Strength. Wedge

STRENGTH STRENGTH

Strength. Between

Between MATERIAL MATERIAL 143.

OF Tensile

ROCK C o m p r e s s i v e ROCK

AND Strength and AND CN/cm (N/cn^)

Strength

)

O o z Ui z o Ui Z H Ui GC SHORE HARDNESS FIGURE FIGURE 0 0.4- 0 0.5- 30- 5 10- 20 40- . 60 .

2 3 0- — - - --

7.4 7.3

Wedge Comparison MIX WEDGE Comparison WEDGE Ml|7

7 ARTIFICIAL MIX

MIX ARTIFICIAL Strength. 100 100

I STRENGTH

6 6

STRENGTH of of B4 5

Cone

Shore MATERIAL

MATERIAL 149.

OF MIX Indenter Hardness

i 200 OF Hardness ROCK 200

5 {

ROCK

AND

AND and (N/cm (N/cm

Wedge 300

2 and 2 ) )

Strength. 150.

size of quartz grains, etc. can all have a large effect and while it is scmetimes used to provide a rapid, cursory measure of cuttability, Figure 7.3 shows that it cannot be used to provide the same information as that obtained frcm wedge tests.

The cone indenter results, as presented in Figure 7.4, show a distinct but non-linear relationship with wedge test.

This is to be expected since both tests rely on the penetration of a wedge or point into the rock surface. However, at wedge strengths of above about 200 N/an2, cone indenter hardness appears to be independent of the wedge result and to remain constant at 0.5. Again this can be attributed to the small size of the probe and shows that once penetration of the harder material is complete further advances of the probe can be achieved without increasing the load.

The three block samples frcm Goonyella were also subjected to cutting tests, as described in Chapter 6. The peak cutting forces, averaged for the four replications at each depth of cut, are plotted against Compressive Strenth and Cone Indenter

Hardness in Figures 7.5 and 7.6. These results shew that both provide seme but not a complete measure of rock cuttability.

Because of the linear relationship between compressive strength and wedge strength, it can be anticipated that the relationship between cutting force and wedge test results will also shew a similar non-linear trend. Figure 7.7 shows this to be the case, even when mean force is normalised and expressed as mean cutting PEAK CUTTING FORCE (KN) UJ O a. < * 3 H H z es O >»/ li o tr LU z * FIGURE FIGURE]

7.6 7.5

Cone R e l a t i o n s h i p Compressive R e l a t i o n s h i p COMPRESSIVE

Indenter CONE

Strength. INDENTER

Between Between

Hardness. STRENGTH

Cutting Cutting

Forces ROCK Forces

DEPTH (MPa) and and

(mm)

DEPTH OF

(mm) CUT

CUT m e a nc u t t i nf g o r c/d e e p t h SPECIFIC ENERGY (KN/mm) 0 0 FIGURE FIGURE . . 4 2 - -

7.8 7.7

Wedge Wedge Specific Overburden WEDGE WEDGE

Strength. Strength.

Energy STRENGTH STRENGTH

C u t t a b i l i t y

152.

Cutting

OF OF

ROCK as ROCK

as a

Function

(N/crrf (N/cm Function

of ) )

of DEPTH

(mm)

CUT

153.

force per unit depth of cut. It is also interesting to see frcm

Figure 7.3 that Specific Energy of cutting increases in the same way with wedge strength. This would imply that the energy required by a bucket wheel excavator would, even at a constant production level, rise rapidly as the machine operates in harder overburden and that wedge strength is as good a measure of ground diggability as any of the other canmonly used parameters

The 0 & K wedge test is designed to use 150 irm diameter cores. In many circumstances, however, it may be more convenient to use cores of seme other (usually smaller) diameter or to use square-section samples sawn frcm the exposed face of the overburden. The effects of specimen shape and size on wedge test results have been reported in Chapter 5. The majority of specimens tested had a constant diameter (or diagonal) to height ratio of 1. This meant that although the load on the wedge increased with specimen size, the area of the failure plane increased with the dimension squared. This resulted in the wedge strength (N/cm2) decreasing in the way shown in Figures

5.10, 5.11 and 5.12, as specimen size increases. It is, therefore critical that specimen dimensions are quoted along with wedge strength results and an attempt made to normalise the results to conform with those obtained frcm 150 mm diameter by 150 mm high cylinders, as defined in the 0 & K test.

The effects of changing height to diagonal ratios was studied using rectangular prisms and cubes. Similar work on the ccmpressive strength of cylinders of rock lias produced 154.

the well known rock mechanics principle that tall, slender

cylinders are weaker than short, squat cylinders. However,

in wedge tests with specimens of constant height (150 mm) and

diagonal dimensions of 150 nm and 210 inn, it was found that

those with the lower Height/Diagonal ratio gave a wedge strength of approximately 10% less as shown in Table 7.1.

Table 7.1 Effect of Height/Diagonal Ratio for Rectangular Prisms of Artificial Material.

Mix Mean Sample Mean Sample Ratio of Wedge Test Height (mm) Diagonal (mm) Height/Dia. Results N/cm2

5 152.1 151.7 1 128.6 151.1 211.5 0.7 124.1

6 152.3 150.9 1 91.1 150.6 211.4 0.7 71.6

7 150.8 152.1 1 85.2 151.5 211.4 0.7 73.5

It can be seen that the predominant effect is a reduction in strength due to increased size rather than an increase in strength due to a lower Height/Diagonal ratio.

Work conducted by ACIRL at Goonyella and reported by Truong (9) involved fully instrumenting the bucket wheel excavator and recording its performance while digging Strip 4. By recording wheel power and rotational speed Truong was able to calculate torque and hence the digging force under different operational conditions. These results showed a relationship between cutting resistance and 155 N/cm

STRENGTH,

MATERIAL

H-LDN3dlS TVIdTIVU IVniJV _ yoiDVd NOIlV13ddOD 33NVlSlS3d DNIDDIQ 156.

production rate i.e. material strength was not the only factor

involved. To quantify this a correlation factor, f was defined

as f = specific resistance on the basis of power consumption material strength from, wedge test

The variation of this factor, f, with the actual material strength is

reproduced frcm this report (9) as Figure 7.9. It can be seen

that f varies between about 12 in soft material to about 3 in

the harder material. It is by no means certain frcm this current work

or frcm a search of the literature, whether this relationship is

specific to the Goonyella machine or to the overburden types tested

or whether it is a more general result.

In conclusion it can be seen that although wedge test results

correlate reasonably well with other measures of material strength, with the standard cuttability tests and with recorded machine data

frcm Goonyella, the relationships are not linear. This means that

other factors are also involved in the "diggability index" and that

tiie search for other methods of determining bulk rock properties,

such as seismic testing, should continue. REFERENCES

Aiken, G. and "Continuous Excavators". Wohlbier, R.H. Surface Mining, American Inst, of Mining and Metallurgical and Petroleum Engineers Inc., Mudd Series, New York, 1968 pp. 478-502.

Rasper, L. "The Bucket Wheel Excavator Development Design Application". Series on Bulk Materials Handling, Vol. 1 (1975) No. 2, Trans. Tech. Publications.

Kolbe, F.F. "Developing the Wheel for American Coal Stripping". Coal Age, March, 1955, pp. 58-65.

Reman, G.H. "United Electrics New Wheel Moves 1,250,000 cu yd. per month". Coal Age, March, 1968, pp. 62-69.

Rodgers, H.C.G. "Developments in Equipment Used for Overburden Removal and Coal Winning in The Brown Coal Industry". Proceedings. The Aus. I. M. M. No: 194, 1960, pp. 127-250.

Roxborough, F.F. "A Laboratory Investigation into the and Rispin, A. Application of Picks for Mechanised Tunnel Boring in the Lower Chalk". The Mining Engineer, Oct. 1973, p. 1.

Evans, I. and "The Strength, Fracture and Workability Pcmeroy, C.D. of Coal". Pergamon, London, 1966, pp. 254. 158.

8. Roxborough, F.F. "Experimental Studies on the Excavation and Phillips, H.R. of Rock using Picks". Proc. of Third Congress of the Int. Soc. for Rock Mechanics. Sept. 1974, Vol. IIB, pp. 1407-1412.

9. Truong, D. "Development of Monitoring System for Heavy, Mobile, Open-cut Equipment". End of Grant Report on NERDDP Project 81/1083 ACIRL, August, 1984. 159.

BIBLIOGRAPHY

Aiken, G.E. "BWEs: How to Choose the Right One for the Job"

Mining Engineering, Jan. 1966, pp. 76-81.

Benecke, K.J. "The Development of Bucket Wheel Excavators

(BWE)". Australian Mining, Feb. 1979,

pp. 232-243.

Benecke, K.J. "Investment Costs Versus Size for BWE-Mining

Systems". Int. Conf. on Mining and Machinery,

July 1979, pp. 176-178.

Benecke, K.J. "BWE Technology for Mining Lignite in Texas".

Mining Engineering, Aug. 1979, Vol. 31, No. 3,

pp. 1209-1213.

Boyd, G.L., "Open Strip Pitwall Instability at Goonyella

Koradeur, W. and Mine-Causes and Effects". The Aust. I.M.M.

Richards, B .G. Conference North Queensland, Sept. 1978,

pp. 139-157.

Bowen, K.G. "Brown Coal-Victoria's Prime Energy Resource".

World Coal, July 1978, pp. 46-48.

Burrows, D. "Power Politics in Victoria - The Latrobe Valley

Australian Mining, Dec. 1982, pp. 19-28. 160.

Cavagnaro, R.L. "Geotechnical Testing for Leigh Creek Coal

Field". 3rd Australia-New Zealand Conf. on

Geonechanics. 1980, Vol. 1, pp. 237-242.

Chugh, Y.P. "Opencast Mining of Brown Coal in Eastern

Europe". Mining Engineering, Nov. 1968,

pp. 1587-1590.

Church, H.K. "Excavation Handbook". McGraw Hill,

pp. 12-78, 85.

Coleman, J.R., "The Geotechnology of Excavation Equipment

Fitzhardinge, Selection with Particular Emphasis on BWE's".

C.F.R. Int. Conf. on Mining and Machinery, July 1979,

pp. 139-146.

Davey, C.J. "Standard Bucket Wheel Excavators for Coal

Mine Applications". Australian Coal Miner,

April 1983, pp. 32-36.

Dorling, I. "Australia's Loy Yang Brown Coal Project".

World Coal, June 1979, pp. 23-25.

Durst, W. "Earth Moving Machines for Larger Open Cuts in

Particular BWE's and Spreaders". Int. Conf.

on Mining and Machinery, July 1979, pp. 9-23. 161.

Gaertner, K. "Handling with the Bucket Wheel Excavator".

Mining Magazine, Feb. 1966, Vol. 114, No. 2,

pp. 72-85.

Goergen, H. and "Lignite Mining in the Ptolemais Region, Greece"

Fiebig, W. Mining Magazine, Feb. 1980, pp. 126-139.

Golosinski, T.S., "Assessment of the Europe Bucket Wheel

McRoberst, E. Excavator Technology". CIM Bulletin,

and Gilmore, July 1984, pp. 57-77.

W.F.

Golosinski, T.S. "Productivity from Bucket' Wheel Excavators" .

and Singhal, R.K. Australian Mining, July 1984, pp. 8-17.

Griffin, T.A. "New Uses for BWEs". Society of Mining

Engineers, Oct. 1974, pp. 50-51.

Hillesheim, L.J. "Design and Construction of Bucket

Wheel Excavators with Special Consideration

of Operating Conditions and Availability".

Int. Conf. on Mining and Machinery,

July 1979, pp. 153-158.

Kharakhash, R.M. "Developments in Soviet Excavating Equipment,

Part II and Part III". Mining Magazine,

July 1967, Jan. 1968, pp. 32-41 and 65-70. 162.

King, D.S. and "Selection of Electrical Systems for BWEs,

Lenz, W. Stackers and Reclaimers". Int. Conf. on Mining

and Machinery, July 1979, pp. 179-192.

Kolbe, F.F. "Developing the Wheel for American Coal

Stripping". Coal Age, March 1955, pp. 58-65.

Krurarey, A. "BWE's Get a Bigger Bite in German Open Cast

Mining". Australian Mining, Oct. 1979, pp. 53-64

Krumrey, A. "BWE's in Open Pit Lignite Mining". World Coal,

June 1979, pp. 18-22.

Krumrey, A. "Optimization of Design of Excavator Bucket

Wheel". Int. Conf. on Mining and Machinery,

July 1979, pp. 147-158.

Leyen, H.V. "Some Recent Aspects of Open Pit Mining with

BWE's in the Lignite Mines of Rheinbraun".

Int. Conf. on Mining and Machinery, July 1979,

pp. 168-174.

Maher, B.J. and "Open Cut Systems for the Eighties". Int. Conf.

Calnam, R.T. on Mining and Machinery, July 1979, pp. 447-451.

Mani, M.S. "Some Features of Excavator Design". Mining

Magazine, March 1966, Vol. 114, No. 3, pp. 152-

163. 163.

Naidu, B.S.D. "Neyveli: India1s Largest Lignite Mine".

World Coal, July 1979, pp. 35-38.

Naidu, B.S.D. "New Dredger for SEVC". Australian Mining,

Nov. 1974, pp. 45-46.

Naidu, B.S.D. "Giant BWEs at Hambach West Germany".

Mining Magazine, March 1978, p. 272.

Naidu, B.S.D. "Huge Bucket Wheel for Lignite Mine".

Mining Journal, Dec. 1978, pp. 431.

Naidu, B.S.D. "Bucket Wheel Excavator". Mining Journal,

Aug. 1977, p. 141.

Naidu, B.S.D. "Loy Yang". Australian Mining, Oct. 1979,

p. 36.

Naidu, B.S.D. "New No. 12 Dredger for SEVC goes for "Walk"

to Yalloum Open Cut". Australian Mining,

May 1974, p. 7.

Naidu, B.S.D. "Giant Mine and Machinery Make History".

Australian Mining, May 1979, pp. 46-48.

Naidu, B.S.D. "New Stripping Team Tackles Deep Overburden

at River King Mine". Excavating Engineer,

Dec. 1960, pp. 16-23. 164.

Naidu, B.S.D. "Poland’s Coal and Lignite Mining Programme

will Ensure its Future Energy Requirements".

Mining Magazine, April 1977, pp. 247-259.

Naidu, B.S.D. "How the Wheel Excavator Works". Excavating

Engineer, Dec. 1960, pp. 27-31.

Naidu, B.S.D. "Lignite Mining in W. Germany". Mining Magazine,

June 1974, pp. 455-457.

Naidu, B.S.D. "W. German Lignite Developments". Mining Magazine,

Nov. 1976, pp. 439-449.

Naidu, B.S.D. "G.D.R. Brown Coal Industry-Current Operations

and Future Plans". Mining Magazine, July 1977,

pp. 37-41.

Peretti, K. "The Combined Use of Continuously and

Discontinuously Operating Open Cast Mine

Equipment". The Aust. I.M.M. Symposium on

Strip Mining-45 m and Beyond. 1981, pp. 1-10.

Pfleider, E. "General Applications and Economics of Brown

Coal Mining West Germany". American Inst.

of M.M. and Pet. Engineers Inc., 1968,

Surface Mining Book, pp. 175 and 960-968. 165.

Phillips, S.C. "Continuous Mining Equipment Cuts Costs at

Waste Storage Project". Mining Engineering,

July 1980, pp. 783-787.

Rasper, L. and "Opening Up of the Lignite Mine of the Neyveli

Rittner, Lignite Corp. (India) and Experience with

Bucket Wheels in Hard Overburden". Braunkohle

Wunde, Vol. 10, 1961, pp. 8-11.

Rixen, W. "Bucket Wheel Excavators for Latrobe Valley".

The Aus. I.M.M. Conference, Aug. 1982,

pp. 289-295.

Rodgers, H.C.G. "Recent Developments and Applications of

and Bunting, H.R. BWEs in Australia". Annual Conf., 1970.

The Aust. I.M.M. paper No. 22.

Rodgers, H.C.G. "The Yalloum Southern Overburden System".

and Mitchell, D.H. The Engineering Conf., April 1978, pp. 248-256.

Rodgers, H.C.G. "Experience with Bucket Wheel Excavators

in Australian Brown Coal". Symposium on

Bucket Wheel Technology, Canada, 1976.

Rodgers, H.C.G. "Availability and Utilisation". The Aust. I.M.M.

Symposium on Strip Mining 45 m and Beyond,

1981, pp. 69-93. 166.

Rodgers, H.C.G. "Basic Design of BWE for the Goonyella Mine".

and Brett, J.R. Bulk Solids Handling Journal, Dec. 1981,

pp. 619-629.

Rodgers, H.C.G. "Developments in Equipment Used for Overburden

Removal and Coal Mining in the Brown Coal

Industry (Excavation Equipment) ". Proceedings.

The Aust. I.M.M. No. 194, 1960, pp. 127-250.

Reman, G. "United Electric's New Wheel Moves 1,250,000 cu.yd.

per Month". Coal Age, March 1968, pp. 62-69.

Runge, I.C. "The Next Generation of Australian Surface Coal

Mines". Int. Conf. on Mining and Machinery,

July 1979, pp. 462-468.

Saunders, B.J. "Assessment of Ground Conditions for Pre-

and Ellery, B.I. Stripping with B.W.E.". The Aust. I.M.M.

Symposium on Strip Mining 45 m and Beyond,

1981, pp. 57-68.

Scharf, W. "Handling Overburden and Brown Coal by

Bucket Wheel Excavators with Belt Conveyors".

The Mining Journal, Nov. 1955, pp. 610-612.

Scott, A. and "Use and Performance of BWE's in Latrobe Valley

Laird, C. Coalfields". The Aust. I.M. Rock Breaking

Symposium 1978, Nov. pp. 87-92. 167.

Sealy, T. "Opencast Mining Machinery from East Germany".

Mining Magazine, Feb. 1978, pp. 119-127.

Smith, W.B. "A BWE and Shiftable Conveyor System at

Work in Washington". Society of Mining

Engineering, July 1979, pp. 796-801.

Sukurs, R. and "Bucket Wheel Units for Tar Sands Mining".

Rodenberg, J. Mining Magazine, April 1981, pp. 307-313.

Strauch, W. "The Present State of Open Cut Engineering

in the G.D.R. and the Possibilities of its

Technological Application". Int. Conf. on

Mining and Machinery. July 1979, pp. 452-461.

Strzodka, K. and "East German Brown Coal Mining". World Mining,

Piatkowiak, N. Nov. 1968, pp. 42-47.

Tweedly, B.W. "The Loy Yang Overburden System". The Aus. I.M.M.

Conf., Aug. 1982, pp. 75-86.

Watson, L.M. "GCOS Future Looks Bright with Improved Mining

Methods, Rising Oil Prices". Canadian Mining

Journal, June 1979, pp. 30-38.