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June - 2010

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PREFACE

Mining Development Cell as a part of the Inspectorate of Mines & Minerals Department, Punjab was established in 1990. Its main function besides others was to develop curricula and books in subjects of mining for the students of Punjab School of Mine, Katas and Mines Survey Institute Makerwal. It was felt that books already available on mining subjects were mainly for degree courses and beyond the reach of most of the students firstly because they were too costly and secondly their contents were beyond the syllabus of diploma/certificate level courses. The first edition of “Elements of Mining” was written in June 2001 for the students of Punjab School of Mines, Katas District Chakwal and Mine Survey Institute Makerwal, District Mianwali. It needed many corrections & improvement. Mining Development Cell put all its effort to bring the new addition with improved, contents; text and topics. I am thankful to Engr. Muhammad Khalid Pervaiz and Engr. Abdul Sattar Mian, Ex-Chief Inspectors of Mines, Punjab, and my colleague, Engr. Rana Nasrullah Khan. Assistant Director, Mining Development Cell for extending full co-operation, guidance and assistance to get revised this book. The book has been prepared in consultation of various mining books mainly. Universal Mining School Courses, Elements of Mining by Lewis and Clarke, Mining Engineers Hand Book by Robert Peele to make it a model guide book for Diploma/Certificate Level studies.

Any comments and suggestions for further improvement of this book would be greatly appreciated.

Engr. Muhammad Tehzib Hassan Ansari Chief Inspector of Mines, Punjab, Lahore.

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Chapter No. CONTENTS Page No.

1. Value and Importance of mining Industry in Pakistan and Definition Relating to Mining.

Introduction 1

Mineral Potential of the Country 1

Nature of Mining Industry 2

Present Status of Mining Industry & Major Constraints 2

Future Prospects 4

Definitions Relating to Mining 6

2. Prospecting & Exploration of Mineral Deposits

Sequence of Activities (Introduction) 10

Prospecting procedures 10

Methods of Prospecting (various Techniques involves) 10

Geological Prospecting 10

Geo‐Physical Prospecting 11

Seismic Prospecting 11

Electrical conductivity Prospecting 12

Magnetic Prospecting 12

Geo‐Chemical Prospecting 12

Exploration 13

Difference between Resource & Reserve 13

Difference between proven, Indicated/Probable & Possible 13

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Reserves

Methods of Exploration 13

Comparison of Diamond Drills & Churn Drills 14

3. Development and Exploitation.

Development (Definition) 15

Sequence of Development 15

Exploitation 16

Factors involved in Selection of a Mining Method 16

Classification of Mining Method 17

Surface Mining Methods 17

Underground Mining Methods 18

4. Drilling and Boring

Introduction 20

Difference between Drilling & Boring 20

Types of Drilling Machine 20

Rotary Drilling 20

Percussive Drilling 21

Churn Drilling 22

Hammer Drills Machines 23

Types of Hammer Drills 23

Drifter 24

Sinker 24

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Stoper 24

Boring Method 25

Types of Boring Method 25

Percussive Boring 25

Rotary Boring 25

Tunnel‐Boring Machines 25

5. Explosives

Definition 27

Types of Explosives 27

Low Explosives 27

Black Powder & Gun Powder

High Explosives 28

Nitro‐Glycerin, Dynamites (its types)

Blasting Gelatin 30

Emulsion Explosives 30

Emulite Explosive Products 30

ANFO 31

Permitted Explosive 31

Characteristics of Permitted Explosive 31

Types of Permitted Explosive 32

6. Blasting

Blasting Properties of Explosive 33

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Firing Methods 36

Non Electric 36

Safety Fuse with plain detonator 36

Detonating Cord (Wabo Card) 37

NONEL 38

ii) Electric Firing 39

Instantaneous – Milli‐Second & Half Second Detonators 39

Blasting Patterns 40

Cut Holes, Drag Cut, V‐Cut, Pyramid Cut, Burn Cut, Toe Cut 40

Underground Blasting 43

Shot holes in coal 43

Shot holes in Ripping 44

Surface Blasting 44

Safety Precautions in Drilling & Blasting 45

Direct & Inverse Initiation 45

Stemming Materials 46

Miss‐Fired Shots 46

Procedure after Miss‐Fire 47

7. Underground Supports

Introduction 48

Types of Supports 48

Pillars Supports 48

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Timber Support. & Types of Timber Supports and advantages 48

One Piece Set 49

Two Piece Set 49

Three & Four Pieces and Polygon Set 50

Square Set 50

Rigid Steel Props Types of Rigid Steel Props 51

Grider type 51

New Battle Prop 51

The Butterley Prop 51

S.F.Prop 52

Steel Arches 52

Continuous Rib Type 53

Rib & Post Type 53

Rib and Wall plate type 53

Rib, Wall plate & Post 54

Full Circle rib. 54

Yielding Arches 55

Steel tubing 56

Roof Bolting 56

Types of Roof Bolting 56

Application of Roof Bolting 57

Application of floor Bolting 57

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Advantages of roof and Floor Bolting 58

Friction Prop 58

Hydraulic Props 59

Concrete 60

Stowing/ Waste Fillings 60

Methods of Stowing 60

8. Material Handling

Introduction 62

Loading Machines 62

Surface Loading – Excavation Machine 62

Power Shovels. 62

Drag Lines. 63

Comparison Between power shovels & drag lines. 64

BullDozer. 64

Scraper. 64

Comparison between bulldozers & scrapers. 64

Bucket Wheel Excavator. 65

Front and Loader 66

Underground Loading Machines. 66

Gathering Arm Loaders. 66

Rocker Shovel (Shovel Loader.) 67

Transportation 67

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Track Haulage 67

Locomotive Haulage‐Advantages.

Types of Locomotive Haulage

Battery Locomotives

Overhead |Trolley wire locomotives.

Rope Haulage 68

Types of Rope Haulage 68 68 Director or Main rope haulage.

Main & tail rope haulage. 69

Endless rope haulage. 69

Gravity Haulage. 70

II) Trackless Haulage 70

Manual (wheel Barrows) 71

Conveyors (Types of conveyors) 71

Shaker Conveyors 71

The Belt conveyor 71

The Scraper chain conveyor 72

III) Shuttle Cars 72

Hoisting – Types of Hoisting 73

Unbalanced Hoisting 73

Balanced Hoisting 73

9. The Atmosphere and Mine Gases

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The Atmosphere 74

Atmospheric Pressure 74

Barometric Changes and their Effects in a Mine 74

Mine Gases 75

Properties, Physiological effects, detection & Uses of

Oxygen. 75

Nitrogen. 75

Carbon Dioxide. 75

Carbon Monoxide. 76

Methane. 77

Hydrogen Sulphide. 78

Sulphur Dioxide (Oxides of Sulphur.) 79

Oxide of Nitrogen. 79 80 Fire Damp 80 Black Damp. 81 White Damp. 81 Stink Damp. 81 After Damp.

Treatment in Cases of Gassing. 82

Procedure to the followed when a person is found unconscious 82 in an irrespirable atmosphere.

10. Ventilation

Natural Ventilation, How it is produced, Calculation for 83 Natural Ventilation.

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Distribution of the Air. 85

Brattice Cloth 85

Stoppings. 86

Doors. 86

Air Crossings. 86

Regulators. 87

Accessional & Descensional Ventilation 88

Homotropal & Antitropal Ventilation 89

Booster Fan (Purpose & Location). 90

Auxiliary Fan (Purpose, types). 90

Advantage & Disadvantages of Forcing Fans. 90

Advantage of Exhaust Fan 91

Fan Ventilation. 91

The Centrifugal or radial flow fan & 91

The Air screw or axial flow fan 92

Comparison between Centrifugal Fans & Air Screw Fan. 93

Reversing of Air. 93

Numericals. 93

11. Mine Water and Its Disposal

Origin and Types of Mine Water 95

Rain Water. 95

Underground Water. 95

Methods of Disposing of Mine Water. 95

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Drain Tunnels. 96

Hoisting the water. 96

Sumps. 96

Pumping. 96

Hazards of Water. 96

Types of pumps. 96

Reciprocating pumps & their types 96

Bucket or lift pump 97

Piston pump. 97

Ram or plunger pump. 98

Centrifugal, pumps. 99

Turbine pumps. 100

Sludge. 100

Mono pumps 100 102 Syphon.

12. Mineral Dressing

Definition 103

Economic Justification of Mineral Dressing. 103

Various Steps in Mineral Processig. 103

Crushing 103

Definition, Brief Description. 104

Types of crushers 104

Jaw Crushers. 104

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Gyratory Crusher and their comparison. 105

Cone crusher. 106

Rolls. 106

Grinding 107

Definition, Brief Description, Ball Mills. 107

Screening & Sizing 108

Definition, brief Description. 108

Types of Screens 109

Stationary Screen 109

Moving Screen 109

Flotation 109

Definition, Brief Description 109

Types of flotation 109

Direct Floatation 109

Reverse Floatation 109

Washing 110

Definition, Brief Description

13. Sampling and Evaluation

Definition, Purpose and Importance. 111

Introduction to Various Sampling Methods 111

Core drilling 111

Churn Driooling. 112

Rock drills. 112

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Channel sampling. 112

Blasting down large samples. 112

Test pits. 113

By Augar and post hole diggers. 113

Trencling. 113

Salting & its prevention. 113

Theory of Sampling, (Conditioning Ore) 114

Coning and Quartering 114

Valuation of Mines, Various method and necessary information 114 required.

14. Organization, Management, Safety & Welfare

Organization & Types of Organization. 116

Management Duties and Responsibilities 116

Safety & Welfare Aspects, Care of employees. 117

Analysis & Causes of accidents 117

Factors of Accidents in Underground Mining. 119

Factors of Accidents in Open Cut Mining. 119

Prevention of Accidents. 119

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CHAPTER-01

VALUE AND IMPORTANCE OF MINING INDUSTRY IN PAKISTAN

1.1 Introduction: Pakistan inherited a low mineral base. Mining activity comprised of rock salt, a few scattered coal mines, chromite, gypsum, lime stone and silica sand. In 1948 the production of only 4 minerals was recorded. Unlike the other sectors of economy, mineral sector did not figure prominently in earlier national economic development plans. There were other pressing needs of the country which attracted higher rating in socio-economic priorities and the government had to attend to them first. Notwithstanding the fact that the country needed a firm mineral base of its own for sustained and self-supporting growth of national economy, the mineral sector suffered from neglect and ignorance which is evident from its insignificant contribution of less than 1% to GNP. Due to insufficient geological knowledge, lack of research and development facilities and systematic planning, shortage of trained and experienced manpower, absence of infrastructure facilities, inadequate financial allocations and paucity of risk capital the sector as a whole remained static. While the need for an urgent attention to mineral sector was always felt but plans of action to achieve the targets remained undefined for lack of proper understanding of the special needs and challenge of the mining industry vis-à-vis other industrial and manufacturing sectors. Because of the low priority accorded by the industrial development strategy to the use of indigenous raw materials the proper exploitation of national resources did not take place. The development of mineral resources in any country constitutes only one element of the national development and needs to be re-structured to fit within the frame work of overall development strategy. The broad objectives of mineral development includes ensuring optimum utilization and conservation of mineral resources, earning and saving of foreign exchange, supply of raw material, inputs to the industries and stimulating socio-economic development of under-developed regions of the country.

1.2 Mineral Potential of the Country

1.2.1 The sedimentary rocks cover about 80% of the total land of the country and therefore major mineral resources are of non-metallic minerals and industrial rocks. These include coal, rock salt, clays, gypsum, lime stone, dolomite, iron ore, barite, fuller’s earth, silica sand, bentonite etc. The known mineral deposits/showings found in igneous rocks are onyx marble, sulpher, porphry copper, chromite manganese, magnesite, lead, zinc while the metamorphic rocks contain fluorite, beryl marble, slates, precious stones garnets etc. 1.2.2 Although about 47 minerals are reported to occur in the country yet the exploration and exploitation is restricted to only a few viable mineral prospects determined, mainly by the overall economics of mining and market demands. 1.2.3 The picture of mineral resources in the country is rather vague. Adequate information about their extent, quality and quantity is not available. This is due to the fact that mineral exploration and evaluation which is essentially carried out to determine the techno- economic viability of mineral prospects was accorded low priority. The private sector

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holding 85% of the mineral properties was shy to invest capital in mineral exploration nor was it worthwhile for them to raise any risk capital. In public sector the pace of mineral exploration and evaluation remained extremely slow for want of adequate risk capital. Thus a very small percentage of national resources have gone into this vital activity and as a result the mineral potential of the country is mainly undetermined and under-utilized. 1.2.4 The industrial rocks and minerals were known to occur before Pakistan came into being but only a few minerals viz coal, sulphur, chromite etc. were exploited on a small scale. On account of low priority accorded to the mineral sector in the overall development strategy no significant progress was made after independence as far as detailed exploration and evaluation was concerned and only lignite deposits of coal in Sindh. Hazara Phosphate Saindak copper, China clay and low grade Nepheline Syenite, marble deposits of NWFP and Baluchistan including the world famous onyx of Chagai and also Barite deposits of Lasbela and Hazara as well as glass sand deposits of Salt Range, Punjab, NWFP and Mohmand territories were added to the mineral inventory. 1.2.5 Apart from iron ore, copper and chromite, the other known resources of metallic mineral is of little economic significance. There are fairly large reserves of iron ore but because of low grade, complex chemical and mineralogical composition and/or difficult accessibility these deposits have not been exploited so far. Apparently large low grade deposits of lead and zinc are known to occur in Baluchistan and the reserves of other metallic minerals are yet to be evaluated. 1.3 Nature of Mining Industry 1.3.1 It is considered necessary that all those who are associated with this basic industry should understand the requirements, complexities, special challenges of the mineral industry. 1.3.2 The nature of mining industry is extra-ordinarily complex. The physical characteristics of mineral resources, their heterogeneity, their remotes, geological certainties and their development and processing requirements cause the industry to operate at the levels of risk higher than those of industrial sector. The elapsed time between mineral discovery and commercial exploitation may range from 10 to 15 years. Because of these complexities, long gestation period and inherent risk to capital, return on capital investment is neither quick nor sure. 1.3.3 Mineral exploration and evaluation is a prime and basic requirement of scientific and commercial mining. It is essentially carried out to convert resources into reserves and to establish the techno-economic viability of a mineral prospect. It is a risk venture and the ratio of risk is at least 1:10 i.e. out of 10 mineral exploration projects only one may prove viable and the expenditure on remaining 9 prospects becomes abortive. However, the technological and financial risks have to be taken perforce as without this no development and expansion in mineral sector can even be envisaged. Moreover due to inherent risks involved in the criteria for financing, the industrial projects cannot rigidly be applied to mining industry. 1.4 Present Status of Mining Industry & Major Constraints 1.4.1 The development of mineral sector in Pakistan has not kept pace with the developments that have taken place in other sectors of economy. Due to low priority, lack of systematic planning and institutional frame work as well as absence of well defined National Mineral

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Policy, the sector as a whole remained static. The situation aggravated because the subject of mineral development was transferred back and forth several times between centre and provinces. The frequent changes in the policy and divided responsibilities led to the mush rooming of a number of agencies in public sector both at Federal and Provincial level. There had been no coordination between these agencies and no rules or guide lines had been laid for this purpose. Besides, the end-using concerns under the Ministry of Production are also involved in mining. They are only interested in retaining and operating the mines under their control to the extent of their own requirements irrespective of production potential of the mineral prospects for other uses internally and abroad. The present situation has defeated the efforts towards concentrated development of mineral resources. 1.4.2 The mining industry was in the hands of the private sector and still nearly 85% of the mining leases/prospecting licenses over more promising and accessible prospects are under their control. The private sector by and large has made no major contribution to mineral exploration with the result that the potential of the areas under their control is not established and the valuable resources have been under-utilized. In the field of commercial mining the private sector has so far concentrated on the surface minerals which are easily accessible and easy to mine using wasteful mining techniques. They have mainly resorted to skimming of high grade deposits which were easily saleable, without any regard to optimum recovery and beneficiation of low grade minerals. Their main objective was to earn maximum and quick profits with minimum capital investment even if it resulted in spoiling of deposits for good. With these short term objectives, they have been doing booming business in coal, marble, limestone, fireclay, silica sand and construction materials. 1.4.3 There are not many known mineral deposits of economic significance in the country. There is, therefore, a growing tendency for competition among public sector agencies as well as private parties to acquire leases of promising mineral prospects. In this scramble the respective merits, competency and capability of the agency concerned is often lost sight of. This has only retarded the progress of mineral sector. 1.4.4 No co-ordination and integrated long-term development plans could be implemented because of diverse interests and different priorities of the existing mineral development agencies. As such flexibility of operations, intra-sectoral adjustments and shift in priorities is almost absent and could not be made since no single organization is responsible for mineral development. 1.4.5 There is still a gap between mineral discovery and development which has been caused by the paucity of risk capital and lack of a well equipped mineral exploration and development agency. 1.4.6 There is no clearly stated National Mineral Policy defining the role of various agencies involved in exploration and mining and indicating national priorities. As a result, the mineral development is sporadic and there is a lack of direction and clear cut goals. The decisions are taken on adhoc basis and this situation puts an obstacle to effective development of mineral resources. 1.4.7 Multiplicity of agencies has resulted into scattering of limited financial, manpower and material resources and consequently no single agency is properly equipped to undertake all facts of mineral development and utilization on its own.

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1.4.8 The policy of fragmented and disjoined mineral leasing is not only uneconomic but also not keeping with requirements of planned development of mineral sector. 1.4.9 There are several large deposits of low grade minerals which may become commercially useable if those could be upgraded. Such minerals have not been exploited and utilized for want of research and development facilities. Whatever arrangements are available they are inadequate and scattered and are as such incapable of providing reliable and quick services to mineral exploration and development. 1.4.10 The Pakistan Mining Concession Rules, 1960 and Mines Act 1923 and the regulation thereto are neither development oriented nor they ensure conservation and optimum utilization of valuable resources. Each province has its own rules which are largely divergent. No significant improvement is possible unless a uniform set of rules with regard to mineral concessions and mine safety are framed and enforced throughout the country. 1.4.11 Mineral deposits are mostly located in remote and under-developed areas of the country devoid of essential infra-structure facilities and social amenities. This is seriously inhibiting the development of even small and medium scale mining. 1.4.12 Last but not the least, the financing policy of the Government is conducive to proper long- term development and expansion of mineral sector. Allocation of interest bearing loan for risk project of exploration has adversely affected the mineral exploration programme. 1.5 Future Prospects 1.5.1 It is generally believed that Pakistan as a result of intensive exploration will not prove to be a highly mineralized country, such as Chile or South Africa. There is no doubt that the mineral industry can be enlarged manifold with more systematic mineral exploration and evaluation and scientific development of mineral resources. 1.5.2 In view of the expansion of the industrial and agriculture sectors and the development of new cement factories, fertilizer plants and iron and steel industry, the future requirements of minerals and energy are expected to increase manifold. Apart from the existing industrial rocks and minerals which are being produced in commercial quantities the production of other major prospects could be increased to meet the requirements of the country. 1.5.3 The estimated coal reserves are of the order of 185 billion tones valuing $ 110 billions priced at oil equivalent of $ 30 per barrel. These resources have the potential to narrow down the gap between energy supply and demands. The potential demand for coal in the year 1988 is estimated to be 5.40 million tones which can be met from indigenous resources provided early measures are taken to re-organize and develop the coal sector on scientific lines. 1.5.4 The total reserves of low grade Sedimentary iron ore at Kalabagh are to tune of 300 million tones with 150 million in proven category. The beneficiation studies conducted by PCSIR revealed that the ore could be upgrade to 58% Fe and used as a blend with high grade ore in Pakistan Steel Mill. Alternatively another Steel Plant could be based on these deposits. 1.5.5 There are very large deposits of rock salt in the country and the production has increased from 0.30 million tones in 1971-72 to 0.578 million in 1983-84. With the development of

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Salt Solution Mining Project and new conventional mines the production can be raised to 1.00 million tones per annum subject to the availability of additional market demand. 1.5.6 Gypsum deposits have been estimated at 5.50 billion tones. Apart from its other industrial uses it is used for reclamation of zodiac soil and for correction of low quality ground water. The potential demand for agricultural gypsum over the next decade would be 1.625 million tones which can be fully met from available resources. 1.5.7 The proven and indicated resources of rock phosphates at Hazara are of the order of 3.48 million tones and 3.606 million tones respectively. These resources will be developed for import substitute. 1.5.8 Virtually inexhaustible reserves of raw materials for cement are available in the country which can meet the requirements of the projected expansion f cement industry. 1.5.9 The proven resources of copper ore are to the tune of 412 million tones which are amenable to commercial exploitation and beneficiation for internal use as well as for export. 1.5.10 The magnesite occurs in NWFP. The available reserves of 3.00 million tones are sufficient to meet the requirements for magnesite and chrome magnesite bricks. 1.5.11 Apart from the reserves of China clay available in Swat, about 3.50 million tones exist at Nagarparkar Sindh. These deposits have not been developed for want of infra-structure facilities. 1.5.12 Nephyline Syenite is an important raw material for alumina, feldspar etc. The total reserves of the mineral in NWFP have been estimated as 6 billion tones which are suitable for use in glass industry. 1.5.13 Naukundi iron ore has been found technically suitable as feed for blast furnace in palletized form in replacement of lump ore. The available reserves are sufficient to meet 47% of the total demand of Pakistan Steel. 1.5.14 The available resources of Chromite in the country are sufficient to meet the demand of chrome based chemicals and refractories project. 1.5.15 According to available data there is a significant potential for increasing the production of Gem stones provided detailed exploration is undertaken. The high quality Mangora Emerald Merits a detailed exploration at depth. 1.5.16 Large deposits of high grade marble exist in different parts of NWFP and Tribal territories. Quarrying, cutting and polishing of the marble are not up to the mark and needs looking into. High grade barite deposits about 6 million tones occur in Gonga area of Lasbela and are being exploited for oil industry. 1.5.17 It is evident from the above that the mining industry in the country, though modest at present, can be enlarged to meet the growing needs of the industrial and agriculture sectors. The potential is under utilized and practical steps need to be taken to improve the performance of this sector. This will pose a challenge at all levels and the Government will have to lay the basis and encourage the creation of a prosperous mining industry in the country.

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DEFINITIONS RELATING TO MINING

1.1 Sketch

Composite sketch illustrating mining Terms Fig 1.1 1.2 Mining It is the process of obtaining useful minerals from the earth’s crust, for the benefit of mankind. Mineral production is actually the mining. 1.3 Prospecting Prospecting is first step/stage in mining operation. It is search for valuable ore/mineral deposits. 1.4 Exploration This is second stage in life of a mine. The work of gaining knowledge of the size, shape, position and value of an ore body is known as exploration. 1.5 Development This is third stage in life of a mine. It is the work of opening a proved ore body, or a coal seam to prepare it for mineral production. 1.6 Exploitation This is final stage in the life of a mine. It is the work of recovering mineral/coal from the earth in economic amounts and processing it for sale in the market. 1.7 Vein A mineralized zone having more or less regular development in length, width and depth to give it a tabular form. A vein is commonly inclined at considerable angle to the horizontal.

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1.8 Shoot The certain portion of a vein where valuable minerals are commonly concentrated. 1.25 Bedded Deposits A mineral deposit of tabular form generally lies horizontally. A coal seam is a typical example of bedded deposit. 1.26 Masses Large ore bodies of irregular shape are called masses. 1.27 Out Crop The surface exposure of a mineral deposit. 1.28 Float A float is composed of loose pieces of ore or rock which have fallen from veins or strata. 1.29 Gossan It is the ferruginous deposit filling the upper part of some mineral veins or forming a superficial cover over masses of pyrite. 1.30 Dip The angle at which a bed, stratum or vein is inclined with the horizontal. 1.31 Strike The bearing of a horizontal line in the plane of an inclined bed, stratum, or vein. It is perpendicular to the direction of the dip. 1.32 Apex The top of the terminal edge of the vein on the surface. The vein has a dip or strike from this point. 1.33 Hanging Wall The wall or rock on the upper side of an inclined vein. In bedded deposit it is known as roof. 1.34 Foot Wall The wall or rock under an inclined vein. It is called the floor in bedded deposit. 1.35 Shaft It is a vertical or nearly vertical opening in a mine connecting the surface face with underground working. It is a principal opening through which the mine is exploited and men, supplies, ore and waste are transported. 1.36 Drift A horizontal or nearly horizontal opening in or near ore body parallel to the strike of the vein. 1.37 Cross Cut It is a horizontal opening driven perpendicular to the strike of the vein or across the direction of the main working. 1.38 Level

Mines are normally worked from shaft through horizontal passages or drifts called levels.

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1.39 Sump II. An excavation made underground to collect or store water, from which water is pumped to the surface. 2.25 Winze III. A vertical or inclined opening driven from a level downward for the purpose of connecting with lower level. 3.25 Raise IV. A vertical or inclined opening driven upward from a level to connect with a level above. 1.26 Stope

An excavation from which ore has been extracted or part of an ore body from which ore is currently being mined. It is usually inclined or vertical, but may also be horizontal. 1.27 Tunnel

It is a horizontal or nearly horizontal opening/passage that is open to atmosphere at both ends. For example: tunnels used in railways. 1.28 Adit

A horizontal or nearly horizontal underground opening into a mountain with single access to surface. 1.29 Collar

This term applies to the thick ring of concrete or other material around the mouth of a shaft. It is the junction of a shaft and the surface. 1.30 Ore

Ore is defined as natural aggregate of minerals which can be extracted from earth’s crust at a profit. An ore contains commercially useful minerals as well as “gangue” minerals. The term ore is used with mineral deposits containing metals. 1.31 Gangue

Worthless minerals associated with economic minerals in an ore are called gangue. 1.32 Country Rocks

The general mass of enclosing rocks adjacent to ore deposit is called Country Rocks. 1.33 Waste

A barren rock which contains no minerals of economic value. 1.34 Mineral

Any naturally occurring, inorganic (Not containing carbon) homogeneous substance in the crust of earth having a composition expressed by a chemical formula, clear physical properties and economic significance (Importance) is known as mineral. Although coal is an organic matter but it is considered as mineral from mining point of view.

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1.35 Metallic/Metals These forms a large part of the earth on which we live. Nearly 80% of the known elements are metals. The metallic minerals have certain properties, which distinguish them from other elements. 1.36 Non Metals / Non Metallic The non metallic lacks the properties of metallic mineral, such as bright metallic luster, Hardness, density and good conductor of heat and electricity. The main non metallic minerals are coal, rock salt, boron, carbon, phosphorus. 1.37 Lode A miner’s term for a fissure filled with a concentration of one or more minerals particularly used to describe quartz and gold veins. 1.38 Drive A horizontal opening like a tunnel lying in or near the ore body parallel to the strike. 1.39 Draw Point A spot where gravity fed ore from a higher level is loaded into hauling units. 1.40 Grizzly A rugged screen for rough sizing at a comparatively large size, it can comprise fixed or moving bars, disks or shaped tumblers or rollers.

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CHAPTER-02

PROSPECTING AND EXPLORATION OF MINERAL DEPOSITS

2.1 Sequence of Activities Introduction

Prospecting is the search for metallic, non metallic ore deposits.

Ever since man’s appearance on earth, he started using weapons of wood and stone more than 200,000 years ago. The use of clay and ornamental stones was also known to them. Following the Stone Age, man, in the Bronze Age, learnt to find and mine copper minerals, extracted the metal from the ore and shaped it for different uses.

Prospecting was an important activity in man’s life since earliest time. Initially prospecting was limited to direct search methods which included physical examination for outcrops (Rekey), geological study and mapping. For shallow deposits, entry to the deposit is made through bore hole to collect the necessary information. Slowly man acquired a specialized knowledge of rocks and minerals around him and developed enough skill and talent in the work to become a prospector.

The earliest miner was very successful prospector. Gradually, the miner based upon his experience and knowledge developed ability to discover unknown deposits.

These days, direct method for Mineral prospecting is difficult, because most of the shallow Mineral deposits have been exhausted and remaining are deeply hidden or concealed in earth. But, now-a-days some indirect methods i.e. Geophysics and Geochemistry in combination with direct methods are used for prospecting purposes.

Indirect methods are expensive and must follow some systematic procedure before their choice and implementation.

2.2 Prospecting Procedures

Generally, prospecting procedure follows these steps:-

1. Search of available literature and records of the area under consideration. 2. Aerial photograph study. 3. Study of available geological and surface maps. 4. Preparation of photo geological map from available information and new aerial data. 5. Conduct of airborne geophysical survey of area under study. 6. Exploratory boring. 7. Establishment of base of operation, set up mapping control and organize ground prospecting parties. 8. Conduct of preliminary ground geological, geophysical and or geochemical surveys. 9. Laboratory studies. 10. Assembling and analysis of findings. 11. 2.3 Methods of Prospecting (Various Techniques Involved)

2.3.1 Geological Prospecting It applies knowledge of geology to mineral search. In this geological data e.g. information of formation and occurrence of mineral deposits, structural mapping, etc. is collected that

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helps to discover, define and appraise the mineral prospect.

In early days search for outcrop of a mineral deposit was main feature of geological prospecting. Now, new deposits are discovered usually by geological methods supplemented by other data (Geo-physical and Geo-chemical). Therefore, searching ore deposits using different techniques is called geological prospecting.

2.3.2 Geophysical Prospecting Geophysics is the science that applies physics to the study of the earth. Geophysical prospecting uses different physical properties of subsurface rocks. Geophysical prospecting is divided into sub fields according to the property of the mineral/rock being measured, such as magnetic, gravity, seismic, electrical conductivity, thermal or radioactive properties.

Geophysical prospecting is a process which searches for any unusual effect or changes in the geophysical properties (anomalies) of the particular portion of the earth on

instruments specifically designed for the detection of that change.

Data received through geophysical prospecting is always ambiguous, that is, doubtful. It requires an expert to interpret the data. Out of many explanations it is always difficult to choose the right one. From most optimistic data, analysis is made to reach at any conclusion. The combinations of different geophysical prospecting methods are used for better results. Some of important and widely used methods are:-

1. Seismic prospecting 2. Electrical conductivity prospecting 3. Electromagnetic prospecting. 4. Gravity prospecting 5. Magnetic prospecting 6.

2.3.2.1 Seismic Prospecting

Investigating the depth and character of sub-surface rock formation by noting the travel times of seismic waves or artificial shock waves through them is known as seismic prospecting. The speed of the seismic waves varies as the wave travels through different kinds of rock.

Seismic prospecting methods involve basically the same type of measurements as earthquake seismology (study of shock waves). Explosives and other energy sources are used to generate the seismic waves. This method is superior to other geophysical methods due to various factors such as high accuracy, high resolution and great

penetration.

Seismic method is principally used in exploring for petroleum and rarely any exploratory well is drilled without seismic information. Seismic methods are also important in

groundwater searches and in civil engineering projects.

Seismometers or seismographs are used to measure and record the resulting motion of the earth produced by seismic waves.

Seismic prospecting has two major classes: refraction and reflection methods.

Refraction seismic techniques are best suited to a flat terrain where the underlying formations show marked changes in seismic speed. The reflection method is used where the reflecting bed is uniform in nature and is horizontal.

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2.3.2.2 Electrical Conductivity Prospecting

This utilizes artificially generated electric currents to find difference in electrical conductivity (quality of a substance to allow pass heat or electricity through it) between ore and the enclosing rocks or between adjacent geological formations. Hence property of electrical conductivity of the earth is measured. Electrical methods are suitable for prospecting for ore bodies like massive sulfide ore body. There is a significant change in measurement when massive sulfide mineralization is present beneath the surface. They are also used to investigate geological structure and determining the depth below the surface to water level or bedrock.

2.3.2.3 Electromagnetic Prospecting

With the exception of magnetic, the electromagnetic prospecting technique is the most commonly used in mineral exploration. It is not suitable for oil search and civil engineering work. In this method, an alternating current of low frequency-500 cycles is sent through a wire loop either horizontal or vertical on the surface. A primary electromagnetic field is produced which penetrates into the earth. This produces a secondary electromagnetic field due to subsurface conducting body when the electric current is induced in it. The result of exploration is to give direction and intensity of the electromagnetic field at various points. When properly mapped these indicate the position of the subsurface conducting body. Ore body of sulfide graphite or associated pyrite or pyrrhotite may be detected by this method.

2.3.2.4 Gravity Prospecting

Gravity exploration is based on the Law of Universal Gravitation. The Earth’s density varies from one location to another. As such the force of gravity varies from place to place. Gravity prospecting deals with measuring these variations.

The gravity effect of ore bodies is generally small despite the fact that there may be large density difference between ore and its surroundings. Therefore, gravity surveys to detect ore bodies have to be very detailed. The instrument which detects changes in gravity is called a gravimeter.

Gravity prospecting is used as initial survey in oil exploration. In mining it is used to detect and help identify geological structures such as faults, anticlines, salt domes and buried channels.

2.3.2.5 Magnetic Prospecting

The earth acts like a huge magnetic. The magnetic material in the earth increases the strength of the earth’s field within itself. This increase in strength over normal field at that location is called the magnetic situation anomaly. The instrument used to investigate the anomaly caused by magnetic body is known as Magneto Meter. A number of observations are made at different points. In general several corrections have to be made for changes in temperature and for daily variations in the earth’s magnetic field. Magnetic ore bodies and ferruginous sediments are detected by measuring their magneto anomalies.

2.3.3 Geochemical Prospecting

Geochemical prospecting for minerals include any method of mineral exploration based on systematic measurement of the chemical properties of naturally occurring minerals.

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Geochemical prospecting detects minute changes in the chemical composition of sample of air, ground water, soil, or botanical specimens caused due to near presence of some metallic ore bodies. These anomalies (changes in chemical properties/pattern of materials) indicate the possible presence of ore. Such anomalies may be formed:-

1. At depth by ingenious or metamorphic process or 2. At the surface by weathering and erosion etc.

In modern prospecting, geochemical prospecting is generally carried out in combination with geological and geophysical surveys.

In different applications of geochemical prospecting main target ores are mainly the sulphids of copper, lead, zinc, nickel and molybdenum and to lesser extent, uranium, tungsten, tin, mercury, gold and silver minerals.

3.1 Exploration The exploration may be defined as to determine the geometry, extent and worth of an ore deposit value and tonnage of a deposit. It also helps in the preparation of feasibility reports.

The series of steps in exploration stage are as follows:

1. The favorable area identified by prospecting is marked out. 2. The mineral deposit marked out be sampled thoroughly and samples analyzed. 3. The sampling data is utilized to prepare estimate of tonnage, grade, extent and value of the deposit. 4. On the basis of above the present worth can be calculated and recommendations made regarding the feasibility of mining.

3.2 Difference between Resource and Reserve

A resource is a concentration of naturally occurring material that is potentially economical to extract.

A reserve is a portion of a resource that can be economically extracted.

3.3 Difference between Proven, Indicated/Probable and Possible Reserves

Proven: Measured: (It is based on complete direct knowledge). Probable: Indicated: (It is based on less comprehensive knowledge). Possible: Inferred: (It is based on assumptions).

3.4 Methods of Exploration

They are Excavation, Analysis and Logging. For a hidden deposit, excavation must be employed, coupled with geological logging, collection and analysis of samples or bore hole logging using geophysics.

Of the four types of drilling usually employed in mining operations (1) pneumatic or hammer drills (2) shot drills (3) diamond drills and (4) churn drills, the last two are employed most frequently for prospecting and exploration purposes. These have comparative advantages and disadvantages, and one may be applicable where other is not. A comparison of both is given below:

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3.5 Comparison of Diamond and Churn Drills

Diamond Drills Churn Drills

1 Can drill in any direction, including 1 Can drill only vertically downward. Large upward from underground. station must be provided for underground drilling.

2 Core sample gives valuable geological 2 No core sample but cuttings give information; texture of rock, attitude of information as to type and value of rock. bedding, etc.

3 Sample is small, though shape and 3 Provides larger sample which may be diameter of core is uniform. May give more representative. accurate sample if core recovery is good. 4 Slower than churn drilling under average 4 Faster to depths of 1000 to 1200 ft. conditions.

a. Successful in very hard rock. a. Slow and expensive in very hard rock. b. In fractured rock gives poor core b. Successful in fractured blocky rock. recovery and progress is slow. c. Suffers operational difficulty and c. Progress satisfactory in excess bit wear in poorly conglomerate. consolidated conglomerate or soft rock with hard veins. d. Yields unsatisfactory core in d. Gives good samples in un- unconsolidated material. consolidated material.

5 Hole usually serves no other purpose 5 Large hole may later serve for ventilation, than exploration. drainage or blasting in some cases.

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CHAPTER-03

DEVELOPMENT AND EXPLOITATION

In this chapter, we shall describe third and fourth stages in the life of mine.

3.1 Development (Definition)

Development is the work of opening a Mineral deposit for exploitation. The steps involved in it are to bring a mine into full scheduled production. These include planning, design, construction, and other phases. Mine development follows generally the feasibility study conducted at the close of prospecting and exploration stages.

The major purpose of development is to provide access to the ore deposit, permitting entry of the miners, equipment, supplies, power, water and ventilating air, as well as egress for the mineral being mined and waste produced. Prior to the start of the exploitation phase of mining, development is limited insofar as possible to the construction of primary or main openings.

In a surface mine, access to an ore body overlain by waste is gained by stripping the overburden. In an underground mine, small sized openings are driven from the surface to intersect the ore body and eventually to connect with large exploitation openings. Because mainly waste material is involved, little income occurs during the excavation of development openings.

SOCIAL ECONOMIC POLITICAL - ENVIRONMENTAL FACTORS These factors can exercise disproportionate influence on mine development and operation. They are difficult to quantify. Some factors are:- a) b) a) Demographic and occupational skills of local populace. b) Means of financing and marketing. c) Political stability of host country. d) Pollution legislation (e.g. air, water, wastes, etc). e) Other governmental aids and restrictions applicable to the Mining Industry. f) These factors govern many critical aspects of both development and exploitation.

3.1.1 Sequence of Development

The steps generally carried out during mine development include the following for both surface and underground mining:-

1. Adoption of feasibility report as a planning document, subject to modification as development progresses. 2. Confirmation of mining method and general mining plan. 3. Arrangement of financing, based on confirmed cost estimates from the feasibility report. 4. Acquisition of land, including mineral rights and surface, as needed. 5. Filling of environmental impact statement, obtaining of mining permit (including reclamation plan, if a surface mine) and posting of bonds subject to both federal and state statutes, as applicable. 6. Provision of surface access, transportation, communication and power supply

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to the mine site. 7. Planning and constructing of surface plant, including all support and service facilities and administrative offices. 8. Erection of mineral processing plant, if required, and ore handling and shipment facilities, and provision of stockpiling and waste disposal facilities. 9. Selection of mining equipment for development and exploitation, with acquisition as needed. 10. Construction of main access openings to ore body and such secondary openings as required including, in surface mining, advanced stripping, and, in underground mining, shafts and certain other sub surface facilities. 11. Recruitment and training of labor force and provision of support services (housing, transportation, consumer stores, etc) as necessary, with attention to other social political economic needs of employees. 12. 13. Several steps in development may proceed nearly simultaneously (e.g.) steps 3, 4 and 5 in one effort and 6, 7, 8, and 10 in another). To ensure proper coordination and timely completion of all development tasks, careful scheduling is required, especially of all construction.

3.2 Exploitation It is the 4th stage in the life of a mine. Exploitation is the work of recovering mineral from the earth in economic amounts. In this process, a number of extractive unit operations are employed, the primary ones constituting the production cycle and the secondary ones the auxiliary or support functions on the surface, pits or cuts are excavated in all kinds of mineral deposits, but in underground, openings are made in rooms or longwalls in coal mines and stopes in non coal mines.

3.3 Factors involved in Selection of a Mining Method A mining method should be selected which best matches geological and environmental characteristics of the mineral deposits, which is to be mined. Beside this, the safety factors the lowest mining cost and maximum profit should also be kept in mind. Experience plays a major role in decision making. The factors which govern selection of a mining method are as under:

3.3.1 Characteristics of Deposit These are probably the most important determinant, because they largely decide the choice of surface Vs underground mining and affect the production rate, the method of materials handling, and the layout of the mine in the ore body. They include size, shape, dip and depth of the deposit.

3.3.2 Geologic and Hydrologic Conditions The geological characteristics of both the mineral deposit and adjacent country rock, influence selection of a method. The extent of support required for underground, control hydrological affects drainage and pumping requirements, both surface and underground are taken into consideration.

3.3.3 Geo-technical (Soil and Rock Mechanics) Properties Again, both ore and waste are involved. The mechanical properties of the materials comprising the deposit and country rock are the key factors in selecting the equipment in a surface mine and choosing among the classes of methods (unsupported, supported, and caving) if underground.

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3.3.4 Economic Considerations Ultimately, economics determines the success of a mining venture. These factors govern the choice of method because they affect output, investment, cash flow, payback period and profit.

3.3.5 Technological Factors The best match between natural conditions and mining method is sought. While a particular method may not be ruled out in mining.

3.3.6 Environmental Concerns Not only the physical environment but the social-political economic climate is involved.

3.4 Classification of Mining Method The classification of mining method applies to surface and underground mining of coal and none coal. (These are basically two Mining Methods). 3.4.1 Surface Mining Methods If the work of mineral extraction takes place entirely open or operated from the surface the process is called surface mining e.g. quarrying/open pit.

3.4.2 Underground Mining Methods If mineral extraction work is done through openings below the surface of the earth, the process is called underground mining e.g. room and pillar mining method and long wall mining method.

3.4.1 Surface Mining Methods

They are:-

a) Open Pit Mining In open pit mining, the over burden is stripped and transported to a disposal area to uncover the mineral deposit. Both stripping and mining are conducted from one or a sequence of benches. Open pit mining is a large scale method in terms of production rate is responsible for 60% of all surface output.

b) Open Cast Mining It is mainly used for coal. This method resembles the open pit mining but differs in only one respect i.e. the overburden is not transported to waste dumps for disposal but cast or hauled into adjacent mined out panels. Open cast mining is also a large scale method and ranks with it as the most popular surface methods.

c) Quarrying It is different from the term quarry which is sometimes applied to any surface mine producing a non metallic mineral.

Quarrying is the most expensive surface mining method and, with square set stopping, the most costly mining method. It is also a highly selective, small scale method, with low productivity.

The products of all dimension stone quarries are non metallic. Prismatic block of rock common dimension stones are granite, marble, limestone, sandstone etc. d) Auger Mining Although the over burden is not removed, and the coal is extracted by an auger or a mining machine working underground, the crew operating the machine is located at the surface, hence we classify it a surface method.

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e) Hydraulicking In hydraulicking, a high pressure stream of water is directed against a placer bank to under cut and cave it.

f) Dredging Dredging is the underwater excavation of a placer deposit. It is usually carried out from a floating vessel. The body of water may be natural or man-made, depending on the sizes of the dredge and deposit.

g) Bore Hole Extraction In bore hole mining, water is injected by wells into a mineral formation where it dissolves, melts and is then returned to the surface through well bores. Some times a reagent is added to the water.

h) Leaching It is the chemical extraction of metals or minerals from the confines of an ore deposit as well as from material already excavated and mined.

3.4.2 Underground Mining Methods

i) Self Supported Mining Methods

It consists of those underground mining methods, which are essentially self supporting and require no major artificial system of support to carry the load.

a) Room & Pillar Mining This is the method which is mostly used in Pakistan alongwith long wall method. In room and pillar mining, openings are driven orthogonally and at regular intervals in a mineral deposit usually flat lying, tabular and relatively thin forming rectangular or square pillars for natural support.

b) Stope & Pillar Mining Stope and pillar mining is the unsupported method in which openings are driven horizontally in a mineral deposit in regular or random pattern to form pillars for ground support.

c) Shrinkage Stoping Shrinkage stoping is a method in which the ore is mined in horizontal slices and remains in the stope as temporary support the walls and to provide a working platform for the miners.

d) Sub Level Stoping Sub level stoping is a vertical stopping method utilizing long hole drilling and blasting carried out from sub levels to break the ore.

ii) Supported Mining Methods These methods require substantial amounts of artificial support to maintain stability in exploitation openings.

a) Cut and Fill Stoping It is the method in which horizontal slices of ore are excavated in the stope and replaced with waste as fill. b) Stull Stoping It is the method in which systematic or random timbering with simple supports is employed for ground control.

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c) Square Set Stopping It is one of the most expensive methods in underground mining. In square set stopping, small blocks of ore are systematically extracted and replaced by prismatic skeleton of timber sets.

iii) Caving Mining Methods This is the third classification of underground mining methods. In this method, the exploitation workings are designed to collapse. There are three major caving methods.

a) Long wall Mining

It is the most used mining methods in Pakistan. Long wall mining is an exploitation method used in fairly flat-lying, thin tabular deposits in which a long face is established across a panel between set of entries and retreated or advanced by narrow cuts, aided by the complete caving of the roof or hanging wall.

b) Sub Level Caving In sub level caving, overall mining progresses downwards while the ore between sub levels is broken overhand. Mining is conducted on sub levels from development drifts and cross cuts, connected to the main haulage level by ramps, ore passes and raises.

c) Block Caving It is the mining method in which masses, panels or blocks of ore are undercut to induce caving, permitting the broken ore to be drawn off below.

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CHAPTER-04

DRILLING AND BORING

4.1 Introduction

In almost all forms of mining, rocks are broken by drilling and blasting especially for underground mining. Drilling is normally done for providing space for placement of explosives. The explosives so placed in the confined holes of rocks are blasted to break the rocks in small pieces.

Several points are kept in view while selecting a drilling plant, such as initial cost and cost of operation; depth of drilling; nature of rock formations drilled and available methods of transportation. The phases involved in breaking rocks by drilling and blasting are:-

1. Drilling hole in the rock. 2. Cleaning of the broken material from hole. 3. Fracturing and fragmentation of rock by using explosives 4. Removal of broken rock. 5. The main components of drilling system are drill (sources or prime mover), rod (transmitter) and bit (applicator). The circulation fluid may be added as fourth component.

Drilling methods vary mainly accordingly to method of mining, sample taking and rock destruction and kind of drive. As such, different drilling machines according to job requirements have been designed e.g. sinker, drifter, stopper, churn drill etc.

4.2 Difference Between Drilling and Boring

Drilling means to drill a hole for blasting purposes. The length and diameter of the hole depends upon the situation whether underground or on the surface.

While boring means to bore a hole from the surface and thereby gain knowledge as to:-

1. The depth, thickness, quality, extent and the number of coal seams or other materials. 2. The amount, direction and variations in the dip of the strata. 3. The existence of any faults or other disturbances of the strata. 4. The existence of water bearing rocks and the nature of strata being passed through.

From the data obtained, a Mining Engineer has a complete picture of conditions below ground and is able to estimate the cost of sinking and the underground difficulties which he will have to face.

4.3 Types of Drilling Machines

Drilling Machines are of three types:-

1. Rotary Drilling 2. Percussive Drilling 3. Churn Drills

4.3.1 Rotary Drilling

In the rotary system the cutting tool receives a rapid rotary motion transmitted from an engine situated on the surface, through the boring rods. The drilling is done by abrasion.

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The cutting tool may be hollow bit with the cutting edge set with diamonds or with an annular groove on the cutting edge in which chilled shot revolves, a saw tooth crown made of finest steel and tipped with a special hard alloy, or a patent roller bit such as the “Hughes Simplex”.

The tool used depends on the strata to be cut.

All rotary drill machines are equipped with water flushing systems and their big advantage is that in most cases a complete core is cut from the strata and brought to the surface for examination.

Diamond System of Drilling

The drilling tool, in this case is the diamond crown. It is a cylindrical cast steel shell having in its lower face a number of small sockets in which pieces of black diamond are set. Half of these are set to the outside to dress the sides of the hole. The others half is set to the inside to dress the core.

Single tube Core Barrel

The barrel is screwed to the upper part of the bevel-shell which connects it to the crown. A steel coupling block with a central passage for the circulating water is screwed to its upper end and serves to connect the barrel to the hollow bore rods above. A mud bucket is provided above the coupling block to receive the large particles of derbies which the circulating water fails to carry to the surface.

Single tube core barrel Fig 4.1

The junction piece between the barrel and the crown is beveled and contains a core lifter. This core lifter is a split ring, corrugated on its inner face and occupies the wider portion of the bevel-shell when boring is taking place so that it does not grip the core. When boring is stopped and the barrel and crown lifted by the rods, the core lifter takes up a lower position, thus tightening on the core. The latter may now be broken off by a twist and raised to the surface.

4.3.2 Percussive Drilling

The principle is to strike a series of continuous blows on the rock by means of a chisel thus shattering the rock and at the same time the chisel is slightly turned between each blow so that a circular hole is formed. The chisel is suspended from the surface by iron-

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rods or wire rope and the weight of the chisel fitments rods; etc is utilized to give the striking force.

Power Operated Percussive Drill

Figure 4.2 shows a sketch of power operated percussive drill.

Boring

Mechanical Percussive Rig Fig 4.1

The beam is mounted on steel springs, which give great elasticity and cause sudden recoil of the boring tool which prevents jamming. The progress of the chisel is followed by controlling the passage of rope through a clamp near the drum. This rope drum is also used to raise the rod from the bore hold to change tools, attached the sludger, etc. With this method it is possible to bore a depth equal to the length of one rod without ceasing operations and as water flush is mixed. A mixture of mud and water is pumped down the column, which in this case is hollow and the mixture returns to the surface on the outside of the rods carrying with it is a large percentage of the debris.

The rotation of the column is by hand by a turning lever clamped to it. i. Churn Drills

The churn drill is used for prospecting placer gravels and also for sampling certain ore deposits, especially those of copper, lead, zinc and iron. It is also used for drilling blast holes, holes used for ventilating purposes or holes through which electric wires and power lines are carried into a mine instead of down the shaft. It is mounted on a wooden or a steel base which is fitted with wheels or with caterpillar tread. A 6 inches drill is largely

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used in sampling ore deposits where holes are drilled up to 600 ft deep. Larger size with starting bits up to 26 inches are used for holes 1000 ft or more in depth and require a derrick 60 to 85 ft. high. Portable machines range from 6 to 9 or 12 inches in size. The larger holes drilled with heavier machines generally give a slightly lower cost per ton of rock or ore blasted. The churn drill is usually driven by electric, diesel or gasoline power, though steam is occasionally used.

4.4 Hammer Drills Machines

It is a percussive type drill machine. Piston drills have now been superseded by a lighter, more mobile and faster cutting hammer drills in which the bit does not reciprocate but remains against the rock in the bottom of the hole, rebounding slightly at each blow. The other end of the steel is struck by a light but rapidly reciprocating hammer drill. Figure 4.3 show a sketch and parts of a hammer drill.

Hammer Drills Fig 4.3

The modern hammer drill strike from 1500 to 2000 blows a minute and is a product of the highest grade of machine work. A rotating mechanism is provided to the bit after each stroke so that a fresh rock surface is presented for each below.

Types of Hammer Drill Machines

There are three types of Hammer Drill Machines:-

i) The Drifter ii) The Sinker and iii) The Stopper

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4.4 (i) The Drifter

These are the heaviest form of hammer drills and are made in various sizes depending upon the severity of the work to be done. The heaviest type weighs over 200 pounds and is used for holes up to 20 ft in depth. Drifters have a stroke of from 21/8 to 3 inches and a standard length of feed of 24 inches but a special feed screw 30 inches long is made also. The drills are heavy and must be mounted on a column or bar.

4.4 (ii) The Sinker or Plugner

This is essential a one-man drill, ranging in weight from 25 to 80 lb. that can be held in the hand but is frequently mounted. As the name indicates, this drill has found a wide application in sinking shafts and is made in several sizes, each suited for a particular kind of work.

Sinker Fig.4.4

4.4 (iii) The Stoper This drill was developed for work in narrow places where it would be difficult to use a drill column and whether the holes are pointed in an upward direction. The drill is provided at the back with a telescoping tube which has a movement of from 18 to 24 inches. The end of this tube is placed on the ground or on a timber and the pressure of the air forces the tube to cut and it holds the drill up to position. The weight of stoppers ranges from about 70 to 108 lb.

Stoper Fig. 4.5

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4.5 Boring Methods

Broadly speaking, all boring methods may be divided into two main classes:-

i) Percussive Boring Method. ii) Rotary Boring Method.

Percussive Boring may further be sub-divided into:-

i) Boring by Rigid Rods; ii) Rope Boring

If rigid rods are used, these may be either solid or hollow, the later being employed when it is desired to keep the hole constantly flushed with water. In general, percussive method is suitable only for vertical holes.

4.5 (i) Percussive Boring

Percussive Boring Methods are chiefly used when the primary object is to make a hole in the ground, without obtaining precise information of the nature of the ground passed through. The rock is broken in to fragments. The American rope system of boring has been extensively used in boring for oil and salt.

4.5 (ii) Rotary Boring

Rotary methods of boring are chiefly used for cutting an annual or grove in the rocks and leaving a central core which can be extracted from the bore hold. These are classified as:-

i) Diamonds ii) Chilled Shot iii) Serrated Steel Cutting Teeth or iv) Some special compound roller bit e.g. the tri-cone bit

4.6 Tunnel – Boring Machines

The present day Tunnel Boring Machine (TBM) competes with drill and blast methods. These are often faster and more efficient than explosives for excavating rock. These machines help in rapid excavation and effective ground support in civil and mining works.

4.6.1 Types of Boring Machine

i) Partial Face (road header) Machine ii) Full Face Machine. iii) Blind Shaft Borer. iv) Raise Borer

Partial Face (Road Header) Machines: attack only a limited area of the tunnel face at any one time using a cutter head mounted on the end of a hydraulically operated boom. Full Face Machines: excavate the complete heading. Blind Shaft Borer: are similar to full face TBM’s but bore downward and have special facilities for removing cuttings. Raise Borers: make use of a pilot hole to pull a rotating cutting upward, with cuttings falling downward.

Irrespective of the category of TBM or shaft borer, all machines have certain essential components. With reference to the most common full face type of machine (as shown in Fig.4.5 below), these are the cutter head armed with cutting tools; a system of propulsion

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and reaction to thrust the cutter head and to rotate it against the rock face, a system for muck removal; and when needed, facilitates for erecting permanent support and a shield to provide temporary ground support and protection for the operating crew.

Components of a typical full-face TBM Fig 4.5

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CHAPTER-05

EXPLOSIVES

5.1 Definition

An explosive is a solid or a liquid substance, or mixture of substances, containing a large store of chemical energy and capable of being converted by chemical action into a large volume of gases at high temperature and pressure. The action at which chemical reaction occurs is very rapid. Its strength depends on the speed with which its chemical energy is released. 5.2 Types of Explosives i) Low Explosives ii) High Explosives

5.2(i) Low Explosives

A low explosive is consisted of a mechanical mixture of finely ground combustible (non explosive) substances and suppliers of oxygen e.g. gun powder. Its characteristics are:-

i) It is fired by simple ignition ii) Its decomposition proceeds by progressive combustion from grain to grain. iii) The gas pressure increases gradually. iv) It produces pushing effect on the material on which it acts. v) vi) Low Explosives are:-

a) Black Powder b) Gun Powder

a) Black Powder.

The black powder is composed of sodium nitrate, charcoal and sulphur in the proportions of about 72%, 16% and 12%. Because of its lower cost, it has a wider sale than blasting powder made with potassium nitrate instead of sodium nitrate. Sodium nitrate has the disadvantage of picking up water. Powders made from potassium nitrate do not have this disadvantage; consequently they have better keeping qualities.

b) Gun Powder.

The composition of gun powder varies in different countries but usually lies within the range of 12% charcoal; 10% to 20% sulphur and 60% to 75% potassium nitrate or saltpeter (an oxidizing agent). In Britain, the usual composition is 15% charcoal, 10% sulphur and 75% potassium nitrate. The normal method of firing Gun powder is by safety fuse. One end of the fuse is freshly cut and placed in the powder, the other end being ignited by naked light by igniter.

The advantages of gun powder are that it is cheap, safe to handle, and stable. Its rending effect makes it suitable where it is undesirable to pulverize the mineral worked.

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The disadvantages of gun powder are that it is effective by water, it is bulky for a given explosive effect and most important from the coal mining point of view its flame is of long duration and a portion of the explosive may continue to burn after the coal or stone has been brought down, so exposing the burning residue to the external atmosphere. It is, therefore, dangerous in any place where there is risk of inflammable gas and it has been replaced for nearly all coal mining purposes by some form of high explosive. All explosives on the Permitted List are of the high explosive type.

5.2 (ii) High Explosives High Explosive is a chemical mixture of explosive compounds convertible into gasses at once. Its characteristics are:- i) It is fired not by ignition but by detonation or shock. ii) Chemical decomposition proceeds at very high speed. iii) The maximum pressure is reached almost at once. iv) It produces a shattering effect on the surrounding material. v) High explosives are substitution products of combustible substances such as:-

a) Cellulose (C6H12O5) b) Benzene (C6H6) c) Glycerin C3H5(OH)3 d) Ammonium NH4

By substitution product is meant the new chemical compound formed when one atom or a group of atoms in the original compound is replaced by another atom or atoms. The substitution products are obtained by the action on the original compound with nitric acid (HNO3). Nitroglycerin and Dynamites are High Explosives. a) Nitroglycerin

This explosive was discovered by Sobrero in 1847 in a laboratory in Paris, but Alfred Nobel in 1863 was the first to manufacture it on a commercial scale. Nitroglycerin is made by mixing sulphuric acid and nitric acid in a steel tank and then adding glycerin. The sulphuric acid takes no chemical part in the reaction but absorbs the water present. To keep the temperature of the reaction within a safe limit, the tank is water jacketed, and coils of lead pipe through which cooling water is circulated are placed inside the tank. The nitroglycerin is washed several times with cold water and once with caustic soda to destroy any remaining trace of acid, which affects its keeping qualities. Nitroglycerin is insoluble in water and is poisonous either when in contact with the skin or when breathed as a vapor. It usually produces a violent headache. Ordinary nitroglycerin freezes or becomes crystalline at from 40 to 460 F., but in a recently discovered form it does not freeze even in usual winter temperatures. Being a liquid, nitroglycerin is especially dangerous to handle, since it will leak through a hole in its container. Because of its sensitiveness to shock, liquid nitroglycerin is dangerous to transport and unsuitable for use in mining and quarrying operations. The chemical formula for NG is C3H5(NO3)3. It has a density of 1.60. Its detonation velocity is about 9.000 meters/sec and the pressure which is developed is almost 200,000 atmospheres.

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When nitroglycerin is mixed with Sodium Nitrate and wood pulp, it forms nitroglycerin dynamites. In a similar manner, blasting gelatin is used to make a series of gelatin dynamites, such as:- i) Straight Dynamites ii) Low Freezing Dynamites iii) Ammonia Dynamites iv) Gelatin Dynamites v) Ammonia Gelatin Dynamites

i) Straight Dynamites

Straight dynamite may contain 50% nitroglycerin, 14% combustible, 35% sodium nitrate and 1% antacid. Straight dynamites are powerful, quick acting and fairly water resistant, but on detonation produce poisonous gases, especially in the higher grades. These gases are largely carbon monoxide, but some oxides of nitrogen may be present. Straight dynamites made from ordinary nitroglycerin will freeze at temperatures slightly above 320 F. It should not be used in the frozen conditions but first must be carefully thawed.

ii) Low Freezing Dynamite

These dynamites are made by replacing part of the nitroglycerin of straight dynamites with some ingredient to render the dynamite incapable of freezing under ordinary conditions of use. The freezing point is depressed by adding nitro substitution compounds, such as nitrated sugars, nitrotoluene, nitrated polymerized glycerin or ethylene glycol dinitrate. These dynamites are made in 20 to 60 % strength, have a rate of detonation from 2700 to 6325 meters/sec.

iii) Ammonia Dynamites iv) In these dynamites parts of the nitroglycerin is replaced by ammonium nitrate, which make them somewhat slower in action than straight dynamite. They produce less objectionable fumes and are safer to handle. Since ammonium nitrate is deliquescent, such dynamites do not resist water well and are dipped in melted paraffin for protection, are made in 15 to 60% strength, and their rate of detonation is from 2400 to 4500 meters/sec.

iv) Gelatin Dynamites.

The gelatin dynamites are dense plastic explosive having high water-resistant characteristics, and they produce the least poisonous fumes of any high explosive. They are made by adding 48.2% nitroglycerin, 1.8% nitrocellulose, 37.4% sodium nitrate, 11.1 % wood meal and 1.5 % maize meal. Gelatin dynamites are made in from 20 to 90 % strength and their rate of detonation is from about 2750 to 7700 meters/sec.

v) Ammonia Gelatin Dynamites

In these dynamites part of the nitroglycerin used in gelatin dynamites is replaced by ammonium nitrate. One 50% ammonia gelatin has the composition of 35.3% nitroglycerin, 0.7 nitro cotton, 20.11% ammonium nitrate, 33.5% sodium nitrate, 7.9% carbonaceous material, 0.8 antacid and 1.7% moisture. Made in 30 to 90%

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strength, these dynamites have rates of detonation from 2750 to 6700 meters/sec and about the same cartridge count as gelatin dynamites.

All gelatin and ammonia gelatin dynamites, regardless of strength, and blasting gelatin have two rates of detonation. The low rate is 2800 meters/sec. The high rate, produced by priming them with 60% nitroglycerin dynamites, varies from about 4700 meters/sec for 20% strength to 7660 meters/sec for 75% strength and 8600 meters/sec for blasting gelatin. The degree of confinement and the condition or age of the dynamite also affects the rate of detonation.

5.3 Blasting Gelatin

When from 90 to 93% of nitroglycerin and 7 to 10 parts of gun cotton are mixed, a tough elastic and jelly like mass, blasting gelatin is formed. In commercial forms it contains about 1% of alkaline substance to improve its keeping quality. Blasting gelatin is the strongest of conventional high explosive and is highly water resistant. It is safe to handle but must be handled carefully when frozen. It has velocity of detonation about 8700 meters/sec. It is not plastic but rubber like.

5.4 Emulsion Explosives

These are composed of very small drops of ammonium nitrate solution and other oxidizer. These are densely dispersed in a continuous phase, which is composed of a mixture of mineral oil and wax.

The emulsion explosives can be distinguished from other liquid and plastic explosives that they can be detonated without the addition of a sensitizer which in itself is an explosive.

To make the emulsion initiable, small cavities are made in the form of micro balloons with a diameter of one tenth of a millimeter. These collapse under the influence of the initiating shock.

The density of the explosive and its capacity of initiation can be adjusted with the amount of micro-balloons in the emulsion. The emulsion explosives retain their consistency over a wide temperature range i.e. from 200C to + 350C.

The stability of emulsions is outstanding compared with other civil explosives. The detonation properties remain unchanged over a long period of time under normal storage conditions.

The water soluble drops of ammonium nitrate in the emulsion are completely surrounded by the oil of a wax film. This makes the emulsion as highly water resistant.

From a handling point of view the emulsion explosives are very safe and a high degree of impact is needed for accidental initiation.

5.4.1 Emulsion Explosives Products

By using different percentages of micro balloons and aluminum wide range of emulsion explosives can be manufactured.

Emulite Explosives

Emulites at present are manufactured in four qualities:-

a) Emulite 100

It is a cap sensitive emulsion explosive which is manufactured in paper cartridge or plastic hoses. Its good fume characteristics and water resistance makes it an excellent all round explosives. It is suitable for mechanized charging.

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b) Emulite 150

It is similar to emulate 100 but aluminum is added to increase the energy content. It is manufactured in paper cartridges plastic hoses and plastic pipes.

c) Emulite 200

It is non cap sensitive emulsion explosives, which is used for bench blasting with medium and large size blast holes. It is supplied in plastic hoses.

d) Emulite 300

It is a non cap sensitive emulsion explosives, which is intended for medium and large diameter blast holes in bench blasting.

5.5 ANFO

ANFO consists of a mixture of Ammonium Nitrate (AN) and Fuel Oil (FO) at a ratio of 94:6. The use of ANFO in larger scale started in the United States in the middle of the 1950’s. Some reasons for its popularity are: - - Low price - Safety in manufacturing, transport and handling - Easy to handle in bulk - Charging can easily be mechanized. - On the other hand, (i) ANFO has a somewhat lower weight strength as compared to gelatine explosives, about 80%. (ii) It is also sensitive to water and should not be used in wet holes unless some type of plastic film hose is used to protect the explosive. (iii) It has also relatively low degree of packing involving a closer drilling than when using gelatin explosives.

Two kinds of ANFO, crystalline and prills are used for blasting. The crystalline types normally have a particle size less than 0.5 mm while a suitable prills size is 0.3 – 2.5 mm. Sometimes also a mixture of these two types is used.

5.6 Permitted Explosive A “permitted explosive” is one, which has been approved for use in gassy and dusty coal mines (where there is a possibility of methane explosion or dust explosion). Permitted explosive must be used were:-

1. Safety Lamps are required in any part of mine. 2. Safety Lamps are required as a temporary precaution. 3. Dry and dusty. 4. Coal is being transported mechanically or by gravity.

5.7 Characteristics of a Permitted Explosive

a) Low detonative temperature b) Flame of short duration i.e. one thousand of the second.

These characteristics have been achieved under following heading: a) b) Cooling agents. c) Sheathed Explosives d) Eq.S. Explosives

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a) Cooling Agents

All permitted explosives have cooling agents in their composition. Cooling agents are sodium chloride (Nacl). Potassium Chloride (KCl) and Sodium Flouride (NaF). Ammonium Chloride (NH4Cl) also absorbs heat.

b) Sheathed Explosives

As an additional safeguard, each cartridge is surrounded length wise by a sheath of sodium bicarbonate (NaHCO3) about one eight inches thick, the ends of the cartridge being left uncovered.

The purpose of the sheath is to reduce the risk of igniting gas. It acts as a blanket of carbon dioxide and water paper around the flame and hot gases from the explosives. A serious disadvantage of the sheathed explosive is that it may be removed or displaced by accident or design and then fail to achieve its purpose.

c) Equivalent to Sheathed Explosives An Eq.S. explosive is one without a sheath, which is “certified to be not less safe than an equivalently sheathed explosive of the same group”. The inert material is incorporated direct and uniformly into the explosive composition itself. This removes the dangers arising from a displaced sheath and simplifies manufacture. The inert material may be sodium chloride used in conjunction with ammonium nitrate or alternatively ammonium chloride used in conjunction with sodium nitrate. 5.8 Types of Permitted Explosives

a) Gelatinized Nitro Glycerin Explosives

It contains about 40% N.G. and nitro glycol gelatinised with nitro cotton, together with some ammonium nitrate, sodium chloride (a cooling agent), wood meal (a combustible) and small percentages of other minor ingredients. Such explosives have high water resistance and high density (specific gravity about 1.5). They are used for heavy duty in stone drifts, sinking shafts and hard ripping. Examples are polar ajax, Nitric NO2 and Driftex. b) Powdery Nitro Glycerin Explosives & Nitrox No. 2

These contain about 18% N-G and Nitro Glycol with or without nitro cotton and from 25% to 50% ammonium nitrate together with sodium chloride and remaining other ingredients. Such explosives have a lower density (specific gravity about 1.0) giving a greater speed of explosive in the shot hole and a less violent blasting action. It is suitable in medium rock and hard coal. Examples are polar viking and minex. c) Powdery Non-Nitro Glycerin Explosives

These contain about 35% to 80% ammonium nitrate, together with sensitizer such as T.N.T. plus some combustible material and a cooling agent. The specific gravity ranges for 0.7 to 1.0 these produce milder and more rending action. They have wide application in coal. Examples are unirend, Tolumite No.1 and Trinite No.1

The normal permissible maximum charge for ordinary permitted explosives (Sheathed or unsheathed) is 28 oz. But for Eq.S. explosive is 36 oz.

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CHAPTER-06

BLASTING

6.1 Blasting Properties of Explosives

To select an ideal explosive for each purpose, the most important properties which should be considered are as under:-

a. Velocity of Detonation (VOD) b. Strength c. Detonation Stability d. Density e. Water Resistance f. Sensitivity g. Safety in Handling h. Environmental properties i. Resistance to Freezing j. Oxygen Balance k. Shelf Life

Now we explain each one by one:-

6.1.1 Velocity of Detonation (VOD)

Velocity of Detonation (VOD) is the speed at which detonation travel through an explosive column.

The velocity of detonation of an explosive is higher when the explosive is confined than un-confined.

Recent researches have confirmed that velocity of detonation should be equal to the velocity of the seismic waves through the rock. High velocity of detonation would thus be favourable in the case of hard rock. Explosives like Dynamites and Emulite are suitable for hard rocks like granite, genesis and basalt while ANFO is suitable for softer rocks like lime stone and sand stone.

6.1.2 Strength

The blasting gelatin was chosen as a standard, as it is well known all over the world and is the most powerful civil explosives so the strength of an explosive is expressed as a percentage of the strength of blasting gelatin.

The weight strength denotes the strength of any weight of an explosive comparing with the same weight of blasting gelatin. The bulks or volume strength denotes the comparison of any volume of an explosive with the same volume of blasting gelatin. The manufacturers have started to compare the weight and volume strength with those of ANFO. The ANFO has become most widely used and well known explosives. In order to measure the strength of explosives different tests have been carried out e.g.

1. Lead Block Test 2. Ballistic Mortar Test 3. Bubble Energy Test 4. Nitrodyn

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6.1.3 Detonation Stability

It means that the detonation goes through the entire explosive column. The sensitiveness of propagation is an important property, which has to be considered in blasting operations. If the sensitiveness is low there can be interruptions in the detonation. If the column of explosive in the charges an explosive with too high a sensitiveness can cause propagation between adjacent blast hole if the holes are closely spaced. In under water blasting the risk of propagation between the blast holes is great. The propagation ability is higher in confined conditions than in un-confined ones.

6.1.4 Density

The density of an explosive is its specific weight expressed as Kilograms per liter or grams per cubic centimeter. The density determines the possible charge concentration in the blast hole. It is one of the most important properties to be considered when designing blasting operations. The drilling pattern will be more widely spaced if the high density dynamics (M) is used instead of low density ANFO.

6.1.5 Water Resistance

The water resistance is an explosive ability to withstand water penetration. It is normally expressed as the time the product remains under water and can still detonate reliably. An explosive can be affected by water in two different ways. Salt can be dissolved in water and leak out of the explosive and the water pressure can reduce the size and amount of air bubbles which act as “Hot Spots” resulting in the explosives becoming decentralized.

Plastic explosives normally have high resistance to water. The emulsion explosives like Emulite have excellent water resistance properties. Dynamax (AM) (Nitro Noble under water explosive) is guaranteed to withstand water pressure with one week and Oynamax (M) for 24 hours.

6.1.6 Sensitivity

The sensitivity of an explosive is expressed as the minimum energy needed to initiate the explosive. The cap sensitive explosives are not needed to be primed while non-cap sensitive explosives need to be primed with an amount of high explosives in order to obtain initiation and stable detonation.

6.1.7 Safety in Handling

It is utmost important that transportation and uses of explosives should be carried out without any risk of personnel injuries. Before an explosive is approved by the authorities, it should undergo the following tests:-

a) The Drop Hammer Test b) It determines the height from which weight must fall on the explosive in order to create detonation;

b) The Friction Test

It is a test in which friction under increased pressure is applied to a small amount of explosives. When a reaction in an explosive is obtained, pressure is recorded. c) c) The Projectile impact Test d) It determines the bullet velocity needed to create reaction in the explosive;

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d) The Heat Test It determines how much heat an explosive can withstand before the reaction starts.

The above Tests form the basis of the authorities to classify the various explosives from the point of view of handling and transportation.

6.1.8 Environmental Properties

These are more and more taken into consideration. The aim is to minimize the toxic fumes. The inhalation of such fumes creates headaches and skin irritation. When handling nitroglycerin explosives, various toxic gases like carbon monoxide, oxides of nitrogen and nitroglycerin vapors are produced. The fumes characteristics differ between different kinds of explosives. No matter which explosive is used some noxious gases will be produced in the detonation.

In underground operations it is essential that toxic gases are kept to the acceptable level. Increased amount of fumes can be produced if explosives within sufficient water resistance are used. In adequate priming, poor confinement, use of wood spacers, and incomplete explosion are other causes of an increased production of noxious gases.

It is important that an adequate amount of air ventilation should flow in the travelling roads and in working faces to dilute/remove the toxic gases as early as possible.

6.1.9 Resistance to Freezing

It is important in the countries where the temperature falls below zero degree centigrade. Dynamites and water gels become stiffer in low temperatures and loose their good tamping characteristics. Emulsion explosives retain excellent tamping characteristics even at the lowest temperatures.

6.1.10 Oxygen Balance

An excess of Oxygen in the explosives can form Nitrogen Oxides (NO and NO2) and deficient oxygen will form carbon monoxide. These gases are toxic and may prove fatal. In open air blasting these gases rarely cause any problem as blasting fumes are dispersed after the detonation.

6.1.11 Shelf Life

The shelf life of an explosive is very important as the explosive frequently has to be keep for long time in storage, and often under un-favourable conditions.

Plastic nitroglycerin explosives should not be stored in high temperature as they tend to soften and the salts in the explosives penetrate the paper wrapping of the cartridges, thus deforming them. Storage temperature around +32 degree centigrade should be avoided.

The ammonium nitrate in the explosive undergoes a physical re-arrangement making the explosives in the cartridge swell thus deforming the cartridge. The blasting effect is not affected.

Powder type explosives in the cartridge are sensitive to moisture. In a humid environment, the salt in the explosive tends to form deposits on the cartridge thus hardening it.

ANFO is sensitive to humidity and cakes easily when stored under such conditions.

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6.2 Firing Methods

The firing methods can be divided into two main groups. 6.2.1 Non-Electric 6.2.1 (a) Safety fuse with plain detonator 6.2.1 (b) Detonating cord 6.2.1 (c) NONEL 6.2.2 Electric Detonators

Accessories of Non-Electric Firing Methods. 6.2.1 Non-Electric 6.2.1.1 Safety Fuse with Plain Detonator

Safety fuse consists of black powder core which is tightly wrapped covering of textile and insulated against moisture by water proofing materials like asphalt and plastics. The covering act as protection for the black powder core against water, oil and other material which can change the burning speed or desensitize the powder. The covering also prevents “Side spit” which can cause pre-mature detonation if it sets fire to the explosives charge.

The Safety fuse has a steady and well controlled burning speed. There are many brands of safety fuse; the burning speed may differ between different branches. The burning rate of most brands in USA is 130 seconds per meter at sea level with allowable variation of 10 seconds from standard. In Europe standard burning rate is 120 seconds per minutes with the same variation.

It should be taken into account that safety fuse will burn faster if it is subject to confinement or pressure and that the use at high altitudes slow down the burning speed. Premature or ‘delayed’ detonations are due to poor staged or improper handling.

Plain Detonator

To initiate the explosive, a plain detonator has to be attached to the safety fuse. Due to varying sensitivity of different explosives, detonators of different strengths are available. The strength of the detonators is expressed in numbers of which # 6 or # 8 is presently available in the market. The # 8 detonators contain approximately 0.8 grams. # 8 detonators have become more widely used.

The plain detonators consist of aluminum or copper cylinder which is closed at one end. A charge of high explosives like hexytol, tetryl is placed in the base of cylinder. On top of base charge a primary charge is placed normally load Azide. The primary charge is sensitive to initiate by the end spit of the safety fuse and subsequently initiate the base charge. The figure shown below shows the different parts of a plain detonator:

Plain Detonator Fig 6.1 Page 36

Assembly of plain detonator to a safety fuse:-

1. Cut the fuse so that black powder core is visible; 2. Cut the end of fuse separately and introduce it gently into the detonator against the primary charge. Leave no air gap. Slanting cuts must be avoided as the tapered end can fold over and block the end spit. 3. Crimp the detonator thoroughly to the fuel with crimper. The types available are hand crimpers and bench crimper. 4. In wet conditions insulate the crimp with grease.

Detonator end Lighting end

ASSEMBLY OF PLAIN DETONATOR AND SAFETY FUSE

Fig 6.2

Length of safety fuels should not be below 1.0 meters but for single shot a length of 0.6 meters may be allowed. However the fuse should have sufficient length to exceed the collar of the blast hole with at-least 0.1 meter.

The safety fuse may be lit by using either matches or better, special ignitor torches. When several fuses are lit, it may be practical to use igniter cord and bean hole connectors. The bean hole connector which contains a pyro-chemical compound is crimped to the end of safety fuse and igniter cord is inserted into a slot in the bean hole connector. When the igniter cord is lit, it ignites the connector which in turn lights the safety fuse.

6.2.1(b) Detonating Card (Wabo Card)

It is a very common firing device. It is used in countries which have difficult climatic conditions with frequent thunder storm and where electric firing is not allowed. It is used where several holes are fired simultaneously. It consists of a PETN core which is wrapped in textile coverings, water proofing materials and plastic sPSU suc.

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The detonating cord strengthens detonator which detonates alongwith entire length with a velocity of 7.0 meters per second. These must be used very carefully with ANFO in small medium size blast holes because it gives incomplete initiation.

Detonating cord is manufactured with core loads ranging from 3 grams per meter to 80 grams per meter. The most widely used cord has a core load of 10 grams per meter. The powerful detonating cord with core load of 40 and 80 grams per meter are mainly used for seismic prospecting and other special purposes. Multiple row blasting can be carried out with detonating cord as shown below in the figure.

Delay DETONATOR Fig 6.3

A wide range of relays with delay times from 5 meters per second to 50 meter per second are available.

Connection of Detonating Cord

Keep each connection at a right angle. Plastic connections are convenient and reliable. The distance between parallel cords should not be less than 0.2 meters. The distance between relay connection and parallel cord shows is at least 1.0 meter. No kinless or loops are permitted in the zoned. The initiating detonator shows always be painted in the desired direction of the detonating cord detonator.

8.2.1(c) Nonel

The NONEL are ideal when electric firing is neither possible not permitted. Nonel Detonator functions as an electric delay detonator but the leg-wires and the fuse head have been replaced by a plastic tube through which shock wave is transmitted. The end spit of the shock wave from the plastic tube initiates the delay element in the detonator

The plastic tube which has outer diameter of 3mm is coated on the inside with a thin layer of reactive material, which transmits the shock wave with a velocity of approximately 2.0 meters per second. The plastic is un-affected by the shock wave and does not initiate any explosives column it goes through. Two Nonel systems are available. i. ii. Nonel GT; iii. Nonel Unidet

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i) Nonel GT Timinings offer both short delays and deci-second and half second delays. The short delay periods meet the needs of bench-blasting and the deci-second and half- second delay periods are intended for tunnel blasting. ii) iii) Nonel Unidet iv) It is all round firing system which is used in most situations when milli second delay is needed like bench blasting, trench blasting and under water blasting etc.

6.2.2 Electric Firing

The introduction of electric firing method gave a higher degree of safety for the people involved in blasting operations. The blaster becomes safe to fire the blast from a protected area and conduct firing completely under control. Moreover it became possible to check with instruments that all the detonators were connected, the risk of misfires decreased.

Electric detonators can be divided into three different classes due to their inherent timing properties:-

6.2.2(a) Instantaneous detonators; 6.2.2(b) Milli-second detonators; 6.2.2(c) Half-second detonators.

6.2.2(a) Instantaneous Detonators

The instantaneous detonator is a development of the plain detonator, where the safety fuse has been replaced by electric legwires and a fuse head which burns and ignites the primary charge when the bridge wire receives an electric current. Instantaneous detonators are used for stone and boulder blasting, prespliting etc, where no delay between the different charges is needed nor desired.

6.2.2(b) Milli Second Detonators

The milli-second delay detonators have a built-in millisecond delay element which delays the detonation for a predetermined time. To be considered a millisecond delay detonator, the delay between each interval in the series should not exceed 100 ms (0.1 sec). The Nitro Nobel milli-second delay between each interval.

The milli-second series may be prolonged with deci-second (100ms) delays for tunneling.

Milli-second delay detonators are mainly used for bench and trench blasting.

Half Second Detonators

The half second delay detonators has a 500 ms (0.5 sec) delay between the intervals. It is intended exclusively for tunnel blasting where longer delays are required to prepare space for the movement of the blasted rock masses.

The electric detonators available in the market may roughly be divided into:-

i) Conventional detonators; ii) High Safety detonators iii)

The classification is based on the detonator’s inherent capacity to withstand extraneous electric hazards.

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High safety detonators of VA type can be used under a 70 KV power line while the safety distance for a conventional detonator is 200m.

FIRING PATTERN FOR A DETONATING CARD BLAST Fig 6.4

SHOTFIRING IN STONE DRIFTS

The technique of blasting in stone drifts differs from that in coal and rippings because there is no free face until one is created by blasting. It is therefore, necessary to arrange the holes in such a way and fire them in such a sequence that each group of holes in succession provides a free face for the next following group. The various blasting patterns are employed where holes are fired in such as way that each group of holes in succession provides a free face to the next group of holes. Various blasting patterns are described below:-

6.3 Blasting Patterns

1. Cut Holes 2. Drag cut 3. V-cut 4. Pyramid cut 5. Burn cut 6. Toe cut

6.3.1 Cut Holes

The first hole or group of holes fired in a drift or tunnel face are known as “Cut Holes” or the cut portion of the blasting round.

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6.3.2. Drag Cut

This is applicable chiefly to small or narrow drift. Each group of holes termed as cut holes, lifters, easers and trimmers are marked as 0,1,2,3, respectively and are fired simultaneously using instantaneous detonators. Alternately, if desired, the whole round may be fired with half second delay detonators.

Fig 6.5 Drag Cut

6.3.3 V- Cut

For hard rock the cut holes meet in a “V” form. In some cases single pair of “V” is sufficient while in other there may be more than one set of “V” holes across the face as shown in Fig.(6.6) below:-

Fig 6.6

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6.3.4 Pyramid Cut

This consists of 3 or 4 or holes drilled in the centre so that they almost meet at a common point forming a pyramid. The remaining holes are arranged as shown in the Fig. 6.7 below.

Vertical Section

Pyramid Cut Fig 6.7

6.3.6 Burn Cut

The principle of burn cut is to drill a series of 5,6 or more parallel holes in cluster at right angle to the face in order to form initial cut. One or more of the holes are left unloaded to form a free face. Fig. shown below is one example of Burn cut.

Burn or Shatter Cut Fig 6.8

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6.3.6 Toe Cut

In toe cut the holes are inclined downward as shown in the Fig (6.9). It is used for small drifts in soft or medium ground.

Toe Cut Fig 6.9 6.4 Underground blasting

a) Shot Holes in Coal

The placing of holes in coal is decided by the thickness of the seam, the position of the undercut, the presence of hard band (if any), the type of roof or floor parting and the direction of the cleats. These are all variable factors. Only experience is the best judge to determine the best method.

In the normal case, the shot is arranged as in Fig. 6.10. The length of the shot holes is kept 6 inches less than the depth of undercut and the burden (distance from the hole to the undercut) is kept between two thirds to three quarters of the length of the holes. The spacing between the holes may be 4 ft 6 inches to 8 ft depending upon the weight of burden. The charge may range from 4 oz to 14 oz, depending on the burden and the hardness of the coal. As far as possible all holes should cross the main cleats at right angles. In thin seam closer spacing may be necessary because the burden is small.

Short Hole Coal Fig 6.10

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b) Shot holes in Rippings

The essential in roof ripping are to get good fragmentation. The burden in medium ground should not exceed 3 ft, and in hard ground 2 ft. The charges may range upto 6 oz in so ft shale, from 10 to 20 oz in hard shale and upto 28 oz in hard stone. In all cases, care should be taken to keep the ripping as near to the face as circumstances permit in order to reduce the dangers arising from the development of roof breaks and bed separations.

Fig. 6.11 shows a common arrangement of holes in hard ground. The shots may be fired singly in the order named but this involves the shot firer going to the face six times for charging the holes, testing for gas and coupling up. Fragmentation also may be poor.

Fig 6.11

Alternatively, the holes in each row i.e. on each horizon may be fired simultaneously with instantaneous detonators. First holes Nos.1,2 and 3 together are fired then holes Nos.4 and 5 and finally hole No.6 by itself. This involves only three visits to the face and results in better fragmentation. It is rarely advisable to fire shots in two or more horizons simultaneously because the burden of the shots in the second and third horizons is likely to be too great and fragmentation ineffective.

Care should be taken to use only one delay number in one horizon.

The advantages of mille second delay firing in ripping are:-

1. Danger of ignition of gas is reduced because the full round is fired within a small fraction of a second. 2. Consumption of explosives is also reduced; 3. Roof is less disturbed; 4. Better fragmentation facilitating the removals of debris and its showage in the packs;

6.5 Surface Blasting

If DG is the blast hole in Fig.6.12 and BG is the shortest distance to free face. The length of the charge should be about twelve times the diameter of the hole at the bottom, depending on the type of rock. Face after shooting would have the outline AFE. This rule does not take the nature of the rock into account; however, the rock coefficient can be

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determined by drilling of holes some one meter deep in a homogeneous bench of rock and loading them with different charges. The holes are so placed that one is not affected when the adjacent holes are fired. If d is the shortest distance to a free face, formula such as W-md3 will give the breakage resistance of the particular rock. Here m is the rock coefficient and W is the weight of the smallest charge that breaks the bench satisfactorily. In practice, hole BG is drilled 1 to 3 meters below level AF to ensure breaking the full depth of the bench. Holes may be drilled vertically by air or churn drills, or practically horizontally by air drills in which case they are called snake holes. A bench may be blasted by a large charge of powder placed in an adit and crosscut driven into the bench at the bottom. This is called coyote or tunnel blasting.

Fig 6.12

6.6 Safety Precautions In Drilling & Blasting

1. The hole should properly be cleared out. 2. The weight of the charge should be carefully chosen to ensure that it is correctly proportioned to the work it has to do. 3. The diameter of the cartridge should be slightly less than the hole diameter. 4. Every charge should consist of the fewest possible number of separate cartridges so as to reduce the risk of air spaces between adjacent cartridge. 5. The detonators must be properly secured in the primer cartridge. The detonator should be inserted by first opening the cartridge at the end and making a hole with a pointed wooden pricker and then burying the detonator until it is entirely covered by explosive. 6. While using sheathed explosives care should be taken that sheathes are not damaged and displaced. 7. Avoid using ammonium nitrate explosives in wet shot holes. 8. Stem the hole thoroughly with an adequate amount of stemming.

6.7 Direct and Inverse Initiation

6.7.1 Direction Initiation

The detonator is placed at the outermost end of the charge, next to the stemming, the business end of the detonator painting to the back of the hole.

Advantages 1. 1. Ignition of firedamp is more certainly prevented.

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2. Complete detonation is ensured. 3. Blown out shot is less likely to occur. 6.7.2 Inverse Initiation

The detonator is placed at the inner most end of the charge with business end pointing towards the front of the hole.

Advantages 1. 1. Less risk of detonator being pulled out of cartridge. 2. In delay firing, less risk of unexploded cartridges. 3. Gives better rock pull.

6.8 Stemming Materials

The object of “Stemming” or “Tamping” a shothole is to confine the explosive, help to ensure complete detonation and reduce the risk of igniting gas, if present. It may be accepted that from the safety point of view, all shot holes be stemmed up to the mouth. Stemming materials include moist clay, sand (limestone chippings) and sand clay mixture.

6.8.1 Moist Clay

This has the advantages that it is cheap and plentiful, needs no preparation before being taken underground can be easily moulded, incombustible and when moistened, it remains moist for a considerable time. It has dis-advantages that clay stemming is liable to be ejected and then fails to fulfill its intended purpose.

6.8.2 Sand

This offers a very high resistance to dislodgement. This often sticks in the hole and becomes immovable. Sand therefore forms a most effective stemming material but it cannot be inserted in the normal way in horizontal or upwardly inclined holes.

6.8.3 Sand Clay Mixture

This is generally accepted as most convenient and effective for general use. It is easy to handle as clay alone and offers almost as high resistance as sand. The mixture should consist of 3 parts of coarse sand, brick dust, and one part of good quality surface clay, together with about 5% calcium chloride to keep it moist. Water should be added to make a stiff paste, not too wet.

In some coal seams, it is found that more round coal is obtained if an air space is left between the outermost cartridge and the stemming, a procedure which is called “cushion firing”. The method is useful where the shothole is long in relation to the burden to be blasted e.g in thin seams or rippings. Its effect is to lessen the shattering effect of the explosive, by distributing the pressure over a larger area.

6.9 Miss Fired Shots

A miss fired shot is one in which the detonator fails to explode, or having exploded, fails to ignite the charge. Imperfect detonation of the charge may occur if the explosive is not is sound condition (e.g. if ammonium nitrate explosives are allowed to become wet); if the cartridge do not touch each other; if cartridges of too small a diameter are used; or if the hole is not properly stemmed. Complete failure of the detonator to explode may be due to: 1. Defective shot firing exploder by which the required voltage is not generated; 2. Bad connection between exploder and shot firing cable; 3. Defective shot firing cable, e.g. broken wires or damaged insulation; 4. Dirty connections between cable and detonator leads;

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5. Broken detonator leads or insulation damaged when charging; 6. Faulty detonator, e.g. broken wire bridge or defective priming composition;

The necessary precautions include; (a) careful testing and maintenance of exploders (b) use of good shot firing cable; (c) careful making of connections; (d) storage of detonators in cool and dry magazine; and (e) careful handling of detonators to avoid damaged leads. The manner of dealing with a miss-fire, if one occurs, is laid down in detail in the Explosives Orders to which reference should be made.

6.10 Procedure after Miss Fire

If a shot fails to explode, the shot firer must;

1. Disconnect cable of firing handle and wait for 5 minutes; 2. Examine cable for connections and defects and remedy them; 3. Make a further attempt to fire, using, if necessary, a multi-shot exploder; 4. If the shot still fails to explode, wait a further 5 minutes; 5. Drill a fresh hole at least 12 inches in a way of equal depth and parallel to first hole. 6. Secure detonator leads of miss fire detonator and charge the new hole and repeat the procedure.

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CHAPTER-07

UNDERGROUND SUPPORT

7.1 Introduction

When minerals are excavated the caritas (open space) are formed. These spaces will collapse if not supported artificially. The roof and sides of mine opening must be supported to ensure safety.

Rocks in natural forms are in stable –equilibrium position Mining activities disturb their balance. The over lying massive weight tends to exert pressure on the roof of mine opening. It may be noted that, in coal measure strata, the rock pressure per foot of depth is about one pound per sq. inch.

7.2 Types of Supports

Following are the types of supports normally used in mining:-

1. Pillars 2. Timber Supports 3. Rigid Steel Prop 4. Steel Arches 5. Roof Bolting 6. Friction Props 7. Hydraulic Props 8. Concrete 9. Waste Fillings/stowing [ 7.2.1 Pillars (Mineral themselves)

Pillars of low grade ore are left un-mined at intervals to support the walls in some methods of stoping. This is a regular procedure in room and pillar mining in bedded formation.

7.2.2 Timber Supports

Timber was probably first material used as a mine support. The timber used as a support should be of good quality. It should be free of defect e.g. knots etc., dry and straight. Wood seasoning (chemical or physical) treatment is done to increase its strength and to prevent decay. Long grained timber such as oak, pine, eucalyptus etc are used in the mines to secure roof and sides.

Advantages of Timber Supports These are cheap in the first cost, light in weight and are easily available and framed.

These relatively have great strength in proportion to their weight.

They fail gradually when loaded beyond their strength.

They give warning of failure by an audible sound.

7.2.2.1 Types of Timber Supports

Timbers can be used as a support in a mine in different shapes as follows:- a. One piece set b. Two pieces set c. Three and four pieces set d. Square set

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a) One Piece Set b) The term is applied to a single stick of timber, called a post, stull or prop. It is used to support the walls of stopes/openings. Post and prop are applied to vertical timbers and stull is applied to inclined timber.

A post is set first by digging a shallow hole or hitch to give a firm even footing as shown in Fig. 7.1 (A) After the post has been placed in the hitch, a head board is put over the top and wedges are driven between the head board and the rock to tighten the post in place. The function of the head board is to distribute the pressure over the end of the post and to prevent the end of the post from splitting as weight comes on it.

In a narrow inclined vein, stulls are not placed perpendicular to the dip but at an angle above the perpendicular that is from one tenth to one quarter of the dip. In this position a downward movement of the hanging wall tightens the stulls in place instead of loosening it. Figure 7.1 (B) illustrates one way of reinforcing a stull. In Fig. 7.1 (C), a narrow and steeply inclined vein is timbered with stulls.

Fig 7.4

Fig 7.4 Fig 7.1 (D) Fig 7.1 (C Fig 7.4 Fig 7.1 (B) Fig Fi7.1g 7.1 (A) Fig 7.4

b) Two Pieces Set

It consists of a cap and a single post. Such a set is shown in figure 7.2 below. It is used to support roof and side of an opening.

Two Pieces Stull Set Fig 7.2

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c) Three and Four Pieces and Polygone Set d) In ground that requires greater support; three and four pieces sets are used as illustrated in fig. 7.3 & 7.4 below. Three pieces set are used to support roof and sides while four pieces set are used to support floor to avoid floor heaving. Sometimes a horizontal support is used between two props or caps that is called distance bar. It helps the props or caps to stay in position.

Three- Pieces Set Included posts Fig 7.3

Four - Pieces Set Sawed Timber Fig 7.4

The posts are spread apart at the bottom to give greater stability. In narrow and steeply dipping veins, the greater pressure is usually from the side walls, but in drifts and cross cuts the pressure may be vertical, lateral or both, if the ground is very heavy. A sill is used in case the pressure is heavy or the bottom is soft.

d) Square Sets

It finds its application in stopes, narrow veins, irregular and small ore bodies where walls and back of the excavations are supported by regular framed timber. Timbering is of units or hollow cubes with a timber along each edge as shown in figure 7.5 Four vertical timbers of a square set are called posts while the caps and struts being horizontal. If the floor is hard sills may be omitted and the posts are set directly hitched

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in the floor. Caps and Girts are placed on the top of the posts. Caps being at right angles to girt.

Square sets may be made of round or sawed timber or of both. Sometimes square sets are filled with waste rock to make it a permanent support.

CROSS SECTION OF SQUARE STOPE ASSEMBLY OF SQUARE SET MODULE

Fig 7.5

7.2.3 Rigid Steel Props

The great advantage of steel props, as compared with wood, is that they are much stronger and can offer more effective resistance. Steel props retain their strength indefinitely and can be used many times. Although the first cost is higher, yet the ultimate cost is less. Provided strict supervision is maintained and the steel props are regularly and systematically withdrawn and re-used.

On the other hand, steel props are heavier to handle, the rigid type have no means of adjustment in length for seams of variable height. They give no warning of roof movement and they are sometimes difficult to withdraw due to floor penetration.

7.2.3.1 Types of Rigid Steel Props

There are four main types of rigid steel props.

a) Girder Prop

The girder type is the most widely used. It is simple, strong, rigid and relatively cheap. It is sometimes difficult to withdraw in seams having a soft floor and causes minor injuries due to workmen striking the edges with their elbows, knees etc.

b) New Battle Prop

It consists of a high tensile steel tube which contains a well fitting soft wood core, leaving 3 inch empty at each end. The purpose of the core is to prevent buckling of the tube. The new battle prop is easier to handle and generally easier to withdraw.

c) The Butterley Prop

This is a composite tubular prop consisting of (i) a steel tube closed at top and bottoms (ii) a sliding sleeve and (iii) a wooden plug when the prop is set and the roof weight comes on, the plug is crushed in the sleeve. This makes the prop to yield up

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to a limited length. The prop may thus be described as semi-yielding prop during the initial compression but behaves as a rigid prop as soon as the sleeve has descended to its lowest position.

d) S.F. Prop

This consists of an H-girder stem and can be tightened against the roof by a wedge. To set the prop, the wedge is driven in until the prop is tightly fixed. The S.F. Prop has the advantage of quick setting and relatively easy withdrawal. It is sometimes used as a breaking off prop at the waste edge.

Girder Newbattle Butterley Fig 7.6

Steel Supports

Steel supports find these applications in both coal and metal mines, especially for wide openings and those of permanent character as on haulage roads, pump stations and shift stations. The steel supports last for much longer time as compared to wood. These are not affected by atmospheric conditions such as temperature and humidity.

7.2.4 Steel Arches

Steel supports are normally used as arches. Steel arches are of two types.

a) Non yielding arches and their types. b) Yielding arches. c) Non-yielding are of different types e.g. d) i. Continuous rib type ii. Rib and post type iii. Rib and wall plate type iv. Rib, wall plate and post v. Full circle rib

vi.

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The factors which must be considered in choosing a support system are

(1) Method of excavation (2) Rock behaviors and (3) The size and shape of the tunnel cross-section.

Methods include the full face method, top heading and various pilot drift methods.

i) Continuous Rib Type

It is usually made in two pieces for maximum speed of erection. It requires lowest first cost and lowest erection cost. It is sometimes used in three or four pieces to meet special conditions and with the following methods of attack (1) full face (2) side drift and (3) multiple drift Fig. 7.9 below shows a two piece continuous rib type.

ii) Rib and Post Type

It is made in three pieces. It is used where opening size is such that two piece continuous ribs cannot be handled. Fig.7.7 below shows rib and post type non yielding arch.

CONTINUOUS RIB TYPE CONTINUOUS POST TYPE

Fig 7.7 (a) Fig 7.7(b)

iii) Rib and Wall plate Type

This type is especially applicable to circular and high sided tunnel sections where only a light roof support is needed. The rib and wall plate type is also usually made in two pieces for maximum speed of erection, lowest first cost and lowest erection cost. Fig.7.8 shows a rib and wall plate type.

RIB AND WALL PLATE TYPE

Fig 7.8

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iv) Rib, wall Plates and Post Type

The Rib, wall plate and post is used where support is not needed tight to the face and for tunnels whose roof makes an angle with the side wall and where post and rib spacing differs. Fig.7.9 shows a sketch of this type of prop.

SHOWN WITH SHOWN WITH DOUBLE BEUM FLAT WALL WALL PLATE PLATE

RIB WALL PLATE AND POST TYPE

Fig 7.9

v) Full Circle Rib Type

A full circle rib type is used where openings are squeezing, swelling and of crushed rock or any rock that imposes considerable side pressure. In case of heavy loads associated with squeezing conditions ribs are closely spaced and heavily logged. Fig.7.10 shows a type of full circle rib.

FULL CIRCLE RIB TYPE

Fig 7.10

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7.2.3.3 Yielding Arches

These arches are so designed that when the ground load exceeds the designed load of the arch, yielding takes place at the joint and radius of curvature and overlaps on the joints as shown in Fig.7.11 below. During yielding, the over burden settle into a natural arch of its own that brings all forces into equilibrium. The shortened arch has increased strength.

Yielding arches are composed of three sections. The top section slides between two side elements. After every 15 days or so, the tightening elements are loosened and the arches slide, converging and thus relieving the stresses on them. This eliminates deformation.

1

Fig 7.11 1

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Steel Tubing

It is a method of permanently lining a shaft sunk in very wet rock formation. This method has been more particularly associated with the freezing process of sinking. The tubbing is placed while ground is still frozen so that the sinkers can work under dry condition. The best way to fill the spaces between tubbing and rock is to fill it with concrete.

There are two types of tubbing, known respectively as:-

i. English Tubbing ii. German Tubbing iii. The difference between English and German tubbing is that English tubbing is built upward while German tubbing is built from to downwards.

The tubbing is built up of cast iron rings or plates. The thickness of the plate depends upon the pressure of the water and the diameter of the shaft.

7.2.5 Roof Bolting

It is a system of roof support, mainly used for bedded deposit. It acts on the principle that immediate roof beds are bound together tightly to form one composite, thick and strong beam. It is applied to the support of narrow roads-ways, entries, room development heading etc.

7.2.5.1 Types of Roof Bolt

These may be broadly classified into:- 1. 1. Split rod and wedge bolt 2. Expansion shell bolts, 3.

Five patterns are shown below

Typical roof bolt anchors, A, standard shell and plug, B, tandem shell and plug, C, bail-type shell and plug, D, roof bolt with plastic another, E, Split roof bolt with forged wedge

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In general, the split rod and wedge type of bolt is the simplest, cheapest and most widely used especially where compressed air is available to provide the necessary percussive action. It requires a hole of smaller diameter than the shell type for corresponding duties. To ensure a satisfactory fix, however, it is essential that the hole be bored to the correct depth and that the diameter of the hole is not more than 3/8 inches greater than the diameter of the bolt.

An advantage of the shell or sleeve type is that it has a greater area of contact at the anchor and may therefore be the more suitable in weak strata. Further, it can be used where the power supply is either electric or compressed air. Both types give satisfactory results when properly installed.

7.2.5.2 Application of Roof Bolting

Roof bolting was initially developed in America and applied to the support of narrow roadways entries, rooms, developing headings, lifts and so on driven in the pillar methods of working customary in that country. Roof bolting is equally applicable to all such roadways in Great Britain, or has been used in conjunction with conventional supports, with complete success. General principles commonly observed are:-

1. Bolts should be installed as close to the working face as possible in order to prevent or reduce bed separation. 2. Bolts nearest the side of the roadway should be not more than 2 ft. from the side. 3. The best pattern of holes must be determined by experience in each case; 4. The holes are generally driven normal (i.e. at right angles) to the seam but sometimes the flank holes are inclined over the solid coal sides and alternate rows of holes next to the face in long wall roadways are sometimes directed forward over the coal. 5. The roof surface may be supported by steel plates, 8 or 99 in square.

Roof bolting is also applicable to longwall roadways and cross gates. It is unlikely that bolting can ever replace conventional supports on longwall faces but they are of value as an additional aid on prop free front faces or where weak cloud immediately above the seam is difficult to support. Bolts may also be used at face ends, machine stables and road heads where props have to be removed for the movement of machines. They are also widely used at roadway junctions and in large excavations such as underground and chutes, shaft sinking, shaft insets and pit bottom reconstruction.

7.2.5.3 Application of Floor Bolting

In many roadways supported by conventional methods, heaving of the floor is of such magnitude that the roadway is completely disrupted.

Floor bolting, like roof bolting, has its object of the formations of a strong compound beam of clamped floor beds which will be strong enough to resist the lifting force acting upon it. As with roof bolting, the best pattern of holes must be found by experiment but it is desirable for successive row of holes across the roadway to be staggered with, say, four holes in one row and three holes in the next and so on. This prevents a continuous fracture line possibly developing right along the roadway. In some cases, it is found sufficient to concentrate the holes near the middle of the roadway where maximum movement is liable to occur.

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7.2.5.4 Advantage of Roof and Floor Bolting

The successful application of roof bolting, either along or in conjunction with conventional supports on a reduced scale is likely to bring many benefits in its train in regard to both economics and safety:-

1. Roof bolts prevent bed separation taking place provided they are installed as soon as the roof is exposed; 2. Improved roof control is obtained, resulting in the reduction or elimination of falls of stone with all the hazards these entail. 3. Reduced lifting or pavement occurs, reducing the need for back brushing and increasing transport efficiency. 4. Large roadway section is available for the operation of machines, mine cars etc., with greater clearance for rapid movement. 5. Less risk of falls of roof due to displacement of supports by haulage mishaps. 6. Reduced resistance to air-flow, resulting in improved ventilation. 7. Lower overall costs per ton for supports and roadway repairs generally.

7.2.6 Friction Prop

A friction prop consist of two telescopic members held together by a wedge and friction device. To set a prop, it is first erected by hand upto just below the height required. The horizontal wedge is then tightened sufficiently to prevent the upper member to slide downward. Another wedge is then inserted to the lower member so raising the upper member tight against the roof. Finally the horizontal wedge is tightened. The lifting wedge is then withdrawn to use it some where else.

To test whether a prop is tightened, hammer 6 to 8 lb is blown until it sound like a ringing bell. The sound can be recognized by the operator. The prop may be withdrawn by hand or mechanically.

For hand withdrawal, two men are employed. One man releases the horizontal wedge by hammering while the other man pulls the prop with a chain.

Fig 7.13

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For Mechanical withdrawal, a hook fitted to a chain or wire rope is fitted through an extension attachment to the release lever and the prop is released and withdrawn by a power winch.

The friction prop is made in a wide range of size. A typical model weighing 144 lb is about one meter long when fully in un-extended position. When in extended position, it can work upto about 1.75 meters.

7.2.7 Hydraulic Props

The hydraulic prop is essentially a self contained hydraulic jack which offers an immediate resistance of 05 tons. This resistance can be raised upto 20 tons or more as roof pressure comes on. The prop yields automatically when the load exceeds the designed maximum figure.

It consist of two concentric tubes, an inner oil reservoir tube A which slides within a outer pressure tube B, the later being protected from injury by outer casing C. The lower end of the tube A is closed by a piston head fitted with a bearing ring, sealing gland and also with a non-return valve. Within the tube A is smaller pump. It is exuded by a pump rod and crank with a square external boss which is fitted on removable handle.

When the pump is operated, oil is pumped from the reservoir tube A into the pressure tube B via the non return valve. This forces the tube A upto the required height and develop initial setting load of 05 tons. The fluid pressure in the pressure tube B is communicated to a pressure relief valve through a stack pipe P when the roof pressure exceeds 20 tons, the valve then relieves the pressure by passing a small quantity of oil to the reservoir tube A, thus allowing the props to yield slightly.

Fig 7.14

To withdraw the prop, a release link (L) is pulled which permits the oil in the tube B to return to the oil reservoir tube. The release link should be operated from a safe distance by a light chain. The prop is made in various sizes upto about 02 meters long when extended and with a yield travel upto 0.4 meters.

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The hydraulic prop possess the advantages of ease, speed, and safety in setting and withdrawal. On the other hand the hydraulic prop is a precision instrument and careful maintenance is essential.

7.2.8 Concrete

Re-inforced concrete is used as a permanent shaft lining at many mines. It may be used as continuous lining and as rings spaced several meters apart where the shaft is in solid rock. If wood cushions are used the concrete lining gives very good results. In some mines cement pillars are built of round slabs of re-inforced concrete about 0.75 meters diameters and 10 cm thick. Fine sand is used around each slab to give even bearing over the surface.

Tunnels are lined with re-inforced concrete that includes steel bars as well. The concrete has advantages of being safe from fire and readily available. It is not affected by atmospheric conditions and has long life. It has the dis-advantages that it breaks without giving any warning. Broken concrete cannot be re-used like steel or timber.

Concrete is a mixture of cement aggregates (gravel or broken stone, sand) and water which is combined using different ratios depending upon it desired used. Some time concrete mortar (cement of lime, sand and water) is also spread of rock surfaces. This is known as grouting.

7.2.9 Stowing/waste Fillings

The term stowing means to fill the gap made by extraction of the seams of materials deposits. It is a part of support system. If stowing is done immediately after the excavations, it lessens the movement of strata and helps the control of roof to a great deal.

The advantages of stowing systems are that they minimize the surface disturbance. Since an area is filled up as soon as an opening is made, the main roof does not sag or cause excessive weighting so strata control is most easily achieved and most effective. However, large amount of material is required for this purpose. Material used for filling includes waste rock sorted out in stopes or mined from rock walls, mill tailing, sand and gravel. It may be brought to the place of filling by tramway or in cars or by scrapers.

7.2.9.1 Method of Stowing

They are:-

a- Hand Stowing b- Gravity Stowing c- Mechanical Stowing d- Pneumatic Stowing e- Hydraulic Stowing f- a) Hand Stowing

Hand Stowing was used when mechanization was not advanced and labour costs were small, In this, workers built dry walls as the packing progress through small rocks by shovel behind the dry walls. The material is obtained from the goaf by partial caving of the roof. If the material is not sufficient blasted roof materials are added.

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b) Gravity Stowing c) In this method, the force of gravity is used to place the stowing material. This method is used in seams steeper than 40O. The stowing material is washing refuse mixed with broken mine rock and it is disposed along the inclination.

If the coal is stable enough, it is easier to work diagonal faces without “Wire Screens” wedges can hold the face coal.

If the coal is unstable, K-Type of support is needed and the stowing material is held in place by a “Stowing Screen” behind the support.

c) Mechanical Stowing

In the mechanical stowing system, materials are delivered by conveyor and are thrown to the back of the face by a Jet Conveyor. The materials are brought by a conveyor. A diagonal scraper transfers the material to a small conveyor below working at a speed of 10 m/s thus materials are thrown to the back of the face. The jet conveyor is pulled up slowly as the stowing progress. The system is adopted to thick and flat seams. In case of limited space, it is replaced by pneumatic stowing which requires much less space.

d) Pneumatic Stowing

In pneumatic stowing the stowing materials are conveyed in pipes and thrown to the back of the face by compressed air. This is very popular system of stowing because it requires smaller installations. However the mine should have sufficient supply of compressed air as the amount of air spent by one stowing machine is almost equivalent to a medium sized compressor at the surface.

The stowing machine consists of a feeder, drum type or screw type that delivers material to the pipes by compressed air at pressure of 5-7 kg /cm2. The capacity of these machines is normally 70-150m3/h.

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CHAPTER – 08

MATERIAL HANDLING

8.1 Introduction

All operations involved in excavating and moving minerals during mining are known as material handling. In cyclic system, loading and haulage/hoisting are two main operations. While in continuous system, excavation and handling of minerals are done by a single machine (continuous miner).

Actually, material handling involves three phases; loading, transportation and dumping. In the past, these operations were normally done manually. In modern mechanized mining, material handling depends on equipment/machines. Although material handling underground has been mechanized a lot, but its effect on surface mining is great, reason for growing scale of surface mining equipment are found in its high productivity and low operating cost.

8.2 Loading Machines

Different loading and excavation machines are used in mining field. Loading and Excavation and Classified on the basis of location of mining activity (surface or underground) and continuity of operation (cyclic or continuous).

Loading refers to the loading of broken ore into mine cars or shuttle cars from faces (stope or room and pillar faces) or development headings. Loading is normally used in underground mining, while for surface mining, the term excavation (extraction by digging) is used.

Different loading and excavation machines are used in mining field. Loading-Excavation is classified on the basis of location of mining activity (surface or underground) and continuity of operation (cyclic or continuous). For surface mining, shovels, loaders, draglines and scrapers are commonly used. For underground mining, loaders, load-haul- dump units (LHDs) and continuous miners are used.

8.2.1 Surface Loading- Excavation Machines

A variety of loading excavation machines are used in surface mining as mentioned below:-

8.2.1.1 Power Shovels

Power shovels are mainly used for excavating earth and loading it into trucks or mine cars. These are also used for loading blasted rock into trucks. These are diesel electric powered now-a-days hydraulically operated power shovels are being used. The parts and working principles are shown in Figure 8.1

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Fig 8.1 Operation of Power Shovel:

1.-Head Block; 2.-Jib; 3.-Crowd arm; 4.-Crown Shaft; 5.-Rope for Releasing Bottom of Bucket; 6.-Derricking Rope; 7.-Foot Pin of Jib; 8.-Ring of Rollers; 9.-Base Frame; 10.-Slewing Platform Drum; 11.-Transmission of Slewing mechanism; 12.-Hoisting Drum; 13.-Derricking Drum; 14.-Hoisting Rope; I, II, III and IV- Successive Positions of the Bucket

8.2.1.2 Draglines

Draglines are purely loading machines. These are used for loading blasted rock or loose material into hauling units or to deposit it in near spoil bank. These normally run on crawler trucks or are of walking types. The parts and working principles are shown in figure 8.2.

Fig 8.1

Fig 8.2

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COMPARISON BETWEEN POWER SHOVEL & DRAGLINE.

Power Shovel Draglines.

i. Power shovel excavates and i. It loads only. loads ii. It is used where power is ii. It is used where reach needed. is needed. iii. It has greater loading iii. It has lower loading efficiency. efficiency. iv. It digs to shallow depth. iv. It digs to greater depth.

8.2.1.3 Bulldozer.

Bulldozers are used to open up roads through mountains and rocky terrain to move earth for short haul distance, maintain haul roads and clearing the floors. These may be classified as cable-controlled or hydraulically controlled based on the method of raising or lowering the blade. In bulldozers, blades are mounted perpendicular to the direction of travel while in angle dozers, blades are mounted at an angle to the direction of travel. These may be wheel mounted or crawler mounted.

BULL DOZER Fig 8.3

8.2.1.4 Scraper.

Scrapers are used on the surface (they are tyre mounted or towered by tractors). These are not just excavators; they are load haul dump machines.

COMPARISON OF BULLDOZERS AND SCRAPERS Bulldozers Scrapers.

i. Dozers push the material i. Scrapers act as load haul and forward and to one side dump machines for short for short distance. distance.

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ii. Dozers can be used on ii. Scraper’s use is limited only rough terrain to smooth terrain to smooth terrain. iii. Dozers are normally iii. Scrapers are usually tyre mounted. crawler mounted.

Fig 8.4

Fig 8.4

8.2.1.5 Bucket Wheel Excavators. (B.W.E)

These are non-conventional (continuous) excavation machines. These are used for excavating, loading and transporting soft coal and overburden i.e. sand, clay and light shales. These are designed to give high output. A typical B.W.E. is shown in figure 8.5

Fig 8.5

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8.2.1.6 Front End Loader.

A front end loader is basically a tractor with a loading bucket on the front (fig 8.6). It may be crawler track or rubber-tyred mounted. Crawler track mounted is used for excavation while rubber-tyred type mainly used for loading.

Fig 8.6

8.2.2. Underground Loading Machine.

Shoveling (Mucking) has been a main method of material handling i.e. loading in underground mining. Now-a-days variety of loading machines is used in underground mining as detail below:-

8.2.2.1 Gathering Arm Loaders.

These can be used for loading rock or coal. These are equipped with arms which sweep the material on to a chain and fight conveyor as shown in figure 6.2.2.1. These are essential part of all the continuous miners now a days.

Gathering-Arm Loader Fig 87

Gathering- Arm Loader Fig 8.7

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8.2.2.2 Rocker Shovel.

It is used both in metal and coal mines. It consists of a bucket in the front, which loads the material and dumps it into a mine car attached to its rare (back) side (fig.8.2.2.2).

Shovel Loader Fig 8.8 8.3 Transportation

It includes all the methods used for transportation in mining i.e. haulage and hoisting.

8.3.1. Haulage

Different types of haulages are used for transportation in mining. These are classified as track haulage and trackless haulage.

8.3.1.1 Track Haulage

It is the haulage system which requires rail track for its operation. For example locomotive haulage, rope haulage.

i) Locomotive Haulage In Larges mines, ore is usually hauled along levels by trains of ore cars drawn by a locomotive. The locomotive is electric, diesel battery or compressed air powered. Use of locomotive is limited to relatively low gradient. Types of Locomotive Haulage:- a. 1. Diesel Locomotives; 2. Battery Locomotives; 3. Overhead (Trolley) wire Locomotives; b. 1) Diesel Locomotives

Diesel locomotive ranges in weight from 3 tons to 15 tons and in horsepower from 20 HP to 100 HP. It meets almost every possible requirement whether for main haulage, gathering haulage a shunting.

It is a completely self contained unit, requiring only a supply of suitable fuel oil for its operation. It can travel anywhere in the mine where a paper track is laid and where the ventilation is adequate to dilute the exhaust gases. It can deal with heavy loads on relatively revere gradients.

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On the other hand, a diesel locomotive requires a skilled maintenance to ensure its safety and efficient operation. The use of fuel oil and high temperature developed introduce a fire risk which must be dealt with by suitable precaution. The analysis of exhaust gases e.g. carbon monoxide, firedamp & nitrous fumes are necessary to ensure that the percentages are kept within prescribed limits.

2) Battery Locomotives

Battery locomotive are generally less powerful than diesel. They require a charging station for periodically recharging the batteries. They have a wide field of usefulness especially as gathering locomotives. There is no contamination of the air, no noise and no vibration. On the other hand, batteries locomotives have higher first cost than diesels. The maximum reactive force is less than that of diesel locomotives of similar weight.

3 Over-head wire (trolley) Locomotives

These differ from diesel and battery locomotive in that they are not self contained. They drive their power from external source. The elective energy is generated at the surface of the mine and transmitted by trolley wires which extend along the haulage roads. Among the advantages, the trolley locomotives can develop high power and speed. They are simple to maintain, they have a low running cost and their over all efficiency cannot be compared with other types of locomotives. Special field of application is on long main haulage roads. Essential requirements are high standard of ventilation, roomy and well supported roadways.

On the other hand, the system introduces risks of open sparking which might cause an explosion, and of electrocution with its resulting danger to life and limb.

ii) Rope Haulage

This haulage is applicable to a limited gradient, up or down, and to undulating floors. These are operated by an engine; steam, electric or compressed air with the help of a rope would on a drum. Different rope haulage systems are available depending upon circumstances (conditions). Gravity Rope Haulage, Direct, Rope haulage or engine plane, endless rope haulage and main & tail rope haulage are the various systems available.

Types of Rope Haulage There are four types of rope haulage.

1. Direct or main rope haulage; 2. Main & tail rope haulage; 3. Endless rope haulage; 4. Gravity haulage. 5. 1) Direct or Main Rope Haulage

This is the simplest system of rope haulage only tub track, one rope and a single geared to a motor or engine is required. It is suitable for hauling tubs uphill on comparatively steep inclines where the gradient is sufficient to enable the empty tub to gravity table in-bye, drawing the rope after them. The drum runs loose on the shaft and is controlled by a suitable brake.

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The direct rope system may be applied to all duties from hauling one tub at a time to hauling long trains. The size and the design of the haulage gear thus vary within wide limits.

With ordinary tubs having plain bearings, the gradient of roadway may be about 1 in 12 or steeper. This system of haulage is suitable for it simple to operate, easily expandable and can deal with large output over fairly long distances.

On the other hand, it operates on high peek power demand, severe breading duty on downward run and high haulage speed (10 miles per hour) demanding a high standard of track maintenance.

2) Main & Tail Rope Haulage In this system, the haulage engine is provided with two separate drums, one for the main rope which hauls the full train out and one for the tail rope which hauls the empty train in when one drum is in gear, the other revolves freely on the shaft but is controlled. The main rope is approximately equal to the length of the plane and the other tail ropes twice this length.

Only one track is required except in the headings or pass-byes. This system of haulage is suitable for undulating roadways where it is not possible or desirable to maintain the double track. It can readily negotiate curves and it is convenient for working branches.

On the other hand, it operates at fairly high speed and with long trains. If a derailment occurs, the resulting damage and delay are likely to be considerable.

3) Endless Rope Haulage. In this system, an endless rope passes from the driving gear at the out-bye end of the plane to a return pulley at the in-bye and back again to the driving gear. Two sets of rail are required, one for the empty tubs going in-bye and one for full tubs being drawn out-bye. The rope may be placed either under the tubs or over them. The tubs are attached to the rope at regular intervals, either singly or in sets, so that there is a constant delivery of full tubs at the surface.

Under-Rope Haulage It has the advantages that there is a more direct pull on the draw bars; the tubs may be more fully loaded. The moving rope, being near the floor, is less liable to cause personal injury. The method is suitable to steep roadways of uniform gradient.

Over-Rope Haulage.

In has the advantage that fewer rollers are required and there is less friction and wear of rope and sleepers. The rope is un-affected by a wet floor and is less liable to corrosion. Attaching and detaching of tubs become easy as rope is at a better working height. The method is suitable for undulating roadways of varying gradient. The endless rope system has a wide application provided that a double road can be maintained. It can negotiate curves, can be easily extended in-bye and can haul large tonnage over long distances. Moreover it has low speed (1.25 to 2.5 miles an hour) less wear tear and less liability to major accidents, and breakdown. The system is well balanced and power costs are smaller than other systems. On the other hand, it is extravagant in manpower; require a large stroke of tubs and the roadways is never free for the haulage of men or material in-bye.

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4) Gravity Haulage.

This includes all systems of self acting haulage in which the gradient is sufficiently in favour of the full tubs. This enables the empty tubs or a balance bogie to draw up without the aid of mechanical power. Figure as shown in a gravity haulage is known as balance layout.

Fig 8.9

The gravity haulage is applicable to a single rise gate way near the face where a single full tub is lowered against a weighted bogie running on rails of narrow gauge at the side of the tub track whilst the empty tub is pulled up as the bogie descends.

The rope posses 1.5 times around the jig pulley or break wheel which is secured to an anchor prop at the top of the gateway. One end of the rope is secured to the tub and the other end posses to the bogie around the pulley and so back uphill to a holding up prop where it is firmly secured by a clamp or a lasting chain. It is also secured to a safety prop and the surplus rope is coiled nearby in readiness for when the face advances.

With the double rope arrangements shown, the travel of the bogie is half that of the tubs, sometimes, the bogie is arranged to travel the full length of the incline being than secured with a single rope. In the later case, the weight of the bogie must be midway between the full and empty tubs. When a double rope is used, a bogie of twice this weight is required. A bumping chock a prop is provided at the bottom of the bogie track to act as a buffer.

6.3.1.2 Trackless Haulage

This haulage does not require rail track for its operation for example; Manual (wheel barrows), conveyors and shuttle cars.

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i) Manual (Wheel Barrows)

Wheel barrows are used in small, irregular mine workings and in some stops as an alternative for shoveling. ii) Conveyors

Different types of conveyors normally driven by electric motor are used. Normally these are used for transporting the material up or downgrade. Belt conveyors, chain and flight conveyors and shaker conveyors are major types.

Underground conveyor may be divided into three main types:

1) Shaker Conveyor 2) The Belt Conveyor 3) The Scraper Chain Conveyor 4) 1) Shaker Conveyor

This consists of a series of steel trays, troughs or pans each 10 to 12 ft long, connected together end to end with an overlap of about two or three inches and supported on pairs of loose wheels or rollers about 6 to 8 inches diameter.

Fig 8.10

This type of conveyor is only suitable for conveying coal or other material on the level or down a favourable gradient, for a distance exceeding 120 yards and for out- puts upto about 30 tons per hour on level and rather more when conveying down hill.

Shaker conveyors have the advantages of cheapness, simplicity and robustness. It can be easily shortened or extended or moved forward as required. It can be easily repaired and also used for diverting dirt down a longwall face for packing the goaf.

2) Belt Conveyor

This consists of a flexible rubber belt or band. With driving gear, tension frame and intermediate rollers to carry both the loaded and the return half of the belt. Either top belt conveyor or bottom belt conveyor may be used for carrying coal underground.

Belt conveyor has the advantage that it can convey coal on the level or uphill or down hill on all gradients upto about 1 in 3. It is comparatively silent in action has a continuous delivery and lower power consumption. It is capable of handling outputs upto 2000 tons per shift.

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It shows disadvantage when alignment is daily needed on longwall face. Moreover belt has high first cost and its life may short unless great care is taken in the initial selection and maintenance.

Fig 8.11

3) Scraper-Chain Conveyor

This type of conveyor combines advantages of both shaker conveyor and the belt conveyor. Like shaker conveyor, it is robust in construction and can be readily dismantled and moved forward or shortened or extended in length. Like the belt conveyor, it can convey material on the level or uphill or downhill. It has an added advantage that it is more positive in action and can therefore cope with somewhat steeper gradients. In its various sizes it can handle outputs upto about 250 tons per hour.

Scraper chain conveyor may be used on longwall faces and also in mechanized room and pillar mining where it features. Scraper chain principle is applied to gate and loaders and to auxiliary feeders receiving and from face conveyors and delivering it to gate belt conveyors.

i) Shuttle Cars

These are used underground to transport coal between two fixed points e.g. from continuous miner to a conveyor belt. They have a shallow load pan with a conveyor in the center. Depending upon source of power, there are different types of shuttle cars.

Shuttle Cars Fig 8.12 ii) Load Haulage Dump Units (LHD) iii) These are compressed air operated machines working on rubber tired. They are used in stops for loading the material, haulage it for a short distance and their dumping it in chutes.

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8.3.2 Hoisting

Hoisting is method of transportation used in vertical or nearly vertical opening (shaft). There are two types of hoisting:-

Fig 8.13

8.3.2.1 Unbalanced Hoisting

In this system there is only one cage working in one compartment of the shaft. This system is used at mine where the output is very small. 8.3.2.2 Balancing Hoisting

In this system there are two cages, which balance each other and usually have one or two drums. The cages move in separate compartment. This system is used in mines with high output. Balanced hoisting can be done in different ways.

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CHAPTER-09

THE ATMOSPHERE AND MINE GASES

9.1 The Atmosphere

The atmosphere or atmospheric air is composed of a number of different gases, combined as a mechanical mixture which contains.

Name of Gas By Volume Oxygen 20.93% Nitrogen 78.11% Carbon Dioxide 0.03% Inert Gases 0.93% Water Vapour Variable

The inert gases comprised mainly of argon with small amount, of hydrogen, neon, krypton etc. They have no physiological reactions and thus can be equated with nitrogen for practical purposes.

Thus the composition of the atmosphere may be considered as being, oxygen 21 per cent, nitrogen 79 percent plus water vapour (according to humidity).

Atmospheric air has a specific gravity of 1. It is colourless, odourless and tasteless. Although air itself is nonflammable, it supports combustion.

9.2 Atmospheric Pressure

The atmosphere forms a covering of air some 300 kilometers from the earth surface. It exerts a pressure by the force of gravity. This pressure varies with temperature, humidity and distance from the surface of the earth.

Atmospheric pressure may be expressed as atmosphere or bar. One atmosphere=1.013 Bars. The average atmospheric pressure at sea level is equal to 101.3 kilo pascals, 1013 millibars, 760 milimeters mercury or in imperial units 14.7 pounds per sq.inch, 30 inches mercury or 34 feet or water.

9.3 Barometric Changes and their Effects in a Mine

• It is very necessary that all persons responsible for the ventilation underground in a mine take regular readings of the barometer provided at the surface because changes in the atmospheric pressure may considerably effect conditions in the mine workings. • There is little danger in a normally well ventilated mine when the barometer is stready or rising slowly.

Danger from gases in the goaf or old working is chiefly liable to occur when the barometer is falling rapidly. In those cases all gases expand from the goaf when the pressure is reduced and conversely they contract when the pressure is increased. A fall in the barometer indicates a reduction in the atmospheric pressure both at the surface as well as underground.

If the fall in the barometer is slow, the gases are given off slowly and if the places are well ventilated, no adverse affect takes place. If the fall is rapid, the volume of gases given off from goaf and old workings shall be rapid and danger for the workers become imminent.

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In practice, of course the ideal situation is to ensure that ventilation shall be adequate under all conditions no matter the barometer is rising or falling.

9.4 MINE GASES 9.4.1 Oxygen (O2)

Oxygen is a colourless, odourless and tasteless gas. It has specific gravity of 1.11. The air contains 20.93 per cent by volume. It is slightly soluble in water and liquefies at -182 Celsius degrees.

It supports life and combustion i.e. helps in burning. The human beings work best when air contains approximately 21 per cent oxygen.

Physiological Effects

Percentage Effects 20.93 No effect, Normal atmospheric conditions 19.00 The luminosity and flame height of an oil safety lamp is reduced by 50%. 17.00 Oil safety lamp extinguished. Men should be withdrawn. 16.10 Candle extinguished. Men should not be allowed to work. 12.50 All flaming combustion ceases. 10.00 Nausea and headache gradually develop. Lips turn blue. 8.00 Breathing becomes very rapid. Palpitations and mental confusion occur. 7.00 Unconsciousness occurs rapidly and death usually follows. 2.00 All combustion ceases, including smoldering.

Detection of Oxygen

It is generally not necessary to detect the presence of oxygen. It is the lack of oxygen which leads to dangerous conditions.

Uses of Oxygen

Without oxygen life is not possible in the universe. When very hot, it is used in welding, cutting and reduction of metals.

9.4.2 Nitrogen (N2)

Nitrogen is colourless, odourless, and tasteless gas. It has a specific gravity of 0.97. It is slightly soluble in water and liquefies at 195 Celsius degrees. It forms 78.11 per cent by volume in atmospheric air. It is non-poisonous, does not support life and is non- flammable.

Physiological Effect

At normal pressures, it has no effect on human body. Under high pressure, it can dissolve in the blood and can be a risk for the human beings.

Uses

In mining, its major use is for fire fighting purposes. Commercially it may used as a refrigerant, a propellant gas and to provide inert shielding in welding. 9.4.3 Carbon – Dioxide (CO2)

Carbon dioxide is a colourless gas with slight pungent or acrid smell and a soda water taste. It has a specific gravity of 1.53 and forms 0.03 per cent of atmospheric air.

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It is quite soluble in water. Its solubility increases with pressure. On cooling it does normally become a liquid but converts into solid state at 78 Celsius degrees to form dry ice. It is incombustible gas and does not support combustion.

Physiological Effects

Percentage Effects 0.03 None: This amount is present in normal air. 0.50 Lung Ventilation is increased by 5 percent. 2.00 Lung ventilation is increased by 50 percent 3.00 Lung ventilation is increased by 100 percent 5.00-10.00 Violent headache, man feels very much tired. 10.00-15.00 Intolerable headache, collapse

Occurrence in Mines Carbon dioxide in mine is a component of black damp and after damp. It is generated by oxidation of coal and wood and from the respiration of men and animals. It is also one of the constituent gases given off by mine fires, explosions, blasting and diesel Exhausts. Uses

Medically it is used as a respiratory stimulant gas which contains, 4 percent carbon dioxide and 96 percent oxygen are sometime used in resuscitation. Other uses include in refrigeration and in fire extinguishers.

Detection

It extinguishes safety lamps due to a reduction of oxygen content in the air. The permissible upper limit in coal mines is 1.25 percent.

9.4.4 Carbon Monoxide (CO)

It is the most dangerous toxic gas encountered in mines. It is considered to be detected by smell or taste. Many lives have lost due to inhaling of even very small percentage of this gas.

It is formed due to incomplete combustion of any carbonaceous material. In any mine where there is or has been or in suspected any fire, explosions or self heating, then carbon monoxide must be suspected.

Remember that carbon monoxide is always present if smoke is visible and it is a constituent of water gas, producer gas, white damp and after damp.

Carbon monoxide is also produced in mines from badly functioning diesel engines, from over heated air compressors and from explosives if proper precautions are not carried out in shot firing.

Carbon monoxide is a colourless, odourless and tasteless gas. It has specific gravity of 0.97. Although its specific gravity is almost equal to air, it is often found as a layer towards roof because it is generally associated with heat. It is slightly soluble in water and is both flammable and toxic. It will burn in air with a pale blue flame to form carbon dioxide. The flammable limits in air are 12.5 to 74.0 percent. Most explosives are being 29 percent.

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Physiological Effects

Percentage Effects 0.02% Slight headache 0.04% Headache, nausea and possible collapse. 0.12% Possible collapse. 0.20% Unconsciousness and death within 10 minutes.

Carbon monoxide positions the human body. It is absorbed in the blood and red blood cells are converted into white blood cells. It blocks the transportation of oxygen to various parts of the body.

Detection

Carbon monoxide can not be detected by colour, taste or smell. To detect it, rescue men should relay on carbon monoxide detectors and monitors. Birds or canaries also help in the detection of this gas because they are much quickly affected than man. A bird shows distress (gasping, reffling of feathers and loss of liveliness) if taken to an atmosphere containing carbon monoxide. The time of its distress depends upon the percentage of carbon monoxide present in that place. ] 9.4.5 Methane (CH4)

It is the most common and inflammable gas which is present in mines. It has been the root cause of many mines explosions with the loss of countless lives. Where the term “gas” is used by miners it is generally methane that they refer to. Methane has no colour, taste or smell when pure. Often however, it is found mixed with other flammable gases which change the mixture to a sweet pleasant smell.

Methane does not support life. It is not itself poisonous. In fact it has a slight anesthetic effect. It is slightly soluble in water.

Occurrence

Methane is a component of carbon and hydrogen. It is thought to have been produced from the decay of vegetation at the same time when coal seams were laid down.

Methane is given off naturally from almost all coal mines. It is also found in some metalliferrous mines and in natural gas field.

a) Gradual exudation- bleeding from the coal itself. b) Blowers-continuous discharge of gas for a period from a definite point. c) Out bursts-sudden discharge of gas.

Flammability

The most important property of methane is that it is highly flammable and explosive when mixed with air or oxygen.

a) Flammability of mixture i) Mixtures of methane in air within the range 0-5 percent methane are not explosive. It burns with a pale blue flame. The approximate percentage can be determined by safety lamps. ii) Mixtures within the range 5-14 percent are flammable. The most explosive mixture is 9.8% and the most easily ignited mixture is 7.5 percent.

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iii) Mixtures above 15 percent are not explosive, do not support combustion but will burn if mixed with air.

b) Ignition Temperature

It can not be defined as a definite. It varies with the mode of ignition. It is generally

between the ranges 650-750 Celsius degrees. Detection

A variety of approved instruments are available to detect and measure methane concentrations in the mines. They include:-

a) Oil flame safety lamp b) Methanometers c) Automatic fire damp detectors d) Interferometers e) Infrared analyzers. f) Note 1 Detector tubes are not accurate or specific enough. Note 2 Infrared analyzers are reliable instruments to use if other flammable gases are present i.e. after a fire or an explosion. 9.4.6 Hydrogen Sulphide (H2S)

It is also known as sulpharetted hydrogen or rotten egg gas. It has no colour but a powerful and unpleasant odour resembling that of rotten eggs. It has a specific gravity of 1.19 and burns in air with a bright blue flame producing sulphur dioxide and water vapour.

Occurrence

It is produced by the decomposition of animals or vegetable matter containing sulphur. It is also produced in seam containing high sulphur coal. It is also a component of after damp of coal dust explosions. Small amounts may also be evolved from stagnant water containing rotten vegetation.

Flammability

It forms flammable mixture in air in the range of 4.5 to 45 percent.

Physiological Effects

Percentage Effects 0.0005 The gas is not poisonous. Does not cause any discomfort. 0.01 Irritation to the eyes and respiratory tract. 0.02 Within 10 minutes intense irritation of the eyes and throat. 0.05 It is the highest percentage that can not breathed without causing death. However this amount causes palpitation, muscular weakness, fainting and cold sweats. Serious symptoms within a few minutes. Pains in the chest. 0.07 Highly dangerous to human life. Depression, unconsciousness and death. 0.10 Very dangerous, death occurs almost immediately.

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Detection

It has rotten egg like smell. Tube Detectors detect the percentage of hydrogen sulphide. White blotting paper saturated with lead acetate is turned black in the presence of this gas. Silver coins are also dis-coloured by the presence of hydrogen sulphide.

9.4.7 Sulphur Dioxide

a) Properties

Sulphur dioxide has no colour but possesses a pungent, suffocating, sulphurous odour and almost intolerable acidic taste. It has a specific gravity of 2.26 and is soluble in water forming sulphurous acid.

It is incombustible and non-flammable.

b) Physiological Effects

Sulphur dioxide is extremely poisonous but owing to its irritating effect on the eyes and respiratory passages, it is intolerable to breathe for any length of time in dangerous concentrations. The physiological effects corresponding to percentage concentrations are given below:-

Percentage by Volume Physiological Effect 0.003 Least quantity detectable by its odour. 0.01 Very uncomfortable to breathe with an irritating effect on the eyes and respiratory passages. 0.05 Dangerous to life for short exposures.

The National Health and Medical Research Council of Australia recommended threshold limit value is 5 parts per millions (0.0005 percent). The recommended first aid treatment is oxygen administration, complete immobility, moderate warmth then seek medical aid because the effects of breathing this gas are often delayed.

c) Occurrence

It is generally found in mines where a heating or fire occurs in coal containing sulphur or occasionally when rubber is burnt and in diesel exhausts.

d) Detection

It can be identified and determined with detector tubes. Its typical odour can be detected by smell at 3 parts per millions.

9.4.8 Oxides of Nitrogen

The oxides of nitrogen include nitric oxide (NO) and nitrogen peroxide (N2O4) and nitrogen dioxide (NO2). Nitric oxides can be converted into nitrogen dioxide in the presence of air so their properties are same.

Oxides of nitrogen have reddish brown colour, an acrid smell and acrid taste. It has a specific gravity of 1.6. Soluble in water and forms nitric oxide and nitrous acids although incombustible and non-flammable it supports combustion.

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Physiological Effects

Percentage Effect 0.004 Can be detected by smell. 0.01 Cause coughing, seriously irritate the respiratory passages. 0.02 Produces great discomfort.

Occurrence

The oxides of nitrogen or nitrous fumes are produced as a component of diesel exhaust, or by explosives of the nitrogylycesive type especially when they are incompletely detonated. Detection

Nitrogen dioxide and oxides of nitrogen can be detected by detector tubes.

9.4.9 Damps

Damps are miner’s term for gaseous formed in coal mines as distinguished from pure air. There are: 2. 1. Fire damp 2. Black damp 3. White damp 4. Stink damp 5. After damp 3. 9.4.10 Fire Damp

A flammable gas usually it is methane but on occasions, the mixture can include hydrogen, carbon monoxide and other products of coal. The properties of Fire damp are similar to methane. It is usually lighter than air. It can accumulate in unventilated mine workings. It issues when the barometer falls. In short, it is almost the same as methane already described. It can be detected by a safety lamp.

9.4.11 Black Damp

This is sometimes called choke damp or stythe and is properly defined as a mechanical mixture of carbon dioxide and nitrogen. Analysis of a large number of samples includes an average composition of about 11-13% carbon dioxide and 87 to 90% nitrogen.

Black damp has the properties of both carbon dioxide and nitrogen. It is usually heavier than air. It can accumulate on floors of mines; can diminish the flame of a safety lamp. For every 5% of black damp results 1% reduction in the %age of oxygen, the luminosity is decreased by 30%. The light is extinguished altogether when the oxygen is reduced to 17% which corresponds about 15% black damp.

Example of calculation of percentage Composition of Black damp in an air sample

θ Suppose that the results of an analysis are O2 = 19.54 percent CO2 = 0.70 percent Ch4 = 1.62 percent

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N2 = 78.14 percent Sol. Find the percentages of Nitrogen and Oxygen. We know that Normal air contains O2 = 20.93% N2 = 79.04% CO2 = 0.03%

In normal air, the ratio of nitrogen to oxygen= 79.04/20/93 =3.776 normal air and in the ratio of CO2 to oxygen=0.03/20.93=1/698

Thus in the given sample, the fresh air equivalent of the oxygen present has the following composition.

Oxygen = 19.54 Nitrogen = 19.54 x 3.776 =73.78% CO2 = 19.54 x1/698 =0.03% Total air = 19.54+73.78+0.03=93.35% Hence the excess nitrogen = 78.14-73.78=4.36% And excess CO2 = 0.70-0.03=0.67% Total black damp = 4.36 +0.67=5.03%

Thus sample contains 93.35% of ordinary air, 1.62% of CH4 and 5.03% black damp making a total of 100%.

The percentage composition of black damp is:-

Nitrogen = 4.36/5 x 100=86.7% CO2 = 0.67/5.03 x 100 =13.3% Total = 100%

9.4.2.1 White damp

White damp is a term applied to carbon monoxide. This gas may be present in the after damp of a gas or coal dust explosion or in the gases given off by a mine fire. It is also one of the constituent of the gases produced by blasting, water gas, producer gas and coal gas. The properties are same as carbon monoxide.

9.4.13. Stink damp

This is term is synonymous as hydrogen sulphide. It is more poisonous than carbon monoxide. It can be easily recognized by pungent smell resembling that of rotten egg. The properties are same as that of hydrogen sulphide.

9.4.14 After damp

This a mixture of very variable composition of gases found in a mine after an explosion of methane or coal dust. After damp is composed of nitrogen, a little oxygen, carbon dioxide, carbon monoxide, water vapour and in some cases methane and hydrogen.

The water vapour usually renders the after damp very humid and in general the atmosphere is irrespirable due to lack of oxygen and often toxic due to the carbon monoxide. The breathing in an after damp atmosphere becomes difficult and dangerous for the health and lives of workers.

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9.5 Treatment in Cases of Gassing • If a person is rendered unconscious by deficiency of oxygen, due to displacement of air by firedamp or the withdrawal of oxygen by slow oxidation or other means result in excess of nitrogen, and death rapidly ensures. The period of unconsciousness preceding death is very short (due to lack of oxygen) and treatment should not be long delayed. • If a person is rendered unconscious by the action of carbon dioxide, a period of several hours may elapse before death occur. A person thus has a greater chance of being rescued from such an atmosphere and moreover, he is likely to recover quickly and completely when artificial is carried out. • If a person is rendered unconscious by the poisonous of carbon monoxide the chances of recovery depend largely on the degree to which the blood has been saturated with the gas. In this case, careful and prolonged treatment is usually required. Death may occur sometime after the victim has regained consciousness. Similar remarks apply to poisoning of sulphuretted hydrogen, although cases of collapse solely to this gas are rare. • In all cases, the administration of pure oxygen to the victim will greatly increase the probability and speed of recovery. • Carbogen which is mixture of 5-7% carbon dioxide and 93% to 95% oxygen should not be given as effect of carbon dioxide would increase the rate and depth of breathing to a patient who has become unconscious in an atmosphere of carbon dioxide.

9.6 Procedure to be followed when a person is found unconscious in an irrespirable atmosphere may be summarized as follows:

1. Loosen all tight clothing 2. Remove any foreign body (tobacco, false teeth) from the mouth. 3. Shift the victim to fresh air as soon as possible. Keeping him lying on his right side. 4. Apply artificial respiration by an approved method. 5. Administer pure oxygen by the help of an approved apparatus. 6. Promote blood circulation by rubbing the limbs and keeping the body warm with water bottle, blankets etc. 7. When the patient is full conscious, give him a stimulant in the form of hot tea or a coffee. 8. Keep the patient at rest and prevent him from becoming excited. Keep him warm, shift him to the surface on stretcher. 9. If a man has poisoned by nitrous fumes, he may be given common salt dissolved in water. Common salt should not be given if the patient is affected by other gases.

If a victim is suffering from severe hemorrhage due to some injury, this must be attended to first of all, before the man is removed to fresh air.

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CHAPTER– 10

VENTILATION

The main purpose of mine ventilation is to provide adequate air, currents to dilute, render harmless and sweep away dangerous gases from roadway and working places in the mines.

In coal mines the quantity of fresh air prescribed is generally from 100 to 150 cu. ft/min for each man and 200 cu. ft/min for each horse or mule in a mine. The difference of pressure or water gauge required to cause a current of air to flow through a mine may be created either:

1. By purely natural means, called natural ventilation. 2. By means of a mechanical ventilator or fan placed at the mouth of down-cast level or high cast level. 3. By a combination of natural and mechanical ventilation. 10.2 Natural Ventilation

Natural ventilation means the current of air that flows through a mine by purely natural means i.e. without the aid of a fan or other mechanical contrivance.

How Produced

Air will flow through a mine when there is a natural difference of density between two vertical or inclined columns who are inter connected with each other. As a result of difference of density the heavier or down cast column over balances the lighter or up cast column and a continuous flow of air takes place so long as the difference of density is maintained.

Let BC and FD in Fig 10.1 represent two levels of a mine at different surface levels, the mine working being level and shown by a single road may CD> At A and F, the air pressures and temperatures are equal as both the points at surface are on the same altitude. Any difference of pressure causing a current of air flow must have it, birth below AF.

Natural Ventilation Fig 10.1

Let us assume the rock temperature in the mine is about 35oC, while the surface temperature in winter is 250C and in summer 450C. Now the direction of flow of air current in cold weather, mild weather and hot weather shall be to some extent as under:

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1) In cold weather: the column AB is in the open and is colder and heavier than the column FE and column BC is also cooler and heavier than ED. The whole column AC is thus heavier and cooler than the column FD and air will flow naturally down AC, through CD and up DF. 2) In mild weather, the air in AC may reach the same mean temperature as the air in DF, so the flow of air may cease altogether. 3) In hot weather, the conditions are reversed. The mean temperature in FD becomes less than AC and thus the air flows down FD and up CA. 4) So to maintain purely natural ventilation, two conditions must normally be satisfied.

1. The inlet and outlet of a mine must be at different surface levels. 2. There must be a difference of temperature and therefore of density, between the two air columns.

10.2.1 Calculation for Natural Ventilation

To calculate difference of pressure or water gauge at a place in mine we calculate the excess weight of air in DC and UC levels which is called Motive Column. Motive Column in feet can be calculated by formula.

Motive Column in feet = H = Fu – Fd x d 459 = F0 And pressure in Ibs per sq. ft. = Motive Column in feet x density fair.

Example 9.1 The mean temperature of the air in a certain DC shaft is 500F and in the UC shaft 700F. Both shafts are 2000 ft deep. Calculate as the natural ventilating pressure in Ibs per sq. ft. be the height of motive column.

Assume a mean barometer of 30 inches at half the depth of down cast.

Solution (a):

The height of motive column in feet may be calculated from the temperatures and depth, without reference to the weight of the columns, by applying the formula.

Motive column in ft = h = Fu – Fd x D 459 + Fu Where D = Depth in ft of whole DC shaft Fu = mean temperature of upcast shaft in 0F. Fd mean temperature of down cast column in 0F Replacing the values, we get h = 70 – 50 x 2000 459 + 70

= 20 x 2000 = 75.6 feet 529

(b) Pressure in Ibs per sq ft = Motive column in ft x density of air = 75.6 x 0.7811 = 5.9 Ib sq ft. = 5.9 = 1.14 inch w.g. 5.2

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10.2.2 Geothermic Gradient

The chief factor causing the air to be heated as it passes through a mine is conduction of heat from the strata. The temperature of strata increases as we descend below the surface, although not everywhere at the same rate. The rate of increase is termed as Geothermic Gradient. In Great Britain the rate of increase of temperature is I degree Fahrenheit per 70 feet of depth. In all countries this varies from place to place.

10.3 Distribution of the Air

Distribution of air to the various portions of a mine is done by using:-

ƒ Brattice Cloth; ƒ Stoppings; ƒ Doors; ƒ Air-crossings; ƒ Regulators; ⎯ These appliances must be kept in good order so that they may be used as and when required in ordinary conditions and in emergencies. Let us describe each one by one.

10.3.1 Brattice Cloth

This is simply a sheet or sheets of canvas hung from props and planks either (a) as a screen across an airway to prevent or reduce the flow of air along it or (b) as a partition along an airway to divide it into two parts intake and return. Canvas screens are suitable only in the in bye workings where the ventilation pressure is small.

A hurdle screen is a canvas cloth which does not reach right to the roof. It is used to divert an air-current upwards into a roof cavity in order to keep it clear of gas. Fig. 10.2 shows arrangements where such a screen is used to divert the air from a long longwall face to the edge of a ripping so as to clear away an accumulation of gas.

Fig 10.3

Brattice partitions are used to ventilate narrow places driven in advance of the general ventilation e.g. in board and pillar workings. Fig. 10.4 shows faces A and B which are ventilated by hanging canvas in the manner shown. The air travels in the direction as

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shown by the arrows when the two places have been driven a proper distance, they are generally inter connected then the brattices can be removed and a door is hung at D. The air then travels along one heading then across towards hand came back along the others headings. Brattices are used at for limited distances.

Brattice in Narrow Platos

Fig 10.4

10.3.2 Stoppings

These are used to block off any old roadway not required for travelling, haulage or ventilation. These are erected between main intakes and returns. They must be explosion proof and constructed to comply with legal requirements laid down in the regulations. In general, they are built of stone, sand or rubbish packing with a well built wall of brick work of concrete at one end in the intake or at both ends. In the intake side road must be kept clear.

10.3.3 Doors These are placed on roadways used as haulage or travelling roads. Normally two doors are used so that one is always closed when the other is open. Fig. 10.5 shows one type of door. Dimension of the door depends upon the place where it is to be erected but care should be taken that it is made of well seasoned wood. The door frame consists of two side pieces, a crown piece and a sole piece and is built into a brick wall which closes the rest of the roadways. The space below the door is made air-tight as far as possible. The door must be arranged to close automatically.

Fig 10.5 10.3.4 Air Crossings

These are required when-ever the return air-current has to cross the intake air current without mixing with it. When air-way rises over the other, the crossing is called an over- cast and when dips under other it is called under-cast. The latter has the disadvantage

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that water may accumulate in it, and so an over-cast should be preferred. An air crossing may be either temporary or permanent in character.

Fig 10.6

10.3.4.1 Temporary Air Crossing

Temporary air crossing is made where the partition between the intake air and return may be of timber or of air tubes. They may be used:

i) Near the working face where the strata has not settled down; ii) In connection with narrow headings which are advancing and require independent ventilation; iii) In restoring workings after an explosion before the erection of permanent crossings. 10.3.4.2 Permanent Air Crossings

These are used where strata have settled down and the crossing is likely to be required for a log period. The chief features of such a crossing are that; i) ii) The structure must be air tight so as to prevent leakage from intake to return; iii) It must be explosion proof; iv) It must be of ample size to permit the free flow of air. v) 10.3.5 Regulators

Fig. 10.7 shows a common form of a regulator. It consists of sliding wooden shutter fitted into brick stoppings or in a ventilation door. The area of opening may be adjusted usually by trial until only the required amount of air passes through. The shutter is then locked in position to prevent un-authorized interference. It will be obvious that the smaller the opening of the regulator, the greater will be the resistance offered by it, the greater will be pressure or w-g. absorbed in forcing air through and the smaller will be the volume of air flowing through

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ROOF

FLOOR Regulator

Fig 10.7

In practice a regulator is placed in a low resistance split, possibly near the shaft which is taking too large a proportion of the total air. It has the effect of reducing the air flowing in that split and increasing flow of air in an unregulated parallel split of high resistance. It is thus a convenient means of controlling the relative flow of air to each district according to the requirements of the district.

It should be understood that a regulator is an added artificial resistance which increases the total resistance of a mine and reduces the volume of air flowing for a given fan drift water gauge.

Example 10.1 Calculate the quantity of air passing through a regulator of which the opening is 2 feet square, when the water gauge on the door reads 1 inch. Assume w = 0.08 Ib. per cub. ft.

Solution By formula (11) Q = 0.65a x 2gh cub. ft. per second.

Where a = 4 sq ft, h = 5.2 = 65 ft; g = 32.2 6.08 Quantity A= 0.65 X 4x √2 X 32.2 X 65 X 60 =10.093 cub.ft per minute

10.4 Ascensional & Descensional Ventilation

10.4.1 Ascensional ventilation

Ascensional ventilation occurs when the air travels uphill along the face as shown in the right hand split or district A as shown in Fig. 10.7. To bring this about the intake air is first taken direct to the lowest point of the district namely X and after travelling up the face leaves by the return airway at the top end of the face.

Fig 10.8

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10.4.2 Descensional Ventilation

Descnsional ventilation occurs when the air enters at a higher level, descends along the face and leaves at a lower level as in split B. It may be said that in general, ascensional ventilation is normally to be preferred because:-

a) The natural ventilation pressure (n.v.p.) developed in the workings assists the fan ventilation; b) Quantity of air flowing is increased more especially where the w.g. developed by the fan is low; c) Firedamp, being lighter than air is readily carried uphill towards the return and d) If the fan should stop, the air will continue to flow in the same direction, although at a reduced rate. These are all very important considerations, especially in a gassy mine.

On the other hand, with descensional ventilation.

a) The n.v.p. opposes the fan and if the fan is stopped the air flow will be greatly reduced and may even be reversed; b) Firedamp newly given off may migrate to the rise, in a thin layer next to the roof and in the opposite direction to the air current and so find its way into the top (intake) roadway; c) A brisk current of air (produced by the fan relatively high w.g.) is essential if safe conditions as to firedamp are to be maintained at the face; and d) If a fire occurs on a descensionally ventilated face the hot gases may reverse the ventilation and so put the fire fighters in a dangerous position, whilst tending to limit the spread of the fire. It may nevertheless be argued that especially in deep hot mines, it may be better to take the intake air into the mine via an upper horizon and ventilate the faces descensionally. The chief advantage of this is that the air reaches the faces in a cooler and drier condition and the climatic conditions on the face are thereby improved, possibly postponing the need for the installation of special air conditioning plant. It is important that the w.g. developed by the fan shall be sufficient to counteract the n.v.p. and the buoyancy of methane in the goaf and that adequate standby ventilating plant shall be installed to ensure continuity of the ventilation at all times. Other advantages arise on a descensionally ventilated face where the lower road is used both as a return airway and as a coal transport road but this is more suitably dealt with under the next headings.

10.5 Homotropal & Antitropal Ventilation

110.5.1 Homotropal Ventilation

Homotropal ventilation occurs when the air and coal flow in the same direction. This apply to the descensional split B as shown in fig above. The return airway is used as the coal transport road. 10.5.2 Antitropal Ventilation

Antitropal ventilation occurs when the air and coal flow in opposite direction. These apply to the ascension split A as shown in fig above.

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10.6 Booster Fan

A booster fan is a more or less permanent installation designed to pass the whole of the air circulating in the district or districts. 10.6.1 Purpose to use Booster Fan

a) To increase the quantity of air at the place of high resistance for in-bye. b) To improve the working conditions in deep hot mines by speeding up the air; c) To reduce the excessive leakage between intakes and returns; d) To reduce or adjust the pressure difference between intakes and returns in mines liable to spontaneous combustion. e) The installation of Booster Fan is considered justifiable where increased quantity of ventilation is urgently required. Booster Fan may be of either centrifugal or the air screw type and may be lace either:-

a) In the return to act as an exhausting fan or b) In the intake to act as a forcing fan.

10.6.2 Location of Booster Fan

It is very important that the correct size of booster fan is chosen and that it is correctly placed to avoid the danger of re-circulation of air, or of leakage from return to intake or of undue interference with the ventilation of other districts. It is necessary to conduct the ventilation survey before the installation of Booster Fan.

10.7 Auxiliary Fan

An auxiliary fan is a more or less temporary installation designed to pass a proportion of the air circulating in the district concerned. 10.7.1 Purposes to use Auxiliary Fan

a) Long headings and cross measure drifts driven in advance of the workings; b) Narrow places in mechanized room and pillar workings. c) Roadways where roof falls has blocked the normal air course.

10.7.2 Type of Auxiliary Fan

a) These are centrifugal fans usually electricity driven. Sizes commonly range up to about 20 diameters. b) Axial flow fan driven by electricity or by compressed air. c) Static blowers which, though not fans, may be used as auxiliary ventilators.

10.8 Advantage & Disadvantages of Forcing Fans

a) A current of cool intake air or high velocity is led to the face so increasing the comfort and efficiency of the men and rapidly dispersing any gas, dust or short firing fumes at the face itself. b) Any gas made in the face is carried out bye away from the face. c) The fan handles clean intake air; d) Flexible ducting can be used and need not to be kept very close up to the face. Disadvantages The main disadvantages of forcing is that only a slow ventilating return current traverses the roadways and it take a long time for dust to be entirely removed there from.

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10.9 Advantage of Exhaust Fan

The main advantages of exhausting is that firedamp, dust and fumes at the face are drawn out direct into the air from the high level side and the working place is kept clear for persons working and travelling therein.

Disadvantages of Exhaust Fan 1. or runner carrying vanes faces get inadequate air current and gases may accumulate in them. 10.10 Fan Ventilation

There are two types of fans.

1. The centrifugal or radial flow fan. 2. The air screw or axial flow fan.

10.10.1 Principle and Working of Centrifugal Fan

The principle of centrifugal fan is that the air is entered in the centre and is discharged more or less tangentially from the circumference.

It consists of a wheel, rotor or blades as shown in fig. below 10.8. The wheel revolves on a shaft at a speed which depends on the size of the wheel and on the pressure difference which is set between the centre of wheel and the periphery. The action of these types of fan is based upon that the air possesses inertia which once set in motion continues to move in a straight line unless it is compelled by an impressed force to change its direction.

Simple Fan Wheel Fig 10.9

Consider a particle of air at a as shown in Fig. 10.8. It is acted upon by the blade which is rotating in a circular path toward b, but due to its inertia, it teds to move in a straight line in the direction ac. The resultant of these two simultaneous movements as that the particle actually follow the spiral both i.e. tangential to the circumference along arrow de as shown in the figure. Strictly speaking the air is said to fly off because of centrifugal force. The continuous movement of air from inlet to periphery set up a difference of pressure or water gauge as a result of which mine is ventilated by mechanical means.

The centrifugal fan has spiral casing and evasee chimney.

The purpose of spiral casing is to enclose the fan wheel and to prevent reentry of the discharged air. Its cross-sectional area increases to accommodate more and more quantity of discharged air from the wheel.

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Fig 10.10

The purpose of evasee chimney is to reduce the final velocity of discharge to a minimum and to promote smooth flow of air without turbulence and eddy currents. By this, the efficiency of the fan is increased and the required w.g. is developed with a smaller expenditure of power.

10.10.2 The Air Screw or Axial Flow Fans

The principle of air screw fan is that it propels the air forward axially i.e. straight through the fan in line with the shaft. It is diverted later in to evasee chimney.

The action of an air screw fan depends on the principles of aerodynamics. In an aero plane, the machine is driven forward through the air when the propeller revolves but in a fan, the machine itself remains fixed to its foundation and the air is driven forward.

In an axial flow fan, much higher peripheral speed is needed to develop a given w.g. than in the case of a centrifugal fan.

The figure below shows a sketch of a fixed pitch, single stage air screw fan.

Fig 10.11

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It consists of multi bladed rotor or runner. When the rotor revolves, it discharges its air through stationary guide vanes towards nose shaped head. This stream lines the flow of air. The cone or nose shaped head extends to the perimeter of the air drift and designed to maintain streamline flow at the outlet also. The rotor and guide vanes are mounted within a cylindrical casing with a small clearance between blades and casing. The casing is fitted with an expanding chimney.

The air screw fans are made in all sizes from 18 inches dia to 12 feet diameter. It is especially high speed machine running from 180 to 3000 r.p.m. It may be driven by an electric motor. Two or more rotor each with a set f guide vanes can be made to produce high w.g. 10.10.3 Comparison between Centrifugal Fans and Air Screw Fans

1. The efficiency of centrifugal fan ranges from 70-75% whereas air screw fan ranges from 80-85%. 2. The centrifugal fan becomes overloaded where as the driving motor of an air screw fan does not become over loaded, no matter how the resistance or equivalent orifice of the mine may change. 3. The air screw fans have smaller weight for a given duty as compared to centrifugal fan. 4. The air screw fans are more suitable for auxiliary ventilation. 5. The centrifugal fans are more suitable for the development of high water gauges (pressure difference) where otherwise a more costly 3-stages air screw fan would be required. 6. The air screw fans have high speed of rotation and for this reason it necessitates careful construction of the rotor with its shaft and bearing. 7. The air screw fans have high noise of operation. This can be avoided by providing two or three stage construction which enables the required w-g to be obtained with a lower tip speed.

10.10.4 Reversing of Air Reversal of air with an air screw fan may be obtained simply by reversing the driving motor and fan runner. It should be noted that volume of air flowing is much reduced on reversal. Sometimes it is reduced to 30% of normal volume and w-g also reduces to one tenth of normal. However, these figures can be improved upon by modification in design.

Reversal of air with centrifugal fans is done by fitting doors in the opposite direction of flow of air. ______

Example 9.2 A fan running at 200 r.p.m. produces 150,000 cub. Ft. per min. at a water gauge of 4 in. (a) What quantity of air and (b) What water gauge will be produced when the speed is increased to 250 r.p.m., assuming the conditions of the mine to remain unaltered?

Solution (a) The quantity of air produced by a fan varies directly as the speed. Hence at 250 r.p.m.

Quantity of air = 150,000 X 250/200 =150,000 X 5/4 =187,500 cub, ft per min

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(b) The water gauge produced varies directly as the square of speed Hence, at 250 r.p.m 250 2 5 2 4 25 Water gauge =4X = 4X = X =25=6.25 inch. W-g ( 200 ) ( 4 ) 16 4

Example 9.3 If a fan which is developing 216 H.P in the air causes 150,000 cub. Ft of air per min through a mine (a) what power will the fan develop when passing 200,000 cub. Ft. of air per min. and (b) what quantity would the same fan produce in the same mine when developing 144 H.P? Solution (a) in a mine of given resistance, the power varies as the CUBE of the quantity 2 200,000 4 4 Hence, when the quantity is increased = times, the power required will be time the original power 150,000 3 ( 3 )

H.P required = 216 x (4/3)3 = 216 x 64/27 = 512 H.P

(b) In a mine of given resistance, the quantity varies as the CUBE ROOT of the power

Hence when the power is reduced in the ratio 144/216 the quantity of air will be reduced ratio 3 44 3 2 = =√0.667=0.874 216 3

3 2 =150,000 X 0.874= 131,100 cub. ft per min Final quantity = 15,000 X 3

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CHAPTER-11

Mine water and its disposal

11.1 Origin And Types of Mine Water

The origin or source of mine water can be any one of the following.

a) Rain Water Surface inflow of water into mine working.

b) Underground Water Water trapped in the rocks around mine working. Underground water can be divided into three classes from a geologic point of view:-

11.1.1 Meteoric Water

This water is derived from rain, water courses or other bodies of water. This water passes down into the earth through pores and cracks a part of this water is stored in pores and cracks and part of it circulates.

Water Table

As far as mine pumping is concerned, meteoric water is the only class of important. The upper limit of ground water is the point at which water constitutes stand in wells or shafts and this elevation is given various names e.g. water level, ground water level or hydrostatic level.

11.1.2 Magmatic or Juvenile Water

This is an important part of fluid magmas. This water is released in part giving rise to hot spring when the magma comes to the surface.

11.1.3 Connate Water

It is included in sedimentary rocks while they are being formed so geological period of this water and enclosing rock is the same.

11.2 Drainage of Mine Water

The water present in a mine is a problem and working is affected badly. It is, therefore, necessary to lower the ground water level by artificial means to keep the mine workings free of water. This operation is known as mine drainage. Different methods are adopted for this purpose.

11.2.1 Methods of Disposing of Mine Water

The method of disposing of water in mines may be classified as follows.

a) Drain Tunnels. b) Water Hoisting. c) Air lifts Location of Sumps d) Pumps. 11.2.1.1 Drain Tunnel

A tunnel is driven for the purpose of passing under the lower workings of several mines which collect the water for the entire area. Sometime the level of the tunnel is higher than the lowest level of the mine and water is pumped to the tunnel. The chief advantages of a

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drain tunnel are saving the cost of pumping and eliminating the danger of the mine being flooded through failure of the pumping. The tunnel might also serve both as haulage way and an air way.

11.2.1.2 Hoisting the Water

It is a simple method of hoisting water in tanks used in shafts. The engine or motor is located on the surface. The machinery can be easily repaired and the plant has no danger of being flooded. But the high cost of plant and shaft can not be used for any other purpose as water is being hoisted are important disadvantages. The method is less economical than pumping but is useful in emergency is reclaiming a flooded mine. 11.2.1.3 Sumps

It is an excavation in an underground mine where water is stored before pumping to the Surface. It is commonly placed at the bottom of the shaft or at one or more level in a mine. A mine may have one or more sump, pumping water from one sump to another. The size of sump depends upon water inflow.

11.2.1.4 Pumping

The pumps are one of the main sources of de-watering a mine. Water from a lower sump to upper sump or to the surface is pumped by the help of pumps.

11.2.2 Hazards of Water

The water in a mine creates a lot of problems. Not only it increases the cost of mining due to pumping but it reduces the overall efficiency as well.

Surface water flowing through cracks/joints into underground working causes troubles and sometimes results in flooding and damaging the whole workings. Mine water can be corrosive, resulting in damage to mining equipments, support systems ventilation and transport equipment by chemical action. The presence of water affects the stability of mine openings, floor heaving swelling up of floor; the roof falls and collapse of sides are common in wet coal mines. The mines water creates harmful working conditions by increasing humidity along with high temperature in deep mines. The maintenance cost of equipment also increases due to water problems.

11.2.3 Definition of Pumps

A pump is a mechanical device used to raise water from a lower level to a higher level. It converts mechanical energy into pressure energy. 11.2.4 Types of Pumps

Different types of pumps are used in mining as listed below:-

i) Reciprocating pumps. ii) Centrifugal pumps. iii) Turbine pumps. iv) Sludge pumps. v) Mono pump. vi) Siphon.

11.2.5 Reciprocating Pumps

The working of reciprocating pumps depends upon to and fro motion of a piston, bucket, ram or plunger within a cylinder (working barrel) the motion may be provided by some engine or electric motor.

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These pumps are classified as:-

a) Bucket or Lift Pump. b) Piston Pump. c) Ram or Plunger Pump. a) Bucket Pumps b) It is also known as “lift pump” because the upward or lifting stroke is the delivery stroke. It is being used in many countries for drawing water from wells.

Essential Parts

These are

i) Bucket (B) ii) Pump Barrel (C) and iii) Suction Valve (V) iv) Figure 11.1 shows a sketch of Bucket Pump

Fig 11.1

The Bucket (B) consists of an outer cylinder of iron or brass tapered towards it base. It is secured to the lower end by a vertical road (r). The bucket moves up and down in the pump barrel (C) by a sample lever. The suction valve (V) is placed at the base of the barrel which in turn is connected to a pipe known as suction pipe, dipping in to the water in the well or sump. The lower end of the suction pipe is fitted with a strainer. The purpose of fitting strainer is to prevent small pieces of wood or debris entering in to the pump.

Action of the Pump 1. Consider the bucket (B) to be at the bottom of its stroke and ready to ascent, the barrel and suction pipe being full of air. 2. On the upstroke, the bucket valve remains closed and the air above is forced out of the delivery pipe. As a vacuum is created behind it, a region of low

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pressure is created within the barrel and a certain amount of water enters from suction. It opens the suction valve (V). 3. On the stroke, valve (V) closed, the bucket valve opens and water passes to the upper side and discharges out through delivery pipe. 4. After several up and down stroke, the whole pump barrel is filled with water and discharge of water becomes continuous.

All types of pumps can work more easily if they are first primed. If this is not done, the pump will fail to draw water and will heat up and become damaged.

The Suction Head

The maximum theoretical suction head at sea level is calculated by the formula: 30 x 13.6 Delivery Pipe Suction head = = feet high 12 Atmosphere pressure at sea level = 14.7 lbs per sq. inch. = 30 inch mercury Specific gravity of mercury at sea level = 13.6 c) Piston Pumps This may be described as a moveable plug which fits inside the pump cylinder and is moved to and from by the piston rod.

Application of Piston Pumps

Piston pumps are suitable only for pumping fairly clean water to moderate heights: up to about 300 feet to 400 feet. They have the merits of being light, cheap and compact. The chief draw back is that the piston and working barrel losses a close internal fitting. It is also not suitable for water of gritty nature and where delivery head is high. d) Ram or Plunger Pump This differs from piston pump in that the piston is replaced by a ram of cast iron, brass or other alloy which does not fit tight in the working barrel. It is made water tight only at the two centrally placed stuffing bites, S and at the point r where the ram rod enters the pump barrel.

Figure 11.3 shows a sketch of a double acting ram pump, directly driven by a Compressed Air engines.

Fig 11.1

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Brief Description

The pump is provided with two suction valves V1 and V2 and two delivery valves D1 and D2 the course of water is shown by arrows. The valves may be of rubber close type. The ram and pump caring are of cost iron, lined, if necessary with brass or gunmetal to resist corrosion.

The air engine has its piston rod coupled direct to the pump rod, the pump being therefore “direct acting”.

Application of Ram Pumps

Ram pumps are preferred to piston pump when the pumping conditions are more rough because of dirty water or high lights or both. They may be designed to deliver water up to 3500 feet or even more.

The special advantage of a ram, as compared with a piston is that it has only to be kept tight at the external stuffing boxes. These can be maintained in good conditions and leakage if it occurs is at once apparent.

These types of pumps are especially suitable for raising water from dip workings for keeping dry the advancing face of an incline where the water is dirty and the pump may frequently be working on air, a condition quite un suitable for centrifugal pump unless specially designed.

11.2.6 Centrifugal Pumps A single stage centrifugal pump is shown in Figure 11.4 as below.

Single- Stage Double-Luiet Centrifugal Pump Fig 11.4 It consists of

a) Impeller keyed to a shaft and b) Spiral or volute casing c)

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The Impeller somewhat resembles a wheel formed of two discs between which are fixed a number of vanes or blades, curved backward usually from the direction of rotation. An opening is left at centre of the discs to permit the entry of water via the suction pipe.

When thee Impeller revolves, the water is carried round by the blades and is thrown off with an increased pressure and at high velocity from the sides of impeller into the volute casing. Here the velocity is gradually reduced and the kinetic energy is converted into pressure energy. This enables the pump to overcome a great head.

Centrifugal pumps are usually designed to deal with very large quantities of water, such as 100,000 gallons per minute, but it is suitable only for low lifts; the maximum being 150 feet or more conveniently up 30 to 70 feet.

Centrifugal pumps are in common use for condenser circulation purposes, coal washeries, irrigation purposes and motor works supplies.

3. The Turbine Pumps

A turbine pump differ from a centrifugal pump in that the simple volute casing is replaced by stationary diffusing channels surrounding the impeller as shown in Figure 11.5 below.

To Stages of a Turbine Pump

Fig 11.5

The Turbine pumps greatly increase the efficiency of conversion of kinetic energy in to pressure energy. A single stage turbine pump can deliver 400 gallons of water per minute against a head as high as 100 feet and so a two stage pump can lift water up to 200 feet. The pump is driven direct by a 3-phase, a.c induction motor running at about 1450 r.p.m. on a 50-cycle supply. 4 Sludge Pumps

These pumps are used for handling sludge. The sludge is liquid having about 2% of solids in it. Different types of sludge pumps are used depending upon the nature of sludge to be handled. The Mono Pump

This type of pumps differs from centrifugal or reciprocating pumps in its construction and action. It is a valve less, rotative pump.

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Fields of Application 1. For in-bye work at the face or in dip workings, where the suction conditions are difficult and variable and where the pumps may have to work on the snore i.e. on air. 2. For cleaning sumps and standages, where the water contains large quantities of fine silt or sludge. 3. For handling coal slurry in coal washeries. 4. Mono pumps can handle from 6.5 gallons per minute up to 100 gallons per minute at total heads ranging up to 100 feet for single stage pump and 300 feet from to stage pumps. The Mono Pumps consist of:

a) A rubber stator b) A helical rotor c) Suction and delivery branches d) Hollow driving shaft.

Section Mono Pump

Fig 11.6

e) The pump requires foundations and will work on any incline.

Operating the Pump 1. The pump must never be run in dry condition otherwise stator shall damage. The pump must first be filled with water before the pipes are connected. 2. When the pump is stopped, sufficient liquid is normally trapped in the pump to provide lubrication on starting again. 3. The pump must be primed up to suction head. 4. When the delivery head exceeds 100 feet, a hand controlled value with a pipe leading back to the sump should be provided below the non return value in the delivery pipe in order to relieve the pressure developed when the pump start up against a full delivery column.

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6. Siphon

It is although not a pump but is used for conveying water from a higher level A to a lower level B over an elevated piece of ground C as shown in Figure 11.7 below.

2

Fig 11.7

The difference of level H1 between A and C must not exceed 26 feet as a practical maximum A non return value is fitted at A and a regulating valve at B. Two other valves are provided at C. One to enable the siphon to be primed with water and the other to permit escape of air during the process. These two valves are kept closed in normal working.

The upper end A of the siphon must be kept continuously immersed in water to prevent access of air, whilst for the same reason it is preferable to keep the end B also immersed in water, although this is not essential.

2

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CHAPTER – 12

MINERAL DRESSING

Introduction

Most of the times many minerals and ores require some preparation before use. With this preparation we can increase their chemical or physical purity. This can be explained by taking the example of trapcock and coal traprock which cannot be used as ballast if is not of required size. Similarly coal is worthless unless it is sufficiently free of waste material.

12.1 Definition

It is a process, which is used to produce marketable mineral products from raw material without changing chemical and physical properties of the original mineral.

Hydrometallurgy, pyrometallurgy and oil refining may also deal with raw materials but they change the character of some or all of the constituents of the raw material.

12.2 Economic Justification of Mineral Dressing-Value Addition

Mineral processing removes bulk of un-wanted material attached to the mineral. It, therefore, helps in: -

i) Saving in Freight, because no payment is made for the discarded material. ii) Metal Losses. During melting metal loss is reduced as less and slag is produced, due to the absence of gangue (unwanted material). iii) Smelter’s cost. This is also reduced considerably. Because smelter treat only pure material without any waste. iv) The oldest dressing method was un-questionably hand sorting. By this meant the choosing of valuable lumps of ore from worth less lumps. This method was so crude that only the highest grade material could be smelted. The hand sorting method was employed both underground and at the surface where cheap labour is available. Now Machinery has replaced the place of hand sorting.

12.3 Various steps in Mineral Processing.

i) Crushing. ii) Grinding. iii) Screening and sizing. iv) Flotation. v) Washing.

12.3.1 Crushing

12.3.1.1 Definition.

Crushing may be defined as that operation or group of operations, which reduces the large lumps to fragments.

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12.3.1.2 Brief Description

Crushing is the first step in the mineral dressing. Material receive from mine is in the form of large lumps. These lumps cannot be used in further processing as such. It is, therefore, required to reduce the size of lumps to get: -

i) Particles of required size. ii) Increase surface area for chemical activity. iii) Liberation. iv) Crushing is done by pressing the material against the stationary part by a moving part. It is a dry operation and usually done in two or three stages. The size of the lumps may be upto 1.5 m and after crushing it may be reduced to a size of 10-20 cm. Or 1/20 of an inch.

Reduction Ratio

The ration between size of feed and in the product is called reduction ratio.

Crushers are heavy duty machines and classified into four main groups:

1. Coarse and Primary breaking Jaw and gyratory crushers are used for coarse crushing. 2. Intermediate or Secondary crushing Cone, disk and spring rolls are used for secondary crushing. 3. Fine crushing – Gravity, stamp mills are used for fine crushing. 4. Special uses – Tooth rolls and hammer mills are used for soft material. 5. Coarse crushing is always conducted on dry materials whereas rolls are used for wet crushing.

12.3.1.2 (a) Jaw Crushers

Jaw Crushers consist of two crushing faces or jaws one of which are stationary and are fixed in the crusher frame and the other moving alternately towards the stationary face and away from it is a small throw.

Jaw Crushers are intended for use as a primary crusher i.e. to receive the coarsest lump produced from the mine or quarry. Accordingly jaw crusher has a relatively much gap (width of receiving opening).

Fig 12.1

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All jaw crushers have an adjustable, discharge opening so that they can produce product i.e. coarse or fine. Figure 12.1 shows the sketch of a Blake type Jaw Crusher. The crushing frame is made of case steel. The jaws are made of cast steel lined with replaceable jaw plates of alloy steel, generally manganese steel. The sides of the crushing opening are made of manganese steel cheek plates. Motion is transmitted from the main crusher shaft by means of a pitman working on an eccentric on that shaft, and of toggles. One of the jaws is fixed and the other is movable. The movable jaw is kept pressed against the toggles by a tension rod and spring. The flywheels are used to equalize intermittent load which is applied on the jaw crusher. b) Gyratory Crushers

Gyratory Crushers consists of two substantially vertical, truncated, conical shells, the outer shell having its apex pointing down and the inner shell having its apex pointing up. The outer shell is stationary and the inner shell is made to gyrate or to rotate. There are several types of gyratory crushers, the best known as supported spindly gyratories, suspended spindle gyratories and the parallel pinch crushers.

Figure 12.2 shows the sketch of suspended spindle Gyratory Crusher. The crusher consists of: -

1. an outer frame made of cast steel 2. a wearing surface known as concaves 3. inner crushing 4. a spindle which is made to gyrate from a fixed fulerum 5. an eccentric sleeve fastened to a beveled gear 6. an other beveled gear which is driven from a horizontal drive shaft.

Fig 12.2

7.

Page 105 c) Comparison Between Jaw & Gyratory Crusher

1. Gyratory crushers are available for the coarsest crushing. The largest crushers to date whereas as the capacity of jaw crusher is less. 2. The Gyratory works continuously, whereas the jaw crusher works intermittently. 3. Reduction ration in the case of gyratory crusher is also better than jaw crusher. 4. d) Cone Crusher

Cone crushers are somewhat newcomers as compared to jaw and Gyratory crushers. These are economical machines for crushing rock pieces of intermediate sizes.

Figure 12.3 shows a sketch of Cone Crusher. It has much large capacity if compared with rolls or even with gyratory crushers. To achieve best results, cone crushers must be provided with a dry feed freed of fine particles. If this is not done, the crusher may clog.

Symons Cone Crusher, Sectional view (From Nordberg Mfg.Co.) Fig 12.3 e) Rolls

Crushing rolls consist of cylinders revolving towards each other so as to nip a falling ribbon of rock and discharge it. Rolls were invented some more than 100 years ago.

Fig 12.4

An early set of rolls after the Cornish style. These rolls were usually

8 to 30 in diameter and 14 to 20 in wide (After Miller)

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Figure 12.4 shows the sketch of early type of roll machine. The rolls were mounted on heavy shafts revolving in open bearings contained within cast iron frames. One of the rolls was driven positively and the other by friction. To assure rotation of the rolls which moves by friction, it is pressed sideways against the positive roll by a heavy weight hung from a yoke. Both rolls are positively driven at much higher speeds and breakage is prevented by mounting the bearings of one roll shaft against coil springs.

Both roll shafts revolving in fixed bearings were used at one time but are now become obsolete. Rolls shells are replaced when worn.

12.3.2 Grinding

12.3.2.1 Definition

There is little difference between Crushing and Grinding. Crushing is employed on coarse materials whilst grinding is the breaking down to the ultimate fineness by combination of Impact and abrasion.

12.3.2.2 Brief Description

The grinding is done by ball mills, rod mills or tube mills. These grinding mills are operated either wet or dry. We shall only describe a ball mills here to familiarize the students about the principle.

a) Ball Mills

Balls mills are characterized by the use of steel or Iron balls as the grinding medium. The crushed rock is feed at one end and ground rock is discharged at the other end or through the periphery. They are either continuous or intermittent.

Balls mills can be classified according to the shape of the mill, the method of discharging the ground ore and whether the grinding is conducted dry or wet.

Figure 12.5 shows a Hardinge ball mill.

Fig 12.5

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It consists of two conical sections connected by a short cylindrical section supported by end bearings on which hollow trunnuous revolve. Feed is taken in through a feeder located beyond one of the trunnuous and a continuous stream of thick plup pours from a discharge end located axially on the other trunnions. Hardinge mills are very widely used, in metallurgical field. They are usually adapted for wet grinding, but they are also used for dry grinding in conjunction with pneumatic classifiers.

Dry grinding harding mills are used for pulverizing coal, clay limestone and cement.

12.3.3 Screening and Sizing 12 12.3.3.1 Definition 13 Practically all mineral dressing operation are the functions of the size of the particles which is to be treated.

There are several methods of sizing mineral particles, the most important of which is screening.

Screening is the process of separation of a mixture of various sizes of grains into two or more portions. After screening we get grains of more uniform size than that of mixture.

12.3.3.2 Brief Description

Screening can be practiced from a dividing size of several centimeters to a dividing size as fine as 0.1 mm. Likewise classification of screening can be practiced from a dividing size as coarse as 2 or 3 mm to as fine as dividing size as 0.02 to 0.03 mm.

It is often said as a mineral dressing rule that for sizing coarser than 20 mesh, screens are preferable and for sizing finer than 35 mesh, classifiers are preferable.

It is a good general rule, but there are many exceptions. For example; the products that are dry like talcum powder, aluminum powder, cement, or foundry sand are screened dry down to 200-mesh.

Conversely it is also desired to introduce the effect of specific gravity in the sizing, or if the material is in suspension in water, classification is preferred.

In screening, consideration must be given to the type of screening surfaces and to the types of machines that are employed with these various screening surfaces.

Screening Surfaces Are Of Three Varieties 8. 9. i) Parallel rod ii) Punched plates and iii) Woven wire

i) Parallel rod screening surfaces are usually made of steel bars, steel rails, Cast Iron or wood. These are usually used for coarsest sizing. ii) Punched plates screening surfaces are made of sheet steel punched by dies in various patterns. The openings are circular, square or slot like. For coarse size, circular opening and of fine size, slotted opening are the rule. iii) Woven wire screening surfaces are woven by gauged wire, generally made of steel but sometimes of copper, bronze, monel metal or some other alloy. The weaving may be such as to produce square or rectangular openings. For coarse screening a square opening, woven wire is preferable whereas for intermediate and fine screening rectangular openings are advantageous. iv)

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Factors Affect the Rate at Which Undersize Material Pass through a Screening Surface

The most important are: -

1. The absolute size of the openings 2. The relative size of the particle to that of the opening it must penetrate 3. The percentage of openings to total surface in the screening surface. 4. The angle at which the particle strikes the screening surface. 5. The speed with which the particle strikes the screening surface. 6. The moisture content of the material that is being screened. 7. The opportunity for satisfaction in size layers afforded to the material which is being screened. 8. a) Types of Screens

Screens are classified into stationary screens and moving screens.

Stationary Screens

They are principally of the type known as grizzlies. They consist of parallel rods set an angle to the horizontal suitable for coarse crushing.

Grizzlies may be made by bars having a rectangular cross-section, or special sectional shape as rails, I-beams. The bars are held together by depressed cross rods.

The slope of grizzlies is generally such that material fed to it will just flow.

Moving Screens

They include moving grizzlies, trammels, vibrating screen and shaking screens.

Shaking screen is used in coal preparation.

13.3.3 Flotation 14 14.3.3.1 Definition 15 Flotation is the process of separation of mineral surface in such a way that particles may be caused to adhere (stick fast) either to the water in which they are Immersed or to air bubbles. The particles are collected in froth or remain in the pulp (soft mass) depending on whether they stick to the air or to the water. 16 16.3.3.1 Brief Description 17 Flotation is the most important mineral processing technique for complex ores such as lead zinc or copper zinc etc. Now its use has been extended to ores such as hematite and cassiterits.

Particle Size

For Flotation, the floatable particles must not exceed some maximum size ranging from 10 to 14 mesh in the case of coal. 48 to 65 mesh for sulphides and 100 to 150 mesh for free gold. There are two types of Flotation: -

i) Direct ii) Reverse iii) i) Direct Flotation

In this method valuable minerals are floated and gangue settles down.

ii) Reverse In this method valuable minerals are collected from the pulp and gangue minerals are floated.

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12.3.5. Washing 12 12.3.5.1 Definition 13 It is the process of cleaning minerals with water.

12.3.5.2 Brief Description

Even in very primitive civilizations man must have noticed that water exerts a cleaning action on fine mineral particles. The ore is passed through high pressure yet of water on mechanically vibrating screens. The screen apertures are usually of similar size to the particles in the feed to the grinding mills.

Washing is normally carried out before secondary crushing. Because the size of mineral become of suitable for washing it remove fine materials.

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CHAPTER-13

SAMPLING AND EVALUATION

13.1 Definition

A sample is a small piece or portion which represents the mean composition of the whole mass. The process of taking samples and evaluation the mine based on samples is called sampling.

13.1.1 Purpose

The purpose of sampling a mineral deposit is to determine the nature, quality and quantity of the valuable minerals present. The future profit to be derived from the sale of recoverable minerals is estimated on the basis of sampling.

13.1.2 Importance

The sampling of minerals in different parts of the bodies help to determine the profit Margin forms the sale of recoverable minerals. The distance from the source of supplies and from the market affects the cost of mining. Only rich deposits can be profitably worked. Costs are also affected by the available supply of labor, water, fuel or electric power and the severity of the climate.

Geologic map of the deposit reports on adjacent or nearby mines and records of production provides information that is helpful in estimating the probable life of the mine. The equipment of the mine should be carefully examined to see whether it is suitable.

13.2 INTRODUCTION TO VARIOUS SAMPLING METHODS

The various ways in which samples are secured may be classified as follows: -

1. Core drilling. 2. Churn drilling 3. Rock drills 4. Channel sampling (by hand) 5. Blasting down large samples 6. Test pits 7. By Augar and post hole diggers 8. Trenching 9. 13.2.1 Core Drilling.

This method is used for deposits where rock is firm enough to give a good core. The diamond drill is used for sampling deposits of Coal, Iron, Copper, Gold, lead and Zinc. Besides this the beds of Oil shale have also been satisfactorily sampled by the diamond drill. In Oil industry, diamond drills are being used to obtain knowledge of the geological structure of Oil field sand to drill for oil.

Non-metallic deposit such as salt, cement material salt, gypsum, clay, talc and lime stone can be sampled by the diamond drills.

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In very soft material and where the ground is badly broken little or no core is discovered and the drilling results may not be satisfactory.

Steps to be followed in sampling by diamond drills are: -

1. The core should be removed and the hole thoroughly cleaned out after each sample. 2. Both core and sludge from each sample should be carefully saved. 3. The core and sludge from each sample should be combined in the ratio of their original masses in the hole. 4. The pieces of core are laid out in proper order and carefully. 5. 13.2.2 Churn Drilling

It is used for soft ores and for placer deposits. The ore samples are usually taken in 5ft. length.

Placer deposits may be divided into two classes, those related to the present system of drainage in river and stream and ancient deposit lying as such due to change of river or stream direction.

The placer of the first type is prospected by drilling a line of holes at right angles to the main course of stream. The second type is generally of unknown out line and is prospected by holes placed at the corners of 50,100,200 and 300ft. or even 10 acres square. 13 13.2.3 By Rock Drill 14 Sometime silver-lead ore occurs as lenses in the bedding planes in limestones. Because of the irregular occurrence of the ore an irregular system of exploration will not find all the ore body. Consequently the proportion of non development work is high. Diamond drill was discarded because of the high loss in carbons. Rock drills are used to drill long holes of sampling purposes. Drills are used to reduce the number of cross cuts driven though barren areas. The sludge from each 3ft length of hole is collected in a powder box placed at the mouth of the hole. The sample is not considered as an accurate sample of the ore but is used to indicate whether the ground is mineralized or not.

13.2.4 By Channel Sampling. (By hand)

Channel sampling is a usual method of taking underground samples of an ore body. It is also applied to sampling exposures of ore on the surface. The method consists in cutting a shallow channel a few inches wide in the ore. The sample should be large enough to be representative of the deposit at a particular point.

The best tool for hand cutting a sample in hard rock is the moil and chisel. Pointed moil is used for sampling very soft material.

For a fresh and unaltered ore sample, the face should be free from dust, dirt or altered ore. The interval between samples may be upto 20ft. This interval varies with uniformity of the value of the ore. The greater the uniformity, the greater can be the interval for sampling.

13.2.5 Blasting Down Of Large Samples.

This method is normally used for spotty ore bodies in which the valuable minerals occur in irregular masses. For a representative sample, it is necessary to take a sufficient number of samples close enough together.

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Large samples are suggested to have double advantage i.e. checking of cutting a series of channel samples and subsequently blasting down about 1 ft. of the back and then repeating this procedure a small stope some 10 ft. high can be excavated. The comparison of the channel samples as assayed and the bulk sample are run through the mill, the difference between the average of the assays and the recovery in the mill plus loss in the tailing give the sampling error for channel sampling.

Bulk samples for a metallurgical test are taken by blasting down a large sample from each stope.

13.2.6 TEST PITS 13 Test pits may be used for sampling placers deposit where the ground is not too wet and does not tend to cave. Otherwise it is tested by drilling. A larger sample is secured from test pits and a vertical section of the deposit is exposed. Definite information is secured regarding the nature and condition of the bedrock. Samples may be taken from a test pit by cutting a channel 12 inches wide and 6 inches deep down one side of the pit or by cutting out a certain volume from the excavated material. Test pits are also used for sampling dumps, in which larger pieces usually accumulate at the bottom.

13.2.7 By Augers and Post Hole Diggers.

These are used for sampling soft and low grade materials such as iron-ore or tailing piles (heaps). Holes averaging 50 ft. in depth were sunk with a post hole digger in a pile of 200- mesh tailing by making a core barrel as 6.5 inches dia and 9.5 inches long. Two inches auger bit is used for sampling iron ore. 14 15 16 13.2.8 Trenching

Trenching may be cut through a shallow superficial deposit, a dump or a tailing pile. A certain portion of the material excavated every 5th of every 10th shovelful, car load or other unit is taken for the sample. If the material is rich and irregular in content then a larger sample is taken than if it is uniformly low grade. If the walls of the trench are smooth a channel sample may be cut from them.

1.3.3 Salting 17 It is a process of raising the value of a sample above that of the actual value determined intentionally or unintentionally. It must be constantly guarded against. The possibility of intentional salting should always be kept in mind, since the common cause of salting is the desire of vendors (seller) to affect a sale. Intentional salting can be done by various ways as described below: -

ƒ Before samples are cut, gold may be shot into the rock with a shot gun. ƒ A solution of chloride of gold may be injected into samples in rocks. ƒ Rich material may be added to samples during crushing and grinding. ƒ A small piece of clay containing a few color of gold may be dropped into a drill hole. ƒ Local miners cutting samples can readily salt them by adding valuable mineral, by breaking into sample an undue proportion of the richer streaks or by picking out pieces of waste during work.

ƒ

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13.3.1 Guard against salting (Prevention). 14 It can be done as follows: -

ƒ ƒ The places where samples are to be cut, should not be marked a long time in advance of sampling. ƒ Some samples of rock known to be barren should be included with the regular samples. Good results for the barren rock indicate either salting or false results. ƒ An excellent protection is to resample 10-30 channel samples from different types of parts of the mine. Original samples are not numbered in regular order and resample are given different numbers in regular order and resample are given different numbers. The resample are not of the same weight as the original samples and it would be very difficult to salt the two samples by exactly the same amount.

13.4 Theory of Sampling (Conditioning Ore)

The correct sampling of ore is the process of obtaining from it a smaller quantity which contains unchanged percentages of all the constituents. The constituents of the ore to be sampled are not always uniformly distributed. Since it is an imperfect mixer of fine and coarse particles, by sampling a same proportion of all its different sized particles from a lot of ore are taken. This can be effectively done by reducing the size of the particles.

Therefore most important features of sampling is crushing. Hand hammer crushing is usually done but power crusher may be employed where feasible. To get a representative and small sample, different ore sampling methods, manual or mechanical are employed. 14 13.4.1 Coning and Quartering. 14 In this method, a cone of the crushed material is shoveled at one point on the quartering floor. The particles are allowed to roll down in all directions from the central point to have a uniform composition of the mass. The top of the cone is flattered with the edge of the shovel. The material is spread equally in all directions until a disk is formed. The thickness of the disk is about 0.1 time the diameter of the core. This disk is them marked into quadrants. The diagonally opposite quadrants are cut out and the material in the rejected quadrants is removed. The mass now contains half the original quantity. After reducing the large pieces proportionally, coning and quartering are repeated. Thus one quarter of the original is obtained. The process of crushing, coning and quartering are repeated until we get a sample of desired size. However the procedure followed during this operation should always be the same. This method is applicable to all kinds and grades of ores, needs no expensive plant and keeps the sample constantly in sight.

13.5 Evaluation of Mines. 14 Mines are valued for the following reasons:-

i) For the purpose of sale. ii) For the dissolution of partnership or corporations. iii) For the purpose of merging different mining companies. iv) For the taxation purposes. v) For loan purposes. vi) For litigation purposes. vii)

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Normally the object of valuing the mines is to determine its salable value at which the property may be transferred from a willing seller to a willing buyer.

13.5.1 Various Methods of Valuation. 14 Mines may be valued in several different ways. One method is on the basis of the market value of the mine stock. Producing mines are generally valued on the basis of operating profit which is obtained from mining the ores and marketing the recoverable metallic content. 15 13.5.2 Information Necessary for valuing a Mine. 14 In order to determine the present value of a mine the following factors need to be evaluated: -

1. Recoverable Contents of the ore. 2. Future price of mineral products. 3. Cost of production.

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CHAPTER-14

ORGANIZATION, MANAGEMENT, SAFETY & WELFARE

14.1 Organization

Organization refers to breaking up various specialized departments and appointment of competent persons. In a mine it starts as and when a licence/lease is allotted to an individual, a Company or a Corporation. The information required by an agency who allots the licence/lease is as under: - viii) i) Name of individual, Company or corporation; ii) Location of the lease according to Survey Sheets, Tehsil, District, Division and Province; iii) Name of minerals which shall be exploited; iv) Amount of capital; v) Name and complete addresses of Directors/Partner; vi) Name and address of site office; vii) Name and address of Principal office of business; viii) Period of existence which is usually unlimited or perpetual.

14.1.1 Types of Organization 15 There are usually two types of organizations;-

1) For small mines, especially if in the prospect stage, line organization may be satisfactory. The Managing Director is the Chief Executive of the Organization. Agent and the Manager are directly answerable to the Managing Director of the firms. The Mine Manager is assisted by a team of Shift Incharges and Miners and other skilled & un-skilled work men. Thus responsibility follows a direct line and the men in the higher positions must necessarily have a wide technical and business knowledge. 2) In a large company business becomes complex. The supervision and control is split into various specialist departments. These departments have a vertical control over their subordinates. Likewise they perform consulting role or horizontal co-ordination with other departments. Chief Executive has a team of experts at Hqr. which provides him advisory assistance in technical, social and managements areas. 3) In the recent years the plan of appointing committees to deal with various questions has emerged. A technical committee of engineering specialist may be appointed to deal with important engineering questions at large mines and at a small mine a committee of shift incharges and miners is formed to improve the working conditions underground this promote a better feeling between the company and its employees.

14.2 Management Duties and Responsibilities 15 The management consists of Owner, Agent and Manager. The Manager generally has absolute control of the business of the Company/Corporation and is in control of the company in which lease is situated. The Manager should not do too much administrative

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work himself. It is preferable to delegate his detailed work to subordinates and to give them freedom of operation, judging them by results.

The duties and responsibilities of Managers are the efficient handling of labour and the infusion of morale into the working force, the following of proper legal and social procedure in the transaction of business, the applying of new discoveries in physical science that would improve the technical work of the organization, the efficient marketing of products, the maintaining of adequate finances and coordinating of all departments of the organizations.

14.3 Safety and Welfare Aspects 15 Importance of safety and welfare aspects in the mines can be summarized as follows: - 16 14.3.1 Care of Employees

The safety and welfare of employees are integral part of mine administration. Under this category are included:

a) Physical examination of all staff/miners who are employed in and around the mines; b) Provision of safety informations through bulletins; c) Display of safety posters; d) Provision of proper residential, water and sanitation facilities; e) Timely payment of compensation, insurance and all other dues which are enforced by the state. f) Committee meetings and personal instructions;

Large mines may maintain an emergency hospital. The training in First Aid and Mine Rescue and Safety Work should be available for all mine workers. An applicant for work is interviewed and must pass a physical examination. A record is made of his previous employment. Before going to work in the mine, he should be instructed in safety matters by a Safety Instructor.

14.3.2 Analysis of Causes of Accidents 15 Often in industrial accidents the cause of the accident is not investigate in a logical and orderly manner and a remedy applied. There should be a classification of terms the first step in this direction is to note the difference between cause and effect. Basic accident causes may be divided into two general classes with a number of sub-divisions as follows;

Supervisory

Faulty instruction ix) a) None b) Not enforced c) Incomplete d) Erroneous; x) Inability of Employee iii) a) Inexperience b) Unskilled c) Ignorant d) Poor Judgment iv)

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Poor Discipline

iv) a) Disobedience of Rules b) Interference by others c) Folling v) Lack of Concentration 10. a) Attention Distracted b) Inattention 11. Unsafe Practice

a) Chance taking b) Short cuts c) Haste d) Mentally Unfit

a) Sluggish or fatigued b) Violent temper c) Excitability d) Physical Unfit

a) Defective b) Fatigued c) Weak

Physical

Physical hazards (include mechanical, electrical, steam, chemical conditions etc.)

a) Ineffectively guarded b) Un-guarded c) Poor House keeping

a) Improperly piled or stored material b) Congestion c) Defective Equipment

a) Miscellaneous materials and Equipment b) Tools c) Machines;

Unsafe Building Conditions

a) Fire Protection. b) Exits c) Floors d) Openings e) Miscellaneous. f) Improper Working Conditions

a) Ventilation b) Sanitation c) Light

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Improper Planning

a) Layout of Operation b) Layout of Machinery c) Unsafe Processes d) Improper Dress or Apparel

a) No goggles, gloves, masks etc. b) Unsuitable long sleeves c) High heels defective etc.

Both Supervisory and Physical causes may also be controlled by the employer. It is apparent that in the last analysis the employee may avoid accidents, even though he is exposed to unsafe conditions.

Accidents due to mechanical or physical exposures should be assigned to causes in the supervisory group, where the foreman has the authority to install or maintain guards. In such cases the chief cause is generally laxity in supervision. By following this line of reasoning the accidents can be reduced.

The value of analysis by the causes listed above, as compared to the existing method of allocation as slips and falls eye injuries and others is apparent. It directly needs attention of supervisory staff.

Carelessness, poor supervision and improper selection of employees have deliberately been omitted because of ambiguity.

14.4 Factors of Accident in Underground Mining 15 The factors causing accidents in underground work may be as caving of the roof, fall of side, emission of noxious gases such as fire damp, black damp, white damp, stink damp etc. fires, breakage of ropes, derailment of tubs and improper alignment of rail line.

14.5 Factors of Accidents in Open-Cut Mining

The accidents are caused due to transportation and operation of machines, electric shocks, blasting may also be a cause of accident in Open-Cut Mining. Appropriate safety measures should therefore be taken in Open-Cut Mining.

14.6 Prevention of Accidents

To prevent injuries by falling rock pieces, the height of banks and the angle of slopes should be kept within normal limits. The slopes of banks, their edges and terms must be systematically and carefully checked for crevices, jointing and detached slabs which may prove to be a source of danger to men working in the pit. Such slabs as well as the snow masses and ice lumps over handling in winter, must be removed as soon as they are sighted.

When work on the banks is completed, the width of the bench should equal 1/10 of the bench height and not less than one meter.

To prevent people from falling in the pits and quarries near settlements and roads should be fenced off.

Drilling and blasting operations should be carried out in accordance with the existing rules and regulations. Special attention should be paid in handling explosives, particularly in winter.

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Accident statistics reveal that transport operations are the main source of industrial injuries. Hence the need of strictly observing the safety regulations concerning trains in pits and waste dumps.

It has been proved statistically that conveyors in open pits are as a rule extremely heavy and bulky and for this reason, one must strictly observe safety rule in setting up and repairing them.

Since electric power is widely used in open-pit work, particular attention should be paid to safety measures against injuries caused by electric current.

The lightening of open pits at night is not only necessary for efficient operations but also for safety. Working places and machines should be provided with ordinary powerful electric lamps or special stationary or portable floodlights. Portable lighting mains should be used at the sites of blasting operations.

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