Lec12 - Explosives and Blasting - I - F2023.pdf

Mining Optimization Laboratory Introduction to Mineral Resources ENGR 2106 - Fall 2023 Lec12 - Explosives and Blasting Dr. Ahlam Maremi Bharti School of Engineering Laurentian University F215B Email: [email protected] 1 Blasting • In most mining operations the rock is too hard to dig without...

Mining Optimization Laboratory Introduction to Mineral Resources ENGR 2106 - Fall 2023 Lec12 - Explosives and Blasting Dr. Ahlam Maremi Bharti School of Engineering Laurentian University F215B Email: [email protected] 1 Blasting • In most mining operations the rock is too hard to dig without blasting; • Excavation performance is dependent on blasting. 2 Ahlam Maremi 2 Mining Optimization Laboratory 3 Rock Fragmentation • Rock fragmentation: – The breakage function carried out on a large scale to fragment masses of rocks. • Blasting is the predominant fragmentation method used in both mining and construction. • Only chemical energy (blasting) has widespread use for all consolidated materials, both surface and underground. 3 Classification of Rock Fragmentation Methods 4 4 Ahlam Maremi Form of energy application Method Agent or Machine Chemical Blasting High explosive, blasting agent, liquid oxygen (LOX), black powder Mechanical Pneumatic Ripping Impact Compressed air or carbon dioxide cylinder Ripper blade, Dozer blade, Hydraulic impact hammer, drop ball Fluid Mining (soil) Mining (rock) Hydraulicking (monitor) Hydraulic jet Electrical Electric arc or current Electrofrac machines Mining Optimization Laboratory Rock Fracturing 5 • Radial cracks and crushes of the rock near the charge, • Extension of cracks and existing discontinuities, • Pushing apart the in-situ fragments, • Spalling at free faces. Video: (https://www.youtube.com/watch?v=WhOjLW0S_-c) 5 Rock Fragmentation • Follows the detonation of the explosives in a drillhole; – The explosion is a very rapid combustion, in which energy contained in the explosives is released in the form of heat and gas pressure. 6 Ahlam Maremi 6 Mining Optimization Laboratory Rock Breaking Sequence in a Normal Blast 7 • Compression: – A pressure wave propagates through the rock at a velocity of 2,500 – 6,000 m/sec, depending on rock type and type of explosives. – This pressure wave creates micro fractures which promote rock fracturing. 7 Rock Breaking Sequence in a Normal Blast • Reflection: – During this stage, the pressure wave bounces back from the free surface, which is normally the bench wall or natural fissures in the rock. – The compression wave is now transformed into tension and shear waves, increasing the fracturing process. 8 Ahlam Maremi 8 Mining Optimization Laboratory Rock Breaking Sequence in a Normal Blast 9 • Gas Pressure: – Large volumes of gas are released, entering and expanding the cracks under high pressure. – Where the distance between the blast hole and the free face has been correctly calculated, the rock mass will yield and be thrown forward. 9 Factors Influence Rock Breakage Three main factors: • Drilling: – Drill depth, pattern and set-up, – Hole diameter, inclination and deviation. • Explosives: – Explosive energy, density, diameter, – Detonator selection, – Explosives containment, distribution and location within the borehole. • Geology: – Rock types, – Rock properties, – Rock structures. 10 Ahlam Maremi 10 Mining Optimization Laboratory Rock Fragmentation and Rock Fracture 11 • Two major differences between rock fracture and rock fragmentation: – Rock fragmentation deals with many cracks, but rock fracture deals with only one or a few; – Rock fragmentation concerns the size distribution of the fragments produced, but rock fracture does not. • There are two important factors in rock fragmentation: – Total energy consumed, – Size distribution of fragments. 11 Explosives Terminology • Explosion: – A rapid expansion of matter into a volume greater than the original volume. • Explosive: – An agent, compound, or mixture that undergoes very rapid decomposition when initiated by heat, impact, friction or shock. • Decomposition: – A high-velocity, exothermal reaction, accompanied by the liberation of vast amounts of energy and very hot gasses at tremendously high pressure. 12 Ahlam Maremi 12 Mining Optimization Laboratory Explosives Terminology 13 • Detonation: – Occurs when the rate of reaction in the explosive product exceeds the speed of sound (sonic velocity) in the product, thus creating a shockwave. – Detonation velocities for commercial explosives range from 1,500 to 7,830 m/s, which is much higher than the sonic velocities • Deflagration: – A process where the reaction occurs at rates much lower than the sonic velocity of the explosive material, so that no shock (primary pressure wave) is produced within the explosive material. • High Explosives vs. Low Explosives – High explosives detonate (e.g. dynamite) – Low explosives deflagrate (e.g. black powder, safety fuses, igniter cords, fuse lighters and “display fireworks”) 13 Explosives 14 • Explosives break rocks because of: – The impact of the shock wave; and – The expanding effect of the high-pressure gas formed during detonation • The resulting fragmentation depends on the explosive and the geology (rock type and rock properties) 14 Ahlam Maremi Mining Optimization Laboratory 15 Geological Effects on Blasting • Geology is one of the primary considerations in every blast design: – Site specific and cannot be controlled, – Factor with the greatest single influence over blasting results. • Geologic characteristics: – Rock types and rock properties – Characteristics of rock structures. 15 16 Rock Types and Rock Properties • Rocks – There are three primary rock classification: igneous rock, metamorphic rock, and sedimentary rock. – These three rocks are formed by magmatism, metamorphism, and sedimentation, respectively. – The knowledge of the rock classifications helps to predict blast results. Igneous rocks 16 Ahlam Maremi Metamorphic rocks Sedimentary rocks Mining Optimization Laboratory Rock Types and Rock Properties 17 • Rock properties: – Measurements for describing specific characteristics of rock specimens (UCS, tensile strength, Poisson’s ratio, Elastic modulus, specific gravity, etc.), – Offer a method for comparing rock types, – Variation in properties within the same geologic unit. • Knowledge of the rock structures helps improve blast performance relative to field conditions; • Rock structures: – – – – Bedding Joints Faults Contacts Loading blast holes according to hard and weak zones 17 Rock Types and Rock Properties • Knowledge of the rock structures helps improve blast performance relative to field conditions; Loading blast holes according to hard and weak zones 18 Ahlam Maremi 18 Mining Optimization Laboratory Explosives 19 • Categories of Explosives: – Primary Explosives, – Secondary Explosives, – Tertiary Explosives: • Ammonium Nitrate, • Water Gels or Slurries, • Dynamite. 19 Properties of Explosives • The key explosive properties are: – Density: • It is expressed in terms of specific gravity. • For difficult blasting conditions or where fine fragmentation is required, a dense explosive is usually necessary. • In easily fragmented rock or where fine fragmentation is not needed, a low-density explosive will often suffice. • The density of an explosive is important when working under wet conditions. – An explosive with a specific gravity of less than 1.0 will not sink in water. – Detonation velocity: • It is a major index of the explosive performance. • It is the velocity at which the chemical reaction traverses the explosive, assuming there is no energy loss at the boundary of the material. 20 Ahlam Maremi 20 Mining Optimization Laboratory Properties of Explosives 21 • The key explosive properties are: – Detonation pressure: • Detonation pressure is a function of the detonation velocity and density of an explosive. • A high detonation pressure is necessary when blasting hard, dense rock. • In softer rock, a lower pressure is sufficient. – Water resistance: • It is a measure of its ability to withstand exposure to water without deteriorating or losing sensitivity. – Strength: • It is the ability of the explosive to move the surrounding material. • It is related to the total gas yield of the reaction, and the amount of heat produced. 21 Properties of Explosives • The key explosive properties are: – Fume class: • Detonation of a commercial explosive produces water vapor, carbon dioxide and nitrogen. • In addition, undesirable poisonous gases such as carbon monoxide and nitrogen oxides are usually formed. • These gases are known as fumes. • The fume class indicates the nature and quantity of the undesirable gases formed during detonation. – Sensitivity: • Sensitivity is the ease with which an explosive detonates. 22 Ahlam Maremi 22 Mining Optimization Laboratory Characteristics of Explosives 23 • The physical characteristics of the explosives: – ANFO type explosives: • Loose, free-flowing, granular compositions. – Emulsion explosives: • Have consistency that varies from that of syrup to firm putty. • There are also various blends of emulsion and ANFO type explosives, notably so-called heavy ANFOs • The physical properties of the explosive can dictate the handling system used to charge the explosive into blast holes 23 Cartridge Explosives Packaging • Cartridge Explosives – Must be smaller in diameter than the hole. – Therefore, until tamped, they will not fill the hole. • In 2008, dynamite represented only 0.5% of all the explosives used in the USA, there was only one remaining dynamite manufacturing plant in North America. 24 Ahlam Maremi 24 Mining Optimization Laboratory Bulk Explosives Packaging 25 Bulk Explosives – They come in bulk containers and are less labor-intensive during loading. – They also fill the entire hole diameter, making them more efficient to use. – The majority of explosives that are used in mining today are bulk explosives, which are blasting agents such as ANFO, emulsions and blends of ANFO and emulsions. 25 Blasting Goals • The primary objectives in rock blasting are to optimize blast performance and ensure the safety of everyone by implementing safe practices in and around the blast site. 26 Ahlam Maremi 26 Mining Optimization Laboratory Blast Design 27 • Primary goal: – Safe, efficient and productive blasting; – Effective in rock fragmentation and lowest overall operation cost associated with the blast. • Good blast performance requires controlled release of explosive energy; • Energy release controlled by: – Design layout, – Hole loading procedures, – Detonation sequence. 27 Highwall Stability • A safe and stable highwall is critical to all aspects of a blasting operation. – Equipment, blasting crews and shovel operators. • Maintaining a stable highwall requires a good understanding of: – – – – 28 Ahlam Maremi Geology, Water conditions, Slope, and Blast design. 28 Mining Optimization Laboratory Definition of Bench Blasting Terms 29 • Burden: – It is the distance from a single row to the free face of the excavation, or between rows. – The proper burden dimension to use a function of hole diameter, relative rock density, and the explosive that will be used in the blast. • Too small a burden can result in excessive air-blast and flyrock; • Too large a burden can result in improper fragmentation, toe problems, and excessive ground vibrations. • The burden, in turn, is the basis for calculating spacing, stemming, and sub-drilling. 29 Definition of Bench Blasting Terms • Spacing: – Spacing is the distance between adjacent blastholes in a row, measured perpendicular to the burden. • In row-to-row shooting, spacing is measured between holes in a row; • When the shot progresses at an angle to the free face, the spacing is measured at that angle. – Spacing is a function of the burden, sometimes dependent on the timing. • Close spacings cause crushing and cratering between holes, boulders, and toe problems. • Wide spacing will result in inadequate fragmentation. 30 Ahlam Maremi 30 Mining Optimization Laboratory Definition of Bench Blasting Terms 31 • Stemming: – Stemming contains explosive energy within a blasthole, so that it will break and move the rock without generating flyrock. • We can use sized crushed stone or drill cuttings as stemming materials. 31 Definition of Bench Blasting Terms • Sub-drilling: – It is the distance drilled below the floor level (or the actual required blast depth) to ensure that the full face of the rock is capable of being removed to the desired excavation limit. – Subdrilling may be required to achieve a smooth pit floor. – The subdrill portion of a borehole is generally backfilled with drill cuttings or other stemming material. – Usually, we do not load explosives into the subdrill! – 32 Ahlam Maremi https://www.linkedin.com/posts/hooman-askari-019aa130_greatshots-activity-6991440585031118849R97G?utm_source=share&utm_medium=member_desktop 32 Mining Optimization Laboratory Learning Outcomes 33 By the end of this lecture you know: – The importance steps of the rock fragmentation process by blasting: • Compression waves pressure, reflection of the pressure wave and gas pressure – The three main factors that influence rock breakage • Drilling, explosives and geology – Some explosives blasting agents available • Must select adequate product according to field conditions – The main properties of explosives that will influence the explosives selection (depending on specific applications) – And understand that the key ingredient for selection is the ability to safely obtain the lowest unit cost of material produced • Effective blasting – Bench Blasting Terms 33 Don’t Forget! • • • • • 34 Ahlam Maremi Check your LU email and D2L regularly. Review additional resources available on D2L Guest Lecture on Oct 31st – Rescheduled on Nov 7th Quiz 2 on Nov 7th Final Exam Dec 7th B-GYM – Lec10 to the end 34