Lec13 - Explosives and Blasting - II - F2023 (PDF)

Mining Optimization Laboratory Introduction to Mineral Resources ENGR 2106 - Fall 2023 Lec13 - Explosives and Blasting Dr. Ahlam Maremi Bharti School of Engineering Laurentian University F215B Email: [email protected] 1 Blast Patterns • A square blast pattern: – It has drilled spacings that...

Mining Optimization Laboratory Introduction to Mineral Resources ENGR 2106 - Fall 2023 Lec13 - Explosives and Blasting Dr. Ahlam Maremi Bharti School of Engineering Laurentian University F215B Email: [email protected] 1 Blast Patterns • A square blast pattern: – It has drilled spacings that are equal to drilled burdens. • A rectangular blast pattern: – It has drilled spacings that are larger than drilled burdens. • A staggered blast pattern: – The drilled spacings of each row are offset, such that the holes in one row are positioned in the middle of the spacings of the holes in the preceding row. – The drilled spacings are larger than the drilled burdens. – It is used for row firing, where the holes in one row are fired before the holes in the row immediately behind them. 2 Ahlam Maremi 2 Mining Optimization Laboratory Millisecond Delay Blasting 3 • The timing between holes in a row and between rows in a shot dictates the movement and fragmentation of the shot; • Rock fragmentation occurs within 5 to 15 ms after detonation. • The gas pressure created by a blast moves the rock out from the blast face at (50 to 100 ft/s). • The movement of rock is important with respect to designing a blast that obtains optimal fragmentation. – As the number of rows increases, the low velocity of the moving rock causes a reduction in relief toward the free face, leading to more vertical rock movement. 3 Typical Detonation Sequences • Row-by-Row: – The rows shooting parallel to the highwall or free face; • A “V”-pattern, or chevron: – It is appropriate for most square or rectangular blast patterns; – The true burden and spacing (B1 & S1 depend on the timing of the shot) will be different from drilled burden and spacing (B2 & S2). 4 Ahlam Maremi 4 Mining Optimization Laboratory Typical Detonation Sequences 5 Charging Blast-holes 6 5 • When an adequate number of holes have been drilled, preparations for blasting will start; – The holes are blown clean with compressed air to remove water and rock fragments, – Then charged with booster bottom charges, detonators and explosives; – Stemming is inserted into the top of each hole, and the detonator leads are connected; – Where electric detonators are used, the circuit resistance is checked with an ohmmeter. 6 Ahlam Maremi Mining Optimization Laboratory Detonators and Initiation Systems 7 • A detonator (a blasting cap): – It is used to trigger an explosive device. – It is a small sensitive primary explosive device used to detonate a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite, or plastic explosive. • An initiation system: – It provides the initial energy required to detonate an explosive used for rock blasting. – Video: (https://www.youtube.com/watch?v=P8VTWqTI154) (5 min) 7 Detonators and Initiation Systems • Three basic types of initiation systems are available for use in commercial blasting: – Electric, – Nonelectric, – Electronic. • An Initiation System consists of three components: – Initial energy source, – Distribution network to convey energy to blastholes, – In-hole detonator that initiates explosives. 8 Ahlam Maremi 8 Mining Optimization Laboratory Selection of Explosives 9 • Both properties of explosives and field conditions (rock strength, structures) affect selection of explosives • The objectives are to select a combination of explosives that balance: – Economic considerations; – Reliable performance; – Safety. 9 Selection of Explosives • Cost comparison should be consisting of drilling, blasting and fragmentation based on the following criteria: – – – – Explosive cost, Charge diameter that is limited by hole diameter Rock blastability, Water conditions, • Wet ground requires use of water resistance explosives. – Fume release, • If fumes are substantial adequate ventilation must be provided. • Other conditions, storage requirements, sensitiveness, explosive atmosphere (e.g., coal mines) 10 Ahlam Maremi 10 Mining Optimization Laboratory Powder Factor 11 • Powder factor is one of the important parameters of bench blasting; • It represents the relationship between how much rock is broken and how much explosive is used to break it. • It can be used for variety of purposes: – As an indicator of how hard the rock is, – The cost of the explosives needed, – As a guide to planning a shot. • Powder factor value varies between 0.1 and 0.7 kg/m 3 for normal bench blasting; 11 Powder Factor • The value is affected by the following factors: – The blastability of rock blasted; – The fragmentation to be required to the blasted rock (higher PF); – The swelling and throwing distance required; • Higher PF, higher displacement and swelling of blasted rock. – The performance of explosive to be used; • Strength and density. – The distribution of explosive in the blastholes and rock mass; • A poor charge distribution in the blastholes, a higher PF. 12 Ahlam Maremi 12 Mining Optimization Laboratory Powder Factor 13 13 Powder Factor • Powder factor (q): q= We Vr or q= We Wr Where : q : specific charge, kg / m3 or kg / ton We : weight of explosive charged, kg Vr : volume of rock to be blasted, m3 Wr : weight of rock to be blasted, ton The volume of rock to be blasted (Vr ) is approximately equal to: Vr =BSH q= We BSH Where: H : is the height of fragmented column such as bench, no inclination. 14 Ahlam Maremi 14 Mining Optimization Laboratory Powder Factor 15 • To calculate the powder factor (kg/m3) – Determine the loading density (kg of explosives per meter of blasthole) – Determine charge length (m) • Careful should be taken in terms of the subdrilling (charged or not charged) – Determine charge weight per hole (kg/hole) – Determine the volume of rock which each hole in the blasthole pattern is responsible (m 3/hole) – Calculate the powder factor (kg/m 3) and what type of rocks you are working on? 15 Charge Length 16 Ahlam Maremi 16 Mining Optimization Laboratory Powder Factor – Example 1 17 • For open pit mine, bench blasting, the following are given: – – – – – – – – – Charge diameter 152.4 mm Explosive density 0.85 gm/cm3 Bench height 14 m Subdrill length 1 m (not charged) Borehole inclination angle 0° Stemming length 3.7 m Burden 4.5 m Spacing 5.2 m No inert deck • Calculate: 1. 2. 3. 4. Loading density, Charge length and charge weight per hole (kg/hole) Rock volume per blast hole Powder factor 17 Powder Factor – Example 1. Loading density, Le e = 0.85 g / cm3 d = 152.4 mm Le (kg / m) =   e  d 2 4, 000 =   0.85 152.42 4, 000 = 15.5 kg / m 2. Charge length and charge weight per hole (kg/hole) Inclination angle,  = 0 H+J →L=H+J cos  inert deck length, i = 0.0 Blasthole length, L = J = 1 m (but subdrill is not charged, excluded) Charge length (m) = H - L2 or L - ( J + L2 + i), Charge length (m) = 14.0 - 3.7 = 10.3 m Charge weight per hole (kg/hole) = Loading density  Charge length Charge weight per hole (kg/hole) = 15.5 kg / m  10.3 m = 159.65 kg 18 Ahlam Maremi 18 Mining Optimization Laboratory Powder Factor – Example 19 3. Rock volume per a blast hole Vr = B  S  H cos  Vr = 4.5  5.2 14 = 327.6 m3 4. Powder factor Powder factor, q ( kg / m3 ) = Charge weight per a blasthole 159.65 kg = = 0.49 kg / m3 Volume per a blasthole 327.6 m3 19 20 Powder Factor • We can combine the previous steps into one big expression: Powder factor (kg/m3 ) =   e  d 2  Charged length 4, 000  B  S  Where : ρ e : Explosive density, gm / cm3 d: Charge diameter, mm H: Bench height, m L 2 : Stemming length, m B: Burden, m S: Spacing, m J: Subdrill length, m β: Borehole inclination angle, m i: Deck length, m 20 Ahlam Maremi H cos  Mining Optimization Laboratory 21 21 Loading density, Le • Interpolation – Explosive density 0.85 gm/cm3 – Charge diameter 152.4 mm Charge diameter 152 mm → Loading density = 15.42 kg / m Charge diameter 159 mm → Loading density = 16.88 kg / m Charge diameter 152.4 mm → Loading density = ??? kg / m 159 − 152 159 − 152.4 = → Loading density = 15.5 kg / m 16.88 − 15.42 16.88 − ??? 22 Ahlam Maremi 22 Mining Optimization Laboratory 23 Drilling Diameter, D Small diameter (65 – 165 mm) Large diameter (180 – 450 mm) 23 Burden, Spacing, Stemming & Subdrilling Small diameter blasthole (89 mm) Large diameter blasthole 24 Ahlam Maremi 24 Mining Optimization Laboratory Stemming & Subdrilling 25 Large diameter blasthole 25 Length of Bottom Charge Small diameter blasthole Large diameter blasthole 26 Ahlam Maremi 26 Mining Optimization Laboratory Learning Outcomes 27 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 27 Don’t Forget! • • • • • • • 28 Ahlam Maremi Check your LU email and D2L regularly. Review additional resources available on D2L Guest Lecture 2 - on Nov 7th – Underground Mining Guest Lecture 3 - on Nov 9th – Biomining Quiz 2 on Nov 14th - Class time - the last 15 minutes Field Trip – Glencore Smelter – on Nov 23rd Final Exam Dec 7th B-GYM – Lec10 to the End 28