Blasting Design. Explosion A chemical reaction involving an extremely rapid expansion of gasses usually associated with the liberation of heat.

Transcription

1 lasting Design lasting 1. Good lasting and Good Drilling go hand in hand.. Drilling is the Foundation of the last Design. Explosion A chemical reaction involving an extremely rapid expansion of gasses usually associated with the liberation of heat. Detonation An explosive reaction that moves at a velocity greater than the speed of sound. Explosive - a substance that contains a great amount of stored chemical energy that can produce an explosion. Explosives 1) Dynamite Contains Nitroglycerin and ensitizer a. Granular b. Gelatin c. emi Gelatin ) Ammonium Nitrate ased a. Ammonium Nitrate & Fuel Oil No water resistance b. lurry (water gel) water resistant Good water resistance c. Emulsion table Oil/Water Emulsion Excellent water resistance

2 he U.. consumed.76 million tons of explosives in % 10% 8% % Coal Mining Construction Quarrying, Non Metal Metal Mining Other 69% Explosive Properties 1) Density ) ength ) pecific Gas Volume ) Detonation Velocity 5) Detonation Pressure 6) lasthole Pressure Explosive Density (d) he weight per volume of an explosive expressed as (kg/m or g/cm or lb/ft ). d anfo kg 800 m g 0.8 cm

3 Weight ength/energy he energy content of an explosive expressed as an amount of energy per weight (kcal/kg or MJ/kg). wanfo 91 kcal kg pecific gas volume he volume of gas produced per unit weight of explosive (liters/kg). Detonation Velocity 1) Detonation Velocity he speed at which the reaction front moves through a cylindrical charge. ) ypical values ranges from 1500 m/s (5500 f/s) to 7500 m/s (5,000 f/s). ) Faster velocities provide a shattering effect to strong s while slower velocities provide a heaving effect. Detonation Pressure 1) Detonation Pressure he pressure of the detonation wave propagating through the explosive column. ) ypical values ranges from 500 MPa (5 kilobars) to 15,000 MPa (150 kilobars). ) Higher detonation pressures provide a better shattering effect for stronger s. lasthole Pressure 1) lasthole Pressure he pressure exerted on the walls of the blasthole perpendicular to the detonation pressure. ) ypical values ranges from 1000 MPa (10 kilobars) to 6000 MPa (60 kilobars). ) Higher blasthole pressures provide a stronger breaking force for stronger s. ulk ength he energy content of an explosive expressed as an amount of energy per volume. ulk strength is the weight strength times the density (kcal/cm ). w Relative ength he blasting energy of an explosive relative to the blasting energy of. Relative Weight ength he weight strength of an explosive relative to the weight strength of. Rel - W-A W-A W-

4 Relative ulk ength he bulk strength of an explosive relative to the bulk strength of. Rel - -A -A - W-A W- A

5 able. Explosive Properties Explosive Property Units Dynamite Gelatin Dynamite emi Gelatin AN(9%) + FO(6%) Emulsion (1000) Emulsion (1070) Density g/cc Energy/ength (Weight) cal/g 1, (ulk) cal/cc 1,510 1, Relative Weight ength Relative ulk ength Detonation Velocity m/s 5,00,00,900 5,800 5,500 ft/s 17,00 1,100 1,800 19,000 18,000 Detonation Pressure Kbars Gas Volume (moles/kg) 7 Water Resistance Excellent Good None Excellent Excellent ulk ength (Problem) One particular mix of has a Weight ength ( W ) of 91 kcal/kg and a Density (d) of 800 kg/m. Explosive A has a Weight ength ( W )of 850 kcal/kg and a Density (d) of 100 kg/m. What is the ulk ength ( ) of the in kcal/cm? - W- kcal kg m 91 *800 * 6 kg m 1x10 cm kcal cm Relative Weight ength (Problem) What is the Relative Weight ength (Rel- W-A ) of explosive A? Rel - Relative ulk ength (Problem) What is the Relative ulk ength (Rel- -A ) of explosive A? Rel - -A W-A -A kcal/kg 91 kcal/kg *100 91* W-A W- W-A W- A

6 Relative lasting Energy he blasting energy of an explosive relative to the blasting energy of. Rel - Rel - V W- V A A W-A G-A G- 5 1 V W-A G-A 6 W- 6 V G- relative strength of explosive A. weight strength of explosive A. weight strength. pecific gas volume of explosive A. pecific gas volume of. Explosive election 1) Rock Properties ) Water Conditions in Hole ) Hole Diameter ) Number of Holes / Required Production Rock Properties 1) Compressive ength ) ensile ength a times lower than compressive strength ) Density ) onic Velocity Compressive Wave peed 5) Fracture Conditions Rock Properties pecific Gravity Uniaxial Comp. ength Uniaxial ensile ength Modulus of Elasticity Poisson's Ratio onic Velocity psi psi ksi ft/sec Rock ype Min. Max. Mean Mean Mean Mean Min. Max. Granite.6.7,070 1,70 6, ,700 19,700 Gneiss.6.9,055,00 8, ,000 19,000 asalt.8.0 1,750 1,885 7, ,000,000 Dolomite ,00,700 Marble..7,000,000 Limestone..7 1,790 1,70 6, oft " " 5,500 1,800 Hard " " 9,100 0,990 Crystalline " " 1,600 1,000 alt.5.6 andstone..8 1,90 75,190 0.,600 1,800 Quartzite.6.8 6,50,65 1, ,000 16,000 hale..8 1,775 5, ,500 15,00 Water ,000 1,000

7 Explosive election In general, the Detonation Velocity (V d ) of the explosive should match, as closely as possible, the onic Velocity (V s ) of the to be blasted. here is no value in using an explosive which has a Vd greatly in excess of the Vs of the (Example) If the to be blasted is a hard limestone with a sonic velocity (V s ) of 17,500 ft/sec, then a 1070 Emulsion (V d = 18,000 ft/sec) might be appropriate. eller (1985) Approach: 1. Determine the Characteristic Impedance (Z) of the : Vs Z 1.1*G * 1000 Where: G = the pecific Gravity of the V s = the onic Velocity of the, in ft/sec. Determine the Characteristic Powder Factor (CPF) for the and particular explosive: CPF Z Where: K = the Detonation Pressure of the explosive, in kbars. he CPF should be between 0.75 and A. If CPF < 0.75 he explosive has a V d and/or density which is Higher than required.. If CPF > 1.00 he explosive has a V d and/or density which is too Low for the (Problem) Using eller s approach, determine if the 1000 Emulsion will be appropriate for a hard limestone which has a V s of 19,000 ft/sec. 1. he Characteristic Impedance (Z) of the Limestone is: Vs 19,000 Z 1.1*G * 1.1*.5* he Characteristic Powder Factor (CPF) for the Limestone and 1000 Emulsion is: K CPF Z K

8 . No, the 1000 Emulsion has a Detonation Velocity and/or Density that is slightly higher than required. CPF Design of Drilling and lasting Pattern: Parameters: 1) Hole Diameter ) urden ) pacing ) ub-drilling 5) Hole Length 6) Hole Inclination 7) temming 8) Charge Length 9) Charge Concentration 10) Column Concentration 11) ottom Concentration 1) otal Charge 1) otal Explosives 1) Volume of Rock per Foot Hole 15) Volume of Rock per Hole 16) Weight of Rock per Hole 17) Powder Factor 18) Number of Required Holes 19) pecific Drilling 0) otal Required Drilling 1) Hole Pattern ) Delay Component ) Firing equence ) lasting Cost

9 lasting Notation Plan View D D H = ench Height D = lasthole Diameter L = lasthole Length = urden = pacing = temming J = ub-drilling Distance Charge Length = L - Charge Length L H J Cross ection lasthole Diameter (D) he diameter of the blasthole, it depends on: 1) Production Requirements - he higher the production requirements, the larger the hole diameter. ) ench Height he higher the bench, the larger the hole diameter. ) Environmental Restrictions he larger the amount of explosives, the greater the ground vibration. lasthole Diameter 1) he larger the diameter, the greater the amount of explosives and the lower drilling cost per ton ) Ranges from 1 in to 17 in (5 mm to 0 mm) ench Height (H) he height of the blasting bench.

10 Figure 1. ench Height vs. Recommended lasthole Diameter (from andvik am, 1999) (Example) According to the chart, if the ench Height is 1 m (0 ft), then the lasthole Diameter should be between 6 mm (.5 in) and 17 mm (5 in). andvik am Formula: Where: D = the lasthole Diameter (in inches) H = the ench Height (in feet) D (0.06 to 0.1)*H (Example) If the ench Height is 0 ft, then using the andvik am Formula, the lasthole Diameter should be between. in and.8 in D 0.06*H 0.06 * 0 ft. in to D 0.1* H 0.1 * 0 ft.8 in urden () he distance from the blasthole to the bench face or nearest free-surface. Also, the distance between rows of holes perpendicular to the bench face. pacing () he distance between the blastholes parallel to the bench or free-surface.

11 lasthole Length (L) he length of the blasthole. L H J ub-drilling Distance (J) he length of the blasthole drilled below the bench level. J L - H If the blasthole is inclined at an angle (α), then the lasthole Length (L) is: temming () he length of the blasthole filled with non-explosive material to contain the blast. urden Factor (K ) pecifies the burden distance as a function of the blasthole diameter. K * D For using with s that have a specific gravity of.5, K averages about 5 for surface mines and 0 underground. urden Factor - Ingersoll Rand recommends a urden Factor of between 0 and 0: 1) 0 for difficult s ) 0 for easy s urden Factor Austin Powder Formula: d e * 1.5 *D Where: d r = the urden (ft) d e = the Density of the Explosive (g/cc) d r = the Density of the Rock (g/cc) D = the lasthole Diameter (in) Problem Determine the urden () for shale s if the explosive Emulsion 1070 will be used with a 6 in lasthole Diameter (D)? From the explosive and properties tables: d e = 1.8 and d r =.6; therefore 1.8 *.6 K L 1.8 *.6 H J cos α (Note: the 1 in the above equation is to properly convert the factor in the original equation, which takes inches and gives feet, into a dimensionless burden factor) 1.5*6 in 1.9 ft 1.5*1 9.8

12 he urden Factor for explosive A (K -A ) can be related to the urden Factor for (K - ) using the Relative ulk ength (Rel- -A ) relationship: K K -A - * Rel - -A (Problem) For the previous explosive A, what would be the burden factor? K -A K - * 5* Rel - -A pacing Factor (K ) pecifies the blasthole pacing as a function of the urden. K K typically equals about for sequenced rows and simultaneous rows. pacing Factor Ingersoll Rand and andvik amrick recommend a pacing Factor (K ) of 1.5. pacing Factor Austin Powder Formula: * H if ; H if ; Where: H = the ench Height (ft) = the urden (ft) = the pacing (ft) 1.* K H 7* 8 1. (Problem) What will be the pacing () if the ench Height (H) is 50 ft and the urden () is 15 ft? ased on Ingersoll Rand and andvik am: 1.5* 1.5*15 ft ft ased on Austin Powder: H H 8. 7* 50 ft 7*15 ft ft

13 ub-drilling Factor (K J ) pecifies the distance of sub-drilling as a function of the burden. J K * K J typically equals about for hard, but J typically equals ft for coal. Ingersoll Rand and andvik am Recommend a ub-drilling Factor (K J ) between Austin Powder Recommends a ub-drilling Factor (K J ) between J temming Factor (K ) pecifies the length of stemming as a function of the burden. K temming Factor - Austin Powder Recommends a temming Factor (K ) between he Particle ize (P) in the stemming is recommended to be 1/1 to 1/18 of the lasthole Diameter (D) * P D/(1 to18)

14 Rock Volume (V) he volume of broken per unit length of blasthole (m /m or ft /ft). V * otal Rock Volume (V ) he total volume of broken per blasthole (m or ft ). Rock Weight (W) he weight of broken per unit length of blasthole (kg/m or lb/ft). W V V **H ** d otal Rock Weight (W ) he total weight of broken per blasthole (kg or lb). W V **H * d Explosive Charge (C) he weight of explosive per unit length of blasthole (kg/m). C otal Explosive Charge (C ) he total weight of explosive per blasthole. *D C *D exp *(L ) Weight Powder Factor (PF weight ) he amount of explosive needed to fragment a certain mass of (kg/ton or lbs/ton). PF weight C W d * D d * D *(L ) *(K * D)*(K * K * D)* H * D d *(K * K * ** H *(L ) * D *(L ) )*H

15 Volume Powder Factor (PF volume ) he amount of explosive needed to fragment a certain volume of (kg/m or lb/yd ). PF volume C V *D (K *D)*(K *D K *D *K **H *D *K *(L ) *(L ) *H *(L ) *D)*H

16 (Problem) At a surface mine, we have a in lasthole Diameter (D)using with a Density(d ) of 0.8 g/cm. he has a Density (d )of.5 g/cm and it has been found that a urden Factor (K ) of 0 and a pacing Factor (K )of 1. effectively fragment the. What is the Weight-ased Powder Factor (PF weight ) of this blast design? *D *(L ) PF weight d *K *K *D *H (We assume, since they do not say anything about bench height, stemming or subdrilling, that the stemming and subdrilling are functionally zero compared to the drillhole length.) PF weight *D d *K *K *(L ) *D *H kg *(.1m) *800 *(L 0) m kg 500 *(1.*0 *(.1m) )*L m 0.5 kg/tonnes urden & pacing In some situations, you may know the Powder Factor (PF) for the and for a given blasthole Diameter (D), you are looking for the urden () and pacing (). PF weight * K * D d * *(L ) or * ** H * D d * D d * H * PF weight * H * PF *(L ) * K *(L ) weight

17 (Problem) Assuming that the hole diameter is 100 mm, the spacing factor is 1., the explosive is with a density of 800 kg/m and the required powder factor is 0.1 kg /tonne, what is the urden? *D d *H *PF *(L ) weight *K (Again, we assume that the stemming and subdrilling are functionally zero.) * D kg g m cm d * H * PF * K anfo Weight kg *(0.1m) *800 *(L 0) m tonnes kg.5 * L*0.1 *1. m tonnes.5m *(L ) ample est Question #50. (otal Explosive Charge) Given a 5-ft deep, 7-7/8 in, diameter hole, 10 ft of stemming, and a prill specific gravity of 0.85; the charge (lb) of free poured ammonium nitrate and fuel oil () prill is most nearly? C *D exp in * 1in ft 8.5 lb *(L ) lb * 0.85* 6. *(5 10)ft ft

18 ample est Question #51. (Powder Factor) Given a 1-1/ in. diameter blast hole, massive volcanic tuff overburden, poured prills, prill specific gravity of 0.85, 0 ft X 6 ft pattern, 8 ft of sub-drill, 1 ft of stemming and a 50 ft shovel bench height; the powder facter (pounds of explosive per bank cubic yard) is most nearly? PF volume * C V 0.80lb yd 1.5in 1in ft *D **H *(L ) lb * 0.85*6. *(50 8 1)ft ft 1 yd 0*6*50* 7 ft Other lasting: Ring lasting Holes are drilled from a central point and radiate outwards (also Fan lasting). Used for: sublevel stoping, draw bell creation, tunneling, etc. Crater lasting Uses a spherical, or near spherical, charge in a half space to create a crater. Used for Vertical Crater Retreat (VCR), other.

19 Fly 1) Uncontrolled material fragments generated by the effects of blasting ) Rock fragments are thrown at excessive distances and can result in human injuries, fatalities, property damage, litigation, etc. Causes of Fly 1) Insufficient burden ) High explosive concentration ) Improper blast design ) Discontinuity in the overburden 5) Inadequate stemming 6) Improper delays Air last 1) ransient increase in air pressure ) Pressure wave travels at the speed of sound ) Caused by the gas released during the detonation of the explosives Controlling Air last o control air blasts, the delay between holes must be greater than t min : Where: t min 1.17 t min = minimum delay time (in ms) = the lasthole pacing (in feet)

20 last Vibrations 1) haking of the ground due to elastic waves emanating from the blast ) Measured in inches per second (in/sec) of particle velocity ) Can result in structural damage he Peak Particle Velocities (PPV) are calculated as: PPV k Where: k = the Ground Response Factor where. < k < with low to high confinement 160 is average D = the caled Distance Factor he caled Distance Factor (D) is calculated as: D Dist D 1.6 Where: Dist = the Distance to the nearest structure C = the otal weight of explosive Charge per delay or per hole C he Office of urface Mining has established the following Peak Particle Velocities based on distance (Problem) For the following conditions: lasthole Diameter (D) = in, lasthole Length (L) = ft, ub-drilling (J) = 7 ft, with a Density (d) of 0.85 g/cm, distance to nearest structure (Dist) = 600 ft, determine the Peak Particle Velocity (PPV) First, we calculate the total explosive charge in a hole (see above), being careful to keep the units consistent: C *D exp in * 1in ft 10 lb *(L ) 6. lb ft * 0.85g cm * 1g cm * ft 7 ft

21 hen the caled Distance (D) is: D Dist C in sec and the Peak Particle Velocity (PPV) is: PPV k D 160/ in sec his is less than the allowable 1.00 in/sec at 600 ft (see table above)