Explosives and Drilling

Chapter 22 - Explosives and Drilling
Number	Topic	Rule of Thumb
21.21	Paste Fill	40% of paste fill distribution piping may be salvaged for re-use. Source: BM&S Corporation
22.01	Powder Consumption	Listed below is typical powder consumption in hard rock.
		Shaft Sinking – 2.5 Lb./short ton broken
		Drifting – 1.8 Lb./short ton broken
		Raising – 1.5 Lb./short ton broken
		Slashing – 0.8 Lb./short ton broken
		Shrink Stope – 0.5 Lb./short ton broken
		O/H Cut and Fill – 0.5 Lb./short ton broken
		Bulk Mining – 0.4 Lb./short ton broken
		Block Cave u/c – 0.1 Lb./short ton to be caved
		Open Pit Cut – 0.9 Lb./short ton broken
		Open Pit Bench – 0.6 Lb./short ton broken
		Various Sources
22.02	Explosive Choice	The strength of pure ammonium nitrate (AN) is only about one-third as great as that of an oxygen balanced mixture with fuel oil (ANFO). Source: Dr. Melvin Cook
22.03	Blasting Strength	Blasting strength is a direct function of density, other things being equal. Typical explosives for dry ground (ANFO) may have a blasthole density (specific gravity) of 0.8 to 1.3, while for wet ground (slurry or emulsion) it varies from 1.1 to 1.3. Developments in explosive technology make it possible to choose any density desired, within the given ranges. Source: Dr. Nenad Djordjevic
22.04	Spacing and Burden	For hard rock open pits or backfill rock quarries, the burden between rows can vary from 25 to 40 blasthole diameters. Spacing between holes in a row can vary between 25 and 80 blasthole diameters. Source: Dr. Nenad Djordjevic
22.05	Spacing and Burden	The burden can vary between 20 and 40 blasthole diameters. Light density explosives require a ratio of 20-25:1. Dense explosives require 35-40:1. Source: John Baz-Dresch
22.06	Spacing and Burden	To obtain optimum fragmentation and minimum overbreak for hard rock open pits or backfill rock quarries, the burden should be about one-third the depth of holes drilled in the bench. Source: Dr. Gary Hemphill
22.07	Spacing and Burden	To obtain optimum fragmentation and minimum overbreak for stripping hard rock open pits or quarrying rock fill, the burden should be about 25 times the bench blasthole diameter for ANFO and about 30 times the blasthole diameter for high explosives. Source: Dr. Gary Hemphill
22.08	Spacing and Burden	The burden required in an open pit operation is 25 times the hole diameter for hard rock, and the ratio is 30:1 and 35:1 for medium and soft rock, respectively. The spacing is 1 to 1.5 times the burden and the timing is a minimum of 5 ms (millisecond) per foot of burden. Source: John Bolger
22.09	Spacing and Burden	The burden and spacing required in the permafrost zones of the Arctic is 10-15% less than normal. Source: Dr. Ken Watson
22.10	Spacing and Burden	When “smooth wall” blasting techniques are employed underground, the accepted standard spacing between the trim (perimeter) holes is 15-16 times the hole diameter and the charge in perimeter holes is 1/3 that of the regular blastholes. The burden between breast holes and trim holes is 1.25 times the spacing between trim holes. Source: M. Sutherland
22.11	Collar Stemming	The depth of collar for a blasthole in an open pit or quarry is 0.7 times the burden. Source: John Bolger
22.12	Collar Stemming	The depth of collar stemming is 20-30 times the borehole diameter. Source: Dr. Nenad Djordjevic
22.13	Collar Stemming	For open pits or back-fill rock quarries, pea gravel of a size equal to 1/17 the diameter of the blasthole should be employed for collar stemming (i.e. ½ inch pea gravel for an 8½-inch diameter hole). Source: Dr. Gary Hemphill
22.14	Relief Holes	Using a single relief hole in the burn cut, the length of round that can be pulled in a lateral heading is 3 feet for each inch diameter of the relief hole. For example, a 24-foot round can be pulled with an 8-inch diameter relief hole. Source: Karl-Fredrik Lautman
22.15	Relief Holes	It has been found that a relief hole of 250 mm (10 inches) will provide excellent results for drift rounds up to about 9.1m (30 feet) in length. Source: Bob Dengler
22.16	Blastholes	The optimium blast hole diameter (in inches) is equal to the square root of the bench height measured in feet. For example, a 7-inch diameter hole is desired for a 50-foot bench. Source: William F. Cahoone
22.17	Blastholes	The cost of drilling blastholes underground is about four times the cost of loading and blasting them with ANFO. Present practice is usually based on the historical use of high explosives where the costs were about equal. An opportunity exists for savings in cost and time for lateral headings greater than 12 feet by 12 feet in cross-section by drilling the blastholes to a slightly larger diameter than is customary. Source: Jack de la Vergne
22.18	Blastholes	The “subdrill” (over-drill) for blastholes in open pits is 0.3 times the burden in hard rock and 0.2 times the burden in medium/soft rock. Source: John Bolger
22.19	Blastholes	The "subdrill" is normally 0.3 times the burden and never less than 0.2. Source: John Baz-Dresch
22.20	Blastholes	“Sub-grade” (over-drill) is in the order of 8 to 12 blasthole diameters. Source: Dr. Nenad Djordjevic
22.21	Noxious Fumes	The heavier the explosive confinement, the lower the production of NO and NO2 for any blasting agent. Excess fuel in ANFO (8% FO) is as good as any additive (with regular ANFO) in reducing NO2 formation. Source: Sapko, Rowland et al
22.22	Ground Vibration	The ground vibration produced by the first delay in a burn cut round is up to five times higher than that generated by subsequent delays well away from the cut. Source: Tim Hagan
22.23	Crater Blasting	Crater blasting will be initiated if the charge acts as a sphere, which in turn requires the length of a decked charge in the blasthole to be no more than six times its diameter. Source: Mining Congress Journal
22.24	Labor Cost	The labor cost for secondary blasting can be expressed as a percentage of the labor cost for primary mucking. For Sub-Level Cave and Crater Blasthole stoping, it is around 30%; for Sub-Level Retreat it is closer to 10%. Source: Geoff Fong
22.25	Drilling	Percussion drilling is required for drilling blastholes in rocks with a hardness of 4 or greater on the Mohs’ scale (refer to Chapter 1). These are mainly the volcanic rocks. Rotary drilling is satisfactory for softer rocks, mainly sedimentary. Source: Dr. Gary Hemphill
22.26	Drilling	The number of drill holes required in a lateral heading, N = Area/5 +16. For example, a 10-foot x 15-foot heading requires 46 holes. (Use N = 2.2 x Area + 16 for metric units.) A few more holes are required if perimeter drilling is to be employed. Source: Tim Arnold
22.27	Drilling	A one-degree adjustment in dip will diplace a longhole one foot for each 60 feet drilled from the collar. Source: Shawn O'Hara