032 - Blasthole Drilling

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CHAPTER 7.2
Blasthole Drilling
Jamal Rostami and Douglas F. Hambley
INTRODUCTION
Drilling is an important unit operation in mining. Drilling is 
required for a variety of mining or mining-related activities 
including blasting, ground support installation, utility installa-
tion, dewatering, exploration, and much more. The term drill-
ing is used for smaller-diameter holes, with a few exceptions 
such as shaft drilling and raise drilling, where larger excava-
tions are created by special machines including cluster drills. 
This chapter is primarily concerned with mine production. 
Most boreholes drilled for mine production are blastholes 
for explosives. However, boreholes drilled for use in solution 
mining will also be discussed.
The majority of blasthole drilling is performed by two 
primary methods:
1. Percussive drilling
• With smaller hole sizes (diameters up to 150 mm 
[6 in.]), the impact and rotation of the bit used to 
fracture the rock is transmitted from the drill (top 
hammer) to the bit through a drill rod or series of 
drill rods coupled together (referred to as a drill 
string).
• With larger hole sizes (diameters from 75 mm to 
508 mm [3 to 20 in.]), the hammer is located down-
the-hole (DTH) or in-the-hole (ITH) at the bottom 
of the drill string immediately above the bit, and the 
impact is transmitted directly to the bit.
2. Rotary drilling
• Drag bits are used for 75–250 mm (3–10 in.) holes in 
soft rock.
• Tricone bits are used for 75–300 mm (3–12 in.) holes 
in medium and harder rock.
• Larger roller bits are used for holes larger than 300 mm 
(12 in.).
A third drilling method, jet piercing, which was formerly used 
to drill blastholes in taconites and other very hard, abrasive 
rocks, has largely been superseded by rotary drilling with tri-
cone bits with tungsten carbide (TC) buttons.
PERCUSSIVE DRILLING
In percussive drilling, the rock is broken by a combination 
of rotation of the bit and high-frequency percussive impacts 
transmitted by the bit to the rock. The percussive impact 
is delivered by either pneumatic or hydraulic pressure. 
Percussive drills were originally powered by compressed air. 
Since the mid-1970s, however, hydraulically powered drills 
have supplanted pneumatic ones, except in the case of small, 
handheld equipment such as stopers and jackhammers. The 
advantages of hydraulic drills over pneumatic drills are the 
fewer moving parts and the significantly higher penetration 
rates. The depth of percussive drilling with top hammer drills 
is limited to approximately 76 m (250 ft), due mainly to losses 
in energy transfer at joints in the drill string. Larger and deeper 
holes can be achieved using DTH drills.
In DTH drilling, compressed air is supplied through the 
drill string to drive the hammer, which is located immediately 
behind the bit. The compressed air activates a hammer that 
delivers impact directly to the bit. This eliminates the loss of 
impact energy in joints and is a more efficient mechanism of 
percussive drilling. Rotation of the bit is provided by the motor 
at the top and transferred through the drill string. The diameter 
of the drill string, usually 150 mm (6 in.) or more, helps limit 
deviation of the hole, which improves drilling accuracy. As an 
example, at a Canadian uranium mine in 1978–1979, the sec-
ond author of this chapter supervised the drilling with a DTH 
drill of 200-mm (8-in.) and 311-mm (12¼-in.) holes to depths 
of approximately 490 m (1,600 ft), with an error of less than 
4.5 m (15 ft) at the target depth.
Percussion Drill Bits
Bits for top hammer percussion drills come in various shapes, 
as shown in Figure 7.2-1. The drill steel with an integral 
“chisel” bit and a single TC insert is used with handheld 
jackhammer (sinker) drills in shaft sinking. More common 
are the hammer-on or screw-on cross-shaped bits with four 
chisel-shaped TC inserts. However, in harder rocks especially, 
the chisel-shaped bits are being replaced with button bits, of 
Jamal Rostami, Assistant Professor, Energy and Mineral Engineering, Pennsylvania State University, University Park, Pennsylvania, USA 
Douglas F. Hambley, Associate, Agapito Associates, Inc., Golden, Colorado, USA
436 SME Mining Engineering Handbook
which the retrac bits are an example. (Retrac bits are designed 
to facilitate removal of the bit and steel from the hole, which is 
crucial in soft or squeezing ground.) The shape of the buttons 
is selected based on the application and the type of rock to be 
drilled. Longer, pointed inserts are used for softer rock, while 
shorter, rounded inserts are used in harder rock. A bit can be 
initially selected using charts from commercial bit manufac-
turers; however, optimum bit geometry and button shape is 
usually determined by trial and error at the job site.
DTH drills were introduced by Ingersoll Rand Company 
in 1955, and the concept has changed little since then. 
Figure 7.2-2 shows a cutaway view of a DTH hammer and 
bit. The weak link in the DTH system is often the plastic foot 
valve between the piston and the bit, which can break easily if 
not seated properly.
Cluster drills are extra-large impact drill heads that incor-
porate a number of DTH hammers and bits. They can be as 
large as 2 m (6½ ft) in diameter. Depending on the size of the 
hole, the drills may have various numbers of hammers at the 
face, with the individual bits receiving impact energy from 
their individual hammers. The entire drill head is rotated via 
a drill string so that the hammers will cover the entire face. 
Cluster drills are often used in very hard and abrasive rocks, 
where a limited number of holes are planned, or in sink-
ing small, shallow shafts less than 300 m (1,000 ft) deep. 
Figures 7.2-3 and 7.2-4 show a typical cluster drill.
Percussive Drilling Equipment for Underground Use
Handheld jackleg and stoper drills are lightweight percussive 
drills powered by compressed air. They are used for drill-
ing small blastholes that are generally 35 mm (1.375 in.) or 
smaller in diameter. They are typically used to drill holes from 
1.8 to 3 m (6 to 10 ft) in length, in 0.6-m (2-ft) increments, as 
that is the approximate extension of the piston in the air leg; 
holes up to 3.3 m (12 ft) long can be drilled by a skilled driller. 
Advance rates are generally inversely proportional to the rock 
strength and the cross-sectional area of the drill hole. Typical 
drilling rates for handheld drills range from 0.3 to 0.5 m/min 
(1 to 1.7 ft/min), depending on the rock mass properties.
Drilling rigs for underground mining applications can be 
divided into face drilling and production (or long-hole) drill-
ing rigs. Face drilling is performed by mobile rigs equipped 
with drills mounted on one boom or multiple booms. A two-
boom jumbo is shown in Figure 7.2-5. The number of booms 
and drills depends on the opening dimensions and rock mass 
properties, the number of holes to be drilled per blast round, 
and the number of faces to be drilled in a shift. In hard rock 
metal mining, two-boom or three-boom jumbos are used, 
whereas in limestone mining, two- or single-boom drill 
jumbos are common. Hole diameters typically range from 
35 mm to 51 mm (13⁄8 to 2 in.) with the exception of the 
reliever holes used in burn cuts, which are somewhat larger. 
Drill feeds are typically 3.7 to 4.3 m (12 to 14 ft); however, 
drill feeds of up to 6.4 m (21 ft) are available. Drill jum-
bos were historically powered by compressed air. Since the 
late 1970s, however, electric/hydraulic and diesel/hydraulic 
units have almost completely supplanted the older pneumatic 
(compressed air) units because of the much faster penetra-
tion rates that are achievable with the larger, more powerful 
hydraulic drills.
Ring-drilling production drills are used in underground 
metal mines to drill the long inclined or vertical blastholes 
(typically >6.1 m [20 ft] long) used in sublevel stoping, sub-
level caving, and vertical crater retreat mining. Figure7.2-6 
A. Drill steel with integral chisel bit
B. Cross bit
C. Retrac button bit
Source: Sandvik 2009.
Figure 7.2-1 Top hammer percussive drill bits
Courtesy of Atlas Copco.
Figure 7.2-2 Cutaway view of a DTH hammer and bit
Source: Atlas Copco 2007.
Figure 7.2-3 Cluster drill head
 Blasthole Drilling 437
shows a typical production drill unit in operation drilling an 
inclined uphole. In such operations, the drilling operation may 
include both long production blastholes and ground support 
installation (primarily cable bolts). To ensure good fragmenta-
tion, it is imperative for these holes to have the correct length 
and direction. To achieve this, it must be possible to easily 
rotate the drill boom to various positions, maintain the proper 
hole alignment, and minimize the deviation from the proper 
location. A bit with a flat or concave front face will create 
a straighter hole than a bit with a convex front face. Retrac 
bits with long bit skirts were introduced to improve drilling 
accuracy and reduce hole deviation. Another method to reduce 
hole wandering is to use larger-diameter drill strings, whereby 
the small difference between the diameter of the bit and the 
drill string limits the amount of bending of the drill string and 
thus keeps the hole straighter. Because of the need to flush 
drill cuttings from the borehole, the drill string on a noncoring 
drill cannot be the same diameter as the bit.
For upholes, drills often use an ITH drilling system that 
delivers the impact directly to the bit. Combined with the 
larger-diameter drill tube, this allows for much higher accu-
racy and lower deviation. For example, in a hole that is 30 m 
(100 ft) long, drill-hole deviation may be as much as 3 m 
(10 ft), or 10%, when a top hammer and a conventional rod 
and bit are used. When the same drill is used with a retrac bit 
and guide tube behind the bit, the deviation can be reduced to 
1.5 m (5 ft), or 5%. With an ITH hammer, however, that devia-
tion can be reduced to 0.5 m (1.7 ft), or 1.7%. For very long 
holes, a stabilizer/reamer behind the ITH hammer will reduce 
deviation even further.
For shaft sinking applications, specialized jumbo drills 
can be used. Shaft drill jumbos use the same drilling equip-
ment and bits as other drilling rigs—the only difference is 
that instead of a drill carriage, they are mounted on a work 
platform that hangs on a set of ropes. The jumbo is lowered 
Source: Atlas Copco 2010a.
Figure 7.2-4 Cluster drill in a shaft excavation
Source: J.H. Fletcher and Company 2007.
Figure 7.2-5 Two-boom jumbo for face drilling
Source: Atlas Copco 2010b.
Figure 7.2-6 Typical ring-drilling production drill for 
underground metal mining
438 SME Mining Engineering Handbook
to drill at the face and raised a safe distance above the face to 
minimize damage from flyrock from the blast.
Typical hole diameters for production drilling with regu-
lar top hammer systems range from 50 to 100 mm (2 to 4 in.); 
with the ITH system, the range is from 100 to 254 mm (4 to 
10 in.). The drill string diameter for regular rods varies from 
38 to 51 mm (1½ to 2 in.), and the lengths of individual drill 
rods typically range from 1.2 to 1.8 m (4 to 6 ft), but can be 
up to 3.0 m (10 ft). For tube drilling in conjunction with ITH, 
drilling rods range from 45 to 87 mm (1¾ to 3½ in.) in diam-
eter and from 1.5 to 3.6 m (5 to 12 ft) in length. (With ring 
drilling, the length of the rod is constrained by the height and 
width of the mine opening.)
Penetration rate is a function of the impact energy 
imparted to the bit, frequency of impacts, feed pressure, 
rotational speed, drill bit type, and rock mass properties. 
A typical drill unit is capable of delivering 10 to 25 kW of 
energy to the drill string with an impact frequency between 
20 and 70 Hz (impacts per second). The drill rotational 
speed ranges from 0 to about 100 rpm, with the maximum 
for a given hole size defined by an angular speed at the bit 
perimeter of approximately 0.4 m/s (1.4 ft/s). Depending on 
the rock mass properties, penetration rates of 0.5–2.5 m/min 
(1.6–8 ft/min) can be achieved. It should be noted here that 
the penetration rates given previously in this paragraph do 
not account for the time required to retract the drill from a 
hole, reposition the boom, and collar a new hole, which can 
take from 30–60 seconds per hole, depending on the type of 
equipment.
For the sizes of blastholes normally encountered under-
ground (35–100 mm [13⁄8–4 in.]), jointing doesn’t usually 
affect the ability to drill blastholes unless the rock is very 
closely jointed, as in a shear zone, or the drill hole is in the 
zone of back break behind the previous blast in the case of 
benching. Hence, other things being equal, the penetration rate 
in underground blastholes can be considered to vary inversely 
with the rock strength.
Percussive Drilling Equipment for Surface Use
Drilling equipment for surface mining applications can be 
categorized into two classes—percussive drills for small to 
medium-sized holes of up to 200 mm (8 in.) and rotary drills 
for larger sized holes of up to 450 mm (18 in.). Surface drill-
ing units are generally crawler mounted. Older percussive 
drills (known as air tracks) may use compressed air as their 
power source; however, newer machines use hydraulic drills 
and are diesel powered. Percussive drilling for surface blast-
ing typically uses holes ranging from 89 to 150 mm (3½ to 
6 in.). Both top hammer and DTH drills are used. Figure 7.2-7 
shows a crawler-mounted, surface percussive drill.
The lengths of drill rods used in surface drilling are selected 
to minimize the time for adding or removing the rods. Typical 
drill rods for percussive surface drilling range from 50 to 
150 mm (2 to 6 in.) in diameter, and from 4 to 6 m (13 to 20 ft) 
long. The weight loading on the bits ranges from 1 to 4 t (1.1 to 
4.4 st). Drilling rates for typical surface drills vary from 2 to 
80 m/h (6 to 240 ft/h). They increase with increased power of the 
rig, and decrease with increasing hole diameter and rock mass 
strength.
Small, handheld drilling equipment has all but disap-
peared from surface mining applications, except for breaking 
oversize boulders or drilling sinking cuts for starting a bench 
in very inaccessible places in the mine. Most surface mines 
use impact hammers for breaking large or oversized boulders 
to avoid secondary blasting.
Percussive Drilling Penetration Rate
Typical penetration rates for various sizes and types of percus-
sive drills are presented in Table 7.2-1.
ROTARY DRILLING
With the exception of special applications that use cluster 
drills, larger holes are typically drilled by rotary drilling. A 
typical rotary drilling rig used in surface mining is presented 
in Figure 7.2-8. With rotary drilling, the drill bit is rotated by 
applying torque at the end of the drill string, which results in 
removal of chips from the face of the hole. Power for bit rota-
tion and penetration is either diesel or electric.
Since their introduction in the early 1900s by the Hughes 
Tool Company, tricone bits have been the traditional type of 
bits used in rotary drilling. They remain the most popular bits 
for blastholes ranging from 150 to 444 mm (6 to 17½ in.) in 
Source: Atlas Copco 2010c.
Figure 7.2-7 Crawler-mounted top hammer percussive surface drill
 Blasthole Drilling 439
diameter. Drag-type bits have gained an increasing share of 
the market since the introduction of polycrystalline diamond 
compact (PDC) bits in 1976 (Baker Hughes 2008). PDC drag 
bits are more expensive than tricone bits, but for relatively 
deep holes, the time saved due to longer intervals between bit 
changes may justify the price.
Bit selection is based on hole size and depth, rock type, 
and operational requirements. Sources of information to guide 
selection of the proper bit include manufacturers such as 
Atlas Copco and Sandvik for percussive drill bits, and Smith 
Internationaland Baker Hughes for tricone and drag bits. 
Figure 7.2-9 shows typical drag and tricone bits used in rotary 
drilling. The weight loading on the bits ranges from 10 to 74 t 
(11 to 81.6 st).
The rate of advance for rotary drilling is a function of the 
rate of rotation, bit diameter, weight on the bit, and rock mass 
properties, and is well predicted by the following empirical 
equation (Calder 1973):
P = (61 – 28 log10 Sc) W R/(250 D) (7.2-1)
where
 P = penetration rate (ft/h)
 Sc = rock compressive strength (thousands lb/in.2)
 W = pulldown weight of drill (thousand lb)
 R = drill rotary speed (rpm)
 D = hole diameter (in.)
In metric units, Equation 7.2-1 becomes
P (214 – 98 log10 (0.145 Sc)) W R/(250 D) (7.2-2)
where
 P = penetration rate (m/h)
 Sc = rock compressive strength (MPa)
 W = pulldown weight of drill (t)
 R = drill rotary speed (rpm)
 D = hole diameter (mm)
Table 7.2-2 provides a general guide to surface blasthole 
drill productivity in various rock types. It is assumed that 
the work is performed on a reasonably prepared bench and 
includes the following operations:
• Moving the drill from prior hole to next hole location
• Jacking/leveling the drill
• Aligning the mast/feed for plumb or desired angle 
orientation
• Collaring and advancing the first rod
• Adding additional rods and advancing them until the 
required hole depth is reached
• Tripping out the drill string until it is clear of the hole
• Checking the hole/collar for depth/condition
• Retracting the jacks and making the drill ready to tram
Table 7.2-1 Comparison of different percussive drilling systems 
and their production rates
Drilling 
Method
Range of 
Diameter, 
mm
Typical 
Depth, 
m
Typical 
Drilling 
Rate, 
m/h*
Accuracy, 
% or 
cm/m Application
Top 
hammer 
pneumatic 
jackleg
25–50 <4 60 2–5 Used in small tunnel 
and drift development, 
small-scale stoping, 
surface operations 
as starter, shallow 
trenching, bolt 
installation, etc.
Jumbo 37–100 4–10 100–200 1–3 Tunneling, stoping, 
fan drilling, bolt 
installation, and probe 
drilling
Surface 
crawler-
mounted 
drills
50–150 5–30 20–150 1–3 Surface and bench 
drilling
Top 
hammer 
hydraulic 
jumbo 
drills
37–125 4–20 30–120 2–3 Tunneling, stoping, 
fan drilling, bolt 
installation, and probe 
drilling
Down-the-
hole
75–150 10–50 20–80 3–5 Surface and bench 
drilling
* Drilling rates are for actual drilling and do not include time for drill retraction, 
boom relocation, collaring, etc. Drilling rates decrease as rock mass strength 
increases and may increase or decrease depending on the number and 
orientation of joints/blocks.
Source: P&H Mining Equipment 2010.
Figure 7.2-8 Large rotary drilling equipment for surface
 
 A. Milled-tooth B. TC insert C. PDC insert 
 tricone bit tricone bit drag bits
Courtesy of Bit Brokers International, Logan, Illinois.
Figure 7.2-9 Three types of rotary drill bits
440 SME Mining Engineering Handbook
The need for a stable drill setup with the jacks in place 
and activated cannot be overemphasized. In addition, for long 
holes, it is important to place centralizers at intervals in the 
drill string, especially if the rods are significantly smaller in 
diameter than the drill holes.
DRILL HOLES FOR SOLUTION MINING
Boreholes drilled for solution mining are not production holes 
in the same sense as blastholes; however, they are production 
holes in the sense that they are used to either inject or remove 
the fluid used to dissolve the rock and have a limited life span. 
Another difference is that after the holes have been advanced 
to their ultimate depth, they are cased and cemented and fitted 
with production tubing, a process known as well completion. 
Several different well-completion types are found in solution 
mines. The Frasch process for solution mining of sulfur uti-
lizes concentric pipes, with hot water injected in one pipe and 
the sulfur-bearing pregnant solution removed in another.
In solution mining of salt and potash, concentric pipes are 
used to develop the injection and recovery wells. When the 
wells have reached the target depth and the sumps have been 
excavated, mining proceeds laterally until the two wells are 
connected. At this point, one well is converted to an injection 
well and the other becomes the recovery well.
Wells used for solution mining are generally drilled using 
oilfield equipment and mud-rotary drilling techniques. As with 
oil and gas drilling, selection of the proper chemistry and den-
sity of the mud is important. In evaporite zones, the saturated 
saline brines used for mud in normal oilfield drilling will dis-
solve potash minerals and should be replaced with oil-based 
invert mud. The outside diameter of solution mine wells typi-
cally ranges from 219 to 346 mm (85⁄8 to 135⁄8 in.) and depends 
on the completion configuration and tubing diameters required 
to transport the fluids.
NEW DEVELOPMENTS IN PRODUCTION DRILLING
The most important advance in drilling equipment since 1990 
has been the development of computer-controlled drilling 
systems. These systems automatically locate and collar the 
holes, based on a preprogrammed blast round design, and 
incorporate real-time monitoring and optimization of the drill-
ing. In surface mining, drill rigs have been fitted with Global 
Positioning Satellite systems, allowing for better control of 
the drill-hole locations.
Drills have been fitted with computer control systems 
that allow for optimization of drilling parameters such as feed 
rate, weight on bit, and torque to achieve the highest possible 
drilling rates. These systems allow for uploading of the drill-
ing pattern into their computer via storage devices or, more 
recently, via wireless communication.
In underground mining, multiboom jumbo drills can be 
programmed to drill the desired blasthole patterns automati-
cally, through coordination with an automated surveying and 
guidance system, and simultaneously monitor the drilling 
parameters and optimize the control parameters. Interfaces 
also exist that allow for ground characterization while drilling 
by comparing the current drilling rates and other parameters 
with stored data for drilling in similar rock types (Atlas Copco 
2004; Schunnesson 1998; E. Tanner, personal communica-
tion). In this manner, the instrumentation system can provide 
an estimate of the rock properties.
Directional drilling has also made significant progress 
and is used with high speed and an advanced degree of accu-
racy for applications in oil well drilling, coal mine degasifi-
cation, as well as civil engineering. Direction changes are 
effected using a bent sub together with a downhole mud motor 
drive unit to rotate the bits. The mud motor drive works in 
conjunction with rotary bits and receives the thrust force and 
torque reaction from the drill string, which in this case does 
not rotate.
Coil tubing, where the drill string is rolled on a reel and 
dispensed rapidly as needed, has been used extensively in oil/
gas well drilling to eliminate the need for breaking and assem-
bling the drill steels. This technique is only possible with mud 
motors, since there is no need to rotate the drill string. These 
systems are capable of making bends with radii as tight as 
6–10 m (20–30 ft) in holes 75–100 mm (3–4 in.) in diameter. 
Because of this capability, coil tubing is commonly employed 
on workover rigs used to rehabilitate wells used for solution 
mining and oil production.
REFERENCES
Atlas Copco. 2004. Atlas Copco Face Drilling Options: Rig 
Control System—RCS. Product brochure. Fagersta, 
Sweden: Atlas Copco Rock Drills AB. Available at 
http://pol.atlascopco.com/SGSite/SGAdminImages/
PrintedMatters/5470.pdf. Accessed February 2010.
Atlas Copco. 2007. Cluster drill. In Secoroc Rock Drilling 
Tools Product Catalogue—DTH Equipment. Fagersta, 
Sweden: Atlas Copco Secoroc AB. p. 31. http://pol.atlas 
c o p c o . c o m / S G S i t e / S G A d m i n I m a g e s / P r i n t e d 
Matters/5126.pdf.Accessed February 2010.
Atlas Copco. 2010a. Rock drilling tools: DTH equipment, 
cluster drills. On-line product information. http://pol 
.atlascopco.com/SGSite/default_prod.asp?cookie_test=1. 
Accessed February 2010.
Table 7.2-2 Generalized production rate of drilling units in 
surface mining
Drilling Conditions Soft Rock
Medium 
Soft Rock
Medium 
Hard Rock Hard Rock
Rock strength, MPa 70–100 100–175 175–225 225–300
Rock strength, 1,000 psi 10–15 15–25 25–35 35–45
Rock fabric condition Drilling rate, m/h*
 Stable, uniformly competent 
ground conditions
55 33.5 30.5 24.5
 Competent rock, fractured 
collar zone 
(top 0.6 to 1.2 m of bench)
49.5 30 27.5 22
 Rock with closed joints, 
fractured collar zone 
(top 0.6 to 1.2 m of bench)
42 25.5 23.5 18.5
 Rock with open joints, 
fractured collar zone 
(top 0.9 to 2.4 m of bench)
33.5 20.5 18.5 15
 Heavily jointed, poorly 
cemented rock, fractured 
collar zone 
(top 1.2 to 3 m of bench)
27 16.5 15 12
Courtesy of W. Hissem.
*To obtain drilling rates in feet per hour, multiply by 3.28.
 Blasthole Drilling 441
Atlas Copco. 2010b. Blasthole drilling rigs: Production drilling 
rigs, Simba M4C. http://pol.atlascopco.com/SGSite/default 
_prod.asp?cookie%5Ftest=1. Accessed February 2010.
Atlas Copco. 2010c. Blasthole drilling rigs: Surface crawler drill-
ing rig, ROC D7. http://pol.atlascopco.com/SGSite/default 
_prod.asp?cookie%5Ftest=1. Accessed February 2010.
Baker Hughes. 2008. Quantec PCD drag bit. www.baker 
hughesdirect.com/cgi/hello.cgi/HCC/public/diamond/
pdf/quantec_brochure.pdf. Accessed February 2010.
Calder, P.N. 1973. Rock mechanics aspects of large hole bor-
ing machine design. In Proceedings of the 8th Canadian 
Rock Mechanics Symposium, Toronto, ON. Ottawa, ON: 
Canadian Department of Energy, Mines and Resources. 
pp. 159–175.
J.H. Fletcher and Company. 2007. Model J-352-LS dual 
boom jumbo. www.jhfletcher.com/jumbos.htm. Accessed 
February 2010.
P&H Mining Equipment. 2010. P&H 250XP blasthole drill. 
www.phmining.com/PHMining/Mining-Equipment/
Blasthole-Drills/250XP.htm. Accessed February 2010.
Sandvik. 2009. Top Hammer Drilling Tools: Product Catalogue. 
Sanviken, Sweden: Sandvik Mining and Construction 
Tools AB. Available at www.miningandconstruction 
.sandvik.com/Sandvik/0120/Internet/Global/S003713 
.nsf/Alldocs/Brochures*2ALinked*Top*Hammer*PDF/
$FILE/TH2009_lowres.pdf. Accessed February 2010.
Schunnesson, H. 1998. Rock characterisation using percus-
sive drilling. Int. J. Rock Mech. Min. Sci. 35(6):711–725.