Rock Drilling and Blasting LECTURES - NN.pdf

Abazar M. A. Daoud, Engineering Geology Department, Faculty of Earth Sciences, RSU
Red Sea University
Faculty of Earth Sciences
Engineering Geology Department

Course Description and Contents
1) Introduction of stress and shock waves.
2) Rock fracture and rock strength.
3) Rock drilling and boring.
4) Explosives and detonators.
5) Burden and spacing.
6) Safety in rock engineering.

Useful References
1) Rock Fracture and Blasting Theory and Application, Zong -Xian
Zhang, 2016.
2) Drilling and Blasting of Rocks, Carlos Lopez Jimeno et al., 1987
and 2006
3) Blasting Principles for Open Pit Mining, William Hustrulid, 1999.
4) Rock Blasting Terms and Symbols, Agne Rustan, 1998.
5) Excavation Handbook, Church Horace.
6) Any Rock Mechanics References.

1/ Stress Waves and Shock Waves
➢ In the study of stress waves and shock waves, we need a coordinate
system. There are two coordinate systems:
1) Eulerian
2) Lagrangian systems.
➢ In stress wave study,
Lagrangian coordinates are
often employed.

CATEGORY OF STRESS WAVES IN
SOLIDS
➢ All stress waves can be divided into two groups: body waves and
surface waves. Within a solid body there is only one kind of stress
wave—body waves. Body waves include primary waves, that is, P-
waves, and secondary waves, that is, S-waves.
➢ On and near the surfaces of a solid body there is another kind of
stress wave - surface waves.

1) Body Waves:
1.1 P-Waves
➢P-waves are shortened from primary waves, and they are also called
longitudinal waves or dilatational waves. P-waves involve no rotation
travel with a wave velocity
.

1.2 S – Waves
➢ S-waves are shortened from secondary waves, often called shear
waves or distortional waves. Like P waves equation under three-
dimensional conditions, the velocity cs of S-waves
➢Remember that an S-wave can
travel in solids, but not in gases
and liquids such as water.

2) Surface Waves
➢ Surface waves include Rayleigh waves, Love waves, and Stoneley waves.
2.1 Rayleigh Waves
➢ Rayleigh waves, predicted by Rayleigh, are one type of surface wave
generated by the interaction of P- and S-waves on a free surface.
2.2 Love Waves
➢Love waves are predicted by Love mathematically, and they are observed
when there is a low-velocity layer overlying a high-velocity layer. Love
waves induce horizontal movement of the earth during an earthquake and
travel with a slower velocity than P- or S-waves, but faster than Rayleigh
waves.
2.3 Stoneley Waves
➢Stoneley waves were discovered by Stoneley and they propagate along a
solid–solid interface. A Stoneley wave is a high amplitude surface wave
with maximum amplitude at the interface. The amplitude then decreases
exponentially away from the interface.

Stress Waves from Rock Blasting
➢When rock blasting occurs under a surface, blasting causes two body
waves—a P-wave and an S-wave. When both waves obliquely
propagate to the free surface, as shown in Figure, at least four waves
are caused:
(1) a reflected P-wave (PP-wave) due to the incident P-wave;
(2) a reflected S-wave (SP-wave) due to the incident P-wave;
(3) a reflected P-wave (PS-wave) due to the incident S-wave;
(4) a reflected S-wave (SS-wave) due to the incident S-wave; and
(5) the Rayleigh waves. If the surface has two layers of media, Love
waves or Stoneley waves may be induced.

Abazar M. A. Daoud, Engineering Geology Department, Faculty
of Earth Sciences, RSU

2/ Rock Fracture and Rock Strength
Rocks:
➢ There are three types of rocks: igneous rock, metamorphic rock, and
sedimentary rock. These three rocks are formed by magmatism,
metamorphism, and sedimentation, respectively.
➢ Most sedimentary and metamorphic rocks are considered to be of
anisotropy in their physical and mechanic properties due to marked
bedding structure.
➢ The term anisotropy refers to a measure of the directional properties
of a material. However, some sedimentary rocks such as sandstone and
limestone can be considered to be isotropy.

➢In general, the physical and mechanical properties in the horizontal
direction to a bedding plane are largely different from those in the
vertical direction to the bedding plane.
➢ The cement or matrix between grains often determines the
mechanical properties of sedimentary rocks.
➢ The sedimentary rocks containing clay minerals are especially
sensitive to pressure and water. Therefore, water can cause a big
problem in the stability of a tunnel or an underground structure that is
surrounded by sedimentary rock containing some clay minerals.

Fundamental Characteristics of Rocks
➢In general, rock refers to either a small piece of rock such as a sample
for laboratory tests or a large-scale body in rock engineering. The rock
in the latter is usually called rock mass in which joints, faults, in situ
stresses, water, and so on are concerned.
➢ The fundamental characteristics of rocks can be concluded as
follows:
1. Compound of Multi-Mineral Grains ???
2. Grain Boundaries ???
3. Discontinuity ???
4. Porosity ???
5. Brittleness ???

Abazar M. A. Daoud, Engineering Geology Department, Faculty of Earth Sciences,
RSU

Effect of Geological Structures on Rock
Fracture
➢ Geological structures include faults, joints, bedding planes, and other
discontinuities in rocks. Here we mainly describe the effects of joints,
faults, and bedding planes on rock fracture.

(A) Effect of geological structures on rock fracture. (a) Structure and
fracture; (b) beddings and fractured surfaces by blast.

(B) Effect of geological structures on blasting. (a) Incomplete breakage
in parts of holes; (b) cracks stopped by structure/original interfaces in
the rock mass.

Moving Geological Structures
➢ In rock engineering, a discontinuity such as a fault may move during
engineering operations. Figure (a) shows a moving fault during
underground mining operation.
➢A moved fault and sheared boreholes
(a) A fault was found in drift AL 992-499
when production was close to it;
the photographs were taken on Jan.
18, 2012.
(b) A typical shearing in a borehole
was photographed in the same drift as in
(a) on Feb. 20, 2012.

ROCK STRENGTH
➢ The strength of a rock is its ability to withstand an applied stress
without complete failure. The most common strengths of rock are
compressive strength, tensile strength, and shear strength. these
strengths are defined as:
➢ Where Fc and Ft are the compressive force, tensile force, and shear
force, respectively, acting on the rock samples when they are failed. A
is the cross-sectional area of the samples.

Compressive strength (a), tensile strength (b), and
shear strength (c) of rock under uniaxial loading.

Rock Fracture in Engineering
➢ Various kinds of rock failure in rock engineering originate from one or
more cracks in either micro-scale or macroscale. For example:
a. in rock drilling, the rock beneath a drill bit is broken due to the initiation
and extension of several cracks;
b. in rock blasting, the rock mass is shattered into fragments because of the
propagation of many cracks;
c. in rock slope engineering, the failure of a slope is often caused by the
unstable extension of a crack such as a fault or a weak zone;
d. in tunnelling, rock failure in the roofs and walls is induced by crack
propagation; and
e. in underground mining, a hanging wall failure, a rock burst or a seismic
event, and a rock fall are all related to the extension of one or multiple cracks.

3/ Rock Drilling and Boring
➢ Rock drilling is used to drill holes for charging explosives in
blasting; for bolting in rock support; for extracting petroleum, shale
gases, and natural gases; for taking out cores; for producing building
stones; for making a slot to reduce vibrations; for water drainage in
rock mass; for monitoring the deformation and fracture in rock mass;
and for storing CO2 in underground rock mass.
➢ Rock boring is employed to make a tunnel for transportation, to bore
a raise for ventilation and an ore pass in underground mines, and to
bore a big hole for nuclear waste depository.

➢The systems of rock drilling that have been developed and classified
according to their order of present-day applicability are:
- Mechanical: Percussion, rotary, rotary-percussion.
- Thermal: Flame, plasma, hot fluid, Freezing.
- Hydraulic: Jet, erosion, cavitation.
- Sonic: High frequency vibration.
- Chemical: micro-blast, dissolution.
- Electrical: Electric arc, magnetic induction.
- Seismic: Laser ray.
- Nuclear: Fusion, fission.

➢ The main components of a drilling system of this type are:
I. the drilling rig which is the source of mechanical energy,
II. the drill steel which is the means of transmitting that energy,
III. the bit which is the tool that exercises that energy upon the rock, and
IV. the flushing air that cleans out and evacuates the drilling cuttings
and waste produced.

TYPES OF DRILLING OPERATIONS
USED IN ROCK BREAKAGE
➢1) Manual drilling: This is carried out with light equipment that is
hand held by the drillers. It is used in small operations where, due to
the size, other machinery cannot be used or its cost is not justified.
➢2) Mechanized drilling: The drilling equipment is mounted upon rigs
with which the operator can control all drilling parameters from a
comfortable position. These structures or chasis can themselves be
mounted on wheels or tracks and either be self-propelled or towable.

➢On the other hand, the types of work, in surface as well as in underground
operations, can be classified in the following groups:
➢- Bench drilling: This is the best method for rock blasting as a free face is available for
the projection of material and it allows work to be systemized. It is used in surface
projects as well as in underground operations, usually with vertical blast holes, although
horizontal holes can be drilled on occasion.
➢- Drilling for drifting and tunnelling: An initial cavity or cut must be opened towards
which the rest of the fragmented rock from the other charges is directed.
➢- Production drilling: This term is used in mining operations, fundamentally
underground, to describe the labors of ore extraction.
➢- Drilling for raises: In many underground and civil engineering projects it is necessary
to open raises.
➢- Drilling rocks with overburden: The drilling of rock masses which are covered with
beds of unconsolidated materials calls for special drilling methods with casing. This
method is also used in underwater operations.
➢- Rock supports: In many underground operations and sometimes in surface ones it is
necessary to support the rocks by means of bolting or cementing cables, in which drilling
is the first phase.

FIELDS OF APPLICATION FOR THE
DIFFERENT DRILLING METHODS
➢ The two most used mechanical drilling methods are rotary-percussion
and rotary.
a. Rotary-percussive methods: These are the most frequently used in
all types of rocks, the top hammer (TH) as well as the down-the-hole
hammer (DTH).
b. Rotary methods: These are subdivided into two groups, depending
upon if the penetration is carried out by crushing, with tricones or by cut
with drag bits. The first system is used in medium to hard rocks, and the
second in soft rocks.

1/ Percussive Drilling:
➢Percussive drilling, also called rotary-percussive drilling, is designed to
break rock mainly by impact energy. There are two types of percussive
drilling: top-hammer (TH) and down-the-hole (DTH).
➢The top-hammer drill rig is often used to drill small holes (diameter is often
smaller than 127 mm) in hard rocks. When boreholes are larger and long,
the top-hammer drilling becomes inefficient. In this case, the DTH
percussive drilling is employed instead. A DTH drill rig with a diameter
smaller than 127 mm can also be efficient in hard rock drilling.
➢A difference between the top-hammer and the DTH drill rigs is the energy
transmission. When top hammer is used to drill a very long borehole, the
loss of impact-caused stress wave energy will increase, especially at the
interfaces between any two drill rods. Therefore, a top-hammer drill rig may
not be energy efficient in drilling a very long hole.

Diagrams for top-hammer drilling (left) and DTH drilling
(right).

A hydraulic drill rig is composed basically of the same elements as the
pneumatic ones. In a hydraulic system, Hydraulic oil, a more efficient
medium than air, is used instead of compressed air as an energy-transmission
medium. The hydraulic oil is pumped around the circuits by gear or piston
pumps, driven by a diesel engine or an electric power pack.
Hydraulic drilling has the following advantages over pneumatic drilling:
(1) lower energy consumption,
(2) lower drilling accessory costs,
(3) greater drilling capacity,
(4) better environmental conditions such as lower noise,
(5) more operative flexibility, and
(6) easier to automatize. Because of these advantages, more and more
pneumatic drill rigs have been replaced by hydraulic ones.

2/ Rotary Drilling:
Rotary drilling is mostly used to drill big holes in large quarries, open
pit mines, petroleum extraction, and other fields.
➢ There are two groups of big rotary drilling:
(1) rotary crushing by high-point loading to the rock from three cones
Fig. (a).
(2) rotary cutting by shear force from drag bits Fig. (b)
The rotary cutting can be also used to drill small boreholes in soft rocks.
For example, rotary drilling is often used to drill small holes down to 25
mm in diameter to install bolts in coal mines. The rotary crushing is
used in medium to hard rocks, and the rotary cutting in soft rocks.

3/ Rock Boring:
Rock boring can be divided into two groups:
(1) raise boring machine, and
(2) ordinary boring machine, including a tunnel boring machine (TBM)
and big hole boring machine.
The basic systems of these boring machines are similar. Two key parts
for rock boring are the cutter head and the cutters, that is, the rock is
broken by the cutters in the cutter head.
The boring machine drives the cutter head to rotate in the big hole or
tunnel, while all the cutters rotate themselves surrounding their own
shafts. The rock beneath each cutter is broken. This mechanism for rock
breakage is similar to that in the rotary crushing.

A TBM machine is often used to make a long and relatively straight
tunnel. In this case, the TBM tunnelling is efficient. If the tunnel is not
long, or it is much curved, the TBM tunnelling will not be efficient or
economic. More and more TBM machines are used to make tunnels for
highways, railways, gas and water transportation, and nuclear waste
depository. The present boring machines can break not only soft rocks
but also hard ones.
The small-scale boring machines are
used in more and more projects for
boring big holes in hard rocks.
For example, boring machines have been
successfully applied to make open cuts in
underground mining.

➢Raise boring is used to make ore passes or big holes for other uses.
The advantages of raise boring are good safety, higher productivity,
smooth walls, and higher advance output, while the disadvantages are
high investment, high excavation cost per lineal meter, low flexibility,
and much preparation work. In raise boring, a pilot hole is drilled first,
and then the reamer (or the cutter head) of a raise machine is
connected to the end of the drill string/pipe. The reamer works
upward.
➢The mechanism of rock breakage in the raise boring is similar to that
in either rotary crushing or rock boring. A notable advantage of the
raise boring is that the discharge of cuttings is very easy since the
cuttings fall down by themselves due to the gravity.

➢ Diagram of raise boring machine 1/ drilling pilot hole down; 2/
attaching reamer; 3/ drill string; 4/ pilot bit; 5/ reaming up; 6/ reamer.

➢ There are two differences between percussive drilling and rotary
drilling:
(1) Rock is loaded by stress waves in percussive drilling but by
quasistatic loading in rotary drilling.
(2) The rotation of the drill bit is mainly to change impact positions in
percussive drilling, so in general the rotation does not play much of a
role in rock breakage. However, the rotation of the drill bit plays an
important role in rotary drilling.
➢ OPERATIONAL SKILLS:
1. Choosing Drilling Methods and Drill Hole Sizes
2. Drilling Speed and Drill Bit Reshaping
3. Correct Operation

4/ Explosives and Detonators
➢ Explosives are the materials that can rapidly decompose chemically,
produce an extremely high pressure, and release a huge amount of
energy at a moment. This part of course will mainly introduce two
widely used commercial explosives: emulsion and ammonium
nitrate/fuel oil (ANFO).
➢CATEGORIES OF EXPLOSIVES:
There are different methods to classify explosives. One simple method
is to separate explosives into three groups:
(1) primary explosives, (2) secondary explosives, and (3) tertiary
explosives.

1. Primary Explosives
➢ The primary explosives are able to transit from surface burning to
detonation within very small distances. Primary explosives are very
sensitive to impact and friction, so they are easily ignited. Therefore,
primary explosives are mainly used in detonators. The examples of primary
explosives are mercury fulminate, silver azide, and lead azide. Lead azide is
the most common initiative explosive used in detonators. It has excellent
thermal stability up to 250°C.
2. Secondary Explosives
➢ The secondary explosives can also burn to detonation, but only in relatively
large quantities. For safety reasons, most secondary explosives are not
considered to be safe in charging boreholes directly. The examples of
secondary explosives are nitroglycerin (NG), nitromethane (NM),
pentaerythritol tetranitrate (PETN), and trinitrotoluene (TNT).

3. Tertiary Explosives
➢The tertiary explosives, under normal conditions, are very difficult to
explode and are officially classed as nonexplosives provided that certain
conditions are observed. The most common tertiary explosive is ammonium
nitrate (AN). Most AN- based commercial explosives such as ANFO,
emulsions, and water gels belong to tertiary explosives.
➢ Industrial explosives can also be divided into two groups:
(1) blasting agents and
(2) conventional explosives.
➢ The most common blasting explosives are ANFO, slurries or water gels,
emulsions, and heavy ANFO.
➢ Conventional explosives are gelatin dynamites, granular dynamites, and
permissible explosives. In the following we will briefly introduce AN, water
gels, and dynamite that are also used in rock blasting, besides ANFO and
emulsion explosives. Since ANFO and emulsion explosives are dominant in
the current industry, we will introduce them separately.

4. Ammonium Nitrate
AN is a white inorganic salt with a melting point of 161°C. AN by itself
is not an explosive. When mixed with a fuel, however, it becomes a
powerful explosive. Because of this, AN is an essential ingredient in
nearly all commercial explosives. In the manufacturing of explosives,
AN is used in the form of small porous spherical prills.
* The main characteristics of AN can be concluded:
(1) greatly soluble in water;
(2) easy to become liquid in the air with a humidity above 60%;
(3) very stable at atmosphere temperature, but may detonate if heated
above 200°C in a closed recipient; and
(4) sensitive to organic compounds which accelerate the decomposition
and lower the temperature at which this is produced.

5. Water Gels or Slurries
The water gels or slurries explosives were produced as early as in the 1950s.
Before the emulsion explosives came into being, the water gels explosives
were often used to replace dynamites. Water gels have the following
characteristics:
(1) fluid and pumpable;
(2) less toxic and less hazardous than dynamite to manufacture, transport, and
store;
(3) dimensionally stable and water resistant, but the water resistance can
significantly decrease if the explosives are not used in the proper manner;
(4) sensitive to conventional priming methods, but more resistant than
dynamite to accidental initiation;
(5) detonator-sensitive in some applications but detonator-insensitive in
others.

6. Dynamite
Dynamite is an explosive material based on NG. Dynamite was invented
by Alfred Nobel in 1867. The classical dynamite explosives are not very
safe since they contain much NG. NG by itself is a very strong
explosive, and in its pure form it is extremely shock-sensitive and
degrades over time to even more unstable forms. This makes it quite
dangerous to transport or use in its pure form. But modern dynamites
are much safer since they do not contain much NG. Dynamite
explosives are detonator sensitive and they are often used to make a
primer together with a detonator. Dynamites are usually sold in the form
of a cartridge.

(1) ANFO EXPLOSIVES
ANFO and emulsion explosives are now the most widely used explosives all over the world. ANFO is
composed of approximately 94% AN and 6% fuel oil by weight.
The main characteristics of ANFO are as follows:
(1) ANFO is detonator- insensitive, so it must be initiated by a primer.
(2) ANFO consists of distinct fuel and oxidizer phases and requires confinement for efficient detonation.
(3) ANFO has a density smaller than 1.0 g/cm3, and it has bad water resistance.
(4) The VOD of ANFO increases with an increasing charge diameter, so ANFO is suitable for large
boreholes.
(5) The VOD of ANFO is much lower than that of emulsions.
(6) The critical diameter of ANFO is influenced by its confinement and charge density and is much greater
than that of emulsions.
(7) ANFO is good in gas production during detonation.
(8) All ANFO products generate a relatively low detonation pressure.

(2) EMULSION EXPLOSIVES
Since the critical diameter of emulsion explosives is much smaller than
that of ANFO, emulsions dominate underground blasting. Emulsion
explosives are compounds of very small drops of AN solution and other
oxygen suppliers that are located close to a surrounding mixture of
mineral oil and wax. Oil/wax mixture as a fuel obtains a large contact
surface with an oxygen supplier, AN solution.
The difference between emulsion explosives and other types of fluid or
plastic explosives is that the latter can be initiated without adding
another sensitive explosive.

* The main characteristics of an emulsion explosive can be listed as follows:
(1) It can well hold its packing and pumping properties stable over a wide range of
temperatures from −20°C to +35°C. This makes its detonation properties kept constant even
after long time storage.
(2) It has much smaller critical diameter than ANFO.
(3) It has a greater resistance to initiation by impact than either water gels or dynamites.
However, if the emulsion is contaminated with foreign materials such as detonators, it may
detonate. An emulsion cartridge is a detonator sensitive explosive.
(4) Its VOD is very high, usually greater than 5000 m/s. (5) It has a relatively high
detonation pressure.
(6) In general, the lower the density of an emulsion is, the more sensitive it becomes. In
addition, the lower the water content of the emulsion is, the more sensitive it becomes.
(7) It is extremely water resistant and suitable for wet holes in underground mines. It may
perform successfully after sleeping underwater for months.
(8) It is a highly efficient explosive mainly due to the microscopic particle size. For
example, the explosive efficiency of an emulsion can be up to 93%, but that of water gels is
55–70%.

(3) ANFO–Emulsion Mixtures
One of the most significant improvements on basic ANFO is the
development of emulsion–ANFO mixtures which are often called heavy
ANFO. Various ratios of emulsion to ANFO change the physical and
explosive properties of ANFO. The heavy ANFO has the following
advantages: Its density and explosive energy are increased; it can be
water resistant and pumpable if the ratio is correct; it has a higher VOD
than ANFO; and it is cheaper than emulsion, although it is more
expensive than ANFO. Because of these advantages, the heavy ANFO is
widely used in engineering blasting all over the world.

(4) Low-Density Explosives
Low-density explosives are often used to reduce overbreak, increase
slope stability, improve safety, and reduce overall costs in wall control,
especially when the rock is soft or in situ fragmented. In general, low-
density explosives are the result of mixing ANFO or emulsions with
diluting or bulking agents. These bulking agents include products like
sawdust, bagasse, rice hulls, and others. The density of a low-density
explosive such as LDRA and PANFO can be down to 0.2 g/cm3 and its
VOD to 1400m/s.

➢ Detonator tubes out of blast holes in a sublevel ring. (B): A
primer with a detonator tube and a detonating cord. The tube and
the cord are connected by a single knot and a black belt. Both the
single knot and the belt are bad connections and they should not
be used. The correct connection between the tube and the
detonating cord should be made by a double knot as shown in next
figure.

➢ Double knot between two wires such as a detonating cord and a
detonator tube. Two (correct) double knots: (a) and (b).

DETONATORS
➢ When William Bickford invented the black powder fuse in 1831, the
initiation of black powder in rock blasting became safer. Alfred Nobel’s
invention of the mercury fulminate detonators in 1867 provided a safer and
more efficient initiation tool for nitroglycerine and dynamite explosives. In
modern blasting, the initiation of an explosive charge is mainly made by a
detonator or a primer.
➢ Various types of detonators used in present rock blasting can be divided
into three types:
➢(1) electric detonators,
➢(2) nonelectric detonators,
➢(3) electronic detonators.

1. Electric Detonators
An electric detonator initiates an explosive charge by a current passing through a
bridge wire, which is surrounded by a pyrotechnic charge. A delay electric detonator
includes a delay element (powder). The delay time is based on the length and
composition of the delay powder.
* The main advantages of an electric detonator are:
(1) circuit testing, which can reduce misfires caused by a wrong connection between
detonators and a firing system, and
(2) availability in coal mines.
* The disadvantages of an electric detonator are:
(1) risk of premature detonation;
(2) extraneous sources of electricity such as lightning, static electricity, stray
currents, and radio frequency energy; and
(3) inaccurate initiation time like nonelectric detonators.
Electric detonators have different delay times such as 25, 500, and 0 which means
the delay time is zero. The zerodelay- time detonators are often used in boulder
blasting.

2. Nonelectric Detonators
A nonelectric detonator is initiated by a signal conductor or a detonating
cord of low energy type, as shown in (b). The detonator can be
manufactured both with and without delay.
* The advantages of nonelectric detonators are noiselessness, still
initiation, down-hole delays, and being safe to use in extraneous
electricity environments.
Their main disadvantages are (1) no circuit testing and (2) inaccurate
initiation time like electric detonators.
3. Electronic Detonator
Electronic detonators were developed in the 1990s. In an electronic
detonator, a computer chip is used to control delay time using electrical
energy stored in one or more capacitors to provide power for a timing
clock and initiation energy.

* The main advantages of an electronic detonator are its high precision
in initiation and its good safety in extraneous electricity environments.
The initiation errors of an electronic detonator can be controlled within
±0.01% of the programmed delay time, which can never be achieved in
any other types of detonators. Electronic detonators provide a necessary
condition for realizing an efficient stress superposition from
neighboring blast holes. The delay time is in a wide range of time from
1 to 16,000 ms.
* Nowadays the major disadvantage of the electronic detonator is that
its price is much higher than other types of detonators, but this will be
changed sooner or later.

4. Detonating Cord
In addition to the three types of detonators, detonating cord can be taken as a
flexible and continuous detonator. In modern detonating cords, PETN cotton
core is surrounded by various textile combinations, plastics, and
waterproofing materials, with a burning speed in excess of 7000 m/s.
* The main advantages of detonating cord are it is versatile, inexpensive, and
safe for use in extraneous electricity environments. For example, in boulder
blasting, detonating cord is convenient, simple, and cheap.
* The disadvantages of detonating cord are noisy initiation, large amount of
cord movement, and disruption to stemming column when down the hole.
Detonating cord can initiate most commercial high explosives such as
dynamite, but not initiate less sensitive explosive agents such as ANFO. In a
long hole blasting aiming at good fragmentation, if the explosive is charged
into the hole together with a detonating cord which is used to initiate the
primer, the detonating cord should be one kind of low energy so as to avoid
initiating the explosive charge.

Basic structures of three types of detonators. (a) Electric detonator,
(b) nonelectric detonator, and (c) electronic detonator

SAFETY IN CHARGING OPERATION
➢ On the safety of explosives in storage and transportation, the books
on explosives engineering and instructions from explosives
manufacturers are recommended reading. Here we will only describe
safety dealing with the operation of rock blasting.
➢ In any case of using and storing explosives, overheating and
accidental fire should be avoided. Generally, blasting produces
harmful gases such as carbon monoxide, nitrogen oxide, and
nitroglycerine vapor, although the gases from modern water-based
explosives are relatively harmless. After a blast happens underground,
one has to ensure that no harmful gases remain when going to the blast
site. To do so, a gas meter can be carried.

➢ In a charging operation, all steel or other metallic tools that may
directly contact and force into explosives are not allowed. In a well-
controlled mechanical charge operation, for example, by pumping
emulsion explosives into boreholes, the feed speed should be well
controlled.
➢ About safe use of detonators, the initiation of various types of
detonators is sensitive to heat, shock, and impact, so any action which
may cause heat, shock, and impact to detonators is forbidden. Since
electric detonators are designed to be initiated by a pulse of electrical
energy, they may also be fired by extraneous electricity such as stray
currents, static electricity, radio frequency energy, electrical storms,
and high-voltage power lines. In addition, it is not allowed to tramp on
a detonator and its tube or wires.

➢ With increasing depth in underground mining, there will be more
rock bursts and seismic events and they will probably be stronger.
Therefore, the safety for miners in the charging operation faces serious
challenges. To have good safety, an automatic charging operation or
remote control in the charging operation is a necessity in the near
future.

ROCK FRAGMENTATION
➢ Rock fragmentation is a consequence of unstable extension of
multiple cracks. Theoretically, rock fragmentation is also a facture
mechanics problem.
➢ Two major differences between rock fracture and rock fragmentation
are:
(1) rock fragmentation deals with many cracks, but rock fracture deals
with only one or a few, and
(2) rock fragmentation concerns the size distribution of the fragments
produced, but rock fracture does not.

➢ Due to many cracks dealt with, rock fragmentation is a very complicated
and difficult fracture problem. To achieve a good fragmentation, we need to
know how the energy is distributed, which factors influence energy
distribution, what is the size distribution.
➢ FACTORS INFLUENCING FRAGMENTATION
In order to improve fragmentation, first we have to know which factors
influence fragmentation. Factors influencing rock fragmentation can be
separated into the following groups:
l/ Explosives:
The following factors influence rock fragmentation:
1. Explosive energy and energy efficiency; 2. Velocity of detonation (VOD);
3. Density; 4. Coupling ratio in charge (full charge or decoupled charge);
5. Specific charge or powder factor; 6. Match between explosive and rock.

2/ Initiators:
Initiators can be either a primer containing a detonator or just a detonator. The
following factors concerning initiators influence rock fragmentation:
1. Quality and type of detonators; 2. Detonator placement;
3. Precision of initiation of detonators; 4. Connection between detonator tube
and detonating cord in a pyrotechnic initiation system.
3/ Rocks:
The following are the main parameters of a rock mass that affect
fragmentation:
1. Density; 2. Sonic velocity;
3. Strengths and fracture toughness; 4. Geological structures such as joints;
5. Local stress field and confinement; 6. Match for explosive.

4/ Drilling plan:
A drilling plan mainly consists of the following parameters that
influence fragmentation:
1. Diameter of blast hole; 2. Length of blast hole;
3. Burden; 4. Spacing; 5. Sub drilling; 6. Quantity of rows (rings) in a
blast.
5/ Blast plan:
A blast plan consists of charge plan and initiation plan. The main factors
concerning a blast plan are in the following:
1. Stemming (materials and sizes); 2. Primer placement;
3. Length of charge; 4. Deck charge and air deck; 5. Free surface;
6. Initiation sequence; 7. Delay time.

Burden and Spacing
1. ANGLE OF BREAKAGE
In Figure this region is the rock
mass between the face BCKJ and
the first hole. The angle 2Ө in
the diagram is called the angle
of breakage of the first hole.

2. SPECIFIC CHARGE
Specific charge q, also called powder factor, is defined as the explosive
consumption (planned or actual) of per cubic meter or per metric ton of
rock; that is,

1) The specific charge defined is an average value of explosive
consumption in the rock to be blasted. In this sense, the specific charge
is a simple parameter representing the capacity of the energy applied to
the rock.
In reality, it is easy to use. However, note that the explosive energy is
used not only in the rock included in Vr or Wr but also in the remained
rock mass which is not completely fragmented.
(2) Specific charge is not a parameter good enough to represent the
actual stress and energy distribution in the rock to be fragmented since
the actual stress and energy distribution is far from even. For example, a
greater specific charge may not always result in a better blast result such
as better fragmentation if the blast design is not reasonable.

3. DIAMETER OF BLASTHOLES
Up to the present day, the diameter of a blasthole has been determined
empirically since there is no theoretical method available.
In this case, in order to choose the diameter more scientifically, we need
consider the main factors which are relevant to the diameter of
blasthole, as follows:
1. Velocity of Detonation (VOD)
2. Quality of Rock Drilling
3. Production and Productivity
4. Fragmentation
5. Cost of Development
6. Back Break

BURDEN
1. Factors Related to Burden
1.1 Diameter of Blasthole
In general, a large burden requires a large borehole, whereas a small burden needs a
small hole if the borehole is fully charged.
1.2 Decoupled Charge
In mining production blasts, boreholes are usually fully charged. In some special
cases such as when water is in boreholes, a cartridge charge (ie, decoupled charge)
is often used. If the diameters of boreholes are the same, the boreholes with a
decoupled charge require a smaller burden than the boreholes with a full charge.
1.3 Rock Properties
Rock properties, particularly the tensile strength and fracture toughness of rock, are
major factors that influence the behaviour of rock fracture and fragmentation. The
rock with lower fracture toughness or lower tensile strength is more easily broken
than that with greater toughness or greater tensile strength.

1.4 Explosive
The relation between burden and blasthole diameter is affected by the explosive.
The investigation indicated that, compared to ANFO, dynamite and emulsion were
able to blast a much larger burden. This is because these two explosives can produce
a much higher borehole pressure than the ANFO. specific charge can partly
represent the average energy used in rock fracture and fragmentation.
1.6 Wave Attenuation
Stress Waves, the attenuation of stress waves in rocks is very large in either one- or
three-dimensional condition. Under three-dimensional condition, the total wave
attenuation includes geometrical attenuation and other forms of attenuation such as
the attenuation caused by heating and friction between mineral grains. The total
attenuation increases with an increasing distance from the blasthole.
1.7 Fragmentation
The burden has a strong impact on fragmentation. In general, a small burden is
favourable to rock fragmentation, compared with a large burden. In other words,
under otherwise identical blast conditions much larger fragments will be produced
for a larger burden according to the experimental investigation.

1.8 Production and Productivity
A large burden usually corresponds to a large-scale production and a greater
productivity if the rock fragmentation with the large burden does not become
worse. However, when the burden is increased but fragmentation becomes
worse, the production and productivity may decrease. Therefore, in order to
have a large production and high productivity, fragmentation must be very
good. To achieve a good fragmentation, the burden should be a proper size
rather than too large or too small.
1.9 Vibrations
Compared with a small burden, a large burden causes higher ground
vibrations. This will be discussed in chapter: Reduction of Ground Vibrations.
Therefore, if the ground vibrations must be controlled, the burden should be
reduced. In addition to the aforementioned factors, other factors such as
burden velocity and back break are also related to the burden. In principle, all
these factors should be considered when a burden is chosen.

Safety in Rock Engineering
➢ Nothing is more valuable than human life. Therefore, Safety First is usually
the watchword of an engineering enterprise.
➢ In quarries, open pit mines, and underground mines, many safety problems
are related to rock blasting either directly or indirectly. Considering this fact,
we will discuss various safety problems connected to rock fracture in the
mining industry in this section. These problems are:
1) rock spalling,
2) remained roofs,
3) seismic events,
4) rock burst,
5) rock fall,
6) shock damage,
7) slope failure,
8) fly rocks, and
9) air blast.

➢Spalling in Tunnel Surfaces
Spalling in the surfaces of tunnels is one of the most common types of
rock failure occurring in mining blasts, and it undermines safety in
underground mines. Spalling happens mostly near a blast place but
sometimes it appears far from the blast place. Spalling is related to
several factors such as
I. primer placement,
II. initiation sequence,
III. charge plan.
IV. In order to reduce and avoid spalling, primer placement, initiation
sequence, and charge plan must be correct.

➢Remained Roof
A remained roof is another kind of safety problem in underground mining,
particularly in sublevel caving. Most remained roof problems are caused by
one or more failed blasts. Remained roofs can be successfully destroyed by
means of special blasting. The method does not require much extra cost. In
addition, it can avoid a big ore loss.
➢Seismic Events
Seismic events in underground mines are all caused by mining activity since
it is the mining activity that makes the whole stress field underground vary all
the time. Many seismic events happen in hanging walls, and others occur in
foot walls and ore bodies. In many cases, seismic events are initiated by a
blast, particularly by a massive or large-scale blast in an underground mine.
Therefore, seismic events can be reduced or lowered by making a correct
blasting and mining plan.

➢Rock Fall
Rock fall in underground mines sometimes happens during blasting, but in
many cases it does not immediately follow a blast. In both situations the
blast-induced disturbed zone surrounding a drift or a tunnel plays an
important role. In consequence, in order to reduce rock fall, it is necessary to
reduce the disturbed zone by improving blasting. Furthermore, correct mining
planning and sufficient rock support are needed.
➢Brow Damage
Brow damage is a common phenomenon in sublevel caving, and it is one of
the main types of safety problems in this mining method. Brow damage can
be effectively reduced by applying shock and stress wave theories.
➢Air Shock Damage
Air shock damage can be caused by either the collapse of a large roof or a
shock wave collision in drifts. The latter happens when two or more blasts are
initiated instantaneously and from nearby drifts. In this sense, such a shock
wave collision can be avoided by using proper blast operation.

➢Slope Collapse
Slope collapse in open pit mines is either related or not related to rock
blasting. In any case, however, the regular production blasts are a cyclic
impact loading to the slope, making the rock mass weaken gradually.
Moreover, the blast-induced disturbed zone in the slope undermines the
quality of the slope. As a consequence, it is necessary to consider these
in all blasts in open pit mines.
➢Fly Rock, Air Blast, and Rock Burst
Fly rock and air blast sometimes occur in open pit blasts, and they are
usually caused by improper blast design and incorrect stemming. Rock
burst does not often have a direct relation to blasting, but sometimes it
does. For example, a strong rock burst can happen immediately when a
massive blast occurs.

Rock Drilling and Blasting LECTURES - NN.pdf

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