Blasting News VOLUME 25 ISSUE 2 2016
IN THIS ISSUE • Equipping Explosives Engineers and Technical Representatives at WEETR (Workshop for Explosives Engineers and Technical Representatives) • AEL expands South American base • Check twice, blast once: The importance of blasthole monitoring
Printed on 100% eco friendly paper
Editor’s Note Welcome to our bumper edition of Blasting News covering our activities for the second quarter of 2016. In this issue we focus on latest innovative technologies and products in our quest to remain relevant to the market we serve.
CONTENTS 3
AEL CAPTAINS OF INDUSTRY: Meet Denvor Govender
4
AEL KNOWLEDGE SHARING: Equipping Explosives Engineers and Technical Representatives at WEETR (Workshop for Explosives Engineers and Technical Representatives)
8
AEL INTERNATIONAL: AEL expands South American base
10 AEL TECHNICAL CAPABILITY: Check twice, blast once: The importance of blasthole monitoring 14 AEL THOUGHT LEADERSHIP: EXPLOSIVES TODAY 17 18 AEL IN THE FIELD: AECI showcases at Expomin 2016 19 AEL PAYING IT FORWARD: AEL partners with Northam Rhinos
In our captains of industry section, we introduce you to another member of our Executive Committee, recently appointed Denvor Govender, Executive: Supply Chain. Govender heads AEL’s streamlined supply chain which offers on-time, in-full delivery to all our customers throughout our global footprint. Under our thought leadership banner, we present the latest instalment of Explosives Today, our technically-driven customer publication, used as vital reference by personnel concerned with safe and efficient blasting around the world. This issue focuses on blasthole drilling and initiation patterns in surface blasting. This technically driven customer publication authored and tailored by our Mining Optimisation team is also available to customers in the form of an A4 folder equipped with a CD and flash drive containing all issues of the publication. To order a copy email Simon.Tose@aelms.com Our knowledge sharing segment, offers insight from our internal Workshop for Explosive Engineers and Technical Representatives which is structured to equip our frontline to provide you with information on our latest featured products and services. On the international front, General Manager for business development in South America, Alois Kwenda enlightens you about the expansion of our global footprint within Latin America. As an international player we demonstrate our support to various markets with our presence at key industry events such as Expomin 2016 where we showcase our trail-blazing innovations and superior service offerings to existing and potential partners and customers. Under our technical capability section, we profile Mining Engineer, Manare Mokoatlo’s work on the importance of blasthole monitoring which she presented at the annual Institute of Quarrying conference in April this year, helping to empower fellow engineers with invaluable insights. This is one example of how our product and service innovation results in purposeful delivery to our customers. To subscribe to Blasting News please visit our website www.aelminingservices.com and fill in the subscription form located under the Publications tab. Enjoy your read!
Eubulus Pillay Cover image: Mirny, Sakha Republic, Russia
Contact Details: Eubulus Pillay - Editor I Tel: +27 11 606 0313 eubulus.pillay@aelms.com I www.aelminingservices.com
Disclaimer This publication does not necessarily reflect the views and opinions of AEL Mining Services Limited management. The copyright to this publication rests in AEL Mining Services Limited. Other product and corporate names used in this publication may be trademarks or registered trademarks of other companies, and are used only for explanation and to the owner’s benefit, without intent to infringe.
2
Blasting News I Second Quarter 2016
CAPTAINS OF INDUSTRY
Meet Denvor Govender Denvor is Executive: Supply Chain. Role: Responsible for AEL’s Global Supply Chain portfolio. Supply Chain is a strategic and integral portfolio that interacts with all stakeholders across the organisation. Product availability is key to customer satisfaction and this requires specialist knowledge in sales and operations planning, warehousing and multimodal logistics. Desmond provides the leadership required for a sustainable and innovative supply chain that is world class. Professional background: Denvor joined AEL in 2014 as Global Supply Chain Manager. With over 22 years of work experience in Global Supply Chain, International Logistics and Global Trade, he has worked at some of the largest multinationals. Denvor holds a BCom degree in Supply Chain Management and post-graduate qualifications in Business Management and Procurement & Supply Chain. He completed an EDP- Strategic Leadership at the University of Cape Town and the AECI SMDP at GIBS Business School. Denvor is also a Certified International Supply Chain Professional (IPSMI) and holds a MBB in Lean Six Sigma (Japan).
Blasting News I Second Quarter 2016
Denvor Govender
3
AEL KNOWLEDGE SHARING
Equipping Explosives Engineers and Technical Representatives at WEETR (Workshop for Explosives Engineers and Technical Representatives)
AEL’s WEETR presents an opportunity to emphasise our company’s values and the relentless focus on innovation and commitment to staff through sharing insights on the latest technical methods and projects. This year’s theme for WEETR was Simplexity technology made simple, fast precise! Simplexity defines AEL’s capabilities in terms of products and services. We offer simplified solutions which are designed and developed for highly complex mining conditions. OUR VALUES Aligning to AEL values of BIGGER (BOLD, INNOVATIVE, GOING GREEN, ENGAGED and RESPONSIBLE), WEETR focused on Being Innovative.
4
At the helm of AEL’s innovative spirit,
delivered, sensitised for use as:
is our R&D department which plays
•
Emulsion only
a vital role in keeping our global
•
Blended with ANA
operations on the frontier of technology
•
and/or sensitised with ANFO and
with the delivery of ground-breaking
mixed to various ratios
innovations. The R&D team is actively involved in partnering with our Mining
The emulsion’s water resistance is
Optimisation
AEL
excellent up to 40%. Depending on the
engineers to develop products and
team
and
our
doping or blending ratio with ANPP,
solutions, tailored for specific mining
the resistance will deteriorate. The
applications.
typical in-hole density of our emulsions are 1.25g/cm3, but density varies with
SIMPLEXITY
ACHIEVED
THROUGH
depth.
FEATURED PRODUCTS AND SERVICES AT WEETR 2016
The eco-range of emulsions has been developed to optimise blast results
Aligned to our WEETR theme of
delivering value throughout the surface
SIMPLEXITY, our featured range of
mining sector. The substitution of
products and services showcase AEL’s
recycled oil for diesel in the emulsion
cutting edge innovations that aide
results in an environmentally friendly
customers to optimise their operations.
range of products helping to simply
AEL’s simplified mining solutions are
reduce environmental impact.
designed to respond to our customers’ complex mining conditions.
Please contact your regional sales office to find the best product and initiating
EMULSION OFFERINGS
system suited to your application.
Our base emulsions are non-detonable
ELECTRONIC DELAY DETONATORS
with the virgin oil emulsions having a honey coloured appearance and the
AEL,
in
Eco emulsions being brown to black
tech
electronic
conjunction
with
in colour. Base emulsions (S100, S200,
developers, DetNet, have pioneered
and S300) are handled and transported
and spearheaded the development and
as an unsensitised product to mines
production of electronic detonators
and/or operational sites.
since the early 1990s.
The product is sensitised as it is
Electronic initiation systems enable
charged into the blast hole and can be
functions that traditional pyrotechnic
initiating
highsystem
Blasting News I Second Quarter 2016
AEL KNOWLEDGE SHARING
Delegates present at the plenary session
AECI Chief Executive, Mark Dytor, opens the WEETR and highlights AECI Mining Solutions vision for the future
systems lack. Besides
the
immediately
utilise accurate blast timing to optimise
AEL
the outcome of the blasting process.
providing
has
extensive the
experience
electronic
in
detonator
obvious
As a result the downstream mining
solution for your specific mining need
benefits of reduced environmental
processes benefit hugely making the
and can assist in optimising your blast
impacts such as blast induced vibration
entire mining cycle much more cost
designs to enhance value through
and
efficient.
precision blasting.
allows for accurate blast modelling
Leading mining companies across
The AEL range of electronic initiating
and
overpressure
systems
(air
increased
optimisation
blast);
timing of
the
the
control initiation
the globe have come to realise the
systems is safe and robust. All of our
sequence before triggering the blast.
substantial cost benefits which AEL
electronic
This increased functionality affords
electronic detonators provide where
designed
the advanced user the opportunity to
they are applied in this manner.
initiation. The systems use safety keys
Blasting News I Second Quarter 2016
detonator to
systems
eliminate
are
unintended
5
with encrypted codes which ensure that only authorized personnel can initiate the systems. The detonator and control equipment designs are subjected to stringent, internationally recognised safety tests, before release to the market. To cope with the mining industry’s varied mining environments, AEL’s electronic
detonator
extremely
diverse,
systems making
are them
ideal to use in both the simplest and toughest situations. These include tunnelling, shaft sinking, underground stoping and all forms of surface mining environments. CUTTING EDGE BLASTING SCIENCE AND SOFTWARE DEVELOPMENT Our blasting science and software development offers simple solutions by looking at the mining operation holistically to ensure that the benefits
pyrotechnic initiating systems, analysis
AEL’s Active Loading system
are derived from improved efficiency
of the timing sequence, direction of
Enables
in equipment, plant and beneficiation.
movement, scatter, control of ground
pertaining to blasting parameters,
AEL will conduct various checks (listed
vibration and single hole firing
i.e.: condition of blast hole, types
below) to ensure that blasted rock
of
real
explosives
time
loaded,
information
quantity
of
suits and complements the design of
AEL Tunnel
explosives loaded, etc. This information
equipment and plant:
Software to assist with the design and
is stored in a database for future
•
Face velocity measurement
optimisation of tunnel layouts in mining
analysis, comparison and fine tuning of
•
3D blast face survey
and civil applications
blast inputs and results.
•
High speed videography
•
Rock mass motion study
AEL Ring
NEW MARKETING COLLATERAL
•
Muck profile study
Software to assist with the design, basic
•
Fragmentation analysis
timing and optimisation of stope ring
Product catalogue
•
Blast modelling
layouts in mining and civil applications
AEL has continuously demonstrated
•
Efficiency
measurement
and
monitoring This is supported by AEL’s sophisticated
its understanding of the industry’s Hybrid Stress Blasting Model (HSBM)
needs and challenges, as well as the
HSBM is a high level blast modeling
importance of responsibly extracting
research tool
valuable minerals from the earth. To
blasting software:
this end, we are proud to present our AEL Designer (SABREX)
Winprof AEL
Predictive
Survey and Blast layout software
fragmentation damage,
AEL Tie-up Blast timing design for electronic and
6
software
blast
latest product catalogue showcasing modelling,
(Kuz-Ram),
Muckpile
profile
our wide range of ground-breaking
Blast
products and comprehensive range of
(Throw)
services on offer to fulfil our customers’ expectations of streamlining operations and increasing productivity as well as Blasting News I Second Quarter 2016
efficiencies, by optimally conditioning
in underground narrow reef mining
studies. AEL partners with customers
rock for further beneficiation. Access
operations. It has been revised to
in order to add value to their operations.
the electronic version of our catalogue
include new products and to give
We listen, analyse and understand the
at http://catalogue.aelminingservices.
greater emphasis to critical questions.
challenges of the customer and deliver
com/
The handbook is available for download
to the required level of requirement
on our website www.aelminingservices.
using the right product mix, optimised
com under our press office portal.
delivery systems and a team of experts
Stope handbook We have launched our new Stope
that are focused to deliver value.
Blasting Handbook which has been
Case Studies
used with great enthusiasm in mine
The WEETR affords our engineers that
blasting syllabi. This booklet has been
operate out in the field, an opportunity
compiled by AEL Mining Services to
to share their learnings with the front
provide a practical guide for blasting
line through the presentation of case
2016 P ROD CATAL UCT OGUE Versio n3
Stope Blasting Handbook Version 1.1 I 2016
Blasting News I Second Quarter 2016
7
AEL INTERNATIONAL
AEL expands South American base for AEL and its parent company
AEL aims to increase its supply of
explosives and specialty chemicals
electronic blasting systems and bulk
manufacturer AECI, it is important,
explosives to South American markets,
specifically because of the continent’s
particularly those of Brazil and Chile,
stability, its status as a major mining
where safety is the main issue for
destination and the potential for new
customers. Kwenda adds that the
mining projects even under the current
company will also expand its on-site
environment of depressed commodity
technical support to maintain the
prices.
highest safety standards and optimise mining operations for its customers.
He cites the Brazilian mining industry, which
enda w K s i Alo
competitive
“Mining operations are looking for
despite the fall of commodities prices
has
remained
suppliers that not only deliver products
and the slowing global economy. Other
but that can also come up with solutions
South American mining industries have
that
displayed similar resilience, which,
efficiency, which we can achieve using
in conjunction with the vast mineral
our suite of explosives, blast initiating
deposits throughout the continent,
systems and technical support through
is indicative of significant business
blast optimisation teams.”
increase
their
operational
opportunity, he adds. Kwenda comments that the company’s
AEL has increased its presence in South America, owing to the nature and resilience of the South American mining industry. AEL GM for business development in
Kwenda says growing AEL’s previously
expansion
established base in South America
exceeded expectations, with it having
through
participated
direct
interaction
with
in
South in
America
several
has
tenders
customers is integral to the company’s
and
global
of electronic blasting systems for
expansion
strategy.
Such
interaction has been characterised
conducting
demonstrations
potential customers.
by increased attendance at South American
mining
exhibitions
and
To date, AEL has performed two
events, as well as several meetings
blasting demonstrations for copper
with potential clients.
mining clients in Chile and expects to
South America and West Central Africa
conduct two more next month. Kwenda
Alois Kwenda notes that, although
AEL has previously supplied customers
notes that the demonstrations, which
South America is a relatively new
on the continent using distributors and
focus specifically on electronic blasting
market (compared with Africa where
other agents, but decided last year
systems, have been successful, as
the company was first established
to offer its full suite of products and
they have led to renewed interest from
more than a century ago and the Asia
technical expertise directly to ensure
stakeholders in Chile and securing new
Pacific region, where the company
high-quality supply and more efficient
clients.
has been established for a decade)
application of explosives on site, he explains.
8
Blasting News I Second Quarter 2016
AEL INTERNATIONAL
Demonstrations, which focus specifically on electronic blasting systems, have been successful AEL field technicians on bench
AEL has consolidated its offices under
which takes place every second year,
AEL under the AECI Mining Solutions
the AECI brand in South America;
is a mining exhibition and conference
banner, also exhibited at Exposibram
therefore, the sales and distribution
for Latin America, attended by about 80
International Mining Exhibition 2015
offices in Brazil and Chile trade under
000 visitors and including exhibitions
from September 14 to 17. The annual
the AECI name. AECI Mining Solutions
from 1 700 companies.
event was held in Belo Horizonte,
brings together the group’s expertise in
Kwenda
the supply of products and services for
attendance had decreased this year
customers in the mining sector.
due to global economic conditions, the
notes
that
even
though
Brazil, and attracted more than 50 000 visitors.
quality of customer interaction was still
According to Kwenda the company
Kwenda and his team recently exhibited
significant, with many customers and
intends to establish manufacturing
as part of AECI Mining Solutions at the
potential customers visiting the stalls
operations in either Chile or Brazil
Expomin 2016 event, held in Santiago,
and asking for meetings.
within the next five years.
Chile, from April 25 to 29. The event,
Blasting News I Second Quarter 2016
9
AEL TECHNICAL CAPABILITY
Check twice, blast once: The importance of blasthole monitoring by Manare Mokoatlo ‘Measure twice and cut once’ is an old adage that every person who works with their hands has heard countless times, usually dispensed by their mentor as they learn the ins and outs of their craft. The learnings behind this phrase are to avoid having to duplicate your efforts, save time and eliminate any possibility of error in your results. In the world of mining operations – where every cubic millimetre of ore and every second of uptime counts – this is especially true. However,
some operations are failing to meet their potential by allowing poorly drilled blastholes to force them into duplicating blasts unnecessarily and ultimately hampering production in the long run. It is crucial that mines measure twice, and blast once. Blasthole surveying is a key part of blast planning and blast optimisation. These two processes are vital in ensuring that every blast goes off without a hitch, that the optimal amount and type of explosives are used and that the right results are achieved.
When drilling blastholes, there are a number of technical and geological factors that can lead to an undesirable drilling pattern. From a technical aspect, excessive drilling and the use of worn out drill bits can lead to errors in blasthole structures while rock types and ground water can lead to drilling deviations. Deviations lead to poor blast results, low productivity, safety risks and environmental impacts. Blasthole surveying can identify drilling deviations as well as burden
Blast hole angle deviation surveying
10
Blasting News I Second Quarter 2016
AEL TECHNICAL CAPABILITY
Manare Mokoatlo presenting on blast hole monitoring at the IOQ conference
Borehole callipher log for measuring diameter deviations
Poor drilling practices
Poor fragmentation as a result of poor blast preparation
lengths and drilling depths. This is crucial to operations because a small burden length can result in too much rock being blasted from the bench face while too long a length results in the explosive energy coming back up the blasthole.
teams can determine the optimal amount and type of explosives that each unique hole requires or if the hole needs slight drilling adjustments.
Using Boretrak™ equipment, for example, operations can check these factors as well as calculate drilling deviation from the design at fixed intervals. Boretrak™ comprises a control display unit (CDU) logger, a rack of rods, a probe and a gyroscope or gravity sensors. All of this equipment feeds into an interface which can represent the status of a drillhole, removing all guesswork from blast planning. Other equipment which is crucial in checking drillholes is borehole calliper logs, which comprise a tripod with a probe on a pulley which is lowered into the hole. The probe is equipped with arms that can open out on command to measure the average diameter and average variance of the drillhole. In an ideal world, the hole should resemble a cylindrical tube – with smooth walls and an equal diameter throughout. In reality, however, there are often deviations.
A well planned and successfully executed blast has several benefits. It can deliver operation-specific fragmentation levels that result in improved productivity and removing the need for secondary blasts. This is because the correct level of fragmentation reduces the levels of loading and hauling, and optimises plant operations by making processes such as crushing more efficient. A successful blast also improves safety because it reduces the amount of flyrock, while its environmental benefits include meeting airblast and ground vibration limits. While the information that surveying provides is crucial, it is what operations do with it that really counts. Through thorough measurement and analysis, AEL can help operations take corrective actions to reduce downtime and unnecessary secondary blasts. By ‘measuring twice and blasting once’, mines can reap the financial and operational rewards of thorough planning and measurement.
By measuring these deviations with the probe, blasting
Blasting News I Second Quarter 2016
11
EXPLOSIVES TODAY Series 4 I No 15
BLASTHOLE DRILLING AND INITIATION PATTERNS IN SURFACE BLASTING Part 1 By Henk Esterhuizen – Senior Mining Engineer The layout of the drill holes, burden and spacing and ratio between them have an important effect on blasting results. In this issue a theme will be developed with particular reference to blasthole drilling and initiation patterns. In order to understand the significance of these patterns however, one of the basic mechanisms of rock fracture by explosives must be briefly considered. 12 12
Radial Fracture Under Gas Pressure
A large burden, on the other hand, promotes the formation of longer
When
blastholes
are
fired
cracks hence a greater diameter plug
independently a cylindrical ‘plug’ of
of fractured ground, accompanied by
broken ground is created around each
minimal heave. The optimum burden
hole before movement of the burden
is that which results in a maximum of
takes place. The diameter of this ‘plug’
ground being broken and heaved into
is determined by the pressure of the
a rockpile loose enough to be handled
explosives gases and the time for
by the available loading equipment.
which they act in the radial cracks and fissures to the free face as illustrated
Blasthole Drilling Patterns
in steps 1 to 4 in figure 1. Seen in plan on the surface of the If the burden is small the gas is
bench, the fractured areas around
released very quickly and its unused
the blastholes can be represented as
energy is spent in heaving the broken
circles. It is logical to assume that
burden forward with great momentum.
every point on the surface must fall
Blasting News News II Second Second Quarter Quarter 2016 2016 Blasting
within at least one of these fracture circles for effective fragmentation to occur. Figure 2 contrasts the arrangement of square drilling patterns with that of staggered drilling patterns, for a Spacing/ Burden (S/B) ratio of 1.25:1.
Figure 1. Gas pressure and crack extension
The staggered pattern produces a more uniform distribution of fracture circles and thus more even fragmentation in the rockpile for the same powder factor. In fact, optimum coverage is obtained when the holes form equilateral triangles, but as can be seen from table 1 this pattern varies only slightly in coverage from the staggered patterns based on S/B ratios of between 1.0 and 1.5.
Figure 2. Bench coverage by blasthole fracture circles assuming constant powder factor and S/B ratio = 1.25 - Note: In the square pattern unfractured areas and excessive overlap between circles; In the staggered pattern, total bench coverage
Implications of Drilling Pattern The greatest potential for good breaking with the most extended drilling pattern thus lies in using a staggered pattern having an S/B ratio of between 1.0 and 1.5. The square layouts all give significantly less coverage. Note that if the S/B ratio increases beyond 2, the radial fractures reach the free face before becoming fully developed.
Figure 3. Interaction of stresses from closely spaced blastholes fired simultaneously
As a result pressure is released earlier resulting in a smaller
Table 1: Effect of drilling patterns and S/B ratios on area covered by fracture circles. Equilateral triangular layout = 100%
diameter fractured area and more flyrock. There can therefore be
S/B Ratio
Square pattern %
Staggered pattern %
little benefit in exceeding an S/B
1.00
77
98.5
ratio of 1.5.
1.15 Δ
76
100
1.25
75
99.5
Real as the benefits of staggered
1.50
71
94.6
patterns may be, they are less
2.00
62
77.0
evident
Note: Δ, equilateral triangle Blasting News News II Second Second Quarter Quarter 2016 2016 Blasting
in
highly
fractured
13 13
ground where the fracture planes seriously hamper the development of radial fractures. Also, with small diameter blastholes in high benches, drilling inaccuracy and hole deviation can result in the pattern at the toe being unrelated
Figure 4. Interaction of stresses from closely spaced blastholes fired with excess time delay
to the laid out pattern on the bench. In these conditions, therefore, the merits of staggered patterns may be outweighed by the convenience of drilling square patterns. Blasthole Initiation Patterns The
overall
performance
of
Figure 5. Interaction of stresses from closely spaced blastholes fired with optimal time delay
production blasts can be controlled by altering delay timing to vary the degree of interaction between adjacent
blastholes.
Whilst
absolute values of inter-row and intra-row delays are important, the ratio of these times is also significant. This can be explained by the following concepts (which are
over-simplifications
of
a
complex subject). •
The intra-row delay controls interaction between adjacent blastholes and determines whether
blastholes
act
independently or together. •
The inter-row delay controls interaction dependent it
affects
between blastholes, the
as
progressive
creation of new effective free faces during the blast. •
The ratio of inter-row delay to intra-row delay controls the geometry and orientation of new free faces created as
14 14
Figure 6. Squared and staggered V-cut chevron patterns
the blast progresses. For a later-
apparent direction of movement
firing
of a blasthole or the overall blast.
blasthole,
the
location,
shape and extent of any effective free face will depend on this ratio of delay times. This influences
Single row fired with excess time
the
delay
direction
and
extent
of
displacement of the burden of each blasthole and thus the final
If a single row of similar blastholes is
muckpile shape and position. This
detonated in sequence with relatively
is sometimes referred to as the
long time delay (e.g. several seconds)
Blasting News News II Second Second Quarter Quarter 2016 2016 Blasting
detonations,
higher than the single hole blast,
the result will be different again as
because of the restraining effects
illustrated in figure 4.
of the broken rock buffer.
between
successive
“Initiation” Burden and Spacing Spacing delay
In general, this type of blast would
Identifying the right intra-row delay is
produce:
Single row firing with optimal time
one of the key factors to predictable
•
delay
and efficient blasting. For a brittle,
Better fragmentation than the instantaneous single row blast, as
•
elastic,
type,
a short intra-row delay is usually
not tend to link up preferentially.
blastholes could be fired in sequence
appropriate. In contrast, a porous,
However,
with a relatively small time (e.g.
plastic, highly jointed rock mass would
be poorer than the single hole
several
require more time between detonation
blast because there is no positive
adjacent detonations. In general, a
interaction
between
adjacent
delay interval of a few milliseconds
blastholes,
and
earlier-firing
per metre of spacing between adjacent
Short delays promote a united effort
charges may disrupt adjacent
blastholes will produce quite different
between adjacent blastholes, tending
explosives charges or the rock
results compared to the previous
to maximise forward displacement
mass surrounding them.
examples.
at the expense of fragmentation and
fragmentation
may
milliseconds)
between
Less forward movement than the
of adjacent blastholes.
vibration levels. Long delays tend
single hole or simultaneous single
Optimal time delay is known as intra-
to make each blasthole work more
row blasts, as the rock displaced
row delay, the essential difference
independently,
by the first holes to fire will come
is that each blast hole charge is
interaction.
to rest and become a buffer which
detonated whilst the surrounding
restrains
burden
rock mass is pre-stressed but not
Results from a wide range of conditions
movement. The opening of cracks
completely disrupted by the effects of
indicate that the appropriate intra-
from earlier-firing charges may
earlier-firing charges.
row delay for conventional blasting
subsequent
reducing
positive
is usually less than 5 milliseconds interact
per metre of burden (as measured
detonations.
positively, producing superior results
between rows of holes). The ideal
Less
the
because the explosives energy is
delay for each situation is clearly
instantaneous row of blastholes,
released in a controlled manner
influenced by rock properties, blast
but more than the single hole blast
and applied to the rock mass more
geometry and the desired result, but 3
because forward displacement
effectively. In fact, for any pair of
to 6 milliseconds per metre of burden
is restrained by the broken rock
blastholes there is a unique delay time
is recommended.
buffer.
which will produce the best possible
Lower ground vibrations and
result as can be seen in figure 5.
of
•
rock
cracks between blastholes would
also permit premature venting
•
homogeneous
Alternatively, a single row of similar
gases
from
overbreak
subsequent than
Adjacent
blastholes
thus
Burden delay
airblast than the instantaneous single hole blast, because energy
Fragmentation
release and ground movement
particularly in the toe region of
are spread over a longer period
blastholes towards the perimeter
of time. Ground vibrations may be
of the blast. The correct inter-row
Blasting News News II Second Second Quarter Quarter 2016 2016 Blasting
will
be
enhanced,
15 15
delay ensures that each blast hole has an effective free face to break towards, because
preceding
blastholes
have
broken and detached their burdens before the next dependent blast hole fires. This progressive relief of burden during the blast will affect the volume of oversize rock produced, although fragmentation is often influenced more by the intra-row delay than by the inter-row delay. Results from a wide range of conditions indicate row
that
delay
for
the
appropriate
conventional
interblasting
is usually less than 18 milliseconds (measured between rows of holes) but 12 – 18 milliseconds per metre of burden is recommended for initial trials. Ground and air vibrations are minimised and can often be maintained at levels similar to a single row blast. This is a
Figure 7. Chevron initiation patterns
direct result of progressive relief of burden during the blast, which promotes lateral movement and minimises uplift, cratering and
stemming
ejection.
Subsequent
blasts are also likely to have less potential for airblast because reduced overbreak means that front row burden rock contains minimum cracking from the previous blast. Types and Features of Chevron Patterns Open or Closed
Figure 8. Squared and staggered V2-cut chevron patterns
Chevron patterns are classed as ‘Open’
pattern causes the rock pile to be
impacts between rocks projected from
or ‘Closed’ depending on whether it is
concentrated in a central position,
opposing echelons.
desired to take V-cut in the bench or blast
and may provide a small bonus in
to two free faces. The closed chevron
terms of fragmentation, owing to
16
Open chevron patterns yield flatter,
Blasting News I Second Quarter 2016
evenly spread rock piles, that are well
considered are:
recommendations
suited to front-end loaders. They also
given
by
AEL
Mining Services Limited (“AEL”) in this
avoid the possibility of a toe problem
•
Rock properties
publication, is given by AEL in good
posed by the tighter breaking conditions
– Strength, Young’s modulus,
faith in order to provide assistance to
of closed patterns, and are rather easier
to connect up in terms of visualising
structure
warrant the correctness of its advice
the correct initiation routes. Figure 6
•
Blast geometry
and/or recommendations; 1.2 warrant
illustrates the difference between a
–
Burden, spacing, bench height
that particular results or effects will
squared and staggered V-cut chevron
and available free faces
be achieved if AEL’s advice and/or
patterns.
•
Explosives
recommendations are implemented;
–
Characteristics, degree of
1.3 accept liability for any losses or
coupling and decking
damages that may be suffered, as a
density, porosity and rock
the reader. AEL does not however: 1.1
If we consider a square pattern of holes
as depicted in figure 6, it is evident that
•
Initiation system
result of a party acting, or failing to act,
several different chevrons can be drawn
–
Surface or in-hole delays and
on the advice and/or recommendations
through the pattern.
type of downline
given by AEL;1.4 accept liability for any
•
Environmental constraints
acts or omissions of its employees.
Considering a single front row hole, the
–
Representatives
chevron which intersects the nearest
frequency
hole in the next row, i.e. the hole
•
The desired result
immediately behind, defines the “VO”
–
chevron. If the angle of the chevron is
Air, ground vibration levels and
and/or
agents,
whether negligent or otherwise.
Fragmentation, muckpile displacement and final profile
flattened so that it extends through the next nearest hole, this defines the “V1”
We will develop this concept in future
chevron, and so on, figure 7.
editions of Explosives Today. AEL Mining Services Explosives Engineers based at
Chevrons
through
hole
the regional offices are available to help
but
and advise on this subject and the use
look rather flatter, as in each case the
of electronic detonators to achieve all
sideways distance is increased by half
controlled blasting scenarios.
patterns are
staggered
similarly
defined
the spacing. Figure 8 illustrates the difference between a squared “V2” chevron and a more flatter staggered
References:
“V2”chevron pattern. This document is a new addition to the Factors which influence the timing of a
Explosives Today series. This document
blast
replaces all previous Explosives Today on this subject including Series 2. No 12:
Several factors which have a direct
June 1978
influence on timing which should be Disclaimer:
Blasting News I Second Quarter 2016
Any
advice
and/or
Copyright: All copyright that subsists in this publication together with any and all diagrams and annexures contained herein, which shall include all and/or any ideas, plans, models and/or intellectual property contained in this document vests in AEL. Any unauthorised reproduction, adaptation, alteration, translation, publication, distribution or dissemination (including, but not limited to, broadcasting and causing the work to be transmitted in a diffusion service) of the whole or any part of this document in any manner, form or medium (including, but not limited to, electronic, oral, aural, visual and tactile media) whatsoever, will constitute an act of copyright infringement in terms of the Copyright Act No.98 of 1978 and will render the transgressor liable to civil action and may in certain circumstances render the transgressor liable to criminal prosecution. This document remains the intellectual property of AEL. Intellectual Property: All ideas, concepts, know-how and designs forming part of this publication belong to AEL, save for where it is clearly indicated to the contrary.
17
AEL IN THE FIELD
AECI showcases at ExpoMin 2016 Expomin has become a benchmark
For AECI this was a great opportunity to
strengthen
event for the Latin American mining
promote our brand and the new concept
current and potential customers during
industry. The event allows industry
of AECI Mining Solutions in the South
this event.
to focus on the widest range of
America mining industry. Additionally,
technological innovation while bringing
being an exhibitor reinforces our
The
together
key
commitment to the region and builds
present at the event included Alois
players. After 12 exhibitions since 1990,
confidence, in a very conservative
Kwenda, General Manager Business
it has become the largest mining event
market, that we are committed about
Development – LATAM & Central
in South America and a worldwide
supplying
Africa; Alejandro Contreras, Operations
benchmark event.
explosives and chemicals for mining.
the
mining
sector’s
Chilean
customers
with
the
AEL
Manager Humeres,
relationship
Latin
–
America
AECI
Latam;
Business
team
Ignacio
Development
Expomin 2016 received more than
The AECI stand was visited by a host
Manager
80,000 professional, and more than
of conference delegates, who sourced
Financial Manager Latam.
1,700 enterprising suppliers from 36
information about the company. The
countries around the world.
AECI team took this opportunity to
and
with
Carlos
Cammás,
The fully equipped interactive exhibition stand 18
Blasting News I Second Quarter 2016
AEL PAYING IT FORWARD
AEL partners with Northam Rhinos AEL is proud to have partnered with Northam Rhinos rugby team for several years. The team won the Assupol Tournament in March 2016 at Loftus Versfeld Stadium enabling them to qualify for the Community Cup which will be a widely televised event. The
club
boasts
players
employed by the mines in the area as well as players from the local communities. Some highlights winning
include the
2015
the
team
Assupol
Tournament (Blue Bulls Rugby Union),
the
2015
Waterberg
League, 2015 Limpopo Club Championships and the 2016 Assupol Tournament (Blue Bulls Rugby Union). As a result of being the 2015 Limpopo Champions, the team will represent Limpopo Blue Bulls Rugby Union in the Gold Cup
Tournament
(previously
called the Cell C Community Cup) in September this year. This is a prestigious national tournament for the top 20 teams in the country. We wish them all the best to bring home the title!
Blasting News I Second Quarter 2016
19