Blasting News VOLUME 26 ISSUE 1 2017
IN THIS ISSUE • Creating a cadence of accountability at the blast operation TM at Symposium Mines Guinee • Highlighting intelliBlastTM
• AECI Burkina Faso in partnership with Bissa Gold Mine create an oasis in the desert
Printed on 100% eco friendly paper
Editor’s Note
CONTENTS
AEL Mining Services is constantly learning about our customers’ businesses and how our competency complements them. We pledge our dedication to the explosives industry and aim to serve all our stakeholders with the implementation of value proposition called intelliBlast™. Some highlights in this issue include:
3
SPECIALIST SPEAK: Simon Tose
4 AEL KNOWLEDGE SHARING: Mining Indaba 2017 6 AEL SAFETY: Creating a cadence of accountability at the blast operation 8 PAYING IT FORWARD: AECI Burkina Faso in partnership with Bissa Gold Mine create an oasis in the desert 10 AEL THOUGHT LEADERSHIP: EXPLOSIVES TODAY Series 4 No.1 16 AEL TECHNICAL CAPABILITY: Case Study – Powder Factor Reduction and Highwall Stability 18 AEL IN THE FIELD: AEL knowledge transfer at the IOQ 18 AEL IN THE FIELD: Highlighting intelliBlastTM at Symposium Mines Guinee
Safety Productive blasts are and always will be top of the agenda for AEL, ensuring that we remain in tune with our customers by delivering peace-of-mind at strategic and operational levels, we offer some food for thought with our recommendations on how to create a cadence for safety within the mining industry through diligence in training and behavioural practices. Case Study In line with our mission is to meticulously apply our learning to developing appropriate technology and helping the mining industry use our energy confidently, we share one of our recent case studies focusing on powder factor reduction and high wall stability. Thought Leadership Furthering our Thought Leadership stance, AEL’s Global Mining Optimisation Manager, Simon Tose, has penned another issue of our sought-after technical publication, Explosives Today, tailored at solving conundrums within the blasting arena. Events On the events front, we provide you with an update of our upcoming participation at key global industry events such as the Institute of Quarrying and Symposia Mines Guinea conferences, where we will showcase our suite of cutting-edge products and services and impart key learnings to delegates through presentations. We endeavour to constantly keep you in touch with the AEL world. Please subscribe to Blasting News by visiting our website www.aelminingservices.com and clicking on the Publications tab. Follow the AEL conversation on Twitter, Facebook, YouTube and LinkedIn. Enjoy your read!
Eubulus Pillay Cover image: Gold-Mine-Tunnel
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 First Quarter 2017
SPECIALIST SPEAK
Specialist Speak by Simon Tose, Global Mining Optimisation Manager
The development of commercial explosives in South Africa can be related to the history of the gold mining industry. In preparing the learning material for a recent student study contact session it was interesting to explore some of these cross industry links. In 1853 Pieter Jacob Marais, a South African prospector, recovered alluvial gold from the Jukskei River, north of what would become Johannesburg. The years that followed brought several modest strikes, but the Witwatersrand Main Reef eluded searchers until 1886, when George Harrison, an Australian prospector, chanced upon an outcropping on a farm called Langlaagte. Ironically, Harrison failed to appreciate the significance of his find and sold his claim for £10 (Around R20 000 in today’s money!). The Witwatersrand gold rush was the catalyst that fuelled industrial awakening in South Africa and with that, the largest market for dynamite exploded into existence. These early gold miners through observation, testing, more often than not with trial and error of different mining practise, introduced some basic rock mechanics fundamentals and blast design. The learning manifested as rules of thumb that still perpetuate in the industry today. Rule of Thumb; the dictionary defines this as; a broadly accurate guide or principle, based on practice rather than theory. Blasting News I First Quarter 2017
The early miners soon realised that stoping width limited the face advance to around not more than the stoping width, for example 1.2m. Increasing the face advance beyond the stoping width created tight breaking conditions and long sockets. The basic concepts of blast geometry and design had been born. Co-incidently this tied to the unsupported span, distance, between the face and permanent support. This created the foundation of understanding rock mechanics, allowing for sufficient time to clean, install temporary support, drill and blast thus reducing the potential for hangingwall collapse. The early drilling equipment used integral steel that provided a wide range of hole diameters from new to discard. The dynamite cartridge diameter tended to be ¾ of the hole diameter to allow for this and to accommodate the width of the fuse. Another rule of thumb was also born, the hole should be charged to ⅔ to achieve reasonable blast results. Today the industry makes use of tapered or knock off bits, resulting in consistent drilled hole diameters, typically only a 2mm variance between new and discard. This has enabled industry to look at drilling efficiencies and adopt drilling to the mining conditions on each operation to match the unique rock types and properties. The explosives industry has had the opportunity of moving away from using cartridge explosives, with the cartridge’s inability to fully couple the explosive and the security risks. Pumped emulsions afford the opportunity to reduce the amount of drilling required and better manage hangingwall conditions. The consistent hole diameters have enabled the development of new rules of thumb, where the uncharged, stemmed, portion can be calculated as 10 x the hole diameter. This ensures blast design specific to the mine and accounts for the unique rock strengths,
properties and geological condones to support the drive for improved safety. The last rule of thumb that really needs updating is the 70o drilling angle derived from the need to manage the explosives, the blast geometry and the timing scatter on the obsolete capped fuse and ignitor initiation systems. Many people still quote the potential improved face advance and the perceived “saving” on explosives consumption. The enclosed shock tube systems have dramatically reduced the fire risk but more importantly tackled the incidents of individuals walking into a re-ignited misfired fuse as a result of friction from a scraper pulling a muckpile. The faster and more consistent timing has enabled the tighter geometry to be blasted and typically we now drill at 85o effectively pulling the full advance equal to the hole length. This has also meant a significant reduction in the possibility of blasting out the permanent support as the direction of rock movement is now effectively perpendicular to the direction of the drilled blast hole. It is important to understand the history of our industry, the learning and focus on moving the industry safely forward. We will look at the effect of some of these rules of thumb on other mining methods in future technical briefs; such as ring blasting where energy distribution is the key or in surface operations with the need to manage environmental factors such as airblast, noise and dust. Reference: All That Glitters - The glitter of gold by Emilia Potenza.
3
AEL KNOWLEDGE SHARING
Mining Indaba 2017 AECI Mining showcased diverse service offerings at the annual Investing in African Mining Indaba from 6 – 9 February in Cape Town. Mining Indaba remains better positioned
infrastructure and interface, world-
than ever to deliver an unparalleled
class R&D capacity, and highly skilled
deal-making and discovery platform
multi-disciplinary teams that share
for global investors and African mining
best practices, identify synergies and
companies. The conference provides a
define strategies that have positive
diverse and proven platform that gives
consequences for mines and mining
all delegates – investors, financiers,
houses.
mining
executives,
officials,
and
government industry
The combined offering of AEL and
stakeholders - exceptional access to
other
Senmin is available in Africa, Australia,
compelling investments across the
Brazil, Chile and Indonesia, while
entire continent.
ImproChem is GE’s Chemical and Monitoring Solutions partner in sub-
Participating at the Mining Indaba
Saharan Africa specifically AEL Mining
under the strategic pillar of AECI
Services.
Mining, AEL Mining Services, Senmin and
ImproChem
aligned
their
AEL
is
a
world
leader
in
the
processes and strategies to add more
manufacture and supply of explosives,
value to mining in Africa, Australasia
initiating systems and blasting services
and South America. The main focus
for mining, quarrying and construction.
areas are explosives, mining chemicals
In the mining industry, it has a wealth of
and water treatment.
experience across a range of minerals,
AECI a world of mining in one company
including coal, chrome, gold, iron, platinum and uranium. The
business’s
newly
launched
Under the umbrella of AECI Mining,
intelliBlast™ system provides a flexible
AEL, Senmin, ImproChem and the
and holistic approach for blasting
customer work together to add value
that is appropriate, optimal and safe.
from
a
Through the diligent application of AEL’s
uniquely collaborative process, AECI
products and services, underscored by
Mining offers the structure and support
its experience, intelligence and R&D,
of an established and reputable brand,
rock is blasted in such a way that it
a comprehensive range of products and
enables enhanced efficiencies across
services, the convenience of a single
the mining value chain.
4
mine-to-mineral.
Through
Blasting News I First Quarter 2017
AEL KNOWLEDGE SHARING
The AECI stand at Mining Indaba 2017
Blasting News I First Quarter 2017
5
AEL SAFETY
CREATING A CADENCE OF ACCOUNTABILITY AT THE BLAST OPERATION by Colin Wilson, Executive Technical and Compliance
As a market leading explosives manufacturer, AEL Mining Services partners with their customers and in doing so creates a joint responsibility to deliver safe, efficient blasting solutions. One of the most important aspects of this is instilling confidence in all blasting team members to prioritise safety. Whether on senior or junior level, each and every employee must adhere to industry safety best practices, legislation and carry out their work efficiently and safely.
in the mining environment. For teams
cadence for accountability, companies
to act as they are trained to do and
can mitigate risks to property, people
understand the magnitude of their
and communities in close proximity to
responsibility. This means, all blasting
the blast site.
teams place safety above production
Assistant
“Often we see the key safety decision
demands at all times.”
courses
teams
assume
full
responsibility
and adopt a zero tolerance for non-
When explosions are managed more
compliance
situations.
effectively, it is possible to ensure a
Continuous awareness and training is
good control blast and to secure the
also an important tool to contribute to
blast area correctly. Often, a lack of
the decision making process.
technically
or
unsafe
skilled
employees
has
implications for this sector. AEL has “We have a programme in place for
established expert training for blasters
blasting teams on our customers’
and supervisors:
sites to help them operate with confidence, and to do only what is
•
The
Blasting
Competency
right from a safety perspective and
Programme is offered for surface
without any compromise,” says Wilson.
as well as underground operations.
“Working in conjunction with the senior management of the mine, our blasting
•
making process disrupted or even over-
The Explosive Handler, and are
Rock the
Blast
Breaking basis
for
certification through the MQA to
powered by a need to meet production
How AEL is addressing safety issues in
become a licensed blaster and
targets. Our role is to intervene in this
the industry?
meet statutory laws.
respect, and stress the importance of •
The Explosive Engineer’s course
safety to all staff and help them deliver
AEL is moving away from being solely
on a promise of zero harm,” says Colin
a product purveyor to being a value
is a graduate level course given to
Wilson, Executive of Technical and
added service provider. The key shift
train technical blasting and field
Compliance at AEL Mining Services.
is into the consulting services realm,
staff, with a focus on advanced
for better collaboration which ensures
blasting applications.
focus
the
safer operations and ultimately greater
time
for
efficiency without the risk factor. By
AEL’s intelliBlast™ approach, which is a
responsible and clear decision making
creating an emphasis on training and a
culmination of over 100 years of market
This
puts
importance
6
into
sharp
of
allowing
Blasting News I First Quarter 2017
AEL SAFETY
leadership in Africa, provides a flexible
and designed with the safety of the
to ensure that blasted rock suits and
and holistic approach for blasting that
explosives handler in mind. Each
complements the design of equipment
is appropriate, optimal and safe.
products is made to comply with the
and plant.
most stringent safety rules, regulations Whether providing customers with
and legislation.
BLAST CONSULT
the products and services they need
AEL’s
to perform their own blast or full
ADAPTIVE DELIVERY SYSTEMS AND
offers
integration into their daily operations
SERVICES
blast
with planning, execution, measurement
An
and tracking, intelliBlast™ has a
designs
solution for every requirement.
Manufacturing
in-house
engineering
and
builds
Mobile
technical monitoring,
fragmentation conversion,
services design,
analysis, i-Mining
division like timing,
technology productivity
programmes, blasting consulting and
mining,
training in basic blasting principles.
Through the diligent application of AEL’s
bulk emulsion manufacturing plants
All of these have critical, far-reaching
products and services, underscored by
and
effects on the safety of people and
experience, intelligence and research
assembly plants. In addition, AEL offers
and development, AEL has developed a
underground mobile and fixed emulsion
blasting solution that enables enhanced
pumping
efficiencies across the mining value
inherent in these solutions is not only
combined with decades of experience
chain.
about realising value, but making sure
and expertise can be the cause of
all activities are conducted safely.
waves of change the mining industry
AEL
has
utilised
intelliBlast™
and
(MMUs)
Optimisation
for
surface
Units
division
Mining
underground
modular
initiating
systems.
The
systems
innovation
to
equipment on a mining site. “Collaboration
with
our
clients,
needs. We want to help our customers
establish long-lasting partnerships,
PREDICTIVE SOFTWARE
improve safety, and preserve cash in a
by adding value that is beneficial to
An important aspect of providing safe
turbulent economic climate,” Wilson
all stakeholders. intelliBlast™ is a
blasting solutions is AEL’s Blasting
concludes.
significant differentiator in a space
Science and Software Development
traditionally defined by silos, and
division that carries out face velocity
is made possible by means of four
measurement, 3D blast face survey,
enablers, namely:
high speed videography, rock mass motion study, fragmentation analysis,
DIFFERENTIATED PRODUCTS
blast
All of AEL’s products are researched
measurement and monitoring in order
Blasting News I First Quarter 2017
modelling
and
efficiency
7
PAYING IT FORWARD
AECI Burkina Faso in partnership with Bissa Gold Mine create an oasis in the desert by Salimata S. Kone, Human Capital Manager (AECI Burkina Faso)
operational high flow, drinking water
clean drinking water.
borehole of six cubic meters (6m3) capacity to neighbouring communities
“The project was initiated in 2016
in close proximity to Bissa Gold Mine.
which consisted of the realization of 7 additional drilling projects to benefit
Salimata S. Kone, Human Capital Manager (AECI Burkina Faso)
The Bissa Gold environment is an area
the communities bordering the mine.
where drinking water is scarce. This
This achievement is an indication of
donation, has tangibly contributed to
the excellent partnership between the
the well-being of a total of 369 persons
two companies to further enhance the
who now have access to clean drinking
vision of community development.
water. I would like to take this opportunity
AECI prides itself in making impactful
contributions
to
the communities where we operate.
Assistant Managing Director of Bissa
to congratulate AEL for this action on
Gold,
behalf of the management of Bissa
Christian
expressed
his
Félix delight
Ouedraogo, at
the
Gold and extend our best wishes
collaborative effort of AEL and Bissa
for continued success in 2017,” he
Gold in furthering the initiative together
concluded.
AECI Burkina Faso, in partnership with
with local authorities to reduce the
Bissa Gold have recently donated a fully
difficulty of communities in accessing
The community members utilising the newly installed borehole
8
Blasting News I First Quarter 2017
PAYING IT FORWARD
Members of the local community alongside AECI Burkina Faso employees before the installation of the borehole containment boundary wall
Me KonĂŠ Salimata, AEL Human Capital Manager and Conrad Norgbey, AEL Operations Manager, represented AEL at the handing over of the borehole
Blasting News I First Quarter 2017
El Hadji SANFO Lamine, on behalf of the communities, expressed his gratitude to both AECI & BISSA GOLD for their great contribution to the well-being of the local communities
9
THOUGHT LEADERSHIP
EXPLOSIVES TODAY Series 4 I No 1
Good Vibrations
Simon Tose, Global Mining Optimisation Manager
People are generally made aware of blasting by the physical sensations of airblast, noise and ground vibrations. The upsurge in building projects, new roads and rail links have and will see an increase in work such as trenching for pipes and cables, blasting close to private buildings, pipelines, power lines and the removal of concrete structures and building demolitions. The encroachment of residential property onto mining operations such as the quarries supplying stone, 10 10
sand and cement to these projects, has resulted in a steady increase in the complaints and claims regarding blasting “damage”.
is no direct correlation between how a blast “feels” or is perceived and its potential for causing structural damage to a house.
It is the perception that people have of explosives, the sudden and unexpected nature of blasting that raises alarm and concern. Individuals are sensitive to airblast and vibrations “feeling” blasting events that are as little as 2% of acceptable vibration guidelines and/ or limits.
Genuine complaints arising from blasting vibrations are very rare. Cracked plaster is usually the basis of complaints but is a common experience in all modern structures. Structural engineers have listed many reasons why plaster will crack other than through vibrations. Many more issues arise from airblast, which is the topic of the second issue of Explosives Today.
People “see” things that have been previously gone unnoticed and associate them with the unanticipated event. Despite these sometimes startling effects, research has shown that there
The response of structures to blasting and in particular airblast and vibration is complex and depends upon many factors.
Blasting News News II First First Quarter Quarter 2017 2017 Blasting
THOUGHT LEADERSHIP
Recent studies have revealed that both “Cultural” and “Natural” events can place even greater stresses to a home than the accepted guidelines for the control of blasting. Dust, paint, cobwebs and loose material in a crack indicate that it is old and probably existed before the blast. This should all be easily identified if a survey of structural damage is carried out and recorded. •
”Cultural” issues such as: • Doors slamming • Heavy traffic • Kids running and jumping • Adherence to minimum building and material standards and regulations: • Foundations, poor concrete mix, building on clay or fill • • • • • •
“Natural” events include: Sunlight Wind Rain Temperature and humidity Changes in soil moisture i.e. expansion and contraction
It is to the blaster’s advantage to understand that many complaints and “damage” claims received as the result of blasting could have been avoided if thought and effort had been given to: •
•
Good public relations by ensuring both mine personnel and the local community have an understanding of the nature of airblast and blasting vibrations: • Notification of blasting procedures and design to minimise noise and the possibility of damage • An audible warning at blasting times reduce the potential for a person being caught unawares Ensure as much of the energy as
Blasting News News II First First Quarter Quarter 2017 2017 Blasting
•
•
•
•
•
possible in a blast is delivered directly to the movement and fragmentation of the rock by selecting appropriate explosives and initiating systems Use a suitable blast design based on acceptable guidelines • It is preferable to have a few large blasts than many small ones provided of course that set vibration levels are not exceeded in doing this and appropriate explosives and initiating systems are used • Apply electronic detonators to achieve single hole firings To minimise noise levels, as this can cause windows and furniture to rattle giving the wrong impression of dangerous vibration levels Good on site practises and the implementation of the planned design Correct use and placement of equipment to monitor and measure Understanding, recording and analysis of the data collected from pre-blast surveys, during and post blast monitoring, in order to minimise disturbance
to the mines neighbours and to revise the blast designs, layouts and practises to seek continued improvement. AEL has had a long history in dealing with the large and complex range of explosives and initiating systems that are supplied to the mining industry. In order to comment on any blast design and the safety of said structure(s) with regard to airblast and vibration, AEL would have to conduct extensive on site tests and measurements prior and during such operations both time consuming and costly.
Blasting Vibrations and their Control Airblast and vibrations are undesirable by-products from the use of explosives to fragment rock for mining, quarrying and construction. When a blast is detonated part of the explosive energy is not utilised in breaking and moving rock, but is lost to the atmosphere and through the ground in all directions as wave motion, similar to the ripple created in a pond when a stone hits the water.
11 11
THOUGHT LEADERSHIP
AEL has had extensive field experience, as well as using well researched International guidelines and our innovative technology to ensure that this loss is kept to a minimum. •
•
• •
•
•
The intensity of the vibrations is dependent upon the amount of explosive energy released at any instant and can be reduced by: • Using explosive product suitable for small diameter holes to reduce the explosive mass in each blasthole Ensuring adequate burden relief by using small burdens and a high enough powder factor for effective breaking. The hole spacing should be 50% greater than the burden Deck charging and possibly use different delays in each deck Reducing the number of holes per delay • NOTE: Simply inserting more delays into the layout does not necessarily achieve this Laying the blast out so that it does not progress directly towards the sensitive area Preventing overlapping of pulses from successive shots by ensuring a minimum intershot delay of 8ms based on a 40m hole depth • This will be subject to the blaster considering the Velocity of Detonation (VoD) of the explosive product and hole depth
damage over the past 30 to 40 years. Where there has been no suitable monitoring or test work, in our experience acceptable vibration levels have always been obtained when using table 1.
however result in unexpected concentration or transmission of ground vibrations especially in waterlogged ground and the table CANNOT therefore be viewed as infallible. If an entirely safe table for all possible conditions is required the equation 1. given by the USBM is applicable.
Distance to nearest structure (m)
Maximum charge mass/ delay (kg)
Distance to nearest structure (m)
Maximum charge mass/ delay (kg)
1
0.05
50
30
2
0.2
60
39
3
0.4
70
49
4
0.6
80
60
5
0.9
90
71
6
1.2
100
83
7
1.5
125
116
Equation 1 Vibration control in absence of
8
1.9
160
150
monitoring equipment
9
2.2
175
188
10
2.5
200
240
16
4.5
250
330
20
7.0
300
430
25
10
400
670
30
13
500
930
35
17
1000
2640
40
21
1500
4800
45
25
2000
7400
Where
Description
Units
D
Distance from the blast
Metres (m)
E
Mass of explosives per delay
Kilograms (kg)
When monitoring is established then for frequencies higher than 50 Hz AEL makes recommendations based on the USBM limits as shown in table 2. For lower frequencies these limits are reduced as shown in the graph in figure 1.
Table 1 Suggested AEL controls for charge mass/ delay when blasting adjacent to private property (PPV<25mm/s)
Freak geological conditions could
Acceptable Vibration Limits AEL has adopted the following guidelines based on recommendations published by the Office of Surface Mining, formally the US Bureau of Mines (USBM) to assist the customer in determining the potential risk to structures. This guide is based on research done into airblast and blasting vibrations and consequential
12 12
Figure 1. USBM damage criteria, based on frequency and Response of structures to everyday activities
Blasting News News II First First Quarter Quarter 2017 2017 Blasting
THOUGHT LEADERSHIP
Blasting Situation
Recommended Max Level (mm/s)
Heavily reinforced concrete structures.
120
Property owned by the concern performing blasting operations where minor plaster cracks are acceptable.
84
Commercial property in reasonable repair where public concern is not an important consideration.
25
Private property if public concern is to be taken into account or if blasting is conducted on a regular and frequent basis.
10
Example Mine
NOTE: Where frequencies of less than 10 Hertz are predicted the above PPV values should be halved. Table 2 AEL vibration levels taken from the USBM
Level
Description
100dB (2.0 Pa)
Barely noticeable
110dB( 6.3 Pa)
Readily acceptable
128dB (50.2 Pa)
Currently accepted by South African authorities as being a reasonable level for public concern. (No more than 10% of measurements should exceed this value. Investigation and action plan(s) to address these measurements should be ongoing)
134dB (100.2 Pa)
Currently accepted by South African authorities that damage will not occur below this level. (No measurements should exceed this value outside of the mining site boundaries.)
Figure 2. Typical Output from vibration equipment
always be taken if the scaled distance is less than 31. Sometimes vibration levels well below acceptable limits appear to cause complaints. If this is the case then it is likely that airblast and not ground vibrations is the real culprit if distance, D = 31.
Table 3 AEL Guide for Airblast criteria
Example:
At the same distance table 1 shows that a maximum of 13kg can safely be used. At distances closer than 30m therefore, it is strongly recommended that vibration measurements should
Blasting News News II First First Quarter Quarter 2017 2017 Blasting
Figure 3. Orientation of three principle components of vibration wave
13 13
THOUGHT LEADERSHIP
Vibration Parameters Type of Blasting
Typical Hole Diameter (mm)
Typical Distance (m)
Typical Frequency (Hz)
Construction and Civil (e.g. Trenching, Demolition etc.)
<89
1 to 50
30 to 60
Quarrying
76 to 127
100 to 500
20 to 40
Open Pit (e.g. Coal, Platinum etc.)
165 to +311
50 to +2000
2 to 20
Table 4 Typical vibration frequencies in blasting
AEL use a variety of instruments to monitor levels and the output from this equipment is used to analyse the field data, Figure 2. The vibrations can be described by three independent, mutually perpendicular components: Vertical, longitudinal (or radial) and transverse (or tangential) as shown in Figure 3. Where all three components are measured the largest is taken, unless the vector sum is shown.
Figure 4. Example of log-log plot of Peak Particle Velocity against Scaled Distance
Peak Particle Velocity, PPV and Frequency are the most important parameters to consider when assessing the potential effect of ground vibration on structures. Peak Particle Velocity, mm/s is the maximum velocity experienced by the ground. The parameter is not to be confused with the propagation velocity of the wave through the ground which is usually measured in thousands of metres per second.
Figure 5. Nomogram showing relationship between frequency, peak particle acceleration velocity and amplitude
Frequency is the number of cycles per second of the vibration (Hertz). This can have a strong influence on the acceptable PPV limits. Buildings have low natural frequencies of vibration and are most vulnerable to low frequency ground waves of less than 10 Hertz. They are however relatively
14
Blasting News I First Quarter 2017
THOUGHT LEADERSHIP
insensitive to frequencies in excess of 40 Hertz. Near the blast, the frequency is closely related to the intershot delay but as distance increases this effect is diminished and other factors influence the frequency experienced. These factors include:
E may vary, the vibration level will remain fairly constant provided the scaled distance is maintained. Hence it is useful to establish the minimum safe scaled distance for a given area to prevent excessive vibration levels, Table 5. shows some estimated ground constants. Rock Type
•
Distance • Frequencies tend to decrease as the distance increases • Blasthole size • Smaller blastholes produce higher frequencies • Geology • Hard unjointed rocks produce higher frequencies It is therefore relatively safe doing small scale blasting at close range where high frequencies are involved. In coal stripping operations with large blastholes and greater distances, special care must be taken due to the likelihood of low frequencies occurring, Table 4.
Scaled distance Vibration levels increase as the charge mass per delay increases and as the distance from the blast decreases. An empirical relationship has been derived by the USBM:
a
b
Massive Granite
700
-0.70
Sandstone
175
-0.78
Shale
400
-1.25
USBM
1140
-1.65
Table 5. Suggested values in the absence of field data for site characteristics a & b.
The minimum Scaled Distance is determined by conducting a survey and measuring the PPV’s for various known scaled distances. These are plotted on log-log graph paper and the best fitting straight line drawn through them, Figure 4. From this graph the appropriate maximum value of V is selected and the corresponding scaled distance read off. This is the minimum permissible scaled distance.
Displacement and Acceleration
In certain cases parameters other than Peak Particle Velocity are specified for controlling ground vibrations: •
•
Peak Particle Displacement (d) which is the maximum amplitude of ground movement in mm Peak Particle Acceleration (a) which is the maximum acceleration experienced and is expressed either in mm/s² or relative to G, the gravitational constant or acceleration due to gravity. (G is taken as 9810mm/s²)
Typically manufactures of sensitive equipment, e.g. computers, restrict Peak Particle Acceleration while owners of large generators place limits on Displacement. The relationship between V, a, d and f is shown in the nomogram, Figure 5. In the example shown, a maximum peak particle displacement of 0.032mm and frequency of 50 Hertz are specified. This is seen to be the equivalent to a PPV of 10mm/s and an acceleration of 0.32G. AEL Mining Services Explosive Engineers based at the regional offices are available to help and advise on any problems related to blasting vibrations. This document replaces all previous Explosives Today on this subject including Series 2. No 27: March 1982 (K S Ireland)
•
Using generic ground constants – PPV = Peak Particle Velocity – D = Distance – E = Mass per delay – a & b ground constants for a given site
The term is called the Scaled Distance and while D and
Blasting News I First Quarter 2017
Disclaimer: Any advice and/or recommendations given by AEL Mining Services Limited (“AEL”) in this publication, is given by AEL in good faith in order to provide assistance to the reader. AEL does not however: 1.1 warrant the correctness of its advice and/or recommendations; 1.2 warrant that particular results or effects will be achieved if AEL's advice and/or recommendations are implemented; 1.3 accept liability for any losses or damages that may be suffered, as a result of a party acting, or failing to act, on the advice and/or recommendations given by AEL; 1.4 accept liability for any acts or omissions of its employees, representatives and/or agents, whether negligent or otherwise. 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.
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TECHNICAL CAPABILITY
POWDER FACTOR REDUCTION AND HIGHWALL STABILITY
CASE STUDY
CONTACT Sandile Zulu +27 11 606 0000 sandile.zulu@aelms.com
BUSINESS CHALLENGE AEL MINING SERVICES 1 Platinum Drive, Longmeadow Business Estate North, Modderfontein, 1645, South Africa www.aelminingservices.com
Anglo Kleinkopje Colliery, a dragline operation, was experiencing problems with damaged highwalls and back break was still occurring after the pre-split had been taken. There were challenges with reducing the powder factor and achieving consistent fragmentation.
SOLUTION Timing was identified as one of the causes of the highwall damage and back break, thus it was decided to implement a change of inter-row delay from 100ms to 200ms between the 2nd and final buffer rows, to reduce the energy going towards the high wall.
The powder factor and the fragmentation issues were resolved by making changes to the hole diameter from 311 mm to 270mm, and drilling pattern from 7.5m x 11.0m (B/S) to 6.5m x 10m (B/S). OUTCOME Change in hole with the same drilling pattern, resulted in a decrease in powder factor from 0.9 kg/ m続 to 0.72 kg/m続 with a 20% saving in costs on explosives, but increase in mean size of 15%. Change of hole diameter and change of drilling pattern, resulted in an increase in powder factor from 0.9 kg/m続 to 0.91 kg/m続 with an 11% costs on explosives and 5% decrease in mean size. Highwall conditions improved significantly with less back break and no overhangs, making it safer to mine the coal below high wall. A potential saving of 24% on explosives that can be achieved when the blast patterns are optimised, equating to R 430 000 per blast* Final pattern of 6.5m X 10.0m (B/S) was agreed upon as the powder factor remained virtually unchanged with an associated saving of 11%; however the fragmentation mean size decreased thus improving dragline efficiency.
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Blasting BlastingNews News I I First Quarter 2017
TECHNICAL CAPABILITY
CASE STUDY
Figure 1 – Highwall conditions prior to optimisation
Figure 2 – Highwall conditions after optimisation
*Given that the same dimension of the blast will be taken as this one in the case study
Blasting News II First FirstQuarter Quarter2017 2017
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AEL IN THE FIELD
AEL knowledge transfer at the Institute of Quarrying (IOQ) conference AEL will participate in the Institute of Quarrying (IOQ) South Africa’s annual conference and exhibition to be held at The Coastlands Hotel in Umhlanga from 20 – 21 April 2017. The Institute of Quarrying is international professional body quarrying, surface mining and related extractive, processing construction industries.
the for the and
in terms of electronics with key focus on our intellishotTM offering and its relevance to the quarrying market. Also on show will be AEL’s portable, lightweight and robust PCU011 pump designed for charging bulk
emulsion in underground narrow reef environments. Read all about AEL’s latest electronics and underground offerings at www.aelminingservices.com
The annual IOQ Conference, designed for the professional development of information exchange between industry peers, attracts in excess of 200 visitors from Southern Africa and abroad annually. In line with our Thought Leadership stance, AEL will be represented at the event by the Mining Optimisation team who will be presenting papers at the plenary sessions and our product management team who will be showcasing our product leadership
Highlighting intelliBlast™ at Symposium Mines Guinée
The Symposium Mines Guinea (SMG)
packaged
United Kingdom.
will be taking place from 9 – 11 May 2017 in Conakry, Republic of Guinea.
explosives;
initiating
systems; and electronics. AEL will exhibit at the symposium and highlight the intelliBlast™ value
Mark Benning, Managing Director:
The event is organised by the Ministry
proposition
African
Burkina Faso, Mali, Guinea and Côte
of Mines & Geology, Republic of Guinea
operations through bulk products and
d’Ivoire, along with the team will
in association with AME Trade Ltd,
systems; mini bulk quarry operations;
represent AEL at the SMG fair.
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in
our
West
Blasting News I First Quarter 2017
OUR COMPANY VALUES
Blasting News I First Quarter 2017
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