Campaign Against Unsafe Blasting: Management responsibility (1)

#campaign_against_unsafeBlast

Brief Introduction

It's clear that unsafe blasting is the father of unwanted occurrences. This make all move in the wrong time give birth to the wrong event. All mining operations must be planned properly before in site action.

A look at explosive energy

 Explosive energy distribution is almost a stochastic  discrete event, the explosion and detonation energy can sometimes be unfamiliar if there is change in rock property stimulation and expectation. Let all blasting put needed factor of safety in place to account for unexpected entities. Rock Mass as a discountinous, heterogeneous, anisotropic and non elastic material host the ore, the unmine rock form the supporting body; damaging the supporting rock is a call to hazardous events. The energy generator is the explosive, but the explosive will always remain calm until the stimulating wave is in touch with it. As mining engineer in this new year, let all our relationship with explosive but in usage, storage and transportation give positive result.

THINGS TO DO

 Balance the rock properties with the explosive energy and make proper adjustment to the controllable parameters in order to ensure all intrinsic conditions had been handled. The blasting result greatly affect the mine management plans, it control the downstream operations and alter the productivity rate.

Both safety and profit must be considered when we are planning our blasting. The high powder factor affect mine cost per ton, and also produces unsafe conditions like, ground vibration, flyrock, over break, backbreak, ore grade dilution, noise, dust pollution to mention few. This year operation in the mine must be different completely.

 Generally, both Artisian and small scale miners (ASM) and Large scale miners (LSM) must put the safety of equipment, personnel and mother Earth into consideration.

 Giant miner advice to mine managers:

Dear mine manager, 

I understood all managers concern about profit and your interest in high production rate so as to meet up with the customer's demand. I am aware that all managers make use of all available managerial and leadership's skill and controlling techniques to ensure the mine operation cost is minimized. In fact, managers have decided to become the blasting engineer in other to reduce all blasting materials, supervise the loading and silent the professional mining because he will always say "This is not safe sir!". As good as profit, profit without safety is fraudulent.

Truly the wall has never fail since, despite the use of unquantifiable explosive charge. In fact, the bench wall is full of multiple joint sets and fracture but yet the mine is still producing. As fine as the state of your mine now because you are producing, do you know the mine slope will definitely fail one day!

 That the wall is standing does not assure the wall is stable!.

 Please, let not the management decision side line the place of safety. The profit is good, but please let the safety be first. 

The wall is dieing, the failure conditions might not be completely met, but you can imagine the wall standing and suddenly little vibration collapse all and cover the mine.

To support our campaign against unsafe blasting, all mine managers must ensure the management decision and blast proposal/design be thoroughly review and approval be granted base on safety first. All mine operators who consider anyone able to supervise to be more effective and efficient than competent Mining engineer is totally wrong! 

Mining engineer is needed to ensure the decision made about the blasting is right for the deposit at every Time. I know the company needs low paid employee but putting mining engineer aside to get electrical engineer or builder as mine manager is inppropriate. The rock behavior is not like current and voltage any way, rock is not cable but a DIANE material

Rock don't obey Kirchoff law at all, not all the release energy entrying a rock Mass node will get out at the same intensity, the heterogeneity of rock call for rock doctor who can diagnostically prescribe the right charge for the right explosion. 

Please dear management, give room for professional mining engineers to carry out there jobs. The mine is build base on plan, do your mine have any plan? The blasting conditions is check to prepare for the future events, do you have any post and preblast checking team?

No, we don't is probably the answer for more than 70% mine in Nigeria, maybe 50% for mines in other Africa countries.

What blasting team do you have? Do you call people who distribute explosive the blasting engineers? I bet you, those team  doesn't even understanding when the Earth is bleeding, when the fragmentation is good or poor, when their is misfire; that is not what Council that regulate engineering activities called Engineering team. Those are event oriented Team who don't show any concern about the aftermath effect. The real Team prepare a good design, implement and supervise the execution of the plan and also check the results from the plan to ensure good recommendation is drawn from it. Good blasting team also ensure all the mine is safe before, during and after blasting.

This is a call back to the real mining, when you fail to plan the mine, the mine will definitely experience premature closure. Let all manager reorganize their company policy, Safety management system and working structure.

The mine Team should be working with a clear blue print, not just work with the idea of getting the ore out by all means; whether safe or unsafe.

Decide to put safety first in year 2022!!!!

Fire in the Hole, charge in the rock, energy and waves within rock grains.

Happy mining

Say no to poor use of explosive

Say no to unwanted blasting event

Use explosive for peace and not for war

Let us mine the Earth safely

Thanks

Appreciate from Taiwo Blessing Olamide (Giant miner) goes to all mining engineers who ensure and see to the proper implementation of mining laws and regulations.

Let us mine the mine and not dig the ground.

Thanks to USA, CANADA, AUSTRALIA, SOUTH AFRICA mining engineers. I salute your great work and practising.

Give zero tolerance for unsafe act and unsafe conditions.

Overbreak: Result of poor Blasting

                        A Technical overview of Overbreak

B.O. Taiwo*

Giant Miner

*Graduate of Federal University of Technology Akure, Nigeria 

author's mail: taiwoblessing199@gmail.com

 

Abstract: The presence of boulders in the blasted muck causes not only loss in production, but also increases the cost of hauling. In another words, the cost and efficiency of mucking, loading, and Comminution operations (crushing and grinding) will be highly altered by the outcome of blasting operation. This article give detail explanation about the causes and effect of overbreak during blasting. It point out the ways to control and minimize blast overbreak and give recommendation on the ways to improve blasting operation and safety. The safety of the mine is important to ensure guarantee of life, therefore generation of overbreak on the mine face affect both profitability and safety status of the mine. All possible means and design must be put in place to mitigated and control the generation of overbreak during blasting operation. Rock mass with existing fractures and joint set likely become detrimental in the present of overbreak fracture, such become unstable and can undergo plane or wedge failure if all require conditions are fulfilled. The ore require high grade status to guarantee high economic value, external dilution resulting from overbreak may increase dilution resulting into increase in haulage cost and processing cost. Overbreak floor also support the out flow of ground water into the mine and demanding for de-watering operation if not result into Acid Mine Drainage or total closure of mine. Overbreak can therefore be control from the Pre-blasting stage which involve proper understanding of the ore deposit geological condition, ground water condition, explosive material knowledge among others. Special blasting techniques like pre-splitting, post splitting, line hole, cushion blasting, air decking among others can also be use to control overbreak in mine wall, toe and face. 

 Keywords: Blast, overbreak, fragmentation

      

1. INTRODUCTION

The profitability of blasting operation depends upon the ability of the Mining Engineer to produce fragment size distribution as close as possible to the optimal range for downstream operations. In addition, from practical standpoint, oversize is defined as size ranges greater than the crusher’s gape and therefore requires secondary breakage before further handling. In most hard rock mining methods, drilling and blasting are the most widely used method of fragmenting the rock for handling (transportation and stock-piling) (sang and Katsuhiko, 2004). Sang and Katsuhiko, (2004) noted that, an optimal blast is that which yields the specified fragmentation size distribution at safe, economic and environmental friendly manner. On the other hand, a poorly conducted blast would typically end in poor fragmentation and may generate adverse effects like fly rocks, ground vibration, air blast and back break (Nassib et al, 2016). Nassib et al, (2016) also discovered that blasting operation is capital intensive due to the following; need for rock mass reduction to smaller size ranges, efficient use of explosive energy at high safety level; and control of blasting to avoid oversize materials. Therefore, there is need for proper blasting optimization using the controllable factors which can be predicted using machine learning packages and other empirical formula (Tiile, 2016).    

The primary requisites for any blast design is to ensure optimum results for existing operating conditions, possesses adequate flexibility and comparatively simple to use (Muhammad, 2009). Several factors affect the output of a blast, these factors can be generally classified into two; uncontrollable factors and controllable factors.  Uncontrollable factors are those that the blast designer has no direct control over. They are controlled by the intrinsic (DIANE) properties of the in-situ rock formation or ore deposit to be blasted. According to Konya and Walter (1990), these factors include: geology, rock characteristics, regulations as well as the distance to the nearest structures. These limitations usually require that the blaster makes correct modification to a standard design to fit the conditions of the in-situ rock conditions.

2. Blast OVerbreak  

 

Fig 1. Theory of blast Overbreak   

The chance of breaking rock beyond the design reference is highly possible during Blasting operation. This is known as overbreak, when the Explosive energy fractures the rock beyond the bench width. This is highly dangerous and even disastrous to both safely and profitability.Deep deposits are mined in benches to ensure easy access to the pit and support of multiple operations within the mine. The pit benches are design such that the height is higher than the loader boom height and selected base on geological condition and grade Control constraints.  Each bench width is designed such that it accommodate truck turning radius and it overall width, this is done with high consideration of grade Control and geological condition also to ensure discontinuity daylight is not supported and likewise external dilution is not supported. With all this in mind, the access road to the pit called ramp is also design, each with consideration width (Be in expectant of my lecture on pit design and ramp design). Over breaking the bench width beyond this design width will compromise the safely in place of bench wall stability and also affect production in place of dilution and poor fragmentation. 

 

Fig 2. Site view of Overbreak effect on mine toe (After ismge.org)

 

2.1 How overbreak occurred during Blasting

 

Muhammad, (2009) establish that blast design usually aimed at providing adequate fragmentation and ensuring that loading, haulage and subsequent processing is accomplished at the lowest possible cost. However, for optimum and efficient blasting performance, it is essential to consider critically the rock mass intrinsic properties. Rocks are usually characterized by several properties. The nature and properties of the rock mass vary sharply over short distance. It is therefore important that the influence of the rock mass parameters must be understood during the blast design process (Bhandari, 1997).

Overbreak begins from the blast design point, selection of Minimum burden distance must be done with good decision and rock condition justification. One important parameters that support overbreak is the wall burden distance. If this is small then the implication is to produce overbreak beyond the bench wall. Such occur because the Explosive energy (shock wave) is under use within the wall and have sufficient strength to proceed slabbing into the wall. Since slabbing is extend into the wall explosion will definitely fall rock beyond the wall Konya and Walter (1990). This follows the law of conservation of energy directly.

Other factor is the powder factor, this is the quantity of explosive designated to fracture a ton of the rock, this depends strictly on the charge weight per hole.

Pf = charge per hole ÷ Tonnage of rock fragment per hole 

From my short study of jack hammer drilling and Blasting operation, a single hole of jack hammer blasted is expected to produce nothing less than one (1) ton of the rock. Meaning if 5 holes are blasted,ore than 5Ton capacity truck will be produced. In situation where at the last hole row, the Explosive weight is more than that to fracture within the holes area o influence then, the unused Energy will definitely be use to overbreak the wall and create problem.

It's important to know that during Blasting of a single hole the burden is divided into two and distributed at the four cardinal direction of the hole to form the area of influence around the hole. Each blast generated energy from Explosive exothermic reaction is expected to be active within this area of influence. Placing our blast holes at the last bench edge should be done with respect to this understanding. This area of influence is define by 1ft/ms of shock energy traveling and it correspondence to the gas Energy explosion time and Rick casing time according to scholars research work in 1970s.  Explosive  shock and gas energy will always be active provided the area of influence is still yet completed. Over breaking in rock mass is easy to control when the place of understanding the blast parameters balancing is fulfilled. This can be prevent by increasing the burden distance.

Nevertheless, if design burden distance is much,  the implication is that,blast charge initiated will have more of the energy contained within the designated region thereby producing back-break or under-break as shown in Fig 1 which generate more oversize. Oversize or  Large Particle size materials  requires secondary Blasting or hydraulic breaker to Re-break the rock. This form a source of additional cost and waste of time which any company will never want.

Another factor that causes overbreak is rock mass Anisotropic and heterogenous nature. Rock consist of various Mineral composition, the response of each mineral components to Explosive energy is different due to their Strength and hardness variation (Bhandari, 1997). This heterogeneity nature makes rock and ore deposit Anisotropic to explosive energy. As a result of the this there will be change in fracturing along the rock wall. For instance, formation containing dyke or sill which are both geological intrusion, this intrusion according to the principle of intrusion which states that, "the rock been intruded is older than the intrusion itself". With the understanding of this principle if all things been equal in absent of weathering and leaching, the intrusion (dyke, batholith, laccolith among others) are proved to have higher strength than the old rock been intruded especially in case of metamorphosed carbonate rocks (marble and dolomite). Blasting such rock, understanding the geology of the area and deposit, with proper strata test, geotechnical mapping work  and observation during drilling will help to put good charge design in place to handle any variation in rock stratigraphy and lithology.

Other factors include discontinuity, Explosive property and conditions, misfire among others which I will explain in my full article.

 

2.2 Effect of Overbreak 

 

Some of overbreak effect are:

1. Produce rough bench wall

2. Support external dilution

3. Support slope and wall failure

4. Poor fragmentation and non uniform size distribution among other 

 

2.3 Ways to control and prevent overbreak

 

1. Proper Blasting design: making balance in blast parameters (burden, spacing, stemming length e.t.c.) Design

2. Proper study of formation geology and lithology during Drilling: This require the implementation of drilling log in mine, the drilling team should provide information of each holes clearly as observes during Drilling and from the drill cutting. Such include interception depth at which a hole lithology changes, the strength variation with depth as indicated by Penetration rate During drilling, collar condition and others.

3. Discontinuity information and joint set mapping to understand the insitu rock stability and competency status.

4. The place of powder factor control is also important and place of drill hole row alignment with design.

5. Preventive measure against misfire such has Explosive checking, proper loading and connection, hole water status checking e t.c should be intact.

 

Conclusion

 

The safety of the mine is important to ensure guarantee of life, therefore generation of overbreak on the mine face affect both profitability and safety status of the mine. All possible means and design must be put in place to mitigated and control the generation of overbreak during blasting operation. Rock mass with existing fractures and joint set likely become detrimental in the present of overbreak fracture, such become unstable and can undergo plane or wedge failure if all require conditions are fulfilled. The ore require high grade status to guarantee high economic value, external dilution resulting from overbreak may increase dilution resulting into increase in haulage cost and processing cost. Overbreak floor also support the out flow of ground water into the mine and demanding for de-watering operation if not result into Acid Mine Drainage or total closure of mine. Overbreak can therefore be control from the pre-blasting stage which involve proper understanding of the ore deposit geological condition, ground water condition, explosive material knowledge among others. Special blasting techniques like pre-splitting, post splitting, line hole, cushion blasting, air decking among others can also be use to control overbreak in mine wall, toe and face.  

References

[1]           Sang Ho, C. and Katsuhiko K. (2004). Rock Fragmentation Control in Blasting. The Mining

        and Materials Processing Institute of Japan , pp. 1722 to 1730.

[2]          Tiile, R. N. (2016). Artificial neural network approach to predict blast-induced ground

        vibration, Airblast and rock Fragmentation . Masters Theses. 7571.

        https://scholarsmine.mst.edu/masters_theses/7571

[3]           Muhammed, A. R. ( 2009). The Effect of Fragmentation Specification on Blasting Cost.

  Unpublished MSc Thesis Report, Queen’s University, Kingston, Ontario, Canada , pp.192-    

  200.

[4]           Konya, C. J. and Walter, E. J.  ( 1990). Surface Blast Design. Prentice-Hall Inc., New Jersey,

  USA , pp 125.

[5]          Bhandari, S. (1997). Engineering Rock Blasting Operations. A.A. Balkema, Rotterdam,

        Brookfield , pp 375