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

MY WORDS TO MY WORLD: GIANT MINER

Undergraduates time is a time to discover who you are! A time to change you level and know the level you belong. Not all about the lecture you are able to receive now, but about what you are able to retain. You need to know this early, so it will not be late. There is a grace that help a man to study, to know, to excel and to win on campus. The issue and challenge is not the lecturer, is not about your head but the limitation is knowledge.

Knowledge about what is available is important, what you have will always remain in you until you unveil it. The grace of the Lord that brings salvation had appear unto all men.. Titus 3:11

You have heard about the great things the Lord did and is doing in my life even when I was still in FUTA as an undergraduate, how I receive grace to defeat many courses and have A's, how I overcome the war of many exam and outrun marking guide by the help of the holy spirit. I don't want you to be ignorant of what God is able to do if you trust HIM and live for HIM, this is why I write to you.

if you believe in HIM and present your life as a platform for him to glorify HIMSELF, you will become another Giant Miner.

The secret behind all you hear about me is this, my desire is always:

*That the LORD Be glorify, even in my Academic, that HIS greatness be visible to man, that my life should be a crystal reflecting is Glory, that I should be a question that lead to what God can do through a man* This is my testimony!!

Not I but GOD, not I but HIS Glory should be revealed in my Academic by HIS mercy.

This is my heart cry always.

I received strange grace that change my life, Strange grace that teaches me, a strange grace that strengthen me, a strange grace that cancel test for my sake, a strange grace that I call unto in the exam and he answers me and tell me what the lecturer likes to see, a strange grace that direct me to what I need to read, a strange grace that opens my eye to see what others can't see, this same grace is what I want you to ask for and wear like a coat just as Joseph wears the coat of many colors given to him by Jacob his father.

Many met me and tap grace, I  give within me just as I am given freely and I give just as I was given, but I think their is yet another measure, because the grace told me their is still another level in Him I am yet to touch. Greater level I am yet to experience. This is what I desire for you, that greater than what I touch you touch double portion, hundred and thousands portion in Jesus name.

THE GREATEST WORD EVER 

By Giant Miner: 

There is a secret that make life, a secret that is hidden from men, a secret many who live just for the things in this world will never know.

It please GOD to help us, He Gave us all we want but we still want what we have...

The secret is Christ in you, the hope of GLORY. Don't be deceived, life is vanity, you can't get all the money in this world even if you have a place to store it. It is time you start building a place for your self after life, what is life that man pay all his time building, life is a piece of paper that become soften when water encounters it... What can I compare life with....

 Life is a pice of matches, when you light it, it glows and shine light but after time has passed, it become darken. The life we are given was a golden ring in a darken shield, you go for the gold and loss destiny to the shield, what is life? a chance to trade, a chance to pay, a chance to look and find nothing to pay for, a time to pay for what you can see, a time to pay for what you can't see or think about! Life is a grass when one is cut another arose again, life is like a new cloth you behold the color at the first sight but wash it away with a matter of time. Life is what you live for if you are here on Earth as a slave, life is what you sell to others if you are here in Earth as a son

 Life is a lot, a deep pit where many content loaded fellow will fall, life is like a flower coming forth from the pod like a new baby, a time to fall for life like a young man Falling in love, a time to see life with a beautiful face as a lady whose hand is held into marriage, a time to sleep at one edge of life like a woman sleeping at one edge of her bed, backing her husband and having many things to attend to in the stope of her mind. Life is like soil, it comes out of rock and at the time of it's burial give birth to Rock, life is just what you keep buildinging like a dome of salt, every situation and circumstances have sufficient heat to melt it down. Life is like your bank accouni, It increase today and decrease tomorrow because everyday have sufficient deposit of resources sucker.

Dear friend, fellow students, dear brother and sisters, life is like a light, a light from the sun that shine forth in the morning time at sun rise and goes down in The evening time at sun set. There is a time in life when you need others light to see, there is a time in life when you need others light to shine, there is a time in life when you shine as a light, there is a time when others need your light to shine, there is a time in life when you need others to initiate your light. life is like an aeroplane, it takes off from the lond later return back to the land. When you take off, remember you are once in the floor level, when you get to the top remember you are once running the track, when you take off remember you are landing soonest. Life is not like the sand of the sea shore that is uncountable, but is limited like a unit course. Life is not like the Star of the universe, you have yours as a running time, the clock moves from 12 and will in due time return back to 12. What are you doing within the 12-12?

Are you living for Christ or for yourself?

Life will laugh out the light in many and leave many to land untimely if not well and properly use.

 Be careful, live like tomorrow is the last day and the judgement day, for a day is coming that all works will be check on the radial of achievement. The works of many will be tested with fire, what will be to yours?

Think about this!

MAKING MINE A SAFE PLACE: DESIGN OR RE-SIGN

MAKING THE MINE A SAFE PLACE: DESIGN OR RE-SIGN

 a typical underground working level in a competent formation

Many will agree with me that, mining is far different from all other profession, the fact that you have potential and title will not be a respectable fact for falling block or wedge not to break the head of mine manager who fails to put a safe design and measure in place for safe Mining. Also, I submit to you that rock formation has a major challenge of heterogeneity, non elastic, Discontinum, and Anisotropic characteristics which make it detrimental to stress field alterations under excavation and Blasting operation. Since Mining involved holing and extracting, by creating artificial cavity into the insitu rock, ground as the case may apply to remove what is supporting the lithosphere all in the name of profit and economic development. The standard is inevitable, you disturb the crust, the crust adjust and react to achieve stability. In view of this, making such as  large as mponeng gold mine in Johannesburg in South Africa ranging from 2.5 to 3.9 km established by jannatac technologies (2018) such mine must be design with high factor of Safety. Imagine workers working in such mine and the wall collapse saving the Miner family from buying coffin,  In such situation, it polite to say, the Miner's life is sacrifices for the mining operation, which is not a good idea. Then how can a mine be a safe and profitable place???Majority of mining operations are dangerous, costly, and risk in nature. Imagine people going into the subsurface as deep as 4.22km below the surface to get Gold! Check how it looks like when you there is poor ventilation, poor lightening, or rock Burst with great release of strain energy... Come out from such depth in a cage suspended by  multi-stranded rope running through series of drums may not be safe if poorly design. Drilling overhand into stole roof, charging, loading and Detonating a highly fractured rock mass during block caving tends to be more dangerous just as the associated surface subsidence and airblast challenge, but with all this Mining Engineers make balance between all and ensure the ore is been mined and transport to the surface for the use for manufacturers. The beginning of all mine safety assurance is the place of mining method selection... The foundation of the production and profit status is getting the best way to select the most suitable method among many available method of Mining. To a Mining Engineer reading this not, you will understand what I am saying, But to you as an individual you will be like, what are the mining methods available and what factors do we consider when selecting the suitable method for a particular deposit and what is the significance?

Actually, many deposit both metallic and nonmetallic are usually known to existing in a host or parents rock. Such host rock in many case have series of she'll which can range from unconsolidated soil to hard rock. The accessibility of such deposit depends on the approach adopted to bypass the cover cloth (host rock). Such constraint is usually capital challenging and as a Mining Engineer we overcome such using....Striping ratio equilibrium limit as a base for justification when selecting mining method. There are basically two methods, is either surface Mining or underground Mining method. Surface Mining method is use for ore deposit with stripping ratio is lesser than one (1). This implication of this is that, the volume of overburden materials (envelope layers) to be removed to access the ore is lower compare to the volume of ore to be mined. Striping ratio is basically explain as the ratio of overburden volume to the minable ore volume. An ore is not economically suitable for surface Mining if the SR>1 i.e the volume of overburden is > volume of ore. This can also to consider in economic point of view, that if the cost of removing the overburden materials is greater than the expected market price equivalent of the total minable ore volume, the such ore is best mine by Underground mining method. In most cases, the senerio maybe that the cost of stripping I'd equal to the sale price of the minable or, such us refer to as break-even stripping ratio. In such case other factors like environmental constraint, equipment among other factors can be use as the judgement vent for decision making decision. Now the first step is overcome, you now have assurance that, the deposit will be best mine by surface Mining method.. the question now becomes, what method among all surface Mining method?

Decision made according to scholars can be base on certainty, risk or uncertainty. the place of I formation can not be disputed in this, to start as a Mining Engineer, researching on similar deposit and the adopted methods for similar ore will likely help in making your decision. I speak as a Mining economist now, if the cost of getting those equipment you need is to high such that you can only buy them, then the cost to operation them is not feasible, It is advicable that you go for that which you can afford both purchase cost and operating cost.Now I am back as a mining Engineer, if the development cost is to high in such that the available capital can only remove the overburden but can start the Mining nor make the ore from mine2mill, then consider another method that will start the Mining and complete the beneficiation safely base on the available capital.

As I have established earlier that, research on similar deposit help a lot, through this you tend to know the possible requirements to win the ore profitably and safely. After this, you can now tabulate the various available methods with their advantage and disadvantage all within the ore geometry and geotechnical properties well understand. Well I will not complete this if I fail to mention the pre-planning operation require for mine selection which comprises geological, hydrological, geophysical, geotechnical, and Geochemical survey to get sufficient information about the deposit. Also, I will like to establish this fact that, there are already existing software, charts, table and graphs by researcher like Morrison, weight, Nicholas, Hartman, University of British Columbia UBC among others. Such method is divided into two, that which is qualitative and that which is quantitative.

Mining operation must be well design to avoid any for of threat to life and properties.

If it is not safe, then is not minable. Work the Earth in a safe and secure way to ensure it is safe for others to enjoy. Mining is not just removing the mineral from the Earth but, doing that in a save and secure way to keep it free from Hazard and accident. We mine the Mineral to build the Earth not to injure and damage the lithosphere, reclamation and rehabilitation is important. If you can not reclaim, you can rehabilitate. Reclamation involve complete restoring of mine out stope back to the initial form. Some case can arise where the available resources can't reform the mine opening, we can rehabilitate it to become a safe and useful place for other activities like pond, tourist center, save stope. Ensure the wall is competent and will stand without falling, treat and control any form of mine waste, Mine affluent that can be a source of acid mine drainage or acid rock drainage. The term AMD is a serious source of acidify water, which is formed when sulphuric mineral, metals, coal is exposed to oxygen and water. Such process result in the formation of acid water which affect the biosphere, the plant, water, soil, and wildlife including human. AMD is common in metallic mines, waste from the mine and stripped overburden contain fillings of metal or weather metallic minerals. Such material when exposed to the atmosphere generate acidify product in two ways,

1. Through geochemical reaction (oxidation)

2. Through microbial activities

The geochemical process involve the metal getting exposed to H2O and Oxygen (O2).

For example, when pyrite (FeSO4) is exposed to water and Oxygen it oxidize Iron (II) to increase the acid level of the mine water.

Improperly manage mine will manage the mine resources and exhaust the mine manager.

Why mining is not like others,

1. Mining operation is capital expensive.

2. It an operation that houses the workers

3. Any failure will fade and fail the workers.

4. It involves different activities that are hazardous if poorly handled e.g blasting operation

I love u all, share with friends, comment and recommend

SUMMARY OF MINE SHAFT AND SHAFT COMPONENTS &USES

INTRODUCTION TO SHAFT AND SHAFT USE IN MINING

BY GIANT MINER

 Shaft as related to underground mine is a vertical or an inclined opening extend from the surface into the ground to provide access to underground working area.

 it not a news that we can mine the ore by surface and underground mining method. Now underground methods requires that the mining Engineers move into the subsurface with their equipments to extract the ore. We can't just disappear at the surface and appear in the underground like a magician!  We provide an access into the ore without stripping the overburden materials. 

These access are reference to two, the primary development and secondary development.

Shaft is a primary development opening as it has a life span greater than that of the mine. It provide access for personnel entrance into the underground mine, provide duct for ventilation, and many more.

Shaft can be classified into categories base on the following:

1 Base in uses

2. Method if excavation

3. Support system

4. Geometry

My joy is to give full explanation on all this today and give a detail explanation of them all... Also, to help give further explanation always send comment over so I can appreciate your reading.

Shaft type base on uses

This can categories into

1. Production shaft: 

2. Exploration shaft

3. Service Shaft

4. Escape Shaft

5. Ventilation shaft

6. Combine shaft

 Production shaft: is that having a skip conveyance that help in transporting mine materials and waste from Underground to the surface. 

Service Shaft is mainly for the handling of personnel, workers and sometimes equipment from in and out the mine.

Ventilation shaft is also refer to as auxiliary Shaft by some textbooks especially the introduction to Mining textbooks. The main function o such is to support inflow and out flow of air into the Working area. Both for dilution and respiration. Underground is not surface, artificial air is required to keep miners alive. Exploration shaft are also refer to as the pilot shaft use for gathering geotechnical, geological, hydrogeological and other information about the ore deposit. Such shaft is sink to retrieve information for planning and Design seek. Escape Shaft are shaft sink to provide alternative evacuation for the mine workers Incase there is any emergency or incall for accident. I wish to have a talk on mine accident and environmental management soon. Components of shaft include, cage, skip, hoisting rope, hoisting drum, shaft liner, Shaft collar, shaft superstructure, and many more.

These all classified into Surface and underground components.

Cage is a conveyance or container use to move personnel in and outside the Shaft. Skip is a container design to be used for moving mine Run-off-mine and waste out of the Shaft during production and into the shaft during backfilling..(speaking like a professional now)

Rope is an energy supply components that assist in the hoisting of the conveyance.

The rope consist of three components, the wire, strand and the core. The wire is the smallest component or entity of a rope, the strand is two or more wire twisted together, the core is the center component of a rope. Selection of the rope is done base on the safety, compatibility, life span and cost. The rope can be use for three functions in a shaft system, for hoisting, for support and for guidance.

The hoist is a general name give to the outside components that controls the lifting and lowering of the conveyance in the Shaft. The hoist can be of two types, it can be friction hoist or drum hoist. The friction hoist involved a wheel been located above the shaft containing a rope passing through it into the Shaft. In such sinerio, the role is not whirr round the wheel but just pass through it, and the wheel is usually located above the shaft.

For drum hoist, it can be position at a distance from the shaft, and such drum allows the whirring of the rope round it. It consists of sheeves that centered the rope in the Shaft.

Okay, let me mention other classification of shaft 

2. Base on geometry, this includes size and shape. Basically shaft with size (2m to 15m) is called small Shaft, 15-200m is medium size Shaft and >200m is large Shaft.

Also, that shaft can be of three main shape, 1. Circular 2. Rectangular 3. Elliptical shaft.

 Actually, you may want to ask what is the advantage of this shape over the safety of the Shaft?

Speaking as a rock mechanics now, the insitu stress is naturally at equilibrium before excavation, any attempt to create excavation into the ground cause a great redistribution of the stresses, this cause the concentration of stress at some Region and relaxation of stress at other region. According to Dr Idris, a rock mechanics professional, a lecturer in the department of Mining Engineering, Federal University of Technology Akure, Stresses insitu will never leave after excavation, rather they become induce stress on the excavation wall. Such Stresses then become threat to the safety of the excavation wall. Examine 2D© a Boundary element method software shows that the circular shaft tends to have low wall damage zone as the induce stress distribute equally round the wall, unlike the rectangular shaft. Such opening with rectangular shape have high stress concentration at the 90° corner sides which make the wall liable to heaving, and oiling depending on the property and strength of the rock formation. This make the use of horse shoe shape in tunneling an advantage to redistribute the insitu stress in such a way that less Concentration is achieved all round the wall.

 But as good as the circular shaft is, it only sink able using shaft boring machine SBM, which can inturn be very expensive, limited in high Strength formation

Prompt to this, the rock is DIANE  (Discontinuous, inhomogeneous, e and non elastic)

in nature, this make the prediction of shaft wall stability inaccurate. Then, Mining Engineer need a means to garantee the safety of this wall and the life of mine workers. This lead me to the place of shaft classification base on support system.

 Classification of Shaft base on support system can be divided into two broadly

1. Base on traditional approach

a. Permanent support: shaft with support system that are meant to stabilize the shaft throughout it life span 

b. Temporary support: shaft with support system that are installed for short periods of time

2. Base on modern Approach

a. Primary support system: shaft with support system done before the excavation e.g the caisson and piling Techniques. Generally, the support system can be active or active, such kind of active supports are those which apply predetermined load or pressure on the shaft wall such as the grouted rock bolt and the hydraulic prop support

 (reinforcement). The passive are those with support approach that involves no predetermined load on the wall. If we leave the wall unsupported, the life of workers will be under threat and we tends to have more confidence for great work. Therefore, giving all to see the wall stabile will facilitate the production rate and also compensate the increase in efficiency. This is why we support the wall.

Finally, Shaft can be classified base on the excavation method, this implies the Technique use in sinking the Shaft. I talk like a Mining Engineer now, in overview, there are two techniques adopted for shaft sinking, mechanical method and conversation method. This methods are selected base on the following factors; Rock strength, shaft use, capital available among others.

The conventional method involve drilling and Blasting. Also known as the traditional approach. It involves the following operation cycle; drilling, charging, connecting, blasting, ventilation, loading and transportation if material, scaling of wall, bolting and drilling again for a new Blasting. This operation continues till we are done with the shaft sinking (excavation). The advantage of this Techniques are; ability to sink any shape shaft, ability to sink shaft in any rock strength nature, low cost of operation to mention few. Disadvantage of this Techniques are; poor/rough Shaft wall and back  due to shock wave inconsistency, requirements for heavy support due to overbreak,  environmental challenge, slow process among others.

The mechanical method involve the deployment of machine which bore the earth and create the shaft mechanically.

Also perform the supporting simultaneously.

Such equipment include shaft boring machine SBM. advantage include, fast sinking rate, smooth and stable wall, Perfect job, quick advance rate, it can be automated, little environmental effect and Many more. Disadvantages include, limited to circular shaft, limited to soft formation as hard rock damage dill bit, downtime during equipment breakdown among others. I talk like a professional now, shaft excavation method can be divided into two professionally,

1. Ordinary method

2. Special techniques.

The process of shaft sinking is divided into sinking from surface to the bedrock, sinking through the bedrock and sinking through unstable conditions. This lead to the above professional classification.

The ordinary method involve Drilling and Blasting when sinking through stable and Continuous rock formation. Such rock are stable and competent! The special techniques are use when the ground is unstable and incompetent such as sinking through sand, watery ground e.t.c. such techniques adopt in such case are: piling method, caisson method, grouting method, freezing method, shaft drilling and boring techniques.

 Remember we go into the subsurface to extract, holes are created in the ground after excavation, it is the duty of Mining Engineer to back fill or support the excavated hole after mining has been done. By this the surface structure will be safe from holing and subsidence...

Remember mine it only when is safe, and when the environment is safe, this is what differenciate mining from other field. If you mine it unsafe, you are unsafe! Your Safety is your profit... Let make Mining a Better profession again.

Thanks

key to Productive Mining: Blast design

Blasting and Mining cost

Blasting operation is one of the Technology use in breaking rock mass into smaller sizes. Since rock exist as an Anisotropic and heterogenous massive solid at the lithosphere it therefore requires the use of energetic Technique like blasting to generate sufficient shock wave for fracturing and gas Energy for casting down. Mining operation is known to be a capital intensive project whether small scale or large scale, likewise the place of safety is insuschangable. At this expenses, Blasting operation dictates the cost of other preceding operation and even the downstream operations. Blasting operation is a professional work that and a bit difficult to design for ordinary person since two major factors affect the output result which are the controllable factors such as burden and other hole geometry parameters and uncontrollable factors such as rock strength and other geological and geotechnical properties of rock.

Making balance between this two factors to ensure maximum energy is supply for optimum fragmentation becomes a difficult task. Failure to achieve this gives high cost Blasting, environmental challenges such as flyrock, misfire, overbreak, ground vibration among others. Minimizing this in small scale mine who make use of jack hammer and other small hole diameter drill machine becomes a problem an therefore causing diverse limitation in Nigeria mining sector and other countries.

Open pit mine design: Key to optimize productivity

Short ways reduce open pit mine operation cost:

1. Proper design: remember proper preparation prevent poor performance (5p's  key of good operation system). When it comes to open pit mining I always like to make mine plan and Design first as the key ways to optimize and garantee profitability.

See through this: The following factors are the dictator of stripping ratio (Stripping cost), Drilling and Blasting, loading and haulage operation, then processing operation.

Find the factors below and how that affects the about operation:

Factor number 1: Bench height: This is the maximum vertical extension of the mine bench also define as the vertical distance from the toe to crest of a bench. This factor determine the type of loading equipment that will be strictly permit in the mine for loading because, the loading boom of the equipment must not be longer than the bench height. Small loading equipment means low production or high cost of getting enough loading equipment that will fit for your production target as shown by your fleet design.

It also affect dilution control in the mine, heigh bench height result into large hole Drilling, and large powder factor which may result in external dilution through overbreak, internal dilution through backbreak. It also affect selective loading. All which increase production cost by increasing haulage cost (more waste move to Processing plant), increase mine life (by reducing recovery mill efficiency) and also reduce ore grade automatically reducing ore market value.

Get other factors explain in my blog @ giantminer.blogspot.com