Contents

CHAPTER ONE. 3

1. INTRODUCTION.. 3

1.1 Background. 3

1.2 Problem statement. 3

1.3 Problem Justification. 3

1.4 Goal and Specific Objectives of the Project. 4

1.5 Scope and Limitations. 4

1.5.1 Scope. 4

1.5.2 Limitations. 4

CHAPTER TWO.. 5

2. LITERATURE REVIEW… 5

2.1 Definitions. 5

2.2 Rock fragmentation. 6

2.3 Importance of Better Fragmentation. 6

2.4 Optimum Fragmentation. 7

2.5 Factors Influencing Fragmentation. 7

2.5.1 The Geology Of The Rock. 7

2.5.2 Rock Characteristics. 9

2.6 Bench blasting. 10

2.6.1 The bench blasting parameters. 11

2.7 Approaches previously applied in determination of rock fragmentation. 12

2.7.1 The Kuznetsov Mean Fragment Size Theory. 13

2.7.2 The Kuznetsov Equation in Powder Factor Form.. 14

2.7.3 The Rosin and Rammler equation. 14

2.8 Modern technology. 15

CHAPTER 3. 16

3. METHODOLOGY. 16

3.1 Study from the literature. 16

3.2 Data collection entailed; 16

CHAPTER 4. 17

4. RESULTS AND ANALYSIS. 17

4.1 Results. 17

4.1.1 Exploration data. 17

4.1.2 Blast parameters. 18

4.1.3 Explosives used at the quarry. 18

4.1.4 Volume blasted. 18

4.1.5 Photographs. 19

4.2 Analysis. 20

4.2.1 Exploration data and photos. 20

4.2.2 Blasting parameters. 20

CHAPTER 5. 21

5. CONCLUSION.. 21

5.1 Discussion. 21

5.2 Recommendations. 22

5.3 Expected Results. 23

REFERENCES. 24

APPEDICES. 25

APPEDIX 1: Work Plan. 25

APPEDIX 2: Budget. 25

CHAPTER ONE

1. INTRODUCTION

1.1 Background

Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO₃) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. It can also be a chemical sedimentary rock formed by the precipitation of calcium carbonate from lake or sea water. When limestone is metamorphosed, it becomes crystalline and is known as marble, but the mineralization remains the same, i.e., calcite.

It is the main source of lime used in manufacture of cement at East African Portland Cement Company (EAPCC). It comprises 60-65% of all primary raw materials used by EAPCC to manufacture Portland Pozzolanic cement and Ordinary Portland Cement. The rock is mined at Kibini Hill Limestone Quarry which is located 120km away from the EAPCC Athi river plant and 19km west of Sultan Hamud town on the Nairobi-Mombasa highway. The quarry covers an approximate area of about 1600acres.

1.2 Problem statement

With the escalating competition in cement production, the general total cost for the complete mining operation has to be optimized. EAPCC incurs high costs in blasting processes due to poor fragmentation of the blasted rock leading to excessive secondary blasting and further reduction using breakers before feeding to crusher. The key objective of production blasting is to achieve optimum rock fragmentation. The degree of rock fragmentation plays an important role in order to control and minimize the overall production cost including, loading, hauling, and crushing costs.

1.3 Problem Justification

Limestone is a major raw material (about 60%) used by the factory in cement production. The factory requires 2000 tonnes daily for manufacture of clinker.

Maintaining this supply is important as it ensures the required ratio for all raw materials is achieved. Limestone therefore has to be mined continuously and at lower costs.

Poor fragmentation or big boulders influence the supply of blasted rock to the crusher as they have to undertake secondary blasting and further breaking with breakers.

Due to the above extra costs on production, there is need for EAPCC to optimize its blasting output

1.4 Goal and Specific Objectives of the Project

The main goal is to attain optimal fragmentation at Kibini hill limestone quarry by effective consideration of rock properties and blasting parameters.

The following specific objectives will aid in achieving the goal.

• To come up with the most effective set of blasting parameters and blasting procedure.
• To outline the most suitable set of explosives and firing pattern for optimal rock fragmentation
• To come up with adequate suggestions and conclusions based on the project findings

1.5 Scope and Limitations

1.5.1 Scope

This project covers mining area 5 which is the current mining area and the study took a period of three months (3). The data employed in the study included:

1. Geological data (rock structure, in place reserve and in pit mineral recovery) of the mining area obtained at the quarry and the Exploration and Tertiary Materials Department at East African Portland Cement Factory.
2. Blasting parameters data obtained at the quarry.
3. Mine production data (total volume in one round) obtained at the quarry

1.5.2 Limitations

1. Considering the age of the quarry (1933) some of the exploration data was not available.
2. The project scope was limited due to insufficient time and finances.

CHAPTER TWO

2. LITERATURE REVIEW

2.1 Definitions

1. Fragmentation: Act of breaking the rock or the distribution of the particle size of the blasted rock
2. Rock: Is a naturally occurring solid aggregate of one or more mineral or mineraloids.

1. Blast: Detonation of explosives to break rock.
2. Blasthole: Hole drilled in rock (or other material) for the placement of explosives.

5. Explosive: chemical mixture that releases gases and heat at high velocity, causing very high pressures.
6. Boulder: Oversized blocks from blasting.
7. Blasting agent: Any material or mixture, consisting of a fuel and oxidizer intended for blasting, not otherwise classified as an explosive and in which none of the ingredients are classified as an explosive, provided that the finished product, as mixed and packaged for use or shipment, cannot be detonated by means of a no.8 test blasting cap when confined.

1. ANFO: Powder form explosive consisting of ammonium nitrate and fuel oil mixture. It is the most commonly used blasting agent.
2. Bottom charge: concentrated charge in the bottom part of the blasthole.
3. Column charge: charge of explosives or blasting agent in the column section of the blasthole, above the bottom charge.
4. Burden: The distance from an explosive charge in a blasthole to the nearest free (or open) face at the time the hole detonates.
5.  Spacing: Distance in meters between adjacent blastholes and is measured perpendicular to the burden.
6.  Subdrilling: Part of the blasthole below the planned grade or floor level.
7. Back break: rock broken beyond the limits of the last row of holes.
8.  Stemming: Inert material used in the collar part of the blasthole to confine the gases from the detonation.
9.  Detonator (Blasting cap): Device containing a detonating charge that is used to initiate an explosive.
10. Blockhole: a hole drilled into a boulder to allow the placement of a small charge to break the boulder.
11. Bulk explosive: Explosive material prepared for use without packaging.
12. Delay blasting: use of delay detonators or relay connectors to cause separate charges to detonate at different times.
13. Delay detonator: detonator, electric or non-electric, with a built-in delay element creating a delay between the input of energy and the explosion of the detonator.
14. Delay time: time between initiation and detonation of a detonator.
15. Detonating cord: plastic covered core of high velocity explosive, used to initiate explosive charges.
16. Detonating relay: device inserted in a line of detonating cord to produce a delay between incoming and outgoing sides.
17. Round: Is one stage of blasting, producing an amount of fragmented rock (m³⁾.

 2.2 Rock fragmentation

Good rock fragmentation is a subject matter and depends on the end use of the rock. The desired degree of fragmentation also depends upon the type and size of equipment which is used for the subsequent handling of the rock. Large loaders, trucks and crushers can allow larger fragmentation, but it is a common misconception that larger fragmentation can be allowed because large loading, transport and crushing is used. The large size equipment is designed to handle volumes of material not large size material. The ideally fragmented rock is the rock that needs no further treatment after the blast. Therefore, the parameters for the subsequent operations are the guide lines for deciding on the desired fragmentation of the rock. If the rock is just to be transported to a dumping area, it should be easy to load and transport. If the rock is intended for crushing, the size of the largest boulder should not exceed 75% of the length of the shortest side of the opening of the primary crusher, thus allowing a free flow through the plant. Since the size of the broken rock is of utmost importance for the subsequent operation, all possible efforts have to be made to optimize fragment size.

2.3 Importance of Better Fragmentation

Blasting results are generally accessed according to the ability of the mining system to cope with the resulting muck. If the blasting fragmentation is poor, then so many difficulties will arise. Some major problems due to poor fragmentation are described below

• Secondary blasting will be necessary that is a cost-additive process.
• The mucking rate gets reduced.
• The loading rate from a draw point is controlled by the size and looseness of the muck (Bhandari, 1996). Extensive maneuvering is required by the excavator to load large rocks and the bucket loads are usually reduced when working coarse grain.
• Poor fragmentation creates problems in handling and transport.
• It affects crushing and efficiency of the transportation.

Hence a better fragmentation is desirable that would reduce all above problems.

 2.4 Optimum Fragmentation

The rock fragmentation is optimum when it contains maximum percentage of fragments in the required range of size. The desired size is the size which is in demand and can be effectively used by the consumers without any further operation. The desired size varies from consumer to consumer, (Venkatesh, 2010). Optimum fragmentation results in higher productivity, less wear and tear of the loading equipments which results in less maintenance of equipment and plant.

 2.5 Factors Influencing Fragmentation

In bench blasting, fragmentation is influenced by the following factors.

• The geology of the rock (faults, voids etc).
• Rock characteristics.
• Specific drilling.
• Specific charge.
• Drilling pattern.
• Firing pattern.
• Hole inclination.
• Hole deviation.
• Size of the round (blast hole diameter).
• Delay times.
• Types of explosives.

By considering the above factors during and blasting operation, it is possible to influence the fragmentation. However, it is not possible to make a completely reliable calculation beforehand. Test blast of some rows is a good way to obtain some impression of the blasting characteristics of the rock.

2.5.1 The Geology Of The Rock

The geology of the rock frequently affects the fragmentation more than the explosive used in the blast. The properties that influence the result of the blast are;

• Compression strength.
• Tensile strength.
• Propagation velocity.

Most rocks have a tensile strength which is 8-10 times lower than the compression strength. This property is an important factor in rock blasting. The rock’s tensile strength has to be exceeded; otherwise the rock will not break.

Table 1. Compression and tensile strength of different rocks

Rock with high density is normally harder to blast than a low density rock because the heavier rock masses require more explosives for the displacement of the rock. The propagation velocity varies with different kinds of rock. Field tests have shown that hard rocks with high propagation velocity are best fragmented by an explosive with high velocity of detonation (VOD). In consequence a rock with low propagation velocity may be blasted with explosives with low VOD. Emulate and dynamex with a VOD of 500-6000m/s are suitable for blasting granite, marble and diabase (propagation velocity 4000-7000m/s) while ANFO is suitable for limestone, sandstone etc with low propagation velocities. The hardness or brittleness of the rock can have a great effect on the blasting result. Soft rock is more “forgiving” than hard rock. If soft rock is somewhat undercharged it will still be muckable and if it is somewhat overcharged excessive throw rarely occurs. On the other hand undercharging of hard rock frequently result in a tight and blocky muck pile that is tough to excavate. Overcharging of hard rock may cause fly rock and airblast. The design of blast in hard rock requires tighter control than in soft rock.  Granite gneiss and marble represent the hard rock while soft limestone and shale are considered soft.  The structure of the rock should be documented before the blasting works starts. The direction, severity and spacing between the joint sets should be mapped out so that drilling and firing patterns can be adjusted to the prevailing conditions. The planning of the drilling with respect to the direction of the joints is very important.

Fig 1 Drilling with respect to the direction of the joints

Table 2. Advantages and disadvantages of each of Fig 1 approach.

2.5.2 Rock Characteristics

When blasting rocks, they are categorized into four types resistant massive rocks, highly fissured rocks, rocks that form blocks, porous blocks. Different types of explosives are recommended for each one of these types. Resistant massive rock formations have very few fissures and planes of weakness. As a result, an explosive is needed that creates a large number of new surfaces based on its strain energy. The strain energy is the potential energy stored in the linear part of a strained elastic solid. An explosive with a high density and detonation velocity will work well in this case. Thus slurries and emulsions would be good choices.

Highly fissured rock formations have many preexisting fissures. Explosives with high strain energy don’t work in this case. ANFO is the recommended choice here because of its high gas energy. When masses with large spacing between discontinuities that forms large blocks, and in ground where large boulders exist within plastic matrixes, the fragmentation of the rock is more based on the geometry of the blast than the properties of the explosive. Thus, you want an explosive with a balanced strain/gas energy relationship such as heavy ANFO. In porous rock formations there are many things to consider when blasting along with selecting the proper explosive. The proper explosive would be one with low densities and detonation velocity, such as ANFO. To retain gases in the blast hole for as long as possible the blaster should:

• Control the stemming material and height.
• Properly sized burden.
• Priming the bottom.
• Reduce blast hole pressure by decoupling the charges.

2.6 Bench blasting

Bench blasting can be defined as drilling of vertical or angled holes in one or several rows from a free surface, which then are blasted again a second free surface.

It is the most common kind of blasting work. The blastholes can have free breakage or fixed bottom.

Fig 2 Blastholes drilled to different depth

The bench blasting operations are classified according to their purpose (Jimeno et al. 1995):

• Conventional bench blasting – the pursuit of maximum fragmentation and swelling of the rock.
• Rip-rap blasting – obtaining large fragmentation of rock.
• Cast blasting – using explosives to not only fragment the rock, but to also project a large quantity of it to a predetermined place.
• Road and railway blasting – conditioned by the terrain and road plan.
• Trench and ramp blasting – lineal operation due to the shape and narrowness of the excavations, the confinement of explosives is high.
• Ground leveling and foundation blasting– usually over a small area and quite shallow.
• Preblasting – increasing the natural fractures in the rock mass with as little displacement as possible.

Bench blasting is classified by the diameter of the blast hole:

• Small diameter blasting – 65 to 165 mm
• Large diameter blasting – 180 to 450 mm

Many formulae and methods for calculating geometric parameters such as burden, spacing, and subdrilling have been around since the early 1950’s and use one or more of the following parameters: hole diameter, characteristics of explosives, compressive rock strength and many more. In small diameter blasting Swedish method developed by Langefors and Kihlstrom (1976) is used (Jimeno et al. 1995).

2.6.1 The bench blasting parameters

Bench blasting design parameters are given in the figure below

Fig 3. Cross section of a bench to blasted.

D is the blasthole diameter (m)

K is the bench height (m)

B the burden (m)

E the blasthole spacing (m)

U the blasthole subdrilling (m)

S (h₀) the blasthole stemming length (m)

H the blasthole length (m)

H_p the length of column charge (m)

H_b the length of bottom charge (m)

The most critical and important dimension in blasting is that of the burden B as it represents the rock mass to be fragmented by the explosive column and is calculated by a formula developed by Langefors & Kihlstrom (1976) as follows:

       …………………………………………………………………….. (1)

Where:

B_max     =maximum burden (m)

d          =blasthole diameter (mm)

P          =packing degree (loading density)(kg/liter)

s           =relative weight strength of the explosive (Emulite=150, ANFO=100)

=is the rock constant (kg/m³)

f           = is the fixation of the hole

S/B      =ratio of spacing to burden

The relation between burden and spacing is as follows

        S= 1.25B                          …………….……………………………………………………… (2)

2.7 Approaches previously applied in determination of rock fragmentation.

Rock fragmentation is considered as the most important matter in quarrying because of its direct effects on the efficiency and cost of drilling and blasting, and subsequent loading, hauling and finally crushing operating. Rock fragmentation depends on two groups of variable: rock mass properties which cannot be easily controlled and blasting parameters that can be controlled.

Total cost of aggregate production in quarry has a minimum value at an optimum fragmentation size (Mackenzie 1967; Morin and Ficarazzo 2005). Prediction of optimum fragmentation size will help the quarry owners in selecting blasting parameters to produce required material size at a known cost and also selecting other crushers and conveyor systems. Optimum fragmentation size may not be the required size but knowing the size distribution for particular blast and rock mass condition, the contractor can adapt the blasting if possible (Morin and Ficarazzo 2005). For prediction of the fragmentation size after blasting, the Kuz-Ram model is generally used. The Kuz-Ram model is an empirical fragmentation model based on Kuznetsov (1973) and Rosin and Rammler equations modified by Cunnigham (1983, 1987), which derives the coefficient of uniformity in the Rosin and Rammler equation from blasting parameters. Rock properties, explosive properties, and design variable are combined in this modern version of the Kuz-Ram fragmentation model.

2.7.1 The Kuznetsov Mean Fragment Size Theory

In the early 1970’s, the Siberian mining engineer V. Kuznetsov published a functional expression for determining the mean size of the fragments that result when explosives are detonated within a rock mass. Kuznetsov determined the form of his expression via regression analysis upon data obtained from laboratory tests, mines, and underground nuclear explosions. Therefore his expression was validated over a wide scale of blasts; the values of the rock test volumes used in the blasts differed by about four orders of magnitude. The form of the Kuznetsov Equation is [Kuznetsov, 1972]:

X = AV_rm^0.80 /M_e ^O.63                        ……………….……………………………. (3)

Where:

X         = mean fragment size (cm)

A         = rock mass “hardness” parameter;

V_rm        = rock mass volume (m³)

M_e        = equivalent mass of TNT applied to rock volume (kg).

Kuznetsov’s hardness parameter attempts to account not only for the physical strength of the rock, but also what he termed the “fissuring” present within the rock volume prior to the blast. To validate his equation, Kuznetsov proposed that his hardness parameter would have to have a total range of 12 units.

Table 3. Kuznetsov proposed hardness for different rock characteristics

Kuznetsov’s attempt to quantify both the strength and structural features of the preblasted rock mass with a single parametric value is summarized by the following reservations he expressed:

1. There appeared to be no concise relationship between the rock’s physical measure of hardness and the mean fragment size of the blasted product;
2. There was no clear association between the average fragment size and the spatial orientation of joints and fractures within the pre-blasted rock.

In addition, Kuznetsov noted that the applicability of his expression for the mean fragment size (Equation 4) was” doubtful” if:

3. A small number of fragments resulted from a blast;
4. A rock mass was repeatedly broken by blasting;
5. A rock mass was composed of different types of rocks.

2.7.2 The Kuznetsov Equation in Powder Factor Form

Cunningham put the Kuznetsov Equation into a form that would incorporate the powder factor term, and made a further simplification to allow for the use of explosives other than Tri-Nitro-Toluene (Cunningham, 1983):

X =A (F_pv) –^0.8 M_e^1/6 (115/E)^19/20            …………..……………………………………..(4)    

Where:

X         = mean fragment size (cm)

A         = rock mass “hardness” parameter (cm/m³)

M_e        = equivalent mass of TNT applied to rock volume (kg).

E          = relative weight strength of explosive used in blast (T.N.T.=115, ANFO ~ 100 )

F_PV         = volumetric powder factor (kg/m³)

2.7.3 The Rosin and Rammler equation

Rosin & Rammler (1933) came up with a formula for calculating the size distribution of materials.

                                 ……………………………………………………………..…………(5)                                                  

Where;            y is the percentage of material less than the size X (%)

x -the diameter of fragment (cm)

X_c -the characteristic size (cm)

n -the Rosin and Rammler exponent (uniformity coefficient)

e -the base of natural logarithms.

Since the Kuznetsov formula gives the screen size X_m for which 50% of the material would pass, the characteristic size is calculated from the average size for use in the Rosin and Rammler equation by substituting X=X_m and y= 0.5 into Equation (4) one finds that

                                      ………………………………………………………………………(6)                            

Average particle size of the material obtained from a blasting operation is not enough information explaining the efficiency of the operation. There could be two broken rock piles having the same average particle size but they could have different particle size distributions. Very coarse and fine particles can give acceptable average particle size but can cause problems in subsequent operations. Uniform particle size distribution is an important parameter that has to be considered.

The uniformity coefficient is calculated from equation developed by Cunnigham (1987). Cunnigham established the applicable uniformity coefficient through several investigations, taking into consideration the impact of such factors as: blast geometry, hole diameter, burden, spacing, hole lengths and drilling accuracy. The exponent n for the Rosin and Rammler equation is estimated as follows:

                 …………………………………………………………….(7)                                      

Where:            B is the blasting burden (m)

S is the blasthole spacing (m)

D is the blasthole diameter (mm)

W is the standard deviation of drilling accuracy (m)

L is the total charge length (m)

H is the bench height (m).

Cunningham (1987) noted that the uniformity coefficient n usually varies between 0.8 and 1.5.

2.8 Modern technology

In the modern technology imaging technique are used whereby views of the blasted rock pile are captured by high-resolution digital camera. These images are then analyzed using suitable computer software to provide a measure of the fragment size distribution in the rock pile. With the widespread use of computer hardware and software, the cost of such imaging techniques is relatively low and the characterization of fragment size can be carried out quickly, precisely and with greater ease.

A wide range of computer software is commercially available for the analysis of such images, e.g.  Fragalyst Version 2.0, developed by the Central Mining Research Institute, Nagpur, in collaboration with the Wavelet Group, Pune, represents an indigenous system which is both cheaper and proven under conditions in India. After enhancement and calibration of the captured images, the software performs an edge-detection function to demarcate the boundaries of fragmented rocks as they appear in the rock pile. The edges detected by the software are observed on a computer screen and corrected where necessary by means of edit network functions. On completion of the edge-detection function the images are subjected to further analysis to generate a typical Rosin-Rammler distribution. This provides the entire range of fragment sizes (with percentages) present in a rock pile, from which the mean fragment size (MFS), coarse fragment size (K95), maximum fragment size (K100) etc, and the uniformity index, of the rock pile can be obtained. In this way, fragment size characterization is conducted in a quantitative manner for all the rock piles generated during a study.

CHAPTER 3

 3. METHODOLOGY

3.1 Study from the literature

We did a thorough and in-depth study of available and existing information pertaining to blasting and rock fragmentation in bench blasting from the books and research theses.

 3.2 Data collection entailed;

1)         Collection of available geological data of the quarry obtained during exploration from the Exploration and Tertiary Materials Department of the company.

2)         Acquisition of the current blast design parameters and the data concerning the explosives used through interviewing workers (quarry manager, blaster) at the quarry and also through observations.

3)         Collection of blast output data.

4)         Visual observation (photos) and measuring of boulder sizes.

CHAPTER 4

4. RESULTS AND ANALYSIS

4.1 Results

4.1.1 Exploration data

           Map1. A section of the quarry showing grid line used during exploration

From the Exploration data done by National Council for Cement and Building Materials (1996) of New Delhi, India for Kibini hill area 5 limestone deposit, grid line 7 had the following details among other grid lines.

DH-1 RL 1296.52m                                                                  DH-2 RL 1295.34m

-1274.45 Volcanic ash.                                                            -1273.27 Volcanic ash

-1253.17 Crystalline limestone                                               -1258.22 Schist

-1217.09 Pegmatite                                                                -1251.99 Cavity

-1235.01 Gneiss                                                                      -1245.91 Limestone with Schist

-1222.99 Pegmatite                                                                -1242.87 crystalline limestone

-1211.64 Gneiss                                                                      -1239.83 Limestone with Gneiss

-1206.85 Crystalline limestone

-1203.72 Limestone with Schist

-1184.30 Crystalline limestone

-1179.21 Limestone with Schist

-1170.13 Gneiss

DH-3 RL 1294.46m                                                                  DH-4 RL 1297.26m

-1278.47 Volcanic ash                                                             -1278.23 volcanic ash

-1275.43 Pegmatite                                                                -1266.07 Crystalline limestone

-1260.43 Schist                                                                        -1244.79 Schist

-1220.82 Gneiss                                                                      -1241.75 Cavity

-1148.52 Crystalline limestone                                               -1238.46 Schist

-1229.73 Gneiss

4.1.2 Blast parameters

We found that the company uses the following parameters for bench blasting:

• Burden = 3m
• Spacing = 4m
• Stemming length = 3 to 4m
• Blast hole length = 20m
• Blast hole diameter = 4inches
• Total number of holes to blast = 24
• Mass of explosive in a blasthole = 45 kg

4.1.3 Explosives used at the quarry

• Instantaneous detonators
• Detonating cord
• ANFO
• Emulsion cartridges

4.1.4 Volume blasted

Approximately 225m³ is blasted in one round. Only 30% of the limestone blasted is hauled to the crusher direct. 70% are boulders. The boulders are then secondary blasted and further broken using a breaker. If no secondary blasting, only the breaker is relied on to reduce the boulders to crusher size (approximately 1m diameter)

4.1.5 Photographs

Photo 1                                                                        Photo 2

Photo 3

4.2 Analysis

4.2.1 Exploration data and photos

From the exploration data and visual observation (photos), the rock is full of faults and incompetent zones. Many of the boulders did not undergo breakage during blasting. This is as a result much of the explosives energy being lost in the faults instead of being used to break the rock. Alternate zones of competent and incompetent rock normally result in too blocky fragmentation. Higher specific charge will rarely correct this problem; it will only increase the risk of flyrock.

4.2.2 Blasting parameters

Considering the geology of the area, the blasting parameters do not suit the prevailing rock conditions. The burden, spacing and the bench height play a big role in the poor fragmentation.

From the Kuz-Ram model;

X_m =A (F_pv) –^0.8 M_e^1/6 (115/E)^19/20

Where X_m = mean particle size, cm;

A = rock factor (it varies between 0.8 and 22, depending on hardness and structure – this is a critical parameter)

K = powder factor, kg explosive per cubic meter of rock

Q = mass of explosive in the hole, kg

RWS = weight strength relative to ANFO,

Table4: Calculations for the Kuz-Ram parameters

X_M          = 10 X 0.25^-0.8X 45^1/6 X (115/100)^19/20                                                        

= 65.29 cm

According to Kuz-Ram, for optimal fragmentation to be achieved, the mean fragment size should be equal or less than 15cm. From the mean fragment size of 65.29 cm obtained above, it depicts how poorly the rock has been fragmented.

The use of instantaneous electric detonators in the quarry contributes highly on poor fragmentation of the rock. Bench blasting is normally carried out short delay blasting. The pattern has to be designed so that each blasting has free breakage. The delay time between blast holes and between rows has to be long enough to create space for the blasted rock from the succeeding row.

CHAPTER 5

5. CONCLUSION

5.1 Discussion

The degree of fragmentation affects the economy of the mining process. Different characteristics of blasted rock such as fragmentation size, volume and mass are fundamental variables affecting the economics of mining operation and the decisive factors for evaluating the quality of a blast. The properties of fragmentation such as size and shape are very important information for the optimization of the production.

The knowledge of the fragmentation mechanism in explosively loaded rock in bench blasting is critical for developing successful methods for excavating the rock. Optimal fragment size will have the following influence on productivity:

1. Minimize oversize boulders hence less secondary blasting or breaking which in turn reduce the overall production cost.
2. Minimize lump products.
3. Muck pile loose enough for fast cycle times for it ensures efficient digging and loading.
4. Operating capacity of loading equipment will be raised i.e Increase in bucket fill factor.
5. Dumper cycle time will be reduced because of less waiting period and loading time.
6. Better fragmented rock requires less energy consumption in crushing and will reduce overall costs.

Currently the company fires a round of 24 holes at a burden of 3m and a spacing of 4m by use of instantaneous detonators. The blast output from this is majorly oversize boulders which have to be further broken through secondary blasting and hydraulic breakers before being hauled to the crusher. This has led higher costs in the overall blasting operations in the quarry.

5.2 Recommendations

1. 1. The quarry manager should consider areas with cavities or a mixture of limestone and waste rock so that these areas are charged as follows:

Fig 4 Charging procedure in fractured rocks.

This will aid in maximum utilization of the explosive energy in breaking the rock and minimize its escape through the faults or incompetent zones. This leads to fewer boulders.

2. 2. The blast parameters should be adjusted. We suggest a 2.5m burden, 3.5m spacing and bench height of 10m to ensure a blastholes of 12m. This will counter the over 3m size boulders caused by just loosening of the limestone rock from mother rock after each blast with the current 3m burden, 4m spacing and 20m blastholes.

3. 3. They should switch from the use of instantaneous detonators to delay detonators. The pattern has to be designed so that each blasting has free breakage. The delay time between blast holes and between rows has to be long enough to create space for the blasted rock from the succeeding row. Bernt Larsson of Nitro Nobel studied the effect of the delay time mining row blasting. He stated that the rock must be allowed to move 1/3 of the burden distance before the next row is allowed to detonate. The delay time between the rows may vary from 10ms/m (hard rock) to 30ms/m (soft rock) but generally 15ms/m of the burden distance is good guide value. This length of delay gives good fragmentation and controls fly rocks. It also gives the burden from the previously fired holes enough time to move forward and accommodate the broken rock from subsequent rows. If the delay between the rows is too short the rocks from the back rows tend to take an upward direction instead of the horizontal. On the other hand too long delay may cause fly rocks, air blast and boulders as the protection from previous fired rows disappears due to great a rock movement between detonations. The increase in boulders is due to the fact that the blast in this case is compared with a single row blast. The following firing pattern:

Fig 5. Firing pattern in bench blasting using delay detonators

5.3 Expected Results

The project is expected to provide a suitable solution to the current fragmentation challenge experienced at the quarry. Adjusting the blasting parameters to favor the prevailing conditions will ensure optimal fragments after each blast hence rising the percentage of the material hauled direct to crusher to over 50%.

This will further pose a great solution to the current oversize boulder production at Kibini limestone quarry which will minimize the high cost incurred in secondary blasting due to poor breakage (oversized boulders).

REFERENCES

Stig O Olofsson, Applied Explosives Technology for construction and Mining, second edition, pp 62-103, Sweden.

Cunninham, C.V.B 1983. The Kuz-Ram model for prediction of fragmentation from blasting. In R. Holmberg & A. Rusta (eds), Proc. 1^st Int. Symp. On Rock Fragmentation by Blasting, Lulea, Sweden, 22-26 August, pp. 439-453. Lulea University Technology.

Rosin, R. & Rammler, E. 1933. Laws governing the fireness of poedered coal. J. Inst.of Fuel 7: 29-36.

Cunnningham, C.V.B 1987. Fragmentation estimations and the Kuz-Ram model- four years on Proc. 2^nd Int. Symp. On Rock Fragmentation by Blasting, Keystone, Colorado, USA, 23-26 August, pp 475-487. Bethel, CT: Society for Experimental Mechanics.

Kuznetsov, V.M. 1973. The mean diameter of the fragments formed by blasting rock. Sovient Mining Science 9(2): 144-148.

Langefors, U. & Kihlstrom,B. 1976. The Modern Technique of Rock Blasting, 3^rd edition. New York: John Wiley and Sons.

Mackenzie, A.S. 1967. Optimum blasting. Proc. 28^th Annual Minnesota Mining Symp. Duluth, MN, pp 181-188.

Morin, M.A. & Ficarazzo F. 2006. Monte Carlo simulation as a tool to predict blasting fragmentation based on the Kuz-Ram model. Computer & Geosciences 32(3): 352-359.

Jimeno, C.L., Jimeno, E.L & Carcedo, F.J.A. 1995. Drilling and Blasting of Rocks. Rotterdam: Balkema.