best bench blasting practices

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Introduction

The portion of the cost of drilling and blasting among the whole operation costs, varies between10-35 % of overall costs(depends on if the optimal blasting conditions are proved or not) in open

pit mining. This cost interval is more important considering the present mines increasing

operational capacities. Choosing the proper explosives, and obtaining the proper blasting patternin use, can ensure important decreases on production costs. The proper blasting conditions which

are to be obtained, must not only fit with the economy, and technology but also ensure a secured

mine, and neighbourhood.

The importance of drilling and blasting can be seen from both cost analyses of the operations,

and the availability of completing the other operations in mine rapidly. However, evaluating thedrilling and blasting costs alone in the cost analyses at mines, is not enough to express the

success of the blasting clearly. As the activities are happening consecutively, the effect of

drilling and blasting also has to be analysed according to the other operations. This is possible

with analysing the performances of each equipments, and machines used for all subsequent

operations. The approach of anticipating the cost minimisation only on drilling and blasting, willcause an overlooking at the increases on consecutive operations costs. Meanwhile when the

optimal drilling and blasting conditions are determined, considering the environmental issuessuch as ground vibrations, air blast, and noise; the total cost of the following operations such as

loading, hauling, crushing and the reclamation could be decreased, and consequently the overall

results of mine would be progressed positively (Kahriman, 1995).

Within the scope of this study an intensive work was realized to determine the optimal blasting

conditions for the blasting operations held on gypsum formations of overburden at celestite open

pit mine owned by Barit Maden Turk Company in Sivas-Ulas Akkaya Village.

Test Site Description

Sivas-Ulas Akkaya region celestite open pit mine which has been produced by Barit Maden Turk

Company , located nearby Akkaya Village, 3 km east of the 27th km of Sivas-Malatya Highway

on the central of Anatolia, near the Sivas province, as seen in figure 1. The encountereddominant rock units formed the overburden at the mine are gypsum and anhydride.

Figure 1: Location of the celestite open-pit mine (Kahriman and Ceylanoglu, 1996)

Copyright 2004 International Society of Explosives Engineers2004G Volume 1 - A Practical Approach for Blasters to Determine the Optimal Bench Blasting Conditions


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The ore production capacity of the mine is about 50.000 tonnes per year and overburden

excavation program is 120.000 m3

per year. The average working period is 5 months. The

drilling and blasting is necessary for both ore and overburden excavation. The available drillersare able to drill holes with 65, 89, 102 mm diameters. One Liebherr 962 excavator with 3,5 m3

bucket and one Caterpillar 973 loader with 2, 8 m3

bucket capacity run the loading operation

(Kahriman and Ceylanoglu, 1996).

Optimization Procedures

As the importance of blasting is well known in the production cycle, many studies have been

concentrated on the parameters affect the blast efficiency. Different working conditions

complicate the blast design. In addition, blasting is a complex operation affected by many factorswhich have been indicated by many authors (Langefors and Kihlstrm, 1978; Tamrock, 1984;

Atlas Powder, 1985; Olofsson, 1988; Konya and Walter, 1990; Bilgin and Pasamehmetoglu,

1993; Singh, 1993).

Before the blasting optimization works, initially the studied rock units were analyzed consideringthe engineering (mass and material) and digability classifications by using the results of field and

laboratory studies. The current blasting system, which had being used by the company, wasobserved with the knowledge of rock characteristics, and new pre-blast designs were done and

applied adopting Langefors blasting model (Langefors and Kihlstrm, 1978). The necessary

planning was done for each shot before, and during the shots, and the researchers accompaniedthe applications.

Each pre-blast designs results were considered by evaluating the muckpile swelling,

displacement, fragmentation, and performance analyses. In order to determine, and record thedata from each shot properly, three practical forms which are given in table 1 (a), (b) and (c)

were developed, and all data were transfered to these forms which give information about theblasting parameters and results such as muckpile displacement, and height, average particle size,back break, and rock fly existence, number of boulders etc. The parameters, and results of 5th

shot which proved the optimal blasting conditions for gypsum I rock unit were given on these

tables as an example.

During the iteration of each shot, the parameters such as hole diameter and inclination, priming

amount and location, burden, bench height, delay pattern, and shot geometry were considered.

Using the existing explosive products (ANFO, gelatine dynamite, electric delay detonators) thathave being used by the company, was an obligation. All pre-blasts were designed considering the

production target in order not to hinder the work program as well (Kahriman and Ceylanoglu,

1996).

The results after each pre-blast design were evaluated by observing the muckpile conditions, and

the other parameters mentioned above. The maximum, and average particle size, and the distanceof muckpile displacement were measured by tape meter in order to determine the muckpile

geometry, and particle size distribution. Additionally 2 m X 2 m wooden grid with 50 cm

fraction, was used as a practical tool to obtain the average particle size. These factors were also

were recorded to the evaluation form which is given in table 1. b).



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Table 1: a) Bench Blast Report Form

Table 1: b) Blast Design Evaluation Form



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There have been some digital image processing softwares which can assess the fragmentation

more easily and accurately in recent years. These kind of softwares are very suitable for

considering the blasting according to fragmentation. However the pratical fragmentationassessment applications as we had realised in this study, can be adopted any optimisation studies,

and give similar results on the field. During the evaluations, when it was necessary to remember

the blast, photographs of the muckpile was shot, and added to the reports.

Additionally in order to measure the equipments performance as being one of the stages of the

optimisation procedure, excavation, and loader operations were observed, and the cycle periodswere taken under record on the tables as seen in table 1 c). In the condition of the necessity of

using the hydraulic hammer to break the boulders, and bulldozer to make the floor smooth, these

operations were also observed and their working times were recorded.

Table 1: c) Performance Analysis Form

On the other hand, the environmental effects of the blasting such as ground vibration, airblast,and fly rocks also have to be observed and monitored to ensure the mine and neighbourhood in

secured. The vibration monitors have to be in charge during the shots for this purpose, and

ground vibration parameters have to be analysed according to the damage risk criteria. Duringthe current study the mentioned concept was take into consideration. The ground vibration

components and air blast were measured by suitable monitors during every trial shots, and theresults of the measurements were considered for progressing to new pre-blast designs.

Blasting Optimization for Gypsum Rock Unit

According to the rock mass and material properties, it was decided that gypsum rock unit mustbe seperated in two sections because of having different discontinuties sets with different

properties (dip, bed separation, hardness, joint sets, orientation and spacing of joints and degree



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of weathering) and the rock must be blasted differently by creating two benchs (Ceylanoglu,

1995). So that in this study gypsum rock unit was assumed to be as Gypsum I and Gypsum II

with 16 m and 15 m bench heights respectively, shown in figure 2. Therefore optimisationstudies for gypsum rock unit was realised in two parts individually.

Figure 2: Layout of the test benchs

O r e

G y p s u m I I

G y p s u m I

1 5 m

1 6 m

Optimization for Gypsum I Rock Unit

Within the scope of this study, 6 trial shots were realised in order to determine the optimal

blasting conditions on gypsum I rock unit at Sivas-Ulas Akkaya celestite open pit mine. At thedesigns of all pre-blasts, the shot results were evaluated by means of muckpile distribution,

fragmentation degree, existence of boulder, back break and toe. Short-term excavator

performance measurements, approximately 1 hour were also carried out to determine blastefficiency. Cycle times (including dipper, swing and unloading times), fill factor, operator

experience, energy consumption etc., were carefully recorded. The condition and the height of

the bench faces were also taken into consideration. The bench face was formed as concave, sothat the occurance of back breaks on the corners were prevented. The parameters of these 6

shots, and the productivity, and the cost analyses are given in table 2 and table 3 respectively.

Table 2: The Parameters of Blast Designs of Gypsum I

Powder Factor(kg/m3)Shot

No.

HoleDiameter

(mm)

BenchHeight

(m)

HoleDeviation(degree)

Burden(m)

Spacing(m)

ANFO Dynamite

SpecificDrilling(m/m3)

1 89-102 15 83-85 2.8 3 0.602 0.121 0.125

2 89 14.5 85 3.8 4.8 0.320 0.021 0.068

3 89 15 83-80 3.8 4.8 0.298 0.013 0.0684 102 15 80-75 4 5 0.551 0.025 0.083

5 89 15 75 3.1 3.7 0.487 0.0081 0.0976 89 3.5 83 2 2.6 0.531 0.045 0.185

Considering the cost analyses results from table 3, it can be seen that after adopting optimal

blasting parameters, an acceptable optimal operational costs can be determined, and rippingoperation can be eliminated.



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Table: 3 The Unit Cost Analyses for Gypsum I Blast Designs

Unit Costs ($/m3)

Loading TotalShotNo. Drilling Explosives

Hydrolic

Crushing

Ripping 962

Exc.

973

Loader

Hauling

962 9731 0.158 0.491 - 0.225 0.97 1.69

2 0.086 0.172 0.02 0.1 0.387 0.226 0.97 1.715 1.554

3 0.086 0.136 0.025 0.09 0.29 0.211 0.97 1.597 1.518

4 0.1055 0.26 0.02 0.23 0.315 0.195 0.97 1.901 1.781

5 0.123 0.178 0.01 0.282 0.193 0.97 1.553 1.4746 0.234 0.33 0 0.188 0.97 1.722

Gathering all these productivity analyses values together, it can be understood that the 5th

blastdesign gives the most proper results on this rock unit. Evaluating the other observative data with

these results as well, the best blasting conditions for this rock is the one which was applied on

the 5th design, so it was finalised as the optimised blast design for Gypsum I at celestite open pitmine (Kahriman, 1995).

Optimization for Gypsum II Rock Unit

Following the same procedures 10 trial shots were realised to obtain the optimal blasting

conditions for Gypsum II rock unit. After applying all pre-blast designs one by one , the

parameters were adjusted to give the best results. The best results were reached after the 8th

blastdesign. The back break, and fly rocks which had been seen at the other shots,were also not seen

on this shot. Finally the 8th

shot was accepted as the best, and finalised as the optimised blast

design (Kahriman, 1995). Additionally the 9th

shot were done to test the parameters of the 8th

shot, and 10th shot was realised at 3.5 m bench height to progress the relation between powder

factor and rock properties.

Table 4: The Parameters of Blast Designs of Gypsum II

Powder Factor(kg/m3)Shot

No.

HoleDiameter

(mm)

BenchHeight

(m)

HoleDeviation(degree)

Burden(m)

Spacing(m)

ANFO Dynamite

SpecificDrilling(m/m3)

1 89 14.5 83 2.8 3 0.631 0.185 0.144

2 89 15 83 3 3.8 0.356 0.059 0.098

3 89 15 83 3.6 4.5 0.323 0.049 0.0714 89 3.5 85 2.4 2.4 0.317 0.042 0.181

5 102 15 83-85 3.3 4.1 0.567 0.007 0.084

6 89 15 78.5-77 3 3.65 0.586 0.009 0.104

7 89 8.5 80 3 3.6 0.589 0.010 0.106

8 89 15 76.5-75 3 3.6 0.570 0.009 0.1039 89 15 75 3.2 4 0.483 0.0095 0.088

10 89 3.25 80 2.1 2.8 0.451 0.045 0.183



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Table 5: The Unit Cost Analyses for Gypsum II Blast Designs

Unit Costs ($/m3)

Loading TotalShotNo. Drilling Explosives

Hydrolic

Crushing

962

Exc.

973

Loader

Hauling

962 9731 0.178 0.6712 0.01 0.336 0.262 0.97 2.1652 2.092

2 0.121 0.2652 0.01 0.286 0.286 0.97 1.6549

3 0.091 0.236 0.029 0.25 0.97 1.576

4 0.223 0.301 0.198 0.97 1.692

5 0.104 0.1998 0.01 0.412 0.214 0.97 1.6958 1.4978

6 0.1285 0.2126 0.005 0.216 0.97 1.5321

7 0.131 0.22 0.189 0.97 1.464

8 0.127 0.205 0.175 0.97 1.4779 0.109 0.1801 0.005 0.386 0.222 0.97 1.6501 1.4861

10 0.2262 0.308 0.193 0.97 1.6972

Conclusion

This paper summarisez the bench blasting optimisation for gypsum rock unit of overburden atSivas-Ulas Akkaya celestite open pit mine, and gives a practical approach for this purpose.

Following the optimisation procedures, every pre-blast design of which parameters, and results

had been measured and recorded carefully, was progressed to get the best fit results considering

the economy, technology, and the productivity of the consecutive operations while alsomaintaining the mine and neighbourhood in secure.

Test results showed that together with the other blast parameters, the hole inclination was an

effective factor on the desirable results (especially isolating of environmental problems such asbackbreak, fly rock, air blast and ground vibration) where it was determined 75 for this mine.

During the study, it has been seen that the excavation and/or loading performances and themuckpile homogeneousity are fairly important when evaluating the blasting productivity.

Furthermore creating a good accurate blast report can ensure so many advantages to a blaster in

order to progress the blast design for the best conditions on a specific site.

Acknowledgement

This work was supported by the Executive Secreterait of Scientific Research Projects of

Istanbul University (Project numbers are 39/11092002, 1056/031297, UDP-46/24072002 andUDP-93/20122002 )

The authors are greatful to the Executive Secreterait of Scientific Research Projects of Istanbul

University for their financial support and to the staff of Barit Maden Turk Company for theirhospitality and help during the field investigations.



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References

Atlas Powder Company, 1985, Handbook of Explosives and Rock Blasting, Dallas, Texas, USA

Bilgin, H.A., Pasamehmetoglu, A.G., 1986, A Study on the Blastability, and Digability of Rocks,

1. National Rock Mechanics Symposium, November 1986, Ankara

Ceylanoglu A., 1995, The Determination and Evaluation of Clestite Ore, and Overburden Rock

Mass and Material Properties in Sivas-Ulas Region, TMMOB, Mining Journal, Vol. 34, No.4,pp. 11-19, Ankara

Gustafsson, R., 1973, Swedish Blasting Technique, Gothenburg, Sweden

Kahriman, A., 1995, Determining the Optimal Blasting Conditions, and Relation of Rock

Properties of Sivas Ulas Region Celestite Ore and Overburde, Doctorate Thesis, C.U., Sivas

Kahriman, A., Ceylanoglu, A., 1996, Blast Design and Optimization Studies for a Celestite

Open-Pit Mine in Turkey, Mineral Resources Engineering, Vol. 5, No.2 pp 93-106

Konya, C.J., Walter, E.J., 1990, Surface Blast Design, New Jersey, USA

Langefors, U., Kihlstrm, B., 1978, The Modern Technique of Rock Blasting, Third Edition,Stockholm, Sweden

Olofsson, S.O., 1988, Applied Explosives Technology for Construction and Mining, Sweden

Singh, O.P., 1993, Blasting Ground Excavations and Mines, Rotterdam, Netherlands

Tamrock, 1984, Handbook of Surface Drilling and Blasting, Painofaktorit, Finland

Copyright 2004 International Society of Explosives Engineers2004G Vol me 1 A Practical Approach for Blasters to Determine the Optimal Bench Blasting Conditions

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