The Effect of Geological Structure and Powder Factor in Flyrock Accident

8/10/2019 The Effect of Geological Structure and Powder Factor in Flyrock Accident

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The Effect of Geological Structure and

Powder Factor in Flyrock Accident,

Masai, Johor, MalaysiaEdy Tonnizam Mohamad

Associate Professor (Dr.), Universiti Teknologi Malaysia, Department of

Geotechnics and Transportation,Faculty of Civil Engineering, 81310 UTM

Skudai, Johor, Malaysia

e-mail: [email protected]

Danial Jahed ArmaghaniPhD Student, Universiti Teknologi Malaysia, Department of Geotechnics and

Transportation,Faculty of Civil Engineering, 81310 UTM Skudai, Johor,

Malaysia

e-mail:[email protected]

Hossein MotaghediPhD in Geotechnical Engineering, Faculty of Civil Engineering, Islamic Azad

University of Qaem Shahr, Qaem Shahr, Iran

e-mail: [email protected]

ABSTRACTRock blasting is the most commonly used method for rock breakage in the field of civil andmining. The main goal of such operation is to produce the desired fragment size distribution

leading to optimize the overall mine/plant economics. Blasting has some environmentalimpact such as ground vibration, airblast, dust and fumes and flyrock. One of the undesirablephenomena in the blasting operation is flyrock, which is a propelled rock fragment byexplosive energy beyond the blast area. A flyrock accident occurred during a blasting workat Masai quarry Johor, Malaysia in 19 July 2013. Due to this accident, a factory worker waskilled while 10 others were injured after being hit by rock debris from an explosion at aquarry that flew up to 700 m away. The main purpose of this study is to investigate thecauses of flyrock accident based on results of geological structure and also powder factor. Inorder to investigate causes of this accident, two continues blasting patterns were considered

and powder factor of these blasts were calculated. It is concluded that blast geometry (suchas burden and spacing), total weight of explosive,close distance between the quarry and theresidential area, and geological conditions were considered the most influentioal parametersin this accident.

KEYWORDS: Rock blasting, Flyrock accident, Blast geometry, GeologicalStructure, Powder factor.

INTRODUCTIONIn civil engineering, rock is removed to create structures such as tunnels, hydraulic channels

or caverns, or deep excavation at the ground surface for road cuts, foundation or basements

(Bhandadari, 1997). For this work, there are some methods such as ripping, blasting and

excavators. Blasting operation is a natural rock formation dislodge from its original location.

Blasting of rock from a quarry face should be designed to obtain the optimum fragmentation and

a rock pile attitude compatible with the plant and equipment used (Bhandadari, 1997). The main

purpose of the blasting operation is to create desired fragment size distribution leading tooptimize the general mine economics (Monjezi et al. 2007). Blasting affects the rock

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fragmentation, so there must be some beneficial measures to decrease undesirable occurrences

such as flyrock. Blasting has some environmental impact such as ground vibration, air blast, dust

and fumes and flyrock (Bhandadari, 1997). As an environmental hazard flyrock causes serious

injury to people, damage to equipment, building and property. According to Roy (2005),

blasting-induced flyrock can travel from a few meters to more than 1000 meters with poorlycontrolled blasting.

DEFINITION OF TERMS

Flyrock

Flyrock, propelled rock fragments by explosive energy beyond the blast area, is one of the

undesirable phenomena in the mining blasting operation (Rezaei et al. 2010). Any mismatch

between distribution of the explosive energy, mechanical strength of the rock mass and charge

confinement can be cause of flyrock (Bajpayee et al. 2004). Flyrock is produced when explosive

energy is excessive for the amount of burden, stemming is inadequate or the energy is toorapidly vented through a zone of weakness in the rock. When this happens, much of the

explosive energy is used to throw rock rather than to create fragmented rock (Roy, 2005).

Flyrock is the source of most of the injuries and property damage in a majority of blasting

accidents in surface mines.

Causes of Flyrock

Flyrock may have different causes depending on the place and situation of this phenomena.

The following factors can lead to flyrock. The first one is related to inadequate burden and

spacing. Burden and spacing need to be calculated taking into account the hole diameter, rock

characteristics and fragmentation requirements. An insufficient (or less) burden will cause

breakthrough of drill hole charges, resulting in flyrock. Spacing appreciably less than the burdentend to cause premature splitting between blast holes and early loosening of the stemming. Too

close a spacing causes crushing between holes and also cratering giving rise to flyrock

(Bhandadari, 1997). The other one is overloaded holes. The distance to which a flyrock travels

will depend on the amount of specific charge. A high specific charge throws flyrock to a longer

distance than a low specific charge. Inadequate stemming is also very important in flyrock

distance. If stemming column is adequate, the explosion gases are not forced to heave up the

partly fractured ground but are simply allowed to rifle out of the top of the blasthole at very

high velocity causing considerable flyrock (Roy, 2005). The other significant parameter is

inaccurate drilling. Accurate drilling provides proper burden and spacing which are essential for

better results. This is achieved by proper positioning of drill to accurately collar the hole and by

proper inclination of holes. However, if during drilling, the driller is not guided properly for the

position and direction of the hole, the drill may deviate from its calculated position and duringthe time of blast the effect may be same as that of reduced burden and overloaded hole thereby

resulting in flyrock (Bhandadari, 1997). The other cause is geological conditions. Zone of

weakness and voids are often causes of flyrock. Any explosive loaded in this zone will have the

line of least resistance and blow out, causing flyrock (Roy, 2005). Other factors such as

powder factor, pattern layout, delay sequence should also be evaluated if any excessive flyrock

is generated.

Powder Factor and Specific Charge

Two terms are often used to relate explosive mass and consequent rock broken: Powder

factor and Specific charge, q. observation of blast designs based on empirical relations has beenoften indicated in terms of powder factors. Powder factor is the ratio between the total weights
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of explosive detonated in a blast divided by the amount of rock that is broken. It is usually

expressed as kilogram per ton or kilogram per meter. As the powder factor in kg/m3 increases,

the average fragment size decreases when the burden B, remains constant (Hemphill, 1981). The

powder factor varies between 0.1 (kg/m3) and 0.53 (kg/m

3) for bench blasting. Powder factor for

tunneling should be larger by 1.25-1.5 times than bench blasting because of the large fixity(Bhandari, 1997).

History of Flyrock Accidents

In a survey of blasting operations carried out in USA, it was observed that out of 34

accidents that occurred during scheduled blasting, 28 were attributed to flyrock (Britton et al.

1977). These accidents resulted in 10 fatalities and 19 injuries. A study of blasting accidents in

India mines indicated that more than 40% fatal and 20% serious accidents resulting from

blasting occurred due to flyrock (Bhandari, 1994). In the United Kingdom during 1980-85 103

incidents were reported of which more than half of these involved flyrock projections to distance

ranging from 350 m to a maximum of 900 m, with rock weighting up to 500 kg. According MineSafety and Health Administration, flyrock is the leading cause of blasting accidents, accounting

over 60 percent of all accidents during 1987-88 (Anon, 1990). Historical data summarized by

Verakis and Lobb (2003) shows that for the period of 19782001, a total of 195 blasting

accidents occurred in US surface coal mine operations. Of the 195 accidents, 89 accidents

(45.64%) were directly attributed to lack of blast area security, 54 accidents (27.69%) to flyrock,

33 (16.92%) to premature blast, and 11 (5.64%) to misfires.

FLYROCK ACCIDENT IN MALAYSIA

Case Study

The Masai quarry is situated in Seri Alam near Pasir Gudang, Johor, Malaysia. The mentioned

quarry is producing granite aggregates for various construction uses with capacity of 30000 per

month. Blasting is carried out between 2-4 times per month at this quarry. Figures 1 and 2 show

the location of the quarry and the affected areas. Area of blasting also is shown in Figure 3.

Figure 1:Location of Blasting Site


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Figure 2:The Location of the Quarry Face and wild Stone Fly (550 m from the site of the

explosion shown yellow arrows)

Figure 3:The Blasting Area

Flyrock Accident

A flyrock accident was occurred due to a blasting in Masai quarry near the Seri Alam, Johor,Malaysia in 19 July 2013. The massive explosion caused rocks and boulders to rain down on the


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Figure 5:Wild Flyrock into the Plant (350 m from the blasting site)

Figure 6:Some Rocks resulted from Wild Flyrock (350 m from the blasting site)


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Figure 7:Thrown Rocks on the Plant, Located 550 m from the Blasting Site

Figure 8:Some Damages to Vehicles Around the Plastic Factory


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Figure 9:The View of the Plastic Factory where the Worker Was Killed

POWDER FACTOR ANALYSIS

Parameters such as burden, spacing, powder factor, stemming length, subdrilling, maximum

charge per delay and so on can affected in blasting results. Among them, powder factor has

pivotal influence in blasting results such as flyrock distance. Powder factor is the ratio betweenthe total weights of explosive detonated in a blast divided by the amount of rock that is broken.

It is usually expressed as kilogram per cubic meter. In this paper, two continues blasting patterns

are shown and the powder factors of these blasting are compered. Some blasting parameters are

shown in Figure 10 schematically.

Figure 10:Some Blasting Parameters

Figure 11 and Table 1 show blasting parameters for the last blasting before accident one.


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ANFO was used as explosive material. Accoring to these blasting parameters, the powder factor

for this blast is 0.619 kg/m3. The normal powder factor in the Masai quarry is between 0.6-0.8.

Figure 12 and Table 2 also show blasting parameters for the accident blasting. The powder

factor for this blasting is 1.18 kg/m3. It was found that the blast geometry played a great role in

this accident. Some parameters of blast geometry such as hole diameter were consideredconstant in both blasting while some other parameters such as burden and spacing were changed

in the accident one. It is worthy to note that total weight of explosive is another important

parameter in the result of blasting. In the almost similar volume of the rock, this is a significant

point in order to minimize environmental impacts of blasting like flyrock.

Figure 11:Blast Geometry for the Last Blasting before Accident One

Table 1:Blasting Parameter for the Last Blasting before Accident One

Property

Blasting Parameters

Holediameter

Holedepth

Averagehole depth

Numberof holes

Averagestemming

Averagecharge

Value 89 26-30 28 39 2 194.1

Unit mm m m - m kg

Figure 12:Blast Geometry for the Accident One


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Table 2:Blasting Parameter for the Accident One

Property

Blasting Parameters

Hole

diameter

Hole

depth

Average

hole depth

Number

of holes

Average

stemming

Average

charge

Value 89 28-32 30 45 2 209

Unit mm m m - m kg

STEREOGRAPHICAL PROJECTION ANALYSIS

A total of four joint sets have been identified around the explosion site (Figure 13). These

discontinuities occur naturally (as a result of tectonic activity and weathering) and some new

cracks because of earlier blasting work. In order to have a better geological investigation,

stereographical analysis was perform. Stereographical analysis results (Figure 14) show the

existence of joint dominant orientation (set 1, 2, 3 and 4) that contribute to the instability

towards the south (toward the plant involved). This proves that the orientation of the

discontinuity that exists is made of rock blasted become easier to excavate.

Figure 13:Four Joint Sets Found in the Blasting Site


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Figure 14:Analysis of Discontinuity Stereographical Analysis

DISCUSSION

There are several causes for this accident. The first is from the skills of trained person

responsible for handling explosives. Error handling explosives operators not only endanger

themselves, but other workers may also be involved. More serious when there are civilians

directly involved in quarrying activities can also be considered. Explosives operators need not

only well versed in handling quantity and type of materials to be used but also they should be

able to control the situation.

The second is geological conditions that cannot be altered and should be understood by the

project proponent. Geological aspect is very important to be aware but there is no body that

makes rules that professional geologists should make periodic reports. There is a discontinuity orcrack rock mass that affects the activity of an explosion. If there are a lot of cracks, and also

orientation sets of discontinuity that causes low stability, the total explosion energy must be

reduced. Sometimes these cracks not visible to the naked eye deck and can only be expected by

an experienced geologist.

The third cause of this accident is designing the blast geometry. In every blasting operation,

blast geometry such as burden and spacing plays an important role in the blasting result. An

insufficient (or less) burden will cause breakthrough of drill hole charges, resulting in flyrock.

Spacing appreciably less than the burden tend to cause premature splitting between blast holes

and early loosening of the stemming. Too close a spacing causes crushing between holes and

also cratering giving rise to flyrock.

Close distance between the quarry and the residential area is another factor that should begiven attention. The shortest distance between the face of the quarry to the plant explosion, is at

a distance of only 350 m. This distance is too close. Under the guidelines of Environmental

Impact Assessment (EIA) should be positioned closest to the development of not less than 1 km

from the quarry. In this situation, many factory workers who worked in a plant is exposed to the

risk of yesteryear. An estimated total of more than 500 factory workers working in this danger

zone.

CONCLUSION

A flyrock accident was occurred due to a blasting in Masai quarry near the Seri Alam, johor,

Malaysia in July of 2013. Due to this accident, a factory worker was killed while 10 others were

injured after being hit by rock debris from an explosion at a quarry. Beside this, 18 cars and 14

factories along the road were damaged. In order to investigate causes of this accident, two

continues blasting patterns were considered and powder factor of these blasts were calculated.


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Some parameters of blast geometry such as hole diameter were considered constant in both

blasting while some other parameters such as burden and spacing were changed in the accident

one. The powder factor of two continues blasting was 0.619 and 1.18 respectively. Apart from

the powder factor analysis, stereographical analysis was also perform to recognize instability of

blasting face. It can be concluded that blast geometry (such as burden and spacing), total weightof explosive, close distance between the quarry and the residential area, and geological

conditions were considered the most influential parameters in this accident.

ACKNOWLEDGEMENTS

This research is being carried out using the Universiti Teknologi Malaysia (UTM) financial

support. The authors would like to thanks UTM for the research grant and facilities available in

the Department of Geotechnics and Transportation, Faculty of Civil Engineering.

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The Effect of Geological Structure and Powder Factor in Flyrock Accident

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