Blast number one.
Abstract
This research seeks to examine the effect of powder factor variability on granite productivity during its quarrying. Schmidt hammer was used for the in-situ determination of rock hardness. Uniaxial compressive strength (UCS) of in situ rock was estimated from the values obtained from Schmidt hammer rebound hardness test and its density determined from laboratory test. After preliminary field studies, ten (10) blasts with varied powder factors were studied and their overall effects on granite productivity examined. Three (3) rock samples were carefully collected from the quarrying site and subjected to laboratory analysis for UCS and bulk density tests. With spacing and burden kept between 1.7 m and 1.8 m and stemming height also varied between 1.5 m and 2 m, charge columns of between 4.5 m to 6.5 m were maintained, while number of holes drilled per blast was between 64 and 88. Results obtained from the test revealed that the average UCS of the granite samples was 80.67 MN/m2 while the average bulk density was 2465.67 kg/m3. Therefore, considering ten (10) blasts with varied powder factors of between 0.77 kg/m3 and 0.97 kg/m3, total volumes of rock of between 1109.76 m3 and 2280.96 m3 was produced. Hence, varied powder factors have been found to have varying effects on rock fragmentation sizes and by extension, granite productivity.
Keywords
- powder factor variability
- explosives
- granite productivity
- blasting
- fragmentation
1. Introduction
Efficiency of blasting operations in underground and surface mines determines, to a large extent, utilization of equipment, productivity and economics. Proper fragmentation of blasted rocks improves the efficiency of downstream operations by loading and crushing to desired sizes. An optimal blast not only results in proper fragmentation but also reduces undesirable effects in ground vibration, fly rock and formation of toe in quarry benches. Drilling and blasting are the first unit operations in the mining process and have a major impact on the performance and cost of subsequent unit operations [1, 2, 3].
According to Salati and Mark [4], powder factor can be defined as the quantity of explosives needed to fragment a unit cubic metre of rock (1m3). Hence, optimum powder factor results in good fragmentation, having less throw and less ground vibration. It can serve as an indicator for rock hardness, cost of explosives used or as a guide to shot firing plan [5].
Improved fragmentation gives loading equipment a higher rate of productivity; hence, it results in lower cost per tonne or cubic yard moved. The effect of wear and tear also decreases giving lower operating cost per hour under similar condition of haul, lift, size and type of truck. Haul/load road condition, truck production per hour also increase with greater degree of fragment due to faster shovel or loader longing rate and a decrease in bridging at the crusher. Therefore, there is a consequent decrease in cycle time. Fragmentation optimization involves breaking of rock to ensure quality control, safe, consistent and efficient blasting [6]. Subsequently, boulder or the opposite, excess fines, result from poorly selected drilling and blasting patterns. A well selected pattern would produce fragmentation that can be accommodated by available loading and hauling equipment and crushing plant with little or no need for secondary blasting. Therefore, it is a well acknowledged fact that the performance of mining operations such as excavation and crushing reeves on fragmentation has been pre-conditioned by blast designs [6, 7, 8].
The effectiveness of hard rock blasting is measured with two basics indices namely, oversize generation and blast hole productivity. Cost per tonne of rock blasted is another index that measures the effectiveness of blasting and is dependent on rockiness and blast design parameter such as hole diameter, burden, spaces among others [9, 10]. Such parameters differ from one mine to the other and some of the blast design parameters could be regulated to deliver the desired blasting effectiveness. The individual influence of the determinant parameter on blasting has been studied by several authors but their cumulative influence on the same is yet to be formulated. However, the huge statistical data generated from the well organized and documented large scale hard rock surface mines operating variables condition worldwide constitute the only readily available resources which could be used for the analysis and regression model of indices that determine effectiveness of blasting of rock blasted on uncontrollable and controllable blasting parameters [1]. Efficiency of drilling and blasting operations must contribute to the best overall economics of a quarry [11, 12]; therefore, variability of powder factor has potentials to improve surface mines’ productivity [13, 14]. Hence, there is need to study the effect of powder factor variability in the productivity of granite quarrying. The study is an attempt to achieve the following specific objectives:
To determine the relationship between the powder factor and uniaxial compressive strength at the quarry.
To determine the effect of varying powder factor in the fragmentation of rock; and
To recommend ways to improve the productivity of granite in the quarry.
The appraised parameters would give optimum blasting results through the regression model generated using indices such as oversize generation and geometric volume of the blasted rock on blast design parameters.
2. Materials, methods used
2.1 Climate, vegetation and relief of typical granite areas
A study carried out by Abaje and Oladipo [15] shows that the temperatures of granite mineralized areas could increase from 0.2 to 0.5°C. A case of rainfall trend and variation characteristics across Kaduna State, North-western Nigeria, using 11 selected stations in the Southern, Central and Northern parts of the State for a period of 50 years (1966–2015) was carried out and the climatic condition of the study revealed that its Southern part, has the highest total rainfall, yet there was no significant trend in the five decadal periods examined. From the early 1970s to the late 1990s the rainfall was below the long-term mean. The rainfall of the remaining years nearly approximates the long-term mean [16]. Local spatial patterning of most granitic areas partly describes their spatial heterogeneity and related to alternation between vegetated and bare areas which are commonly found in savanna systems [17].
Ladan [18] also shows that granitic areas which have natural rain forest vegetation often fall within the Savanna. Their two distinct characteristic seasons are rainy and dry, while their annual rainfall is between 80 cm and 100 cm. Their temperature variation throughout the year could vary from 20° to 27°. The vegetation in such area may be Guinea Savannah and can be characterized by long and short grasses as well as low trees and shrubs. Their sparse distribution is sometimes accompanied by dense vegetation along streams and river channels [19].
2.2 Brief geology granite areas
The areas consist of rocks that range in age from Pre-Cambrian to Lower Paleozoic and Quaternary period. Four groups of rocks can be distinguished for the Basement Complex Terrain in the area. The crystalline basement rocks which consist of gneisses and migmatites with different varieties of the gneisses like the banded gneiss, granite gneiss, biotite gneiss, hornblende gneiss and ortho genesis [20]. Figure 1 shows the exposure of a typical granite outcrop.
In the older granite underlain by the Precambrian Basement Complex rock, porphyritic granite could be the most common basement rock intruding both magnetite and metasediments. Pegmatites are widely distributed throughout the Precambrian Basement Complex of the area studied by Abere
2.3 Field studies and data collection
The operation of the selected granite site was studied in order to obtain information about the various explosives, drilling machines, blasting parameters such as burden, spacing and depth of hole. Their physical condition and quantity available were studied. Observation was also made to estimate the size of fragmented rocks. Three samples of blasted boulders were collected at three different faces of the quarry in the study area. The coordinates of each location were taken and recorded with the aid of global positioning system (GPS).
2.4 Drilling/blasting and powder factor variability procedures
As shown in Tables 1–10, the various drilling and blasting parameters used at Tutu quarry including the parameters for burden and spacing, depth of blast holes, column charge, base charge, tonnage factor, quantity of material blasted and their corresponding powder factors adopted for rock fragmentation are presented for ten (10) blasting operations.
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Staggered | |
3 | Hole depth | 6.30 | M |
4 | Diameter | 76.00 | Mm |
5 | Burden | 1.70 | M |
6 | Spacing | 1.70 | M |
7 | Stemming height | 1.60 | M |
8 | Charged column | 4.70 | M |
9 | Number of holes | 64.00 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 4.00 | — |
12 | High explosive | 400.00 | Kg/Hole |
13 | ANFO | 3.72 | Kg/m |
14 | ANFO | 719.00 | Kg/Hole |
15 | Total weight of explosive | 1119.00 | Kg |
16 | Volume of rock | 1165.25 | m3 |
17 | |||
18 | Tonnage factor | 2.70 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Staggered | |
3 | Hole depth | 7.90 | M |
4 | Diameter | 76.00 | Mm |
5 | Burden | 1.80 | M |
6 | Spacing | 1.80 | M |
7 | Stemming height | 2.00 | M |
8 | Charged column | 5.90 | M |
9 | Number of holes | 88.00 | — |
10 | High Explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 6.00 | — |
12 | High explosive | 825.00 | Kg/Hole |
13 | ANFO | 3.72 | Kg/m |
14 | ANFO | 1106.48 | Kg/Hole |
15 | Total weight of explosive | 1931.48 | Kg |
16 | Volume of rock | 2252.45 | m3 |
17 | |||
18 | Tonnage factor | 2.70 | T/m3 |
S/N | Parameters | Numeric Value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Staggered | |
3 | Hole depth | 6.80 | M |
4 | Diameter | 76.00 | Mm |
5 | Burden | 1.90 | M |
6 | Spacing | 1.90 | M |
7 | Stemming height | 1.50 | M |
8 | Charged column | 5.30 | M |
9 | Number of holes | 74.00 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 4.00 | — |
12 | High explosive | 462.50 | Kg/Hole |
13 | ANFO | 3.72 | Kg/m |
14 | ANFO | 996.51 | Kg/Hole |
15 | Total weight of explosive | 1459.01 | Kg |
16 | Volume of rock | 1816.55 | m3 |
17 | |||
18 | Tonnage factor | 2.70 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Staggered | |
3 | Hole depth | 7.76 | M |
4 | Diameter | 165 | Mm |
5 | Burden | 4 | M |
6 | Spacing | 4 | M |
7 | Stemming height | 1.8 | M |
8 | Charged column | 5.5 | M |
9 | Number of holes | 92 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 4 | — |
12 | High explosive | 650 | Kg/Hole |
13 | ANFO | 18.73 | Kg/m |
14 | ANFO | 102.99 | Kg/Hole |
15 | Total weight of explosive | 10,137.00 | Kg |
16 | Volume of rock | 11,425.60 | m3 |
17 | |||
18 | Tonnage factor | 2.7 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Staggered | |
3 | Hole depth | 13.28 | M |
4 | Diameter | 165 | Mm |
5 | Burden | 3 | M |
6 | Spacing | 4 | M |
7 | Stemming height | 1.3 | M |
8 | Charged column | 9.82 | M |
9 | Number of holes | 52 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 4 | — |
12 | High explosive | 408 | Kg/Hole |
13 | ANFO | 10.93 | Kg/m |
14 | ANFO | 107.34 | Kg/Hole |
15 | Total weight of explosive | 10,295.00 | Kg |
16 | Volume of rock | 8286.00 | m3 |
17 | 1.24 | ||
18 | Tonnage factor | 2.7 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Staggered | |
3 | Hole depth | 14.41 | M |
4 | Diameter | 165 | Mm |
5 | Burden | 3 | M |
6 | Spacing | 4 | M |
7 | Stemming height | 1.8 | M |
8 | Charged column | 12.15 | M |
9 | Number of holes | 52 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 4 | — |
12 | High explosive | 760 | Kg/Hole |
13 | ANFO | 19.52 | Kg/m |
14 | ANFO | 107.34 | Kg/Hole |
15 | Total weight of explosive | 11,094.60 | Kg |
16 | Volume of rock | 8994.48 | m3 |
17 | |||
18 | Tonnage factor | 2.7 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Square | |
3 | Hole depth | 16.44 | M |
4 | Diameter | 102 | Mm |
5 | Burden | 2.5 | M |
6 | Spacing | 2.5 | M |
7 | Stemming height | 1.52 | M |
8 | Charged column | 14.44 | M |
9 | Number of holes | 87 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 3 | — |
12 | High explosive | 4.68 | Kg/Hole |
13 | ANFO | 6.70 | Kg/m |
14 | ANFO | 91.53 | Kg/Hole |
15 | Total weight of explosive | 8237.95 | Kg |
16 | Volume of rock | 8938.06 | m3 |
17 | |||
18 | Tonnage factor | 2.7 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Square | |
3 | Hole depth | 12.07 | M |
4 | Diameter | 102 | Mm |
5 | Burden | 2.8 | M |
6 | Spacing | 2.8 | M |
7 | Stemming height | 1.8 | M |
8 | Charged column | 10.27 | M |
9 | Number of holes | 92 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 3 | — |
12 | High explosive | 4.68 | Kg/Hole |
13 | ANFO | 6.70 | Kg/m |
14 | ANFO | 60.30 | Kg/Hole |
15 | Total weight of explosive | 6046.37 | Kg |
16 | Volume of rock | 8707.57 | m3 |
17 | |||
18 | Tonnage factor | 2.7 | T/m3 |
S/N | Parameters | Numeric value | |
---|---|---|---|
1 | Explosive used | High Explosive + ANFO | |
2 | Drilling pattern | Square | |
3 | Hole depth | 15.59 | M |
4 | Diameter | 102 | Mm |
5 | Burden | 2.5 | M |
6 | Spacing | 2.5 | M |
7 | Stemming height | 1.5 | M |
8 | Charged column | 12.83 | M |
9 | Number of holes | 105 | — |
10 | High explosive | 1.56 | Kg/Cartridge |
11 | Number of explosives used per hole | 3 | — |
12 | High explosive | 4.68 | Kg/Hole |
13 | ANFO | 6.70 | Kg/m |
14 | ANFO | 60.30 | Kg/Hole |
15 | Total weight of explosive | 9176.62 | Kg |
16 | Volume of rock | 10,033.30 | m3 |
17 | |||
18 | Tonnage factor | 2.7 | T/m3 |
Sample | Maximum load (KN) | Specimen length (m) | Specimen width (m) | Cross sectional area (m2) | Uniaxial compressive strength (MN/m2) |
---|---|---|---|---|---|
Tutu Quarry | 133.2 | 0.06 | 0.03 | 0.0018 | 74 |
F&P Quarry | 145.8 | 0.06 | 0.03 | 0.0018 | 81 |
AAY Quarry | 157.5 | 0.06 | 0.03 | 0.0018 | 87.5 |
Details of the variability results are follows:
Staggered.
High explosive (Gelatin) + ANFO.
6.30 m: 16.44 m.
76 mm, 102 and 165 mm.
1.7 × 1.7: 2.8 × 2.8.
1.2 M: 2.7 m.
4.0 M: 14.44 m.
58: 105.
1119.00 kg – 11,094.60 kg.
1165.25 m3–11,425.60 m3.
0.77–1.24.
2.7.
2.5 Sample preparation and laboratory analysis
A circular saw with a diamond blade was used to cut the specimens to their final lengths. The surfaces were then ground after cutting in a grinding machine in order to achieve a high-quality surface for the axial loading. The measurement of the specimen dimensions was made with a sliding caliper and metre rule. Furthermore, the tolerances were checked by means of a dial indicator and a stone face plate. The specimen preparation was carried out in accordance with ASTM test procedure (ASTM, 39-71) and as adopted by Vandergrift and Schindler [23] in their experiment. The sample was cut using cutting machine to a dimension suitable for uniaxial compressive stress (UCS) test. The specimen was placed in horizontal direction but perpendicular to the direction of cutting edge of the blade. Then the vice was used to hold the specimen firmly to obtain a smooth surface as accurately as possible. The machine was switched on and the necessary shield applied. Water was allowed to lubricate the blade during the cutting process.
2.5.1 Procedure for uniaxial compressive strength test
The ASTM test procedure (39-71) was adopted. The specimen was placed in the ELE ADR 2000 compression machine. The load is continuously applied on the specimen until it failed. The failure mode was noted as well as the pressure or load at failure. The type of failure and the maximum load carried by the specimen were recorded. The unconfined UCS of the rock sample was obtained by dividing the maximum load carried by the cross-sectional area. Testing machine of standard recommended ASTM C 39-71 was used to load the squared sample until it failed.
2.5.2 Test specimens
Squared samples were used for this test. The four sides of each sample were ground flat, smooth and perpendicular to axis, that is they were parallel to each other 4 cm × 4 cm cube specimen were cut from block samples supplied (in the absence of core which are commonly used). The platens on the compression machine were altered to suit this configuration. The edges were cut to shape and smoothened by polishing them with carborundum powder.
3. Discussion of results
Findings from field studies and observations as shown in Table 11 have revealed that the trend in the spread of GPS coordinates of granite samples collected indicates that the samples were taken at relatively close intervals. Results shown in Tables 1–10 also indicate the various specifications of drilling and blasting parameters as used in the study site. From the tables it can be deduced that the stemming heights, burden spacing, column of charged holes and bulk density were varied as the depth of blast holes increases. It is also shown that the number of explosives charged per hole indicates an increase in the depth of hole drilled, thereby increasing more explosives consumption and equally implying that more volume of granite has been fragmented. Table 10 shows uniaxial compressive strength (UCS) MN/m3 of granite from the studied quarries, Table 12 on the other hand shows the bulk densities of granite from the selected quarries. Also as apparently shown in Table 13, the mineralogy of the granitic constituents of granite is partly influenced by either a corresponding increase of decrease in PF. Hence, some sort of correlation seems to be found between granite mineralogy and PF. In addition, the PF for the nine (9) blasts was not the same, which means that it was varied at different times of the blast as shown in Table 14. For all the selected quarries, bigger blasthole diameter also varies with increased PF.
Sample | Latitude | Longitude |
---|---|---|
1 | N260 51′7.2” | E0070 59′ 71.4” |
2 | N26051’8.1” | E007059’75.5” |
3 | N260 51′13.3” | E007059’64.5” |
Sample ID | Mass of specimen (g) | Height of specimen (m) | Width of specimen (m) | length of specimen (m) | volume of specimen (m3) | Bulk density (Kg/m3) |
---|---|---|---|---|---|---|
Tutu Quarry | 2742.6 | 0.1 | 0.1 | 0.1 | 0.001 | 2743 |
F&P Quarry | 2742.4 | 0.1 | 0.1 | 0.1 | 0.001 | 2742 |
AAY Quarry | 2183.3 | 0.1 | 0.1 | 0.1 | 0.001 | 2183 |
Mineral | Sample 1 (%) | Sample 2 (%) | Sample 3 (%) | Average (%) |
---|---|---|---|---|
Quartz Syn | 39 | 40 | 30 | 36.33 |
Microcline | 0 | 0 | 28 | 9.33 |
Albeit | 34.6 | 31 | 10 | 25.20 |
Orthoclase | 25 | 17 | 16 | 19.33 |
Anorthite | 0.3 | 10 | 6 | 5.43 |
Muscovite | 0.1 | 0.8 | 2 | 0.97 |
Osumilite | 0.9 | 0.7 | 8 | 3.20 |
TOTAL | 99.9 | 99.5 | 100 | 99.80 |
S/N | Powder factor (Kg/m3) | Volume of rock produced (m3) | Location |
---|---|---|---|
1 | 0.96 | 1165.25 | Tutu quarry, Kaduna |
2 | 0.86 | 2252.45 | Tutu quarry, Kaduna |
3 | 0.80 | 1816.55 | Tutu quarry, Kaduna |
4 | 0.89 | 11,425.60 | F&P Quarry, Abuja |
5 | 1.24 | 8286.00 | F&P Quarry, Abuja |
6 | 1.23 | 11,094.60 | F&P Quarry, Abuja |
7 | 0.89 | 8938.06 | AAY Quarry, Kano |
8 | 0.69 | 10,033.30 | AAY Quarry, Kano |
9 | 0.91 | 8707.57 | AAY Quarry, Kano |
Results from this study have shown the level of relationship between the strength of rock and PF. For instance, it can be deduced from Figures 2–4 that the Uniaxial Compressive Strength (UCS) of rock increases as the PF increases. This is also true in the reverse case as PF reduces. In the same vein, keeping UCS as a constant, PF increases as volume of blasted materials increases which is also true for the reverse case.
From the figures, it is evident that PF increases as the volume of blasted rock increases. Thus, more volume of rocks means higher PF to fragment the rock. Therefore, more explosives are charged in the holes to get the required results as the volume of rock increases. It can be deduced that to reasonably vary the PF of rock, the ratio of burden to spacing must be carefully selected with a view to increasing its productivity. Hence, PF variability becomes more effective with careful and staggered increment of burden and spacing.
As evident from Figures 5–7, more explosives are consumed when the volume of fragmented rock increases. Therefore, varied PF with carefully varied and selected drilling and blasting parameters are required for optimum blast and higher productivity.
4. Conclusions and recommendations
The PF used at the selected quarries has been examined for nine (9) blasts to ascertain its effects on the level of granite productivity in the three selected quarries. It can therefore be concluded that:
PF variability can lead to increase or decrease in the level of productivity of granite.
Blasthole diameter varies with increase in PF of granite.
PF selection and variability can lead to higher cost of productivity.
The apparent correlation between PF and granite mineralogy can be a factor for consideration in blast design and the desired productivity.
The strength of granite influenced the PF selected at the selected quarries.
Also, the quantity of explosives for some of the sizes of the fragmented rock at the quarries was found to be moderate, while for some, it was optimal for the blast. Hence, it can be concluded from the observed blasts that the productivity of granite at a quarry can be improved for optimum economic benefit, if the PF is varied as appropriate for any blast design and the quality and properties of the explosives selected are adequate for the strength of the rock to be blasted.
Having observed and examined the effects of PF variability on the level of granite productivity, the following measures are hereby recommended for optimum rock fragmentation:
The strength of granite should be examined before selecting a suitable PF.
Since the PF variability has great impact on the productivity of granite, its selection must be guided by expertise and experience.
Economy and productivity of granite quarries have potentials for improvement when serious attention is given to the blast design and study of explosive characteristics and properties.
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