- Email: [email protected]
Field experiment for blasting crater
JOURNAL OF CHINA UNIVERSITY OF
MINING & TECHNOLOGY J China Univ Mining & Technol 18 (2008) 0224–0228 www.elsevier.com/locate/jcumt
Field experiment for blasting crater YE Tu-qiang School of Civil & Environment Engineering, University of Science and Technology, Beijing 100083, China
Abstract: A series of single hole blasting crater experiments and a variable distance multi-hole simultaneous blasting experiment was carried in the Yunfu Troilite Mine, according to the Livingston blasting crater theory. We introduce in detail, our methodology of data collection and processing from our experiments. Based on the burying depth of the explosives, the blasting crater volume was fitted by the method of least squares and the characteristic curve of the blasting crater was obtained using the MATLAB software. From this third degree polynomial, we have derived the optimal burying depth, the critical burying depth and the optimal explosive specific charge of the blasting crater. Key words: blasting crater; collecting and processing of data; optimal burying depth; critical burying depth; optimal explosive specific charge
1
Introduction
The Yunfu Troilite Mine was put into production in 1980 and after more than 20 years of open-pit mining, it was turned into a middle and deep concave mining enterprise. Variability in orebodies and rock is great, specific explosive charges are high, the residual root and clump ratio is rather high and the blasting results are not ideal. The geological structure of the main ore-bearing rocks and the physical properties of the blasting body have all changed in varying degrees. Given the different conditions of ore-bearing rocks, the blasting parameters of the specific explosives will vary. In order to choose and confirm suitable blasting parameters based on different rock characteristics, improve blasting results and reduce mining cost, it is necessary to carry out an experiment in blasting craters in scene.
2 Experiment rationale In blasting, when the column charge blows up, the energy of demolition compressed gas is nearly all vertical to the axes of the borehole according to blasting rules. Action perpendicular to this direction is only a small part of the energy released at both ends of the column charge. When a spherical charge blows up, the energy released by the gas expands its action along a radial axis from the center of the charge and presents an overall spherical, homogeneous radiation pattern. After a long period of experiments with blasting Received 12 November 2007; accepted 20 February 2008 Corresponding author. Tel: +86-13421780594; E-mail address: [email protected]
craters, Livingston came to the conclusion that if the ratio of length over diameter ratio of the charge is not more than 6, the crater blasting mechanism is similar to the blasting mechanism of a spherical charge. Research shows that the amount and velocity of the energy released by blasting rest with the lithology, characteristics of Livingston the explosives and the mass of the charge. From the point of view of the energy released to the demolition rock, the result of keeping the burying depth of the charge constant while changing the mass of the charge is the same as keeping the mass of the charge constant while changing the burying depth. If the mass of the charge is constant, when the burying depth increases, the volume of the blasting crater will increase and when the burying depth reaches a certain value, again with an increase in the burying depth, the volume of the blasting crater will decrease and eventually there will be no blasting crater at all. The maximum burying depth for the appearance of a blasting crater is called the optimal burying depth. If the depth only produces crannies and pieces fall free to the surface, the depth is called the critical burying depth. The ratio of the optimal burying depth to the critical burying depth is called the optimal burying depth ratio. The elastic deformation equation when the charge is at the critical burying depth Le is: Le = EQ1 3 or Lo = ∆ o EQ1 3 (1) where Le is the critical burying depth (cm), E the strain energy modulus, Q the quality of the spherical charge (kg), Lo the optimal burying depth (m), ∆ o the optimal burying depth ratio, i.e., ∆o = Lo Le .
YE Tu-qiang
Field experiment for blasting crater
Assuming that the detonating gas results in isothermal expansion in continuous column blasting, according to detonation rules and that the pressure keeps the volume constant, and then it is easy to work out the effective pore pressure of the coupling charge. The ratio of the effective pore pressure Pe and the detonation pressure Px is directly related to the ratio of the volume Vx of explosives and the borehole volume Vb , i.e., Pe Px = Vx Vb . According to the blasting volume and its charge, the relation between the direct ratio, in the case of continuous column blasting and the charge, can be shown by a drill charge weight, as: 13 Wx Wb = (Qx Qb ) (2) where Wx , Wb are the blasting burdens of the non-coupling and coupling charge (m) and Qx , Qb the drill charge weights of the non-coupling and coupling charge (kg/m). From a series of single hole blasting crater experiments, it is easy to obtain parameters such as the critical burying depth Le , the strain energy modulus E, the optimal burying depth Lo , the optimal burying depth ratio ∆ o and the specific charge of the optimal conditions for the volume of the blasting crater, etc. After we obtain the optimal burying depth from this series of experiments, we can carry out widespaced and simultaneous blasting crater experiments, in order to determine the range of parameters of the maximum hole bottom space[1–4].
3 Series of single hole blasting crater experiments 3.1 Choice for site test The site for the test is on the 370–380 step, 1–4' stage and the location of the stage is between F1 and F3. The main part of the site is ore and a small amount of rock. The rock type is thick and strip shaped and consists of iron pyrites, compact and massive, (f =20), density of the rock is 3.78 t/m3. Before the test, the field of the test site was cleaned in order to have a canonical blasting crater. The principle for borehole disposition is to require that craters be formed by blasting without interfering with other craters. The orifice should have a wide enough flat free surface and the axes of the drill hole should be vertical to the ground. The parameters are as follows: the space between neighboring boreholes should be larger than or equal to 7 m, the depths of the holes are: 0.67, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.25, 1.3, 1.35, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6 and 1.8 m, i.e., 20 boreholes altogether. Explosives used for the test were #2 rock emulsion explosives, produced by the Lauding Chemical Plant
225
and used by the mine. Its capability index is as follows: brisance 12 mm, sympathetic detonation distance 5 cm, detonation velocity 4500 m/s and density 1.05–1.2 g/cm3. Its specification is Φ60 mm× 400 mm and quantity is 1 kg. According to the design depth of the boreholes, the load consists of one 1 kg casing of emulsion explosive for each borehole with a charge length in each hole of 400 mm. We used the initiation system of the electric detonator-nonelectric Nonel detonator. The center depth of the charge was 0.67–1.8 m. Ultra deep boreholes can be adjusted to the designed charge depth using soil. The orifice should be stamped by soil for a length of about 60 cm. 3.2
Experimental test and data processing
3.2.1 Blasting crater volume survey Given the rule of vertical profiles, we design the plane, vertical to the axes of the borehole, as the datum plane and measure the original free surface before and the distance between crater figure and datum plane after the blasting according to a 20 cm×20 cm network. The difference between these two is the blasting depth of each measuring point for which we determine the area Si and the crater volume Vi at each cross section.
1 n ∑ ( yi + yi+1 )l 2 i =0 1 n Vi = ∑ ( Si + Si +1 )l 2 i =0 Si =
(3) (4)
where yi , yi +1 are the blasting depths of measuring points at the cross section (m); Si , Si +1 crater area at each cross section, (m2) l is the space of the measuring points, l=0.2; V crater volume (m3). After blowing up the boreholes, we removed the rock debris around each crater and selected its boundary. We chose the borehole as the center and measured the crater boundary Ri at eight points, one for every 45° of orientation and then determined the average value as the radius of each blasting crater. Visible depths were measured by ruler. 3.2.2 Data processing After blowing up of the boreholes and measuring the radius and volume of each blasting crater in turn, we calculated the result shown in Table 1. 3.2.3 Analysis for experiments From the data in Table 1, we estimated the V-L curve of the blasting craters (Fig. 1), by the method of least squares. We used the MATLAB software to obtain the characteristic curve, a third degree polynomial regression equation of the experimental data, from the charge burying depth (L) of the #2 rock emulsion explosive and the expression of the blasting crater volume (V)[5–6]: V= –6.4079L3+16.5350L2–12.5747L+3.5628 (5)
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Journal of China University of Mining & Technology
Table 1
Test data of single hole craters
4
Vol.18 No.2
Wide-space and simultaneous blasting crater experiments
No.
Center depth of the charge (m)
Crater radius (m)
Crater volume (m3)
1
0.80
0.9502
0.827
4.1 Determination for maximum spacing
2
0.67
0.8681
0.618
3
0.85
0.9392
0.854
4
1.20
1.0511
1.272
5
1.50
0.775
0.1886
6
1.40
0.875
0.3205
7
1.30
0.9675
1.019
8
1.45
0.8125
0.2976
In order to determine the maximum spacing, we carried out wide-spacing and simultaneous blasting crater experiments. The disposition of the boreholes is shown in Fig. 2. There are five groups altogether, with three boreholes in each group and spacing among boreholes of: 1.2, 1.4, 1.6, 1.8 and 2.0 m. The depth of each borehole is 1.15 m, i.e., the optimal burying depth determined from the single hole blasting crater experiment. The amount and length of the charge are the same as in the single hole blasting crater experiments, i.e., loading 1 kg emulsion explosives and a charge length of 40 cm. Fig. 3 shows typical photographs of blasting craters, where (a) is a single hole blasting crater and (b) a wide-spaced and simultaneous blasting crater. Portray the contour lines from the real figures of every blasting crater, it can be seen from Fig. 4 and Table 2 that when the spacing is equal to or less than 1.6 m, the neighbouring borehole blasting crater overlaps and the hole at the bottom of the ore-bearing rocks broken effectively. Therefore, the maximum spacing parameter should less than 1.6 m and when it is equal to 1.6 m, the specific charge is 0.7442 kg/m3 (Table 2).
9
1.35
0.8953
0.906
10
1.25
0.9935
1.157
11
0.70
0.8828
0.668
12
0.75
0.9234
0.763
13
0.90
0.9657
0.961
14
0.95
0.9687
1.017
15
1.00
0.9807
1.057
16
1.10
1.0638
1.303
17
1.35
0.9287
0.975
18
1.55
0
0
19
1.60
0
0
20
1.80
0
0
1.2 1.0
3.5 1.2
V (m3)
0.8 0.6
1.8
1.8
0.4 0.2
3.5 1.4
0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 L (m)
Fig. 1
7 1.2
7
8
L-V curve of the #2 rock emulsion explosive
By solving Eq.(5) for optimum values of various technical parameters of the blasting crater, we obtain: the critical burying depth: Le=1.5412 m; the optimal burying depth: L =1.1529 m; the optimal burying depth ratio: ∆ o ˙0.748 m (Annotation: in brittle rock the value of ∆ o is small, about 0.5–0.55; in plastic rock the value of ∆ o is much bigger, about 0.9–0.95. Therefore, given the data from the test area in our mine, the rock is brittle and plastic, its tenacity very big and we conclude that the rock is a hard-explosion ore); the optimal blasting crater volume: V=1.2237 m3; the strain energy modulus: E˙1.5412; the explosive specific charge of the optimal blasting crater volume: qoptimal = 1(kg)/1.2237(m3) = 0.8172 kg/m3.
1.6
1.4 2
1.6
2
20
Fig. 2
Arrangement plan of the multi-hole crater test with same delay time (m)
(a) A single hole blasting crater
Fig. 3
(b) A wide-spaced and simultaneous blasting crater
Crater photographs
YE Tu-qiang
Field experiment for blasting crater
(a) Spacing is 1.2 m
227
(b) Spacing is 1.4 m
(d) Spacing is 1.8 m
Fig. 4
(c) Spacing is 1.6 m
(e) Spacing is 2.0 m
Landmark of the multi-hole crater with the same delay time
1. Level lines; 2. Contour lines of pre-dynamite; 3. Contour lines of dynamited
Table 2 Hole No.
4.2
Center depth of the charge (m)
Results of the broad hole-space crater test with same delay time
Spacing (m)
Rate of spacing andoptimal volume radius
Center width of the blasting trench (m)
Volume of the blasting trench (m3)
Specific charge (kg/m3)
12
1.15
1.2
1.29
1.5
1.2734
0.7853
13
1.15
1.4
1.51
1.4
1.3053
0.7661
14
1.15
1.6
1.72
1.3
1.3437
0.7442
15
1.15
1.8
1.94
1.0
1.3118
0.7623
16
1.15
2.0
2.15
0.7
1.2585
0.7946
Relation of minimum burden and loading density
The maximum spacing becomes the minimum burden of the boreholes in each row in the test above and the minimum burden and line charge density of the boreholes has corresponding relations. The test shows that when the charge is 1 kg, it is suitable to take the minimum burden ≤1.6 m. When the length of the charge in the boreholes where apertures are 140 mm and 250 mm, less than 0.84 m and 1.5 m respectively, the ratio of length-diameter is less than 840/140=6 and 1500/250=6, given the theory by. Livingston, the following data can be calculated according to globose charge[7–15]. The data in Table 3 are derived from Eq.(1). Table 3
Relation of minimum burden and charge density
Explosive density (g/cm3)
1.05
1.10
1.15
1.20
Charge density (kg/m) (140 mm hole)
16.16
16.93
17.70
18.47
Minimum burden (m)
3.82
3.88
3.93
3.99
Charge density (kg/m) (250 mm hole)
51.52
53.97
56.42
58.87
Minimum burden (m)
6.82
6.92
7.02
7.13
From these test results and the information in Table 3, we can determine the perfect row spacing and the specific charge: 1) Row spacing b. Table 3 indicatesˈthat when the explosive density is 1.05–1.20 g/cm3 for the 140 mm borehole, the minimum burden or row spacing is 3.82–3.99 m, while for the 250 mm boreholeˈthe minimum burden or row spacing is 6.82–7.13 m; 2) Specific charge q. The single hole series blasting crater experiments shows that when the charge is at
the optimal burying depth (the volume of the blasting crater is the largest one), the specific charge is 0.8172 kg/m3. According to the wide-spaced and simultaneous blasting crater experiments, when the spacing is 1.6 m, the specific charge is 0.7442 kg/m3. During mine operation, the specific charge should be 0.75– 0.82 kg/m3. Because of differences in the composition of the orebearing rocks and the geological structure, when designing the blasting parameters, i.e., the optimal burying depth, row spacing and the specific charge, should be adjusted appropriately according to the rigidity of the ore and other prevailing conditions.
5
Conclusions
1) The optimal burying depth, row spacing and the specific charge we obtained were suitable for the blasting designs in the testing ground of the mine, but because of the differences in composition of the orebearing rocks and their geological structure, the parameters we determined are only a reference for other mine areas or blasting conditions and should be adjusted appropriately according to condition of the blasting medium. 2) Blasting crater experiments are necessary in the course of mine blasting designs, but the methods are different under various circumstances. Our method consisted of a small, scientific serial type of experiment, worthwhile for promoting in our profession. By carrying out our single hole series of blasting crater experiments we obtained the optimal burying depth under the test conditions and then continued with wide-spaced and simultaneous blasting crater experiments to arrive at maximum spacing and mini-
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Journal of China University of Mining & Technology
mum burden. 3) Analyzing our results according to a basic rule of blasting crater experiments and by using the MATLAB software to derive a third degree polynomial regression equation from the experimental data, this third degree polynomial of the charge depth and the blasting crater volume, provided us with optimal burying depth. The analytical method is suitable and the results reliable. It should be an important reference for data processing of blasting crater experiments.
[7]
[8]
[9]
[10]
References [1]
[2]
[3]
[4]
[5] [6]
Zheng R C. Livingston blasting crater theory and bond crush work theory and the application in the blasting classification. Blasting, 1989(1): 32–35. Zhu Y M. Preliminary analysis of series blasting hopper tests of medium and deep holes mining. Express Information of Mining Industry, 2004(12): 34–35. Guo Z L. The study of a series of blasting crater tests of medium-length hole mining. Jiangxi Nonferrous Metals, 2004(3): 3–6. Yang H B. Method of determining medium-length hole blasting parameters by blasting cratertest. Xinjiang Nonferrous Metals, 2005(3): 13–14. Zhou J X. Practical Regression Analysis Method. Shanghai: Shanghai Technology Press, 1990. Su J M, Ruan S Y. MATLAB6.1 Practical Guide. Beijing:
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[12] [13]
[14] [15]
Vol.18 No.2
Publishing House of Electronics Industry, 2002. Li Z H. Crater tests and choosing of parameters in large diameter deep hole mining. Nonferrous Metals, 1999(3): 12–15. Zhou C B, Luo X D, He X G. Investigation on application of blasting crater test in shaft excavation by one blasting. Metal Mine, 2005(8): 20–23. Liu H Y, Yang J, Chen P W. Simulation of the process of explosion crater formulation by means of discontinuous deformation analysis. Engineering Blasting, 2004(2): 17–20. Zhou C B, Fan X F, Li Z, et al. Study of parameters of large diameter deep hole blasting based on blasting crater test. Mining and Metallurgical Engineering, 2006(2): 9–13. Liu N G, Wan B. Application and study of serial blasting crater test method in medium and deep hole mining. Metal Mine Design & Construction, 2000(5): 3–5. Jin X H, Lu W B. Discuss on the theory of blasting crater. Rock and Soil Mechanics, 2002(S): 205–208. Li S J, Liu Y X, Wu Y L. Tensile and shear theory of deforming process of blasting crater. Chinese Journal of Rock Mechanics and Engineering, 1996, 15(S1): 515– 518. Lou D L. Pilot study on loose break crater. Blasting, 1993(2): 4–7. Pan J L. Application and theory of c.w. livingston blasting crater. Interpret of Tunnelling, 1978(5): 14–18.
MINING & TECHNOLOGY J China Univ Mining & Technol 18 (2008) 0224–0228 www.elsevier.com/locate/jcumt
Field experiment for blasting crater YE Tu-qiang School of Civil & Environment Engineering, University of Science and Technology, Beijing 100083, China
Abstract: A series of single hole blasting crater experiments and a variable distance multi-hole simultaneous blasting experiment was carried in the Yunfu Troilite Mine, according to the Livingston blasting crater theory. We introduce in detail, our methodology of data collection and processing from our experiments. Based on the burying depth of the explosives, the blasting crater volume was fitted by the method of least squares and the characteristic curve of the blasting crater was obtained using the MATLAB software. From this third degree polynomial, we have derived the optimal burying depth, the critical burying depth and the optimal explosive specific charge of the blasting crater. Key words: blasting crater; collecting and processing of data; optimal burying depth; critical burying depth; optimal explosive specific charge
1
Introduction
The Yunfu Troilite Mine was put into production in 1980 and after more than 20 years of open-pit mining, it was turned into a middle and deep concave mining enterprise. Variability in orebodies and rock is great, specific explosive charges are high, the residual root and clump ratio is rather high and the blasting results are not ideal. The geological structure of the main ore-bearing rocks and the physical properties of the blasting body have all changed in varying degrees. Given the different conditions of ore-bearing rocks, the blasting parameters of the specific explosives will vary. In order to choose and confirm suitable blasting parameters based on different rock characteristics, improve blasting results and reduce mining cost, it is necessary to carry out an experiment in blasting craters in scene.
2 Experiment rationale In blasting, when the column charge blows up, the energy of demolition compressed gas is nearly all vertical to the axes of the borehole according to blasting rules. Action perpendicular to this direction is only a small part of the energy released at both ends of the column charge. When a spherical charge blows up, the energy released by the gas expands its action along a radial axis from the center of the charge and presents an overall spherical, homogeneous radiation pattern. After a long period of experiments with blasting Received 12 November 2007; accepted 20 February 2008 Corresponding author. Tel: +86-13421780594; E-mail address: [email protected]
craters, Livingston came to the conclusion that if the ratio of length over diameter ratio of the charge is not more than 6, the crater blasting mechanism is similar to the blasting mechanism of a spherical charge. Research shows that the amount and velocity of the energy released by blasting rest with the lithology, characteristics of Livingston the explosives and the mass of the charge. From the point of view of the energy released to the demolition rock, the result of keeping the burying depth of the charge constant while changing the mass of the charge is the same as keeping the mass of the charge constant while changing the burying depth. If the mass of the charge is constant, when the burying depth increases, the volume of the blasting crater will increase and when the burying depth reaches a certain value, again with an increase in the burying depth, the volume of the blasting crater will decrease and eventually there will be no blasting crater at all. The maximum burying depth for the appearance of a blasting crater is called the optimal burying depth. If the depth only produces crannies and pieces fall free to the surface, the depth is called the critical burying depth. The ratio of the optimal burying depth to the critical burying depth is called the optimal burying depth ratio. The elastic deformation equation when the charge is at the critical burying depth Le is: Le = EQ1 3 or Lo = ∆ o EQ1 3 (1) where Le is the critical burying depth (cm), E the strain energy modulus, Q the quality of the spherical charge (kg), Lo the optimal burying depth (m), ∆ o the optimal burying depth ratio, i.e., ∆o = Lo Le .
YE Tu-qiang
Field experiment for blasting crater
Assuming that the detonating gas results in isothermal expansion in continuous column blasting, according to detonation rules and that the pressure keeps the volume constant, and then it is easy to work out the effective pore pressure of the coupling charge. The ratio of the effective pore pressure Pe and the detonation pressure Px is directly related to the ratio of the volume Vx of explosives and the borehole volume Vb , i.e., Pe Px = Vx Vb . According to the blasting volume and its charge, the relation between the direct ratio, in the case of continuous column blasting and the charge, can be shown by a drill charge weight, as: 13 Wx Wb = (Qx Qb ) (2) where Wx , Wb are the blasting burdens of the non-coupling and coupling charge (m) and Qx , Qb the drill charge weights of the non-coupling and coupling charge (kg/m). From a series of single hole blasting crater experiments, it is easy to obtain parameters such as the critical burying depth Le , the strain energy modulus E, the optimal burying depth Lo , the optimal burying depth ratio ∆ o and the specific charge of the optimal conditions for the volume of the blasting crater, etc. After we obtain the optimal burying depth from this series of experiments, we can carry out widespaced and simultaneous blasting crater experiments, in order to determine the range of parameters of the maximum hole bottom space[1–4].
3 Series of single hole blasting crater experiments 3.1 Choice for site test The site for the test is on the 370–380 step, 1–4' stage and the location of the stage is between F1 and F3. The main part of the site is ore and a small amount of rock. The rock type is thick and strip shaped and consists of iron pyrites, compact and massive, (f =20), density of the rock is 3.78 t/m3. Before the test, the field of the test site was cleaned in order to have a canonical blasting crater. The principle for borehole disposition is to require that craters be formed by blasting without interfering with other craters. The orifice should have a wide enough flat free surface and the axes of the drill hole should be vertical to the ground. The parameters are as follows: the space between neighboring boreholes should be larger than or equal to 7 m, the depths of the holes are: 0.67, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, 1.2, 1.25, 1.3, 1.35, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6 and 1.8 m, i.e., 20 boreholes altogether. Explosives used for the test were #2 rock emulsion explosives, produced by the Lauding Chemical Plant
225
and used by the mine. Its capability index is as follows: brisance 12 mm, sympathetic detonation distance 5 cm, detonation velocity 4500 m/s and density 1.05–1.2 g/cm3. Its specification is Φ60 mm× 400 mm and quantity is 1 kg. According to the design depth of the boreholes, the load consists of one 1 kg casing of emulsion explosive for each borehole with a charge length in each hole of 400 mm. We used the initiation system of the electric detonator-nonelectric Nonel detonator. The center depth of the charge was 0.67–1.8 m. Ultra deep boreholes can be adjusted to the designed charge depth using soil. The orifice should be stamped by soil for a length of about 60 cm. 3.2
Experimental test and data processing
3.2.1 Blasting crater volume survey Given the rule of vertical profiles, we design the plane, vertical to the axes of the borehole, as the datum plane and measure the original free surface before and the distance between crater figure and datum plane after the blasting according to a 20 cm×20 cm network. The difference between these two is the blasting depth of each measuring point for which we determine the area Si and the crater volume Vi at each cross section.
1 n ∑ ( yi + yi+1 )l 2 i =0 1 n Vi = ∑ ( Si + Si +1 )l 2 i =0 Si =
(3) (4)
where yi , yi +1 are the blasting depths of measuring points at the cross section (m); Si , Si +1 crater area at each cross section, (m2) l is the space of the measuring points, l=0.2; V crater volume (m3). After blowing up the boreholes, we removed the rock debris around each crater and selected its boundary. We chose the borehole as the center and measured the crater boundary Ri at eight points, one for every 45° of orientation and then determined the average value as the radius of each blasting crater. Visible depths were measured by ruler. 3.2.2 Data processing After blowing up of the boreholes and measuring the radius and volume of each blasting crater in turn, we calculated the result shown in Table 1. 3.2.3 Analysis for experiments From the data in Table 1, we estimated the V-L curve of the blasting craters (Fig. 1), by the method of least squares. We used the MATLAB software to obtain the characteristic curve, a third degree polynomial regression equation of the experimental data, from the charge burying depth (L) of the #2 rock emulsion explosive and the expression of the blasting crater volume (V)[5–6]: V= –6.4079L3+16.5350L2–12.5747L+3.5628 (5)
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Journal of China University of Mining & Technology
Table 1
Test data of single hole craters
4
Vol.18 No.2
Wide-space and simultaneous blasting crater experiments
No.
Center depth of the charge (m)
Crater radius (m)
Crater volume (m3)
1
0.80
0.9502
0.827
4.1 Determination for maximum spacing
2
0.67
0.8681
0.618
3
0.85
0.9392
0.854
4
1.20
1.0511
1.272
5
1.50
0.775
0.1886
6
1.40
0.875
0.3205
7
1.30
0.9675
1.019
8
1.45
0.8125
0.2976
In order to determine the maximum spacing, we carried out wide-spacing and simultaneous blasting crater experiments. The disposition of the boreholes is shown in Fig. 2. There are five groups altogether, with three boreholes in each group and spacing among boreholes of: 1.2, 1.4, 1.6, 1.8 and 2.0 m. The depth of each borehole is 1.15 m, i.e., the optimal burying depth determined from the single hole blasting crater experiment. The amount and length of the charge are the same as in the single hole blasting crater experiments, i.e., loading 1 kg emulsion explosives and a charge length of 40 cm. Fig. 3 shows typical photographs of blasting craters, where (a) is a single hole blasting crater and (b) a wide-spaced and simultaneous blasting crater. Portray the contour lines from the real figures of every blasting crater, it can be seen from Fig. 4 and Table 2 that when the spacing is equal to or less than 1.6 m, the neighbouring borehole blasting crater overlaps and the hole at the bottom of the ore-bearing rocks broken effectively. Therefore, the maximum spacing parameter should less than 1.6 m and when it is equal to 1.6 m, the specific charge is 0.7442 kg/m3 (Table 2).
9
1.35
0.8953
0.906
10
1.25
0.9935
1.157
11
0.70
0.8828
0.668
12
0.75
0.9234
0.763
13
0.90
0.9657
0.961
14
0.95
0.9687
1.017
15
1.00
0.9807
1.057
16
1.10
1.0638
1.303
17
1.35
0.9287
0.975
18
1.55
0
0
19
1.60
0
0
20
1.80
0
0
1.2 1.0
3.5 1.2
V (m3)
0.8 0.6
1.8
1.8
0.4 0.2
3.5 1.4
0 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 L (m)
Fig. 1
7 1.2
7
8
L-V curve of the #2 rock emulsion explosive
By solving Eq.(5) for optimum values of various technical parameters of the blasting crater, we obtain: the critical burying depth: Le=1.5412 m; the optimal burying depth: L =1.1529 m; the optimal burying depth ratio: ∆ o ˙0.748 m (Annotation: in brittle rock the value of ∆ o is small, about 0.5–0.55; in plastic rock the value of ∆ o is much bigger, about 0.9–0.95. Therefore, given the data from the test area in our mine, the rock is brittle and plastic, its tenacity very big and we conclude that the rock is a hard-explosion ore); the optimal blasting crater volume: V=1.2237 m3; the strain energy modulus: E˙1.5412; the explosive specific charge of the optimal blasting crater volume: qoptimal = 1(kg)/1.2237(m3) = 0.8172 kg/m3.
1.6
1.4 2
1.6
2
20
Fig. 2
Arrangement plan of the multi-hole crater test with same delay time (m)
(a) A single hole blasting crater
Fig. 3
(b) A wide-spaced and simultaneous blasting crater
Crater photographs
YE Tu-qiang
Field experiment for blasting crater
(a) Spacing is 1.2 m
227
(b) Spacing is 1.4 m
(d) Spacing is 1.8 m
Fig. 4
(c) Spacing is 1.6 m
(e) Spacing is 2.0 m
Landmark of the multi-hole crater with the same delay time
1. Level lines; 2. Contour lines of pre-dynamite; 3. Contour lines of dynamited
Table 2 Hole No.
4.2
Center depth of the charge (m)
Results of the broad hole-space crater test with same delay time
Spacing (m)
Rate of spacing andoptimal volume radius
Center width of the blasting trench (m)
Volume of the blasting trench (m3)
Specific charge (kg/m3)
12
1.15
1.2
1.29
1.5
1.2734
0.7853
13
1.15
1.4
1.51
1.4
1.3053
0.7661
14
1.15
1.6
1.72
1.3
1.3437
0.7442
15
1.15
1.8
1.94
1.0
1.3118
0.7623
16
1.15
2.0
2.15
0.7
1.2585
0.7946
Relation of minimum burden and loading density
The maximum spacing becomes the minimum burden of the boreholes in each row in the test above and the minimum burden and line charge density of the boreholes has corresponding relations. The test shows that when the charge is 1 kg, it is suitable to take the minimum burden ≤1.6 m. When the length of the charge in the boreholes where apertures are 140 mm and 250 mm, less than 0.84 m and 1.5 m respectively, the ratio of length-diameter is less than 840/140=6 and 1500/250=6, given the theory by. Livingston, the following data can be calculated according to globose charge[7–15]. The data in Table 3 are derived from Eq.(1). Table 3
Relation of minimum burden and charge density
Explosive density (g/cm3)
1.05
1.10
1.15
1.20
Charge density (kg/m) (140 mm hole)
16.16
16.93
17.70
18.47
Minimum burden (m)
3.82
3.88
3.93
3.99
Charge density (kg/m) (250 mm hole)
51.52
53.97
56.42
58.87
Minimum burden (m)
6.82
6.92
7.02
7.13
From these test results and the information in Table 3, we can determine the perfect row spacing and the specific charge: 1) Row spacing b. Table 3 indicatesˈthat when the explosive density is 1.05–1.20 g/cm3 for the 140 mm borehole, the minimum burden or row spacing is 3.82–3.99 m, while for the 250 mm boreholeˈthe minimum burden or row spacing is 6.82–7.13 m; 2) Specific charge q. The single hole series blasting crater experiments shows that when the charge is at
the optimal burying depth (the volume of the blasting crater is the largest one), the specific charge is 0.8172 kg/m3. According to the wide-spaced and simultaneous blasting crater experiments, when the spacing is 1.6 m, the specific charge is 0.7442 kg/m3. During mine operation, the specific charge should be 0.75– 0.82 kg/m3. Because of differences in the composition of the orebearing rocks and the geological structure, when designing the blasting parameters, i.e., the optimal burying depth, row spacing and the specific charge, should be adjusted appropriately according to the rigidity of the ore and other prevailing conditions.
5
Conclusions
1) The optimal burying depth, row spacing and the specific charge we obtained were suitable for the blasting designs in the testing ground of the mine, but because of the differences in composition of the orebearing rocks and their geological structure, the parameters we determined are only a reference for other mine areas or blasting conditions and should be adjusted appropriately according to condition of the blasting medium. 2) Blasting crater experiments are necessary in the course of mine blasting designs, but the methods are different under various circumstances. Our method consisted of a small, scientific serial type of experiment, worthwhile for promoting in our profession. By carrying out our single hole series of blasting crater experiments we obtained the optimal burying depth under the test conditions and then continued with wide-spaced and simultaneous blasting crater experiments to arrive at maximum spacing and mini-
228
Journal of China University of Mining & Technology
mum burden. 3) Analyzing our results according to a basic rule of blasting crater experiments and by using the MATLAB software to derive a third degree polynomial regression equation from the experimental data, this third degree polynomial of the charge depth and the blasting crater volume, provided us with optimal burying depth. The analytical method is suitable and the results reliable. It should be an important reference for data processing of blasting crater experiments.
[7]
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