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Empirical guidelines for drift blast design
37
Mining Science and Technology, 11 (1990) 3 7 - 4 4 Elsevier Science Publishers B.V., A m s t e r d a m - P r i n t e d in T h e N e t h e r l a n d s
Empirical guidelines for drift blast design S.P. Singh School of Engineering, Laurentian University, Sudbury, Ont. P3E 2C6 (Canada) (Received August 18, 1989; revision accepted December 12, 1989)
ABSTRACT Singh, S.P., 1990. Empirical guidelines for drift blast design. Min. Sci. Technol., 11: 37-44. Drifts are the nerve centre of underground mining operations. They provide essential communication between the shafts and the stoping areas and have varying dimensions and inclinations. In view of their strategic importance in the overall safety, economy and productivity of mines, empirical guidelines to estimate the drift blast design parameters have been described in this paper. The skill of the driller and the constant attention of the superviser to the accuracy achieved are essential ingredients to the successful application of these guidelines. The extra time spent in planning and accurately drilling the holes pays off in the form of higher advance, "bootleg" free round and the minimum damage to the back and sides of the drift. The application of this computerized empirical approach to practical situations has been described with an example.
Introduction The driving of drifts is a very important aspect of underground mining. They provide essential communication between the shafts and the stoping areas. They also serve as an access for men and material, means for transporting ore and a passage for air flow. The drifts have to be driven in the initial stages of a mining venture when the details of future stoping operations are unknown. It is important that they remain functional throughout the life for which they were designed. Due to their proximity to stoping areas, they are strongly influenced by a wide range of changing stress conditions. The planning and excavation of drifts play a major role in the overall safety, economy and productivity of the mines. In view of their strategic importance, an empirical approach to estimate the drift design parameters has been described in this paper.
The present approach was developed and verified on the basis of: (a) The information through a questionnaire a n d / o r visit to 27 different hard rock mines in Canada. The provincial distribution of the mines was as follows: Ontario, 16; Quebec, 5; Manitoba, 2; North-West Territories, 2; Newfoundland, 1; New Brunswick, 1. (b) The blast design in tunnels by Holmberg [1]. (c) The blasting of physical models of rock simulated material.
Drift blast design parameters Size of the drift depends upon its function, method of excavation, rock characteristics and state of stress. The dimensions of a drift determine both the type of the drilling equipment and the depth of pull which usually is no greater than the least dimension of
0 1 6 7 - 9 0 3 1 / 9 0 / $ 0 3 . 5 0 © 1990 - Elsevier Science Publishers B.V.
38
S.P. S I N G H
a drift. The widths and heights of drifts in Canadian hard rock mines vary from 2.0 m (6.7 ft) to 6.4 m (21.3 ft) and 2.4 m (8.0 ft) to 4.5 m (15.0 ft) respectively.
j
J
~o
Z
Size of holes The blast hole diameter is governed by the required degree of fragmentation, damage control, blast hole depth and drilling cost [2]. Hole diameter affects the accuracy of drilling and the geometry of blasting. The depth of pull is usually determined by the dimensions of the drift, rock type, drilling equipment and the expertise of the driller. Longer holes mean more drilling, higher explosive consumption, larger tonnes for mucking and increased roof area for support. The practical advance per round is normally around 90-95% of the depth of the hole. In longer holes the advance per round tends to decrease because of poor drilling accuracy of the later portion of the hole. An estimate of the blast hole depths for different drift areas can be made by utilizing Fig. 1. Comparison between the calculated and actual hole depths for different operating mines has been displayed in Fig. 2.
~3
~/// .~
2
I
0
--I
Actua I Calculated I
I
I
5 10 15 20 25 Area of the drift (square meters)
30
Fig. 2. Area of the drift vs. actual and calculated hole
depths.
Number of holes The number of holes needed to distribute the explosive charge over the drift area depends mainly on the rock type, explosive characteristics, hole size, cut to be used and the smooth blasting requirements. It is not an easy task to determine the accurate number of holes needed for each site without field tests. The number of total and charged holes in the case of a " b u r n cut" can be estimated on the basis of drift area with the help of Figs. 3 and 4 respectively. The number and sizes of holes with respect to the respective
4.0 57
~3.5
.... i
52
E o 47
°3.o
~
....
J~ E
~4~
2.5
37
32
2.0
0
r
I
I
I
I
5
10
15
20
25
6
30
Area of the drift (square meters)
Fig. 1. Area of the drift vs. the depth of the holes.
8
ID
12
14
18
Ig
20
22
25 24
30 28
Area of the Drift (square meters) Fig. 3. Area of the drift vs. total number of holes.
EMPIRICAL
GUIDELINES
FOR
DRIFT
BLAST
39
DESIGN
56
2 4c
---
u
x~ z
D,25
I
B
I
10
I
12
I
I
14
16
I
18
I
29
I
I
22
I
oO[] e O e
.q
[]
I
2~ 24
[]O
30 28
Area of the D r i f t (square meters)
Fig. 4. Area of the drift vs. number of charged holes.
,-
®
drift areas for C a n a d i a n hard rock mines have been provided in Table 1.
®
®
-,
LEGEND @
Charged or loaded hole
O
Empty hole
[]
Cut helpers
Knee ho]es
Side holes
Blast design The holes during a drift blast play different roles depending upon their location. Therefore in order to make the design process realistic, the holes in a drift have been divided into different zones as follows: (a) cut, (b) cut helpers, (c) diamonds, (d) stoping holes, (e) lifters, (f) knee holes, (g) side holes, and (h) back holes. The typical location of the different catagories of holes in a drift has been shown in Fig. 5. Sometimes, additional holes like diamond helpers, side hole helpers, etc., are also needed.
Diamonds
,
~Stopingholes
Lifters Back holes
Fig. 5. The typical location of the different catagories of holes in a drift.
Cut The purpose of the cut is to provide a free face to which the remainder of the round may break. Various types of cuts are available but the most c o m m o n prevalent in C a n a d i a n hard rock mining industry is " b u r n cut". This in-
TABLE 1 The number and sizes of holes for Canadian hard rock mines Area of Drift (m2)
Number of charged holes
Number of uncharged holes
Depth of holes (m)
Diameter of charged holes (mm)
Diameter of uncharged holes (mm)
<9 9-15 15-25.5
31-36 38-40 40-48
34-40 43-45 43-55
2.1-2.4 2.7-3.0 3.0-3.6
32-35 38-57 32-63.5
45- 63.5 76-102 38-102
40
S.P. SINGH
volves drilling of parallel holes with one or more left uncharged to provide free face for the hole that fires first [3]. Thus drilling rather than blasting is utilized to create initial free faces. The different types of " b u r n cut" used in Canadian mines are shown in Fig. 6. The cut is the most critical part of the round because the balance of the holes yet to fire cannot possibly pull to the desired depth unless the cut comes out as planned [4]. The extra time spent in planning and accurately drilling the cut would result in the full advance of the face and " b o o t leg" free round. Proper spacing and alignment of the burn cut holes are necessary to successfully pull the desired depth. Holes must be accurately positioned at the collar and drilled so that the b o t t o m is at the planned location. Generally,
•
O
O •
•
O
•
O
O
•
O
•
Ca)
•
O
0
O O O
•
•
0
0
•
•
0
0
•
0
•
0
O
•
0
O
0
0
•
0
0
0 Cg)
0
•
•
0
o
0
•
0
0
•
•
O
•
0
•
0
•
0
O
•
•
O
•
0
0
0
0
•
0
o
o
O
•
0
•
(1)
0
(m) 0
Empty Holes
(n) •
O
(k)
O
O •
O
0
Q)
(i)
(h)
(1)
where D = diameter of the uncharged hole/holes, n = n u m b e r of uncharged holes B = brisance of the explosive w.r.t. A N F O R = rock coefficient and is inverse of the rock's resistance to blasting. The value of R varies between 0.85 and 1.2. For the rocks in the Sudbury area, value of 1.0 appears realistic.
(f)
O O 0
vch = 1.5 D . n . / 3 . R
0
0
•
(e)
O
The m a x i m u m b u r d e n for the cut helpers, Vch, can be determined as follows:
(c)
0 (d)
Cut helpers
0
(b)
•
the greater the volume of the void space, the deeper the round can be drilled and successfully pulled.
•
0 (o)
Cut Blastho]es
Fig. 6. Various patterns of "burn cut" prevalent in Canadian mines.
O o
41
EMPIRICAL GUIDELINES FOR DRIFT BLAST DESIGN
f = fraction of the role loaded with the explosive
\\J
spacing for the stoping holes, = 1.2 V~
E~=
i \
It~ __ ._el_ -
(5)
N
_~
Lifters
/ 7
f
The number, spacing and b u r d e n for the lifters is obtained by utilizing eqns. (7), (8) and (9) respectively:
f
D L = Lifter factor
LEGEND
= 1.12
@
Charged or loaded hole
0
Empty hole
[]
Cut h e l p e r s Diamonds
Fig. 7. Length of the free face for the diamonds in a six-hole "Burn cut".
(l . f . B . R) 1/2
(6)
N L = n u m b e r of lifters = integer of ( W / D L + 2)
(7)
E L = spacing between the lifters, = W / ( N L - 1)
(8)
where W is the width of the drift, VL = b u r d e n for the lifters, = 0.5 E L
(9)
Diamonds Knee holes
The following equation provides the b u r d e n for the diamonds, Vd: (2)
Va= S" B" R
where S is the length of the free face for the diamonds and for a cut shown in Fig. 7 is given by (3): S - - 2[Vgh + (1.25D)2] 1/2
(3)
VK = Burden for the knee holes, = VL
(10)
E K = spacing for the knee holes, = E L
(11)
N K = n u m b e r of knee holes = N L -
1
(12)
Contour holes Stoping holes
(a) If smooth blasting is desired: The spacing and burden for the spacing holes is provided by eqns. (4) and (5) respectively:
E c s = 1 5 d. C. B. R
V~ = burden for the stoping holes, =0.55(l.f.B.R)
1/2
where l = charge concentration, k g / m
1. Side holes:
(4)
where Ecs = spacing for the side holes, C = coupling ratio d = diameter of the charged hole,
(13)
42
S.P. SI N G H
If Vcs is the burden for the side holes, then: Vcs = 1.2E
(14) Example of drift pattern design
2. Back holes: EcB = 14 d . C . B . R
(15)
Vc~ = 1.25E
(16)
where VcB and EcB are the burden and spacing for back holes respectively. (b) If smooth blasting is not required: Vc = 0.55 l . f . B . E c = 1.2Vc
The application of the computer program to a practical situation is given below.
R
(17) (18)
where Vc and E c are the burden and spacing for the contour (both side and back) holes respectively.
C o m p u t e r program
A computer program was written on the basis of the empirical guidelines described before to calculate and plot the location of the cut and the boreholes in the different segments of the drift. The input information required for the computer program is as follows: (1) Diameter of the uncharged h o l e / h o l e s in meters (2) Diameter of the charged holes in meters (3) Rock coefficient (4) Brisance of the explosive w.r.t. A N F O (5) Charge concentration in k g / m e t e r (6) Depth of the drill holes in meters (7) N u m b e r of uncharged holes (8) Coupling ratio (9) Width of the drift in meters (10) A b u t m e n t height in meters (11) Arch height in meters (12) Border contour in meters (13) Fraction of the holes l o a d e d with explosive
A drift pattern is to be designed based on the following information: Diameter of the charged holes = 47 m m Diameter of the uncharged holes = 62.5 m m N u m b e r of uncharged holes =3 Width of the drift =4.2m A b u t m e n t height of the drift =3.2m Arch height =0.8m Rock coefficient = 1.0 Charge concentration = 1.4 k g / m Explosive to be used = ANFO Depth of the drill holes =3.6m Coupling ratio for the contour holes = 1.0 Border contour in meters = 0.125 m Solution The drift pattern design was carried out with the computer program mentioned before. The calculated results have been presented in Table 2 and the blast pattern has been displayed in Fig. 8. The blast pattern has been designed assuming that the smooth blasting is desired. The
TABLE 2 Blast pattern design parameters generated by the computer program Type of hole Cut Cut helpers Diamonds Lifters Knee holes Stoping holes Back holes Side holes
Burden (m) 0.28 0.58 0.525 0.525 0.65 0.82 0.846
Spacing Number of (m) holes 6 (3 uncharged) 4 4 1.05 5 1.05 4 0.78 9 0.66 6 0.705 8
EMPIRICAL GUIDELINES
43
FOR DRIFT BLAST DESIGN
Ok | .,P
.P
°.P•
-.,
,~
1 T Fig. 8. Blast pattern generated by the computer program. total number of holes to be drilled is 45 including the uncharged holes.
Conclusions
Any blast optimization programme can be successful only if a clear understanding of the effects of the principal blast parameters has been developed and properly applied. Rock breakage by explosives involves the action of an explosive and the response of he rock being attacked. The response of the rock to explosive action is determined by both the explosive properties and the rock characteristics [5]. The drift blast design approach described in this paper is simple in principle as well as in application. This involves the application of basic principles of rock fragmentation by
Im
'I'
l"
explosives to the existing practice. There is no doubt that the empirical formulas comprising in this approach provide guidelines for a drift blast design but they cannot be literally applied to all mining situations. This approach does not completely eliminate the trial and error method of blast design. While blasting in areas with changing rock characteristics, efforts should be made to modify and optimize the design to give desired results.
Acknowledgements
The author wishes to thank NSERC for the funding through grant A4945 and the mining companies for their contribution in the survey. Thanks to Mekoya Wondrad, Sue Ducharme and Lionel Rudd for their assistance in this study.
44
References 1 Holmberg, R., Charge calculations for tunnelling. In: W. Hustrulid (Editor), Underground Mining Methods Handbook, SME of AIME (1982) pp. 1580-1589. 2 Hagan, T.N., Blast design considerations for underground mining and construction operations. Proc. Design and Performance of Underground Excavations, ISRM/BGS, Cambridge (1984), pp. 255-262.
S.P. SINGH
3 Anonymous, Explosives and Rock Blasting. Atlas Powder Company, Dallas, Texas (1987), 662 pp. 4 Hemphill, G.B., Blasting Operations. McGraw-Hill, New York, N.Y. (1981), 258 pp. 5 Brady, B.H.G. and E.T. Brown, Rock Mechanics for Underground Mining. George, Allen and Unwin, London (1985), 527 pp.
Mining Science and Technology, 11 (1990) 3 7 - 4 4 Elsevier Science Publishers B.V., A m s t e r d a m - P r i n t e d in T h e N e t h e r l a n d s
Empirical guidelines for drift blast design S.P. Singh School of Engineering, Laurentian University, Sudbury, Ont. P3E 2C6 (Canada) (Received August 18, 1989; revision accepted December 12, 1989)
ABSTRACT Singh, S.P., 1990. Empirical guidelines for drift blast design. Min. Sci. Technol., 11: 37-44. Drifts are the nerve centre of underground mining operations. They provide essential communication between the shafts and the stoping areas and have varying dimensions and inclinations. In view of their strategic importance in the overall safety, economy and productivity of mines, empirical guidelines to estimate the drift blast design parameters have been described in this paper. The skill of the driller and the constant attention of the superviser to the accuracy achieved are essential ingredients to the successful application of these guidelines. The extra time spent in planning and accurately drilling the holes pays off in the form of higher advance, "bootleg" free round and the minimum damage to the back and sides of the drift. The application of this computerized empirical approach to practical situations has been described with an example.
Introduction The driving of drifts is a very important aspect of underground mining. They provide essential communication between the shafts and the stoping areas. They also serve as an access for men and material, means for transporting ore and a passage for air flow. The drifts have to be driven in the initial stages of a mining venture when the details of future stoping operations are unknown. It is important that they remain functional throughout the life for which they were designed. Due to their proximity to stoping areas, they are strongly influenced by a wide range of changing stress conditions. The planning and excavation of drifts play a major role in the overall safety, economy and productivity of the mines. In view of their strategic importance, an empirical approach to estimate the drift design parameters has been described in this paper.
The present approach was developed and verified on the basis of: (a) The information through a questionnaire a n d / o r visit to 27 different hard rock mines in Canada. The provincial distribution of the mines was as follows: Ontario, 16; Quebec, 5; Manitoba, 2; North-West Territories, 2; Newfoundland, 1; New Brunswick, 1. (b) The blast design in tunnels by Holmberg [1]. (c) The blasting of physical models of rock simulated material.
Drift blast design parameters Size of the drift depends upon its function, method of excavation, rock characteristics and state of stress. The dimensions of a drift determine both the type of the drilling equipment and the depth of pull which usually is no greater than the least dimension of
0 1 6 7 - 9 0 3 1 / 9 0 / $ 0 3 . 5 0 © 1990 - Elsevier Science Publishers B.V.
38
S.P. S I N G H
a drift. The widths and heights of drifts in Canadian hard rock mines vary from 2.0 m (6.7 ft) to 6.4 m (21.3 ft) and 2.4 m (8.0 ft) to 4.5 m (15.0 ft) respectively.
j
J
~o
Z
Size of holes The blast hole diameter is governed by the required degree of fragmentation, damage control, blast hole depth and drilling cost [2]. Hole diameter affects the accuracy of drilling and the geometry of blasting. The depth of pull is usually determined by the dimensions of the drift, rock type, drilling equipment and the expertise of the driller. Longer holes mean more drilling, higher explosive consumption, larger tonnes for mucking and increased roof area for support. The practical advance per round is normally around 90-95% of the depth of the hole. In longer holes the advance per round tends to decrease because of poor drilling accuracy of the later portion of the hole. An estimate of the blast hole depths for different drift areas can be made by utilizing Fig. 1. Comparison between the calculated and actual hole depths for different operating mines has been displayed in Fig. 2.
~3
~/// .~
2
I
0
--I
Actua I Calculated I
I
I
5 10 15 20 25 Area of the drift (square meters)
30
Fig. 2. Area of the drift vs. actual and calculated hole
depths.
Number of holes The number of holes needed to distribute the explosive charge over the drift area depends mainly on the rock type, explosive characteristics, hole size, cut to be used and the smooth blasting requirements. It is not an easy task to determine the accurate number of holes needed for each site without field tests. The number of total and charged holes in the case of a " b u r n cut" can be estimated on the basis of drift area with the help of Figs. 3 and 4 respectively. The number and sizes of holes with respect to the respective
4.0 57
~3.5
.... i
52
E o 47
°3.o
~
....
J~ E
~4~
2.5
37
32
2.0
0
r
I
I
I
I
5
10
15
20
25
6
30
Area of the drift (square meters)
Fig. 1. Area of the drift vs. the depth of the holes.
8
ID
12
14
18
Ig
20
22
25 24
30 28
Area of the Drift (square meters) Fig. 3. Area of the drift vs. total number of holes.
EMPIRICAL
GUIDELINES
FOR
DRIFT
BLAST
39
DESIGN
56
2 4c
---
u
x~ z
D,25
I
B
I
10
I
12
I
I
14
16
I
18
I
29
I
I
22
I
oO[] e O e
.q
[]
I
2~ 24
[]O
30 28
Area of the D r i f t (square meters)
Fig. 4. Area of the drift vs. number of charged holes.
,-
®
drift areas for C a n a d i a n hard rock mines have been provided in Table 1.
®
®
-,
LEGEND @
Charged or loaded hole
O
Empty hole
[]
Cut helpers
Knee ho]es
Side holes
Blast design The holes during a drift blast play different roles depending upon their location. Therefore in order to make the design process realistic, the holes in a drift have been divided into different zones as follows: (a) cut, (b) cut helpers, (c) diamonds, (d) stoping holes, (e) lifters, (f) knee holes, (g) side holes, and (h) back holes. The typical location of the different catagories of holes in a drift has been shown in Fig. 5. Sometimes, additional holes like diamond helpers, side hole helpers, etc., are also needed.
Diamonds
,
~Stopingholes
Lifters Back holes
Fig. 5. The typical location of the different catagories of holes in a drift.
Cut The purpose of the cut is to provide a free face to which the remainder of the round may break. Various types of cuts are available but the most c o m m o n prevalent in C a n a d i a n hard rock mining industry is " b u r n cut". This in-
TABLE 1 The number and sizes of holes for Canadian hard rock mines Area of Drift (m2)
Number of charged holes
Number of uncharged holes
Depth of holes (m)
Diameter of charged holes (mm)
Diameter of uncharged holes (mm)
<9 9-15 15-25.5
31-36 38-40 40-48
34-40 43-45 43-55
2.1-2.4 2.7-3.0 3.0-3.6
32-35 38-57 32-63.5
45- 63.5 76-102 38-102
40
S.P. SINGH
volves drilling of parallel holes with one or more left uncharged to provide free face for the hole that fires first [3]. Thus drilling rather than blasting is utilized to create initial free faces. The different types of " b u r n cut" used in Canadian mines are shown in Fig. 6. The cut is the most critical part of the round because the balance of the holes yet to fire cannot possibly pull to the desired depth unless the cut comes out as planned [4]. The extra time spent in planning and accurately drilling the cut would result in the full advance of the face and " b o o t leg" free round. Proper spacing and alignment of the burn cut holes are necessary to successfully pull the desired depth. Holes must be accurately positioned at the collar and drilled so that the b o t t o m is at the planned location. Generally,
•
O
O •
•
O
•
O
O
•
O
•
Ca)
•
O
0
O O O
•
•
0
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•
•
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0
•
0
•
0
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•
0
O
0
0
•
0
0
0 Cg)
0
•
•
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o
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•
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0
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•
•
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•
0
0
0
0
•
0
o
o
O
•
0
•
(1)
0
(m) 0
Empty Holes
(n) •
O
(k)
O
O •
O
0
Q)
(i)
(h)
(1)
where D = diameter of the uncharged hole/holes, n = n u m b e r of uncharged holes B = brisance of the explosive w.r.t. A N F O R = rock coefficient and is inverse of the rock's resistance to blasting. The value of R varies between 0.85 and 1.2. For the rocks in the Sudbury area, value of 1.0 appears realistic.
(f)
O O 0
vch = 1.5 D . n . / 3 . R
0
0
•
(e)
O
The m a x i m u m b u r d e n for the cut helpers, Vch, can be determined as follows:
(c)
0 (d)
Cut helpers
0
(b)
•
the greater the volume of the void space, the deeper the round can be drilled and successfully pulled.
•
0 (o)
Cut Blastho]es
Fig. 6. Various patterns of "burn cut" prevalent in Canadian mines.
O o
41
EMPIRICAL GUIDELINES FOR DRIFT BLAST DESIGN
f = fraction of the role loaded with the explosive
\\J
spacing for the stoping holes, = 1.2 V~
E~=
i \
It~ __ ._el_ -
(5)
N
_~
Lifters
/ 7
f
The number, spacing and b u r d e n for the lifters is obtained by utilizing eqns. (7), (8) and (9) respectively:
f
D L = Lifter factor
LEGEND
= 1.12
@
Charged or loaded hole
0
Empty hole
[]
Cut h e l p e r s Diamonds
Fig. 7. Length of the free face for the diamonds in a six-hole "Burn cut".
(l . f . B . R) 1/2
(6)
N L = n u m b e r of lifters = integer of ( W / D L + 2)
(7)
E L = spacing between the lifters, = W / ( N L - 1)
(8)
where W is the width of the drift, VL = b u r d e n for the lifters, = 0.5 E L
(9)
Diamonds Knee holes
The following equation provides the b u r d e n for the diamonds, Vd: (2)
Va= S" B" R
where S is the length of the free face for the diamonds and for a cut shown in Fig. 7 is given by (3): S - - 2[Vgh + (1.25D)2] 1/2
(3)
VK = Burden for the knee holes, = VL
(10)
E K = spacing for the knee holes, = E L
(11)
N K = n u m b e r of knee holes = N L -
1
(12)
Contour holes Stoping holes
(a) If smooth blasting is desired: The spacing and burden for the spacing holes is provided by eqns. (4) and (5) respectively:
E c s = 1 5 d. C. B. R
V~ = burden for the stoping holes, =0.55(l.f.B.R)
1/2
where l = charge concentration, k g / m
1. Side holes:
(4)
where Ecs = spacing for the side holes, C = coupling ratio d = diameter of the charged hole,
(13)
42
S.P. SI N G H
If Vcs is the burden for the side holes, then: Vcs = 1.2E
(14) Example of drift pattern design
2. Back holes: EcB = 14 d . C . B . R
(15)
Vc~ = 1.25E
(16)
where VcB and EcB are the burden and spacing for back holes respectively. (b) If smooth blasting is not required: Vc = 0.55 l . f . B . E c = 1.2Vc
The application of the computer program to a practical situation is given below.
R
(17) (18)
where Vc and E c are the burden and spacing for the contour (both side and back) holes respectively.
C o m p u t e r program
A computer program was written on the basis of the empirical guidelines described before to calculate and plot the location of the cut and the boreholes in the different segments of the drift. The input information required for the computer program is as follows: (1) Diameter of the uncharged h o l e / h o l e s in meters (2) Diameter of the charged holes in meters (3) Rock coefficient (4) Brisance of the explosive w.r.t. A N F O (5) Charge concentration in k g / m e t e r (6) Depth of the drill holes in meters (7) N u m b e r of uncharged holes (8) Coupling ratio (9) Width of the drift in meters (10) A b u t m e n t height in meters (11) Arch height in meters (12) Border contour in meters (13) Fraction of the holes l o a d e d with explosive
A drift pattern is to be designed based on the following information: Diameter of the charged holes = 47 m m Diameter of the uncharged holes = 62.5 m m N u m b e r of uncharged holes =3 Width of the drift =4.2m A b u t m e n t height of the drift =3.2m Arch height =0.8m Rock coefficient = 1.0 Charge concentration = 1.4 k g / m Explosive to be used = ANFO Depth of the drill holes =3.6m Coupling ratio for the contour holes = 1.0 Border contour in meters = 0.125 m Solution The drift pattern design was carried out with the computer program mentioned before. The calculated results have been presented in Table 2 and the blast pattern has been displayed in Fig. 8. The blast pattern has been designed assuming that the smooth blasting is desired. The
TABLE 2 Blast pattern design parameters generated by the computer program Type of hole Cut Cut helpers Diamonds Lifters Knee holes Stoping holes Back holes Side holes
Burden (m) 0.28 0.58 0.525 0.525 0.65 0.82 0.846
Spacing Number of (m) holes 6 (3 uncharged) 4 4 1.05 5 1.05 4 0.78 9 0.66 6 0.705 8
EMPIRICAL GUIDELINES
43
FOR DRIFT BLAST DESIGN
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1 T Fig. 8. Blast pattern generated by the computer program. total number of holes to be drilled is 45 including the uncharged holes.
Conclusions
Any blast optimization programme can be successful only if a clear understanding of the effects of the principal blast parameters has been developed and properly applied. Rock breakage by explosives involves the action of an explosive and the response of he rock being attacked. The response of the rock to explosive action is determined by both the explosive properties and the rock characteristics [5]. The drift blast design approach described in this paper is simple in principle as well as in application. This involves the application of basic principles of rock fragmentation by
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explosives to the existing practice. There is no doubt that the empirical formulas comprising in this approach provide guidelines for a drift blast design but they cannot be literally applied to all mining situations. This approach does not completely eliminate the trial and error method of blast design. While blasting in areas with changing rock characteristics, efforts should be made to modify and optimize the design to give desired results.
Acknowledgements
The author wishes to thank NSERC for the funding through grant A4945 and the mining companies for their contribution in the survey. Thanks to Mekoya Wondrad, Sue Ducharme and Lionel Rudd for their assistance in this study.
44
References 1 Holmberg, R., Charge calculations for tunnelling. In: W. Hustrulid (Editor), Underground Mining Methods Handbook, SME of AIME (1982) pp. 1580-1589. 2 Hagan, T.N., Blast design considerations for underground mining and construction operations. Proc. Design and Performance of Underground Excavations, ISRM/BGS, Cambridge (1984), pp. 255-262.
S.P. SINGH
3 Anonymous, Explosives and Rock Blasting. Atlas Powder Company, Dallas, Texas (1987), 662 pp. 4 Hemphill, G.B., Blasting Operations. McGraw-Hill, New York, N.Y. (1981), 258 pp. 5 Brady, B.H.G. and E.T. Brown, Rock Mechanics for Underground Mining. George, Allen and Unwin, London (1985), 527 pp.