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8/17/2019 CE 3220 12 Blasting Rock.pdf
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Blasting Rock
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BLASTING
ROCK
Practical
Exercise
Blast Design
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PRACTICAL EXERCISE Design a delayed initiation blast
(would like to shoot a minimum of
10 holes per delay). Base the
plan on the following:
Rock - limestone, in thin layers
w/tight joints
Bench height - 24 ft
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PRACTICAL EXERCISE
Explosive - bulk ANFO, SG
e
0.8 dry holes, no liner
required.
Explosive - dynamite, SG
e
1.4 Cartridge size: 2 to 3.5
inch diameter in ¼ in.
increments, by 16 in. long.
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PRACTICAL EXERCISE
Drills can use 6 in.
bits.
Regulatory scale
distance factor 55
Nearest structure is
1,400 ft away
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STEP 1:
BURDEN DISTANCE
?
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STEP 1:
BURDEN DISTANCE
Explosive density empirical
formula for burden distance:
B ft
SG
SG D ine
r
e( ) . ( )
2
1 5
Equ. 13.1
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STEP 1:
BURDEN DISTANCE
SG
e
ANFO = 0.8
SG
r
Limestone (Table 13.2)?
D
e
= ? try 6 in. the maximum
B ft SG SG
D ine
r
e( ) . ( )
2 1 5
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STEP 1:
BURDEN DISTANCE
SG
r
Limestone (2.4 - 2.9)
Lets use an average
number of 2.7
B ft SG
SG D ine
r
e( ) . ( )
2 1 5
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STEP 1:
BURDEN DISTANCE
B 2 0.8
2.71.5 6
= 12.6 ft
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STEP 2:
BURDEN
corrected
Burden distance corrected for
geological conditions (Table 13.3).
B B K K corrected d s
K
d
= 1.00, no information assume
“other cases ”
K
s
= 1.10, thin layers w/tight
joints
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STEP 2:
BURDEN
corrected
Burden distance corrected
for geological conditions.
Bcorrected 12 6 1 0 1 1. . .
Bcorrected = 13.8 ft
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STEP 3:
STIFFNESS RATIO
Need a Stiffness Ratio of
3 or greater.
Bench height = 24 ft
Burden
corrected
= 13.8
ft
SRbench height
burden distance
24
13.81.7
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STEP 4: BURDEN
ADJUSTED
Want a Stiffness Ratio of 3
therefore: 3 24
Bcorrected
B 24
38
corrected
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STEP 4: BURDEN
ADJUSTED
ft8useBDo not complicate the
field work, try to use
one foot or half foot
increments.
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STEP 4: BURDEN
ADJUSTED
Burden distance corrected
for geological conditions.
1101BBcorrected ..
ft371101Bft8 ...
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STEP 5: EXPLOSIVE
DIAMETER
)( . )( inD51SG
SG2ftB e
r e
eD3
1.5
2.70.827.
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STEP 5: EXPLOSIVE
DIAMETER
3.52.09
7.3
eD
Explosive Diameter
3 1/2 in.
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STEP 6: BLASTHOLE
SIZE
Bulk ANFO dry holes, no
blasthole liner, explosive
diameter and blasthole size
are the same.
Use a 3
1/2
in. size bit,
therefore
3
1/2
in.
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STEP 6: BLASTHOLE
SIZE
Bulk ANFO, explosive
diameter and blasthole
size are the same, i.e.
there is no liner.
EXPLOSIVE
BORE HOLE
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Explosive diameter and
blasthole size are the same.
ANFO
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Worked
with awooden
pole to
prevent
bridging.
ANFO
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STEP 7: STEMMING
Stemming depth (T) =
5.6
T B 0.780.7T
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STEP 8: SUBDRILLING
J B 0.380.3J
Subdrilling depth (J) = 2.4
use 2 ft
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STEP 9: SPACING
Delayed initiation: SR greater than1 but less than 4 (Equ. 13.8)
Spacing controlled by initiation
timing and stiffness ratio.
S L B 78
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STEP 9: SPACING
L (bench height) = 24 ft.
B (burden distance) = 8
ft.
8
8)(724
SSpacing = 10 ft
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STEP 9: SPACING
Spacing in the field should be
within plus or minus 15 of the
calculated value.
Calculated spacing
+15-15
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STEP 9: SPACING
Spacing = 9, 10, 11 ft?
If this is an
estimate
for a
bid it might be better to be
conservative and use an 9 ft
spacing.
That would mean more
holes and a higher drilling
cost.
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STEP 9: SPACING
Spacing = 9, 10, 11 ft?
If we are in the field
drilling for the first shot
we might try a 10 ft
spacing. This would
lower cost.
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STEP 9: SPACING
Pull the first shot and evaluate the
results: fragmentation etc. If it is ok,
use 11 ft, if it is not satisfactory
reduce the spacing.
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Throw rock
STEP 9: SPACING don’t
forget -- SAFETY
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STEP 10:
POWDER COLUMN
Powder column length is the blasthole
depth minus the stemming depth.
Blasthole Depth = 26 ft
Bench height (24 ft)
+ Subdrilling ( 2 ft)
Powder column = 26 ft - 6 ft
= 20 ft
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STEP 10:
POWDER COLUMN
Powder column = 20 ft or 240 in.
Dynamite cartridge size: 2 to 3.5
inch diameter in 1/4 in.
increments, by 16 in. long.
Dynamite:
16 in or 1.3 ft
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STEP 10:
POWDER COLUMN
Powder column = 240 in.
ANFO
240” powder column
- 16” dynamite
= 224 in
or
18.6 ft
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STEP 11:
LOAD DENSITY
Have to prime the
dynamite to fire the
shot.
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STEP 11:
LOAD DENSITY
3
1/2
in. borehole
Dynamite
: Cartridge size:
2 to 3.5 inches in 1/4 in.
increments. Use
3
in.
diameter
cartridges, will fit
easily into the hole.
NFO
: 1/2 in. diameter
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STEP 11: LOAD DENSITY
Dynamite Cartridge
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STEP 11: LOAD DENSITY
Dynamite: 3 in dia. SG
e
= 1.4
ANFO: 3 1/2 in dia. SG
e
= 0.8
Explosive Loading Density
Table 13.5
Dynamite: 4.29 lb/ft
ANFO: 3.34 lb/ft
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STEP 12:
AMOUNT of EXPLOSIVE
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STEP 12:
AMOUNT of EXPLOSIVE
Amount of explosive (lb) =
powder column (ft)
X
loading density (lb/ft)
Dynamite: 1.3 ft X 4.29 lb/ft = 5.6 lb
ANFO: 18.6 ft X 3.34 lb/ft = 62.1 lb
Explosive per blasthole 67.7 lb
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STEP 13:
AMOUNT of ROCK
Amount of rock (cy) =
pattern area (ft
2
)
X
depth to grade (ft)
X
1/27 (ft
3
/cy)
Rock per blasthole:
cy5
27
248896.
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STEP 14:
POWDER FACTOR
Powder Factor (lb/cy) =
Amount of explosive (lb)Amount of rock (cy)
Powder Factor:
lb/cy1.19cy56.9
lb67.7
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D
s
= 55
d = 1,400
Want to shoot 10 holes per delay.
W = 10 X 67.7 lb or 677 lb
STEP 15: VIBRATION
D d
W s
Check vibration formula
13.12
53.8677
1,400sD
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STEP 15: VIBRATION
D
s
= 55
A scaled distance value of 55
or greater is required for this
location.
Therefore, can not
shoot 10 holes at one
53.8 55
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STEP 15:
VIBRATION
How many holesat one time.
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STEP 15: VIBRATION
D
s
= 55
?W
1,40055
lbW 647.955
1,4002
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STEP 15: VIBRATION
Therefore, can only
shoot
9 holes at one time.
9.6
67.7
647.9HolesNo.
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Shoot 9 holes at one
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PRESPLITTING
ROCK
To limit overbreak,develop apresplitting blast
plan, for theprevious example.
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STEP 1:
EXPLOSIVE LOAD
28
3.5 2 ) / ( ftlbloadExplosive
Explosive load = 0.4375 lb/ft
Equation 13.10
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STEP 2:
AMOUNT of EXPLOSIVE
Explosive load = 0.4375 lb/ft
Amount of explosive / hole =
(24 ft X 0.4375 lb/ft)
+ (3 X 0.4375 lb)
= 11.8 lb/hole
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STEP 3:
HOLE SPACING
Hole spacing = 10 X 3 ½ in.
= 35 inches
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FIRE IN
THE HOLE
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FIRE IN THE HOLE
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Time to load and haul.