—9¥s" Hole Diameter

Stemming-drill cuttings

1lb. Procore Primer
sant |g —— AN/FO ; 840 lbs.
loys}
ot
re)
i)
———Scufflex Downline
———1 |b. Procore Primer
1 I —— Design Grade
leo —— 200 Ibs. Slurry (Hydromex T-3)
Ue) or Aluminized AN/FO
jr He

1 Ib. Procore Primer
~———Sub grade

FIGURE 2— Cross section of a typical blasthole.

CREST (free face)

1 To cop

LEGEND

—— Delays(numbers indicate blasting sequence)
Trunk Line (reinforced primacord)
—@— Blast Holes

[___[seaons | euRoen_ | beLave |

ORE 18! ig! 15 ms
WASTE 22' 22 25ms.

BENCH

30'-45'

BENCH LEVEL

FIGURE 3— Typical blast initiation.

constitute 40% of all holes loaded. Borehole dewater-
ing is carried out using a Canadian Industries Lim-
ited borehole dewatering unit, powered by a hydraulic
pump, driving a Prosser Hymergible pump rated at
65 gallons per minute at 150-ft (45.7-m) head. The
unit is mounted on a 4x4 pickup (two similar units
are available). When using ANFO in wet holes, the
hole is pumped dry, and a double-wall, 9-in.-diameter,
.004-mill.-thick polyethylene liner is inserted. A base
charge of either packaged slurry Hydromex T3 or
aluminized ANFO is inserted; the charge is 150 to
200 Ib, depending on the material to be blasted. The.
hole is then column-charged with ANFO, inserting
three 1-lb procore primers (Fig. 2). If it is found to
be impossible to dewater a drill hole successfully,
packaged slurry is substituted, using basically the
same charging configuration as shown in Figure 2.
No allowance is made for the difference in relative
weight or bulk strength of the Hydromex packaged
slurry. ANFO comprises 85% of the explosives con-
sumed on site, with excellent fragmentation results.

The charging ratio is varied, depending on the type
of rock being blasted. However, an average powder
factor to ensure good fragmentation is of the order
of 1.3 lb per cu. yd. Reinforced primacord is used,
employing a single downhole line and single trunk lines
connecting the holes. The delays used are the 15- or
25-m.s. primacord type, depending on whether the blast
has a free face or a choke blast. Initiation is in a “V”
pattern, as shown (Fig. 3). High-speed filming of
blasts on site have confirmed that the hole spacing,
charge patterns, blasting ratios and delays being used
are in accordance with the computerized program de-
veloped by the explosives manufacturers, Canadian
Industries Limited.

The charging ratio, although appearing slightly
high, has ensured good fragmentation of muck piles
and high loading rates with minimum stress on the
shovel, and has produced suitable material for front-
end loader applications. This also produces a sized ma-
terial, ensuring that a smooth dump area and bench
level can be maintained, thus reducing tire wear.

Wall control between catchments is of major con-
cern, with controlled blasting or perimeter blasting
having been practised at various times. The present
practice is to survey in the drill line delineating the
catchment crest; this line is normally offset 15 ft
(4.6 m) away from the designed crest line. Spacing
of holes is reduced to 15 ft (4.6 m) on this line and no
subdrilling is carried out directly above a crest or
catchment. The next production line of drill holes will
be set out parallel to this line and 15 ft (4.6 m) distant,
but with the normal 22-ft (6.7-m) spacing being used
on the blast pattern.

The holes on the drill line are charged with 250 lb
of 8-in.-diameter packaged slurry and partially back
stemmed with drill cuttings; the next row of blast
holes are charged according to the standard hole
charge for that particular blast pattern. Where pos-
sible, the drill-line holes are detonated in groups, using
15-m.s. delays. Experiments continue using different
hole spacings, the possible use of ANFO in cardboard
tubes of 6-in. diameter and the use of primadets.

Scaling of walls is carried out by using a complete
track pad from an old shovel, attached to a Caterpillar
D8 or D9 tractor blade by means of a swivel which
allows the track to turn and prevent it from riding up
the face when in use. A ship’s anchor chain of 4-in.-
diameter links, having a tire secured to the trailing
end, has also been used in a similar manner with suc-
cess (Fig. 4).

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