CA 02360771 2001-12-14
wo oor~t~st Pcri~u~ro~ ~o~
Title
METHOD AND APPARATUS FOR CHARGING A HOLE
Field of the Invention
The present invention relates to a method of charging a hole, particularly
though not
exclusively, for the purposes of the fracturing or excavating hard material
such as rock and
concrete.
Background of the Invention
The excavating or fracturing of hard material is a pivotal activity in the
mining and
construction industries. One known way of achieving this is the drill and
blast method.
This involves drilling a hole in the hard material and charging the hole with
a quantity of
energetic material and usually some type of stemming. Not surprising, the way
in which a
hole is charged has a substantial effect on the efficiency and result of the
drill and blast
method.
A typical procedure for charging a hole is simply to insert an energetic
material together
with an initiator into the hole then fill the hole either completely or to a
predetermined
depth with some type of stemming eg sand, gel or a stemming bar and set off
the initiator
2 o which in turn initiates the energetic material. At times, particularly if
a stemming ber is
used, a heavy vehicle or machine (eg a jumbo) or some other mass is used to
hold the
stemming bar in place so that it does not turn into a projectile upon
initiation of the
energetic material. This requires that the vehicle or machine holding the
stemming bar in
place is able to withstand the transmission of substantial forcxs without
itself becoming
2 5 damaged. Mine managers and construction supervisors are, not surprisingly,
reluctant to
use there machinery as shock absorbers in this meaner. Damage may also be
incurred to
machinery by fly rock generated by fragmentation of the collar area of the
hole.
When involved in excavation or civil construcfion in built up areas safety is
an absolute
3 o requirement and authorities are unlikely to allow pmcedurea that will lead
to the creation
of fly rock or other projectiles. One is free to use non explosive methods in
such
instances, however generally these are a more expensive option and often can
reduce the
CA 02360771 2001-12-14
Pc~riAU~roi lo?
Received 0? December 2000
-Z-
margin to the contractor to a level where it is no longer eeo~mic to tender
far a particular
job.
S In the case of a particulate s<amnin~ eg sand, drill cutting etc the
ejection of the ding
from the fi~ee face of the hole is common place. This is evidence of a lack of
e~ciency in
the charg;ng process as a non industrial part of the blast energy is
dissipated by imparting
energy to the stemming to eject it from the hole.
~,Lf~3Yg~l,$~
It is an objoct of the rt invention to pmvide a method for charg~g a hole and
a
method of producing a clanged hole that to alleviate at least one of the
paroblems
in the above descxibed prior art.
1 S Acxording to the pco~nt invention there is provided a method of charging a
hole inchu3mg
the steps of
(a) inserting an energetic material and an initiator into the hole;
(b) filling the hole to a ~ecktamined level with an enetg~r absorbing
. . 2A . steaming rnatraial;a _ , , , -.
(c) inserting a plug into the hole to rest on the arming material the plug
being providod with means for facilitating the coupling of the initiaot~r with
an initiation source; and
2S
(d) mechanically holding by extraneous means the plug in the hole to
substantial movement of said plug away from a toe of the hole, whereby, in
use, on coupling of said initiator to said source via said plug, said
energetic
material is initiated providing a rapid increase in gas pressure near the
30 bottom of the hole and said stemming matarat acts to absorb
generated by said gas acting away firm the toe of the hole to st~antially
isolate said plug from said gas pressure and concentrating the action of said
CA 02360771 2001-12-14
PCT/AU99/O110?
Received 07 December 200a
- 3 - _
gas pressin~e on the toe of the hole.
Preferably stop (b) comprises filling the hole to a level substantially
adjacent or below the
collar area of the hole.
Preferably step (c), includes providing a plug with an aperh~re, recess or
slot through which
a lead can pass from said initiator to said initiation source to facilitate
coupling
therebetvveen; and, threading said lead through said apectum or r~ss when
inserting the
plug into said hole.
1a an altero~ate embodimear, step (c) above. includes providing said plug with
a transducer
for facilitating wireless elcehomagiietic coupling of said initiator to said
initiation source.
Preferably step (d) comprises bearing or placing a mass on an upper end of
said plug.
According to another aspect of the invention there is provided a metiwd of
producing a
charged hole in a hard material to be fragmented, said method including the
steps of
(a) providing a drill for drilling a hole in said hard ruaterial;
2p ; . , , . . ,,~) ~ ~ o . ~ as icatiator into said~ole;
(c) sterntning the hole up to a prodeurmined level with absorbing
material;
(d) inserting a plug into the hole to rest on said sta~aming, the plug being
provided with means for facilitating the coupling of the initiator with an
initiation source; and
(e) mechanically holding by extraneous mans said plug in the hole Zo prevent
substantial most of said plug away from a toe of said lmle, whereby,
in use, on coupling of said initiator to said source by said plug, said
energetic material is initiated providing a rapid incising gas pmessure near
CA 02360771 2001-12-14
PCT/AU99/0I 107
Received 07 December 2000
the toe of the hole and said stanming acts to absorb gas pressure acting
away fmm the bottom of the hole thereby substantially isolating said plug
fmm said gas pressure.
Preferably step (e) comprisGR bearing at least a portion of the weight of said
driQ on an
upper and of said plug.
According to aiwther aspect of the invention there is provided a medal of
charging a hole
including the steps of:
(a) insetting an energetic material and an initiator into the hole;
(b) filling the hole to a ~edate~mined level with an au~r absorbing
~8
(c) providing a multioomponent plug and inserdng the plug into the hole to
rest
on the stemming material, the plug being lnovidod with a means f~
facilitating the coupling of the initiator with an initiation source;
(d) moving the components of the plug relative to each other to facilitate
self
... . . E Z0 wodging of skid plug is the hole; and, ...
(e) mechanically holding, by extraneous means, said plug in the hole.
According to a further aspect of the invention there is provided a method of
charging a
hole including the steps of
(a) inserting an energetic malarial and an initiator into the hole;
(b) filling the hole to a predetermined level with an absorbing
stanaaing material;
(c) mechanically retaining the stemming material in tla; hole by providing a
plug and insetting the plug into the hole and mechanically holding by
CA 02360771 2001-12-14
PCT/AU99/01107
Received 07 December 2000
- S - _
extraneous means said plug in the hole.
Preferably the method fiuther includes providing the plug with mesas for
facilitating the
coupling of the initiator with an initiation source.
According to another aspect of the present invention there is ~ovided a
stemming bar for
stctnming a hole in a hard material the bolt having a charge of energetic
material disposed
at or near a toe of the hole, the steanrn;ng bar including a first opening at
a f rst end, a
second opening distant the first opening so that when the Brat end of the
stemming bar is
10 placed in a hole, the second opening is outside the hole, and a slot,
passage or recess
extending betvveen the first and sxond openings through which an initiator
means can be
delivered for initiating or detonating the energetic material in the hole.
Preferably the stemming bar is provided with means at said fast end to
facilitate
attaclunent to a container beating said energetic material, so that when the
st~m~g bar is
inserted into the hole, the energetic mattrial is simultaneously placed in the
hole.
Accordingly aa4tixr aspect of the p:as~t invention there is provided a method
charging a
hole to effect the fi~aah~ring of hard material including the steps of
drilling a hole in the hard material;
placing a quantity of energetic material in the bolt;
providing a s<esnming bar formed with a slot, passage or taxes having a
first opening at a first end of the bat adapted for insertion into the hole
and a
second opening spaced from the first opening by a distance so that the second
opening is e~cternal to the hole;
inserting the stemming bar with said first end fast into the hole;
delivering initiator mesas through said second opening, down said slot,
passage or
recess and out said first opening and into operational contact with the a
material so that the initiator means can initiate the wxrgetic material to
effect
frachuing of the hard material.
CA 02360771 2001-12-14
WO 00/36364 PCT/AU99/01107
-6-
Preferably the method further incudes the step of mechanically holding or
retaining the
stemming bar in the hole.
Preferably the step of placing the energetic material in the hole includes
supporting the
energetic material at the first end of the stemming bar so that the energetic
material is
placed in the hole by insertion of the first end of the stemming bar into the
hole.
Preferably the step of supporting the energetic material at the first end of
the stemming bar
includes providing a container for containing the energetic material and
attaching the
container to the first end of the stemming bar and in communication with said
first
opening.
In one embodiment, the container is attached to the stemming bar by means of
mutual
threaded engagement.
In alternate embodiments, the container is push fitted, or snap fitted to the
first end of the
stemming bar.
2 o The initiator means is in any form that can be delivered through the slot,
passage or recess
in the stemming bar and can include for example a detonator, an electric
match, a non
electric igniter, a length of fuse cord; or a flame directed down the slot,
passage or recess.
In the event that the initiator means is a flame, the flame can be produced by
a shotgun
cartridge filled with appropriate pyrotechnic material or a theatrical shell
or cap. The
2 5 energetic material can be in the form of an explosive or a propellant.
Brief Description of the Drawings
Embodiments of the present invention will now be described by way of example
only with
reference to the accompanying drawings in which:
Figure 1 is a schematic representation of a charged hole produced in
accordance
with embodiments of the present method;
CA 02360771 2001-12-14
WO 00/36364 PCT/AU99/01107
_ 'j _
Figure 2 is a schematic representation of a charged hole formed in accordance
with
the second embodiment of the invention;
Figure 3 is a schematic representation of a charged hole formed in accordance
with
the third embodiment of the invention;
Figure 4 is a schematic representation of a charged hole formed in accordance
with
the fourth embodiment of.the invention;
Figures 5-8 illustrate different embodiments of wedging plugs that can be used
in the
present methods;
Figure 9 is a front view of a stemming bar adapted for use in embodiments of
the
method of charging a hole;
Figure 10 is a view of section AA of Figure 10;
Figure 11 is a cross sectional view of a second embodiment of the stemming bar
and
also illustrating an alternate method of charging a hole; and,
Figure 12 is a sectional view of a further embodiment of the stemming bar and
method of charging a hole.
Detailed Description of Preferred Embodiments
2 5 The general methodology employed in embodiments of this invention is
depicted in
Figure 1. The figure illustrates a bench 10 of hard material such as rock in
which a hole
12 has been drilled using a conventional drill rig. Once the hole 12 has been
drilled, a
cartridge or quantity of energetic material such as an explosive or propellant
14 is inserted
into the hole and sits on or near the bottom of the hole 12. Located in
operative
3 o association with the energetic material 14 is an initiator 18. The
initiator 18 may be part of
an integral package also containing the energetic material 14. Alternately, it
may be a
separate initiator that is inserted into the hole with the energetic material
14. The hole 12
CA 02360771 2001-12-14
WO OOr36364 PCT/AU99/01107
_g.
is then filled with stecaming material 20 to a predetermined level L
commensurate with
the end of the collar area C of the hole 12. The stemming material 20 used is
one that is
capable of absorbing energy or shock waves rather than one that transmits the
energy or
sl~c waves. For example, the stemming will ideally be in the form of a loose
or self
packed granular or particulate material such as sand, gravel, clay, crusher
fines, or drill
cuttings, or a liquid or colloidal suspension that has the property that its
viscosity increases
with increasing shear.
Once the stemming 20 has been inserted into the hole, a plug 22 is then
inserted into the
1 o hole. In the embodiment shown in Figure 1, the plug 22 is of a T shaped
section having a
central short bar 24 and a transversely extended cxoss bar 26. The length of
the plug 22 or
more particularly the bar 24 is equal to or greater than the depth of the hole
12 when filled
with the stemming 20. That is, the bar 24 should be of a length to retain tlx
st~mning
from a location at or below the collar area C of the hole 12.
The plug 22 is able to facilitate a coupling of the initiator 18 with an
initiation source (not
shown). In the embodiment shown in Figure 1, this is done by providing the
plug 22 with
a passage, slot or recess through which a lead 28 can pass to facilitate
connecting the
initiator 18 with the initiation source. Embodiments of such stemming bars are
illustrated
2 o in Figures 9-12 attached and described in greater detail below.
Finally, the upper end of the plug 22 protruding from the hole 12 is
mechanically held
down. In this embodiment, this is done by placing a mess, such as the bucket
30 of an
excavator 32, on the end of the plug. However the same effect can be achieved
by
2 5 placement of the drill rig used to initially drill the hole 12, or another
mass such as a block
of concrete or a sand bag.
When the initiator 18 is connected to the initiation sourcx, it initiates the
energetic malarial
14, which in turn explodes or combusts. When this occurs, theta is a very
rapid rise in gas
3 o pressure near the bottom of the hole 16. The pressure acts in all
directions including the
upward direction and thus on a stemming 20. Gas pressure acting in this
diroction
compacts or locks the stemming 20 together as the stemming 20 is prevented
from being
CA 02360771 2001-12-14
WO 00/36364 PCT/AU99/01107
blown out of the hole by the plug 22 and mass 30. As the plug 22 is of the
length at least
commensurate with the length of the collar area C of the hole 12, the
likelihood of the
collar area C being fragmented and energised to the extent of producing fly
rock is remote.
Further, by preventing the stemming 20 from being ejected from the hole 12,
and as the
stemming 20 is able to be compacted and locked into place against the surface
of the hole,
a greater proportion of the blast energy and gas pressure, than otherwise
would be the
case, is able to act at the bottom of the hole 16. As such, the blast
efficiency is improved.
Accordingly either smaller charges can be used to excavate or fracture the
same volume of
hard material or alternately, use of the same amount of energetic material as
in the prior art
would lead to an increased volume of excavation or fracturing.
Figure 2 illustrates a minor variation in the equipment used to effect the
current method.
In this figure, like reference numbers are used to denote like features. The
substantive
differences between the embodiments of Figure 1 and Figure 2 are that the
stemming 20 is
provided in a package 34 and that the plug 22 is a simple stemming bar that
does not
include the cross bar 26 as depicted in Figure 1. For different applications,
the package 34
may be of different lengths and diameters and may contain different types of
stemming 20.
Also if desired or necessary, more than one stemming package 34 can be
inserted into the
hole 12. The performance of the method using the stemming package 34 and
simple plug
-- 2 0 22 is the same as described in relation to Figure 1. The plug 22 is
again arranged of a
length to ensure that it holds or retains the stemming at a level at or below
the collar area
C of the hole 12. In the method, the energetic material 14 and initiator 18
are initially
inserted into the hole 12. The stemming package 34 is then inserked into the
hole.
Typically, the lead 28 will be disposed between the outside of the packaged
stemming 34
2 5 and the surface of the hole 12. The lead 28 is then threaded through a
passage or recess in
the plug 22 and connected to a suitable initiation source. Any suitable
available mass is
then placed on the top of the plug 22 and the initiation source activated to
cause initiation
of the energetic material 14. The functioning of the packaged stemming 34,
plug 22 and
mass (not shown) is the same as that described in relation to Figure 1 above.
The plug 22
3 0 could also be provided with a cross bar 26 or upper plate, grate or flange
to increase the
area on which the mass can bear.
CA 02360771 2001-12-14
WO 00/36364 PGT/AU99/Ol 107
-10-
In a further variation depicted in Figure 3, instead of having a lead 28
extending from the
initiator 18 through the plug 22 to an initiation source, a transducer 36 is
provided in the
plug 22 for providing wireless electromagnetic/magnetic coupling of the
initiator 18 to an
initiator source (not shown). In order to achieve this coupling, a receiver 38
is coupled or
associated with the initiator 18 to decode appropriate firing codes andlor
extract
operational power from signals transmitted by the transducer 36. To assist in
the
transmission of signals from the transducer 36 to the receiver 38, the
stemming 20 may be
formed of, or include, magnetically and/or electrically conductive particles.
An
appropriate transducer 36 and receiver 38 are described in International
Application No
PCTlAU98/00929. In this embodiment, the stemming 20 is again shown as loose,
ie
unpackaged stemming. However the stemming can also be packaged stemming 34 as
in
Figure 2 with the container or packaging per se formed of a magnetically
aad/or
electrically conductive material or otherwise carrying or having embeddod
therein
particles or wires etc having such properties. Because of the manner in which
the plug 22
facilitates the coupling of the initiator 18 to an initiation source, there is
no need to thrrraid
a lead through the plug 22 as in the methods described in relation to Figures
1 and 2.
However, in all other respects, the metlwd of chargiag the hole 12 is the
same.
A Rather variation in the equipment capable of performing the method is
illustrated in
2 0 Figure 4. In this embodiment, the plug 22 is provided with electrical
leads 40 and 42
connectable to an AC or DC ignition source. Lead 40 may be a ground or
reference lead
that is electrically coupled to the ground 10 either via the plug 22 itself or
by the provision
of an extension (not shown) that bears against the inside of the hole 12. The
other lead 42
is a control lead that is electrically isolated from lead 40 to allow for the
creation of a
2 5 potential difference with lead 40. The initiator 18 is in this instance an
electric initiator
and has one terminal 44 arranged to be in electrical connection with the lead
40 say via
grounding with the surface of the hole 12 and a second lead 4b that is
arranged to be in
electrical connection with the lead 42. This connection may occur via the
packaged
stamning 34. As with the Imevious embodiments, once the energetic material 14,
initiator
3 o 18, stemming 20 and plug 22 are placed in the hole, the upper end of the
plug 22 is
mechanically held down. Leads 40 and 42 extending from the plug 22 can be
connoctcd
to an electrical power source for providing an AC or DC curncnt as required to
cause
CA 02360771 2001-12-14
WO 00/36364 PGTIAU99/01107
-11-
activation of the initiator 18 and subsequent initiation of the energetic
material 14, The
gas dynamics within the hole 12 are the same as described in relation to the
previous
embodiment. The packaged stemming 34 is maintained in the hole by the
mechanically
held plug 22. As gas pressure increases, the stemming 20 compacts and
substantially
isolates the plug 22 and thus the mass or other mechanical means acting
thereon from a
substantive gas pressure so that there is insubstantial shock applied to the
mass/means.
Also, as the plug 22 is maintained within the hole 12 and has its lower end
out or below
the level of tlx collar area C there is little likelihood of the collar area C
of the hole being
blown away. Thus, the action of the mass, plug 22 and stemming 20/packsged
stemming
34 is to concentrate the build up in gas pressure to the bottom of the hole
16. This
maximises the efficiency of the process.
The above described embodiments relate to c)~tging of the bola 12. However,
methods in
accordance with this invention can extend to the method of actually forming a
charged
hole which in substance is the same as in methods described above but with the
additional
initial step of fus~t providing a drill and then drilling the hole 12. Ia this
method, it may be
most convenient to use the drill cuttings created when drilling the hole 12 to
act as the
stemming 20. Also, given that a drill is initially providing for drilling the
hole 12 the drill
may also itself be used as the mass applied to the top of the plug 22 to
mechanically hold
2 o it in place.
Figures S-8 illustrate alternate rn~Ods for mechanically retaining the
stanming 20 in tlx
hole by use of various types of acpa~able plugs.
In Figure 5, the plug 22 comprises tapered bars 22a and 22b that can be slid
over each
other to increase the overall diameter of the plug 22 when in the hole 12 in
order to
m~hanically retain the plug 22 in the hole by a wedging action. The bar 22a is
provided
with a passage, slot or recess through which the lead 28 can pass to
facilitate connecting
the initiator 18 with an initiation source in a similar manner as depicted
with referencx to
3 o the embodiments shown in Figures 1 and 2.
In Figure 6, the plug 22 is composed of a tapered torte 22c and a
complementarily tapered
CA 02360771 2001-12-14
WO 00/36364 PCT/AU99/O1107
-12-
upper wedge 22d. The cone 22c is pieced in the hole 12 with its largest
diameter end first
and bears against the stemming 20. The wedge 22d is then placed over the cone
22c and
pressure then applied to it to push it downward over the cone 22c so as to
effectively
wedge into the hole 12. In order to assist or facilitate the wedging action,
the wedge 22d
can be provided with a plurality of longitudinal f ngers or slits that can
radially spread
outwardly when pushed against the cone 22c. Further, upon initiation of the
energetic
material the build up in gas pressure acts to try to eject the stemming 20
from the hole 12.
This in turn acts to tighten the core 22c/wedge 22d combination against the
hole 12 thus
further resisting ejection of the stemming 20. In this embodiment, both of the
components
22c and 22d of the plug 22 are provided with collinear passages through which
the lead 28
can pass.
Figure 8 illustrates a plug 22 comprising a cone 22e for seating inside a
wedging base 24f.
In essence, the plug 22 shown in Figure 8 is in the inverse of the plug 22
shown in Figure
6. In Figure 8, the base 24f sits on the stemming 20 and has a central tapered
aperture for
receiving the cone 22e. As the cone 22e is pushed further down into the base
22f the
upper end of the base 22f expands radially outwardly to wedge against the
surface of the
hole 12. Collinear passages of slots are formed in the base 22f and cone 22e
to allow for
the passage of the lead 28.
Figure 9 depicts perhaps the simplest form of plug 22 comprising a stemming
bar 22g of a
form substantially identical to that shown in Figure 2 together with a simple
wedge 22h
that is wedged or forced in between the stemming bar 22g and the side of the
hole 12.
2 5 In each of the embodiments shown in Figures 5-8 further mechanical
retention of the
stemming 20 or stemming package 34 can be achieved by bearing a weight or mass
on the
end of the plug 22 in a manner similar to that depicted with reference to the
embodiment
shown in Figure 1.
3 0 By mechanically retaining the stemming material the elect of the stemming
is enhanced
while at the same time reducing noise and flyrock. The functiow of the
stemming 20 is to
direct the axial pressure force created by the initiation of the energetic
material into radial
CA 02360771 2001-12-14
WO 00/36364 PCT/AU99/01107
-13-
compression forces against the wall of the hole, thus leading to large
friction force
resisting ejection of the stemming from the hole and consequently longer
retention of gas
pressures at the bottom of the hole 12. Clearly, by mechanically retaining the
stemming
thus preventing its ejection from the hole, its effect and benefit is
enhanced. Blasting
e~ciency is further enhanced by mechanically retaining a stemming at a
location in the
hole adjacent or below the collar area. This acts to isolate the collar area
from the
substantive pressure forces thereby reducing the likelihood of the collar area
being blown
away generating flyrock. As previously described, the mechanical retention of
the
stemming caa be by way of an expandable plug that is insertai into the hole in
an
unexpended condition and then expanded to bear against the sides of the wall.
Pressure
forces transmitted by the stemming 20 to the expandable plug act to further
expand the
plug outwardly increasing the mechanical retaining force on the stemming. It
forms in
effect an self tightening or locking system for retaining the stazuning
material.
Altenaately, mechanical retention can be achieved by inserting an unexpandable
rod or
plug into the hole and bearing a weight or mass on the plug. This can be
achieved by use
of equipment typically available on mine sites such as earth moving equipment,
chains,
sandbags, and the like. It is also of cxria~se possible to combine the use of
both an
expendable plug and an external weight or mass acting on the plug to
mechanically retain
the summing material.
ao
Figures 9 and 10 depict a stemming bar 22k that can be incorporated into
several of the
embodiments of the method described above. For example the sttmnning bar 22k
or a
stemming bar of like form can lx usod is tlu embodiments depicted in Figures
1, 2, 5
(replacing the tapered bar 22a) and Figure 8.
The stemming bar 22k is in the general form of a cylindrical bar of metal
(such as steel)
having a first opening 44 at a fast end 46, being tho end of the bar 22k that
is inserted into
the hole 12; and, a second opening 48 at a location at or near upper end SO at
a location so
that when the fu~st end 46 is inserted into the hole 12 the opening 48 is
located outside of
3 0 the hole 12. A slot 52 is cut or otherwise formed longitudinally along the
stemming bar
22k running from the first opening 44 to the second opening 48. A plurality of
pins 58
extend transversely across the slot 56. The pins 58 are roughly evenly spaced
along the
CA 02360771 2001-12-14
WO 00/363b4 PCT/AU99/01107
-14-
length of the slot 56. The main purpose of the pins 58 is to form a guide to
attempt to
maintain an initiator or detonator cord within the confines of the bar 22k.
In an alternate form of the stemming bar 221 depicted in Figure I 1 instead of
the slot 56
extending along the outer surface of the stemming bar 22k, an internal passage
56a is
provided. The passageway 56a runs between the first opening 44a at the bottom
of the
stemming bar 221 and second opening 48 located on the outer cixcumferential
surface of
the stemming bar 221 near upper end 50 of the stemming bar 221. An initiator
cord or lead
28 extends through the passageway 221.
l0
The form of the stemming bar depicted in Figures 10-11 Leads to the provision
of alternate
methods of charging a hole. One such alternate method is shown in Figure 11.
Here, the
energetic material 14 is contained within a cartridge 60 that is coupled to
end 4b of the
stemming bar 221. The coupling is by way of an interference fit with the end
46 of the
stemming bar 221 being tapered so as to reduce in diameter in a direction
toward the
bottom of the hole 12. The method includes initially drilling a hole in hard
material 10
such as a rock or boulder, pushing the cartridge 60 onto the end 45 of
stemming bar 221,
inserting the stemming bar 221 into the hole 12 within 46 first and then
feeding the
initiator cord 28 through opening 48a down passageway 221 and out of opening
44a into
2 0 the bottle/cariridge 60 into operational contact with the energetic
material 14.
To prevent the stemming bar 221 from ejecting from the hole 12 upon detonation
of the
energetic material 14 it may be held in place by a massive object such as a
bull dozer, bob
cat, jumbo or other vehicle bearing against the end S0. A penetrating cone
fracture (PCF)
2 5 would typically be formed as shown by fracture line F in Figure 11 as a
result of the
initiation of the energetic material 14.
It is to be understood that the stemming bar 22k depicted in Figures 9 and 10
can of course
be used in place of the stemming bar 221 in the embodiment shown in Figure 12.
A further embodiment is shown in Figure 12. In this embodiment, the container
60
holding energetic material 14 is not supported or otherwise directly coupled
to the
CA 02360771 2001-12-14
WO 00/36364 PGT/AU99/01107
-1S-
stemming bar 22m. Rather, the container 60 is lowered into the hole 12 prior
to insertion
of the stemming bar 22m. The energetic material 14 is held in a bag which is
flamrnable
or readily melts upon contact with a flame. In the further variation from the
embodiment
shown in Figure 12 initiation is elected by way of a flame that passes through
the
passageway 56b rather than through a physical initiator such as a detonator,
electric match,
non electric match or fuse cord. The flame can be created by a shot gun
ca~rG~idge 62 filled
with a pyrotechnic material. The cartridge 62 is held within a chamber 64
located at upper
end 50 of the stemrrling bar 22m, and is triggered in a conventional manner by
use of a
fi 'nng pin. Thus, in this embodiment, upon flying of the cartridge 62, a
flame enters the
1 o passageway 56b through opening 48b and exits at the opposite end of the
stemming bar
22m through opening 44b burning through the bag holding the energetic material
14
causing the energetic material to ignite or detonate. The embodiments depicted
in Figures
12 and 13 are particularly well suited to small charge blasting. A substantial
benefit of
these embodiments is that the initiator is delivered to the energetic material
14 after the
1 s stemming ~r 22 has been placed in the hole 12. Because the initiator 30 is
placed in the
hole 12 after the stemming bar 22, thGrc is no risk of it being accidentally
or pt~ariuely
set off by the insertion pressure of the stemming bar 22, or being damaged by
the system
in bar 22 so as to be non effective.
2 o Now that embodiments of the invention have been described in detail it
will be apparent to
those skilled in the relevant arts that numerous modifications and variations
may be made
without departing from the broad inventive concept. For example, any type of
packaged
or unpackaged st«nming 20 may be used provided that the stemming is able to be
compacted by or otherwise absorb the pressure generated following initiation
of the
2 5 energetic material.
However as previously described, liquids that have the cll~n~acteristia of
increased viscosity
with inaeasod shear would be suitable. Furthtr, it is noted that in
embodiments shown in
Figure 1, the plug 22 is provided with a cross bar 26. In a variation, instead
of placing a
3 o mass oa the plug 22, bolts or pegs may be driven through or about the
cross bar 26 to
mechanically hold the plug. However, it is believed that this variation would
lead to
increased costs due to the additional labour and plant required. Additionally
tho cross bar
CA 02360771 2001-12-14
1 v
WO fl0/36364 PCT/AU99/01107
-16-
26 could be replaced with a plate. Also, it is preferred that the plug 22 is
of a length or
disposed so that its lower end when inserted into the hole is at a level
substantially
adjacent or below the collar area of the hole 12. It will be appreciated that
the collar area
C varies in accordance with the hole configuration and the nature of the
material in which
the hole 12 is made.
All such modifications and variations together with those that would be
apparent to a
person of ordinary skill in the art are . deemed to be within the scope of the
present
invention the nature of which is to be determined from the above description
and the
1 o appended claims.
