BLASTING SYSTEMS & METHODS
FIELD OF THE INVENTION
The present invention relates to blasting systems and methods. In one preferred form of
the present invention there is provided a stemming method and a stemming arrangement
for a blast hole.
BACKGROUND TO THE INVENTION
Control plugs or stemming devices such as the industry standard aggregates being typically
5mm, 10mm, 15mm in diameter, StemPlug™ blast control plug and the MaxBlast™ blast
control plug have been developed and used to improve the efficiency of blasting in the
mining industry.
When the stemming devices or control plugs operate as intended, they provide the
advantage of reducing the costs of explosives required for blasting operations and
associated downstream processing costs.
In circumstances where conventional stemming with aggregates or the control plugs fail in
their operation, inconsistent rock breaking can occur which has associated problems with
safety, re-blasting and rock processing.
It is against these problems and difficulties associated therewith that the present invention
has been developed.
SUMMARY OF THE INVENTION
According to a first aspect of preferred embodiments herein described there is provided
a method of stemming a blast hole, the method comprising: providing a gel type
substance as a gelled length in the blast hole, as a pressure wave reflecting stem to
increase the efficiency of an explosive during blasting with the explosive being located
in the blast hole.
According to a second aspect of preferred embodiments herein described there is
provided a blast hole arrangement comprising: an explosive and a gel type substance
in a blast hole; the gel type substance providing a gelled length in the blast hole as a
pressure wave reflecting stem to increase the efficiency of the explosive in the blast
hole during blasting.
Preferred embodiments relate to the use of water as a stemming device in blast holes.
In such embodiments the water is transformed into a gel using Super Absorbent
Polymers (SAP) or any similar reagents having the ability to absorb equal to or more
than 25: 1 their own weight in demineralised water.
SAP's are also known by the name of Hydrogels. A 25: 1volume to weight ratio being
the uptake of demineralised water into the polymer structure officially defines SAP's
or Hydrogels as per the Australian Customs Tariff Schedule. For example lgram of
Super Absorbent Polymer (SAP) must absorb 25 cubic centimetres of demineralised
water to be classified as a SAP.
The gelling reagent used has the ability to gel water over a broad range of water types.
From very low TDS to very high TDS (TDS = Total Dissolved Solids). This allows a
broad range of water quality to be utilised. For example the TDS that may
accommodated can range from 0 mg/1 to 100,000 mg/1 Sodium Chloride. Preferably
the reagent is able to accommodate 25,000 mg/1 Sodium Chloride or more.
In one preferred form a gelled or solidified column of water is created on top of the
explosive charge. The gelled water is pumped down the bore hole after the explosive
charge is set. The column of gelled water fills a column of a desirable height above the
explosive charge for the blasting conditions. The gelled column of water may fill the
entire bore hole to the surface or be much less than this depending on the
circumstances.
In preferred forms an almost instantaneous gelling characteristic of the reagent allows
the gel stemming of blast holes from vertical to horizontal bore holes over 360 degrees.
Preferred gel stemming systems according to the invention, find application on surface
or in underground blasting. The gel water column may be applied in horizontal bore
holes as well as vertical bore holes as the stiff gel will not flow out of the bore hole.
The gelled column of water may have its density increased by the use of soluble or
insoluble weighting agents such as sodium chloride (NaCl) or barite, (barium sulphate).
This allows the hydrostatic pressure being exerted by the gelled column of water on
the bottom and sides of the bore hole to be adjusted. This in turn may relate to balancing
of the explosive blast pressure characteristics to the height of the gelled column of
water acting as a stemming device.
Both the reflection of the blast pressure wave by the column of gelled water and the
hydrostatic pressure being exerted on the bottom and sides of the bore hole
advantageously result in controlling explosive blast gases direction and focus.
This may inturn enable the reduction in stem height as compared to conventional
methods.
In one preferred method, application is made by dosing the reagent at a measured rate
into a water stream. The raw water can be supplied from a water truck, site dam or
water storage vessel and pumped in line to the reagent mixing equipment. The raw
water constituents or analysis may be from very low Total Dissolved Solids to very
high Total Dissolved Solids. The reagent is then dosed into the water stream.
Sufficient residence time is allowed for the reaction between the reagent and water to
take place forming the gel. Kinetic energy is applied to allow the reaction to occur
effectively. A flexible hose is placed in the bore hole and the resulting gelled water is
pumped down the bore hole at a measured rate. The resulting gelled water column may
fill the entire bore hole. A positive displacement pump is used to pump the gelled water.
The hose is removed from the bore hole. The hose is then placed in the next bore hole
and the process repeated.
In preferred forms the Super Absorbent Polymer (SAP) reagent may be in the form of
a solid (ie. a powder or granulate), as a fibre or as a liquid. The liquid may be in the
form of a solution or in an emulsion form or as a dispersion of discrete particles
suspended in a carrier fluid. The SAP's may be of any particle size. The SAP's may
or may not be of one or more particle sizes of various chemistry. The SAP's may be
applied as cross-linked polymers or they may be cross-linked insitu or they may be
used in a combination of both in various proportions. A rheological modifier may be
added to the reagent.
In the first aspect there is provided a method of stemming a blast hole, the method
comprising: providing a gel type substance as a gelled length in the blast hole to
increase the efficiency of an explosive during blasting as a pressure wave reflecting
stem, the explosive being located in the blast hole.
Preferably the method includes ensuring that gel type substance includes a substantial
quantity of water, the substantial quantity being sufficient to reflect the pressure wave
generated by the explosive.
Preferably the method includes providing the gel type substance in the blast hole as a
gelled water column that freely contacts the walls of the blast hole.
Preferably the gel type substance is unrestrained so as not to be contained in a plug
structure that limits the gelled length, the plug structure and limitation of the gelled
length for exerting pressure on the walls of the blast hole.
Preferably providing a gel type substance comprises providing a super absorbent
polymer gel; and the method includes pumping the super absorbent polymer gel into
the blast hole to create a gelled column of water.
Preferably providing a gel type substance comprises providing a super absorbent
polymer gel having hydroscopic and other properties allowing the gel to contact the
explosive.
Preferably the method includes ensuring that a zero to near zero interstitial free water
volume is provided over a substantial portion of the gelled length; the zero to near zero
interstitial free water volume serving to reflect the pressure wave generated by the
explosive.
Preferably the method includes pumping the super absorbent polymer gel into the blast
hole to proactively fill fissures in the wall of the blast hole.
Preferably the method includes ensuring that the super absorbent polymer gel is
substantially water absorbed, at least along a substantial portion of the gelled length of
the super absorbent polymer gel.
Preferably the method includes ensuring that the super absorbent polymer gel is
substantially water absorbed before entering the blast hole.
Preferably the method includes ensuring that the super absorbent polymer gel is fully
water absorbed before entering the blast hole.
Preferably the method includes providing the gelled length as a length of at least
100mm.
Preferably the method includes providing the gelled length as a length of at least
200mm.
Preferably the method includes providing the gelled length as a length of at least
500mm.
Preferably the method includes providing the gelled length as a length of at least lm.
Preferably the method includes providing the gelled length as a length of at least 2m.
Preferably the method includes providing the gelled length as a length of at least 3m.
Preferably the method includes providing the gelled length as a length of at least 4m.
Preferably the length provided a vertical height, the vertical height providing a vertical
hydrostatic pressure under the action of gravity.
Preferably the method includes providing the gel type substance with a specific gravity
of between or equal to 1 and 2 .
Preferably the method includes providing the gel type substance with a specific gravity
of greater than 1.0.
Preferably the gelled length provides a structure that operates to provide a reduction in
detonation pressure, over the gelled length, of at least 99%; at least 98%; at least 90%;
or another beneficial amount.
Preferably the gelled length provides a structure that operates to provide a reduction in
the velocity of detonation of at least 60%; at least 50%; at least 40%; or another
beneficial amount.
Preferably the method includes forming the gel type substance by combining a super
absorbent polymer with brackish waste water having a total dissolved solids between
100 to 5000 mg/L.
Preferably the method includes forming the gel type substance by combining a super
absorbent polymer with saline waste water having a total dissolved solids greater than
5000 mg/L.
In a second aspect of preferred embodiments herein provided there is provided a blast
hole arrangement comprising: an explosive and a gel type substance in a blast hole; the
gel type substance providing a gelled length in the blast hole to increase the efficiency
of the explosive in the blast hole during blasting.
Preferably the gel type substance includes a substantial quantity of water, the
substantial quantity being sufficient to reflect the pressure wave generated by the
explosive.
Preferably the gel type substance is unrestrained to form a gelled water column.
Preferably the gel type substance is unrestrained so as not to be encapsulated in a
structure that limits the length of the gelled water column to exert increased lateral
pressure on the walls of the blast hole.
Preferably the gel type substance comprises a super absorbent polymer gel that has
been pumped into the blast hole to create a gelled column of water.
Preferably the gel type substance comprises a super absorbent polymer gel having
hydroscopic and other properties allowing the gel to contact the explosive.
Preferably a zero to near zero interstitial free water volume is provided over a
substantial portion of the gelled length; the zero to near zero interstitial free water
volume serving to reflect the pressure wave generated by the explosive during blasting.
Preferably the super absorbent polymer gel extends into fissures in the wall of the blast
hole to fill the fissures.
Preferably the super absorbent polymer gel is substantially water absorbed, at least
along a substantial portion of the length of the super absorbent polymer gel.
Preferably the super absorbent polymer gel is substantially water absorbed before
entering the blast hole.
Preferably the super absorbent polymer gel is fully water absorbed before entering the
blast hole.
Preferably the gelled length is provided as a length of at least 100mm
Preferably the gelled length is provided as a length of at least 200mm
Preferably the gelled length is provided as a length of at least 500mm
Preferably the gelled length provides a length of at least lm.
Preferably the gelled length provides a length of at least 2m.
Preferably the gelled length provides a length of at least 3m.
Preferably the gel type substance has a specific gravity of between or equal to 1 and 2 .
Preferably the gel type substance has a specific gravity greater than 1.0.
Preferably the gel type substance is formed by combining a super absorbent polymer
with brackish waste water having a total dissolved solids between 100 to 5000 mg/L.
Preferably the gel type substance is formed by combining a super absorbent polymer
with saline waste water having a total dissolved solids greater than 5000 mg/L.
The super absorbent polymer preferably: (i) retains more than 25 times its own mass; (ii)
retain more than 100 times its own mass; (iii) retains more than 200 times its own mass;
(iv) retains more than 300 times its own mass; (v) retains more than 400 times its own mass;
and so forth.
According to an aspect of preferred embodiments herein described there is provided a
method of stemming a blast hole, the method comprising: providing a gel type
substance as a gelled length in the blast hole to increase the efficiency of an explosive
during blasting; the explosive being located in the blast hole.
According to an aspect of preferred embodiments herein described there is provided a
blast hole arrangement comprising: an explosive and a gel type substance in a blast
hole; the gel type substance providing a gelled length in the blast hole to increase the
efficiency of the explosive in the blast hole during blasting.
Preferred systems and methods herein described may provide a number of advantages
including:
1) Being able to be applied fast and easily to all blast holes as compared to
conventional technologies.
2) Providing a manner of addressing conventional aggregate or plug type
stemming devices being ejected from the hole from time to time thus causing
ineffectual blast pattern, reduced impact to rock and associated increase in down
stream processing issues and costs. The use of the gelled water column in preferred
stemming systems is considered to reduce the propensity for such events to occur.
3) Allowing the operator to re-enter the hole if an explosive charge misfires. All
other stemming devices known to the applicant provide a plug creating a physical
barrier which stops access to the unexploded change.
4) Increasing efficiency in comparison to traditional mechanical or physical
stemming devices. To the best of the applicants knowledge no prior art or systems have
the ability to reflect or reverse an explosive blast pressure wave in a blast hole
application.
5) Because of achieving higher efficiencies in the direction and focus of the
explosive gases less explosive is required. Consequently blast hole geometry, i.e. the
depth and diameter of the blast hole may be reduced. Also the number of blast holes
required may also be reduced delivering substantial savings to industry.
6) The gelled water column may be applied in 360 degrees in blast bore holes above
or below ground.
It is to be recognised that other aspects, preferred forms and advantages of the present
invention will be apparent from the present specification including the detailed description,
drawings and claims.
BRIEF DESCRIPTION OF DRAWINGS
In order to facilitate a better understanding of the present invention, several preferred
embodiments will now be described with reference to the following drawings in which:
Figure 1 provides a perspective view of a blasting bench;
Figure 2 provides a schematic view of an explosion within a borehole;
Figure 3 provides an illustration of a method according to a first preferred embodiment of
the present invention;
Figure 4 provides a further illustration in relation to the method shown in Figure 3;
Figure 5 provides an illustration of a blast-hole arrangement according to a further preferred
embodiment of the present invention;
Figures 6 and 7 illustrate the operation of another embodiment of the present invention;
Figures 8 and 9 provide graphs illustrating a number of test results; and
Figure 10 provides a tabulated summary of the test results shown in Figures 8 and 9 .
DETAILED DESCRIPTION OF THE EMBODIMENTS
It is to be appreciated that each of the embodiments is specifically described and that the
present invention is not to be construed as being limited to any specific feature or element
of any one of the embodiments. Neither is the present invention to be construed as being
limited to any feature of a number of the embodiments or variations described in relation
to the embodiments.
Referring to Figure 1, there is shown a blasting bench 10. The blasting bench 0 includes
a number of drill boreholes 12 arranged in a grid configuration. The blasting bench
provides a burden 14, a spacing 16, a bench height 18, a sub drill depth 20. In operation
there is an initiation sequence for detonation and successive row and hole firing.
Depending on the structure of the rock the holes 12 may have a 6 inch diameter and be
spaced about say 12 feet apart. The amount of explosive used in each borehole depends on
a number of factors including the type of the explosive, borehole depth and diameter, sub
drill depth, spacing, burden and the borehole detonation sequence. Each of these factors as
well as other factors define the parameters of a blasting programme.
Assuming that conventional stemming aggregates or control plugs are used in the boreholes
12 and function as intended, the control plugs operate to constrain explosion gasses. The
rock is blasted and fragmented into rock suitably sized for subsequent processing.
If however one or more of the control plugs do not function as intended and are blasted out
the boreholes 12, the associated blasting programme can be compromised. In
circumstances this can result in having to remove large pieces or sections of rock from the
blasting bench 10 as well as possibly having to reblast. The process of removing such rock,
secondary blasting and mechanical breaking have associated time and labour costs.
Producing rock that has been blasted and fragmented into suitably sized pieces is the
primary role of ore production. Unsatisfactory blasting resulting in downstream increase
in materials handling costs are of concern to quarry and mine site operators.
Turning to Figure 2 there is shown an explosion 22 within a borehole 12. A stemming
device 24 in between two sections of rock packing 26 is provided. By having the stemming
device 24 in position above the explosion 22 this serves to prevent explosion gases from
venting upwards. When explosion gases vent, this has the effect of reducing the explosive
force on the adjacent rock as well as creating air blast and fly rock.
In the case of the stemming device, depending on the conditions, the stemming device 24
could be blasted out of the borehole 12 and adversely disturb the effect of the blast
sequence.
Figure 3 illustrates a method 28 according to a first preferred embodiment of the present
invention. The method 28 provides several advantages discussed in further detail below.
At block 30 of the method 28, an explosive 32 is inserted into and positioned at the bottom
of a blast hole 34. At block 36 a gel type substance 38 (a gel or otherwise) is prepared for
pumping into the blast hole 34.
The process at block 36 comprises providing a pressure wave stemming reagent 40. The
pressure wave stemming reagent 40 provided is reacted with water 42 to form the pressure
wave stemming media gel 44 (the super absorbent polymer gel). The water 42 is provided
from a water source 46.
Advantageously the pressure wave stemming reagent 40 is transported to the location of
the blast hole 34 at a mine site. The pressure wave stemming reagent 40 is provided as a
package that is mixed with the water 42.
At block 48, the method .10 includes pumping the reacted pressure wave stemming media
44 from a system 50 into the blast hole 34 using a pump 52.
As part of block 48, the reacted pressure wave stemming media 44 is pumped directly at
the lower end 54 of the blast hole 34. For this purpose a tube 56 extends down the blast
hole 34 to deliver the reacted pressure wave stemming media 44 into the desired position.
As the reacted pressure wave stemming media 44 is delivered through the tube 56 the tube
56 is raised as part of the method 10. In this manner the blast bore 34 is progressively filled
with the reacted pressure wave stemming media 44 from above the explosive 32 in a
direction extending towards the upper opening 58 of the blast hole 34.
Notably the reacted pressure wave stemming media 44 is provided as a gelled length 60
that fills a portion of the remaining length 62 of the blast hole 34. The gelled length 60
provides a pressure wave stem media 60 in the form of a gelled water column 60 that is of
a height suited to the blasting conditions.
As will be detailed in relation to Figures 8 to 12, it is considered that pressure wave stems
of the embodiments will be effective in confining and controlling gas pressure in the
blasting. Presently, the differential in energy loss is considered to only be attributable to
the majority of the pressure wave energy being reflected.
With water being substantially incompressible the gelled water column 60 is
advantageously provided with a substantial quantity of water, the amount of water and form
of the column being sufficient to advantageously operate on what would be the pressure
wave from the explosive after detonation.
The gelled water column 60 provides a substantial continuous length that serves to
desirably reflect the pressure wave to increase the efficiency of the explosive 32 during
blasting.
Referring to Figure 4, the explosive 32 is provided as an explosive 65 of a particular form.
Advantageously the reacted pressure wave stemming media 44 has characteristics
(hydroscopic and other properties) that allow the reacted pressure wave stemming media
44 to contact the explosive 65. Advantageously in the reacted pressure wave stemming
media 44, a zero to near zero interstitial free water volume is provided.
The column of reacted pressure wave stemming media 44 and the pumping of the reacted
pressure wave stemming media 44 at block 48 is considered to advantageously have the
ability to fill fissures 64 in the wall .66 of the blast hole 34.
The reacted pressure wave stemming media 44 is provided with a specific gravity over 1.0
while substantially maintaining the gel type properties of the reacted pressure wave
stemming media 44. Increasing the specific gravity of the reacted pressure wave stemming
media will increase the hydrostatic pressure exerted by the gelled length of water 44.
Although the length of the water column 60 will be determined by the blasting parameters,
the gelled length provided could provide a substantial hydrostatic head that assists with
reflecting the pressure wave from the explosive 65.
Referring to Figure 5, the method 28 is considered to provide a blast hole arrangement 70
according to a further preferred embodiment of the present invention. The blast hole
arrangement 70 comprises an explosive 32 and a gel type substance 38 (the gel 44) in a
blast hole 34. The reacted pressure wave stemming media 44 is in contact with the
explosive 32 and reflects the pressure wave through a path of least action to the region
below the reacted pressure wave stemming media 44,
Notably the reacted pressure wave stemming media gel 44 extends into fissures 64 in the
wall 66 of the blast hole 34. The reacted pressure wave stemming media gel 44 is
substantially water absorbed before entering the hole, and as a result, when in the blast hole
34,
The reacted pressure wave stemming media gel type substance has a specific gravity greater
than 1.0 During detonation of the explosive 32 .and e...subsequent .generati
pressure wave the reacted pressure wave stemming media gel 44 (remaining or otherwise)
acts to reflect the energy of the pressure wave away from the open stemmed hole redirecting
the explosion gases downwardly into the blast hole 34 and laterally into walls thereof and
preferentially towards any ridged surface.
In this embodiment the reacted pressure wave stemming media gel 44 is advantageously
formed by combining the pressure wave stem reagent with saline waste water having a total
dissolved solids greater than 10,000 mg/L from a mine site desalination process waste.
Generally such waste water has to be discharged into the environment and comprises salt
water with high total dissolved solids. Waste water of this type is known to be particularly
problematic and to be associated with several environmental problems. The present
embodiment provides an advantageous manner of disposing of such water.
As would be apparent the embodiments make advantageous use of water as a stemming
device in blast holes. As a part of the process the water is transformed into a gel using the
pressure wave stem reagent.
The gelling reagent that is used advantageously has the ability to gel water over a broad
range of water types. From very low total dissolved solids (TDS) to very high total
dissolved solids.
The gelled fluid is pumped down the bore after the explosive charge is set. This creates a
gelled column of water on top of the explosive. The column of gelled fluid could be of any
suitable height above the explosive charge and may fill the entire bore hole to surface.
Notably the almost instantaneous gelling characteristics of the reagent could allow for gel
stemming of blast holes from vertical to horizontal bore holes, over possibly a full 360
degrees. Consequently the gel stemming system may find application in surface blasting or
underground blasting. In non-vertical applications the gel could be made stiff to not flow
out of the bore hole. Various gel retaining systems could also be used. As would be
apparent the gelled fluid may be used: (i) above, (ii) below, (iii) above and below or (iv)
consecutively above and below the explosive charge depending on the operators desired
blasting requirements. This traditionally is known as decking.
The density of the gel may be increased by the use of a soluble or insoluble weighting
agents such as sodium chloride (NaCl) or weighting agent such as barite, (barium sulphate).
This allows for the adjustment of the hydrostatic pressure exerted on the bottom of the bore
hole and to the sides of the bore hole. This in turn may relate to balancing the explosive
charge to the gel stemming system.
It is considered that both the reflection of the blast pressure wave by the column of gelled
fluid and the hydrostatic pressure exerted on the bottom of the bore hole should result in a
substantial decrease of explosives required to do comparable work. This is considered to
have demonstrated by testing as will be discussed in relation to Figures 8 to 12.
With conventional stemming devices, despite their all being only attempts to physically
confine the explosives gas pressure , improvements have been seen. It is considered that
substantially incremental improvements should accordingly be seen with the pressure wave
stemming embodiments, as compared to all conventional stemming devices.
WO2012/090165 is entitled 'Tamping Device and Method' to Roderick Smart and filed 28
December 2011. The document describes a stemming device that uses a super absorbent
polymer. The super absorbent polymer is contained in a short length of semipermeable
material that is positioned in the borehole.
The document envisages a plug type stemming device where the semi-permeable
membrane is soaked with an aqueous liquid, either before or after its insertion into the blast
hole, so that it expands into contact with the wall of the blast hole. The use of a capsule of
the form envisaged by WO2012/090165 is considered to be largely equivalent to a
conventional plug. Example tap sizes discussed in WO2012/090165 include a 240mm and
300mm stemming devices.
Firstly soaking merely before entry is unlikely to provide a ready fit with the borehole.
Soaking in the borehole could provide other complications. In the case of a capsule that is
wet in the manner envisaged by WO2012/090165 the applicant considers that the capsule
might continue to suck the water into the super absorbent polymer until there is no more
interstitial water left in between the particles leaving air gaps. Thus acting as traditional
stem. To remedy free water would have to be introduced to the blast hole. This is not
compatible with water sensitive explosive types. Free water in blast holes also creates other
disadvantageous issues in blast management.
Moreover, the document envisages only a restrained membrane that absorbs water that
forces the membrane laterally outwardly. For this purpose there is an excess of super
absorbent polymer to water for absorption for continually expanding the membrane. The
system does not envisage the provision of a gelled water column that is able to redirect a
pressure wave from an explosive charge. The applicant considers that the pressure wave
would pass through the plug of WO2012/090165 for the reasons discussed. The plug of
WO2012/090165 is likely to be ejected out of the bore restraining the explosion gases only
relatively short period of time if at all.
In the present embodiments described there are no air pockets and no enclosing semi
permeable membrane. The pressure wave caused by the explosion is redirected by the
column of the gel. The hydrostatic head may play a role in the restraint and reflection of
the pressure wave..
Super absorbent polymers (SAP) noted in WO2012/090165 include polyacrylamide,
polyvinyl alcohol, cross-linked polyethylene oxide, polymethylacrylate and polyacrylate
salts. The polyacrylate salt is said to be preferably selected from sodium polyacrylate,
potassium polyacrylate, lithium polyacrylate and ammonium polyacrylate.
Figure 6 illustrates the basic operation of another embodiment of the present invention. In
the embodiment a raw water source 7 is connected to a positive displacement pump 74.
The pump 74 delivers the water to a reagent dosing station and mixer 76. The resultant
reacted pressure wave stemming media gel 78 is then delivered to a bore hole 80. As
shown in Figure 7 the reacted pressure wave stemming media gel 78 is delivered above an
explosive charge 82.
In the embodiment, the application is made by dosing the reagent into a fluid stream. The
water could be supplied from a water truck, site dam, waste stream of Reverse Osmosis
(RO) plant or water storage vessel and pumped in line to the reagent mixing equipment.
Sufficient residence time is allowed for the reaction between the reagent and water to form
the gel. Appropriate kinetic energy is applied to allow the reaction to occur. A flexible
hose is placed in the bore hole and the resulting gelled fluid is pumped out at a measured
rate for filling the hole. The hose is raised as the gel flows into the hole.
A positive displacement pump is used to pump the gelled fluid. After filling, the hose is
removed from the bore hole. The hose is then placed in the next bore hole and the process
is repeated.
As discussed the propensity for conventional aggregate stemming or plug type stemming
devices to be ejected from the hole is problematic. Failure of one or more traditional
stemming devices in a blasting programme can result in an ineffectual blast, reduced impact
to the rock, and an irregular blast pattern. This causes downstream processing issues that
affect the profitably of the mine site and the plant. The present embodiment should provide
repeatable and consistent blasting performance.
In terms of the waste water advantage, many mine sites provide portable water through
Reverse Osmosis (RO) equipment. The waste stream from Reverse Osmosis plants is often
very high in TDS and problematic to dispose of. The embodiments provide an
advantageous manner of disposal.
In terms of explosives the embodiments should provide for a reduced amount of explosive
consumption in a blasting programme.
Due to the reduced explosive power required it may consequently be possible to make
beneficial adjustments to the bore hole depth, diameter and other blasting characteristics.
This may provide savings in time and energy required for drilling and preparing the blasting
bore hole array.
Another advantage is that it is possible to re-enter the hole through the gel column if an
explosive charge misfires. Traditional stemming devices provide a plug that creates a
physical barrier that prevents ready access to the unexploded charge. All other
conventional plug type barriers create a physical barrier which stops the easy access to the
unexploded change.
Additionally traditional stemming devices are time consuming and difficult to put in place.
They often require a tight fit which can be difficult to provide given the broken ground of
the bore hole. The time and reliability aspects of the gel fluid stemming system in
embodiments is considered to be advantageous.
The applicant also considers that the pressure wave stemming (PWS) system of the
embodiments can be applied readily in a variety of conditions.
Referring to Figure 8 there is shown the results of a transducer control test of an explosion
in a bore hole having a depth of 670mm above the explosive. The transducer was located
200mm above the explosive. The borehole was filled with the reacted pressure wave
stemming reagent and water. The testing was performed by QMR Blasting Analysis
Queensland, Australia considered to be a leading internationally recognised industry
specialist
In terms of result output from the transducer as shown in Figure 8, the data recorded
measured the pressure wave at 0.082ms to travel 200mm (pressure wave stem height) at an
average Velocity of Detonation (VOD) of 2,439m/sec. The calculated Velocity of
Detonation (VOD) of the explosives used was 5,000m/sec. This corresponds with a
reduction in VOD of approximately 51% over 200mm.
The measured detonation pressure at 200mm above the explosive was 0.14 GPa. The
calculated detonation pressure of the explosives used was 7.5GPa, ie. a 98% reduction in
detonation pressure from the calculate 7.5 GPa).
Referring to Figure 9 there is shown the results of the transducer at 660mm above the
explosive. The output from the transducer is considered to illustrate the presence of a
pressure wave taking 0.406ms to travel 660mm at average speed of l,625m/sec. This
indicates a reduction in VOD of 67.5% over 660mm and a measured detonation pressure
of 0.084 GPa at 660mm being 99% reduction in detonation pressure, (again with the
explosive used having a detonation pressure calculated at 7.5 GPa
As discussed, the new stemming material attenuated 98% of the detonation pressure over a
distance of 200mm. The velocity of propagation of the detonation pressure wave decreased
over the length of the stemming indicating changes in the physical characteristics along the
length of the stemming. The differential in energy loss can only be attributed to the majority
of the pressure wave energy being reflected.
Thus, it is considered that the embodiments provide an advantageous pressure wave
stemming (PWS) product technology that operates to reflect the pressure wave energy
generated by the detonation pressure which in turn redirects expanding gases and associated
pressure preferentially towards any ridge surface (towards the sides of the bore hole away
from the bore hole opening).
The blast pressure wave as demonstrated by the tests is reflected by our PWS system thus
reversing and focusing the expanding gases towards any ridge surface. In existing systems
it is considered that the blast pressure wave will pass through existing stemming devices
potentially destabilising the stem and play no part in gas containment.
The embodiment advantageously make use of the relationship between: the detonation
energy; the hydrostatic pressure exerted by the column of PWS; the speed at which the
pressure wave is generated, usually being 3-5 msec's after detonation as compared to 24
msec's for the propagation of gases; blast hole geometry; and operational requirements.
For dosing purposes the PWS reagent is provided as a liquid to be reacted with water before
admission into the borehole. In embodiments, the liquid PWS reagent (before adding to
water and pumping down the bore hole) may be a solution, an emulsion, a dispersion of
soluble or insoluble hydrophilic molecules. The liquid PWS reagent preferably takes on a
minimum of 25: 1 its own weight in water.
The advantages of the system, potential or otherwise include: having the ability to be
applied fast and easily to all blast holes; providing a manner to address ineffectual blast
pattern by focusing energy to rock reducing the propensity to create oversize and
subsequent down-stream processing issues; allowing the operator to re-enter the hole if
required; the depth and diameter of the blast hole being able to be reduced; the number of
blast holes required being able to reduced - delivering substantial savings to industry;
practical disposal of waste water (for example from RO plants); the potential for
conventional aggregate stemming to strip or damage detonation wiring; and reducing stem
height required.
Additional advantages may include the ability to alter the drill pattern, reduce air/dust blast,
control fly rock, control rock fragmentation and so forth. The advantages associated with
conventional stemming are of course also provided.
The embodiments do not employ a bore cartridge or semi permeable sheath. The gel is
pumped into the hole without free water. This allows cheaper water sensitive explosives
like ANFO to be more cost effectively used.
As would be apparent, various alterations and equivalent forms may be provided without
departing from the spirit and scope of the present invention. This includes modifications
within the scope of the appended claims along with all modifications, alternative
constructions and equivalents.
There is no intention to limit the present invention to the specific embodiments shown in
the drawings. The present invention is to be construed beneficially to the applicant and the
invention given its full scope.
In the present specification, the presence of particular features does not preclude the
existence of further features. The words 'comprising', 'including' and 'having' are to be
construed in an inclusive rather than an exclusive sense.
It is to be recognised that any discussion in the present specification is intended to explain
the context of the present invention. It is not to be taken as an admission that the material
discussed formed part of the prior art base or relevant general knowledge in any particular
country or region.

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:
1. A method of stemming a blast hole, the method comprising: providing a gel
type substance as a gelled length in the blast hole, as a pressure wave reflecting
stem, to increase the efficiency of an explosive during blasting with the
explosive being located in the blast hole.
2 . A method as claimed in claim 1 wherein the method includes ensuring that the
gel type substance includes a substantial quantity of water, the substantial
quantity being sufficient provide the pressure wave reflecting stem.
3 . A method as claimed in claim 2 wherein gelled length provides a structure that
operates to provide a reduction in detonation pressure, over the gelled length,
of at least 99%.
4 . A method as claimed in claim 2 wherein gelled length provides a structure that
operates to provide a reduction in detonation pressure, over the gelled length,
of at least 98%.
5 . A method as claimed in claim 2 wherein gelled length provides a structure that
operates to provide a reduction in detonation pressure, over the gelled length,
of at least 90%.
6 . A method as claimed in any one of claims 1 to 5 wherein method includes
providing the gel type substance in the blast hole as a gelled water column that
freely contacts the walls of the blast hole.
7 . A method as claimed in any one of claims 1to 6 wherein the gel type substance
is unrestrained so as not to be contained in a plug structure that limits the gelled
length to exert increased pressure on the walls of the blast hole.
8 . A method as claimed in one of claims 1 to 7 wherein providing a gel type
substance comprises providing a super absorbent polymer gel; and the method
includes pumping the super absorbent polymer gel into the blast hole to create
a gelled column of water.
9 . A method as claimed in any one of claims 1 to 8 wherein providing a gel type
substance comprises providing a super absorbent polymer gel having
hydrophilic and other properties allowing the gel to contact the explosive.
10. A method as claimed in claim 8 or 9 wherein the method includes ensuring that
a zero to near zero interstitial free water volume is provided between the swollen
particles of the super absorbent polymer gel, over a substantial portion of the
gelled length; the zero to near zero interstitial free water volume serving to
reflect the pressure wave from the explosive.
11. A method as claimed in claim 8, 9 or 10 wherein the method includes pumping
the super absorbent polymer gel into the blast hole to proactively fill fissures in
the wall of the blast hole.
12. A method as claimed in any one of claims 8 to 11 wherein the method includes
ensuring that the super absorbent polymer gel is substantially water absorbed,
at least along a substantial portion of the gelled length of the super absorbent
polymer gel.
13. A method as claimed in any one of claims 8 to 12 wherein the method includes
ensuring that the super absorbent polymer gel is fully reacted before pumping.
14. A method as claimed in any one of claims 1to 13 including providing the gelled
length as a length having a vertical height of at least 100mm.
15. A method as claimed in any one of claims 1to 14 including providing the gelled
length as a length of at least 150mm.
16. A method as claimed in any one of claims 1to 15 including providing the gelled
length as a length of at least 200mm.
17. A method as claimed in any one of claims 1to 16 including providing the gelled
length as a length of at least 500mm.
18. A method as claimed in any one of claims 1to 17 including providing the gelled
length as a length of at least lm.
19. A method as claimed in any one of claims 1to 18 including providing the gelled
length as a length of at least 2m.
20. A method as claimed in any one of claims 1to 19 including providing the gelled
length as a length of at least 3m.
2 1. A method as claimed in any one of claims 1to 20 including providing the gelled
length as a length of between 1 and 4 meters.
22. A method as claimed in any one of claims 1 to 2 1 including providing the gel
type substance with a specific gravity of between or equal to 1 and 2 .
23. A method as claimed in any one of claims 1 to 2 1 including providing the gel
type substance with a specific gravity of greater than 1.0.
24. A method as claimed in any one of claims 1 to 23 wherein the method includes
forming the gel type substance by combining a super absorbent polymer with
brackish waste water having a total dissolved solids between 100 to 5000 mg/L.
25. A method as claimed in any one of claims 1 to 23 wherein the method includes
forming the gel type substance by combining a super absorbent polymer with
saline waste water having a total dissolved solids greater than 5000 mg/L.
26. A method as claimed in any one of claims 1to 25 wherein gelled length provides
a structure that operates to provide a reduction in the velocity of detonation of
at least 60%.
27. A method as claimed in any one of claims 1to 25 wherein gelled length provides
a structure that operates to provide a reduction in the velocity of detonation of
at least 50%.
28. A method as claimed in any one of claims 1to 25 wherein gelled length provides
a structure that operates to provide a reduction in the velocity of detonation of
at least 40%.
29. A method as claimed in any one of claims 1to 25 wherein gelled length provides
a structure that operates to provide a reduction in the velocity of detonation of
at least 30%.
30. A method as claimed in any one of claims 1to 25 wherein gelled length provides
a structure that operates to provide a reduction in the velocity of detonation of
at least 20%.
31. A method as claimed in any one of claims 1to 30 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 80%.
32. A method as claimed in any one of claims 1to 30 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 70%.
33. A method as claimed in any one of claims 1to 30 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 60%.
34. A method as claimed in any one of claims 1to 30 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 50%.
35. A method as claimed in any one of claims 1 to 30 gelled length provides a
structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 40%.
36. A method as claimed in any one of claims 1 to 30 gelled length provides a
structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 30%.
37. A method as claimed in any one of claims 1 to 30 gelled length provides a
structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 20%.
38. A method as claimed in any one of claims 1to 30 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 10%.
39. A blast hole arrangement comprising: an explosive and a gel type substance in
a blast hole; the gel type substance providing a gelled length as a pressure wave
reflecting stem in the blast hole to increase the efficiency of the explosive in the
blast hole during blasting.
40. A blast hole arrangement as claimed in claim 39 wherein the gel type substance
includes a substantial quantity of water, the substantial quantity being sufficient
to reflect the pressure wave from the explosive.
4 1. A blast hole arrangement as claimed in claim 40 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 99%.
42. A blast hole arrangement as claimed in claim 40 wherein gelled length provides
a structure that operates to provide a reduction in detonation pressure, over the
gelled length, of at least 98%.
43. A method as claimed in claim 40 wherein gelled length provides a structure that
operates to provide a reduction in detonation pressure, over the gelled length,
of at least 90%.
44. A blast hole arrangement as claimed in any one of claims 39 to 43 wherein the
gel type substance forms a gelled water column that freely contacts the walls of
the blast hole.
45. A blast hole arrangement as claimed in claim 44 wherein the gel type substance
is unrestrained so as not to be contained in a plug structure that limits the gelled
length to exert increased pressure on the walls of the blast hole.
46. A blast hole arrangement as claimed in any one of claims 39 to 45 wherein
gelled length provides a structure that operates to provide a reduction in the
velocity of detonation of at least 60%.
47. A method as claimed in any one of claims 39 to 45 wherein gelled length
provides a structure that operates to provide a reduction in the velocity of
detonation of at least 50%.
48. A method as claimed in any one of claims 39 to 45 wherein gelled length
provides a structure that operates to provide a reduction in the velocity of
detonation of at least 40%.
49. A method as claimed in any one of claims 39 to 45 wherein gelled length
provides a structure that operates to provide a reduction in the velocity of
detonation of at least 30%.
50. A method as claimed in any one of claims 39 to 45 wherein gelled length
provides a structure that operates to provide a reduction in the velocity of
detonation of at least 20%.
51. A blast hole arrangement as claimed in any one of claims 39 to 50 wherein the
gel type substance comprises a super absorbent polymer gel that has been
pumped into the blast hole to create a gelled column of water.
52. A blast hole arrangement as claimed in any one of claims 39 to 5 1 wherein the
gel type substance comprises a super absorbent polymer gel having hydrophilic
and other properties allowing the gel to contact the explosive.
53. A blast hole arrangement as claimed in any one of claims 5 1 or 52 wherein a
zero to near zero interstitial free water volume is provided between the swollen
particles of the super absorbent polymer gel, over a substantial portion of the
gelled length; the zero to near zero interstitial free water volume serving to
reflect the pressure wave from the explosive during blasting.
54. A blast hole arrangement as claimed in any one of claims 5 1 to 53 wherein the
super absorbent polymer gel extends into fissures in the wall of the blast hole to
fill the fissures.
55. A blast hole arrangement as claimed in any one of claims 5 1 to 54 wherein the
super absorbent polymer gel is substantially water absorbed, at least along a
substantial portion of the length of the super absorbent polymer gel.
56. A blast hole arrangement as claimed in any one of claims 5 1 to 55 wherein the
super absorbent polymer gel is substantially reacted with water before pumping.
57. A blast hole arrangement as claimed in any one of claims 39 to 56 wherein the
gelled length has a height of at least lm.
58. A blast hole arrangement as claimed in any one of claims 39 to 57 wherein the
gelled length has a height of at least 2m.
59. A blast hole arrangement as claimed in any one of claims 39 to 58 wherein the
gelled length has a height of at least 3m.
60. A blast hole arrangement as claimed in any one of claims 39 to 59 wherein the
gelled length has a height of between 1 and 4 meters.
6 1. A blast hole arrangement as claimed in any one of claims 39 to 60 wherein the
gel type substance has a specific gravity of between or equal to 1 and 2 .
62. A blast hole arrangement as claimed in any one of claims 39 to 6 1 wherein the
gel type substance has a specific gravity greater than 1.0.
63. A blast hole arrangement as claimed in any one of claims 39 to 62 wherein the
gel type substance is formed by combining a super absorbent polymer with
brackish waste water having a total dissolved solids between 100 to 5000 mg/L.
64. A blast hole arrangement as claimed in any one of claims 39 to 63 wherein the
gel type substance is formed by combining a super absorbent polymer with
saline waste water having a total dissolved solids greater than 5000 mg/L.