Note: Descriptions are shown in the official language in which they were submitted.
AECI 748/761/765
PUMPABLE STEM~lING
THIS INVEN IION relates to the stemming of boreholes containing explosives.
~ore particularly it relates to a method of sternming a borehole, and to a stemming
system suitable for stemrning a borehole containing a flowable explosive such as an
emulsion explosive.
S According to the invention, there is provided a method of sternming a borehole
having a mouth and a blind end and containing a charge of explosive loaded therein,
which method comprises inserting a plug of stemrning material from a bulk supply in a
flowable state along a conduit into the borehole, between a charge of explosive loaded
into the borehole and the mouth of the borehole, and so that it forms a plug which closes
off the borehole by engaging the wall of the borehole.
By a bulk supply is meant a supply sufficient for stemrning a plurality of boreholes,
present as a continuous mass, eg in a container or in the forrn of a heap or from
continuous production thereof.
According to the inve~tion, the material of the plug fills the cross-section of the
borehole and conforms with surface irregularities of the wall of the borehole, the plug
being inserted so that it fills a desired length of borehole. If the plug sets, engagement
between these irregularities and complementary irregularities on the plug grip the plug
longitudinally in position. The plug can thus act to retain explosive in position in the
borehole, and, at least momentarily, can keep the borehole closed when the explosive is
detonated, thereby to render the detonation more effective in producing heave in the
surrounding rock or other material, before the plug is ejected from the borehole mouth
by the detonation. However, the plug need not necessarily set, and provided that,
although remaining in the flowable state, the flowable material remains as a plug which
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fills the cross-section of the borehole for long enough to permit detonation before it
slumps, engagement between the plug and irregularities of the borehole wall can permit
the plug adequately to keep the borehole closed during detonation.
Inserting the plug into the borehole may be via a said conduit in the form of a
S flexible hose, from said supply thereof, the hose being cormected to a displacement device
which urges the material from the supply along the hose, such as a pump, auger, piston
and cylinder assembly, or the like. Inserting the plug may be such that it issues from the
conduit at an elevated pressure, so that the plug fills the cross-section of the borehole and
engages the wall thereof along the length of the plug, typically at or adjacent the explosive
10 and/or at or adjacent the mouth of the borehole, the method including selecting a said
flowable material of a consistency which resists slumping of the plug until the explosive
has been detonated.
The method may include causing or allowing the stemming material to set so that
it forms a non-flowable said plug.
According to another aspect of the invention there is provided a system for
stemming a borehole having a mouth and a blind end and containing a charge of
explosive loaded therein, the system comprising a bulk supply of flowable stemrning
material and a displacement device having an outlet connected to a conduit, for inserting
the stemming material from the supply along the conduit into the borehole.
The displacement device may be selected rom pumps, augurs and piston and
cylinder assemblies.
Various possibilities exist for the sternming material.
Thus, the stemming material may comprise a pumpable mixture of water and an
inert filler material such as sand, and at least one flow-modifying agent selected from
suitable gelling agents and thickening agents, which agents may be selected from:
alginates such as propylene glycol a]ginate;
oxides and/or oxyhydroxides of aluminium such as A1203 or AlOOH;
aluminium carboxylates such as aluminium monostearate;
animal glues;
benzylidene sorbital;
colloidal organic compounds such as polyacrylarnide;
natural gums such as guar gum optionally cross-linked with one or more cross-
linking additives such as antimony potassium tartrate/zinc chromate, potassium
pyroantimonate (with or without thiourea or citric acid), borax, or salts of
transition metal iOllS, such as those of cerium, tellurium or titanium; and cross-
linking agents such as diammonium phosphate or tartaric acid may also be used;
pectinic substances;
derivatives of silica such as silicates;
modified starches such as polysaccharides;
clays such as bentonite;
cellulosic compounds such as sodium carboxymethyl cellulose; and
synthetic polymers such as poly(methylmethacrylate).
A suitable settable gelling agent/thickening agent is that sold under the Trade Mark
'Terrasorb' by Soil Services - a division of AECI Industrial Chemicals Limited, and the
synthetic polyacrylamide sold by the same supplier under the Trade Mark 'Synpol' can be
used instead.
Instead, the stemrning material may comprise a multi-component settable mixture.The multi-component settable mixture may comprise a two-component liquid
polyurethane mixture containing up to 80æ by mass of a suitable inert filler material such
as sand or particulate calcium carbonate. Thus, while in principle no inert filler material
need be used, it will usually be used as it can increase the bulk and volume of the settable
mixture at low cost without unacceptably affecting the setting and stemming properties
of the rnixture. The components may be selected such that they set to form a plug which,
as desired can be more or less flexible on the one hand, or more or less rigid on the
other, and the plug can be either solid or of porous foamed consistency. In this case the
components and the filler material may be mixed prior to insertion, eg by pumping, into
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the borehole before the II~ixture has set; or they may be mixed during said insertion into
the borehole.
Further possibilities for the stemn~ing material include pumpable mixtures of aninert filler material such as sand together with one or more of the following non-aqueous
liquids:
synthetic resins such as polyester resins, polyvinyl compounds, epoxy resins andfuran compounds, examples being polyvinyl resins and alcohols, which alcohols are
optionally cross-linked with one or more cross-linking additives such as glyoxal, urea-
formaldehydes or melamine formaldehydes;
vulcanizable oils such as unsaturated oils;
bituminous compositions or similar compounds whose viscosity alters substantially
with heating; and
non-aqueous solutions containing, as solutes dissolved therein, bituminous
compositions or epoxy resins.
Instead, emulsions may be mixed with the inert filler material such as sand, theemulsions comprising an aqueous phase emulsified with an organic phase selected from
one or more of:
biturninous compositions;
epoxy resins;
polyester resins;
polyvinyl compounds as described above;
latexes; and
paraffin waxes.
Instead, colloidal suspensions in water may be employed with an inert filler
material, the suspended colloidal particles being selected from one or more of the
following organic materials:
alginate bases;
cellulose-derived bases such as sodium carboxyrnethyl-cellulose salts;
starch bases;
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protein bases such as gelatin;
casein bases;
polyvinyl pyrrolidone bases.
Furthermore, mineral colloids having suspended mineral colloid particles such asS bentonite grouts or similar clay grouts may be employed.
Instead, a fast-setting grouting system, eg a cementitious grouting system, may be
employed, for example whereby the mixture of high-alumina cement and fly-ash,
optionally containing an accelerator such as calcium chloride, is pumped into the
borehole, the accelerator optionally being pumped into the borehole as a separate stream
and mixed into the rnixture as it enters the borehole.
Other materials and additives which may be incorporated into such grouting
systems include one or more of:
gypsum;
quicklime;
silica derivatives such as silica fume and silica gel;
aL~ali metal silicates such as sodium silicate in aqueous solutions;
fluorosilicates;
powdered slags such as blast furnace slag;
mine waste slurries;
kaolin;
asphalt;
expanded clays such as expanded bentonite;
resins such as polyacrylamide and polyacrylate resins;
triethanolamine;
ammonium persulphate;
aluminium phosphate;
ethylene glycol;
dibutyl phthalate;
copolyrners of organic compounds;
latexes; and
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starches such as corn starch.
In addit;on, particular additives may be incorporated into the grouting systems, selected
from:
retarders such as boric acid;
water reducing agents such as ~alcium lignosulphonate;
expanders such as atomized aluminium;
carbonates and bicarbonates such as those of calcium;
foaming agents such as calcium silicone;
plasticizers such as formaldehyde- and melamine resins;
air entraining agents such as sodium lauryl sulphate; and
cellulosic agents such as hydroxylethyl cellulose.
In a preferred case, the stemming material comprises a mixture of a silicate, such
as an alkali metal silicate, water and an inert filler material, such as sand, the setting
agent being carbon dioxide or the like. The mixture is inserted into the borehole to form
the plug, and is hardened in place by the setting agent which reacts with the silicate to
cause it to set.
In one version of this possibility, a pumpable mixture of aqueous sodium silicate
solution with sand is employed, together with a suitable setting agent such as sodium
bicarbonate, sodium aluminate, a settable organic ester, or the like. In this case the
setting agent can be admiYed into the mixture immediately before pumping of the plug
into the borehole, or it can be added as a separate stream in an aqueous solution during
the pumping and admLYed during the pumping. Suitable pumpable mixtures have a
moisture content of 10 - 50% by mass, preferably 15 - 25% by mass, the proportions of
sodium silicate and setting agent used being selected by routine experimentation to
achieve an acceptable degree of hardening after a desired time.
As indicated above, in a preferred version of this possibility the setting hardening
agent is carbon dioxide. In this case an aqueous sodium silicate solution can be admixed
with the filler material to form a damp porous mouldable but flowable particulate
mixture, having a moisture content of 0,25 - 30% by mass, preferably 1,0 - 3,0% by mass,
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the mixture comprising 0,1 -20% by mass sodium silicate on a dry basis. This mL~ture can
then be forced into the borehole along a conduit from a buL~ supply into the borehole to
form a plug, eg by means of a displacement device such as an auger or piston alld cylinder
assembly, after which carbon dioxide gas is blown at a suitable pressure into the pores of
5 the mixture, eg via a pipe provided with a tubular probe such as a narrow lance or nozzle
which is inserted into the plug, from a carbon dioxide store or carbon dioxide generator.
Mouldable bulk mixtures of sand and aqueous sodium silicate have a shelf-life of1-2 days, which can be extended if air is excluded, eg by packing in a hermetic container,
and can be transported to the site of use in bulk from a central mixing station.
Additional aqueous solutions, which may be incorporated into the abovedescribed
mixtures of alkali metal silicates, water and inert filler material such as sand, include
aqueous solutions of one or more of the following:
rnineral products other than alkali metal silicates and including ethyl- or methyl
silicates, silicate derivatives, fluorosilicates, alumina (A1203), and magnesia (MgO);
derivatives of lignosulphite or tannin;
other plant derivatives including colophane-type natural resins such as rosin and
vinsol, and resins derived from furfuryl such as furfurylidene acetone and furfuryl alcohol;
acrylamide derivatives such as polyacrylarnide/polyacrylate systems, including
polymer systems cross-linked by reaction compounds such as N,N-methylene bisacrylamide0 and acrylamide monomers;
phenoplasts such as resorcinol-formaldehyde;
aminoplasts such as urea-formaldehyde; and
combination grouts such as sodium silicate mixed with acrylamide resin, or sodium
silicate and/or lignochrome rnixed with phenoplasts.
The various grouting systems described above may be combined in various ways.
Examples of these combinations are:
inert ~ïller materials such as sand together with aqueous solutions and aqueous
colloidal suspensiorls, an example being sand together with a silicate solution and a
bentonite colloidal suspension;
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inert filler materials together with a mixture of an aqueous solution and an
emulsion, optionally together with a colloidal suspension, an example being sand mixed
with a dilute sodium silicate solution together with an ultracolloidal bentonite suspension,
a polyphosphate- or tannin-type peptizer and a sodium silicate setting reagent;
S inert filler material together with a phenoplast and an emulsion, an example being
sand with an aqueous solution of an acrylic resin and a bentonite suspension.
Flame retardants may be incorporated into any of the above stemrning
formulations. Such flame retardants may be selected from one or more of the following:
chlorinated hydrocarbons such as chlorendic acid;
1~) brominated hydrocarbons such as decabromo-diphenyl oxide;
antimony trioxide (Sb4O6);
borates such as zinc borate or boric acid/sodium borate mixtures;
brominated bisphenol A's such as tetrabromobisphenol A;
aluminium oxide;
molybdenum oxide;
arnmonium salts of sulphuric- phosphoric- and/or hydrochloric acid, with our
without borax;
calcium carbonate or -bicarbonate;
halide salts of alkaline earth metals such as calcium chloride; and
halide salts of aLkali metals such as sodium chloride.
Furthermore, flow enhancers such as talcum powder can be blended into the
various stemming materials to irnprove their workability, llow properties or the like.
The invention will now be described, by way of example, with reference to the
accompanying diagrammatic drawings, in which:
Figure 1 is a schematic flow diagram of a system employing the method of the
present invention; and
Figures 2 and 3 show respectively schematic diagrams of displacement devices forinserting a plug of mouldable settable stemming mixture into a borehole.
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In Figure 1 of the drawings, reference numeral 10 generally designates a system
in accordance with the invention, for stemming a borehole containing a charge ofemulsion explosive loaded therein. In Figure 1 a foot wall of a mine is designated 12, and
a stope face is shown at 14, having a borehole 16 bored therein, the borehole having a
5 blind end 18 and a rnouth 20.
Displacement means (described in more detail hereunder with reference to Figure
2 and 3) for inserting a plug of stemming material is designated 22, and has a flexible
outlet hose 24. The borehole 16 is shown containing a charge 26 of emulsion explosive
previously loaded therein, and a plug 28 of stemming material. Adjacent the borehole is
10 shown a cylinder 30 containing compressed carbon dioxide, having a flexible outlet hose
32 provided at its free end with a hollow tubular probe 34.
In Figure 2 the displacement device of Figure 1 is generally designated 22 and
comprises an auger 36 driven by an electric motor 38 and housed in a tubular casing 40.
The casing 40 has an inlet chute 42 and an outlet at 44 leading into the flexible hose 24.
15 In Figure 3, where the same reference numerals designate the same parts as in Figure 2,
unless otherwise specified, the casing 40 is in the form of a cylinder and the auger 36 and
motor 38 of Figure 2 are replaced by a piston 46 having a piston rod 48 reciprocable in
the direction of arrow 50, to form a piston and cylinder assembly.
In accordance with the method of the invention a buLIc supply of stemming material
20 is prepared by n~ixing . This supply is in the form of a mixture of clean silica sand of an
average particle size of 90 ~m, such as that used for sand moulds in the casing of
aluminium shapes, mixed with an aqueous sodium silicate, to obtain a damp mouldable
and flowable sand comprising 2,3 % by mass sodium silicate on a dry basis, and having
a moisture content of 2,5 ~o by mass. The stemming material is taken underground in the
25 mine in bulk, where it has a shelf-life of 1-2 days, together with a store of carbon dioxide
in gas cylinders (see 30 in Figure 1) under pressure.
In a typical case the borehole 16 is bored in the stope face 14 and is loaded with
a gas-sensitized emulsion explosive 26 in known fashion, a fuse and detonator (not shown)
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being placed in position in the borehole for detonating the explosive. As soon as
convenient thereafter, the plug 28 is inserted into the borehole 16, between the explosive
26 and the mouth 20 of the borehole, using the displacement device æ.
When the device 22 is in accordance with Figure 2 the stemming material is loaded
S into the chute 42 and the motor 38 is used to rotate the auger 36 to force the stemming
material along the casing 40 to the outlet 44 and via said outlet 44 into and along the
hose 24. Stemming material issues from the free end of the hose 24, which is located in
the borehole 16 adjacent its mouth 20, to insert the plug 28 in position there as shown.
When the device 22 is according to Figure 3, the piston and cylinder assembly is extended
10 (dashed lines) prior to loading stemming material into the chute 42, after which the
assembly is contracted so that the piston 46 forces the stemming material in sirnilar
fashion along the casing 40 into the hose 24 via the outlet 44, the capacity of the cylinder
being selected so that a simple stroke of the piston 46 conveniently delivers an entire plug
28 of sternming material to the borehole 16.
When the plug 28 is in place the hose 24 is withdrawn from the borehole 16 and
the probe 34 is inserted into the plug. A valve 52 on the cylinder 30 is opened, and a
desired amount of carbon dioxide is blown into the plug 28 via the hose 32 and probe 34.
This carbon dioxide enters the pores in the mixture and reacts with the sodium silicate
in the plug 28 to cause it to set and harden, after which the explosive 26 can be
20 detonated.
It should be noted that the stemming material is forced into the borehole with
sufficient force for the plug to occupy the full cross-section of the borehole over a desired
length, stemrning material flowing into and engaging with surface irregularities on the
borehole wall, so that when the plug sets, complementary irregularities are formed on the
25 plug surface which lock the plug in position in the borehole 16 against longitudinal
movement out of the borehole mouth 20.
The consistency of the plug 28 is such that it can be made resistant to slumpingand can retain the emulsion explosive in the interior of the borehole, even for upwardly
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extending boreholes whose mouths 2~ are lowermost, which retention is improved by
setting of the plug. More importantly however, the set plug upon detonation of the
explosive contains the detonation momentarily to promote good heaving of the rock 54
surrounding the borehole. Furthermore, upon detonation, the physical presence of the
S plug in the mouth 20 of the borehole 16 can act, at least partially, to douse the flash
caused by the detonation, which dousing is promoted by steam generation arising from
moisture in the plug 28 or by means of the explosively inert nature of the stemming
material eg sand particles. When the explosive is sensitized by gas bubbles formed in situ
from a gassing solution, the plug can be spaced from the explosive, to allow expansion of
10 the explosive as the gas bubbles form, and desensitizing of part of the explosive by
ramming a solid plug against the explosive during tamping can be avoided or at least
reduced.
The Applicant has, furthermore, carried out tests using a non-setting stemming
material, and using apparatus substantially as shown in the drawings, but, naturally,5 omitting the carbon dioxide cylinder 30. This stemming material comprised:
0,7% by mass SYNPOL (Trade Mar}~) polyacrylamide;
66,2% by mass plaster sand; and
33,1~o by mass water.
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