US3791255A

US3791255A - Method of filling boreholes with viscous slurried explosives

Info

Publication number: US3791255A
Application number: US00216431A
Authority: US
Inventors: R Fox; D Williams; A Wisinski
Original assignee: ICI Australia Ltd
Current assignee: Orica Ltd
Priority date: 1971-01-18
Filing date: 1972-01-10
Publication date: 1974-02-12
Anticipated expiration: 1991-02-12
Also published as: DE2202246B2; DE2202246C3; DE2202246A1; GB1344773A; CA959316A; ZA72100B; PH11042A; BE778210A

Abstract

A method of filling a void with a viscous product prepared by mixing two or more free flowing materials which method comprises firstly supplying separate streams of said free flowing material to the required position in a void and secondly mixing the separate streams at said required position to form the said viscous product in situ within said void. Apparatus used in the operation of the method is also described.

Description

waited States Patent Fox et a1. Feb. 12, 1974 METHOD OF FILLING BOREHOLES wiTii 3,523,048 s/1970 HoplerJr ..149/44 X v scous IE EXPLOSIVES 3,409,486 11/1968 Partridge 149/44 X 3,619,308 11/1971 Caldwell et al. 86/20 C [751 Inventor h r F Hawthorn; Darrell 3,676,236 7/1972 Kilma et a1. 149 44 x Andrew Williams, West Heidelberg; Adam Prus Wisinski, Parkdale, Vi toria, ll f A tr li Primary Examiner-Leland A. Sebastian [73] Assigneez 1C1 Ausl fa Limied victoria, Attorney, Agent, or FtrmCushman, Darby &

Australia Cushman [22] Filed: Jan. 10, 1972 [21] App]. No.: 216,431

[57] ABSTRACT [30] Foreign Application Priority Data Jan. 18, 1971 Australia 3736/71 A method of filling a void with a viscous product prepared by mixing two or more free flowing materials [52] U.S. Cl. 86/20 C, 149/19, 149/21, which method comprises firstly supplying separate 149/22, 149/44, 149/92, 149/114 streams of said free flowing material to the required [51] int. Cl. C061) 119/00, C06b 19/04 position in a void and secondly mixing the separate [58] Field of Search 149/44; 86/20 C streams at said required position to form the said viscous product in situ within said void. Apparatus used [56] I References Cited in the operation of the method is also described.

UNITED STATES PATENTS 3,473,983 10/1969 Cook et a1. 149/44 X 5 Claims, 3 Drawing Figures METHOD OF FILLING BOREHOLES WITH VISCOUS SLURRIED EXPLOSIVES This invention relates to a method of filling voids with viscous material, to an apparatus of use in the filling of voids with such material, and to new composite structures.

It is often necessary to fill voids such as boreholes or cracks and other cavities with material which is too viscous either to flow down the void by the force of gravity or to be pumped into position with pumps of conventional construction using hoses small enough to fit into the void.

Even if the void is large enough to allow the insertion of a hose of large diameter, the use of such a hose has the disadvantage that the total weight of hose and contents is greater than if a small hose is used; conse quently it will be more difficult to manipulate the hose and contents and also the amount of material remaining in the hose on withdrawal from the void will be greater. in many cases this material will solidify and therefore be wasted.

In mining operations it is often desired to fill boreholes with a viscous slurried explosive such as a crosslinked slurried explosive composition. The crosslinked material is preferable in such operations because it has a greater resistance to leaching by underground water. Another major advantage of highly viscous slurried explosives is that the explosive will not flow under the force of gravity and therefore the slurry will be selfsupporting and stay in position in boreholes which are either horizontal, inclined at an angle upwardly or even run vertically upwardly into the roof of a mine. Such upwardly inclined holes are known as up-holes. In the past it has been found very difficult to fill upholes with a satisfactory slurried explosive since any free-flowing material, under gravity, will run out from the hole. To remain in situ the material requires such as high viscosity that it is too viscous to be pumped through hoses which will fit into the normal bore-holes used in underground mining operations. Conventionally this difficulty has been overcome by cartridging the explosives in cardboard or the like containers. The cartridges have been then loaded manually into the hole. Such systems have disadvantages of higher cost, incomplete filling of the cross-sectional area of the bore-hole and in the case of cardboard cartridges susceptibility to slumping under moist conditions. A further disadvantage is that the manual loading of cartridges is timeconsuming.

Although it might have been possible in the past to fill at least downholes (i.e., holes which are inclined downwardly at an angle from the horizontal) with a free flowing blasting slurry the resultant explosive charge has often been unsatisfactory as the hydrostatic pressure caused the lower portion of the slurry to be come desensitised.

In the past there has also been a practical lower limit to the size of a bore-hole which can be filled with a cross-linked slurried explosive composition. The pressure required to pump material through a hose increases as the length of the hose increases and the diameter of the hose decreases, and in practice it has not been found possible to fill boreholes completely with a highly viscous crosslinked slurried explosive composition when the diameter of such holes is less than 3 inches and the length is greater than about feet without causing the slurry to become desensitised. Such a limitation severely curtails the use of crosslinked slurried explosives. In underground mining operations, in

particular, the size of bore-holes employed is often less 5 than 3 inches in diameter; consequently cross-linked slurried explosives could not in the past be used in such small holes.

It has also been found difficult in the past to fill other constricted voids with polymeric material if the polymeric material was too viscous to be easily pumped into the void using conventional pumps and hoses. The more constricted the void to be filled the greater has been the difficulty of filling the void completely with viscous product such as, for example, foamed polymers.

We have now found a method whereby even constricted voids of small diameter may be filled completely with viscous products.

Accordingly, we provide a method of filling a void with a viscous product prepared by mixing two or more free flowing materials which method comprises firstly supplying separate streams of said free flowing material to a required position in a void and secondly mixing the separate streams at said required position to form the said viscous product in situ within said void.

By viscous product we mean any material which is too viscous to be pumped through a conventional hose from the pump into the void and which may be formed by mixing two or more free flowing materials as defined hereinbelow.

Our invention is of particular use when the viscous product is formed quickly on mixing the free flowing materials. In the past it has been particularly hard to handle mixtures of interacting free flowing materials if the viscosity rises substantially within a few seconds of mixing.

By free flowing materials we mean throughout this specification materials which may be pumped through conventionally constructed hoses inserted into the void to be filled and which, on mixing, will interact to form a viscous product.

Suitable viscous products are, for example, crosslinked slurried explosives, polyurethane foam, epoxy resin, polymeric material prepared by mixing, for example, a monomer such as methyl methacrylate with a catalyst such as benzoyl peroxide and polymeric material prepared by mixing a polymer with a crosslinking agent.

Suitable voids are, for example, blast-holes in mining operations, tubes, cartridges, cavities in buildings, holes and cracks in masonry and rocks, and the voids left in rocks by underground mining operations.

Our invention may also be employed in filling voids such as foundations with quick setting cement, in manufacturing and laying sealant strips in large concrete structures such as dams and also in laying long strips of explosive charges by the known technique of mole ploughing. In mole ploughing with explosives; highly sensitised, highly viscous ammonium nitrate slurry can be laid safely if the sensitising agent, e.g., aluminium powder, is added by the apparatus of our invention to the slurry at the point of mixing and laying the charge. The danger of a premature explosion of a preformed highly sensitive explosive slurry is thereby minimised.

A further embodiment of our invention is in the production of foams for fire-fighting purposes in confined areas.

In a further, preferred embodiment the viscous product is a viscous slurried explosive and the void is a borehole in a rock structure, in particular when the borehole is less than 3 inches in diameter and more than feet in length. The boreholes may be inclined in any direction including up-holes.

Slurried explosives normally comprise at least one oxygen releasing salt selected from the group consisting of inorganic nitrates, and perchlorates and mixtures thereof, a thickening agent, a fuel and water. Optionally additives, for example agents increasing sensitivity and fuel content, may be added.

We prefer that the oxygen releasing salt be chosen from the nitrates of the alkali metals or ammonium and of these we prefer ammonium nitrate and sodium nitrate. The amount of oxygen releasing salt in our com positions is not narrowly critical; we have found that compositions containing amounts of oxygen releasing salts from 50% w/w to 90% w/w of the total composition are satisfactory. The particle size and shape of the oxygen releasing salt is not critical and is well known from the art of ammonium nitrate manufacture; powders and prilled particles are satisfactory.

The nature of the fuels in such compositions is determined by t he requirements that they burn in the presence of oxygen or an oxygen containing gas and that their physical nature is such that they may be incorporated in such compositions in a manner so as to be substantially uniformly distributed throughout the compositions. Such fuels are well known in the art and they may be organic or inorganic and may also be derived from animals and plants.

The fuels employed in such compositions can be, for example, self-explosive fuel, non-explosive carbonaceous, non-metallic and metallic fuels or mixtures of the aforementioned types of fuels. They can be varied widely provided that, in the composition in which any particular fuel is used, the fuel is stable, that is, prior to detonation, during preparation and storage, the fuel is chemically inert to the system. Examples of selfexplosive fuels include one or more organic nitrates, nitro compounds and nitramines such as trinitrotoluene, cyclotri (or tetra) methylene tri (or tetra)- nitramine, tetryl, pentaerythritol tetranitrate, explosive grade nitrocellulose and nitrostarch.

The self-explosive fuel can be for example in any of the well-known flake, crystalline or pelleted forms. In general up to 35 percent and preferably from 10 to 30 percent by weight based on the weight of composition of self-explosive fuel is used.

Suitable water soluble fuels are organic water soluble substances, for example urea, carbohydrates such as sugars or molasses, water soluble alcohols or glycols, glues or mixtures of these. The proportion of water soluble fuel in such compositions should be at least 0.8% w/w and may be as high as 8% w/w of the total composition.

Suitable water insoluble or sparingly water soluble fuels may be chosen from inorganic materials for example sulphur, aluminium, silicon, magnesium, titanium, boron, mixtures thereof and mixtures of aluminium with ferrosilicon or organic materials for example finely divided charcoal, anthracite, gilsonite, asphalt, cellulosic materials such as sawdust, or cereal products for example flours, dextrins or starches. When the inorganic fuel is a metal it is preferably in powder form ranging in particle size from very fine, for example a powder passing a 200 8.8.8. sieve, to coarse, for example a powder retained on a 30 B.S.S' sieve. In particular aluminium powder passing a 300 B.S.S. sieve, for example paint fine aluminium having a hydrophobic coating, may often be used with advantage as a fuel; it also acts as a sensitiser. The proportion of water insoluble or sparingly water soluble non-metallic fuels in such compositions should be in the range from 1% w/w to 10% w/w of the total composition. The proportion of metallic water insoluble fuels, such as aluminium, when present in such compositions may be as high as 25% w/w and amounts in the range from 1% w/w to 15% w/w of the total composition are preferred.

The proportion of water in such compositions should be sufficient to dissolve at least part of the water soluble fuel when present, and part of the oxygen releasing inorganic salt, say from 5% w/w up to 35% w/w, but not be in excess of the explosive limit of the composition. We prefer that the water be in the range from 5% w/w to 25% w/w of the total composition and more preferably in the range from 8% w/w to 15% w/w of the total composition.

Many thickening agents are known which have been employed with varying degrees of success, either alone or in combination, in water-bearing explosive slurries. amongst these may be mentioned galactomannan polysaccharides such as guar gum, Tara and Paloverde gums, pregelatinised starches, hydroxyethylcellulose, carboxymethylcellulose, tamarind seed flour and hydrophilic vinyl polymers such as polyacrylamide. The most widely used of these thickening agents have been the galactomannans, particularly guar gum.

For use in our invention the final viscosity increase must be made in situ by mixing two or more free flowing components. For example when compositions comprising polysaccharides such as guar gum are mixed with appropriate cross-linking agents, the viscosity of the composition is increased. Any of the known crosslinking agents conventionally employed for galactomannans can be used including potassium and sodium dichromate, sodium tetraborate, borax, certain transition metal salts and certain soluble antimony and bismuth compounds. However, alkali metal dichromates, for example sodium and potassium dichromates, are especially preferred.

The proportion of polysaccharide and conventional cross-linking agent used in preparing the thickening agent component of the viscous slurried explosives can vary over quite wide limits depending on the agent used as is well known in the art. For example, using guar gum with zinc chromate as the crosslinking agent the proportion of guar gum may vary from 0.1 to 5% w/w of total composition and the proportion of zinc chromate may vary from 0.01 to 3% of total composition.

Alternatively a mixture of sodium or potassium dichromate and a soluble iron, zinc, aluminium or antimony salt may be used. The proportion of sodium or potassium dichromate in the viscous slurried explosive should be in the range from 0.003 to 0.9% w/w, the proportion of soluble salt should be in the range from 0.001 to 0.3% w/w of the viscous slurried explosive.

In this embodiment of our invention using crosslinked thickening agents there are many alternative combinations of free flowing materials which will on mixing give a viscous cross-linked slurried explosive, for example the explosive slurry comprising water, fuel, an oxidising compound and a galactomannan is pumped in one stream down a borehole and a stream comprising a suitable cross-linking agent is pumped down in a separate second stream and mixed in the borehole to form a rapidly gelling composition.

Explosive slurries may also be thickened by the in situ polymerisation of monomers or mixtures of monomers.

Examples of monoethylenically unsaturated monomers which are suitable for use in accordance with this embodiment of our invention include amides such as acrylamide, methacrylamide and N-methylacrylamide and hydroxyalkyl derivatives such as alpha,2-hydroxyethylacrylamide and alpha-hydroxymethylacryl-amide; acids such as acrylic acid and methacrylic acid; salts of acrylic acid such as sodium, potassium or ammonium acrylate; and soluble salts of monovinylpyridines, particularly and preferably the nitrate salts of the 4- vinylpyridine. Acrylamide is a particularly preferred monomer because of its low cost and rapid polymerisation in the aqueous phase of the blasting compositions. Usually, the concentration of acrylamide used ranges from 0.3 to percent and especially from 0.5 to 5 per cent. As an example of this embodiment of our process using polymeric thickening agents the explosive slurry comprising water, fuel, an oxidising compound and a monomer or mixture of monomers is pumped in one stream down a borehole and a stream comprising a free radical polymerisation promoter or initiator is pumped in a separate stream and mixed in the borehole to form in situ a rapidly gelling composition. Suitable promoters include sodium, potassium and ammonium salts of inorganic peracids such as persulphates, perborates and pervanadates; hydrogen peroxide; and organic peroxide and azo catalysts such as azobis(isobutyronitrile), alpha, alpha'-azobis(alpha, gamma-dimethylgamma-methoxyvaleronitrile), tertiary butyl hydroperoxide, methylvinyl ketone peroxide, benzoyl peroxide and peracetic acid. Persulphates are usually preferred. Redox systems, that utilise a source of persulphate ion (S 05) as one component throughout a range of concentrations of inorganic persulphate salt, can be used alone in the solution of inorganic oxidising salt to promote the copolymerisation reaction or an added reducing agent can also be employed to form a redox couple. Reducing agents that can also be used if desired include nitrogen bases such as hydroxylamine, carbohydrazide and, particularly, hydrazine. If needed, higher rates of polymerisation are achieved at lower temperatures when the polymerisation system also includes a minor amount of metal ion, usually a Group 18 metal ion. These metal ions are introduced as soluble inorganic or organic salts, e.g., as the nitrates, sulphates or acetates. Other useful persulphate couples are HSO (S O,;) and Fe (S O and S O (S O and nitro-trispropionamide (S O In general, the total amount of promoter used varies with the particular promoter and monomers, and increases proportionately with the desired speed of polymerisation, but usually is at least 0.002 percent and preferably within the range of about from 0.002 to 3 percent based on the total weight of aqueous phase containing monomers to be polymerised, large excesses of promoter having no detrimental effect on the gel structure. The optimum concentration of the preferred persulphate ions, based on total monomers, i.e., both monoand polyethylenically unsaturated, can vary considerably depending on the particular polymerisation system, the desired consistency of the gel, and the presence or absence of supplementary promoter components, but in general will be about from 0.005 to 2 percent by weight of the aqueous phase.

It is necessary for the propagation of an explosion that the column of slurry in the borehole is continuous because the presence of voids in the slurry can cause the explosion to fail to propagate.

lt is also necessary for the propagation of an explosion that the column of slurry in the borehole is not desensitised. As the viscosity of slurried explosive compositions increases, the pressure required to pump such compositions through hoses also increases. This increase of pressure results in a reduction in the sensitivity of the slurried explosive so that the slurried explosive is no longer detonable. It has not hitherto been possible to obtain narrow boreholes filled completely with a detonable viscous slurried explosive. It has been possible in the past to bulk load narrow boreholes with an explosive powder such as a mixture of ammonium nitrate and fuel oil, the so-called AN/FO explosives. Such explosives have the disadvantage of not being waterproof; they cannot, therefore, be used in wet holes. Also their explosive power is lower than that of viscous slurried explosives. Another conventional method of charging narrow boreholes hitherto has been to fill them by pushing cartridges of explosive down the hole,

. for example, sticks of dynamite or cartridges filled with slurried explosives, nitroglycerine or other explosives, have been used. In practice, it has proved difficult to retain these cartridges in up-holes; also, it is difficult to ensure that the cartridges are pushed together tightly and do not have spaces between them. A further disadvantage is that the borehole is not fully filled with explosive but that there is of necessity a gap between the cartridge case and the wall and that the cartridge case itself takes up valuable space. Consequently, a smaller borehole having its complete cross-sectional area filled with slurried explosive formed in situ will hold as much explosive as a somewhat larger borehole filled with cartridges. The advantage of using narrow boreholes in underground mining operations is that the cost of drilling boreholes decreases rapidly with decrease in diameter of hole and in addition the size of drill rig increases with increase in diameter; large rigs are inconvenient in restricted underground passages.

Accordingly we provide a new composite structure comprising a rock structure contiguous with a continuous column of a viscous slurried explosive as hereinafter defined, said column being less than 3 inches in diameter and greater than 10 feet in length.

The columns of viscous slurried explosive may be horizontal, vertical or inclined at an angle. The columns are of particular practical use when they are inclined upwardly into the rock structure. The rock surrounding the column of viscous slurried explosive is in intimate contact with the walls of the column.

We have also devised a method of manufacturing our novel composite structures.

Accordingly we provide a method of manufacturing a composite structure comprising a rock structure contiguous with a continuous column of a viscous slurried explosive which method comprises firstly, drilling into a rock structure a narrow borehole of less than 3 inches in diameter and more than 10 feet in length, secondly, supplying separate streams of at least two free flowing components of viscous slurried explosive to the required position in the borehole and thirdly, mixing the components thoroughly at the required position in the borehole so as to obtain in situ a column of viscous slurried explosive completely filling the cross-sectional area of the borehole.

In this specification we mean by a viscous slurried explosive a composition which is sufficiently viscous to be self-supporting when placed in an up-hole, will propagate an explosion and'which can be detonated by the usual methods known in the art. It must also be possible to prepare the composition by mixing free flowing components.

The free flowing components of the viscous slurried explosive are any combination of components which are capable of being pumped into narrow boreholes but on mixing form a viscous slurried explosive.

In mining operations it is normal to load explosive charges into boreholes up to 100 feet in length. The length of hose through which the components have to be pumped may be up to 600 feet in length because conditions underground are such that often the pumps cannot be brought near to the collar of the borehole. Free flowing components of slurried explosives suitable for use in any particular application of our invention should therefore be pumpable through the length of hose required to transport the component from the pump to the end of the borehole. The column of slurried explosives must propagate an explosion and this limits the minimum diameter of the boreholes.

We also provide a novel apparatus for use in carrying out the method of our invention.

Accordingly we provide an apparatus for filling voids with a viscous product prepared by mixing two or more free flowing materials which apparatus comprises a means of supplying separate streams of free flowing material to the required position in a void in combination with a means of mixing said streams at said required position in the void.

The means of supplying separate streams of free flowing material may be any means known in the art, for example a combination of pumps and hoses. The hoses may be rigid but for many purposes flexible'hoses are more convenient. The hoses must be of such size that they may all be inserted together into the void without undue difficulty and should also be of sufficient diameter to allow the free flowing material to be pumped easily along their length. The pumps are designed so that the free flowing material may be pumped easily along the length of the hoses. The particular hoses and pumps to be used are thus interdependent.

We prefer to encase the hoses carrying the separate streams of material in an outer casing or hose. in our preferred embodiment the hose carrying the major component of the viscous product is used to encase the hoses supplying the streams of the minor components of the viscous product. Alternatively a single hose may be used comprising two or more conduits.

The means of mixing the streams of free flowing material to form the viscous product is any mixer of such dimensions that it can be inserted into the void when the mixer is attached to the end of the means for sup plying the separate streams of free flowing materials.

Preferably the mixer is of the type known in the art as an interfacial surface generator mixer. Such a mixer is characterised by having no moving parts, but the mixer comprises a plurality of interfacial surface gener- 5 ators. It is also characteristic of such mixers that they may be made in any suitable external diameter. A suitable mixer, for example, is the Static Mixer" manufactured by the Kenics Corporation of the U.S.A.

Preferably the casing of the interfacial surface generator mixer is flexible and most preferably the interfacial surface generators are built directly into the end of the hose and the hose thus forms the casing for the generators. Flexible mixers are advantageous because boreholes often are not straight but have a slight spiral twist due to movement of the drill during boring operations. A flexible mixer can follow curves in the path of the borehole.

When the apparatus is used to fill boreholes with a viscous slurried explosive, ideally the hose and mixing means should be withdrawn from the hole at, or approximately at, the rate at which it is being filled; however, it is, of course, impossible to observe the rate of charging visually and recourse must therefore be taken to indirect control, such as empirical operation or at tempts to synchronise the linear rate of withdrawal with the linear rate of filling calculated from the pumping rate. As a rule this is a coarse approximation only and often maloperation results; if the hose is withdrawn too slowly, it becomes embedded in the material and is likely to leave a columnar gap or cavity on being withdrawn or may even become permanently embedded in the slurry by excessive friction or blockages. Conversely, if the hose is withdrawn too rapidly, the material is likely to be dropped from a height above the rising surface of the slurry and entrap pockets of air or water. In most of these operations, discontinuity in the material filling of the hole is undesired or detrimental for the intended purpose.

Yet another problem is that boreholes frequently contain substantial quantities of water. Slurried explosives dropped into such holes may be adversely affected by excessive dilution; for instance, the blasting agent mixture may not be initiated by a detonator or the explosion may fail to propagate through the mixture.

These difficulties may be overcome by use of a withdrawal apparatus. Withdrawal apparatus is defined as apparatus comprising a tube which is sealingly connected to the smaller opening of a truncated conical mantle made of a material sufficiently rigid or reinforced to be incapable of inversion, which mantle is mounted coaxially with, on and around said tube at or near its lower end and the wider opening of which mantle is nearer to the bottom end of said tube, and a flexible hose connecting the inlet end of said tube to the mixing means. The tube is either sealingly attached to the mixing means or may itself be the outer case of the mixing means.

The purpose of the truncated conical mantle is to seal the hose against the wall of the borehole; thereby the cavity into which the blasting agent is being discharged is sealed, ingress of water into it is minimised and the fluid discharge pressure of the pump is exerted against the enclosed end of the hole thus producing upward thrust against the seal formed by the hose and the surrounding truncated conical mantle. Consequently the pump pressure aids or effects the raising of the hose synchronously with the rate of charging.

Preferably said conical mantle can be folded axially, downwardly but not upwardly towards the axis of said tube, so as to envelop it at least partly; in this folded down position, not unlike an inverted, folded-up umbrella, said assembly of tube and mantle may readily be inserted into the hole and subsequently on withdrawal of the hose the mantle is unfolded into its conical shape.

The material of construction of the mantle is not critical, but it must be strong enough to withstand upward thrust into the cone of up to several hundred pounds without collapsing, without being inverted upwardly and without tearing; its ability to resist upward inversion is critical and determines the choice of material,

' its thickness and its reinforcement. It may be made of rigid material, e.g., a metal or plastic sheet or, preferably, of flexible material of sufficient thickness, e.g., a rubber or polyethylene terephthalate sheet; preferably the sheet is pretreated to facilitate the operation of folding it downwards, centrally around the tube, e.g., by providing axial folds in the rubber sheet or by making the cone of a number of metal vanes slideable against each other and capable of being unfolded into a progressively wider cone.

Preferably, also, flexible truncated cones, particularly rubber sheet cones, are reinforced by rods or strips running along the length of the cone in several, say, 2, 3, 4 or 6 symmetrically placed positions; these strips may be made of particularly strong materials, e.g., spring steel and prevent inversion and expansion of the bottom opening of the cone beyond a predetermined size.

Optionally the larger opening of the truncated cone may be fitted at its widest (bottom) section with a skirt, which is an extension of the truncated cone, but is made of a more flexible material such as rubber or foam rubber sheet and may act as a sealing washer at the walls of the hole between the discharged slurry and any water above it.

The term truncated cone implies that the central angle of the cone is, at all times, less than 180, in practice preferably less than 140 and most preferably less than 120. The larger, bottom outlet of the truncated cone, in its fully unfolded position forms a circle or quasicircle having a diameter which approximates the diameter of the borehole, but which is characterised in that it is substantially smaller than 2 l, where 1 is the length of the conical mantle. By this means the above stated angles cannot be exceeded. Consequently, the cone can at no time be inverted upwardly without destruction since the tensile strength of the sheet resists expansion beyond its maximum diameter; the term truncated cone includes cones of less regular shapes, such as bulging cones, bell-like shaped cones of somewhat irregular, quasicircular cross sections, the essential feature of the cone being that it is capable of enveloping a fluid thrust upwardly into it, without folding backward and that, inserted into a cylindrical or quasicylindrical hole, it is capable of forming against the wall of said hole a seal, or a restriction reducing the flow of liquids past it.

The truncated cone may be sealingly attached to the tube exactly at or near the lower end of the tube which is to be inserted into the borehole; it may be wired on, or fitted removably by means of a screw or bayonet filling; the tube may protrude into the interior of the cone or even through both the top (small) and bottom (large) opening of the truncated cone. More than one, say 2 or 3 cones, mounted in series may also be used.

Preferably, additionally, we also provide a cap closing the bottom (larger) opening of said truncated cone and removable from it by the pressure of fluid being discharged from the tube.

Accordingly we provide an apparatus for filling boreholes with a viscous slurried explosive which apparatus comprises in combination:

a at least two separate pumping means;

b separate feeding lines attached to said pumping means;

c a chamber into which said feeding lines lead;

d an interfacial surface generator mixer in said chamber;

e optionally a withdrawal apparatus as described hereinabove attached to said interfacial surface generator mixer; the dimensions of the said separate feeding lines, said chamber and said withdrawal apparatus being such that they may be inserted into the borehole to be filled.

Although the separate feeding lines may be two or more separate hoses we prefer that the separate feeding lines are encased in an outer casing; in a more preferred embodiment the hose carrying the major component of the slurried explosiveis used to encase the hoses supplying the streams of the minor components of the slurried explosive. Alternatively a single hose may be used comprising two or more conduits.

The pumps may be any suitable pumps for metering constant proportions of materials, for example the pump may be'of the constant displacement type. So as to reduce the hazard of accidental explosion and also to reduce pollution by exhaust gases of internal combustion engines in underground situations we prefer that the pumps are driven by high pressure fluid for example, pneumatically operated pumps.

Our apparatus may be used to fill boreholes with a viscous slurried explosive.

Accordingly we provide a method of filling boreholes using an apparatus comprising in combination;

a. at least two separate pumping means;

b. separate feeding lines attached to said pumping means;

0. a chamber into which said feeding lines lead;

d. an interfacial surface generator mixer in said chamber;

e. optionally a withdrawal apparatus as hereinbefore described attached to said interfacial surface generator mixer; said method comprising i. inserting the said feeding lines, said chamber, said interfacial surface generator mixer and optionally said withdrawal apparatus into a borehole so that the said mixer is at the toe of the borehole;

ii. pumping two or more free flowing components of a viscous explosive slurry down the separate feeding lines so that a viscous explosiveslurry is formed at the exit of the said interfacial surface generator mixer;

iii. withdrawing said feeding lines and mixer optionally with the aid of the said withdrawal apparatus at such a rate that the exit of the mixer is contiguous with the advancing surface of the viscous slurried explosive.

Our method of filling boreholes is of particular use in the techniques of mining known as open stoping, cut and fill, and caving.

The process and apparatus of our invention may also be used for filling tubes such as for example, narrow plastic tubes, with explosive slurry in the manufacture of explosive cartridges.

Typical embodiments of the invention are depicted in the accompanying drawings. More particularly, FIG. 1 and FIG. 3 are schematic illustrations depicting a cross section of the components of apparatus according to this invention and suitable for filling voids with a viscous product prepared by mixing two or more free flowing materials. FIG. 2 is an isometric sketch of a typical interfacial surface mixer used to mix free flowing materials.

In FIG. 1 a first free flowing liquid is supplied to a pumping means 2 and pumped in a stream through a pipe or hose 4 to a mixing chamber 6. A second free flowing liquid is supplied to a pumping means 1 and pumped in a stream through a pipe or hose 3 to a mixing chamber 6. The first and second free flowing liquid streams are mixed in a chamber 6 by mixing means not shown and the resultant viscous product is transferred from chamber 6 to a void by means of the pumping pressure within the apparatus.

FIG. 2 depicts an interfacial surface generator mixer 7 comprising a plurality of interfacial surface generators 9 enclosed in a casing 8 which may be either rigid or flexible and is very suitably a flexible hose.

In FIG. 3 a first free flowing liquid is supplied to a pumping means 2 and pumped in a stream through a hose 13 to an interfacial generator mixer 7 located in a borehole l7 and having attached thereto at its extremity more remote from the pumping means 2 a withdrawal apparatus 16 as hereinbefore described and being connected at its extremity less remote from the pumping means 2 to hose 13. A second free flowing liquid is supplied to a pumping means 1 and pumped in a stream through hose 12 to interfacial generator mixer 7. Hose 12 is located at least in part within hose 13 and the ratio of the external diameter of hose 12 to the internal diameter of hose 13 should be suitably chosen such that the flow of the first free flowing liquid through hose 13 is not unduly impeded. The first and second free flowing liquids are mixed in the interfacial generator mixer 7 and the resulting viscous liquid is transferred to the borehole 17 by means of the pumping pressure within the apparatus. As the borehole 17 is filled with the viscous liquid the withdrawal apparatus 16, the attached mixer 7 and hoses l2 and 13 are Withdrawn from the borehole 17 at a suitable rate.

Our invention is now illustrated by, but not limited to, the following examples in which all parts are parts by weight unless otherwise specified.

EXAMPLE I This example describes a suitable apparatus of our invention for use in filling boreholes with explosive slurry. A inch internal diameter high pressure nylon tube 120 ft. in length was threaded through a 1 inch internal diameter high pressure PVC loading hose I20 ft. in length. The nylon tube was attached by means of a hook arrangement to the entrance of an interfacial surface generator mixer of conventional design comprising 16 X 2% inch auger elements alternately pitched to the right and left hand and fixed so that the leading edge of one element was at right angles to the trailing edge of the abutting element. The mixer was housed in a metal tube of internal diameter l inch and length 3 feet, said metal tube being attached to the PVC hose.

By means of a suitable metal coupling the nylon tube was attached to one head of a pneumatically driven dual headed diaphragm metering pump capable of delivering two separate streams, and the PVC hose was connected to a high speed rotary mixer which was in turn connected to a Mono pump fitted with a screw feed (Mono is a registered trade mark for a constant displacement pump). The other head of the diaphragm metering pump was connected to the high speed rotary mixer. A withdrawal apparatus as hereinbefore described was attached to the tube encasing the interfacial generator mixer. A cap was provided both to prevent material escaping from the mixer and to hold the mantle of the withdrawal apparatus together while it was being inserted into a borehole.

EXAMPLE 2 This example describes the manufacture of a composite structure comprising a rock structure contiguous with a continuous column of viscous slurried explosive using the apparatus of Example I.

Boreholes were drilled into a rock structure comprising a chalcopyrite ore body using conventional percussion drills. These boreholes were filled with a viscous slurried explosive in the following general manner.

The interfacial surface generator mixer attached to the PVC hose was pushed to the toe of the borehole to be filled.

A mixture of ammonium nitrate 720 parts, water 125 parts, sugar 50 parts, guar gum 3.5 parts, sulphur 30 parts, atomised aluminium 50 parts and paint fine aluminium 20 parts was pumped with the Mono pump through the high speed rotary mixer at the rate of 100 lb/minute. A solution of potassium antimony tartrate (1.5 lb/IOO lb water) was injected at a rate of 270 ml/minute into the high speed rotary mixer using one head of the dual headed diaphragm metering pump and mixed with the ammonium nitrate mixture therein. The resultant composition leaving the high speed rotary mixer was passed through the PVC loading hose. Simultaneously the second component of the crosslinking system, sodium dichromate solution (l0 lb/l00 lb water), was metered down the nylon tube at a rate of 270 ml/minute using the second head of the dual headed diaphragm metering pump.

The separate streams from the PVC loading hose and the nylon tube were mixed by the interfacial surface generator mixer. From laboratory tests it was known that the resultant mixture would become viscous after about seconds. The loading hose was slowly withdrawn from the borehole at such a speed that the mantle of the withdrawal apparatus was always just level with the surface of the advancing column of slurry. After the borehole was filled the loading hose remained full of material and could be capped in a conventional manner and reused to fill a further borehole.

By this method a series of eleven 2 A inches diameter wet down-holes from 66 ft. to 98 ft. deep were charged with slurry. The charges were fired after 2 days standing and gave satisfactory results. The successful firing proved that the column of slurry in the borehole to have been continuous. Also by this method two 2 5 inches internal diameter inclined up-holes were charged to a depth of and 28 feet respectively using the same technique. The slurry remained in the holes and the charged fired satisfactorily after standing for 2 days.

EXAMPLE 3 This is a further example of a suitable apparatus of our invention for use in filling boreholes with explosive slurry. A V8 inch internal diameter high pressure nylon tube 100 ft. in length was threaded through a 1 inch internal diameter semi-rigid polythene hose (class D). One end of the polythene hose was connected to a Mono pump with a special adaptor for bringing out the A; inch nylon hose from the interior to the exterior of the polythene hose, thence connected to a metering pump. At the other extremity of the polythene hose, the elements of the static mixer (as described in Example 1) were inserted inside the hose, such that a close tolerance fit was achieved. The 76 inch nylon tube terminated in a jet which was attached to the static mixer element furthest from the end of the hose. Screwed to the end of the hose was a loading cone having an aluminium holder and a flexible rubber truncated cone. The aluminium holder for the cone held the static mixer elements within the polythene hose.

EXAMPLE 4 The apparatus described in Example 3 was used to manufacture a composite structure comprising a continuous column of viscous slurried explosive contiguous with a rock structure.

Boreholes having a nominal diameter of 2 V; inches were drilled in a chalcopyrite ore body in a manner consistent with the long hole ring drill technique for open stoping. The boreholes were filled with viscous slurried explosive in the following general manner.

The priming charge consisting of the detonator and booster were placed into the cap for the loading come. The cap was then fitted to the cone and the loading hose inserted to the toe of the borehole.

A mixture of ammonium nitrate 600 parts, sodium nitrate 130 parts, water 136 parts, sugar 50 parts, sulphur 30 parts, aluminium 70 parts, guar gum 4 parts, gilsonite parts, potassium antimony tartrate 0.2 parts was pumped by the Mono pump into the 1 inch polythene loading hose at a rate of 70 lbs/min. A solution of sodium dichromate (1 lb/9 lb water) was pumped by the metering pump at (150 mls/min.) into the via inch nylon tube and injected through the jet into the slurry stream before the latter passed through the static mixer and out of the loading hose. From laboratory tests it was known that the slurry issuing from the hose rapidly increased in viscosity and that after 10 15 seconds a stiff cohesive gel would be formed.

The initial slurry issuing from the hose pushed the cap off the loading cone and located the primer in the toe of the hole. Freed from its cap, the loading cone expanded to seal the borehole. The operator could then readily feel the thrust of the slurry against the loading cone and could adjust the withdrawal rate of the hose to create a continuous column of the slurry blasting agent. After the desired quantity of explosive had been loaded into the borehole, the pumps were shut off, the loading hose retracted from the hole and recapped for insertion into the next borehole.

By this method a series of 12 open stope rings, each ring containing from 30 40 boreholes, were loaded and successfully fired.

During the course of the loading operation the following type of holes were charged and fired successfully:

a. Holes inclined below the horizontal plane up to 98 ft. deep filled or containing substantial quantities ofwa ter.

b. Holes (ranging in depth from 50 80 ft.) inclined below the horizontal plane which had been drilled through into the underlying open slope, and therefore had no bottom. In loading these holes the hose was inserted into the hole to within 5 ft. of the breakthrough depth before starting to load. In this manner, holes containing columns of explosive up to ft. long were formed. No slurry slumped from the bottom end of the borehole.

c. Holes, inclined above the horizontal plane, ranging in depth from 20 ft. This included several vertical up-holes of 70 80 ft. in length.

EXAMPLE 5 Using the apparatus described in Example 3 and the method described in Example 4, a series of 4 vertical upholes ranging in length from 60 80 ft. were charged with slurry explosive. After standing 2 weeks the slurry was still retained in the holes and the charge fired satisfactorily.

EXAMPLE 6 A loading hose of an apparatus as described in Example 3 was inserted into the toe of a polythene tube 2 inches in diameter and 3 ft. long closed at one end. The loading hose was 20 ft. in length. A mixture of the explosive slurry used in Example 4 was pumped through the Mono pump at a rate of 8 lbs/min. Simultaneously a 10% w/w solution of sodium dichromate (1 lb. in 9 lbs. water) was pumped at 7 mls/min. through the 9 8 inch nylon tube and injected into the slurry. The polythene tube was filled with viscous slurry. The package of slurry was used for secondary breaking.

We claim:

1. A method of filling a borehole inclined upwardly into a rock structure with a viscous slurried explosive prepared by mixing two or more free flowing materials which method comprises firstly supplying separate streams of said free flowing material to the required position in the borehole and secondly mixing the separate streams at said required position within said borehole to form the said viscous slurried explosive in situ within said borehole, wherein the viscosity of the mixture rises substantially within a few seconds of mixing and wherein the mixing is carried out entirely within the borehole.

2. A method according to claim 1 wherein the borehole is less than 3 inches in diameter and more than 10 feet in length.

3. A method according to claim 1 wherein the separate streams are mixed by means of an inter-facial surface generator mixer situated in the borehole.

4. A method of manufacturing the composite structure comprising a rock structure contiguous with a continuous column of a viscous slurried explosive which method comprises firstly, drilling into a rock structure a narrow borehole ofless than 3 inches in diameter and more than 10 feet in length, secondly, supplying separate streams of at least two free flowing components of hole.

'5. A method according to claim 4 wherein the separate streams are mixed by means of an inter-facial surface generator mixer situated in the borehole.

Claims

4. A method of manufacturing the composite structure comprising a rock structure contiguous with a continuous column of a viscous slurried explosive which method comprises firstly, drilling into a rock structure a narrow borehole of less than 3 inches in diameter and more than 10 feet in length, secondly, supplying separate streams of at least two free flowing components of viscous slurried explosive to the required position in the borehole and thirdly, mixing the components thoroughly at the required position in the borehole so as to obtain in situ a column of viscous slurried explosive completely filling the cross-sectional area of the borehole.

5. A method according to claim 4 wherein the separate streams are mixed by means of an inter-facial surface generator mixer situated in the borehole.