HK1056389A - Cartridge shell and cartridge for blast holes and method of use - Google Patents

Description

Cartridge case and cartridge for blastholes and method of use

Technical Field

The invention relates to a cartridge casing and a corresponding cartridge for blastholes intended for the fragmentation of hard materials. The invention also relates to a method of using such a cartridge, and in particular to a method of loading a blasthole with a cartridge.

Background

A typical cartridge for a blasthole is in the form of a cylindrical tube closed at both ends. Some cartridges may contain only energetic materials while others may contain both energetic materials and detonators. The cartridge will be inserted to rest adjacent the bottom of a drilled or otherwise made borehole in the rock or other hard material to be broken. The blastholes may then be plugged with particulate stemming material. When the energetic material in the cartridge detonates, gas is rapidly generated and thus gas pressure is rapidly established near the bottom of the blasthole. The resulting gas pressure can cause a fracture to propagate from the borehole through the hard material, provided that the gas generation is suppressed for a short period of time.

The efficiency and effectiveness of this process is largely determined by factors such as the configuration and quality of the gas seal formed on the side of the cartridge closest to the blasthole port, and the ability to hold this seal in place. Obviously, if the seal is poor, gas will escape around the seal, thereby reducing the gas pressure and the rate of rise of the gas pressure. Secondly, the escaping gas has adverse effects in ejecting the stemming material from the borehole, generating reactive forces and producing flyrock. However, even if the seal is one that has a high degree of integrity, if the seal is not held firmly in place and can be pushed back towards the bore hole aperture, the physical volume of the void confined within the bore in which the gas acts increases, thereby reducing the gas pressure.

Disclosure of Invention

It is an object of the present invention to provide a cartridge shell and related cartridge shell which can help alleviate the various disadvantages mentioned above in use. It is a further object of the present invention to provide a method of loading a blasthole with such a cartridge.

According to a first aspect of the present invention there is provided a cartridge shell for breaking up hard material, the shell comprising at least: a body defining a volume for containing energetic material, the body having first and second opposed ends, the first end being generally planar and the second end being tapered to form a tip or wedge directed away from the first end.

Preferably, the body includes a line or region of weakness adjacent the first end.

Preferably, the cartridge casing includes closure means at the first end which is provided with or defines in combination with the body a line or zone of weakness.

Preferably, the body is provided with an opening at the first end, and the closing means comprises a lid for closing said opening.

In one embodiment, the cartridge shell further comprises an aperture at the first end through which the detonator lead passes. Preferably, the aperture is formed in the closure device.

Preferably, the cartridge shell includes a recessed channel on the outer surface around the first end for receiving the detonator lead.

In another embodiment, the cartridge shell includes an aperture at or near the second end through which the detonator lead passes. In this embodiment, the cartridge shell may include an internal groove or passage through which the detonator lead passes.

Preferably, the second end is provided with two or more inclined surfaces which converge towards each other in a direction from the first end to the second end.

However, in another embodiment, the second end is in the form of a truncated cone.

According to a second aspect of the present invention there is provided a cartridge shell for rupturing and/or breaking hard material by inserting a cartridge in a blasthole followed by initiation of a particulate stemming material, the shell comprising at least one body defining a volume for containing an energetic material, the body having first and second opposed ends, the second end comprising a surface for exerting a radially compressive force on the stemming material in use.

According to another aspect of the present invention there is provided a cartridge for use in the fragmentation of hard materials, the cartridge comprising at least:

a cartridge casing according to the first or second aspects of the invention and a quantity of energetic material contained within the body of the cartridge casing.

Preferably, the cartridge further comprises an initiator disposed within the body.

Preferably, the cartridge further comprises an initiator lead connected at one end to the initiator and passing through an aperture in the cartridge shell.

Preferably, the energetic material is an emitting agent (propellant).

Preferably, the initiator is an explosion-proof initiator.

Preferably, the cartridge includes a booster for the initiator.

In another embodiment, the cartridge further comprises one or more booster cartridges, each containing a quantity of energetic material, the one or more booster cartridges being connectable to the first end of the main body in end-to-end relationship and to each other such that the total quantity of energetic material charged by the cartridge is varied by connecting the one or more booster cartridges to the main body.

Preferably, said main body and said booster cartridge each contain no more than 10 grams of energetic material.

Preferably each booster cartridge has first engagement means at a first end and second complementary engagement means at an opposed second end, such that the first engagement means of a booster cartridge is engageable with the second engagement means of an adjacent booster cartridge.

Preferably, the first engagement means is received inside the second engagement means such that the plurality of connected booster cartridges have a substantially uniform outer diameter.

Preferably, each booster cartridge comprises a substantially cylindrical body having a first outer diameter; an axially extending section at the first end forming the first engagement means having a reduced second outer diameter; and a recess at the second end forming the second engagement means with an inner diameter smaller than an outer diameter of the axially extending section to enable the first engagement means to fit into the second engagement means.

Preferably, said first engagement means and said second engagement means are configured in relation to each other so as to form an interference fit therebetween.

Preferably, the axially extending section comprises a plurality of circumferential, axially spaced ribs.

In another embodiment, the first and second engagement means may be threadedly engaged with each other.

Preferably, the booster cartridges are closed at opposite ends by respective webs, where the webs are combustible, or frangible, or both.

According to another aspect of the invention there is provided a cartridge shell comprising at least:

a main housing having a body defining a volume for containing energetic material, the body having first and second opposed ends, the second end being tapered to decrease in cross-sectional area away from the first end; and

one or more secondary housings, each secondary housing having a generally cylindrical body for receiving a quantity of energetic material, said one or more secondary housings being releasably connected to said first end of said primary housing in an end-to-end fashion and to each other.

According to another aspect of the present invention there is provided a method for loading and stemming a borehole in a hard material, the borehole having an aperture adjacent a free surface of the hard material and a base at an opposite end of the borehole, the method comprising at least the steps of:

inserting a cartridge according to the second aspect of the invention into the blasthole with the first end of the cartridge facing the aperture of the blasthole;

preparing a particulate packing material comprising a mixture of dry binder, fines and coarse material;

depositing said stemming material into said borehole;

the stemming material is mechanically fixed in the borehole.

Preferably, the depositing step comprises blowing the stemming material into the blasthole.

Preferably, the method further comprises the steps of: blowing the stemming material into the borehole at a height below the free surface of the hard material; inserting a stemming bar into the borehole, pressing on the stemming material at one end and projecting from the free surface of the hard material at the opposite end of the stemming bar; and mechanically securing the opposite end of the stopper rod.

Preferably, the method comprises the steps of: one end of the stopper rod is formed with a tip or wedge away from the opposite end of the stopper rod.

Preferably, the method further comprises the steps of: after insertion into the cartridge, a quantity of liquid or gel is injected into the blasthole to fill the space between the outer surface of the cartridge and the blasthole and form a layer of liquid or gel between the second end of the cartridge and the particulate stemming material.

Preferably, when the method is used in an underground mine having a sidewall in which a blasthole is formed and an opposed sidewall, the step of mechanically securing the stemming material in the blasthole includes the step of operating the jack such that one end of the jack bears against the sidewall above the blasthole and an opposite end of the jack bears against the opposed sidewall.

According to another aspect of the present invention there is provided a stemming material for loading a blasthole, the stemming material comprising a mixture of a dry binder, fines and coarse material.

Preferably, the binder is one of the group consisting of coal ash, furnace waste or other fines containing binding material.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is an exploded cross-sectional view of a cartridge shell according to the present invention;

FIG. 2 is a bottom view of an end cap included in the cartridge shell;

FIG. 3 is a cross-sectional view A-A of FIG. 1;

FIG. 4 is P of FIG. 1₁-P₁A sectional view;

FIG. 5 is P of FIG. 1₂-P₂A sectional view;

FIG. 6 is P of a second embodiment of a cartridge shell₁-P₁A cross-sectional view;

FIG. 7 is P of a second embodiment of a cartridge shell₂-P₂A cross-sectional view;

FIG. 8 is a cross-sectional view of the upper end of the third embodiment of the cartridge shell;

FIG. 9 is a cross-sectional view of the bottom of the cartridge shell of FIG. 1 showing the arrangement of the detonator and detonator lead;

FIG. 10 is a cross-sectional view of a fourth embodiment of a cartridge shell;

FIG. 11 is a cross-sectional view of the bottom of the fifth embodiment of the cartridge shell;

FIG. 12 illustrates a method of utilizing a cartridge made from a cartridge shell according to an embodiment of the present invention;

FIG. 13 illustrates a second method of use of a cartridge containing a cartridge shell according to an embodiment of the present invention;

fig. 14 shows another embodiment of a cartridge shell/cartridge;

FIG. 15 is an exploded cross-sectional view of the auxiliary housing shown in FIG. 14; and

fig. 16 is a plan view of a closure disc mounted in the casing/cartridge shown in fig. 14 and 15.

Detailed Description

Fig. 1-5 show a first embodiment of a cartridge shell 10. The cartridge shell includes a body 12 defining a volume 14 for containing energetic material (not shown). The body 12 has a first end 16 and an opposite second end 18. The first end 16 is generally planar and actually constitutes a planar base of the housing 10. Whereas the second end 18 is tapered to form a point or wedge 20.

The taper of the second end portion 18 is designed such that the area of the second end portion 18, measured in a plane transverse to the longitudinal axis of the body 12, decreases in a direction from the first end portion 16 to the second end portion 18. Thus, referring to FIGS. 4 and 5, plane P₂And the area of the second end 18 and the plane P₁The area measured above is reduced compared to the area measured above.

The second end 18 may take one of a number of different specific shapes. As can be seen in fig. 1, 4 and 5, the second end 18 is in the form of two inclined surfaces 22 and 24 converging towards each other. However, in another embodiment, the second end 18 may be in the form of a truncated cone. This is illustrated in fig. 6 and 7, which fig. 6 and 7 show, respectively, a plane P passing through₁And P₂The second end 18 cross-section. In yet another embodiment shown in fig. 8, second end 18 is in the form of a chisel tip. Of course, other shapes are possible, such as, but not limited to, a three, four or five sided pyramid.

Desirably, the body 12 and the second end 18 are integrally formed and made of a plastic material. However, it is possible for the second end 18 to be made separately from the body 12, and if so, the two parts can then be secured together. The body 12 is conveniently of cylindrical form as shown in figure 3 which shows section a-a of figure 1.

The body 12 has an opening 26 at a first end to allow the housing 10 to be filled with energetic material. A closure in the form of a cap 28 is provided for insertion into and closing the opening 26. The cover 28 is press/interference fit into the opening 26. This forms a line or area of weakness at the first end 16.

An aperture 30 is centrally formed through the cover 28 to allow an initiator, such as an electrical igniter 32 (see fig. 9), to be pushed into the body 12. A lead 34 from an igniter 32 passes through the aperture 30 for connection to a power source.

In another embodiment shown in fig. 10, the outer surface 36 of the housing 10 adjacent the first end 16 is provided with a groove 38 for seating the detonator lead 34. The groove includes a first length 40 disposed on the body 12 and a second length 42 disposed on the cover 28. The cover 28 is oriented when inserted into the body 12 such that the lengths 40 and 42 of the groove 28 are aligned. The lead 34 may be seated within the groove 38 when the electrical ignitor 32 is inserted through the aperture 30 to provide protection against accidental injury or severing when the casing 10 is inserted into a blasthole. In another modification, the length 40 of the groove 38 may extend along the body 12 to at least a point where the wedge 20 begins.

In another modification shown in fig. 11, the aperture 30 is provided in the tip or wedge 20 rather than in the cover 28. In this embodiment, the housing 10 may also be provided with an internal passage 35 through which the lead 34 passes to deposit the initiator 32 inside the body 12 proximate the first end 16.

Fig. 12 illustrates one method of use of the housing 10. The volume 14 of the casing 10 is filled with an energetic substance, such as a propellant, to form the cartridge 10 c. Cartridge 10c is previously inserted with first end 16 into a borehole 46 formed in a hard material 47 such that first end 16 is adjacent the bottom 48 of the borehole. Accordingly, the second end 18 faces or points towards the bore hole aperture 50. Next, a quantity of particulate stemming material 52 is placed in the borehole 46. Typically this is done by blowing. Stemming material 52 is blown into the bore 46 to a depth below the free end surface 54 of the hard material 47 in which the bore 46 is formed. The stemming material 52 is then mechanically secured within the borehole 46.

In the embodiment of FIG. 12, mechanical securement is achieved by inserting a stemming bar 56 into the borehole 46 such that one end 58 of the stemming bar rests on the stemming material 52 and an opposite end 60 of the stemming bar protrudes from the free surface 54. A pocket (cup)62 is placed over and straddles the end 60. The opposite side 64 of the recess is formed with a planar base and supports a sagittal strut 66(acrow prop). The saggital strut 66 extends lengthwise or is otherwise jacked up so that its opposite end 68 rests against a side wall 69 disposed opposite the free surface 54.

By connecting the lead wires 34 to a power source, the initiator 32 generates a high temperature flame to initiate the propellant or other energetic material within the cartridge 10 c. The gas generated upon detonation initially bursts through the body 12 around the line of weakness formed by the attachment of the cap 28 to the body 12. The increase in gas pressure may tend to force the cartridge 10c toward the opening 50 of the blasthole 46. As this occurs, the point or wedge 20 acts on the stemming 52 to increase the radial compressive force on the stemming in the annular region between the periphery of the second end 18 and the adjacent portion of the surface of the blasthole 46 to increase the sealing effect of the stemming 52. The stemming 52 is prevented from blowing out of the blasthole 46 by the mechanical resistance provided by the stemming bar 56 and the saggital struts 66.

The sealing effect of the packing material 52 is enhanced by forming the packing material 52 from a mixture of dry binder, fines and coarse material. It has been found that coal ash is a particularly beneficial binder, while mixtures containing coal ash have a tendency to sag when blown under pressure into blastholes 46. The binder and fines comprise a plurality of solid particles having a particle size of less than about 1 mm. Coarse material within the packed aggregate contains particles up to about 6mm in size. Various binders other than coal ash, such as furnace scrap or fines containing binding material, may be used in the packing material.

In another method of stemming a blasthole 46, after the cartridge 10c has been inserted into the blasthole, a quantity of a liquid formulation or gel 70 is poured into the blasthole 46 to fill any gaps between the outer surface of the cartridge 10c and the surface of the blasthole 46 and form a liquid formulation or gel layer 72 between the particulate stemming material 52 and the cartridge 10 c. The gel 70 helps seal the blasthole 46 to prevent gas from escaping upon detonation of the energetic material held within the cartridge 10 c. In all other respects, the method shown in FIG. 13 is the same as that shown in FIG. 12.

Either the use of the packing material 52 alone or in combination with the liquid/gel 70 provides a highly complete seal that substantially limits the escape of gas. In these embodiments, the stemming 52 from moving toward the blasthole orifice 50 is prevented by mechanically blocking the stemming using the stemming bar 56 and the saggital struts 66, thereby keeping the volume of the blasthole 46 in which the gas acts relatively constant.

Fig. 14 and 15 show a casing 10 and corresponding cartridge 100c according to another embodiment of the invention. The cartridge 100c is in fact a stackable cartridge comprising a casing 10 substantially identical to that shown in figure 1, however with a body 12 of smaller length; and two auxiliary cartridges 102a and 102b (hereinafter collectively referred to as "auxiliary cartridges 102"). Various embodiments of cartridge 100c may include either a single secondary cartridge 102 or more than two secondary cartridges 102. When loaded with energetic materials, the casing 10 constitutes the primary cartridge 10 c.

Each auxiliary cartridge 102 comprises a quantity of energetic material (not shown) and is formed to be attachable to the first end of the main body 12 and to one another in an end-to-end connection. In this manner, the total amount of energetic material contained by cartridge 100c may be varied by attaching one or more secondary cartridges 102 to body 12. This has a significant effect in the transportation and storage of energetic materials. For example, by forming the main body 12 and auxiliary cartridges 102 to each contain no more than 10gm of energetic material, a 50gm cartridge can be constructed by joining together a single main body 12 and four auxiliary cartridges 102. However, in accordance with the United nations Security Classification (UN SalyClassification) with respect to the transportation of such cargo, body 12 and cartridge 102 may be separately transported as 10gm cartridges under less stringent requirements than a 50gm cartridge alone.

Each auxiliary cartridge 102 has a first engagement means 104 at one end and a second complementary engagement means at a second, opposite end. This enables the first engagement means of one auxiliary cartridge, such as the engagement means 104 of auxiliary cartridge 102b, to engage with the second engagement means of an adjacent auxiliary cartridge, such as the second engagement means 106 of booster cartridge 102 a.

Each auxiliary cartridge 102 has a casing 108 which includes a substantially cylindrical body 110 with first engagement means 104 in the form of an axially extending section 112 at a first end of the cartridge 102 for the body 110. The extension 112 forms an outer diameter that is smaller than the outer diameter of the cylindrical body 110. The second engagement means 106 is in the form of recesses 114 formed at opposite ends of the cylindrical body 110.

The outer surface of the axially extending section 112 is surrounded by two axially spaced apart projections 116. The two protrusions 112 have a saw-tooth profile, as can be seen in fig. 15.

The inside surface of each groove 114 is likewise surrounded by two axially spaced ridges or ribs 118.

As is evident from fig. 15, the inner diameter of the recess 114 is greater than the inner diameter of the cylindrical body portion 110 of the housing 108 and forms an annular seat 120 therebetween. The groove 114 is formed by inserting a closure disc 122 into the end of the housing 108 to be placed against the annular seat 120. Another ridge or rib 124 is formed around the inside surface of groove 114 at a location spaced from annular base 120 by a distance substantially equal to the thickness of the perimeter of disk 122. Second, the ridge 124 and the disk 122 are dimensionally related such that the ridge 124 is positioned behind the disk 122 and effectively secures the disk 124 against the base 120. The disc 122 is made of a combustible material such as plastic, paper or cardboard.

When the cartridge 100c is assembled, the casing 108 is held in a vertical position with the axially extending section 112 down and energetic material is poured through the groove 114 to the maximum height of the annular base 120. The closure disk 122 is then inserted over the ridges 118 and 124 and against the annular base 120.

To join two auxiliary cartridges 102 together, the axially extending section 124 of one cartridge is pushed into the groove 124 of an adjacent cartridge. In the process, the protrusion 112 snaps over the ridge 118 until the front end of the extension abuts the disk 120. In this position, the ridges 118 are effectively seated behind the corresponding protrusions 116 with a snap fit. The last secondary cartridge 102b of cartridge 100c is closed with an end cap 28 identical to the end cap described in relation to fig. 1 and 10.

A longitudinal channel 126 is made along the outside surface of cartridge 100 c/casing 10' with a separate length on each of casing 10 and casing 108 of each cartridge 102a and 102 b. The channel 126 receives the lead 34, which is provided with the electric ignitor 32 inserted into the end cap 28. Prior to insertion of end cap 28, a hole is pierced in disc 122 in cartridge 102b through which primer 32 may be inserted.

To facilitate alignment of the individual lengths on both the housing 10 and each housing 108, the outside surface of each extension 112 and the inside surface of each recess 114 are provided with a flat surface. This plane is shown as a bar 128 on the axially extending section 112 in fig. 14. A corresponding flat surface (not shown) is provided on the inside surface of each groove 114.

In order to allow the closing disc 122 to be inserted into the recess 114, the disc 122 is also provided with a flat surface 130.

To facilitate the connection of the primary cartridge 10c to the booster cartridge 102a, the casing 10 is also modified as compared to that shown in fig. 1 by including a recess 114 to receive the extension 112 of the secondary cartridge 102 a. The recess 114 in the primary cartridge 10c has the same shape and configuration as described and illustrated with respect to the secondary cartridge 102 and is closed by a disc 122.

Although embodiments of the present invention have been described in detail, it will be apparent to those skilled in the art that many modifications and variations can be made without departing from the basic inventive concept. Instead of mechanically securing the stemming 52 within the blasthole 46 using the saggital supports 66, such as in the methods illustrated by FIGS. 12 and 13, a variety of different mechanical devices can be used, such as, for example, a weight or bulk object, or such as, for example, placing a bucket of an excavator over the blasthole opening 50. In another variation, the second end of the housing 10 may be formed with a circumferential cutback 74 as shown in FIG. 14 for receiving one end of a sleeve or bushing 76. The sleeve 76 is filled with the packing material 52. Desirably, sleeve 74 is made of a thin-walled, frangible and/or pliable material, such as paper, thin plastic, rubber, or cardboard. In practice, the housing 10 may also be made of such a material. In this case, upon receiving an axial compressive force provided by the saggital strut 66 or other mechanical stop, the sleeve 76 and/or the casing 10 may expand radially to press against the sidewall of the borehole 46 and eliminate any empty volume within the borehole. End 58 of stopper rod 56 may be press fit to the opposite end of casing 76 to allow one-step insertion of cartridge 10c, stemming material 52 and the stopper rod.

Additionally, the end 58 of the stemming bar may be formed with a point, taper or wedge 58, as shown in phantom in FIGS. 12 and 13, to facilitate radial expansion and compaction of the stemming material 52 against the sidewall of the borehole 46, thereby enhancing the sealing effect.

Referring to the embodiments shown in fig. 14-16, various other types of connection types may be employed as an alternative to a snap-type fit between the primary cartridge 10c and each secondary cartridge 102. For example, in the simplest manner, the axially extending section 112 and the groove 114 may be relatively configured to provide an interference fit. In other alternatives, complementary threads may be made on the inner surfaces of the extension 112 and the groove 114. In a further variant, a bayonet connection may be provided.

Alternatively, the closure disk 122 may be replaced by a frangible and/or combustible web. Additionally, a closure disk 122 or web may be placed at the end of housing 108 distal from axially extending section 112. To subsequently permit engagement of adjacent cartridges 102, cartridge 102 is filled with a quantity of energetic material less than its volume to provide space for receiving the inserted axial extension 112.

Additionally, in fig. 14, a single electrical ignitor 32 is depicted at the end of the lead 34 for insertion into the end cap 28. However, multiple electric igniters or other detonators may be incorporated. For example, one or more electrical igniters may be attached to the lead 34 via the branch leads and sandwiched between the closure disk 122 and the adjacent axially extending sections 112 of the attached primary and secondary housings, or between the adjacent attached secondary housings.

All such modifications and variations are considered to be within the scope of the invention, the nature of which is to be determined from the above description and the appended claims.

Claims (49)

1. A cartridge shell for breaking hard materials, the shell comprising at least: a body defining a volume for containing energetic material, the body having first and second opposed ends, the first end being generally planar and the second end being tapered to form a tip or wedge directed away from the first end.

2. The cartridge shell according to claim 1 wherein the body includes a line or area of weakness adjacent the first end.

3. The cartridge shell according to claim 2 further comprising closure means at the first end, said closure means being provided with or in combination with the body to form a line or zone of weakness.

4. The cartridge shell according to claim 3 wherein the body is provided with an opening at the first end and the closure means comprises a lid for closing said opening.

5. The cartridge shell according to claim 4 further comprising an aperture at the first end through which the detonator lead passes.

6. The cartridge shell according to claim 5 wherein said apertures are formed in the closure means.

7. The cartridge shell according to claim 5 or 6 wherein the cartridge shell includes a recessed channel on the outer proximal surface of the first end to seat a detonator lead.

8. The cartridge shell according to any one of claims 1 to 3 further comprising an aperture at or near the second end through which an initiator lead passes.

9. The cartridge shell according to claim 8 further comprising an internal groove or passage through which the detonator lead passes.

10. The cartridge shell according to any one of claims 1 to 9 wherein the second end is provided with two or more inclined surfaces which converge towards each other in the direction from the first end to the second end.

11. The cartridge shell according to any one of claims 1 to 9 wherein the second end portion is in the form of a truncated cone.

12. A cartridge shell for rupturing and/or breaking hard materials by: placing a cartridge in the blasthole with a particulate stemming material in succession and then detonating the cartridge, the casing comprising at least a body defining a volume for containing the energetic material, the body having first and second opposed ends, the second end comprising a surface for exerting a radial compressive force on the stemming material in use.

13. The cartridge shell according to claim 12 wherein the body includes a line or area of weakness adjacent the first end.

14. A cartridge shell comprising at least:

a main housing having a body defining a volume for containing energetic material, the body having first and second opposed ends, the second end being tapered to decrease in cross-sectional area away from the first end; and

one or more secondary housings, each secondary housing having a generally cylindrical body for receiving a quantity of energetic material, the one or more secondary housings being releasably connected to the first end of the primary housing in an end-to-end manner and to each other.

15. The cartridge shell according to claim 14 wherein each secondary shell has a first engagement means at one end and a second complementary engagement means at a second opposite end, the first engagement means of a secondary shell being releasably engageable with the second engagement means of an adjacent secondary shell.

16. The cartridge shell according to claim 15 wherein the second engagement means is receivable within the first engagement means.

17. The cartridge shell according to claim 16 wherein said first end of said primary shell is provided with first engagement means for engaging with second engagement means of an adjacent secondary shell.

18. The cartridge shell according to claim 17 wherein said cylindrical body has a first outer diameter and said second engagement means is in the form of an axially extending section having a second outer diameter smaller than said first outer diameter and first engagement means is in the form of a groove for receiving said axially extending section.

19. The cartridge shell according to claim 18 wherein an outer surface of said axially extending section is provided with one or more protrusions and an inner side surface of said recess is provided with one or more ridges for seating behind said one or more protrusions with a snap fit.

20. The cartridge shell according to claim 19 wherein said projection has a saw tooth like profile.

21. The cartridge shell according to claim 20 wherein said projection surrounds an outer surface of said axially extending section.

22. The cartridge shell according to claim 21 wherein said ridge encircles said inside surface of said groove.

23. The cartridge shell according to claim 22 further comprising respective closure disks for closing the first ends of said primary and each secondary shell at respective locations inboard of the first ends of said primary and secondary shells.

24. The cartridge shell according to claim 23 wherein said main shell and each auxiliary shell include annular seats at said locations for seating respective closure disks.

25. The cartridge shell according to claim 24 wherein a second one of said ridges is axially spaced from said annular seat for retaining said closure disc against said annular seat with a snap fit.

26. A cartridge for use in breaking hard materials, the cartridge comprising a cartridge casing according to any one of claims 14 to 25, and a quantity of energetic material contained within the primary casing and the one or more secondary casings, whereby the total quantity of energetic material contained by the cartridge is varied by connecting one or more secondary cartridges to the primary cartridge.

27. A cartridge for breaking hard materials, the cartridge comprising at least:

a cartridge casing according to any one of claims 1 to 13 and a plurality of energetic materials contained within the cartridge casing body.

28. The cartridge according to claim 26 or 27 further comprising an initiator disposed within the body.

29. The cartridge according to claim 28 further comprising an initiator lead attached at one end to the initiator and passing through an aperture in the cartridge shell.

30. The cartridge according to any one of claims 27 to 29 wherein the energetic material is a propellant.

31. The cartridge according to any one of claims 28 to 30 wherein the initiator is an explosion-proof initiator.

32. The cartridge according to claim 31 further comprising a booster for the initiator.

33. The cartridge according to claim 27 further comprising one or more auxiliary cartridges each containing a quantity of energetic material, said one or more auxiliary cartridges being connectable to said first end of said main body and to each other in an end-to-end manner such that the total quantity of energetic material contained by a cartridge is varied by connecting one or more auxiliary cartridges to said main body.

34. The cartridge according to claim 26 or 33 wherein said main body and each said secondary cartridge each contain no more than 10 grams of energetic material.

35. The cartridge according to claim 34 wherein each auxiliary cartridge has a first engagement means at a first end and a second complementary engagement means at an opposed second end, whereby the first engagement means of an auxiliary cartridge is engageable with the second engagement means of an adjacent auxiliary cartridge.

36. The cartridge according to claim 35 wherein said first engaging means is received inside said second engaging means such that the outer surface of the plurality of connected secondary cartridges is of substantially uniform outer diameter.

37. The cartridge according to claim 36 wherein each secondary cartridge comprises a substantially cylindrical body of a first outer diameter; an axially extending section of the first engagement means forming a reduced second outer diameter at the first end; and a groove forming the second engagement means at the second end, the axially extending section being received in the second engagement means.

38. The cartridge according to claim 37 wherein said first engagement means and said second engagement means are oppositely configured to provide an interference fit therebetween.

39. The cartridge according to claim 38 wherein said axial extension includes a plurality of circumferentially and axially spaced ribs.

40. The cartridge according to claim 37 wherein said first and second engaging means are threadably engageable with one another.

41. The cartridge according to claim 33 wherein the secondary cartridge is closed at each opposite end by a respective web or disc, where the web or disc is combustible, or frangible, or both.

42. A method of stemming a borehole in a hard material, the borehole having an opening adjacent a free surface of the hard material and a bottom at opposite ends of the borehole, the method comprising at least the steps of:

inserting a cartridge according to any of claims 26 to 41 into a blasthole with a second end of the cartridge facing an aperture of the blasthole;

preparing a particulate packing material comprising a mixture of dry binder, fines and coarse material;

depositing said stemming material into said borehole;

the stemming material is mechanically fixed in the borehole.

43. The method of claim 42, further comprising the steps of: depositing a stemming material into the borehole at a depth below the free surface of the hard material; inserting a stemming bar into the borehole so as to bear on the stemming material at one end thereof, while the opposite end of the stemming bar projects from the free surface of the hard material; and mechanically securing the opposite end of the tucker bar.

44. The method of claim 43, further comprising the steps of: one end of the stemming bar is formed with a tip or wedge that points away from the opposite end of the stemming bar.

45. The method of claim 44, further comprising the steps of: a quantity of liquid formulation or gel is injected into the blasthole after insertion of the cartridge to fill any voids between the outer surface of the cartridge and the blasthole and form a layer of liquid formulation or gel between the second end of the cartridge and the particulate stemming material.

46. A method according to any one of claims 42 to 45, wherein, when the method is used in an underground mine having a side wall in which a blasthole is formed and an opposed side wall, the step of mechanically securing the stemming material in the blasthole comprises the step of operating the jack such that one end bears on the side wall on the blasthole and the opposite end of the jack bears on the opposed side wall.

47. A method as claimed in claim 42, wherein the depositing step comprises blowing said stemming material into said blasthole.

48. A stemming material for filling a blasthole, the stemming material comprising a mixture of a dry binder, fines and coarse material.

49. The packing material of claim 47, wherein the binder is one of the group consisting of coal ash, furnace waste, or other powders containing cementitious materials.