GB2204343A - Loading explosives into bore holes - Google Patents

Abstract

A method of, and an apparatus 10 for, loading a flowable bulk explosive into a borehole comprises feeding a non-capsensitive emulsion base and a sensitizing agent for sensitizing the base into a pipe 18 and mixing them together before they issue from the downstream end of the pipe into a borehole 13. Apart from the pipe 18, the apparatus includes explosive base feed means 62. Feed means 84 is connected to the pipe 18 for feeding sensitizing agent separately into the pipe 18; and a mixing device 16 is mounted in the pipe 18 for mixing the base and sensitizing agent together. <IMAGE>

Description

METHOD AND APPARATUS FOR LOADING EXPLOSIVES INTO BOREHOLES THIS INVENTION relates to a method and apparatus for loading explosive into boreholes. More particularly it relates to a method and apparatus suitable for charging a slurry- or emulsiontype explosive into small and intermediate diameter [21-110 mm boreholes.

According to the invention a method of loading a flowable bulk explosive into a borehole comprises separately feeding a non-cap-sensitive explosive base and a sensitizing agent for sensitizing the base into a flexible pipe or hose so that they pass together along the pipe towards the downstream end of the pipe, the method including the step of mixing the explosive base and sensitizing agent together after they have been fed into the pIpe, the rlxture issuing from the downstream end of the pipe nto the borehole, where it provides a booster-sensitive explosive.

The explosive base may be an emulsion or slurry base, the sensitizing agent being a density reducing agent, so that the explosive which is provided in the borehole is a slurry or emulsion explosive The explosive base may be non-booster- sensitive, being capable of having its viscosity increased by subjecting it to shear, the sensitizing agent being a chemical gassing solution, and the method including subjecting the liquid passing along the pipe to mixing and shear at or adjacent the downstream end of the pipe.

More particularly, the mixing of the explosive base and sensitizing agent may be effected by passing the liquid passing along the pipe through an orifice plate or static mixer at or adjacent the downstream end of the pipe, thereby to mix the explosive base and sensitizing agent together while subjecting the liquid to shear. Subjecting the liquid to shear, particularly in the case of an emulsion base, leads to the production of a booster-sensitive explosive in the borehole which has substantially increased viscosity compared with that of the explosive base, the emulsion in fact being refined by being subjected to the shear. Because of the increased resistance which this increased viscosity can provide to pumping, the mixing preferably takes place as close as possible to the outlet or downstream end of the pipe.Any mixing device such as a nonreturn valve, orifice plate or static mixer which provides the desired degree of mixing and shear can be used.

In this fashion relatively small cr inte=nedlate --a..e.e- ;2-- iO mn] boreholes can be loaded with booster-sensitive slurs or emulsion, employing an explosive base which is cn-ct- sensitive and preferably non-booster-sensitive.The increase in viscosity also means that the explosive can, in principle, depending on its actual viscosity, be charged into boreholes which slope upwardly, indeed vertically upwardly, frcs their mouths, and this can be achieved using an explosive base such as an emulsion base, of substantially lower viscosity than the eventual explosive, and which can be relatively easy to pump.

The downstream end of the pipe may be provided by a lance in which the mixing takes place. Using the lance facilitates loading into the borehole, and the mixing device can conveniently be provided in the lance, at or adjacent the downstream or free end of the lance, or at the upstream end of the lance, where the lance 25 connected to the pipe.

The explosive base may be fed under pressure, eg supplied by compressed air, from a hopper into the pipe, the gassing solution being fed in similar fashion from a tank into the pipe, at or closely spaced downstream and usually as close as practicable to, the point where the explosive base is fed into the pipe.

Preferably, however, the explosive base is fed into the pipe by means of a rotary helical positive displacement pump, such as a Mono pump.

The method may include lubricating the passage of the explosive base along the pipe by feeding a lubricating liquid into the pipe so that it at least partially forms an annular lubricating layer around the explosive base as it passes along the pipe. Conveniently the lubricating liquid is in fact a chemical gassing solution which provides the sensitizing agent an is fed by a positive displacement dosing - -p into tne pipe through an annular inlet into the pipe, at or downstream adjacent the position where the explosive base is fed into the pipe.The gassing solution thus forms an annular cr cylindrical layer around the explosive base in the pipe, at the inner surface of the pipe, so that its acts as a lubricant for lubricating flow cf explosive base along the pipe, thereby reducing pumping pressures It is for this reason that the gassing solution is fed into the pipe via an inlet to the pipe which extends circumferentially around the periphery of the inner surface of the pipe.

The borehole may have a diameter of 21-110 mm, and the borehole may slope upwardly from a mouth at its lower end, the explosive issuing upwardly into the borehole from the downstream end of the pipe.

The method thus in principle can involve the handling and storage of non-cap-sensitive and preferably non-booster-sensitive base at all times until the explosive base is mixed with gassing solution by the mixing device, and issues into the borehole, where it provides a booster-sensitive explosive, which may optionally be cap-sensitive. In this regard by 'non-capsensitive' is meant that no detonation can take place in 21 mm diameter with 0,36 g pentaerythritol tetranitrate [PETN] whereas 'cap-sensitive' correspondingly means that detonation can take place in 21 mm diameter with 0,36 g PETN.In turn 'boostersensitive', ie 'primer-sensitive', means that detonation can take place in a 2i0 1 [45 gallon) drum using 400 g Pento 1 ite; and 'non-booster-sensitive' means detonation cannot take place in a 210 1 r45 gallon) drum using 400 g Pentolite, je a m. xt-ure of equal proportions by mass of PETN and TNT rtriniWro toluenel.

According to another aspect of the invention there Is provided apparatus for loading a flowable bulk explosive into a borehole which comprises 2 flexible pipe or hose; feed means connected to the pipe for separately feeding a non-cap-sensitive explosive base and a sensitizing agent for the base into the pipe so that they pass together along the pipe towards a downstream end of the pipe remote from the feed means; and a mixing device mounted in the pipe for mixing the explosive base and sensitizing agent together as they pass along the pipe, after they have been fed into the pipe and before they issue from the pipe, to form a booster-sensitive explosive.

The downstream end of the pipe may be provided by a lance, the fixing (device being mounted in the lancs, and being in the.

form of a non-return valve, orifice plate or static mixer, although other mixing devices can be employed, particularly if they exert shear on liquids passing therethrough.

The feed means may comprise a rotary helical positive displacement pump, which may be a Mono pump such as a multiple stage Mono pump or a piston pump, for feeding explosive base into the pipe, and a positive displacement dosing pump such as a piston pump for feeding sensitizing agent in the form of a chemical gassing solution into the pipe.

The pipe may have an inlet for explosive base to which the feed means is connected, and which inlet leads centrally ito the upstream end of the pipe, the pipe having an inlet for liquid sensitizing agent to which the feed means is connected, the inlet for liquid sensitizing agent being in the form of an annular groove cr slot directed into the pipe and extending c ircumferentially along the periphery of the pipe arranged to feed sensitizing agent into the pipe in the form of a cylIn-ical or annular layer of sensitizing agent between explosive base fed into the pipe and the wall of the pipe.

The apparatus may include an explosive base supply vessel and a sensitizing agent supply vessel, the vessels being releasably connected to the feed means to permit the feed means to feed explosive base and sensitizing agent respectIvely therefrom into the pipe. The explosive base supply vessel may thus be a suitable hopper, and the sensitizing agent supply vessel may be a suitable tank, eg for chemical gassing solution.

As indicated above, when a liquid sensitizing agent is used as a lubricant, the connection from the tank to the pipe is preferably as close as practicable to the connection from the hopper to the pipe, being a circumferentially extending inwardly facing groove or slot directed into the pipe. For this purpose the flexible pipe may have a rigid, eg metallic, inlet portion to which the hopper and tank are connected. The releasability of the connections between the vessels and the feed means permits the vessels in use to be taken underground, and connected directly to the pumps to form part of the apparatus, being replaced from time to time, as necessary and as their contents are exhausted.

Although the use of dosing pumps is preferred, feeding the explosive base and sensitizing agent into the pipe may take place as indicated above by pressurizing the vessels, eg with compressed air, operated by a pneumatic control system which can be controlled from the lance, which control system acts eg on alr Inlet valves into the pipe, hopper and tank whereby a user holding the lance can control flow of base explosive and liquid gassing solution along the pipe. In similar fashion, the Apparatus tay include a control system for operating the dosing pumps when they are employed, by a user holding the lance.

The hopper and tank may be potable to and away from the blasting site, having a mass or neo ore than say 50 kg.

Alternatively, however, the hopper and tank may be of such a size that it is more convenient to mount them on a motorized vehicle. In this case the whole apparatus may be mounted on said vehicle for easy transport of the apparatus, explosive base and sensitizing agent.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 shows a schematic sectional side elevation of an apparatus mien acecDrdance. with the invention for loading explosive into a borehole; Figure 2 shows a schematic sectional side elevation of another apparatus in accordance with the invention for loading explosive into a borehole; and Figure 3 shows a similar view of part of the apparatus of Figure 2 loading into an upwardly inclined borehole.

In Figure 1 of the drawings, reference numeral 10 generally designates an apparatus in accordance with the present invention, shown in schematic sectional side elevation. The apparatus 10 comprises a lance 12 for loading an explosive such as a slurry explosive or an emulsion explosive into a borehole. The lance will have a length, eg of 1 to 2 m, suitable for the depth cf the boreholes which it is intended to load, and an outside diameter of eg 20 mm whereby it is suitable for loading boreholes of the diameter range 21-110 nm. The lance 12 has an outlet at 14, and, in Its interior, a static mixer 16 z-.eiate1y adjacent true outlet 14. The upstream end of the lance 12 is connected to a flexible hose or pipe Ic, t-pically having an inside diameter of about 25 = and a length of about 30 =.

The upstream end of the flexible portion of the pipe 18 has a metal extension 20, which has a shut off valve 22 therein, ard a branch 24 leading to the outlet of a 25 kg emulsion base hopper 26. The hopper 26 is connected to the pipe 24 by a quick coupling at 28.

A branch pipe 30 from the pipe 20, upstream of the valve 22, extends to the top of the hopper 26, to which it is connected by a quick coupling 32.

A tubular jacket 34 surrounds the pipe 20, downstream of the branch pipe 24, and, at the downstream end of the jacket 34, the pipe 20 is interrupted at 36 in the jacket 34 to provide an annular slot leading into the pipe 20 from the interior of the jacket 34. The jacket 34, at a position spaced from the interruption 36, communicates via a pipe 38 and quick coupling 40 with a gassing solution tank 42. The tank 42 is smaller than the hopper 26.

A branch pipe 44 from the pipe 30 is connected by a quick coupling 46 to a position at the top. of the tank 42. The pipe 30 has a shut-off valve 48 between the branch pipe 44 and the quick coupling 32, and the pipe 44 has a shut-off valve 50. The upstream end of the pipe 20 is shown connected to a compressed air supply pipe 52.

A control valve in the form of a compressed air shut-off valve 54 having a spring loaded plunger 56 connected to the clcsure tiember of the valve 54 and resiliently b zssed to the closed position, is mounted on the upstream end cf the lance 12.

A flexible compressed air supply pipe 58, leading fron the supply ipe 52, extends along the pipe 18, to which -t is attaoned at intervals. A further compressed air control pipe 60, si-ilarly flexible and connected to the pipe 18, extends jack along the pipe 18 from the valve 54, having branch pipes 62, 64 and 66 connected respectively to the valves 22, 48 and 50.The valves 22, 48 and 50 are arranged so that, if the valve 54 is operated to supply air under pressure to said valves 22, 48 and 50, the valves 22, 48 and 50 are opened thereby, and when the plunger 56 is released to close the valve 54, valves 22, 48 and 50 will automatically close in response to a drop in air pressure.

In use, it is contemplated that a plurality of hoppers 26 and tanks 42, containing respectively eg a water-in-oil emulsion explosive base which is non-booste-sensitive, and & sodium nitrite aqueous sensitizing solution, will be transported to a blasting site, eg underground in a mine. One of the hoppers 26 will be connected by its quick couplings 28 and 32 respectively to the pipes 24 and 30, and one of the tanks 42 will be connected respectively via its quick couplings 40 and 46 to the pipes 38 and 44.

To operate the apparatus 10, there should be a supply of air under pressure from the supply line 52 into the pipe 20. When a borehole is to be loaded, an operator will insert the lance 12, free-end-first, into the borehole, into a position adjacent the blind end of the borehole. The plunger 56 will be operated to open the valve 54, thereby opening the valves 22, 48 and 50.

In response thereto, air under pressure flows along the pipes 20 and 18 and through the lance 12 into the borehole, and, si3ul,aneously, air pressure in the hopper 26 forces emulsion base down the pipe 2 into the pipe 20. This emulsion or base is cried by the air passing along the pipe 20 in siug- or plug- flow fashion along the pipe 20, pipe 18 and lance 12, into the borehole.Simultaneously, air pressure in the tank 42 urges gassing solution lnto the jacket 34, and this gassing solution is drawn by suction caused by the venturi effect of emulsion flowing along the pipe 20, and by pressure in the tank 42, through the slot 36 from the jacket 34 into the pipe 20.

The gassing solution will typically have a substantially lower viscosity than the emulsion base, and will flow as a cylindrical coating along the interior of the pipe 20, pipe 18 and lance 12 as far as the static mixer 16. This coating or layer of gassing solution will lubricate the plug-flow of emulsion base along said pipes 20 and 18 and lance 12.

In the static mixer 16, the gassing solution will be thoroughly end homogeneously mixed with the emulsion base, immediately whereafter the mixture , in the form of a capsensitive explosive, or a precursor for such explosive, is loaded into the borehole.

slugs of explosive are loaded successively into the borehole, until the borehole is sufficiently full, compressed air passing through the lance into the borehole escaping from the mouth of the borehole.

When the borehole is full, the plunger 56 of the valve 54 will be released, closing the valves 22, 48 and 50, and stopping low c; compressed air, emulsion base and gassing solution along the pipes 20 and 18 and lance 12.

Successive boreholes will be loaded in similar fashion, and, rom time to time as necessary, empty hoppers 26 and tanks 42 can be exchanged for full ones.

Naturally, if desired, the initial portion of explosive issuing from the lance 14 [which may. not be appropriately mixed if steady-state operation has not been achieved] can be discarded. It will also be appreciated that the dimensions of the slot 36 in the jacket 34 will be matched by routine experiment with the other parameters of the apparatus and its operation, such 2S the viscosities of the emulsion base and gassing solution, the air pressure of the air supply, the lengths and diameters of the various pipes, etc. so that the appropriate or an acceptable proportion of gassing solution is carried along the pipe 18 together with the emulsion base.The proportion of eg sodium nitrite in s'ich gass1r.tI solution san also be adjusted within limits and if necessary, by altering the concentration of the sodium nitrite in the gassing solution.

With reference to Figures 2 and 3, the same reference numerals are used for the same parts, as in Figure 1, unless otherwise specified.

In Figures 2 and 3 the apparatus 10 is shown loading explosive into a borehole 13 in a rock face 15.

Unlike the construction shown in Figure 1, a mixing device in the form cf a homogenizer 16 is shown in Figure 2 at the upstream end of the lance 12, rather than the static mixer 16 shown in Figure 1 at the downstream end of the lance.

n Figures 2 and 3, the upstream end of the flexible portion cf the pipe 18 is fed by a Mono pump 62 whose inlet is connected by a shunt off valve 64 to the outlet of an emulsion base hopper 25. The valve 64 is connected to the pump 62 by a quick coupling [not shown). The hopper 26 has a filling point 66, a manhole 68 and 2 breather 70.

The pump 62 has an outlet pipe 72 provided with a pressure gauge 74.

A jacket 76 surrounds the downstream end of the pipe 72 and in the jacket 76, the pipe 18 has an expanded inlet 78 into which the pipe 72 projects to provide an annular slot 79 leading around the outlet of the pipe 72 into the pipe 18 from the interior of the jacket 76. The jacket 76, at a position spaced from the inlet 78, communicates via a pipe 80 with a gassing solution tank 82.

The tank 82 is smaller than the hopper 26. The pipe 80 is provided with a piston pump 84, a pressure gauge 86 and a flow meter 88. A quick coupling [not shown] is provided between the tank 82 and the pipe 80.

The tank 82 has a filler point 90 and a breather 92, and its outlet to the pipe 80 is provided with an in-line filter 94 and optionally with a shut off valve [not shown].

Use of the apparatus of Figures 2 and 3 is broadly similar to that of Figure 1. Thus, in use for small-scale operations, eg involving 25 kg loads, it is contemplated that a plurality cf hoppers 26 and tanks 82, containing respectively eg a water-inoil emulsion base, and a sodium nitrite-based aqueous sensitizing solution, will be transported to a blasting site, eg underground n z rine. One of the hoppers 26 will be connected by Its quick coupling to the pump 62 and one of the tanks 82 will be connected via its quick coupling to the pipe 80.

or larger-scale operations it is contemplated that the hopper 25 and tank 82 ill be pe=anently fixed to the pumps 62 and 84 respectively and filled from time to time by pumping fre other transportable vessels.

To operate the apparatus 10 of Figures 2 and 3, there should be 2 power supply to the pumps 62 and 84 and switch means for operating said pumps. When a borehole 13 is to be loaded, an operator will insert the lance 12, free-end first , into the borehole, into a position adjacent the blind end of the borehole.

The switch means will then be operated to operate the pumps 62 and 84.

In response thereto, emulsion base is pumped down the pipe 72 into the pipe 18. This emulsion passes along the pipe 18 and lance 12, into the borehole 13. Simultaneously, the gassing solution is pumped into the jacket 76, through the annular slot 79 between the inlet 78 and the pipe 72, into the pipe 18.

The gassing solution will typically have a substantially lower viscosity than the emulsion base, and will flow as a cylindrical coating along the interior of the pipe 18 as far as the homogenizer 16. This coating or layer of gassing solution will lubricate the flow of emulsion base along said pipe 18.

In the homogenizer 16, the gassing solution will be thoroughly and homogeneously mixed with the emulsion base, immediately whereafter the mixture, in the form of a sensitized cap-sensitive explosive, or a precursor for such explosive, passes through the lance 12, from the free end of which it is loaded into the borehole 13.

xplosive is loaded into the borehole 13, until the borehole is sufficiently full.

When the borehole 13 is full, pumps 62 and 84 will be switched off, stopping flow of emulsion base and gassing solution along the pipe 18 and lance 12.

In Figure 2, horizontal boreholes 13 are shown being filled via the lance 12. In Figure 3, on the other hand, vertically upwardly inclined boreholes 13 with their mouths lowermost are shown being filled from below, the lance 12 being omitted and the homogenizer 16 being shown at the end of the hose at the outlet end of an inflatable packer 96 located in the borehole 13 adjacent its mouth, the packer 96 being connected to the outlet of the pipe 18.

Successive boreholes 13 will be loaded in a similar fashion, and, from time to time as necessary, empty hoppers 26 and tanks 82 can be exchanged for full ones, or refilled through their filler ports 66 and 90 respectively.

Examples of suitable emulsion bases can have the following representative compositions: Constituent Emulsion 1 Emulsion 2 % bv mass % bv mass Ammonium Nitrate [88% by mass solution in water 79,70 79,70 Sodium nitrate 13,09 Calcium nitrate 13,0 Additional water 0,78 0,78 Mineral Oil 5,03 5,C3 Scrbitan monooleate or sorbitan sesquloleate [surf actant emulsifier] 1,40 1,40 These emulsion bases will be emulsified to a degree and to a droplet size such that they have sufficiently low viscosity for easy handling by the apparatus shown in the drawings, and will have a density of about 1,40-1,45 g/ml. ifi this regard a static mixer or homogenizer 16 will be selected which, while mixing the gassing solution with the emulsion base, subjects the emulsion base to sufficient shear, to reduce its droplet size to an extent that its viscosity is increased sufficiently to allow it to be loaded into vertically downwardly opening boreholes, without its running or dropping out of such boreholes.

It is further contemplated that routine experimentation as i:eards size size of the slo~ , 79 and the concentration of the sodium nitrite solution will be employed to obtain a capsensitive sensitized emulsion explosive product, issuing from the lance 12 or mixer 16, which is chemically gassed and which has a density in the range 0,7 - 1,3 g/ml, and with a viscosity of about 20 000- 3 000 000 cP at ambient temperature, compared with a viscosity of the emulsion base at the same temperature of about 10 000 - 35 000 cP, as measured on a Brookfield Viscometer using a number 7 spindle at 1 rpm and 50 rpm respectively.While the emulsion issuing from the lance may not be fully gassed, once it is loaded into the borehole 13, nitrite ions from the gassing solution will react with ammonium ions in the emulsion, to produce nitrogen bubbles in situ which gas the emulsion and reduce its density. The bubbles are homogeneously dispersed in the emulsion and the viscosity of the emulsion is sufficiently high to prevent their migrating undesirably before detonatIon.

Various tests have been carried out on the invention, usIng various ammonium nitrate-based water-in-oil emulsion bases of about 6% by mass oil phase, of the type identified as Sample hereunder, and using a sodium nitrite-based gassing solution. The tests were carried out in plastics test pipes and at mining sites in 57 mm, and 76 mm and 110 = boreholes of lengths cf about 235 m. Mono pump outlet pressures of the order of 1 900- 4 000 kPa were employed.

In a first series of tests in plastics pipes emulsion flow rates to 30 - 70 kg/min were employed with gassing solution flow rates of 1,3 - 2,3ask by mass of the emulsion flow rate, the emulsion base having viscosities of the order of 19 000 cP at 30"C and 32 000 cP at 200C. Gassed emulsion densities of 0,71,2 g/ml were achieved. A homogenizer 16 with an outlet jet nozzle of 7 mm diameter was used to provide a strong jet which helped to compact the explosive in the pipe.

In a second series of tests, the boreholes were filled to depths of about 2 - 35 m with explosive, ie about 5 - 120 kg of explosive. In each case an inflatable packer was used to form a plug at the mouth of the borehole during charging to prevent loss of explosive during charging. Boreholes extending upwardly at angles of 60 - 90 to the horizontal were successfully charged and the product was sufficiently viscous to prevent explosive from dropping out of the charged boreholes. The homogenizer 16 was connected either at the outlet or open end of the packer 46, as shown in Figure 3, or to the downstream end of the pipe 18, inmeciately before the packer 46.

An example of emulsion base actually tested was: Consituent a bv rass Ammonium nitrate 73,0 Sodium nitrate ,7 Thiourea 0,05 Acetic Acid 0,04 Mineral [=uelJ oil 5,13 Sorbitan monooleate or Sorbitan sesquioleate 0,87 Water 15,13 pH 3,4 - 3,8 It is believed that the above constituents can be varied, within limits, if desired, eg by omitting sodium nitrate, or by including calcium nitrate, or by replacing some of the sodium nitrate with calcium nitrate, or by increasing the proportion of sodium nitrate or calcium nitrate or by varying the proportion of fuel between 5 and 7,0%. Furthermore, different oils and emulsifying agents can be used, eg a paraffin oil or a polyisobutyl sl.locinamide e lsifier.

The gassing solution employed was a solution of sodium nitrite in water, at the flow rates given above and at concentrations such as to give the degree of gassing and density reduction given above.

The charges were successfully detonated.

It is a particular advantage of the invention that a noncap-sensitive and preferably non-booster-sensitive emulsion base can be employed, and that the explosive will only become sensitized ie booster-sensitive or optionally cap-sensitive as it enters the borehole. Any sensitized explosive which is possibly generated in the homogenizer 16 will not be prone to detonation, bearing in mind the relatively very small diameter passages encountered in such static mixers.

Claims (17)

1. A method of loading a flowable bulk explosive into a borehole which comprises separately feeding a non-cap-sensitive explosive base and a sensitizing agent for sensitizing the base into a flexible pipe or hose so that they pass together along the pipe towards the downstream end of the pipe, and the method including the step of mixing the explosive base and sensitizing agent together after they have been fed into the pipe, the mixture issuing from the downstream end of the pipe into the borehole, where it provides a booster-sensitive explosive.

2. A method as claimed in claim 1, in which the explosive base is an emulsion or slurry base and the sensitizing agent is a density reducing agent, so that the explosive which is provided in the borehole is a slurry or emulsion explosive.

3. A method as claimed in claim 1 or claim 2, in which the explosive base is non-booster-sensitive and is capable of having ts viscosity increased by subjecting it to shear, and in -*s c:- r se-.st1zing agent is a chemical gassing solution, the method flcluaIng subjecting the liquid passing along the pipe to mixing and shear at or adjacent the downstream end of the pipe.

z. A method as claimed in any one of the receding claims, in which the mixing of the explosive base and sensitizing agent 15 effected by passing the liquid passing along the pipe through a non-return valve, orifice plate or static mixer at or adjacent the downstream end of the pipe, thereby to mix the explosive base and sensitizing agent together while subjecting the liquid to shear.

5. A method as claimed in any one of the preceding claims, in which the downstream end of the pipe is provided by a lance in which the tniYirg takes place.

6. A method as claimed in any one of the preceding claims, in which the explosive base is fed into the pipe by means of a rotary helical positive displacement pump.

7. A method as claimed in claim 6, which includes lubricating the passage of the explosive base along the pipe by feeding a lubricating liquid into the pipe so that it at least partially forms an annular lubricating layer around the explosive base as it passes along the pipe.

8. A method as claimed in claim 7, in which the lubricating liquid is a chemical gassing solution which provides the sensitizing agent and is fed by a positive displacement dosing tumt into the pipe through an annular inlet into the pipe1 at or downstream adjacent the position where the explosive base is fed nto the pipe.

c A method as claimed in any one of the preceding cla~ ifi which the borehole has a diameter of 21-110 mm.

10. A method as claimed in any one of the preceding claims, in which the borehole slopes upwardly from a mouth at its lower end, the explosive issuing upwardly into the borehole from the downstream end of the pipe.

11. Apparatus for loading a flowable bulk explosive into a borehole which comprises a flexible pipe or hose; feed means connected to the pipe for separately feeding a non-cap-sensitive explosive base and a sensitizing agent for the base into the pipe so that they pass together along the pipe towards a downstream end of the pipe remote from the feed means; and a mixing device mounted in the pipe for mixing the explosive base and sensitizing agent together as they pass along the pipe, after they have been fed into the pipe and before they issue from the pipe, to form a booster-sensitive explosive.

12. Apparatus as claimed in claim 11, in which the downstream end of the pipe is provided by a lance, the mixing device being mour.ted in the lance, and being in the form of a non-return valve, orifice plate or static mixer.

13. Apparatus as claimed in claim 11 or claim 12, in which the eed means comprises a rotary helical positive displacement pur for feeding explosive base into the pipe, and a positive displacement dosing pump for feeding sensItizing agent in the form of a chemical gassing solution into the pipe.

4. Apparatus as claimed in any one of claims 11 to 13 inclusive in which the pipe has an inlet for explosive base to which tre feed means is connected, and which inlet leads centrally into the upstream end of the pipe, the pipe having an inlet for liquid sensitizing agent to which the feed means is connected, the inlet for liquid sensitizing agent being in the fcrr of an annular groove or slot directed into the pipe and extending circumferentially along the periphery of the pipe arranged to feed sensitizing agent into the pipe in the form of a cylindrical or annular layer of sensitizing agent between explosive base fed into the pipe and the wall of the pipe.

15. Apparatus as claimed in any one of claims 11 to 14 inclusive, which includes an explosive base supply vessel and a sensitizing agent supply vessel, the vessels being releasably connected to the feed means to permit the feed means to feed explosive base and sensitizing agent respectively therefrom into the pipe.

16. A method of loading a flowable bulk explosive into a borehole, substantially as described herein.

17. Apparatus for loading a flowable bulk explosive into a borehole, substantially as described herein.