WO2019053527A1

WO2019053527A1 - Explosives blasting

Info

Publication number: WO2019053527A1
Application number: PCT/IB2018/055837
Authority: WO
Inventors: Laurence Justin Pienaar Wilson; André Pienaar
Original assignee: AEL Mining Services Ltd
Current assignee: AEL Mining Services Ltd
Priority date: 2017-09-12
Filing date: 2018-08-03
Publication date: 2019-03-21
Anticipated expiration: 2020-03-12
Also published as: WO2019053528A1; ZA201906906B; ZA201906905B

Abstract

La présente invention concerne un ensemble de sautage subaquatique pour sautage sous l'eau à l'aide d'un explosif à émulsion, ledit ensemble comprenant deux éléments d'ensemble de sautage subaquatique reliés ou plus, dont au moins un est un contenant d'explosif en émulsion qui est creux et contient un explosif en émulsion, l'ensemble de sautage et/ou au moins certains des éléments d'ensemble de sautage respectivement, ayant une gravité spécifique, par rapport à l'eau, dans une plage d'environ 0,90 à environ 1,25.The present invention relates to an underwater blasting assembly for underwater blasting using an emulsion explosive, said assembly comprising two or more connected subaqueous blast assembly elements, at least one of which is a blister pack. an emulsion explosive which is hollow and contains an emulsion explosive, the blast assembly and / or at least some of the blast assembly elements respectively, having a specific gravity, with respect to the water, within a range of about 0.90 to about 1.25.

Description

EXPLOSIVES BLASTING

FIELD OF THE INVENTION

THIS INVENTION relates to explosives blasting, i.e. blasting using explosives. More specifically, the invention relates to blasting under water. The invention provides an underwater blasting assembly. The invention also provides a method of blasting under water. The invention further provides an underwater blasting installation.

SUMMARY OF THE INVENTION

IN ACCORDANCE WITH A FIRST ASPECT OF THE INVENTION IS PROVIDED an underwater blasting assembly for blasting under water using an emulsion explosive, the assembly comprising two or more connected underwater blasting assembly elements, at least one of which is an emulsion explosive container that is hollow and contains emulsion explosive, wherein the blasting assembly and/or at least some of the blasting assembly elements respectively and/or the contents of at least some of the blasting assembly elements respectively, have a specific gravity, relative to water, in a range of from about 0.90 to about 1 .25.

Emulsion explosive to which the invention herein described applies may in particular be bulk emulsion explosive as used in earth blasting applications, e.g. mining applications. The specific gravity of the blasting assembly and/or at least some of the blasting assembly elements respectively and/or the contents of at least some of the blasting assembly elements respectively may, for example, be about 0.90, about 1 , about 1.15, about 1 .18, or about 1 .25.

It will be appreciated that an effect of a specific gravity smaller than 1 would be that the assembly and/or a particular element thereof sinks in water, and that an effect of a specific gravity greater than 1 would be that the assembly and/or a particular element thereof floats, i.e. is buoyant, in water. In accordance with the invention, by utilising elements of varying specific gravity in constructing the assembly, e.g. in accordance with the method hereinafter described, which would typically comprise a plurality of blasting assembly elements (the number depending on the depth to which the assembly should extend and the lengths of the respective elements), the specific gravity of the assembly can be varied as the assembly is constructed, typically in water, thereby facilitating handling of the assembly and thereby facilitating the location of emulsion explosive at an underwater location, e.g. in a water-logged borehole.

The blasting assembly elements of the assembly may be connected in series, i.e. one following the other.

In one embodiment of the invention, the blasting assembly elements may each have two, opposite, ends, and may be connected in series and end-to-end with at least one adjacent element. The ends of the blasting elements may therefore be configured for such connection and/or the blasting assembly may include connection pieces that enable end-to-end connection of adjacent elements. The blasting assembly elements would typically be elongate elements, and would preferably all be hollow, optionally containing a substance such as emulsion explosive or a different non-explosive substance to provide a heavier-than-water blasting assembly element as hereinafter described. For example, at least the emulsion explosive containers, but preferably all of the blasting assembly elements, may be in the form of elongate lengths of rigid hollow pipe. Each length of pipe may typically have a length dimension in a range of from about 1 meter to about 6 meters, more preferably from about 3 meters to about 6 meters.

The pipe may have a diameter of from about 25mm to about 300mm, more preferably from about 63mm to about 75mm.

The emulsion explosive contained in one or more of the emulsion explosive containers may be sensitised emulsion explosive, i.e. it may be gassed emulsion explosive which has been sensitised by gassing, e.g. with the aid of a gassing agent such as a gassing solution. Gassing changes the density of the emulsion explosive

The emulsion explosive contained in a particular emulsion explosive container may have been gassed before being loaded into the container, or after having been loaded into the container. It may also have been gassed partly before being loaded into the container, and may then have been further gassed after having been loaded into the container. When gassed (partly or fully) inside of the container, the container may for the whole or for a part of the gassing have been separate of the assembly, or may have been part of the assembly. It follows that the emulsion explosive containers containing emulsion explosive may be pre-filled with emulsion explosive, i.e. they may have been filled with emulsion explosive prior to being included in the assembly. As noted above, emulsion explosive contained by one or more such containers may have been or may have become sensitised separately of the assembly. In another embodiment, the emulsion explosive contained by one or more such containers may have been or may have become sensitised during or after inclusion of the emulsion explosive container that contains it, in the assembly.

In one embodiment of the invention, all of the elements of the assembly may comprise emulsion explosive containers, each of which contains emulsion explosive. Such containers, filled with emulsion explosive, may respectively be heavier or lighter than water, or have a specific gravity approximating 1 , in accordance with the invention. Such variation in specific gravity may typically be achieved by controlling the extent to which the emulsion explosive contained by each emulsion explosive container is gassed. In this regard it is noted that the density of an emulsion explosive varies depending on its composition and, more sensitively, on its degree of sensitisation (gassing). The density of emulsion explosive contained in respective emulsion explosive containers included in the assembly may, for example, vary between about 0.90 and about 1 .25, e.g. being about 0.90, about 1 , about 1 .15, about 1 .18, or about In another embodiment of the invention, at least one of the elements of the assembly is a lighter-than-water element devoid of emulsion explosive. Typically, such one or more elements would be empty containers, e.g. empty emulsion explosive containers. In yet another embodiment of the invention, at least one of the elements of the assembly is a heavier-than-water element devoid of emulsion explosive. Typically, such one or more elements would be emulsion explosive containers filled with a substance, other than emulsion explosive (e.g. sand), that renders such heavier-than- water elements heavier than water.

In a further embodiment of the invention, the blasting assembly elements of the assembly may comprise a combination of one or more emulsion explosive containers containing emulsion explosive, one or more lighter-than-water blasting assembly elements, and one or more heavier-than-water blasting assembly elements.

Typically, where the assembly comprises emulsion explosive containers following one another, i.e. a series connection (typically an end-to-end connection of blasting assembly elements as described above) whether empty or filled with either emulsion explosive or a substance that renders it heavier than water, the interiors of the containers would be separated from one another, i.e. would not be in communication. Where, strictly speaking, communication does exist, such communication would be materially restricted, i.e. such that the contents of one container cannot readily pass to the interior of another container. An exception to this situation is provided for below. At least some of the blasting assembly elements, and particularly the emulsion explosive containers containing emulsion explosive, may be in blasting communication, e.g. may be provided, typically at their ends, with detonation propagation means, by means of which detonation of emulsion explosive, in use, is propagated from one emulsion explosive container containing emulsion explosive, to an adjacent container containing emulsion explosive, to detonate the emulsion explosive in the last-mentioned container. For example, when connection pieces are used, the connection pieces may comprise explosive boosters or, more typically, detonator-booster assemblies that propagate the detonation. It will be appreciated that in this embodiment it is envisaged that the assembly includes at least two adjacent, e.g. end-to-end connected, emulsion explosive containers.

In the case of the lighter- and heavier-than-water elements, which do not contain emulsion explosive, separating emulsion explosive containers containing emulsion explosive from each other, blasting cord or another detonation propagating means such as shock tube or the like, may be employed to achieve propagation of detonation from one emulsion explosives container to another. Thus, the assembly may include at least two emulsion explosive containers containing emulsion explosive that are separated from each other by one or more lighter- and/or heavier-than-water blasting assembly elements, which emulsion explosive containers thus separated may be in blasting communication with each other e.g. by means of blasting cord that extends from the one emulsion explosive container to the other along the one or more lighter- and/or heavier-than-water blasting assembly elements. The blasting cord may then extend through or along such lighter- and/or heavier-than-water elements to propagate detonation to an earlier (i.e. more distal) emulsion explosive container containing emulsion explosive that is spaced by such lighter- and/or heavier-than-water elements from a later (i.e. more proximal) emulsion explosive container containing emulsion explosive ("earlier" and "later" referring to the sequence of construction of the assembly, i.e. an earlier emulsion explosive container would be located deeper beneath the surface of the water in which blasting is to be effected, than a later emulsion explosive container).

All of the blasting assembly elements of the blasting assembly may have the same specific gravity. More typically, however, the specific gravity of the blasting assembly elements of the blasting assembly may vary. Within such variation, some of the blasting assembly elements may incidentally or purposefully have about the same specific gravity, regarded overall the blasting assembly elements of the assembly would then not all have the same specific gravity. The specific gravity of the blasting assembly may be maintained within the abovementioned range, and may in fact be selectively varied within this range, by progressive construction thereof to establish one of the abovementioned embodiments. Such construction would typically be in accordance with the method of the second aspect of the invention, and statements relating to the currently discussed first aspect of the invention that relate to the assembly and the manner in which the assembly is constructed therefore apply also to the method of the second aspect of the invention which is in particular a method of constructing the assembly of the first aspect of the invention. It is envisaged that, from time to time, the specific gravity of the assembly and/or of one or more individual elements thereof, could incidentally move outside of the abovementioned range. This may be the case in particular where the specific gravity of the contents of a particular blasting assembly element is within the characterised range, as opposed to the specific gravity of the blasting assembly element itself.

The abovementioned maintenance and variation of the specific gravity may be achieved by configuring the respective elements such that at least some of the elements individually each have a specific gravity between 0.90 and 1 .25, as mentioned in the main statement of invention above. It will be appreciated in this regard that the addition of lighter-than-water elements decreases the specific gravity of the assembly (i.e. increases the buoyancy of the assembly), while the addition of heavier-than-water elements increases the specific gravity of the assembly (i.e. deceases the buoyancy of the assembly).

In use the assembly may, as described in accordance with the method of the second aspect of the invention, be progressively constructed in a body of water in which blasting would be effected, by connecting "later" elements to a surface-side end of the "latest" element of that part of the assembly that is already in the water. The addition of emulsion explosive containers containing emulsion explosive, lighter-than-water elements or heavier-than-water elements, would then be determined at least with reference to observed buoyancy characteristics of the assembly as it is constructed, typically in the context of operational blasting considerations (e.g. the desired volume of emulsion explosive at various depths in the body of water). The ability to control, i.e. vary, the specific gravity of the blasting assembly through adaptive progressive construction thereof using the elements described above, is regarded as being particularly advantageous to handling bulk quantities of emulsion explosive in a body of water in which blasting would be effected using the emulsion explosive.

The assembly may typically, in use, have any desired length, dictated by the depth of the body of water in which blasting would be effected. For example, the assembly may have a length of up to about 80 meters or more, i.e. it may extend to a depth in a body of water that is up to about 80 meters or more. Typically, the assembly would have a length of at least 40 meters or more.

The assembly would, in an installation thereof as described above, typically extend substantially vertically into the body of water.

In some embodiments, a section of the assembly may comprise emulsion explosive containers the interiors of which are in full, or virtually full (i.e. not materially constricted) communication with one another. The emulsion explosive containers of such a section may then not be pre-filled with emulsion explosive, but be filled with emulsion explosive in situ in the body of water. This may typically be the case for the "surface side" of the assembly, e.g. the first 40 meters of the assembly, measuring from the end of the assembly that would be or, in use, is at the surface of a body of water in which the assembly is located. Blasting assembly elements, whether emulsion explosives containers or not, may have been pressure-tightly sealed at least at the time when they are submerged in the body of water during progressive construction of the assembly, e.g. in accordance with the method hereinafter described. Such pressure-tight sealing, of a particular blasting assembly element, may be achieved by connection of the blasting assembly element to an earlier blasting assembly element at one end thereof, and by connection of a later blasting assembly element to the blasting assembly element at the other end thereof, optionally by means of respective connection pieces. It may, in some embodiments of the invention, be connection pieces that pressure-tightly seal a particular blasting assembly element.

By "pressure-tightly sealed" is meant that a blasting assembly element is closed such that the pressure inside of the blasting assembly element after sealing, to which the gassed emulsion explosive is subjected in a case in which the blasting assembly element is an emulsion explosives container, remains substantially unaffected by changes in ambient pressure outside of the explosives blasting container.

Thus, for example, pressure tightly sealing a blasting assembly element would be such that an increase in ambient pressure e.g. due to submergence of the blasting assembly element in water, does not result in a concomitant increase in pressure inside of the explosives blasting container, with the pressure inside of the explosives blasting container remaining substantially constant.

In this regard it is noted that in certain embodiments "pressure tightly sealed" may include a case in which the contents of a blasting assembly element are still exposed to the atmosphere, but is sealed off from the body of water. In some cases, that do not fall within but may include such embodiments, some earlier blasting assembly elements may be air-tightly closed, e.g. may be air-tightly connected with later blasting assembly elements, with such air-tightly closed blasting assembly elements thus being fully isolated from other blasting assembly elements, and also from the body of water. In such a case, the contents of such a blasting assembly element would of course not be exposed to the atmosphere. In other embodiments however, for example in respect of the latest blasting assembly element of the assembly at any given time, a blasting assembly element, or a plurality of blasting assembly elements that are not air-tightly connected to and thus separated from each other, may be open to the atmosphere, e.g. at the mouth of the latest element that would typically be located above the surface of the body of water, and sealed off from the body of water. This may, for example, be the case during construction when a lighter-than-water or heavier-than-water blasting assembly element devoid of emulsion explosive is added to the assembly, having a proximal end that is open, or when a plurality of such elements would make up a section of the assembly, or when one or a plurality of emulsion explosive containers would make up a section of the assembly and would be filled only as part of the assembly, i.e. would be included in the assembly empty and filled after such inclusion.

IN ACCORDANCE WITH A SECOND ASPECT OF THE INVENTION IS PROVIDED

a method of blasting under water using an emulsion explosive, the method including progressively constructing, in a body of water, an underwater blasting assembly in accordance with the first aspect of the invention, by progressively connecting later blasting assembly elements to earlier blasting assembly elements such that earlier blasting assembly elements progressively extend deeper into the body of water, selectively using

emulsion explosive containers containing emulsion explosive selected from emulsion explosive containers containing emulsion explosive that are lighter-than-water,

emulsion explosive containers containing emulsion explosive that are heavier-than-water, and

emulsion explosive containers containing emulsion explosive, the specific gravity of which, relative to water, approximates 1 ;

lighter-than-water blasting assembly elements devoid of emulsion explosive; and

heavier-than-water blasting assembly elements, devoid of emulsion explosive based at least on observed buoyancy characteristics of the assembly as it is constructed.

In this sense, "progressively" effectively means one blasting assembly element at a time, although it is not excluded to pre-assembly two or more blasting assembly elements and then connecting such pre-assembled blasting assembly elements to elements already forming part of the assembly, or commencing the assembly in this manner.

It is further appreciated that the method does not require a blasting step (i.e. a step of detonating the emulsion explosive contained in the emulsion explosive containers), and in this regard the method may probably be better characterised as forming part of a method of blasting. As in the case of the first aspect of the invention, lighter than water and heavier than water is determined with reference to the specific gravity of the relevant blasting assembly elements, relative to water.

The method may thus include observing buoyancy characteristics of the assembly as it is constructed, i.e. whether at any particular stage of its construction the assembly favours sinking, or sinks, or favours floating, or floats. The selection of containers containing emulsion explosive, lighter-than-water elements and heavier-than-water elements may be made in the context of operational blasting considerations, e.g. the depth at which blasting is required..

The method may include pre-loading at least some of the blasting assembly elements that are in the form of emulsion explosive containers, with emulsion explosive, i.e. loading emulsion explosive into the emulsion explosive containers before using such containers in constructing the blasting assembly.

The method may also include allowing or causing the emulsion explosive to be sensitised (i.e. to be gassed) before using containers containing the emulsion explosive in constructing the blasting assembly.

The method may include detonating the emulsion explosive. IN ACCORDANCE WITH A THIRD ASPECT OF THE INVENTION IS PROVIDED an underwater blasting installation for blasting under water using an emulsion explosive, the installation comprising an underwater blasting assembly in accordance with the first aspect of the invention, the blasting assembly being at least partly submerged in a body of water in which blasting is to be effected.

BRIEF DESCRIPTION OF THE DRAWINGS

THE INVENTION WILL NOW BE DESCRIBED IN MORE DETAIL with reference to the accompanying drawings in which

FIGURE 1 shows, diagrammatically in sectional side view, a first embodiment of the installation of the invention;

FIGURE 2 shows, diagrammatically in sectional side view, a second embodiment of the installation of the invention;

FIGURE 3 shows, diagrammatically in sectional side view, a third embodiment of the installation of the invention; and

FIGURE 4 shows, diagrammatically in sectional side view, including a partial detail plan view inset, a blasting assembly element support in use.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION REFERRING TO THE DRAWINGS and in particular to Figure 1 , reference numeral 10 generally indicates a blasting installation in accordance with the invention.

The installation 10 comprises a first embodiment of a blasting assembly 12 in accordance with the invention, submerged in a body of water 14 contained in a waterlogged borehole 16. The borehole 16 has a depth D of about 80 meters, as does the body of water 14.

The assembly 12 comprises six blasting assembly elements 18.1 to 18.6. Each element 18.1 to 18.6 is an emulsion explosive container in the form of an elongate length of plastic rigid pipe of a length L that is in the range of about 1 meter to about 6 meters, more preferably from about 3 meters to about 6 meters. Further, each pipe has a diameter in a range of from about 25mm to about 300mm, more preferably from about 63mm to about 75mm. Hereinafter, reference numeral 18 refers to the containers collectively or to unspecified containers.

Adjacent containers 18 are connected to each other end-to-end, such that the "earliest" and therefore deepest container is the one referenced 18.6 and such that the latest and therefore shallowest container is the one referenced 18.1 .

Each of the containers 18 contains a sensitized emulsion explosive formulation. The containers 18 were pre-filled with emulsion explosive, prior to construction of the assembly 12. The emulsion explosive was sensitised, i.e. was allowed to gas out fully (i.e. to be fully gassed), before the containers were used in constructing the assembly 12. In accordance with the invention the extent of gassing of the emulsion explosive may have been limited, however, in order to achieve a desired density thereof so as to provide a blasting assembly element with a specific gravity within the range provided in accordance with the invention. Although not illustrated in the drawings, each of the containers 18 has female screw- thread end pieces at opposite ends thereof. Male connection pieces with oppositely extending complementally screw-thread male connection portions connect adjacent containers 18 to each other by engaging with adjacent end pieces of adjacent containers. Thus, an airtight connection is established between the interiors of adjacent containers 18.

The connection pieces each include a booster explosive that serves, in use, to assist propagation of detonation of emulsion explosive along the assembly 12.

Construction of the assembly 12 involved partly submerging the earliest emulsion explosive container 18.6 in the body of water 14, holding one of its ends, carrying an end piece, in a position in which it is exposed above the surface of the body of water 14. One of the connection portions of a connection piece was then screwed into the exposed end piece.

Thereafter, a first "later" emulsion explosive container 18.5 was connected to the earliest container 18.6 by screwing engagement of one of its end pieces to the other connection portion of the connection piece already connected to the exposed end piece of the earliest container 18.6. Thus, the assembly 12 became partly assembled.

The partly assembled assembly 12, comprising the earliest and first "later" containers 18.6, 18.5, was then allowed, in a controlled manner, to submerge deeper into the body of water 14, to a level at which the free end of the first "later" container 18.5 is exposed above the surface of the body of water 14, in which position it is held for further construction of the assembly 12.

It will be appreciated that the abovementioned controlled submergence of the partially constructed assembly 12 supposes a specific gravity approximating 1 , i.e. such that the partially constructed assembly does not rapidly sink or have excessive buoyancy obstructing its submergence (such incidences are provided for in the second embodiment of the assembly 12 that is discussed with reference to Figure 2). A second "later" container 18.4 was then connected to the free end of the second container 18.5 in the same manner in which connection between the earliest and first "later" containers 18.6, 18.5 was established.

Thus, construction of the assembly 12 proceeds progressively with further addition of fourth, fifth and sixth "later" containers 18.3, 18.2, 18.1 .

The engagement of the adjacent end pieces of the containers 18.1 & 18.2, 18.2 & 18.3, 18.3 & 18.4, 18.4 & 18.5, 18.5 & 18.6, with respective connection pieces establishes separation of the interiors of the containers 18 that prevents passage of emulsion explosive between them.

In the assembly 12, the density of the emulsion explosive and the specific gravity of the assembly, as it was being constructed, was such that the containers 18 and the progressively growing assembly 12 could be handled in the body of water 14 without great difficulty, i.e. without rapid sinking or obstructive buoyancy being encountered. In light hereof, and in light of detonation requirements in the borehole 16, the assembly 12 can consist of an uninterrupted series of emulsion explosive containers 18 containing emulsion explosive. It is noted that the assembly 12 also includes a detonator and booster 20 typically in the form of a detonator/booster assembly, at the free end of the uppermost, or latest (i.e. most proximal), container 18, in order to initiate detonation of the emulsion explosive. Hereinafter reference may from time to time be made only to the detonator, but it is understood that it would typically comprise a booster as well.

Referring now Figure 2, and using the same reference numerals to refer to features that also appear in Figure 1 , but with the additional designation "a", reference numeral 10a generally indicates another embodiment of a blasting installation in accordance with the invention.

The installation 10a comprises a second embodiment of a blasting assembly 12a in accordance with the invention, submerged in a body of water 14a contained in a waterlogged borehole 16a. The borehole 16a has a depth D of about 80 meters, as does the body of water 14a.

The assembly 12a comprises emulsion explosive containers 18a.2, 18a.4, and 18a.6 all of which are in the same form as containers 18.2, 18.4, and 18.6 of the assembly 12 of Figure 1. Instead of containers 18.1 , 18.3 and 18.5, however, the assembly 12a includes, respectively, lighter-than-water element 21 .1 , heavier-than-water element 23, and lighter-than-water element 21 .2. Each of these are in the form of emulsion explosive containers devoid of emulsion explosive, with the lighter-than-water elements 21 .1 , 21.2 being empty and the heavier-than-water elements 23 being filled with sand. Thus, containers 18a.1 and 18a.5 are rendered lighter-than-water and container 18a.3 is rendered heavier than water.

Physical construction of the assembly 12a took place in the same manner as described above in relation to construction of the assembly 12 illustrated in Figure 1 . Considerations taking into account during construction differed, however, as discussed below.

Each of containers 21 .1 , 23, and 21.2 has a length of blasting cord extending therethrough, into the adjacent emulsion explosive containers 18a.2, 18a.4 and 18a.6 that contain emulsion explosive. Thus propagation of detonation initiated by the detonator/booster assembly 20a through the empty and sand-filled containers 18a.1 , 18a.3 and 18a.5 is achieved in use. The inclusion of containers 21 .1 , 23 and 21 .2 serve to control the buoyancy of the assembly 12a. More particularly, it may have been found during construction of the assembly 12a that container 18a.6 is not sufficiently buoyant for constructing the remainder of the assembly 12a, thus motivating the inclusion of empty container 21 .1 to increase the buoyancy, which may have been allowed for by blasting considerations at the site. The addition of the emulsion explosive container 18a.4 containing emulsion explosive may not have been sufficient to reduce buoyancy to a desired level, thus motivating inclusion of sand-filled container 23 further to reduce the buoyancy. Addition of the emulsion explosive container 18a.2 containing emulsion explosive may then again have further decreased the buoyancy of the assembly 12, to an undesired level, thus motivating inclusion of the empty container 21 .2. Thus, as construction of the assembly 12a progressed, its buoyancy was controlled in accordance with the method of the invention, insofar allowed by blasting considerations.

Finally, referring to Figure 3, reference numeral 10b indicates a third embodiment of a blasting installation in accordance with the invention.

The installation 10b comprises a third embodiment of a blasting assembly 12b in accordance with the invention, submerged in a body of water 14b contained in a waterlogged borehole 16b. The borehole 16b has a depth of about 80 meters, as does the body of water 14b, divided for the purpose of illustration into two 40 meter sections respectively designated as D1 and D2.

The assembly 12b comprises the containers 18a.4, 21 .2 and 18a.6 of the assembly 12a illustrated in Figure 2. In this part, the assembly 12b is constructed in the same manner as the assembly 12a. For the assembly 12b, the three containers 18a.4, 18a.5 and 18a.6 occupy the lower 40 meters of the borehole 16b (i.e. D2 shown on the drawing of Figure 3) and therefore also of the body of water 14b.

The upper 40 meters of the borehole 16b (i.e. D1 shown on the drawing of Figure 3), and therefore also of the body of water 14b, is occupied by three further emulsion explosive containers 19 containing emulsion explosive. In contrast to the containers 18a.4 and 18a.6, the containers 19 were not pre-filled with emulsion explosive. Also in contrast to the containers 18a.4, 21 .2 and 18a.6, the interiors of the containers 19 are not separated from one another, i.e. they are in communication such that emulsion explosive can pass between them. This allows for the assembly 12b to be constructed using the containers 19 while empty, and to fill them jointly by pumping emulsion explosive into their communicating interiors and thus fill their jointly defined interior volume with emulsion explosive, to provide the configuration of the assembly 12b illustrated in Figure 3.

Finally, in Figure 4, reference numeral 100 shows a stage in the construction of the assembly 12 of Figure 1 , more specifically the connection of container 18.5 to container 18.6. As mentioned above, such connection requires container 18.6 to be held in a position at which one of its ends is exposed above the surface of the body of water 14, or above the surface of the blast hole 16. This holding is effected by means of a support 102 that acts as an interfering flange.

As will be seen from Figure 4 and the plan view inset to it, the support 102 comprises a planar body 104 in which an elongate U-shaped cut-out 106 is defined, in which cut- out the exposed end of container 18.6 is received.

DISCUSSION

THE APPLICANT has found that by controlling the specific gravity of the individual blasting assembly elements and/or of the blasting assembly such that it remains within 0.90 to 1 .25, relatively heavy weights of emulsion explosive can be conveniently handled in a body of water, specifically a deep body of water, to facilitate blasting in the body of water.

Furthermore, by connecting respective elements, and particularly emulsion explosive containers, in an airtight manner, detrimental effects of pressure on emulsion explosive at depths beyond 40 meters, e.g. around 80 meters, are avoided.

The Applicant therefore regards the invention as addressing difficulties that are usually encountered in blasting under water with bulk emulsion explosives, particularly in mining applications, e.g. where deep boreholes are naturally waterlogged or if blasting is required in open stretches of water such as the deepening of a harbour trench, in a water way.

It is expected that the invention could also generally find application in deep blasting applications, by pre-charging a dry borehole with water, to allow for the invention to be exploited in such artificially wetted boreholes.

Claims

1 . An underwater blasting assembly for blasting under water using an emulsion explosive, the assembly comprising two or more connected underwater blasting assembly elements, at least one of which is an emulsion explosive container that is hollow and contains emulsion explosive, wherein the blasting assembly and/or at least some of the blasting assembly elements respectively, has/have a specific gravity, relative to water, in a range of from about 0.90 to about 1 .25.

2. The assembly according to claim 1 , wherein

all of the blasting assembly elements comprise emulsion explosive containers, each of which contains emulsion explosive,

or wherein

at least one of the blasting assembly elements is a lighter-than-water element devoid of emulsion explosive; and/or

at least one of the blasting assembly elements is a heavier-than-water element devoid of emulsion explosive.

3. The assembly according to claim 2, in which the blasting assembly elements of the assembly comprise a combination of one or more emulsion explosive containers containing emulsion explosive, one or more lighter-than-water blasting assembly elements and one or more heavier-than-water blasting assembly elements.

4. The assembly according to any or claims 1 to 3, wherein the blasting assembly elements of the assembly are connected in series, each blasting assembly element having two, opposite, ends, and being connected end-to-end with at least one adjacent blasting assembly element.

5. The assembly according to any of claims 1 to 4, wherein the blasting assembly elements comprise elongate lengths of rigid hollow pipe, each with a length dimension in a range of from about 1 meter to about 6 meters, more preferably from about 3 meters to about 6 meters.

6. The assembly according to any of claims 1 to 5, which includes at least two adjacent emulsion explosive containers containing emulsion explosive, the emulsion explosive containers being in blasting communication by means of detonation propagation means, by means of which detonation of emulsion explosive, in use, is propagated from one emulsion explosive container containing emulsion explosive, to the adjacent emulsion explosive container containing emulsion explosive.

7. The assembly according to claim 3, which includes at least two emulsion explosive containers containing emulsion explosive that are separated from each other by one or more lighter- and/or heavier-than-water blasting assembly elements, and wherein the two emulsion explosive containers thus separated are in blasting communication with each other by means of blasting cord that extends between the two emulsion explosive containers thus separated along the one or more lighter- and/or heavier-than-water blasting assembly elements.

8. The assembly according to any of claims 1 to 7, wherein all of the blasting assembly elements have about the same specific gravity; or not all of the blasting assembly elements have the same specific gravity.

9. The assembly according to any of claims 1 to 8, which has a length of up to about 80 meters, or more.

10. A method of blasting under water using an emulsion explosive, the method including progressively constructing, in a body of water, an underwater blasting assembly in accordance with any of claims 1 to 9, by progressively connecting later blasting assembly elements to earlier blasting assembly elements such that earlier blasting assembly elements progressively extend deeper into the body of water, selectively using blasting assembly elements selected from

emulsion explosive containers containing emulsion explosive selected from emulsion explosive containers containing emulsion explosive and that are lighter-than-water,

emulsion explosive containers containing emulsion explosive and that are heavier-than-water, and

emulsion explosive containers containing emulsion explosive and the specific gravity of which, relative to water, approximates 1 ;

lighter-than-water blasting assembly elements devoid of emulsion explosive; and

1 1. An underwater blasting installation for blasting under water using an emulsion explosive, the installation comprising an underwater blasting assembly in accordance with any of claims 1 to 9, the blasting assembly being at least partly submerged in a body of water in which blasting is to be effected.