COMPOSITION AND METHOD FOR BLAST HOLE LOADING

Abstract

A method of loading a blast hole, the method comprising the step of applying a composition to a blast hole wherein the composition provides a barrier layer between an explosive loaded in the blast hole and water in the blast hole.

Claims

1. A method of loading a blast hole, the method comprising the step of applying a composition to a blast hole wherein the composition provides a barrier layer between an explosive loaded in the blast hole and water in the blast hole.

2. The method of loading a blast hole according to claim 1, wherein the barrier layer is formed by reaction, adsorption or absorption of water by the composition.

3. The method of loading a blast hole according to claim 1, wherein the composition includes a gelling agent.

4. The method of loading a blast hole according to claim 3, wherein the gelling agent is chosen from the group comprising starches, surfactants, natural polymers, synthetic polymers and combinations thereof.

5. The method of loading a blast hole according to claim 4, wherein the gelling agent is chosen from the group comprising wheat starch, corn starch, carboxy methyl cellulose, di octyl sulphosussinate, organic clays, gelatine, high molecular weight linear polyacrylamide or combinations thereof.

6. The composition for loading into a blast hole according to claim 1, the composition comprising high molecular weight linear polyacrylamide, wherein the composition forms a barrier to water ingress to an explosive.

7. The composition according to claim 6, wherein the barrier comprising the high molecular weight linear polyacrylamide is a solid particulate, a liquid or a combination thereof.

8. The composition according to claim 6, for loading as a solid or finely divided solid into a blast hole, wherein the proportion of high molecular weight linear polyacrylamide is typically from 25 to 100 wt %, more preferably from 25 to 75 wt %, or even more preferably from 40 to 60 wt % of the total composition.

9. The composition according to claim 6, for loading as a gel, colloid or other semi-solid, the proportion of high molecular weight linear polyacrylamide is typically from 0.001 to 50 wt %, more preferably 0.001 to 25 wt %, or even more preferably 0.001 to 10 wt % of the total composition.

10. The composition according to claim 7, which further includes air bubbles.

11. The composition according to claim 10, wherein the air bubbles are included in the composition by reaction, entrainment or incorporation as microballons or combinations thereof.

12. The composition according to claim 7, which further includes one or more natural or synthetic materials.

13. The composition according to claim 12, wherein the proportion of natural or synthetic materials in the formulation is typically from 0.001 to 50 wt %, more preferably 0.001 to 25 wt %, or even more preferably 0.001 to 10 wt %.

14. The composition according to claim 13, having a viscosity of 2,000 to 6,000 Cp, more preferably 3,000 to 5000 Cp and a density of 1,000 to 1,500 kg/m.sup.3, more preferably 1,100 to 1,300 kg/m.sup.3.

15. A method of inhibiting water ingress to a column of explosive in a blast hole, the method including the step of loading the composition of claim 6, into the blast hole to form at least one barrier to water ingress to the explosive.

16. The method according to claim 15, wherein the composition of claim 6 is loaded as packages.

17. The method according to claim 15, wherein the composition of claim 6 is bulk loaded.

18. The method of inhibiting water ingress to an explosive in a blast hole according to claim 15, wherein the at least one barrier is located at the top, at the bottom or intermediate the column of explosive.

19. A method of loading a blast hole including the steps of: introducing bulk and/or packaged explosive to the blast hole, and introducing the composition of claim 6 in particulate and/or liquid form to the blast hole, wherein the composition forms a barrier to water ingress to the explosive.

20. The A method of loading a blast hole according to claim 19, wherein the composition is applied to the walls of the blast hole prior to the step of introducing the explosive to the blast hole.

21. The method of loading a blast hole according to claim 20, wherein the composition is applied to the top surface of the explosive after the step of introducing the explosive to the blast hole.

22. The method of loading a blast hole according to claim 19, wherein the composition is additionally used as a support for decking.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0094] Further disclosure, objects, advantages and aspects of preferred and other embodiments of the present application may be better understood by those skilled in the relevant art by reference to the following description of embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the disclosure herein, and in which:

[0095] FIG. 1 illustrates in cut-away view a typical mine bench prepared for blasting;

[0096] FIG. 2 illustrates a cross-sectional view of simulated blast holes loaded (a) with a standard blasting configuration, (b) with a configuration according to one embodiment of the composition and method of the present invention, and (c) with a standard blasting configuration which has been subjected to water ingress;

[0097] FIG. 3 illustrates preferred embodiments of the method of the present invention;

[0098] FIG. 4 illustrates further preferred embodiments of the method of the present invention;

[0099] FIG. 5 illustrates a further embodiment of the method of the present invention having the barrier loaded on stemming and as a decking layer; and

[0100] FIG. 6 illustrates the method of the present invention as applied to various aspects of blast hole loading.

DETAILED DESCRIPTION

[0101] The composition and method of the present invention is intended principally for use in blast holes of the type used for mining and quarrying, particularly above ground mining. FIG. 1 illustrates in cut-away view a typical mine bench prepared for blasting marked up to indicate the following features:

TABLE-US-00001 2 Bench height 4 Drill burden 6 Floor 8 Blast hole spacing 10 Blast hole diameter 12 Back break 14 New crest (after mucking) 16 Crest burden 18 Crest 20 Stem height 22 Blast hole length 24 Explosive column height 26 Toe burden 28 Sub-drill 30 Free face 32 Face angle

[0102] The method and composition of the present invention optionally forms a barrier to ingress of water into an explosive. FIG. 2 illustrates a cross-sectional view of simulated blast holes loaded (i) with a standard blasting configuration, (ii) with a configuration according to one embodiment of the composition and method of the present invention, and (iii) with a standard blasting configuration that has been subjected to water ingress. The blast hole loading was simulated using glass, graduated cylinders. The amount of each component loaded into the graduated cylinders was scaled to reflect the proportions used in full size blast holes.

[0103] The simulated blast hole of FIG. 2(a) comprises particulate stemming (40) loaded on top a column of ANFO explosive (42). The simulated blast hole of FIG. 2(b) comprises particulate stemming (40) loaded on top a gel of high molecular weight linear PAM (44) and a column of ANFO explosive (42). The simulated blast hole of FIG. 2(c) comprises particulate stemming (40) loaded on top a column of ANFO explosive (42) as per FIG. 2(a), following addition of water to the top of the stemming.

[0104] A comparison of FIGS. 2(a) and 2(c) illustrates how the ingress of water through the stemming (40) and into the ANFO (42) so that the ammonium nitrate has started to dissolve and the structure of the prill has collapsed. Instead of having air pockets and interstices necessary for propagation of a detonation front, the ANFO is a solid mass that would be unlikely to detonate. By contrast, the gel (44) included between the stemming (40) and ANFO (42) acts as a plug that is a barrier to water ingress to the ANFO (42) yet has sufficient structural integrity to support the stemming (40). By contrast, prior art efforts have not been directed to forming a barrier, but to super-absorb water present in the blast hole. The super-absorbents of the prior art have typically been cross-linked polymers that form lumps (rather than gels) that can work their way into the ANFO. Furthermore, they have no structural strength to support the stemming, and particles of stemming fall through and become mixed with the super-absorbents.

[0105] FIG. 3 illustrates preferred embodiments of the method of the present invention which include a barrier at the toe of the blast hole. After drilling, due to geological or meteorological factors, some blast holes collect water at the toe (base of the hole). The water will subsequently contaminate explosive loaded in the blast hole1 metre of water in a drill hole can contaminate up to 7 metres of an explosive column. This can have disastrous affects on blast quality due to poor quality rock breaking and release of a large volume of (fume) that often contains poisonous gases such as nitrates.

[0106] FIG. 3(a) illustrates in cross-sectional plan view a blast hole loaded with a high molecular weight linear PAM in gel (50) and particulate (52) form at the toe. A column of ANFO explosive (54) rests on the gel/particulate barrier (50/52). Closer to the collar of the blast hole, the top of the column of ANFO (54) is loaded with a sandwich barrier of high molecular weight linear PAM comprising a layer of gel (50) between two particulate (52) layers. Finally, a layer of stemming (56) is included at the collar.

[0107] The barrier may be formed at the toe of the wet blast hole by any convenient means. In one embodiment of the present invention, one or more bags of linear PAM are dropped down a blast hole to float on the water. The bag is made of porous or water soluble packaging that permits the linear PAM to react with the water to form a barrier. Explosives subsequently loaded onto the barrier are thus protected from the water.

[0108] FIG. 3(b) is a similar illustration of another blast hole with the barrier of the present invention in gel (50) and particulate (52) form at the top and bottom of a column of ANFO (54), the blast hole loaded with a primer/detonator combination (60) at the end of a detonator cord (62). Some blasting applications, such as quarrying, may not require stemmingothers may not require a barrier at the toe of the blast hole. FIGS. 3(c) and 3(d) illustrate some other alternative loadings using the barrier of the present invention that would typically be used in quarrying.

[0109] FIG. 4 illustrates further preferred embodiments according to the present invention. FIG. 4(a) illustrates application of a barrier (60) to the walls of a blast hole using a spray head (62) supplied with high molecular weight powder or gel pumped through a hose (64). The spray head (62) can be lowered and raised along the length of the blast hole to line part, or all of the walls. An alternative may be available to spray the powder or gel via the drill bit. Once the blast hole is lined with the barrier, it can be loaded, for example as shown in FIG. 4(b) with ANFO (66), and further particulate (68) and gel (70) linear PAM.

[0110] The present invention may further be used as FIG. 5 illustrates a further embodiment of the method of the present invention. FIG. 5a illustrates a blast hole loaded with ANFO (78) and stemming (76). The composition (74) of the present invention has been loaded onto the top of the stemming and subsequently reacted with water (72) that has collected in the blast hole. The reaction of the water (72) and composition (74) has formed a gel that prevents further water ingress so that the stemming (76) and more importantly the ANFO (78) remain dry.

[0111] FIG. 5b illustrates the use of the barrier according to the present invention to add structure to decking layers. Decking layers of the prior art have previously comprised air, water or other inert materials. The present invention provides barriers that can contribute to decking by providing structured water layers that can support upper decking layers. Specifically FIG. 5b illustrates a decked blast hole loaded at the toe with powdered composition (80) according to the present invention, the upper layer (82) having reacted with water to form a gel barrier to water ingress to ANFO (84). The upper surface of the ANFO (84) is loaded with a sandwich barrier of gel (86), powder (88) and more gel (90). The sandwich layer has sufficient structural strength to support a layer of stemming (92). A final layer (94) of gel barrier prevents ingress of water (96) that finds its way into the blast hole.

[0112] FIG. 6 illustrates a blast hole which has had the composition of the present invention added to drilling water to absorb water present. When used in this manner it acts as a pre-treatment to reduce friction, increase cuttings removal, act as a barrier that seals the drill collars for dust control and stabilises the blast hole walls to resist wall collapse. The explosives (115) are loaded into the toe of the pre-treated blast hole. The barrier (112) according to the present invention forms a water and structural barrier, protecting the explosive (115) from water contamination, and creating a structural foundation on which further layers can be placed whilst minimising cross contamination of layers.

[0113] A further, thicker barrier (110) according to the present invention can improve the redistribution of energy as the detonation wave is transmitted from the column of detonated explosive. A layer of crushed rock (105) acts as stemming, capped with a further barrier according to the present invention that acts as a blast hole plug, sealing the blast hole from ingress and contamination by surface water.

[0114] Thus the barriers according to the present invention can be loaded as a very thick layer to provide a type of decking. Air and water decking are well known in the explosives industry, but it has not hitherto been the practice to combine air and water in a single deck. Thus, the barrier of the present invention can combine the advantages of air decking (compressible thus acting as an energy accumulator and works well it the upper layers of a blast hole) with the advantages of water decking (not readily compressible which intensifies the blast energy and works well in the toe and lower layers of the blast hole).

[0115] By forming or incorporating gas bubbles into the barrier it is possible to control the density of the barrier to suit the type of explosive used, the type of decking required and to optimise energy accumulation.

[0116] Controlling the density of the barrier can also be useful for loading. The barrier density can be adjusted to displace water and/or emulsion and multiple gels of different densities can be layered or used as decking. For example, one commonly used emulsion explosive has a density of 1.15 g/cm.sup.3 which is higher than water (1.0 g/cm.sup.3). If the barrier of the present invention is manufactured with a nominal density between these two figures (say 1.09 g/cm.sup.3), this allows the barrier composition of the present invention to be loaded from the collar, displacing water in the blast hole and forms barriers.

[0117] Alternatively, barrier in the form of a gel of density 1.30 g/cm.sup.3 can be pumped into an empty hole, followed by emulsion explosive having a density of 1.15 or 1.20 g/cm.sup.3 then a further decking gel of density 1.10 g/cm.sup.3, then a barrier and stemming. If the hole is full of water (1.0 g/cm.sup.3) the alternative method would involve pumping barrier in the form of a gel of density 1.30 g/cm.sup.3, then emulsion explosive having a density of 1.15 g/cm.sup.3, then a decking gel of density 1.10 g/cm.sup.3, then a barrier through the water on top of the gel, then stemming.

[0118] As described previously, use of the present invention can reduce the amount of explosives required for blasting as compared with prior art methods. The barrier can contain or direct the pulse of a detonation shockwave so that it releases energy more evenly in the blast hole. In particular, use of a barrier comprising a sandwich of gel layer between two particulate layers of linear PAM may change the explosive pulse through the water contained in the gel. For example, in some blasting applications, use of the barrier of the present invention may allow miners to use up to about 25 wt % less explosives and up to about 50 wt % less stemming.

[0119] Typical explosive volume and cost savings achieved using the composition and method of the present invention can be exemplified with reference to Table 1. The values in the table relate to a typical coal mine in the Hunter Valley of New South Wales, Australia utilising 100,000 drill holes per annum (measuring 300 mm diameter, 15 m depth, 1.06 m.sup.3 volume). The potential reduction in explosive usage is between 10 and 30%.

TABLE-US-00002 TABLE 1 Amount of Volume of Explosives explosives explosives Cost (@ used (MT) used (m.sup.3) AUD$0.90 per kg) Prior art method 50,000 70,000 $45,000,000 Present Invention 43,000 60,000 $38,700,000 Reduction 7,000 9,800 $6,300,000 (Based on a bulk density of about 0.8 tns/m.sup.3 for ANFO.)

Further Example

[0120] In another example of use, the method of loading and barrier according to present invention, were trialled at a quarry bench in Toowoomba, Queensland comprising over 80 blast holes having a diameter of 102 mm, drilled to a depth of 16.5 metres. Approximately 50% of the blast holes were dry, and the remainder were wet. The blast holes were loaded with two detonators, the lower of the two detonators being located above any water in the blast hole.

[0121] The dry blast holes were loaded with a 13.5 m column of ANFO explosive and 3 m of crushed rock stemming.

[0122] The wet holes were contaminated with varying amounts of water and (all but the six test blast holes discussed below) were loaded with a 14 m column of emulsion explosive and 2.5 m of crushed rock stemming.

[0123] Six of the water contaminated holes were selected to be loaded according to the present invention. The six test blast holes held various volumes of water, from 1 to 3 metres in depth. A composition according to the present invention was slowly poured onto the water in the blast holes using a 3 m long, 80 mm diameter, purpose built funnel. A good structural barrier formed and ANFO was immediately loaded with ANFO, leaving 3 m of the blast hole empty. The height to the top of the blast hole was checked 30 mins later to confirm that the barrier had not collapsed. The blast hole was then stemmed with a 3 m column of crushed rock. Using a constant volume of stemming in blast holes holding various amounts of water meant that the length of the explosive column varied between holes.

[0124] Results: All 6 test holes detonated successfully. The barrier according to the present invention sealed the water and provided a structural, waterproof base on which ANFO could be loaded. No evidence of ANFO contamination from water was detected. In particular the stemming height did not change, and no orange fume was noticeable after detonation. Furthermore, it was apparent that even though water was sealed into the toe of a blast hole, adequate toe break was still achieved.

Compositions

[0125] Compositions according to the present invention have been successfully loaded into a blast hole according to the method of the present invention along with explosives and the blast hole detonated.

TABLE-US-00003 TABLE 2 Composition 1 Density (kg/m.sup.3) Volume (ml) Weight (kg) Truebond MW 900 500 4.50 Magnafloc 1011 750 500 3.75

[0126] Composition 1 is formulated with the intention of creating a barrier in the blast hole having a thickness that is half the diameter of the blast hole (ie 102 mm blast hole requires a 50 mm thick barrier; 280 mm blast hole requires a 150 mm thick barrier).

[0127] Barrier type formulations have also been prepared using formulations comprising up to 100% starch, PAM:Starch 50:50, montmorillonite clay up to 100% and blends thereof.

TABLE-US-00004 TABLE 3 Composition Wt % Weight (kg) Magnafloc 1011 0.15% 10 Acti-Treat Extra 1.00% 1.5 Water Balance Balance Salt As per density required

[0128] Composition 2 is formulated to achieve a viscosity of 4,000 Cp or higher and a desired density based on the application. In particular, the optimal density will depend on the size of the barrier required and the position of the barrier in the blast hole. Typically the amount of salt or other product used is added to achieve a density of between 1,000 to 1,500 kg/m.sup.3. More preferably between 1,100 to 1,300 kg/m.sup.3.

[0129] Magnafloc 1011 from BASF, is a very high molecular weight anionic polyacrylamide. In acidic conditions, such as in the presence of acidic ground water, it may be preferable to mix the composition using cationic PAM or carboxymethyl celluslose (eg at 2 or 3%) with a salt added, such as magnesium chloride to adjust the density. Other PAMs will also be suitable for use with the present invention.

[0130] Truebond MW from Sibelco Australia Limited, is a bentonite product comprising >74% smectite, <19% quartz/cristobalite, <8% plagioclass feldspar/kaolinite. Bentonite is one of a number of forms of fine gelling clays that may be suitable for use with the present invention. Different PAM mixes with super fine clays at different ratios will perform better under different circumstances, optionally with other material added such as starch or CMC. Furthermore it is within the scope of the present invention to use a single formulation when loading a blast hole or multiple formulations.

[0131] Other gel compositions having a viscosity of between 2,000 and 4,000 Cp have been prepared using the following: [0132] starch 3%-5%; [0133] carboxy methyl cellulose (0.5 to 5%); [0134] di octyl sulphosussinate (1%-2%); [0135] organic clays (eg bentonite 5%-10%); and [0136] gelatine (0.1%-5%).

[0137] While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[0138] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

[0139] Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, means-plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures.

[0140] Comprises/comprising and includes/including when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words comprise, comprising, includes, including and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of including, but not limited to.