AU746434B1 - A method of stemming a blast hole and a blast hole stemming material - Google Patents

Description

S&FRef: 578864

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant: Actual Inventor(s): Address for Service: Invention Title: Brambles Australia Limited Level 40, Gateway 1 Macquarie Place Sydney New South Wales 2000 Australia Myles Huntly Spruson Ferguson St Martins Tower,Level 31 Market Street Sydney NSW 2000 (CCN 3710000177) A Method of Stemming a Blast Hole and a Blast Hole Stemming Material ASSOCIATED PROVISIONAL APPLICATION DETAILS [33] Country [31] Applic. No(s) AU PR1691 [32] Application Date 27 Nov 2000 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815c -1- A METHOD OF STEMMING A BLAST HOLE AND A BLAST HOLE STEMMING MATERIAL Field of the Invention The invention relates to a method of stemming a blast hole and to a stemming material for a blast hole. The invention has been primarily developed in relation to stemming blast holes in open cut mines and will be described hereinafter with reference to this application. However, the invention is not limited to this particular field of use and is equally applicable for use in underground mining or construction.

Background of the Invention Stemming material is inert material which is placed in a blast hole for the purpose of separating explosive charges from each other or from the atmosphere. Stemming material is used in blast holes for three reasons. Firstly, the stemming material contains the explosive energy in a particular part of the blast hole, long enough for the full effects of that explosive energy to work on that section of the surrounding rock mass to which the explosive energy was intended. Secondly, stemming material placed at the top of a blast hole reduces the noise generated by a blast. Thirdly, stemming material placed at the top of a blast hole reduces the danger of fly rock being ejected from the blast hole on initiation of the explosive charges.

The measure of a good stemming material is whether these three functions can be achieved without using excessive column lengths of the stemming material. More particularly, if excessive column lengths of stemming are required because of the stemming material has weak locking characteristics, then the stemming material will occupy a part of the blast hole that should otherwise have been charged with explosive. A shot with excessive stemming applied will generally result in poor fragmentation in the upper part of the last bench.

Hitherto, rocks and other like materials are used as stemming material in blast holes. An example of a common stemming material is crushed andesite, which is sized to +14mm to -20mm. The primary disadvantage of such known stemming materials is that they are expensive to purchase or, if possible, quarry on site. Also, known stemming materials are dense and manually handling them in large quantities is difficult and also expensive in both labour and machinery cost. As an example, an open cut coal mine with an expected overburden removal of 30 million bank cubic meters would consume over [I:\DayLib\L1BDDJ02869.doc:AVS -2- 16,000 tonnes of bulk explosives and approximately 6,500 tonnes of rock based stemming material per annum.

Object of the Invention It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages.

Summary of the Invention Accordingly, in a first aspect, the present invention provides a method of stemming a blast hole, the method comprising filling a portion of the blast hole with pieces of rubber material.

In a second aspect, the present invention provides a stemming material comprising pieces of rubber material.

In a third aspect, the present invention provides a method of blasting comprising the following steps: drilling a blast hole; at least partially filling the blast hole with explosives; at least partially filling the blast hole with stemming material formed from pieces of rubber; and detonating the explosives.

The pieces can be regular or irregular in size and shape.

The pieces of rubber material preferably have embedded metal strands protruding therefrom. The pieces of rubber material with embedded metal strands protruding therefrom are preferably produced from steel belted vehicle (ie. car or truck) tyres. The pieces are desirably produced by chopping or shredding the steel belted vehicle tyres, with the chopped/shredded steel belts becoming the strands.

In a preferred embodiment, a tyre shredder machine is configured to produce the pieces in a size range of +10mm to -50mm pieces.

Brief Description of the Drawings A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which; Figs. l a and b are photographic top views respectively showing piles of known gravel stemming and an embodiment of stemming material according to the invention; [I:\DayLib\LIBDD]02869.doc:AVS -3- Fig Ic is a photograhic top view of individual pieces of the stemming material shown in Fig. lb adjacent a 50mm x 90mm card; Figs. 2a, 2b and 2c are schematic side, end and top views respectively of an embodiment of a tyre shredder machine suitable for producing an embodiment of stemming material according to the invention; and Figs. 3a and 3b are schematic side and end views respectively of a vehicle suitable for delivering an embodiment of stemming material according to the invention to a blast hole.

Detailed Description of the Preferred Embodiments Referring to Figs. l a and ib, there is respectively shown photographic top views of a pile of known gravel stemming material 10 and a pile of rubber pieces of stemming material 12 according to an embodiment of the invention. As best shown in Fig. i b, the stemming material 12 is fairly random in size and shape and is produced by chopping or shredding rubber steel belted vehicle, for example car or truck, tyres into pieces.

In this preferred embodiment, the greater majority of the pieces of the stemming material 12 are then left with strands or spikes of the embedded steel belting protruding therefrom. The chopping/shredding process also elongates/stretches the protruding strands in some pieces.

Figs. 2a to 2c shows a commercially available tyre shredding machine 14, produced and sold by Rubber Tek Pty Ltd of P.O. Box 536, Oxenford, 4210, Australia having truck tyres 15 being fed into it. The distance between the shredding blades of the machine 14 is adjustable. The blades of machine 14 were adjusted to provide a minimum piece size of in excess of 10mm and a maximum piece size less than 50mm to produce the stemming material 12 shown in Fig. lb.

Figs. 3a and 3b show a vehicle 16 having a stemming material hopper 17 which is used to deliver the stemming material 12 to a blast hole (not shown), for example at an open cut mine. The vehicle 16 is similar to that presently used by many mines in loading gravel stemming material, except the auger 18 used to transport the stemming material 12 from the hopper 17 to the hole is of a slightly larger size. The stemming material 12 according to the invention is loaded into blast holes in a similar manner to that used for known gravel stemming material. However, some tamping can be required to assist in the passage of the stemming material 12 into the blast hole.

An initial trial of the stemming material 12 was conducted in a normal blast pattern using the same conditions as the stemming material 10 currently in use at the mine [I:\DayLib\LBDD02869.doc:AVS -4- (andesite crushed to +14mm to -20mm). Four blast holes were stemmed with the stemming material 12. The average depth of the blast holes was 20 metres, the holes were 270mm in diameter and the average stemming depth was 5 metres. The pattern was designed as a standard vertical shot with all holes drilled vertically to stand off a coal seam by 2 metres. After the shot was fired, no excessive stemming rejection was observed from the area stemmed with the stemming material 12.

A second trial in an almost identical pattern was then prepared with six holes stemmed with the stemming material 12 and fired. At least five of the six holes stemmed with the stemming material 12 performed as well as those stemmed with the stemming material A large trial was then conducted in a mine area sensitive to over pressure noise and ejection of material outside the mine area. In light of these conditions, a more conservative approach was taken with the application of the stemming material 10. More particularly, a calculation known as Scale Depth Burial was performed resulting in a suggested minimum depth of stemming material 12 according to the invention of 6.6 metres, compared to the 5 metres of the (andesite) stemming material 10. The details of the shot design parameters are set out below.

Bench Width Average Bench height Hole Diameter Stemming depth Water in holes Primary Explosive Primers In-hole Delay Initiation System Surface Delays Burden Distance Spacing Distance Average relief time 44m 270mm 5m for holes with stemming material 10 and for 17 holes with stemming material Nil ANFO (Ammonia Nitrate and Fuel Oil) 2 x 390 gram PPP Primers Top 650ms Bottom 600ms Shock Tube (Orica, Primadet System) 17ms, 42ms, 100ms G to B rows 16.79ms/m B to A row 6.89ms/m II:DayLib\LBDD]02869.doc:AVS Angle of Initiation G to B rows 16.13 deg (from line of free face) A to B row 42.65 deg (from line of free face) Average Powder Factor 0.6 kg/cubic metre After firing, the blast was assessed by personal observation, video camera records, velocity of detonation traces and post blast inspection. No evidence of ejection was found from the blast holes loaded with the stemming material 12. Further, the area where the stemming material 12 had been used appeared to have the same profile as the rest of the shot in that region.

It is thought that the reason for the success of the stemming material 12 according to the invention is the high co-efficient of friction between adjacent rubber pieces causes them to grip one another, particularly under the influence of explosive pressure during a blast, to link or lock the pieces together. It is also thought that this is assisted by the embedded metal strands protruding from some of the edges of the pieces sticking into other pieces.

The invention provides for the use of stemming material produced from pieces of rubber material in place of conventional aggregate based stemming materials.

The advantages associated with the invention are as follows. Firstly, conventional aggregate stemming material must be purchased or quarried by a mine, which incurs expense. The preferred raw material for producing the stemming material according to the invention is discarded car and truck tyres, which, in contrast, collectors of same (such as new tyre retailers) presently pay to have removed. This represents a negative raw material purchase price. In addition, many mine sites already have a large stock of disused vehicle tyres from their own vehicles, which they can use as an alternative to paying to them have removed and disposed.

Secondly, use of the invention will lead to a reduction in the impact of the environmental problem facing many countries that have an excess number of old stockpiled car tyres. For example, it has been estimated that mines operating in the Hunter Valley region of New South Wales in Australia could utilise 100,000 tonnes of rubber car tyres a year by using the method and stemming material according to the invention.

Thirdly, the stemming material is less dense than known aggregate stemming materials but can be used in similar volumes. This reduces transport and manual handling costs.

[I:\DayLib\LIBDD]02869.doc:AVS -6- Fourthly, the stemming material is generally used in a ratio of about 1 metre cubed stemming material to 10,000 metre cubed broken earth which results in a post blast mix which is substantially inert.

Although the invention has been described with reference to a specific example, it would be appreciated by those skilled in the art that the invention may be embodied in many other forms. For example, rubber pieces from sources other than vehicle tyres can be used.

[IADayLib\LIBDD02869.doc:AVS

Claims (24)

1. A method of stemming a blast hole, the method comprising filling a portion of the blast hole with pieces of rubber material.

2. The method claimed in claim 1, wherein the pieces are of regular size and shape.

3. The method claimed in claim 1, wherein the pieces are of irregular size and shape.

4. The method claimed in claim 1,2 or 3, wherein the pieces of rubber material have embedded metal strands protruding therefrom.

5. The method claimed in claim 4, wherein the pieces of rubber material having embedded metal strands protruding therefrom are produced from steel belted vehicle tyres.

6. The method claimed in claim 5, wherein the pieces of rubber material having embedded metal strands protruding therefrom are produced by chopping or shredding the steel belted vehicle tyres, with the steel belts becoming the strands.

7. The method claimed in claim 6, wherein a tyre shredder machine is configured to produce the pieces in a size range of +10mm to

8. A stemming material for a blast hole, the stemming material comprising pieces of rubber.

9. The stemming material claimed in claim 8, wherein the pieces are of regular size and shape.

The stemming material claimed in claim 8, wherein the pieces are of irregular size and shape.

11. The stemming material claimed in claim 8, 9 or 10, wherein the pieces of rubber material have embedded metal strands protruding therefrom.

12. The stemming material claimed in claim 11, wherein the pieces of rubber material having embedded metal strands protruding therefrom are produced from steel belted vehicle tyres.

13. The stemming material claimed in claim 12, wherein the pieces of rubber material having embedded metal strands protruding therefrom are produced by chopping or shredding the steel belted vehicle tyres, with the chopped/shredded steel belts becoming the strands.

14. The stemming material claimed in claim 13, wherein a tyre shredder machine is configured to produce the pieces in a size range of +10mm to

15. A method of blasting comprising the following steps: [:\DayLib\LIBDDO02869.doc:AVS drilling a blast hole; at least partially filling the blast hole with explosives; at least partially filling the blast hole with stemming material formed from pieces of rubber; and detonating the explosives.

16. The method claimed in claim 15, wherein the pieces are of regular size and shape.

17. The method claimed in claim 15, wherein the pieces are of irregular size and shape.

18. The method claimed in claim 15, 16 or 17, wherein the pieces of rubber material have embedded metal strands protruding therefrom.

19. The method claimed in claim 18, wherein the pieces of rubber material having embedded metal strands protruding therefrom are produced from steel belted vehicle tyres.

The method claimed in claim 19, wherein the pieces of rubber material having embedded metal strands protruding therefrom are produced by chopping or shredding the steel belted vehicle tyres, with the chopped/shredded steel belts becoming the strands.

21. The method claimed in claim 20, wherein a tyre shredder machine is configured to produce the pieces in a size range of +10mm to

22. A method of stemming a blast hole, the method substantially as described herein with reference to Fig's lb to 3b of the accompanying drawings.

23. A stemming material for a blast hole, the stemming material substantially as described herein with reference to Fig's lb to 3b of the accompanying drawings.

24. A method of blasting, the method substantially as described herein with reference to Fig's lb to 3b of the accompanying drawings. Dated 19 October, 2000 Brambles Australia Limited Patent Attorneys for the Applicant SPRUSON FERGUSON [I:\DayLib\LIBDD]02869.doc:AVS