AU2008229811A1

AU2008229811A1 - Charging a Blast Hole with an Explosive

Info

Publication number: AU2008229811A1
Application number: AU2008229811A
Authority: AU
Inventors: Michael Kenneth Gillard
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-07-10
Filing date: 2008-10-06
Publication date: 2010-01-28

Description

CHARGING A BLAST HOLE WITH AN EXPLOSIVE Field of the Invention The present invention relates generally to blasting with explosives. In particular, the present invention relates to charging a blast hole with an explosive. 5 Although the present invention will be described with particular reference to underground excavating operations such as underground mining or tunnelling operations, it will be appreciated that it is not necessarily limited to this use. Brief Discussion of the Prior Art 10 In underground excavating operations such as underground mining or tunnelling operations where solid rock is being excavated, explosives are often used to blast the rock into small loose pieces that are able to be readily carted away. Typically, when explosives are used to excavate an underground passage such as, for example, a development drive or tunnel, in solid rock, a plurality of 15 perimeter blast holes are drilled into the rock face to an appropriate depth at locations that are distributed around the perimeter of the profile of the development drive or tunnel. For example, in some mining operations 12 to 20 perimeter blast holes will be drilled into a rock face to depths of 4 to 5 metres. Figure 1 of the drawings depicts a development drive in an underground 20 mine. The arrows in the drawing point to various locations around the perimeter of the development drive profile where perimeter blast holes will typically be drilled into the rock face. After the perimeter blast holes have been drilled into the rock face, a "perimeter blasting product" in the form of a small, elongate high-powered explosive 25 charge is inserted into each perimeter blast hole as depicted in figure 2. When the explosive charges in the perimeter blast holes are fired, the rock adjacent to the perimeter holes is blasted into small pieces. The small cross-sectional size of each charge relative to the cross-sectional size of the perimeter blast holes means that there is an uncharged area in each hole. 30 The uncharged area results in a decoupled charge that is designed so that the remaining rock at the backs (roof) and walls of the development drive is protected against overbreak and other damage from blasting.

2 One type of explosive charge that is loaded into blast holes is ammonium nitrate fuel oil or ANFO. ANFO powder is typically pneumatically/blow-loaded into a blast hole by inserting a charge hose into the hole and then pneumatically feeding the ANFO into the hole through the hose while gradually withdrawing the hose from 5 the hole so that a trail of ANFO is left in the hole. When snowloading ANFO into a blast hole, care needs to be taken to ensure that neither too much nor too little ANFO is loaded into the hole. If too much ANFO is loaded into the hole, the explosive charge will not be sufficiently decoupled from the surrounding rock to prevent overbreak or other unwanted damage to the remaining 10 rock. If too little ANFO is loaded into the hole, the charge will not be powerful enough to sufficiently blast the rock. The amount of ANFO that is blow-loaded into a blast hole can be regulated with the aid of a DynoTracker@ device which is a device that is screwed on to the end of a charge hose in a similar manner to a hose nozzle. The DynoTracker@ device is 15 able to limit the amount of ANFO that is loaded into the hole. When using the DynoTracker@ device to blow-load ANFO into a blast hole, the pressure of the charging kettle that is used to blow-load the ANFO into the hole through the hose must be turned down considerably, and the rate at which the charge hose is retracted or withdrawn from the hole must be precise. If the hose is retracted 20 too slowly, the DynoTracker@ device will get jammed in the hole. If the hose is retracted too quickly, not enough ANFO will be loaded into the hole, and the charge will be too weak to blast the rock. The DynoTracker@ device has been found to be difficult to use and not very reliable. It is perhaps because of these problems, that to the inventor's knowledge, 25 the use of the DynoTracker@ device is not particularly widespread in underground mining activities. One particular major problem with existing perimeter blasting products in general is that when a development heading is being fired by firing an explosive charge in an easer hole that is located beneath a perimeter blast hole, the firing of the 30 explosive charge in the easer hole tends to drag out the charge in the perimeter hole and cause that charge to fire as it rifles out of the perimeter hole. This leaves a miss fired hole in the rock face that has to be re-fired at another time.

3 In general, all of the currently available perimeter blasting products are unreliable and expensive. Their lack of reliability means that they often have to be recharged and blasted again, which causes delays that can be quite costly. 5 Summary of the Invention It is an object of the present invention to overcome, or at least ameliorate, one or more of the deficiencies of the prior art mentioned above, or to provide the consumer with a useful or commercial choice. Other objects and advantages of the present invention will become apparent 10 from the following description, taken in connection with the accompanying illustrations, wherein, by way of illustration and example, a preferred embodiment of the present invention is disclosed. According to a first broad aspect of the present invention there is provided a method of charging a blast hole, the method comprising the steps of: 15 (i) inserting a filler into the hole; and (ii) loading an explosive into the hole. According to a second broad aspect of the present invention there is provided a charged blast hole comprising a blast hole, a filler inserted into the hole, and an explosive loaded into the hole. 20 According to a third broad aspect of the present invention there is provided a filler for insertion into a blast hole, wherein the filler is adapted to limit the amount of an explosive that is able to be loaded into the blast hole. The amount of the explosive that is able to be loaded into the blast hole is able to be restricted by the filler to prevent too much of the explosive being loaded 25 into the hole. The filler is able to protect the material (e.g. rock) which the blast hole extends into from overbreak or other unwanted damage as a result of firing the explosive. The filler is able to act as a shock absorber so that cracks are not allowed to 30 form in the material (e.g. rock) in which the blast hole extends on initial detonation of the explosive. By not allowing such cracks to form, gases produced by firing the explosive are prevented from travelling along such cracks and opening the rock up.

4 Thus, the filler is able to protect the perimeter of a drive or tunnel. It has been found to be less expensive to use the filler in combination with the explosive instead of other perimeter products because the filler can be used with an explosive (e.g. ANFO) that is relatively inexpensive and common in many 5 underground mines. Also, because the filler is not an explosive charge like other perimeter products, it is not dangerous to manufacture, transport, store or handle, and does not pose a security threat. Moreover, unlike explosives which have a very short shelf life, the filler can 10 be stored indefinitely. The blast hole may be any suitable type of blast hole. Preferably, the blast hole is a perimeter blast hole. The blast hole may be any suitable shape. However, in practice, the blast hole is usually circular. 15 The blast hole may be any suitable width. Preferably, the blast hole has a width of 25 mm to 55 mm. It is particularly preferred that the blast hole has a width of 45 mm to 55 mm. The blast hole may be any suitable length. Preferably, the blast hole has a length of 3.5 m to 6.5 m. 20 Preferably, the filler is an elongate member. It is also preferred that the filler is hollow. The ends of the filler are preferably closed/sealed. In a particular preferred form, the filler is a tube. The filler may have a profile that has any suitable shape. In one particular preferred form, the filler has a generally crescent-shaped profile. In another particular 25 preferred form, the filler has a generally arcuate profile. The filler may alternatively have a generally kidney-shaped profile. Preferably, the filler has a profile that is constant along the length of the filler. The filler may be manufactured from any suitable material or combination of materials. Preferably, the filler is manufactured from plastic or rubber. The filler is 30 preferably manufactured from a soft material. For example, the filler may be manufactured from sponge/foam rubber. The filler is preferably compressible so that the filler is able to absorb at least 5 some of the blast which is produced by firing the explosive in the blast hole. By absorbing at least some of the blast, the filler is able to prevent the blast from causing overbreak or other unwanted damage to the material which the hole extends into. The filler may be inserted into the blast hole in any suitable manner. 5 Preferably, the filler is inserted into the blast hole such that the filler extends lengthwise along the blast hole. The filler is preferably inserted into the blast hole such that the filler is located substantially opposite the explosive. Preferably, the filler is inserted into the blast hole such that the filler extends along a side of the blast hole. It is preferred that the filler is located adjacent to a side of the blast hole which 10 is to be protected from overbreak or other damage. The explosive that is loaded into the blast hole may be any suitable type of explosive. Preferably, the explosive is an explosive powder. In a particular preferred form, the explosive is ammonium nitrate fuel oil or ANFO. The explosive may be loaded into the blast hole in any suitable manner. 15 Preferably, the explosive is pneumatically or blow-loaded into the blast hole. The explosive may be loaded into the blast hole such that the explosive extends along a side of the blast hole. The explosive may be loaded into the blast hole through a hose by inserting the hose into the hole and then withdrawing the hose out of the hole so that a trail of the explosive is left in the hole. The hose and the filler are preferably 20 detachably secured to each other so that inserting the hose into the blast hole results in the filler being inserted into the hole, and so that the hose is able to be withdrawn from the hole without withdrawing the filler from the hole. Preferably, a clip detachably secures the hose and the filler to each other. 25 Brief Description of the Drawings In order that the invention may be more fully understood and put into practice, a preferred embodiment thereof will now be described with reference to the accompanying illustrations, in which: Figure 1 depicts an example of a development drive tunnel in an 30 underground mine; Figure 2 is an end view of a blast hole containing a high-powered explosive charge; 6 Figure 3 is an end view of a blast hole containing a filler; Figure 4 is a cross-sectional side view of the blast hole depicted in figure 3 after an explosive charge and a primer have also been inserted into the hole; Figure 5 is an end view of a blast hole containing a filler and an explosive 5 charge; Figure 6 depicts a portion of a tunnel perimeter that includes the remnants of a perimeter blast hole that contained a filler; Figure 7 is another view of the tunnel perimeter shown in figure 6 which shows the remnants of two perimeter blast holes that each contained a filler; 10 Figure 8 is a perspective view of another filler for inserting into a blast hole; Figure 9 is an end view of a blast hole containing the filler depicted in figure 8; Figure 10 is an end view of a blast hole containing a filler and a charge hose; Figure 11 is a perspective view of the filler and charge hose depicted in 15 figure 10 as the charge hose is moved relative to the filler; Figure 12 depicts a clip for securing together the filler and charge hose depicted in figure 10; and Figure 13 depicts a blast hole containing a filler, an explosive, and a detonator's signal tube. 20 Detailed Description of the Drawings Figures 3 and 4 depict a circular perimeter blast hole 20 that has been drilled into a rock face. The blast hole 20 has a diameter of 45 mm and a depth of 4 - 5 m. It will be appreciated however that the blast hole 20 may have any suitable diameter and 25 any suitable depth. However, when pneumatically loaded ANFO is used as an explosive in the hole 20, the minimum recommended diameter is 25 mm. An elongate filler 21 has been inserted into the blast hole 20. The filler 21 depicted in figure 3 has a generally crescent-shaped profile, however it may have any other suitable profile. 30 Filler 21 is a hollow tube that is closed at both ends to prevent explosive entering into the filler 21. It will be understood though that provided the filler need not be hollow or closed at both ends, but that it should be able to displace an 7 explosive which is loaded into the blast hole in which the filler is inserted. Filler 21 is preferably made from rubber or plastic, and is able to be coiled up for storage or transport. The length of the filler 21 is determined by the length of the blast hole 20. In 5 the embodiment illustrated in figure 4, the filler 21 is slightly shorter than the length of the hole 20. In other embodiments, the filler 21 may be the same length as the blast hole 20, or have a length which is greater than the length of the blast hole 20. The width or cross-sectional area of the filler 21 depends on the geology of the rock in which the hole 20 is drilled, or how hard the rock is to blast. If the rock is 10 relatively hard, the filler 21 needs to have a reduced width/cross-sectional area so that more explosive is able to be loaded into the hole 20. If the rock is relatively soft and easily broken, filler 21 needs to have a greater width/cross-sectional area so that less explosive is able to be loaded into the hole 20. Filler 21 is able to reduce the amount of explosive that is able to be loaded 15 into the blast hole 20. It is also able to create a space between the explosive and the side wall of the hole 20. The space that is created by the filler 21 is able to reduce the amount of energy that is released by the explosive and transferred to the surrounding rock. Filler 21 has been inserted into the hole 20 such that it is located adjacent to 20 a side of the hole 20, and such that it extends lengthwise along the hole 20. The side of the hole 20 that the filler 21 is located adjacent to is the side that it is adjacent to the rock that is to be protected against overbreak or other damage after blasting. With particular reference to figure 3, the region 22 beneath the filler 21 is the region of the blast hole 20 that is to be filled with explosive. 25 Filler 21 is inserted into the hole 20 along with a primer 23 that includes a detonator and a 32/200 stick of explosive. The hole 20 is then charged with a bulk explosive 24, which is preferably ANFO, by inserting a charge hose of a pneumatic/blow-loader into the hole 20 and then allowing the explosive 24 to flow through the hose and into the hole 20 while steadily withdrawing or retracting the 30 hose from the hole 20 so that a trail of explosive 24 is left in the hole 20, and so that the explosive 24 fills the region 22 beneath the filler 21 as shown in figure 4. Hole 20 is charged with the explosive 24 in accordance with standard 8 charging procedures, except that the charge hose is withdrawn at a faster rate than normal so as to avoid the hose from becoming blocked as a result of the hole 20 being filled at a faster rate than would normally be the case due to the presence of the filler 21. 5 Referring to figure 5, hole 20 has a width of 45 mm. If, for example, the width Y of the filler 21 is 11 mm, the width X of the explosive charge 22 may, for example, be 32 mm. As another example, if the width Y of the filler 21 is 13 mm, the width X of the explosive charge 22 may be reduced to 30 mm. As yet another example, if the width Y of the filler 21 is 15 mm, the width X of the explosive charge 10 22 may be 28 mm. If the width Y of the filler 21 is 18 mm, the width X of the explosive charge 22 may be 25 mm. Figure 6 depicts a portion of a tunnel perimeter 30 that includes the remnants of a perimeter blast hole 31 that contained a filler similar to the filler 21 at the time an explosive charge in the hole 31 was fired. It can be seen how little damage there is to 15 the rock 32 around the blast hole 31 as a result of using the filler. Figure 7 is another view of the tunnel perimeter 30 shown in figure 6 which shows the remnants of two perimeter blast holes 31 that each contained a filler similar to the filler 21 at the time an explosive charge in each of the holes 31 was fired. Again, little if any damage has been done to the rock 32 around the blast holes 31. 20 Referring to figure 8, a filler 40 is depicted that is similar to the filler 21 except that the filler 40 has an arcuate profile. Filler 40 has a length of 4 m - 5 m. Figure 9 is an end view of a perimeter blast hole 41 that has a diameter of 45 mm. The filler 40 has been inserted into the hole 41 so that there is a region 42 beneath the filler 40 where an explosive charge is able to be loaded. 25 Using a filler when charging a perimeter blast hole with an explosive is relatively easy as the filler can be slid into the hole along with the charge hose. The filler functions to restrict the amount of explosive that is loaded into the perimeter blast hole so that the explosive is able to deliver a softer blast. It also enables the explosive to be evenly loaded into the hole. 30 Figure 10 is an end view of a perimeter blast hole 50 that has a diameter of 45'mm. A filler 51 along with a charge hose 52 are shown inserted into the hole 50, as would occur when the hole 50 is being filled with an explosive through the hose 9 52. Filler 51, which is manufactured from sponge/foam rubber, is resiliently compressible, and has a generally crescent-shaped profile. The curve of the outer surface 53 of the filler 51 has a diameter of 40 mm. The curve of the inner surface 54 5 of the filler 51 has a diameter of 27 mm. Filler 51 includes a circular channel 55 and a pair of teardrop-shaped channels 56. Channels 55 and 56 extend the length of the filler 51. The parts of the channel 55 and the inner surface 54 that are closest to each other are separated from each other by a distance of 2.75 mm. 10 Charge hose 52 has a circular profile and has a diameter of 25 mm. The wall of the hose 52 has a thickness of 2.5 mm. The parts of the channel 55 and the inner surface of the wall of the hose 52 that are closest to each other are separated from each other by 5.25 mm. Figure 11 depicts the charge hose 52 being moved relative to the filler 51 in 15 the direction indicated by the arrow A as would occur if the hose 52 was being withdrawn from the blast hole 50 while dispensing an explosive into the hole 50 and beneath the filler 51. Before inserting the filler 51 and the hose 52 into the blast hole 50, they may be clipped together so that inserting the hose 52 into the hole 50 results in the filler 51 20 being inserted into the hole 50. Figure 12 depicts a clip 60 which may be used for this purpose. Clip 60 is hook-shaped and includes a first arm 61 for insertion into the lumen of the hose 52, and a second longer arm 62 for insertion into the channel 55 of the filler 51. The cross-sectional dimensions of the arm 61 are such that the arm 61 is able to readily withdrawn from the lumen of the hose 52. Arm 62 includes a plurality 25 of barbs 63 for inhibiting removal of the arm 62 from the filler 51 once the arm 62 has been inserted into the channel 55. The maximum transverse distance between the first and second arms 61, 62 is 5.5 mm. Once an end of the filler 51 has been secured to an end of the hose 52 with the clip 60, those ends of the filler 51 and hose 52 are inserted first into the blast hole 30 50, and the filler 51 and hose 52 are fed simultaneously into the hole 50. After the filler 51 and hose 52 have been fed into the hole 50 by the desired amount, the hose 52 is steadily withdrawn from the hole 50 while an explosive flows through the hose 10 52 and into the hole 50. As the hose 52 is withdrawn from the hole 50, the arm 61 of the clip 60 slips out of the hose 52 so that the filler 51, clip 60 and a trail of the explosive are left behind in the hole 50. Figure 13 depicts a rock face 70 in which a blast hole 71 has been drilled. 5 The filler 51 along with an explosive charge 72 and a detonator's signal tube 73 have been inserted into the hole 71. Tube 73 extends from a primer (not depicted) which has also been inserted into the hole 71, to an electronic igniter circuit which will usually be located a safe distance away from the hole 71. Throughout the specification and the claims, unless the context requires 10 otherwise, the term "comprise", or variations such as "comprises" or "comprising", will be understood to apply the inclusion of the stated integer or group of integers but not the exclusion of any other integer or group of integers. Throughout the specification and claims, unless the context requires otherwise, the term "substantially" or "about" will be understood to not be limited to 15 the value for the range qualified by the terms. It will be appreciated by those skilled in the art that variations and modifications to the invention described herein will be apparent without departing from the spirit and scope thereof. The variations and modifications as would be apparent to persons skilled in the art are deemed to fall within the broad scope and 20 ambit of the invention as herein set forth. It will be clearly understood that, if a prior art publication is referred to herein, that reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

Claims

1. A method of charging a blast hole, the method comprising the steps of: (i) inserting a filler into the hole; and (ii) loading an explosive into the hole. 5

2. The method of claim 1, wherein the filler is an elongate member.

3. The method of claim 2, wherein the filler is hollow.

4. The method of claim 3, wherein the ends of the filler are closed.

5. The method of any one of claims 2 to 4, wherein the filler has a profile selected from the group comprising: a generally crescent-shaped profile; a generally 10 arcuate profile; and a generally kidney-shaped profile.

6. The method of any one of the preceding claims, wherein the filler is compressible.

7. The method of any one of the preceding claims, wherein the filler is inserted into the blast hole such that the filler extends lengthwise along the hole. 15

8. The method of any one of the preceding claims, wherein the filler is inserted into the blast hole such that the filler is located substantially opposite the explosive.

9. The method of any one of the preceding claims, wherein the filler is inserted into the blast hole such that the filler extends along a side of the blast hole.

10. The method of any one of the preceding claims, wherein the filler is inserted 20 into the blast hole such that the filler is located adjacent to a side of the blast hole which is to be protected from overbreak or other damage.

11. The method of any one of the preceding claims, wherein the explosive is an explosive powder.

12. The method of any one of the preceding claims, wherein the explosive is 25 loaded into the blast hole such that the explosive extends along a side of the blast hole.

13. The method of any one of the preceding claims, wherein the explosive is loaded into the blast hole through a hose by inserting the hose into the hole and then withdrawing the hose of the hole so that a trail of the explosive is left in the hole. 30

14. The method of claim 13, wherein the hose and the filler are detachably secured to each other so that inserting the hose into the blast hole results in the filler being inserted into the hole, and so that the hose is able to be withdrawn from the hole 12 without withdrawing the filler from the hole.

15. The method of claim 14, wherein a clip detachably secures the hose and the filler to each other.

16. A charged blast hole comprising a blast hole, a filler inserted into the hole, 5 and an explosive loaded into the hole.

17. A filler for insertion into a blast hole, wherein the filler is adapted to limit the amount of an explosive that is able to be loaded into the blast hole.

18. A method of charging a blast hole, the method being substantially as herein described with reference to: figures 3 and 4; figures 8 and 9; figures 10 and 11; 10 figures 10 to 12; or figure 13.

19. A charged blast hole substantially as herein described with reference to: figure 4; figure 5; or figure 13.

20. A filler for insertion into a blast hole, the filler being substantially as herein described with reference to: figures 3 and 4; figure 5; figures 8 and 9; or figures 10 15 and 11.