WO2002101196A1

WO2002101196A1 - A method of excavating a hard material body

Info

Publication number: WO2002101196A1
Application number: PCT/IB2002/002174
Authority: WO
Inventors: Barry Anthony Hodgkinson; Mihailo Gavrilovic
Original assignee: Barry Anthony Hodgkinson; Mihailo Gavrilovic
Priority date: 2001-06-12
Filing date: 2002-06-12
Publication date: 2002-12-19

Abstract

A method of excavating a hard material body is provided which includes operating a hole forming apparatus to move along a surface of the body to form a series of holes in the body, pressurising at least some of the holes using a gas producing substance to fracture the body, and operating a breaking device to move along a surface of the body and to break fractured material from the body. The holes will preferably be pressurised during operation of the hole forming apparatus or of the breaking device.

Description

A METHOD OF EXCAVATING A HARD MATERIAL BODY

FIELD OF THE INVENTION

This invention relates to a method of excavating a body consisting of a hard material such as rock or concrete.

BACKGROUND TO THE INVENTION

The underground mining of ores, particularly hard ores, usually entails blasting with high explosives. Blasting is, however, often inefficient as it invariably necessitates clearing of the workings for a number of hours to prevent injuries from flying debris and inhalation of noxious gases and dust.

Mechanical fracturing of ores which includes the use of breaking devices has been proposed. However, where the ore being mined exists in a narrow vein such devices have been found to be cumbersome. More importantly, such devices have been found to be ineffective where the ore is hard and competent.

South African patent No 96/6727 describes a method of fragmenting hard rock and concrete by firstly fracturing the rock or concrete using a small explosive charge and then breaking the fractured material using a breaking device. The specification of this patent is incorporated in its entirety herein by reference. While the method described has been found to be effective, the patent does not indicate how such a method could be effectively practised to excavate large bodies.

In this specification "breaking device" denotes any mechanical device which may be used to fracture hard material, including hydraulically or pneumatically operated impact hammers.

Further in this specification "gas producing substance" means any substance which can be activated to result in the production of large volumes of gas and includes explosives, propellants and similar substances which can undergo a rapid transformation from either a solid or liquid to a gas.

OBJECT OF THE INVENTION

It is an object of this invention to provide a method of excavating a hard material body which will, at least partially, alleviate some of the abovementioned problems.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a method of excavating a hard material body which includes: operating a hole forming apparatus to form a series of holes in the body; pressurising at least some of the holes using a gas producing substance to fracture the body; and operating a breaking device to move along a surface of the body and to break fractured material from the body. Preferred features of the invention provide for the hole forming apparatus to be operated to move along a surface of the body, preferably the surface along which the breaking device moves; for the holes formed to be parallel to a free breaking surface; and for at least some of the holes to be pressurised during operation of the hole forming apparatus or of the breaking device.

Further preferred features of the invention provide for the broken material to be removed during operation of the breaking device; for the broken material to be removed to a gulley extending transverse to the surface along which the breaking device moves; for the broken material to be removed using a haulage system associated with the breaking device; and for the haulage system to include a plurality of reciprocating blades, and to preferably be a reciprocating flight conveyor.

Still further preferred features of the invention provide for the breaking device to include a hydraulically or pneumatically operated hammer; for the breaking device to be moved along a track extending adjacent to the surface; for the hole forming device to be moved along the track; for the track to be flexible in its length and moved by rams, preferably hydraulic rams; and for the track to form part of the haulage system.

According to one aspect of the invention there is provided for holes to be pressurised by inserting a charge of a gas producing substance into such holes, stemming such holes to contain gasses generated by the gas producing substance and initiating at least some of the charges.

Further preferred features according to this aspect of the invention provide for at least some of the charges of a gas producing substance to be inserted into holes during operation of the hole forming apparatus or of the breaking device; for the charges to be inserted by an indexing device associated with the hole forming apparatus; and for a number of charges to be sequentially initiated, alternately simultaneously, further alternately individually and subsequent to the hole becoming adjacent a substantially parallel free breaking face formed by the breaking device.

Still further preferred features according to this aspect of the invention provide for a propellant to be used in the charges; for the propellant to be contained in cartridges; for each cartridge to be secured in a hole using a stemming material, preferably a particulate stemming material; for the stemming material to be held in place by a plug, preferably an expanding plug; alternately for the stemming material to be held in place by a stemming bar; and for the stemming bar to have a recoil absorbing mechanism associated therewith.

Yet further preferred features according to this aspect of the invention provide for the propellant to be mixed with an oxidising agent; for the oxidising agent to be ammonium nitrate; and for the ammonium nitrate to be in a prilled form.

A further preferred feature according to this aspect of the invention provides for the propellant to be initiated using a non-electric igniter, preferably an igniter which can be initiated using shock tube.

According to a second aspect of the invention there is provided for holes to be pressurised by injecting gas therein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described, by way of example only, with reference to the drawings in which:

Figure 1 is a schematic plan view of a first embodiment of a hard material body being excavated; and Figure 2 is a schematic plan view of a second embodiment of a hard material body being excavated.

DETAILED DESCRIPTION OF THE DRAWINGS

An underground mining operation is partly shown in Figure 1 and includes a hard rock ore body (1 ) to be excavated. Excavation occurs along panel (2) which extends transversely from a gulley (3) or similar advance heading. Support units (4) of a type and density most appropriate to the depth, ground conditions and mining layout are installed in the back area behind the panel (2). These include elongate timber supports and mechanical supports.

According to the invention, excavation takes place by firstly laying a flexible track (10) along the panel (2). A drilling rig (11 ) is then mounted to run on the track (10) as is a pneumatically operated hole stemming device (12) and a breaking device (15).

The drilling rig (11 ) is used to form a series of holes (20) along the panel (2) starting from the side adjacent the gulley (3). The holes (20) are formed generally parallel to the free face (5) at the side of the panel (2) defining part of the gulley (3) and will generally be longer than 15 hole diameters. In this embodiment, a set of three vertically spaced holes are simultaneously formed in the panel (2) by the drilling rig (11).

Once a set of holes (21) has been drilled and the rig (11 ) moved along the panel (2) the holes each have a propellant charge (22) inserted therein. As shown more clearly in inset A, the charge (22) includes a waterproof plastics cartridge (25) which is filled with a mixture of a propellant and prilled ammonium nitrate (26). Embodiments of such cartridges are described in South African patent application number 2000/1407 and the specification of this patent application is incorporated in its entirety herein by reference. However, any suitable cartridge can be used. Each cartridge (25) has an igniter (27) extending from a length of shock tube (28) secured through an end thereof to initiate the propellants.

After a charge (22) has been inserted into a hole (20) and pushed to the end thereof, the hole (20) is filled with particulate stemming material (30) using the pneumatic charger (12). The charger (12) has a flexible hose (31 ) through which the stemming material is conveyed into the hole (20). Such device is described in South African patent application number 2001/6766 the specification of which is incorporated in its entirety herein by reference. After the hole (20) has been substantially filled with stemming material (30) a plug (not shown) is inserted into the hole to assist in preventing expulsion of the stemming material by initiation of the charge.

When a number of holes (40) have been so charged the shock tube (28) from each charge (22) is connected to a trunkline (45) using surface delay connectors (not shown) which enable sequential initiation of the charges. The trunkline (45) is connected to an initiating device (46) and once all the charges have been connected to the trunkline (45) they are initiated by an operator (46). The delay connectors have the result that charges (22) are initiated commencing with those in the set of holes nearest gulley (3). The shock tube (28) will be initiated by a device which does not rely on the use of a detonator or detonating cord. Such devices are typically either pyrotechnic in nature, often being based on the use of a percussion cap, or electrical in nature.

Initiation of the charges produces fractures in the body (1 ) which propagate from the base of each hole (20) and extend generally parallel to a free face as well as from the base of each hole towards the nearest exposed surface.

Importantly, the charges (22) are selected and positioned to ensure that instead of material breaking away from the body (1) fractures are created in the body (1 ) initiating from the bottom of each hole. This is done by effectively over burdening the charges. Very little dust and noxious gas thus results from the initiation of the charges (22) and there is a significantly reduced risk of fly rock to potentially cause injuries to personnel in the area and damage to the infrastructure.

After initiation of the charges (22) the breaking device (15) is used to break the fractured material from the body (1 ). In this embodiment, the breaking device (15) has a hydraulically operated hammer (50) secured through an articulating link to a carriage (51) which runs on the track (10). The hammer (50) is moved to engage and break e body (1) while the carriage allows advancement along the panel (2). Such devices are well-known in the art and are often referred to as "impact rippers". Typically, these devices do not operate effectively in excavating hard competent rock as they tend to lack sufficient power to break the rock efficiently. However, it is envisaged that such devices will be highly effective where the rock is fractured as described above as they were originally designed to operate in deep mining environments where they could₍ exploit the extensive stress fracturing encountered behind previously excavated rock surfaces.

Also secured to the track (10) is a haulage system (52) for removing material (60) broken by the pneumatic hammer (50). The haulage system (52) includes a plurality of blades (53) which are hingedly secured to a link bars (not shown) operable by hydraulic cylinders (not shown) to reciprocate the blades (53). The blades (53) pivot and extend along the track (10) on the forward stroke and then pivot outwardly to extend normally to the track (10) on the reverse stroke. Such systems are often referred to as reciprocating flight conveyors. On the reverse stroke the broken material (60) is thus scraped by the blades (53) towards and eventually into the gulley (3).

Reciprocal movement of the blades (53) is slow enough to allow personnel to easily avoid the blades (53). Hydraulic rams (65) secured to movable hydraulic supports (66) allow the track (10) to be advanced towards the panel (2). As the track (10) is flexible, part thereof is advanced into the newly excavated part of the panel (2) to commence removing the broken material (60). This assists in providing continuity to the entire excavation operation as all the essential processes can take place simultaneously.

Broken material in the gulley (3) is removed to an ore pass (not shown) using a conventional winch scraper system (70).

Once the entire panel (2) has been broken and removed drilling is again started from adjacent the gulley and the above process repeated.

As shown in Figure 2, however, where like numerals indicate like features, a panel (100) could extend between a pair of gullies (102, 103) and be separated from each gulley (102, 103) by an upwardly stepped shoulder (104, 105) each of which is substantially level with the footwall (106). The shoulders (104, 105) provide an overrun area for the breaking device (15), drilling rig (11 ) or hole stemming device (12) to wait in while the other of the devices completes operations at the ends of the panel (100).

Also in this embodiment the broken material (110) is moved by the reciprocating flight conveyor (115) in the direction of movement of the breaking device (15). It is envisaged that this configuration will assist in loading the broken material (110) onto the flight conveyor (115) which, in this embodiment, has the flights (116) running in a shallow channel (117).

As it will be difficult to operate any devices above broken material (110) on the flight conveyor (115) in narrow stopes, the drilling rig (11 ) and hole stemming device (12) will follow the breaking device (15) and operate on the part of the panel (100) newly exposed by the breaking device (15). In order to create fractures in the panel (100) ahead of the breaking device (15), as described below, holes will initially have to be drilled across the entire panel prior to the breaking device's first run across the panel (100).

The holes (120) have charges inserted therein and are stemmed as described above. Hereafter, an operator individually initiates the charge in each hole (120) in the path of the breaking device (15) subsequent to the hole (120A) becoming adjacent to the substantially parallel free breaking face (125) created by the breaking device (15) in the panel (100). It is envisaged that ideal fracturing will occur where there is a free breaking face as described adjacent to the charge being initiated. It is further envisaged that a hole depth greater than 15 hole diameters will be most effective.

Also in this embodiment, the broken material (110) is moved onto a belt conveyor (140) in the gulley (102). The gullies (102, 103) will preferably be pre-developed to a holing point, typically between raise lines, to avoid having to regularly halt excavation while the gullies are excavated.

Where it is not desired to individually initiate charges, a number of charges in different holes could be simultaneously initiated, either in the path of the breaking device or soon after drilling. In this event it will probably be best to drill the holes to a depth of between 3 and 15 hole diameters to exploit the cratering effect of penetrating cone fracture ("PCF") and to create face parallel fractures.

It is envisaged that fracturing the body prior to use of the breaking device will result in a highly cost and time effective system. It will be appreciated, however, that many other embodiments of the excavation method exist which fall within the scope of the invention especially as regards the equipment used. For example, any suitable device can be used to break the material, including oscillating discs and raise boring machines and these devices need not operate on a track. Mobile excavating machines are also envisaged which incorporate all, or at least combinations of, the functions of drilling, charging, initiating, breaking and cleaning. These would allow hard rock mining operations to be modelled more closely along the lines of coal mining operations which, because of the ease of mechanical excavation of coal, have long enjoyed the benefits of continuous mining. In areas where geological disturbances are minimal "impact ripper" or "longwall" type systems can be used with the method of the invention. In areas where there is significant geological disturbance, or where the grade of material being mined is erratic compact, mobile excavating machines will probably be necessary.

The geology of mineral bodies will also determine the hole configuration and formation.

Furthermore, the drilling rig could be air, oil, water or electrically operated. Also, it is not necessary to use a stemming device for the stemming material and any suitable stemming material can be used, including gels. While plugs have been found to be useful in retaining the stemming material in the hole during initiation of the charge it is envisaged that these will not be necessary in many instances. However, it is also envisaged that stemming bars could be used to hold the stemming in position in the holes. These will preferably be secured in position by an indexing device which automatically inserts the stemming bars into the holes and includes a recoil absorbing mechanism. The indexing device would preferably form part of the hole forming apparatus and further include means to automatically charge and stem each hole and initiate each charge. In such an event the charge in each hole will be initiated as soon as the hole is properly stemmed rather than simultaneously initiating a number of charged holes.

Also, stemming could be inserted into each hole in a packaged form. Such packages could be manually inserted into each hole but will preferably be inserted using an automatic loader. Such a loader would preferably be pneumatically operated. Each hole could have more than one charge inserted therein and these could be separated by stemming material to provide "decked charges". Where holes are very long decked charges may assist in obtaining fracturing at different places along the length of the hole as the stemming should create a false hole bottom from which fractures propagate for the charge adjacent the hole mouth.

Still further, any suitable gas producing substance can be used, including high explosives, to pressurise the holes. Where a propellant is used this can be a single propellant or a mixture of propellants and these could be single, double or triple base propellants. The propellants may be mixed with any suitable oxidizing agent and while it is preferred to use a non-electric igniter, electric igniters can also be used to initiate the gas producing substance. Also, multiple charges could be inserted into each hole and such charges could each make use of a different gas producing substance.

Depending on the stope height, vertical rows could consist of more or less than three holes. Depending on the length of the panel it may also be desirable to operate drilling and material breaking and removal operations from opposite sides of the panel towards each other. In such instances, a gulley would be provided on either side of the panel.

It is also possible that holes could be formed parallel to the panel by, for example, drilling from the gulley preferably using directional drilling techniques. Such holes will preferably extend the length of the panel and have multiple charges separated by suitable amounts of stemming. One advantage of this approach to forming holes is that the hole forming apparatus will not be in the path of the breaking device.

The method of excavation of the invention is, however, not limited to mining and may be used in any excavation of hard bodies including tunnelling and the demolition of structures. Importantly, the body may be fractured by injecting a gas under pressure into the holes drilled into the panel. Devices which could be used to inject gas into the holes are described in South African patent numbers 91/6180 and 2000/1056 and the specifications of these patents are incorporated herein by reference. While such devices have been found to be effective in breaking hard bodies, it is envisaged that they may be too bulky for effective use in narrow vein mining and that the use of cartridges may consequently be preferable for pressurising holes.

Claims

1. A method of excavating a hard material body which includes operating a hole forming apparatus to form a series of holes in the body, pressurising at least some of the holes using a gas producing substance to fracture the body, and operating a breaking device to move along a surface of the body and to break fractured material from the body.

2. A method of excavating a hard material body as claimed in claim 1 in which the hole forming apparatus is operated to move along a surface of the body.

3. A method of excavating a hard material body as claimed in claim 2 in which the hole forming apparatus is operated to_ move along the surface along which the breaking device moves.

4. A method of excavating a hard material body as claimed in any one of the preceding claims in which the holes formed are substantially parallel to a free breaking surface.

5. A method of excavating a hard material body as claimed in any one of the preceding claims in which at least some of the holes are pressurised during operation of the hole forming apparatus or of the breaking device.

6. A method of excavating a hard material body as claimed in any one of the preceding claims in which the broken material is removed during operation of the breaking device.

7. A method of excavating a hard material body as claimed in claim 6 in which the broken material is removed to a gulley extending transverse to the surface along which the breaking device moves.

8. A method of excavating a hard material body as claimed in claim 6 or claim 7 in which the broken material is removed using a haulage system associated with the breaking device.

9. A method of excavating a hard material body as claimed in claim 8 in which the haulage system includes a plurality of reciprocating blades.

10. A method of excavating a hard material body as claimed in claim 9 in which the haulage system is a reciprocating flight conveyor.

11.A method of excavating a hard material body as claimed in any one of the preceding claims in which the breaking device includes a hydraulically or pneumatically operated hammer.

12. A method of excavating a hard material body as claimed in any one of the preceding claims in which for the breaking device is moved along a track extending adjacent to the surface.

13. A method of excavating a hard material body as claimed in claim 12 in which the hole forming device is moved along the track.

14. A method of excavating a hard material body as claimed in claim 12 or claim 13 in which the track is flexible in its length.

15. A method of excavating a hard material body as claimed in claim 14 in which the track is moved by rams.

16. A method of excavating a hard material body as claimed in claim 15 in which the rams are hydraulically operated.

17. A method of excavating a hard material body as claimed in any one of claims 12 to 16 read with any one of claims 8 to 10 in which the track forms part of the haulage system.

18. A method of excavating a hard material body as claimed in any one of the preceding claims in which a hole is pressurised by inserting a charge of a gas producing substance into such hole, stemming such hole to contain gasses generated by the gas producing substance and initiating the charge.

19. A method of excavating a hard material body as claimed in claim 18 in which at least some of the charges of a gas producing substance are inserted into holes during operation of the hole forming apparatus or of the breaking device.

20. A method of excavating a hard material body as claimed in claim 18 or claim 19 in which the charges are inserted into holes by an indexing device associated with the hole forming apparatus.

21. A method of excavating a hard material body as claimed in any one of claims 18 to 20 in which a number of charges are sequentially initiated.

22. A method of excavating a hard material body as claimed in any one of claims 18 to 20 in which a number of charges are simultaneously initiated.

I 23. A method of excavating a hard material body as claimed in any one of claims 18 to 20 in which charges are individually initiated.

24. A method of excavating a hard material body as claimed in claim 23 in which a charge is initiated subsequent to the hole in which it is located becoming adjacent to a substantially parallel free breaking face creating by the breaking device.

25. A method of excavating a hard material body as claimed in any one of claim 18 to 24 in which a propellant is used in the charges.

26. A method of excavating a hard material body as claimed in claim 25 in which the propellant is contained in cartridges.

27. A method of excavating a hard material body as claimed in claim 26 in which each cartridge is secured in a hole using a stemming material.

28. A method of excavating a hard material body as claimed in claim 27 in which the stemming material is particulate.

29. A method of excavating a hard material body as claimed in claim 27 or claim 28 in which the stemming material is held in place by a plug.

30. A method of excavating a hard material body as claimed claim 27 or claim 28 in which the stemming material is held in place by at least one stemming bar.

31. A method of excavating a hard material body as claimed in claim 30 in which the or each stemming bar has a recoil absorbing mechanism associated therewith.

32. A method of excavating a hard material body as claimed in claim 25 or claim 26 in which the propellant is mixed with an oxidising agent.

33. A method of excavating a hard material body as claimed in claim 32 in which the oxidising agent is ammonium nitrate.

34. A method of excavating a hard material body as claimed in claim 33 in which the ammonium nitrate is in a prilled form.

35. A method of excavating a hard material body as claimed in any one of claims 32 to 34 in which the propellant is initiated using a non-electric igniter.

36. A method of excavating a hard material body as claimed in claim 35 in which the propellant is initiated by a shock tube operated igniter.

37. A method of excavating a hard material body as claimed in any one of claims 1 to 17 in which holes are pressurised by injecting gas therein.

38. A method of excavating ,a hard material body substantially as herein described and as illustrated with reference to Figure 1 or Figure 2.