UNDERGROUND SHAFT DEVELOPMENT METHOD

Abstract

An underground shaft development method comprises: (a) drilling blastholes extending into a rock formation, each drilled from a starting location defining a first blasthole end to an ending location defining a second blasthole end; (b) loading the blastholes with alternating layers of explosives charges and stemming material to provide multiple blasting decks across and within the formation, including at least a first blasting deck corresponding to the first blasthole ends and a final blasting deck corresponding to the second blasthole ends, wherein each blasting deck carries wireless blasting devices; and (c) detonating the explosive charges in a series of blasting stages based on blasting deck by initiating the wireless blasting devices in each blasting deck, proceeding consecutively from the first blasting deck to the final blasting deck, wherein after each blasting stage excavation takes place to progress the shaft in an intended direction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of the specification of Singapore Patent Application No. 10201703958T is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for shaft development or shaft sinking in rock formations.

BACKGROUND OF THE INVENTION

Shafts are a core feature in many civil engineering and mining operations. Shafts are typically required for movement of personnel, equipment, materials and water, and for ventilation purposes. Shaft sinking (or shaft mining) refers to the process by which a shaft is developed. Shaft sinking in rock formations is typically undertaken by a process in which the shaft is lengthened in a series of stages. Each stage involves drilling rounds of blastholes in a predetermined arrangement, loading the holes with explosives, and blasting. After suitable ventilation, rock is excavated from the area blasted and ground support installed as necessary. The next stage of drilling, blasting, excavation, and ground support installation is then carried out, and so on in a repeated manner. Thus, the shaft is extended in each stage.

This conventional process has a number of limitations and disadvantages associated with it. The process is very labour intensive and potentially hazardous. For example, drilling of blastholes and loading of explosives into blastholes per stage is a manual process requiring personnel to work in the shaft for many hours at a time. The shaft is developed over relatively small distances per drilling cycle, and the drilling equipment used is relatively small and often hand-operated. Typically, the blastholes will have a diameter 38-64 mm and their length per drilling cycle will be restricted to between 0.5 and 3.0m.

The present invention seeks to provide a new approach to shaft sinking that provides benefits when compared with the conventional blasting approach discussed.

SUMMARY OF THE INVENTION

Accordingly, in accordance with an aspect of the present disclosure, a method of sinking a shaft in a rock formation comprises: drilling blastholes extending into the formation, the blastholes having a top end and a bottom end; loading the drilled blastholes with alternating layers of explosives charges and stemming material to provide a series of blasting decks extending across and within the formation; and initiating the explosive charges in a series of blasting stages based on blasting deck and proceeding consecutively from the blasting deck located at the top of the blastholes to the blasting deck located at the bottom of the blastholes, wherein after each blasting stage, excavation takes place to progress the shaft in an intended direction.

In accordance with another aspect of the present disclosure, a method of sinking a shaft in a rock formation comprises: during a selected shaft development interval: (a) drilling blastholes extending into the formation, each blasthole drilled from a starting drilling location defining a first end of the blasthole to an ending drilling location defining a second end of the blasthole such that the blasthole has a depth between its first end and second end; (b) loading the blastholes with alternating layers of explosives charges and stemming material to provide a series of blasting decks extending across and within the formation, including at least first blasting deck corresponding to the first ends of the blastholes and a final blasting deck corresponding to the second ends of the blastholes, wherein each blasting deck includes wireless blasting devices; and (c) detonating the explosive charges in a series of blasting stages based on blasting deck by way of initiating the wireless blasting devices in each blasting deck, proceeding consecutively from the first blasting deck corresponding to the first ends of the blastholes to the final blasting deck corresponding to the second ends of the blastholes, wherein after each blasting stage corresponding to the selected shaft development interval, excavation takes place to progress the shaft in an intended direction.

In some embodiments, the series of blasting decks extending across and within the formation includes at least three blasting decks, including at least one blasting deck disposed between the first blasting deck and the final blasting deck.

In some embodiments, in the selected shaft development interval the depth of each blasthole is between 10-80 m. In other embodiments, in the selected shaft development interval the depth of each blasthole is greater than 80 m.

Depending upon the direction of shaft development, the final blasting deck will be deeper within the earth than the first blasting deck (shaft development having a downward directional component), or the final blasting deck will be closer to the surface of the earth than the first blasting deck (shaft development having an upward directional component). The shaft can be developed to intersect an underground excavation (e.g., an existing underground passage or tunnel).

In the selected shaft development interval, the wireless blasting devices in each blasting deck can be programmed with a unique group identifier corresponding to the blasting deck.

In accordance with a further aspect of the present disclosure, the method further comprises: during an additional shaft development interval following the selected shaft development interval, repeating steps (a) through (c), wherein after each blasting stage corresponding to the additional shaft development interval, excavation takes place to progress the shaft in an intended direction.

In the additional shaft development interval, the depth of each blasthole can be between 10-80 mm, or longer than 80 m depending upon embodiment and/or situational details.

In the additional shaft development interval, the wireless blasting devices in each blasting deck can also be programmed with a unique group identifier corresponding to the blasting deck.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated in the accompanying non-limiting drawings in which:

FIG. 1 is an illustration showing the steps associated with each stage of a conventional shaft sinking technique;

FIG. 2 is a schematic illustrating a conventional shaft sinking technique;

FIG. 3 is an illustration showing the steps involved with stages of the method of the present invention; and

FIGS. 4-7 are schematics illustrating the shaft sinking method of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention involves drilling of blastholes and loading of blastholes with explosives charges and stemming material in a single event. The explosives charges and stemming material are provided in the blastholes to provide blasting decks within and across the rock formation into which shaft sinking takes place. The blasting decks divide the rock formation into rock volumes/regions that will be blasted in a stage-wise approach. Each blast will break rock in the immediate vicinity of the relevant explosives charges and the broken rock is then excavated before the explosive charges in the next blasting deck are initiated, and so on.

Key differences between the present invention and the conventional approach can be explained with reference to FIGS. 1-4.

With respect to FIG. 1 a conventional shaft sinking technique in a rock formation involves a repeated cycling of the following steps:

• • drilling blastholes
  • charging blastholes with explosives
  • blasting (and ventilating the area)
  • excavating rock from the area blasted
  • installing ground support

By following this approach, a shaft will be developed by approximately the length of the blastholes per cycle. In practice this length will be up to about 3 m.

FIG. 2(a)-(g) shows steps involved in the conventional shaft sinking technique, consistent with FIG. 1. In FIG. 2(a) blastholes are drilled in accordance with a predetermined pattern to define an area in which a shaft is to be formed. The blastholes are loaded with explosives and blasted (not shown). FIG. 2(b) shows an excavator removing blasted rock thereby commencing shaft sinking. In FIG. 2(c) new blastholes are drilled and loaded with explosives, and blasted (not shown). FIG. 2(d) shows excavation of blasted rock and extension of the shaft in a downward direction. These steps are repeated in FIG. 2(e)-(g) thereby developing a shaft. The Figures do not show installation of any ground support, but this will invariably take place after each cycle of drilling, loading, blasting and excavating.

With respect to FIG. 3, the method of the present invention involves one or more shaft development time periods, intervals, iterations, or cycles, where for a given shaft development time period, interval, iteration, or cycle under consideration, the method includes drilling blastholes and loading the blastholes with multiple layers of explosive charges corresponding to multiple blasting decks in a single blasthole drilling and loading event or procedure. Thereafter, within the current shaft development time period, interval, iteration, or cycle, the method involves repeated cycling of the following steps:

• • blasting (and ventilating the area);
  • excavating rock from the area blasted; and
  • installing ground supportuntil no more blasting decks along the depth of the blastholes drilled during the current or most-recent shaft development time period, interval, iteration, or cycle are available for blasting. Depending upon embodiment and/or situational details, after completion of the shaft development iteration or cycle under consideration, another or subsequent shaft development time period, interval, iteration, or cycle can be performed, e.g., on a selective basis depending upon whether a target overall shaft length or depth or target overall shaft destination has been reached or realized.

By following this approach, the need to carry out drilling and loading explosives after each stage of excavation is eliminated. That is, the present invention eliminates the conventional requirement to carry out blasthole drilling and explosives loading corresponding to a next shaft level or shaft depth increment to be blasted after each excavation of the most recent shaft level that was blasted. Rather, a single blasthole drilling and explosives loading event or procedure is performed that physically or spatially encompasses or defines multiple blasting decks along the depth of the blastholes, where each blasting deck (a) corresponds to a particular shaft level or shaft depth increment, and (b) includes explosive charges that have been pre-positioned at predetermined depth(s) within the blastholes during the single blasthole drilling and loading event or procedure. Following the single blasthole drilling and explosives loading event or procedure spanning multiple blasting decks corresponding to multiple shaft levels or shaft depth increments, individual blasting decks across these multiple blasting decks can be sequentially or consecutively blasted and excavated to progressively extend the depth of the shaft.

The method of the invention involves a single drilling and explosives loading stage of multiple relatively long blastholes, which means that larger scale, automated equipment may be used. Typically, the blasthole diameter may be 76-165 mm and the blasthole length or depth may be at least 10-20 m, for instance, 25-30 m or longer (e.g., 80 m). Even though in various embodiments the blasthole depth is between 10-80 m, it may be possible to drill to depths more than 80 m (e.g., up to 100 m, 120 m, 150 m, 180 m, 200 m, 220 m, or 250 m) depending upon the characteristics of the rock formation and the sophistication of the drilling equipment being used. Contrast this with the conventional approach where multiple drilling stages of relatively short blastholes is necessary.

FIG. 3(a)-(e) shows steps involved with the method of the present invention, consistent with FIG. 2. In FIG. 3(a), blastholes are drilled in accordance with a predetermined pattern to define a region or area in which a shaft is to be formed. The blastholes extend over the full length of the proposed shaft corresponding to a particular shaft development time period, interval, iteration, or cycle. The blastholes are loaded with explosives charges and stemming material to provide a series of blasting decks, i.e., multiple blasting decks. For shaft development along a downward direction (e.g., away from the surface of the earth), explosives charges in the blasting deck at the top of the blastholes are then initiated, thereby breaking rock in the immediate vicinity. This broken rock is then excavated as shown in FIG. 2(b). Undetonated explosive charges are slept. After this excavation, the explosive charges in the next blasting deck down are initiated and broken rock excavated, and so on, as shown in FIGS. 2(c), (d) and (e). For purpose of brevity and simplicity, the Figures do not show installation of any ground support, but this will take place after each cycle of excavation in a manner readily understood by individuals having ordinary skill in the relevant art.

A key feature of the present invention is that it minimises the steps involved in sinking a shaft over a given distance. For example, using the conventional approach to extend a shaft over 30 m could require 10 or more cycles of drilling and explosives loading. In contrast, using the present invention the same may be achieved in a single event of drilling and explosives loading. Depending upon the desired target overall depth of the shaft and the characteristics of the rock formation, the method of the invention may be applied to sink a shaft to its target overall depth in association with a single shaft development time period, interval, or iteration. However, if this is not possible, the method of the invention may be repeated across multiple shaft development time periods, intervals, iterations, or cycles to develop the shaft to its intended target overall depth. For example, if the intended target overall shaft depth is 100 m or greater, the shaft may be developed by applying the method of the invention over multiple (e.g., 2 or more) shaft development time periods, intervals, iterations, or cycles.

The invention requires loading of blastholes with a plurality of explosive charges and the selective, sequential initiation of those charges, such that charges in a first deck (e.g., an uppermost or top deck) or a deck directly adjacent to a current excavated blasthole depth are detonated, while charges in other decks that are deeper relative to the blasthole's depth (e.g., decks below the uppermost or top deck, correspondingly) are slept. Herein, reference to loading blastholes with explosive charges means that blastholes are loaded with explosive formulations and initiation systems, in a manner that will be readily comprehended by individuals having ordinary skill in the relevant art. The initiation systems used in a given blasting deck will need to remain operational and unaffected by the initiation of explosives formulations in previously blasted decks in the same blasthole and in adjacent blastholes. This effectively precludes the use of wired initiation systems that rely on cables for communication of command signals. Such cables will most likely be compromised by blasts within the same blasthole and/or in adjacent blastholes. This issue may be addressed in accordance with the present invention using a wireless electronic blasting system (WEBS) to initiate explosives formulations.

The WEBS is an electronic initiation system suitable for initiation of explosive charges. The WEBS includes multiple wireless blasting devices (e.g., wireless explosive primers), each of which is powered by an energy source (e.g., an internal (on-board) energy supply such as a battery), and each of which receives command instructions wirelessly, for example, by way of very low frequency magnetic resonance signals that can be transmitted through rock, air and/or water. The WEBS does not rely on any physical (wired) connections to an external power supply or to a blasting machine for communications necessary for blasting functionality (e.g., issuing FIRE commands to WEBS blasting devices). In the context of the present invention, this means that blasting horizons will not be damaged by preceding blasts and communication channels to each WEBS blasting device will remain intact. In the WEBS, individual blasting devices can also be programmable with respect to WEBS group/subgroup identity and/or detonation delay time, and this will enhance implementation of the invention as will be discussed.

Suitable WEBS and corresponding WEBS blasting devices for use in the present invention are known and described for example in Applicant's own International Patent Publication No. WO2015/143501 and International Patent Publication No. WO2015/143502, the contents of which are incorporated herein by reference. Suitable WEBS are commercially available through Orica International Pte Ltd., Singapore.

Additional aspects of the invention will be elaborated upon with reference to FIGS. 5-7.

FIG. 5 illustrates a series of 8 vertical blastholes. Each blasthole is loaded with explosives charges and stemming material (inert horizon). The explosives charges and stemming material are arranged in a series of blasting decks denoted Blast 1, Blast 2 . . . Blast X+2. In various embodiments, in a given blasting deck, the explosive charges and stemming material are at approximately the same depth, and extend over approximately the same length within the blastholes.

A layer of stemming material (e.g., graded rock gravel) covers the explosive charge(s) in any given deck, where such stemming material is intended to prevent transmission of explosives energy to an adjacent blasting deck. Using the nomenclature of FIG. 5, the blasting deck denoted Blast 1 is blasted first, followed by excavation of broken rock and installation of ground support as required. Thereafter, the blasting deck denoted Blast 2 is blasted (followed by excavation of broken rock and installation of ground support as required), and so on until blasting deck denoted Blast X+2 is blasted. During a blast directed to a currently selected deck, and in between blasts, remaining explosive charges corresponding to other decks in the blasthole (i.e., explosive charges in decks deeper relative to the depth of the blasthole than the currently selected deck) are slept. Once rock broken by the most recently blasted deck has been cleared and ground support installed, a next sequential deck in the blasthole (i.e., the next deeper deck relative to the depth of the blasthole, directly adjacent to the most-recently blasted deck) can be blasted.

After each blasting deck has been fired it is not essential for the floor of the developing shaft to be cleared or cleaned completely before the next blasting deck is fired, since there is no need to undertake any further drilling and explosives loading that would otherwise necessitate a suitably cleared or clean floor for effective operation of equipment and safety of personnel.

The length of rock blasted in each blasting deck may vary depending upon such things as:

• • the geological and geotechnical conditions;
  • the blasthole design (density and pattern of holes, burden, and relief);
  • the initiation sequence (e.g., the inter-deck and/or intra-deck initiation sequence);
  • the explosives type/types and energy/energies; and/or
  • restrictions on blast induced ground vibration and/or noise

FIG. 6 shows a typical arrangement of blastholes for a shaft. In the embodiment shown, the blastholes are arranged in concentric rings around a central relief hole. The use of a relief hole may not be essential, but it can be useful in providing vacant space for broken rock to move into during the various blasts that will take place.

The outer ring of blastholes are intended to define the outer walls of the shaft. Blasts in this outer ring may take place with a lower volume of explosives and/or lower energy explosives to ensure that excessive damage does not occur in the rock that will form the outer walls of the shaft. The explosive charges in blastholes in the outer ring may be initiated at the same time as other explosives charges within the same blasting deck. Preferably, however, the explosive charges in the outer ring of blastholes are initiated before the other explosives charges in the same blasting deck as this may lead to less overall damage to the walls of the shaft. It will be appreciated that the blastholes in the outer ring are typically pre-split blastholes.

The remaining blastholes may be arranged in any suitable pattern to achieve suitable breakage of rock in the vicinity of the blasthole. The characteristics of the rock formation and the nature of the explosives formulations being used will influence the grouping and/or density of blastholes used.

The explosives in each blasting deck are initiated completely independently of explosives in other blasting decks. Within the same blasting deck, the explosives charges may be initiated at the same time or with delay times relative to each other. The latter may be preferred in terms of blasting effectiveness. As explained, blastholes that are at the boundary of the shaft (pre-split blastholes) may be initiated before other blastholes within the same blasting deck. This may provide relief at the perimeter of the shaft and minimise wall damage.

To achieve suitable initiation control of explosives formulations the WEBS blasting devices in the same blasting deck may bfse allocated a unique group identifier that ensures that only wireless commands (including FIRE commands) intended for those WEBS blasting devices are actioned. This approach allows each WEBS blasting device being used to be programmed before or on deployment in a blasthole to enhance effectiveness and efficiency of operation. This approach also allows a specific (predetermined) group of WEBS blasting devices to be detonated in a desired sequence, while other pre-programmed WEBS blasting devices do not initiate. Rather, those WEBS blasting devices sleep in the blastholes until they are commanded by a suitably coded signal to wake up and detonate. The use of group identification features to ensure that command signals are actioned by a predetermined group of wireless devices is the subject of International Patent Publication No. WO2010/085837, the contents of which are incorporated herein by reference.

FIG. 7 shows the blastholes, explosives charges and stemming material from a different perspective. In this figure, wireless electronic primers are used as the WEBS blasting devices.

The explosives formulations used will be of known composition and will be selected based on their suitability for the shaft sinking situation under consideration. Typically, the explosive formulation will be an emulsion explosive formulation.

When ground support is required, conventional components and methodologies will be used; including rock bolts, wire mesh and pre-formed concrete shaft liners. Individuals skilled in the art will be familiar with the appropriate ground support to use, depending on context.

The present invention may be applied to “Conventional Shaft Sinking” and to “Rise Mining”. In “Conventional Shaft Sinking” the free or accessible surface is initially at the top of the blastholes, with shaft development extending downwards. The shaft produced is usually vertical or just off vertical (by up to about 15° for example). In the invention, broken rock is excavated using conventional shaft sinking digging apparatus, such as cactus grabs and bucket excavators or manually using shovels. Each subsequent layer of rock is blasted only when enough broken rock has been removed so that the next blast remains unaffected.

The method may also be applied to “Rise Mining,” e.g., where the shaft blastholes have been designed to intersect an underground excavation such as an existing underground passage or tunnel. In this case, the free or accessible surface is initially at the bottom of the blastholes, and shaft development proceeds upwards. When the invention is used for Rise Mining, broken rock that results from blasting a given deck falls under gravity and can be removed, for example by mechanical loading machines (i.e., front end loaders). A subsequent blasting deck can be blasted when there is enough space beneath the blast to allow the newly broken rock to expand into it.

In a variation of this, the method of the invention may be applied to produce drawbells in a block cave mining operation. In this case the free or accessible surface is again at the bottom and removal of rock proceeds upwards. As rock is broken it falls under gravity and may be removed. Applying the method of the invention to produce drawbells may allow larger sized drawbells to be produced when compared with single shot production techniques. This is because in accordance with the invention, rock may be blasted and removed incrementally in controlled volumes based on blast design.

Claims

1. A method of sinking a shaft in a rock formation, comprising: during a selected shaft development interval:(a) drilling blastholes extending into the formation, each blasthole drilled from a starting drilling location defining a first end of the blasthole to an ending drilling location defining a second end of the blasthole such that the blasthole has a depth between its first end and second end;(b) loading the blastholes with alternating layers of explosives charges and stemming material to provide a series of blasting decks extending across and within the formation, including at least first blasting deck corresponding to the first ends of the blastholes and a final blasting deck corresponding to the second ends of the blastholes, wherein each blasting deck includes wireless blasting devices; and(c) detonating the explosive charges in a series of blasting stages based on blasting deck by way of initiating the wireless blasting devices in each blasting deck, proceeding consecutively from the first blasting deck corresponding to the first ends of the blastholes to the final blasting deck corresponding to the second ends of the blastholes,wherein after each blasting stage corresponding to the selected shaft development interval, excavation takes place to progress the shaft in an intended direction.

2. The method of claim 1, wherein the series of blasting decks extending across and within the formation includes at least three blasting decks, including at least one blasting deck disposed between the first blasting deck and the final blasting deck.

3. The method of claim 1 or 2, wherein in the selected shaft development interval, the depth of each blasthole is between 10-80 m.

4. The method of claim 1 or 2, wherein in the selected shaft development interval, the depth of each blasthole is greater than 80 m.

5. The method of any one of claims 1-3, wherein the final blasting deck is deeper within the earth than the first blasting deck.

6. The method of any one of claims 1-3, wherein the final blasting deck is closer to the surface of the earth than the first blasting deck.

7. The method of claim 1 or 2, wherein the shaft is developed to intersect an underground excavation.

8. The method of claim 1, wherein in the selected shaft development interval, the wireless blasting devices in each blasting deck are programmed with a unique group identifier corresponding to the blasting deck.

9. The method of claim 1, further comprising: during an additional shaft development interval following the selected shaft development interval, repeating steps (a) through (c), wherein after each blasting stage corresponding to the additional shaft development interval, excavation takes place to progress the shaft in an intended direction.

10. The method of claim 9, wherein in the additional shaft development interval, the depth of each blasthole is between 10-80 m.

11. The method of claim 9, wherein in the additional shaft development interval, the depth of each blasthole is greater than 80 m.

12. The method of claim 9, wherein in the additional shaft development interval, the wireless blasting devices in each blasting deck are programmed with a unique group identifier corresponding to the blasting deck.