Patent Grant
9243879
The invention relates to the field of mining, including the blasting and fragmentation of rock. More specifically, the invention relates to the blasting of rock at a location underground.
In mining operations, the efficient fragmentation and breaking of rock by means of explosive charges demands considerable skill and expertise. The explosive charges are placed in appropriate quantities at predetermined positions within the rock and are then actuated via detonators having predetermined time delays, thereby providing a desired pattern of blasting and rock fragmentation. Traditionally, signals are transmitted to the detonators from an associated blasting machine via non-electric systems employing low energy detonating cord (LEDC) or shock tube. Alternatively, electrical wires may be used to transmit firing signals to electrical detonators or more sophisticated signals to and from electronic detonators. For example, such signalling may include ARM, DISARM, and delay time instructions for remote programming of the detonator firing sequence. Moreover, as a security feature, detonators may store firing codes and respond to ARM and FIRE signals only upon receipt of matching firing codes from the blasting machine. Electronic detonators can be programmed with time delays with an accuracy down to lms or less.
The establishment of a wired blasting arrangement involves the correct positioning of explosive charges within boreholes in the rock, and the proper connection of wires between an associated blasting machine and the detonators. The process is often labour intensive and highly dependent upon the accuracy and conscientiousness of the blast operator. Importantly, the blast operator must ensure that the detonators are in proper signal transmission relationship with a blasting machine, in such a manner that the blasting machine at least can transmit command signals to control each detonator, and in turn actuate each explosive charge. Inadequate connections between components of the blasting arrangement can lead to loss of communication between blasting machines and detonators, and therefore increased safety concerns. Significant care is required to ensure that the wires run between the detonators and an associated blasting machine without disruption, snagging, damage or other interference that could prevent proper control and operation of the detonator via the attached blasting machine.
Wireless detonator systems offer the potential for circumventing these problems, thereby improving safety at the blast site. By avoiding the use of physical connections (e.g. electrical wires, shock tubes, LEDC, or optical cables) between detonators and other components at the blast site (e.g. blasting machines) the possibility of improper set-up of the blasting arrangement is reduced. Another advantage of wireless detonators relates to facilitation of automated establishment of the explosive charges and associated detonators at the blast site. This may include, for example, automated detonator loading in boreholes and automated association of a corresponding detonator with each explosive charge, for example involving robotic systems. This would provide dramatic improvements in blast site safety since blast operators would be able to set up the blasting array from entirely remote locations. However, such systems present formidable technological challenges, many of which remain unresolved. One obstacle to automation is the difficulty of robotic manipulation and handling of detonators at the blast site, particularly where the detonators are not wireless electronic detonators and require tieing-in or other forms of hook up to electrical wires, shock tubes or the like.
Underground mining presents distinct challenges compared to surface mining. For example, the fragmentation and extraction of a body of ore located underground requires careful planning and execution. Typically, the body of ore is accessed via tunnelling, or one or more drives, to expose a face of the ore on at least one side. Boreholes are then drilled into the face, and loaded with explosive charges. Actuation of the charges by means of associated detonators fragments a portion of the rock behind the free face, thereby to expose a new face to be drilled and loaded. Meanwhile, fragmented rock from the initial blast can be removed via the access tunnel for processing. Through repeated cycles of drilling, loading, blasting and extraction, the exposed face retreats into the ore body and fragmented ore is retrieved.
Extraction of the fragmented ore may be performed using driven vehicles or remotely controlled vehicles, but as noted above remotely controlled location of the detonators in the boreholes and their operative association with the explosive charges has yet to be developed.
Whilst simple in nature, underground blasting as described above presents significant technical and organizational challenges. For example, on the technical side, the void created must be structurally sound, and may require internal support to prevent ceiling collapse. To this end, columns or pillars of ore are frequently left in place to assist in providing ceiling support, particularly during the active phase of blasting and extraction of the remaining ore. Thus, portions of the valuable ore body are effectively “left behind” at the underground blast site, at least until the void has been structurally reinforced, reducing the efficiency of the ore extraction process.
The complexity of underground mining operations is further exacerbated by organizational challenges at the mine site. Teams of mine workers must be co-ordinated carefully in order to optimize both mining operations and access to the free face and fragmented rock. For example, different teams may be required to access the free face at different times to drill boreholes, load explosives, set up blasting equipment, extract fragmented rock etc. Each team will need a different set of equipment to effectively perform its designated task, and yet there may be insufficient space at the free face to accommodate more than one team, and associated equipment, at any given time.
Furthermore, fragmented material from one blast, or a void resulting from that blast, may prevent access to the ore body on a remote side of that blast, again meaning that portions of the valuable ore body are effectively “left behind”, at least until the fragmented material has been extracted or access has been otherwise facilitated. Moreover, team movement and co-ordination at the mine site is further complicated by safety concerns. Depending upon the integrity of the rock, or the safety rules at the mine site, it may be a requirement to completely evacuate the mine site of all mining personnel (and perhaps equipment) when blasting takes place. Alternatively, or in addition, it may be necessary to reinforce the remaining rock mass before personnel are allowed to access it for further drilling and blasting. Without such reinforcement, that remaining rock mass may also have to be “left behind”. All of these possibilities further constrain the scheduling of all other operations at the mine site for all working faces.
In addition, it may be difficult to access the retreating face of the ore body. Each blasting cycle requires the substantial removal of fragmented rock before the newly exposed ore face can be drilled and loaded for the next blasting cycle. If the rock fragmentation is inefficient or inappropriate in some way, it may be difficult to fully extract the ore via the access tunnel, and this in turn may delay the extraction process. On occasion, undesirable rock fragmentation or throw may result in the ore body being completely inaccessible from an existing access tunnel, such that a new tunnel must be formed to approach the ore body from a different angle. Clearly, this will delay the extraction process, and increase the costs significantly.
It follows that there is a continuing need in the art for improved blasting methods for underground mining. This need extends to blasting arrangements that employ either wired or wireless communication with detonators and associated components.
It is an object of the present invention to provide methods for improved blasting of rock at an underground location.
In selected exemplary embodiments there is provided a method of blasting rock at an underground blast site, the method comprising the steps of:
By this method, the efficiency and safety of blasting underground can be greatly enhanced. By pre-drilling all of a selected rock mass or body of ore, or a selected portion of the mass or body, and then charging all of the drilled boreholes as desired and placing the detonators in operative association with the explosive charges, all of the charges may be initiated by at least two distinct initiation events in a desired sequence without personnel having to access any portion of the mass or body between initiation events. This means that a stranded portion of the rock mass can be readily and safely blasted and the fragmented material recovered.
The method of the invention allows entirely new sequences of blasting to be achieved. In particular, it is no longer necessary to perform retreat mining—that is, blasting at the furthest point of the rock mass from an access point—or to drill and blast individual levels at a time. It is now possible to perform steps a), b) and c) to the full height of the rock mass, or selected portion of the rock mass, and, if desired, selectively blast different levels of the rock mass in respective initiation events. The rock mass or selected portion of the rock mass may be between two drives or tunnels, one above the other.
Generally, the boreholes will be drilled in the rock mass from a top drive or a bottom drive, which bottom drive may be the only drive, and in one embodiment the boreholes are drilled in step a) from along the entire length of the drive. Thus, the length of the drive defines the extent of the rock mass that is to be blasted in the at least two initiation events.
The method of the invention requires accurate initiation of the detonators, and in embodiments the detonators may be electric or electronic detonators. In a particular embodiment, the detonators are electronic. Such electronic detonators may be wired or wireless. However, there is a risk that wiring connecting, for example, a blasting mechanism to the detonators that are initiated in a subsequent one of the at least two initiation events may be damaged by the earlier initiation, and for this reason wireless detonators are likely to be selected.
In an embodiment, each detonator forms part of a wireless detonator assembly for receiving and responding to wireless command signals, the step of conducting a sequence of at least two initiation events comprising transmitting at least two wireless command signals from one or more associated blasting machines to selectively FIRE the wireless detonator assemblies.
In a particular embodiment, each wireless detonator assembly is a wireless electronic booster.
In some embodiments, the detonators associated with the subsequent one or more of the at least two initiation events enter a sleep mode prior to their actuation.
Since the charges of explosive material for the subsequent one or more initiation events must be in place during the earlier of the at least two initiation events, the explosive material must be relatively stable, for example ANFO or a bulk emulsion explosive. A suitable bulk emulsion explosive may be selected from the Fortis™ range from Orica Mining Services.
The effect of each initiation event is to fragment the blasted portion of the rock mass, which may then fall into a bottom drive. It may be necessary to extract all or some of that fragmented rock prior to a subsequent one of the at least two initiation events. This may be done remotely, or safely from a portion of the bottom drive that has been drilled and loaded, and that has had at least one detonator placed in operative association with each charge, but that is not unsupported ground so remains stable—that is, it is not a stranded portion of the rock mass.
Such a stranded portion of the rock mass may be a pillar of rock that is left in place after one of the at least two initiation events to support other portions of the rock mass.
In one particular embodiment, the rock mass comprises a body of ore above a bottom drive and the boreholes are drilled in an upwards direction from the bottom drive into the body, the method further comprising forming at least one rise in the ore extending in a generally upward direction from the bottom drive, optionally by actuating detonators and associated charges in at least one borehole, whereby in said one of the at least two initiation events material from the body of ore adjacent the rise is fragmented and falls into the rise and the bottom drive for extraction via the bottom drive, leaving a void, perhaps with unsupported ground, and whereby in a subsequent one or more of the at least two initiation events, remaining material of the body of ore is fragmented and falls at least partly into the void.
In this embodiment, in the subsequent one or more of the at least two initiation events portions of the body of ore adjacent the void and upper ends of the boreholes may be fragmented, and optionally extracted via the bottom drive, prior to the last of the body of ore between said portions and the bottom drive being fragmented.
In one version of this embodiment, said material of the body of ore fragmented in the one of the at least two initiation events is to one side of the rise, in the longitudinal direction of the bottom drive, and said material of the body of ore fragmented in a subsequent one or more initiation events is to the opposite side of the rise.
The portion of the body of ore fragmented in a subsequent one or more initiation events may be above the portion of the body of ore fragmented in the one of the at least two initiation events.
The initiation events may be repeated along the bottom drive. The bottom drive may have one or two blind ends.
In this one particular embodiment, there may be no drive above the bottom drive.
In another particular embodiment, the rock mass comprises a body of ore extending between a bottom drive and an upper drive, said bottom and upper drives each having a corresponding blind end, and the boreholes are drilled in a downwards direction from the upper drive into the body, the method further comprising forming at least one rise in the ore extending between the upper and bottom drives and remote from said blind end of the drives, optionally by actuating detonators and associated charges in at least one borehole, said one of the at least two initiation events being adjacent the rise and leaving a void, perhaps with unsupported ground, and a subsequent one or more of the initiation events being performed in one or more portions of the body of ore between the rise and the blind end of the drives to fragment the material of said one or more portions such that the fragmented material can be extracted via the bottom drive.
In yet another particular embodiment, the rock mass comprises a body of ore extending between a bottom drive and an upper drive adjacent a stope formed between the bottom and upper drives at a remote end thereof and the boreholes are drilled in the body of ore from one of the drives towards the other drive, the method further comprising forming at least one rise in the ore between the bottom and upper drives and remote from said stope to form a portion of the body of ore between the stope and the rise, said one of the at least two initiation events being in the body of ore adjacent said rise to leave a pillar formed from said portion of the body of ore and a subsequent one or more of the at least two initiation events being performed in the residual body of ore to the side of the location of the rise remote from the pillar, followed by extraction of fragmented material from the bottom drive, and a further subsequent one or more of the at least two initiation events being performed to fragment the material of the pillar.
In this embodiment, the stope may be at least partially filled with backfill material, which may be introduced from the upper drive to replace the fragmented and extracted material of the body of ore.
Each of said another particular embodiment and said yet another particular embodiment may be performed using features of said one particular embodiment.
The boreholes in these embodiments may be drilled in any known manner, for example at from 0 to 45° to vertical. In one embodiment, at least some of the boreholes are arranged in a ring of boreholes centred on the drive from which they are drilled for ring-firing of some of the detonators in accordance with pre-programmed delay times.
Embodiments of methods of blasting according to the invention, and a prior art method, will now be described, with reference to the accompanying drawings, in which:
a provides a schematic perspective view of body of ore, that may be blasted according to the invention;
b provides a schematic sectional view of the body of ore illustrated in
a-h illustrate sequential stages in the blasting and extraction of a body of ore located underground, in accordance with methods that are known in the art;
a-h illustrate sequential stages in the blasting and extraction of a body of ore located underground in accordance with an embodiment of the method of the invention;
Actuate or initiate: refers to the initiation, ignition, or triggering of explosive materials, typically by way of a primer, detonator or other device, such as a booster, capable of receiving an external signal and converting the signal to cause deflagration of the explosive material.
Array: refers to a group of discrete explosive charges, preferably emulsion explosive charges, each located in adjacent borehole in operable association with a detonator such that the charges are located generally within a layer or section of rock, whereby actuation of the charges causes blasting and fragmentation of the layer or section of rock. In selected embodiments, the group of charges forms an array that is substantially arranged about a plane generally perpendicular to a general direction of the axes of the boreholes. In further selected embodiments, the groups of charges that forms an array may be arranged in a manner other than planar. Numerous array configurations and arrangements are known in the art including but not limited to rings, fans, and cuts of various kinds.
Base charge: refers to any discrete portion of explosive material in the proximity of other components of a detonator and associated with those components in a manner that allows the explosive material to actuate upon receipt of appropriate signals from the other components. The base charge may be retained within the main casing of a detonator, or alternatively may be located nearby the main casing of a detonator. The base charge may be used to deliver output power to an external explosives charge to initiate the external explosives charge.
Blasting machine: refers to any device that is capable of being in signal communication with a detonator to actuate the detonator. In the case of electronic detonators, the signal communication may be, for example, to send ARM, DISARM, and FIRE signals to the detonators, and/or to program the detonators with delay times and/or firing codes. The blasting machine may also be capable of receiving information such as delay times or firing codes from the detonators directly, or this may be achieved via an intermediate device such as a logger to collect detonator information and transfer the information to the blasting machine.
Booster: refers to any device that can receive command signals from an associated blasting machine, and in response to appropriate signals such as a signal to FIRE, can cause actuation of a discrete explosive charge that forms an integral component of the booster. In this way, the actuation of the discrete explosive charge may induce actuation of an external quantity of explosive material, such as material charged down a borehole in rock. The booster may be wired or wireless. In selected embodiments, a booster may comprise the following non-limiting list of components: a detonator comprising a firing circuit and a base charge; an explosive charge in operative association with said detonator, such that actuation of said base charge via said firing circuit causes actuation of said explosive charge; a transceiver for receiving and processing at least one wireless command signal from a blasting machine, the transceiver being in signal communication with said firing circuit such that upon receipt of a command signal to FIRE said firing circuit causes actuation of said base charge and thereby actuation of said explosive charge.
Detonator: refers to any form of detonator, but in advantageous embodiments to an electronic or electric detonator, and many forms of detonators are known in the art. As a minimum, a detonator comprises a base charge to be initiated upon receipt of an appropriate signal, and means such as a firing circuit to convey an appropriate signal to actuate the base charge. Typically, many detonators will also comprise some form of shell to contain one or more components of the detonator. Traditionally, a shell is composed of a substantially tubular section of material (e.g. metal) to define a percussion actuation end of the detonator, at which the base charge resides, and an opposite end for connection to other components or signal transmission lines. In selected embodiments, ‘detonator’ relates to those detonators that include programmable initiation means, for example that include means to store unique detonator identification information, and/or detonator firing codes. The detonator may be wired or wireless. Electronic detonators are known in the art and may include memory means to store data such as delays times, firing codes, or security information, and/or be connected to top-boxes or other components of a wireless initiation device.
Distal: refers to an end of a borehole opposite a proximal end (wherein a proximal end is at, adjacent, or near a free face of rock from which the borehole was drilled into the rock, or from which fragmented rock was removed following blasting of rock at a free face). Such a free face may form part of a drive. The distal end may be a closed end of the borehole some distance away from a free face of rock, for example produced by the penetration into the rock of a drilling device such as a drill bit. In alternative embodiments, the distal end of a borehole may also be an open end if the distal end extends into another drive in the rock remote from the free face.
Drive: refers to a horizontal or generally horizontal cut or void extending underground through, above or below a body of ore. Typically, a drive is formed by fragmentation and extraction of rock, for example by tunnelling. The drive may provide access for mine operators and their equipment to drill boreholes extending into the body or ore in any direction for loading with explosive materials, blasting and fragmentation of the body of ore, for extraction via the drive and drive access. Any underground mine site may include one, a few, or many drives for example at different levels relative to the surface of the ground, or the body of ore. A drive is sometimes referred to herein as a tunnel.
Explosive charge/charge: generally refers to a specific portion of an explosive material in or for placing into a borehole. An explosive charge is typically of a form and sufficient size to receive energy derived from the actuation of a base charge or a detonator, or alternatively energy from explosive material forming part of a booster. The ignition of the explosive charge should be sufficient to cause blasting and fragmentation of the rock. The chemical constitution of the explosive charge may take any form that is known in the art. In some embodiments the explosive charge is of a bulk emulsion explosive that has good stability such as those provided under the Fortis™ brand by Orica Mining Services.
Layer: refers to any layer of rock, in any orientation relative to horizontal, that contains an array of explosive charges associated in use with detonators. The layer may include an array that is arranged in a substantially planar manner in the layer, or an array that is less organized in terms of its geometry. In this way, the detonators associated with the explosive charges may be controlled and actuated within the layer as a group, thereby to selectively fragment the layer as desired in accordance with a designed blast.
Proximal: refers to an end of a borehole at, adjacent, or near a free face of rock from which the borehole was drilled into the rock, or, in some embodiments, from which fragmented rock was removed following blasting of rock at a free face.
Rock: includes all types of rock, including valuable ore. Such valuable ore includes shale. Stranded portion of the rock mass: refers to any portion of the rock mass or ore that is “left behind”, or which will be “left behind”, at an underground location during a blasting process because it is physically inaccessible as a result of the one and/or an earlier one of the at least two initiation events and/or because it is unsupported ground that is potentially dangerous for personnel to access (so that personnel access may be prohibited under relevant regulation(s)) and/or because it may be required to remain at the blast site to maintain the structural integrity of the blast site, including any void created by extraction of rock ore at the blast site. The stranded portion of the rock mass comprises ore that has value and that in accordance with the invention is blasted in a subsequent one or more of the at least two initiation events without personnel accessing the stranded portion.
Wireless: refers to there being no physical wires (such as electrical wires, shock tubes, LEDC, or optical cables) connecting the detonator of the invention or components thereof to an associated blasting machine or power source. The wireless energy may take any form appropriate for wireless communication and/or wireless charging of the detonators. For example, such forms of energy may include, but are not limited to, electromagnetic energy including light, infrared, radio waves (including ULF), and microwaves, or alternatively make take some other form such as electromagnetic induction or acoustic energy.
Wireless detonator assembly: in general the expression “wireless detonator assembly” encompasses a detonator, most preferably an electronic detonator (typically comprising at least a detonator shell and a base charge) as well as means to cause actuation of the base charge upon receipt by said wireless detonator assembly of a signal to FIRE from at least one associated blasting machine. For example, such means to cause actuation may include signal receiving means, signal processing means, and a firing circuit to be activated in the event of a receipt of a FIRE signal. Preferred components of the wireless detonator assembly may further include means to transmit information regarding the assembly to other assemblies or to a blasting machine, or means to relay wireless signals to other components of the blasting apparatus. Other preferred components of a wireless detonator assembly will become apparent from the specification as a whole. The expression “wireless detonator assembly” may in very specific embodiments pertain simply to a wireless signal relay device, without any association to a detonator unit. In such embodiments, such relay devices may form wireless trunk lines for simply relaying wireless signals to and from blasting machines, whereas other wireless detonator assemblies in communication with the relay devices may comprise all the usual features of a wireless detonator assembly, including a detonator for actuation thereof, in effect forming wireless branch lines in the wireless network. A wireless detonator assembly may further include a top-box as defined herein, for retaining specific components of the assembly away from an underground portion of the assembly during operation, and for location in a position better suited for receipt of wireless signals derived for example from a blasting machine or relayed by another wireless detonator assembly.
Wireless electronic booster: refers to any device that can receive wireless command signals from an associated blasting machine, and in response to appropriate signals such as a wireless signal to FIRE, can cause actuation of an explosive charge that forms an integral component of the booster. In this way, the actuation of the explosive charge may induce actuation of an external quantity of explosive material, such as material charged down a borehole in rock. In selected embodiments, a booster may comprise the following non-limiting list of components: a detonator comprising a firing circuit and a base charge; an explosive charge in operative association with said detonator, such that actuation of said base charge via said firing circuit causes actuation of said explosive charge; a receiver or transceiver for receiving and processing said at least one wireless command signal from said blasting machine, said receiver or transceiver in signal communication with said firing circuit such that upon receipt of a command signal to FIRE said firing circuit causes actuation of said base charge and actuation of said explosive charge. Preferably the detonator is an electronic detonator comprising means to cause actuation of the base charge upon receipt by said booster of a signal to FIRE from at least one associated blasting machine. For example, such means to cause actuation may include a transceiver or signal receiving means, signal processing means, and a firing circuit to be activated in the event of a receipt of a FIRE signal. Preferred components of the wireless booster may further include means to transmit information regarding the assembly to other assemblies or to a blasting machine, or means to relay wireless signals to other components of the blasting apparatus. Such means to transmit or relay may form part of the function of the transceiver.
Underground mining operations, including the blasting and extraction of ore bodies located underground, require considerable technical skill and expertise. Compared to surface mining, underground mining requires detailed planning. First, blasting must be conducted in a sequence and manner for optimal access to the ore body both prior to blasting (to set up the explosive charges and detonators), and during and after blasting (to extract the fragmented rock). For example, poor planning of an underground blasting event may lead to unwanted rock fragmentation and movement, such that access tunnels for extraction of the ore become blocked or unusable.
Other complications of underground blasting include the structural integrity of the rock surrounding the body of ore to be fragmented and extracted. During blasting an underground void is created, and techniques are known in the art to help improve the structural integrity of the “walls” and “ceiling” of the void. These include refilling the void, or portions thereof, for example with materials such as previously fragmented waste rock, concrete or cement. Other techniques include “leaving behind” columns or other masses of the ore to be extracted, to help support the roof of the void. Whilst useful, these techniques inevitably reduce the efficiency of the blasting and extraction process, either due to increased costs or the need to leave behind valuable ore at the blast site.
Still further complications of underground mining involve limited access to a free face for blasting and extraction of rock, and the challenges of logistics and co-ordination to bring multiple teams of mine workers (and their equipment) to the free face at appropriate times. Each team is required to perform a specific task at the free face (e.g. drilling or loading boreholes, setting up the blasting apparatus, removal of fragmented rock etc.) Careful management of the teams, and their movement underground, is required to maximize the efficiency of the mining operations. The costs associated with the operation of each team may be significant, and time wasted by any team at the mine site, for example due to poor management and co-ordination of the teams' activities and movement, may result in significant costs and poor efficiency of the mining operation.
Thus the present invention, at least in preferred embodiments, aims to increase the efficiency of mining operations by providing improved methods for the blasting of a body of ore or rock located underground. In selected embodiments, the invention even permits the formation of more than one free-face, such that sequential blasting, rock fragmentation, and removal of a body of ore can occur from more than one direction. In other words, selected methods of the invention permit a body of ore to be fragmented and extracted from more than one ‘side’, thus alleviating the limitations of extraction via a single free face.
In selected embodiments, the invention disclosed herein extend previous advancements in the art relating to the selective control of detonators or detonator assemblies in groups. For example, WO2010/085837 and its corresponding United States patent application US2010/0212527 published 26 Aug. 2010, which is incorporated herein by reference, discloses examples of methods that are suited to selective control of detonators in groups. The present invention is not limited to the methods of US 2010//0212527 for selective control of detonators at the blast site, and other examples of such selective control methods and apparatuses that are known in the art, or which have yet to be developed in the art, may be applicable to the methods disclosed herein.
Certain exemplary embodiments provide methods for blasting rock at an underground blast site, the methods comprising the steps of: (a) drilling boreholes into the rock, the boreholes having sufficient depth to permit loading of more than one discrete charge of explosive material; (b) loading each borehole with said more than one charge, such that the charges in adjacent boreholes form layers of discrete charges; (c) placing detonators in operative association with the charges of each layer; and (d) selectively actuating the detonators and associated charges of the layers, thereby to fragment some or all of the rock in each layer according to a desired blasting sequence for the layers.
Such embodiments are illustrated by way of example only with reference to
Regardless, in a manner typical for blasting operations, the boreholes 11a, 11b, 11c extend into the rock in an upwardly direction from the exposed face 12 of the body 10. The boreholes 11a, 11b, 11c have sufficient depth for the loading therein of more than one explosive charge and may open into another drive or other void at their distal ends or may be blind. For the sake of illustration, three explosive charges are shown to be loaded in each borehole, with explosive charges 13a, 13b, 13c being loaded in borehole 11a, explosive charges 14a, 14b, 14c being loaded in borehole 11b, and explosive charges 15a, 15b, 15c being loaded in borehole 11c. Explosive charges 13a, 14a, and 15a each located in adjacent boreholes may be considered to lie within a first layer 16 within the body 10, wherein layer 16 consists of a portion of rock directly adjacent face 12. Likewise, explosive charges 13b, 14b, and 15b lie within layer 17 of body 10 adjacent to layer 16. Finally, explosive charges 13c, 14c, and 15c lie within layer 18 of body 10 adjacent to layer 17. Further boreholes, explosive charges and layers may also be present although these are not shown in
A respective detonator (not shown) is placed in operative association with each explosive charge such that actuation of each detonator causes actuation of its associated explosive charge. The detonators may be controlled via wired or wireless communications with an associated blasting machine, such that they are selectively actuated. They may be selectively actuated in groups, with each group corresponding to detonators and explosive charges located within each layer 16, 17, 18 in body 10. In this way, each layer may be selectively fragmented in accordance with a desired sequence for the layers. For example, the blast operator may desire to actuate first those detonators and associated explosive charges 13c, 14c, and 15c located in layer 18 of body 10, at the distal ends of the boreholes 11a, 11b, 11c relative to face 12, with subsequent actuation of the explosive charges in the other layers 16 and 17. The fragmented material may fall into a rise or other void (not shown) adjacent the illustrated body 10 and into the drive beneath exposed face 12 for extraction. The blast in layer 18 may result in a stranded portion of the rock mass, for example in the layers 16 and 17 and/or above the location of layer 18. However, the layers 16 and 17 may still be blasted safely in a subsequent one or more initiation events because the boreholes have already been formal and loaded with explosive charges 13a, 14a, 15a and 13b, 14b, 15b and had detonators placed in operative association with the charges. Thus, personnel access is not necessary.
In variations, given by way of example only, the layer 16 may be blasted first, leaving layers 17 and 18 as stranded portions of the rock mass but that may be blasted safely because they have already been prepared for blasting, or charges 14a-c may be initiated first to form a rise, followed by charges 13c, 15c to leave stranded portions that can still be blasted safely. Alternatively, all of the explosive charges in boreholes 11a and 11c may be initiated in one or more discrete initiation events, to leave a pillar or column of rock with charged borehole 11b through it. The pillar or column of rock may be fragmented at a later time by initiation the explosive charges 14a, b, c in a subsequent discrete user-controlled initiation event without personnel access.
In accordance with the methods disclosed, it is no longer necessary to drill (boreholes), load the boreholes with explosive charges and associated detonators, blast and extract portions of rock in a progressive manner commencing with the portion of rock nearest the exposed face. Instead, all of the drilled boreholes are loaded with explosive charges and associated detonators and the charges, or groups or arrays of them, are initiated sequentially in discrete user-controlled initiation events. The blast operator can now choose which portions of rock are fragmented first, regardless of their position relative to the exposed face, in accordance with a desired blast plan.
As discussed, the detonators associated with the explosive charges may be electronic and controlled by one or more associated blasting machines issuing command signals for the sequential initiation events. The command signals may take any form, including signals transmitted over a wired network or harness, or alternatively they may be wireless command signals communicated via any wireless means, including electromagnetic signals such as radio signals. The use of wireless command signals, including the transmission of wireless command signals through the ground, has been proposed in, for example, international patent publications WO2006/047823, WO2006/076777, WO2006/096920, and WO2007/124539, all of which are incorporated herein by reference.
The detonators associated with the explosive charges that are initiated in a later or subsequent one or more discrete user-controlled initiation events may be caused to enter a “sleep” mode prior to their initiation. The sleeping detonators (i.e. those that have entered a sleep mode) may remain in an inactive state for an extended period of time, prior to their subsequent actuation. In this way, the selected explosive charges and their associated detonators may be forced to enter a sleep period wherein the sleeping detonators are unable to actuate absent a special command signal.
Fragmented ore derived from blasting in the at least one initiation event may be extracted by automated (e.g. robotic) means, especially where the structural integrity and safety of the unsupported void is questionable.
The inventors have identified significant advantages to the combined use of relatively stable explosives (such as bulk emulsion explosive materials or other explosive materials such as slurry explosives; ANFO; dynamites; black powder; propellants) with electronic detonators to extract stranded portions of the rock mass in a subsequent one or more of the at least two blast initiation events. For example, both emulsion explosives and electronic detonators, at least in selected embodiments, may be resistant to degradation by contact with water. Emulsion explosive materials may withstand extended periods in a borehole prior to actuation. Electronic detonators may comprise at least substantially sealed casings and/or be integrated into detonators assemblies that include a housing to at least substantially prevent egress of water and dirt. For example, electronic boosters are known in the art, which include a housing for containing a portion of explosive booster material, and a detonator in operable association with the explosive booster material. International patent publication WO2006/096920, which is incorporated herein by reference, discloses a wireless electronic booster that is substantially sealed, that is robust for underground placement and which is capable of receiving wireless command signals, for example LF radio signals through rock.
Thus, to summarise steps (a) to (c) occur in all of the rock mass to be blasted in the at least two initiation events, prior to conducting the at least two initiation events in step (d). Therefore, the invention includes embodiments in which the drilling and loading of the boreholes within what will become the stranded portion of the rock mass, or the “stranded ore”, with emulsion explosives and electronic detonators occurs before the fragmentation and extraction of ore surrounding the stranded ore in the one initiation event. In this way, an entire volume of underground ore may be drilled and loaded ready for blasting, but only selected portions of the volume may be fragmented and extracted by way of an initial initiation event, leaving behind selected portions of unfragmented ore for example to help maintain the structural integrity of the underground void or that are otherwise stranded ore. However, since the selected portions of the underground ore have already been drilled and loaded with a combination of emulsion explosive material and electronic detonators, the detonators may be required to enter a “sleep mode” and remain inactive, possibly for an extended period, until the subsequent one or more of the at least two initiation events. Once the period has elapsed, a mine operator may then choose to fragment and extract the selected portions of unfragmented ore that were left behind after the initial blasting cycle. For example, a wireless command signal to FIRE may be transmitted from a blasting machine located at or above a surface of the ground, through the ground to the wireless electronic detonators located within the selected portions of unfragmented rock in association with emulsion explosives. In this scenario, the pre-loading of pillars or other support structures, or other stranded ore, with a combination of emulsion explosives and wireless electronic detonators permits the pillars and support structures to be “dropped” at a later date from a location above the ground, without need for personnel or equipment to be present in the underground blast site. If the underground blast site remains safe, in spite of the fragmentation of the pillars or other support structures, or other stranded ore, then the fragmented ore derived from blasting the stranded ore may then be extracted either by conventional or automated means.
In selected embodiments, in step (a) of the method each borehole is drilled to a depth sufficient to be loaded in step (b) with more than one discrete charge such that the charges in adjacent boreholes form layers of discrete charges, and in step (d) the detonators and associated charges of each layer are selectively actuated, thereby to fragment the rock about each layer in the pillar or mass of rock according to a desired blasting sequence for the layers. For example, each layer of charges may comprise a substantially planar array of discrete charges located in adjacent boreholes, each substantially planar array being arranged about a plane generally perpendicular to the axis of the boreholes. Each planar array may be oriented at any angle relative to horizontal. For example, each substantially planar array may be arranged about a plane that is at least substantially horizontal or vertical, or a plane that intersects a horizontal plane at an angle of from 0 to 90 degrees. In selected embodiments, at least some of the layers are blasted in a sequence commencing with a layer at the distil ends of the boreholes, with subsequent blasting of layers retreating towards the proximal ends of the boreholes. In this way, a void may be created in the rock at a location remote from the rock face, thereby to generate a support pillar or other support structure between the face and a new face created by blasting layers in a retreating sequence towards the proximal ends of the boreholes.
Still further embodiments include methods for extracting a body of ore extending above a drive formed across a lower portion of the body. Such methods are encompassed by and expand upon previously described embodiments of the invention, to permit extraction of a large volume of ore from a single drive, with reduced need for multiple drives, as will be evident from the following description and accompanying figures. In selected embodiments such methods further comprise forming at least one rise in the ore extending in a generally upward direction from the bottom drive whereby in said one of the at least two initiation events material from the body of ore adjacent the rise is fragmented and falls into the rise and the bottom drive for extraction via the bottom drive, leaving a void, and whereby in a subsequent one or more of the at least two initiation events, material of the body of ore is fragmented and falls at least partly into the void.
Whilst this method, at least upon initial consideration, appears to be fairly simple in nature, the provision of a single drive to extract the entire body of ore is enabled with only one cycle of drilling and loading the boreholes, and placing the detonators, by virtue of selective actuation of detonators. Further advantages of such methods, as well as additional steps, will become apparent from the following description of
a to 2h illustrate techniques that are known in the art for blasting and extraction of the body of ore shown generally at 30, which is located underground and at least substantially surrounded by other underground rock or material 31.
In
Subsequently, as shown in
In accordance with the prior art embodiments illustrated in
In contrast, the methods of the present invention permit loading of charges in all boreholes in a single cycle, with the option of multiple charges into each borehole, with selective control of the charges and associated detonators in at least two user-controlled initiation events.
a to 3h show a progressive sequence of events for an exemplary embodiment of a method of blasting or extracting rock from an underground location, in accordance with the teachings herein. For each figure, a cross-section A-A′ is provided to aid understanding and orientation of the rock to be extracted. As for
With specific reference to
In
In
In
In
The selective blasting of the upper layers of column 59 and then of the remaining rock in the body of ore 30 is shown in
Therefore, by comparing the sequence of events across
Turning now to
Drawbell mining is a standard part of block cave mining and other large scale underground mining methods. Typically, the drawbell, the body of ore 100, is blasted in two stages because the available void, the drive 102 and a rise 104 formed in the body of ore, is not sufficiently large to fire the drawbell in one blast without risk of “freezing” the fragmented ore.
Typically, the drawbell 100 is predrilled with boreholes (not shown for the sake of clarity) that extend in a series of fans or rings regularly spaced along the body (in the direction of the drive 102) from the bottom drive 102 to the top 106 of the body, or adjacent to the top. Thus, the outermost boreholes in each fan would extend substantially parallel to the inclined lateral faces 108 and 110 of the drawbell, while the intermediate boreholes will extend at gradually reducing angles to a central, approximately vertical one.
The rise 104 is formed adjacent the lateral face 110 by loading one or more of the boreholes at that location with explosive charges and associated detonators, and initiating those charges. The fragmented material will fall through the resultant void into the bottom drive 102 for remotely controlled extraction or otherwise. At this stage, the drive 102 beneath the drawbell 100 is still safe for personnel access because they may pass through the drive 102 without being beneath the void created by the rise 104. Extracted material may be removed from the bottom drive 102 by way of an access drive (not shown) at the left hand end of the drive 102 (in the Figure).
Traditionally, boreholes in the body of ore 100 to the side of the rise 104 remote from the access drive would then be loaded with explosive charges and associated detonators and fired to fragment the whole body of ore, or a selected portion of it, to that side of the rise 104. The fragmented material expands into the rise 104 and falls into the bottom drive 102. This is shown in
Access to the remaining portion 116 of the body of ore closer to the access drive is prevented by the fragmented rock 118 in the bottom drive 102, and this must be removed remotely or otherwise prior to blasting of the portion 116.
Prior to the portion 116 being blasted, in the traditional procedure, the boreholes in it must be loaded with explosive charges and associated detonators. It will be appreciated that any reference herein to associated detonators includes locating them in or adjacent the explosive charges in the boreholes, wiring them in if they are not wireless, and ensuring they are in operative communication with an associated blasting machine.
A problem with clearing the fragmented rock in the bottom drive 102 beneath the ore portion 116 and loading the boreholes and associated detonators in the portion 116 is that the portion 116 is likely to have been damaged by the blast to create the fragmented material 112, leaving the portion 116 potentially as unsupported ground and therefore stranded ore even after the material 118 has been removed. This can make accessing the portion 116 to load the explosive charges and associated detonators risky and/or contrary to regulations. To overcome this, the portion 116 would have to be structurally supported and/or reinforced.
This difficulty is alleviated in accordance with the embodiment of the invention by loading the portion 116 with explosive charges and associated detonators initially, that is at the same time as the first portion of the body 100 to be blasted. As with the detonators in the first portion, the detonators in the portion 116 may be wired or wireless, but are advantageously wireless so as to alleviate risk of damage to their connection to the blasting machine(s) during the blasting of the first portion to create the fragmented material 112.
The bulk emulsion explosive in the explosives charges in the portion 116 should also be stable against desensitising as a result of the blast in the first portion, preferably requiring stable bulk emulsion explosives such as of the type previously mentioned. The emulsion explosives should also be sufficiently stable to not desensitise in the time period between the first stage blast and blasting the second portion 116. The delay may be merely for the time it takes to clear the fragmented material 118 in the bottom drive 102, including all or most of the fragmented material 112 as it continues to fall into the bottom drive 102 as new void is created in the bottom drive by the removal of the material 118.
Alternatively, the blasting of the portion 116 may be delayed longer for any technical, safety or commercial reason. During this time, no personnel access should be required beneath the portion 116. Likewise, the extraction of the fragmented material 118 should be performed remotely. It will be appreciated from the above that the blasting of the portion 116 is a separate and sequential user-controlled initiation event to the blasting of the first portion resulting in the fragmented material 112. All of the individual explosive charges in each of these portions may be initiated together, that is at the same time or in a staged manner, or groups of them may be initiated as discrete events.
The fragmented material from the portion 116 will fall into the void left by the fragmented material 112 from the first portion and into the bottom drive 102, and may be extracted remotely from the bottom drive 102 and the access drive.
Turning now to
The difference in
The desired outcome of the first of the sequential, discrete user-controlled initiation events is shown in
The upper, second portion 128 of the body of ore is stranded ore, in the sense that it may have been damaged during the blasting of the lower, first portion, it is unsupported ground, and access to it is blocked by the material 122 and 124. Some or all of that material may be removed by remote extraction prior to blasting the second portion 128, but this may not be necessary at all since that material when blasted can fall into the void 126. If the fragmented material 122 and 124 from the first portion is removed first, the fragmented second portion 128 can fall directly into the bottom drive 102, at least in part for recovery by remote extraction. As in the embodiment of
This method could apply to multiple stoping methods, whereby vertical retreat through multiple discrete initiation events can take place without human access. It would also be possible to develop “blind”, up hole long hole rises using the same methodology.
Referring firstly to
In current practice, the blasting of the ore body 150 may be as described with reference to
Prior to each initiation event, the fragmented material from any previous initiation event is extracted via the bottom drive 156 and access drive 158 and the resultant void alongside the remaining ore body is filled with backfill, for example and for present purposes only, as illustrated in
The embodiment in accordance with the invention is illustrated in
Referring to
As noted above, in addition to the boreholes in the pillar material 170, the boreholes blasted in this phase may be the only ones loaded with explosives material and associated detonators. Alternatively, the boreholes in the residual portion 174 of the ore body may also have been loaded with explosive charges and associated detonators to await one or more separate initiation events.
In
In
After removal of the fragmented material 176, the residual ore body 174 could be blasted in a traditional retreat sequence, following loading with explosive charges and associated detonators if that has not already occurred. However, as shown in
Whilst the present invention has been described with reference to specific embodiments and specific methods for blasting, it will be appreciated that such embodiments and methods are merely exemplary, and other embodiments and methods other than those described herein, will be encompassed by the invention as defined by the appended claims. In particular, features of any one embodiment described above may be applied mutatis mutandis to any other embodiment, and this description should be read accordingly.
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 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.
This application is the National Phase of PCT/AU2010/001273 filed on Sep. 29, 2010, which claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application No. 61/246,653 filed on Sep. 29, 2009, all of which are hereby expressly incorporated by reference into the present application.
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