An anchor for a rock bolt and a rock bolt

Abstract

An anchor (60) for a rock bolt, the anchor (60) being expandable between a hole insertion condition and a hole anchor condition. The anchor (60) comprising a leading end and a trailing end, and a connector (64) for connecting to a tendon (14). At least one gripper (70) is expandable outwardly from the insertion condition of the anchor (60) to the anchor condition for gripping the facing surface of a hole in which the anchor (60) is installed. The gripper (70) is biased by a coil spring (74) towards the leading end of the anchor (60) to expand the gripper (70) outwardly. A protection shroud (80) circumferentially surrounds an outside portion of the coil spring (74) to protect a portion of the coil spring (74) against ingress of grout within the hole.

Description

Technical Field of the Invention

[0001] The present invention relates to a rock bolt for use in rock strata to support the rock strata against collapse or failure, and to an anchor for use in such a rock bolt.Background of the Invention

[0002] The discussion of the background to the invention that follows is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any aspect of the discussion was part of the common general knowledge as at the priority date of the application.

[0003] Rock bolts are used for reinforcing rock strata by inserting the bolt into a hole drilled into the rock strata and fixing the bolt within the hole. Bolts can be fixed within a hole by anchors that frictionally engage with the wall of the hole or they can be embedded within the hole with grout or resin, or both. The anchor of the present invention has been developed for use in reinforcement in which grout or resin is used, although the anchor of the present invention can still be used in reinforcement in which grout or resin is not used.

[0004] The trailing end of a rock bolt will usually extend out of the open end of the hole and a rock plate can be attached to the trailing end and can be tightened to press firmly against the rock face that surrounds the hole opening. The fixing of the bolt within the hole resists egress of the bolt from the hole and the rock plate supports the rock face against fracture and displacement. Safety mesh can be installed broadly across the rock face by anchoring the mesh to multiple rock bolts. In this manner, the rock bolts support the rock strata against fracture and collapse and the safety mesh can restrain any dislodged pieces of the rock strata. The use of bolts and mesh is widespread in the underground mining industry to protect workers and equipment in underground mines and tunnels from strata fracture.

[0005] Rock bolts can employ a rigid or flexible tendon that extends between leading and trailing ends of the rock bolt. A rigid tendon can comprise a bar or rod, or a tube, such as a longitudinally split tube. Other rock bolts employ a flexible tendon, which is usually a cable.

[0006] Rock bolts can employ an anchor at a leading end and a rock plate at the opposite and trailing end. The anchor is used to frictionally engage against facing surfaces of the hole. The anchor can be activatable once the rock bolt is properly positioned within the drilled hole.

[0007] Rock bolts that employ a rod, bar or tube are rigid and typically have a length of between 1.8m to 3m. In underground tunnelling, the length of the rigid rock bolt is generally limited by the room available within the tunnel. In underground mining, the available room often precludes the use of rigid rock bolts that have a length greater than 3m. In underground tunnelling in general, the available room often precludes the use of rigid rock bolts that have a length greater than 6m.

[0008] Rock bolts that employ a cable are usually used where the depth of the hole into which the rock bolt is installed exceeds the maximum length of rock bolts that employ a rod, bar or tube. For example, rock bolts that employ a cable can be used in holes having a depth of 10m or more. For these forms of rock bolts the cable can be unrolled from a cable reel, so that any length of cable can be used.

[0009] Rock bolts that employ a cable are not rigid and therefore they must be pushed into the hole without significant frictional resistance. In some installations, the hole is empty, while in other installations, cement grout is pumped into the hole before the rock bolt is inserted and once the hole is sufficiently filled with grout, the cable bolt is fed from a reel into the hole, pushing through the grout. Once sufficient cable has been fed into the hole, the trailing end of the cable is severed, usually leaving about 0.3m extending from the opening of the hole.

[0010] Cable rock bolts can include an anchor at the leading end. Where the hole is filled with grout, the anchor can be pushed through the cement grout to the inner end of the hole or to the appropriate position within the hole. Where an anchor is employed, the anchor is provided to engage against the facing internal surface of the hole and to grip the internal surface so as to anchor the leading end of the rock bolt within the hole. The anchors are normally expandable anchors that have an insertion condition and a hole anchor condition, whereby the anchor travels into the hole in the insertion condition and once the anchor is positioned at the correct depth within the hole, the anchor is activated by expansion to the anchor condition, to grip the facing internal surfaces of the hole. The diameter of the anchor in the insertion condition is typically at least slightly less than the diameter of the hole, so that the anchor can travel into the hole without significant frictional resistance. Once the anchor has reached the installation position, expansion of the anchor to a greater diameter allows the anchor to engage and grip facing internal surfaces of the hole to anchor the leading end of the cable and the rock bolt.

[0011] Activation of the anchor to the anchor condition provides an immediate connection of the bolt within the hole, so that 1) the rock bolt can be loaded immediately by application of a rock plate at the trailing end of the rock bolt against the rock strata surrounding the opening of the hole and 2) the cable is secured from falling out of the hole as soon as the anchor is activated. The rock bolt thus immediately provides strata support and secures the cable within the hole, allowing immediate re-entry of mining personnel and equipment into the area of the tunnel being bolted. If the anchor is omitted and the cable is secured in place by cement grout, the cable bolt is not operational and the cable is not secured within the hole, until the cement grout has cured. Fear of the cable falling out of the hole commonly stops miners travelling through that part of the excavation (tunnel) until the grout sets (approximately 12 hours). The present invention relates to rock bolts that include an anchor at the leading end.

[0012] One form of prior art rock bolt comprises an anchor that includes grippers that are mounted for relative movement on a tapered mandrel so that during insertion of the anchor into a hole, the grippers can assume a reduced diameter on the mandrel (the insertion condition) and once the anchor has reached the activation position within the hole, the anchor can be activated to shift the mandrel relative to the grippers to an expanded and increased diameter (the anchor condition). The anchor is activated by pulling on the tendon that is connected to the mandrel, to pull the mandrel rearwardly relative to the grippers and to force the grippers into firm engagement with the wall of the hole.

[0013] In the above described form of prior art rock bolt, the grippers are biased towards the leading end of the anchor by a coil spring. The grippers can shift rearwardly on the mandrel against the bias as the anchor is pushed into the hole. This rearward shifting is beneficial, because a hole is usually drilled to be a close fit about the anchor and so the grippers will tend to scrape against the facing surface of the hole as the anchor is inserted. If the scraping load applied to the grippers is sufficient, progress of the anchor into the hole will be impeded or prevented. Accordingly, by facilitating shifting of the grippers to a smaller diameter against the bias of the coil spring, the scraping load can be reduced and the anchor can progress. The grippers are biased towards a larger diameter on the tapered mandrel so that when the anchor has reached its activation position within the hole, the grippers will be biased towards the leading end of the anchor and into initial engagement with the facing surface of the hole. The anchor is then ready for activation, whereby the grippers will be pressed into firmer engagement with the facing surface of the hole. The initial engagement of the grippers with the facing surface of the hole prevents the anchor from being pulled backwards in a direction out of the hole when the tendon is pulled to activate the anchor. This initial engagement gives the anchor sufficient purchase against the facing surface of the hole for the anchor to retain its position in the hole prior to the tendon being pulled to fully activate the anchor.

[0014] A potential difficulty with the anchor of the above described form of prior art rock bolt, is that the coil spring is exposed to grout within the hole as the anchor pushes through or into the hole and because the grout is flowable, it can enter into spaces between the coils of the spring, sometimes clogging the spring and affecting compression and expansion of the spring. This difficulty is reduced if the grout is more flowable, however installation preference is for thicker grout for several reasons, including the potential for quicker setting, reduced likelihood of the grout flowing out of the hole under gravity and higher compressive strength and greater durability once the grout sets. If the operation of the spring is reduced sufficiently, the grippers will not be able to shift relative to the mandrel sufficiently to assume a reduced diameter on the mandrel during insertion of the anchor into the hole, and / or the grippers will not be able to shift relative to the mandrel sufficiently to assume an increased diameter for initial engagement of the hole wall, prior to activation of the anchor.

[0015] The present invention has been developed to overcome or at least alleviate the above drawback of the prior art.Summary of the Invention

[0016] In one form of the invention, an anchor for a rock bolt is provided, in which the anchor is expandable between a hole insertion condition and a hole anchor condition. The anchor comprises a leading end and a trailing end, and a connector for connecting to a tendon. The anchor further comprises at least one gripper that is expandable outwardly from the insertion condition of the anchor to the anchor condition of the anchor for gripping the facing surface of a hole in which the anchor is installed. The at least one gripper is biased by a coil spring towards the leading end of the anchor. A protection shroud circumferentially surrounds an outside portion of the coil spring to protect a portion of the coil spring against ingress of grout.

[0017] An anchor according to the present invention provides protection for at least a section of the coil spring against grout entering or accessing that section of the coil spring. This means that the section of the coil spring about which the protection shroud extends should continue to operate to contract or expand even if other sections or the remaining section of the coil spring becomes inundated or invaded by the grout when it is wet and flowable, to reduce or prevent the inundated section from compressing or expanding. This allows the coil spring to continue to compress, albeit in a reduced section of the full length of the coil spring, when it is necessary for the grippers to assume a reduced diameter or contracted position and that advantageously allows the coil spring to continue to allow the anchor to progress into a hole and to push or urge the gripper into engagement with the facing internal surface of the hole once the anchor has reached its final destination within the hole.

[0018] The protection shroud can be positioned at any suitable position along the length of the coil spring. The protection shroud can be positioned at the leading end of the coil spring, at the trailing end, or intermediate the leading and trailing ends. Positioning the protection shroud at the leading end of the coil spring has advantages, in that the leading end of the coil spring can be substantially closed to ingress of grout and with the protection shroud at the leading end, as the anchor is pushed into a hole, the grout will tend to flow about the leading end and the protection shroud without any, or much ingress into the coils at the leading end. However, the protection shroud can be positioned elsewhere along the length of the coil spring with the protection shroud configured to resist entry of grout into that portion of the coil spring that the coil spring surrounds, or it may be acceptable for some ingress of grout into that portion of the coil spring that the coil spring surrounds, on the basis that the grout will not progress fully into the protection shroud and thus the protection shroud will still provide protection for a portion of the coil spring against ingress of grout. For example, the grout may clog at or just into the entrance into the protection shroud and thus may not progress into the protection shroud sufficient to prevent the coil spring from contracting or expanding within the protection shroud.

[0019] The protection shroud can be a close fit about the outside portion of the coil spring. Clearance between the inside surface of the protection shroud and the outer surface of the coils of the coil spring can be in the region of 0.5mm radially.

[0020] The leading and trailing ends of the coil spring correspond to the leading and trailing ends of the anchor and by this, it is meant that the leading end of the coil spring is closest to the leading end of the anchor and the trailing end of the coil spring is closest to the trailing end of the anchor. The anchor will usually have a longitudinal axis and the axis of the coil spring can be co-axial with the axis of the anchor.

[0021] The coil spring typically will be of constant diameter, ie cylindrical and the protection shroud can also be cylindrical and co-axial with the axis of the coil spring. The protection shroud can of course be of a different shape and may for example, be tapered outwardly towards the trailing end of the anchor, thereby tending to divert or push grout away from the coil spring as the anchor pushes through the grout.

[0022] The protection shroud can have any suitable lengthwise extent along the length of the coil spring. Where the protection shroud extends from the leading end of the coil spring towards the trailing end the protection shroud can extend for at least about 30% of the axial length of the coil spring. In alternative arrangements, the protection shroud can extend for at least about 50% of the axial length of the coil spring. The protection shroud could even extend the full length, or almost the full length of the coil spring.

[0023] The protection shroud can be mounted to the anchor relative to the coil spring in any suitable manner. In some arrangements, the protection shroud can be mounted to the coil spring, such as to the leading end of the coil spring. In some arrangements, the protection shroud can fit over the leading end of the coil spring to locate the protection shroud on the leading end of the coil spring. For example, the protection shroud can comprise one or more abutments against which the leading end of the coil spring abuts and which locate the protection shroud on the leading end. An abutment can comprise an inwardly extending annular flange that fits over the leading end of the coil spring, or one or multiple inwardly extending tabs could extend over the leading end of the coil spring.

[0024] In other arrangements, the protection shroud can comprise an annular channel, or the protection shroud can extend from an annular channel for the leading end of the coil spring to fit into for locating the protection shroud on the leading end.

[0025] An anchor according to the present invention comprises a coil spring. Coil springs having a spring constant in the order of 1.4n / mm and 1.9n / mm are considered appropriate. In the development of the present invention, coil springs having greater, or even much greater spring constants were trialled in order to overcome the resistance to compression and expansion when grout inundated or invaded the space between the coils of the coil spring. These coil springs having greater spring constants increased the cost of the anchor, as well as the weight and bulk of the anchor. Moreover, simply increasing the spring constant did not necessarily mean that the coil spring could overcome the resistance from grout inundation, unless a coil spring having a significantly large spring constant was adopted. However, such a coil spring would likely be unnecessary for many applications and therefore would add unnecessary cost, weight and bulk for most applications. The development of the protection shroud was therefore pursued and has been found to provide a solution to the problem of grout inundation, without the drawbacks associated with the use of coil springs having larger than often necessary spring constants.

[0026] The protection shroud can be formed of any suitable material. For example metal, such as steel metal plate could be used. However, the development to date has employed plastic as the material of the protection shroud. Plastic is cheap, easily formed, durable in a grout immersed environment and light weight. Example plastic material that is considered suitable for the protection shroud includes high-density polyethylene, reinforced nylon and unreinforced nylon.

[0027] The protection shroud can be a stand-alone component in that it can be a separate component to other parts of the anchor and assembled separately as part of the anchor. Alternatively, the protection shroud can be formed as part of another component of the anchor. The development to date has formed the protection shroud from plastic and integrally as part of another bracket component of the anchor.

[0028] In some forms of the present invention in which the protection shroud is formed as part of another component of the anchor, the anchor comprises a tapered mandrel on which the at least one gripper is mounted for relative movement between contracted and expanded conditions corresponding to the hole insertion condition and the hole anchor condition of the anchor, the mandrel being tapered between a larger diameter leading end and a smaller diameter trailing end corresponding to the leading and trailing ends of the anchor. In some forms of the anchor, the at least one gripper comprises multiple grippers, such as two grippers, but more preferably three grippers. Preferably, the two or three grippers are equidistantly spaced around the mandrel.

[0029] In the above forms of the anchor, the trailing end of the mandrel proximate the leading end of the coil spring and a bracket is mounted to the leading end of the coil spring, or to the trailing end of the mandrel. The bracket comprises an abutment associated with each gripper that is provided to limit movement of the gripper along the mandrel in the direction of the trailing end of the mandrel. The bracket further comprises the protection shroud. In some forms of the anchor, the protection shroud extends from the bracket at the leading end of the coil spring in a direction towards the trailing end of the coil spring. Alternatively, the protection shroud can connect to the bracket to extend from a portion of the coil spring spaced from the leading end of the coil spring, such as to extend from a position closer to or adjacent to the trailing end of the coil spring, or to extend from a position intermediate the leading and trailing ends.

[0030] The abutments of the bracket can be formed as arms or fingers. In some forms of the anchor, the protection shroud extends from the bracket at the leading end of the coil spring in a direction towards the trailing end of the coil spring and the arms extend in the opposite direction.

[0031] In a further development, the present invention provides for engagement between the arms or fingers of the bracket with each gripper that is more than abutting engagement. The arms or fingers of the bracket can thus by connected to the gripper or grippers against disconnection. This can be important if multiple grippers are provided and if, during insertion of the anchor into a hole, one of the grippers jams against the facing hole wall. In that circumstance, it may be necessary to withdraw the anchor a short distance to remove or dislodge the jam and advantageously, with this connection between the arms of the bracket and the grippers, reverse movement of the anchor and the bracket will withdraw the non-jammed gripper as well as the jammed gripper. This is beneficial because if the non-jammed gripper does not move in the reverse direction with the jammed gripper, as anchor is withdrawn, the mandrel will move in the reverse direction, so that the non-jammed gripper might move along the mandrel towards the larger diameter leading end, tending to increase grip against the hole wall and tending to retain the anchor against the withdrawal and maintaining the jammed gripper jammed.

[0032] In a different circumstance, as the anchor is being inserted into a hole, if one of the grippers engages the hole wall in a manner that it cannot continue to move forward (it engages a protruding rock for example), the bracket can continue to push against the non-jammed grippers and shift out of abutting connection with the jammed gripper. This leads to the anchor tilting about the jammed gripper and becoming jammed itself. However, with the arms of the bracket connected to the gripper or grippers against disconnection, the bracket cannot shift out of connection with the jammed gripper and so the anchor will not tilt and jam.

[0033] The arms or fingers of the bracket can be connected to the gripper or grippers against disconnection in any suitable manner. In some forms of the invention, the leading end of the arms or fingers are in pin connection with the trailing end of each gripper. The orientation of the pin of the pin connection can be generally tangential to the circumference of the mandrel, or it can be generally radial. Pin connection allows some movement between the arms or fingers of the bracket and the grippers as may occur as the grippers mover relative to the mandrel. The pin can thus form an axle about which relative rotation between the arms or fingers of the bracket and the grippers is facilitated.

[0034] The pin connection can be a pin that is separate to the arms or fingers of the bracket and to the grippers, or one of the arms or fingers of the bracket and the grippers can include a pin or pins that extends into an opening or openings in the other of the arms or fingers of the bracket and the grippers.

[0035] The pin can be fixed in place in any suitable manner. The pin can be a friction fit within at least one of the openings it extends through, or alternatively, the pin can be glued or brazed in place.Brief Description of the Drawings

[0036] In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which: Figure 1 is a perspective view of a prior art rock bolt. Figure 2 is an exploded view of the prior art anchor of the rock bolt of Figure 1. Figure 3 is a perspective view of a prior art gripper and bracket of the anchor of Figure 2. Figure 4 is a perspective view of an anchor according to a first embodiment of the present invention. Figure 5 is an exploded view of the anchor of Figure 4. Figure 6 is a perspective view of the bracket of Figures 4 and 5. Figure 7 is a perspective cross-sectional view of the bracket of Figure 6. Figure 8 shows the bracket of Figures 6 and 7 in connection with a pair of grippers. Figure 9 is a perspective view of a gripper according to one embodiment of the present invention. Detailed Description of the Drawings

[0037] Figure 1 is a perspective view of a prior art rock bolt.

[0038] The rock bolt 10 comprises an anchor 12, a tendon in the form of a cable 14 and a rock plate installation comprising a rock plate 16 and a barrel and wedge arrangement 18. The cable 14 is shown broken to indicate that it can be of any length.

[0039] It will be appreciated that the rock bolt 10 is intended to be installed in a hole that is drilled within a body of rock or a rock strata. The anchor 12 is provided at the leading end of the rock bolt 10 and is fed into the hole by bolting equipment in connection with a leading end of the cable 14. The cable 14 is fed from a cable reel. The anchor 12 is fed into the hole to be positioned usually at the inner end of the hole and the cable 14 extends rearwardly from the anchor 12. With the anchor 12 and the cable 14 installed in the hole, the anchor 12 can be initially activated by the bolting equipment pulling on the cable 14. With the anchor 12 activated and thus anchored within the hole, the cable 14 is also secured so that it can be severed at the open end of the hole, disengaging it from the bolting equipment and usually leaving about 300mm extending out of the opening of the hole. The bolting equipment can then move onto the next bolting location, while personnel and tensioning machinery can move into place to apply the rock plate assembly to the trailing end of the cable 14 and to then apply the operating or working tension to the cable 14. This process is highly advantageous, as personnel are prohibited from approaching the installed rock bolt if the cable of the bolt is loose and can fall out of the hole. The rock bolt 10 can initially secure the cable within the hole sufficiently to allow personnel to approach while the bolting equipment moves to the next upstream bolting location.

[0040] The rock plate 16 has a central opening through which the trailing end of the cable 14 extends and the barrel and wedge arrangement 18 is attached to the cable 14 to the side of the rock plate 16 shown in Figure 1.

[0041] The rock bolt 10 can be installed within an empty hole, or in a hole that has been filled with a cement grout or resin, so that the anchor 12 and the cable 14 pushes through the grout as it is installed within the hole.

[0042] The barrel and wedge arrangement 18 can be of a known form that attaches to the trailing end of the cable 14 and which grips the trailing end and bears against a facing surface of the rock plate 16. The barrel and wedge arrangement 18 is constructed with an outer sleeve 20 which accommodates inner wedges (not visible in Figure 1), in a manner that the cable 14 can be pulled through the wedges in the direction of arrow A, but which grips the cable 14 to prevent it from moving in the opposite direction. The barrel and wedge arrangement 18 thus allows the cable 14 to be tightened by pulling it in the direction of arrow A, which results in the arrangement 18 pressing the rock plate 16 into firm engagement against a facing rock strata.

[0043] Figure 2 is an exploded view of the anchor 12. The anchor 12 comprises a cap 24, a connector for connecting to a tendon in the form of wedges 26, a first spring 28, a body section, anchor body or mandrel 30, shells or grippers 32, a bracket 34, a second coil spring 36 and a tube 38.

[0044] To connect the cable 14 to the anchor 12, the leading end of the cable 14 extends through the anchor 12 and into the wedges 26. The leading end of the cable 14 can push into the wedges 26, but if the cable 14 is pulled in the opposite direction, the wedge 26 grips the leading end of the cable 14 and securely connects to it.

[0045] The wedges 26 are accommodated within the mandrel 30 and the proximal end of the cap 24 connects to the leading end of the mandrel 30 by screw thread connection. One end of the spring 28 bears against the cap 24, while the other bears against the wedges 26 so that when the leading end of the cable 14 is pushed into the wedges 26, the wedges 26 can push against the spring 28 to open and accept the leading end of the cable 14 and thereafter the spring 28 biases the wedges 26 into gripping engagement with the cable 14. That gripping engagement increases as the cable is pulled in the direction A of Figure 1.

[0046] The mandrel 30 tapers from the leading end 40 the trailing end 42. The bracket 34 fits to the trailing end 42 and includes three arms 44 that extend toward the leading end 40 as shown in Figure 1. There is one arm 44 for each of the grippers 32. As shown in Figure 3, the grippers 32 have a rear end 46 that includes a recess or slot 48 to accept or receive a leading end 52 of the arms 44. The slot 48 has an inner end 50 against which the leading end 52 of each arm 44 abuts.

[0047] The leading ends 47 of the grippers 32 also include a key 54 that is formed in a T- shape and that is in sliding connection with a complementary shaped keyway (not shown). The keyway is open at the leading end 40 of the mandrel 30 and is closed at the trailing end 42, so that the key 54 can be fitted to the keyway at the leading end 40 of the mandrel 30, but the key 54 cannot slide out of the keyway at the trailing end 42. The grippers 32 can thus slide longitudinally relative to the mandrel 30. Travel of the grippers 32 is prevented in the direction towards the trailing end 42 of the mandrel 30 either by reaching the end of the keyway at the trailing end 42, or upon abutment between the leading end 52 of the arms 44 with the inner end 50 of the slots 48. As will be apparent, the grippers 32 move away from the bracket 34 in a direction towards the leading end 40 of the mandrel 30 during expansion of the anchor 12 by the grippers 32 sliding longitudinally relative to the mandrel 30 by sliding movement of the key 54 within the keyway.

[0048] The present invention can be applied the anchor 12 as well as other anchors that employ a coil spring. Figures 4 and 5 show an anchor 60 that is very similar to the anchor 12 of the earlier figures and thus the anchor 60 comprises a cap 62, wedges 64, a first spring 66, a mandrel 68, shells or grippers 70, a bracket 72, a second coil spring 74 and a tube 76.

[0049] The anchor 60 operates in the same general manner as the anchor 12, in that, in accordance with Figure 1, a cable 14 can be pushed into the anchor 60 and gripped by the wedges 64. The anchor 60 can thereafter be pushed into a hole that is filled with grout and once the anchor reaches the inner end of the whole, the anchor 60 can be activated by pulling on the cable 14, to pull the mandrel 68 in a direction towards the opening of the hole, causing the grippers 70 to expand outwardly into firm gripping contact with the facing internal surface of the hole, thus anchoring the anchor 60 and the rock bolt within the hole.

[0050] As described earlier herein in relation to Figures 1 and 2, as the anchor 12 is pushed into a grout filled hole, grout can enter into the spaces between coils of the coil spring 36. This can prevent or at least limit compression and expansion of the coil spring 36 thus preventing or limiting allowable movement of the grippers 60 relative to the mandrel 30. The present invention has been developed in order to maintain the coil spring 36 operational during insertion of the anchor 12 into a hole.

[0051] In Figures 4 and 5, the bracket 72 is shown to be different from the bracket 34 of Figures 1 to 3. The bracket 72 includes a protection shroud 80 that is formed as a circular or cylindrical section that extends in a direction towards the trailing end 82 of the coil spring 74 that seats against the flange 84 of the tube 76. The protection shroud 80 therefore covers a portion of the coil spring 74 from the leading end 86 of the coil spring 74, so that the covered portion of the coil spring 74 is protected from ingress of grout between the coils of that covered portion as the anchor 60 is pushed into a grout filled hole. In Figure 4, the protection shroud extends for about 30% of the axial length of the coil spring 74. While the protection shroud 80 is shown as having a coverage of about 30% of the length of the coil spring 74, the protection shroud 80 could be longer or shorter depending on requirements.

[0052] Figure 6 shows the bracket 72 in isolation in perspective view, while Figure 7 shows the bracket in cross-sectional perspective view. It can be seen that the bracket 72 has three arms 88 and in the cross-sectional view, it can be seen that the protection shroud 80 either comprises an annular channel 90, or extends from the annular channel 90. The channel 90 accepts the leading end 86 of the coil spring 74 for locating or connecting the protection shroud 80 to the leading end 86. Advantageously, the connection between the leading end 86 of the coil spring 74 is very simple and the coil spring can be made to have a slight compression in the assembled arrangement of Figure 4, so that the leading end 86 of the coil spring 74 is always biased to engagement within the channel 90.

[0053] Returning to Figure 4, is the anchor 60 is pushed into a grout filled hole, the type add cap 62 will push through the grout and the grout will flow about the cap 62 and about the mandrel 68 and the grippers 70. Grout will then flow about the arms 88 before it reaches the protection shroud 80. Some grout will flow into the gaps between the arms 88 and therefore some grout may flow into any gaps existing between the leading end of the protection shroud 80 and the tube 76. However any gaps will be small and so it is not expected that grout ingress will be sufficient to inundate the coils within the protection shroud 80. Most of the grout will flow over the protection shroud 80 and will potentially inundate the exposed coils below the protection shroud 80, but advantageously, the coils within the protection shroud 80 should remain operational.

[0054] In the arrangement of the anchor 12 of Figure 1, there is abutment of the end surfaces of the arms 44 against the inner end 50 of the slots 48 in the grippers 32. This abutment is a pushing connection rather than a fixed connection. As shown in Figures 6 to 9, the arms 88 of the bracket 72 have distal ends 92 that incorporate openings 94. The openings 94 are provided to accept a pin 98 (see Figure 8 and Figure 5 as well) that extends through the openings 94 and through openings 100 in the trailing end 102 of the grippers 70. This pin connection securely fixes the grippers 70 to the arms 88 so that under circumstances such as described above, in which there would be the potential for a gripper 70 to disconnect from an arm 88, the pin connection prevents that disconnection.

[0055] It is to be noted that in the arrangement of Figure 8, distal ends 92 of the arms 88 extend into blind openings or pockets 104 in the grippers 70. Openings 100 extend through opposite walls of the openings 104 and it will be appreciated that the distal ends 92 are oriented so that the openings 94 align with the openings 100, so that a pin 98 can extend through the respective openings 100 and 94 to secure the distal ends 92 and thus the arms 88 to the grippers 70. This differs from the arrangement of the anchor 12, in which the grippers 32 have a rear end 46 that includes a recess or slot 48 to accept or receive a leading end 52 of the arms 44.

[0056] The pin can be fixed in place in any suitable manner. The pin can be a friction fit within at least one of the openings 100 for example. Alternatively, the pin can be glued in place, or brazed in place.

[0057] The pin connection shown in the figures shows the pins 98 oriented to extend generally radially relative to the longitudinal axis of the anchor 60. It will be appreciated that equally, the openings 94 could extend perpendicular to the direction shown in Figures 6 to 8 as long as the openings in the grippers were oriented in a similar direction for passage of a pin through both the grippers 70 and the arms 88.

[0058] Unless the context requires otherwise, where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0059] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0060] Future patent applications may be filed in on the basis of or claiming priority from the present application. It is to be understood that the following claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the claims at a later date so as to further define or re-define the invention or inventions.

Examples

Embodiment Construction

[0037]Figure 1 is a perspective view of a prior art rock bolt.

[0038]The rock bolt 10 comprises an anchor 12, a tendon in the form of a cable 14 and a rock plate installation comprising a rock plate 16 and a barrel and wedge arrangement 18. The cable 14 is shown broken to indicate that it can be of any length.

[0039]It will be appreciated that the rock bolt 10 is intended to be installed in a hole that is drilled within a body of rock or a rock strata. The anchor 12 is provided at the leading end of the rock bolt 10 and is fed into the hole by bolting equipment in connection with a leading end of the cable 14. The cable 14 is fed from a cable reel. The anchor 12 is fed into the hole to be positioned usually at the inner end of the hole and the cable 14 extends rearwardly from the anchor 12. With the anchor 12 and the cable 14 installed in the hole, the anchor 12 can be initially activated by the bolting equipment pulling on the cable 14. With the anchor 12 activated and thus anchored ...

Technical Field of the Invention

[0001] The present invention relates to a rock bolt for use in rock strata to support the rock strata against collapse or failure, and to an anchor for use in such a rock bolt.Background of the Invention

[0002] The discussion of the background to the invention that follows is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any aspect of the discussion was part of the common general knowledge as at the priority date of the application.

[0003] Rock bolts are used for reinforcing rock strata by inserting the bolt into a hole drilled into the rock strata and fixing the bolt within the hole. Bolts can be fixed within a hole by anchors that frictionally engage with the wall of the hole or they can be embedded within the hole with grout or resin, or both. The anchor of the present invention has been developed for use in reinforcement in which grout or resin is used, although the anchor of the present invention can still be used in reinforcement in which grout or resin is not used.

[0004] The trailing end of a rock bolt will usually extend out of the open end of the hole and a rock plate can be attached to the trailing end and can be tightened to press firmly against the rock face that surrounds the hole opening. The fixing of the bolt within the hole resists egress of the bolt from the hole and the rock plate supports the rock face against fracture and displacement. Safety mesh can be installed broadly across the rock face by anchoring the mesh to multiple rock bolts. In this manner, the rock bolts support the rock strata against fracture and collapse and the safety mesh can restrain any dislodged pieces of the rock strata. The use of bolts and mesh is widespread in the underground mining industry to protect workers and equipment in underground mines and tunnels from strata fracture.

[0005] Rock bolts can employ a rigid or flexible tendon that extends between leading and trailing ends of the rock bolt. A rigid tendon can comprise a bar or rod, or a tube, such as a longitudinally split tube. Other rock bolts employ a flexible tendon, which is usually a cable.

[0006] Rock bolts can employ an anchor at a leading end and a rock plate at the opposite and trailing end. The anchor is used to frictionally engage against facing surfaces of the hole. The anchor can be activatable once the rock bolt is properly positioned within the drilled hole.

[0007] Rock bolts that employ a rod, bar or tube are rigid and typically have a length of between 1.8m to 3m. In underground tunnelling, the length of the rigid rock bolt is generally limited by the room available within the tunnel. In underground mining, the available room often precludes the use of rigid rock bolts that have a length greater than 3m. In underground tunnelling in general, the available room often precludes the use of rigid rock bolts that have a length greater than 6m.

[0008] Rock bolts that employ a cable are usually used where the depth of the hole into which the rock bolt is installed exceeds the maximum length of rock bolts that employ a rod, bar or tube. For example, rock bolts that employ a cable can be used in holes having a depth of 10m or more. For these forms of rock bolts the cable can be unrolled from a cable reel, so that any length of cable can be used.

[0009] Rock bolts that employ a cable are not rigid and therefore they must be pushed into the hole without significant frictional resistance. In some installations, the hole is empty, while in other installations, cement grout is pumped into the hole before the rock bolt is inserted and once the hole is sufficiently filled with grout, the cable bolt is fed from a reel into the hole, pushing through the grout. Once sufficient cable has been fed into the hole, the trailing end of the cable is severed, usually leaving about 0.3m extending from the opening of the hole.

[0010] Cable rock bolts can include an anchor at the leading end. Where the hole is filled with grout, the anchor can be pushed through the cement grout to the inner end of the hole or to the appropriate position within the hole. Where an anchor is employed, the anchor is provided to engage against the facing internal surface of the hole and to grip the internal surface so as to anchor the leading end of the rock bolt within the hole. The anchors are normally expandable anchors that have an insertion condition and a hole anchor condition, whereby the anchor travels into the hole in the insertion condition and once the anchor is positioned at the correct depth within the hole, the anchor is activated by expansion to the anchor condition, to grip the facing internal surfaces of the hole. The diameter of the anchor in the insertion condition is typically at least slightly less than the diameter of the hole, so that the anchor can travel into the hole without significant frictional resistance. Once the anchor has reached the installation position, expansion of the anchor to a greater diameter allows the anchor to engage and grip facing internal surfaces of the hole to anchor the leading end of the cable and the rock bolt.

[0011] Activation of the anchor to the anchor condition provides an immediate connection of the bolt within the hole, so that 1) the rock bolt can be loaded immediately by application of a rock plate at the trailing end of the rock bolt against the rock strata surrounding the opening of the hole and 2) the cable is secured from falling out of the hole as soon as the anchor is activated. The rock bolt thus immediately provides strata support and secures the cable within the hole, allowing immediate re-entry of mining personnel and equipment into the area of the tunnel being bolted. If the anchor is omitted and the cable is secured in place by cement grout, the cable bolt is not operational and the cable is not secured within the hole, until the cement grout has cured. Fear of the cable falling out of the hole commonly stops miners travelling through that part of the excavation (tunnel) until the grout sets (approximately 12 hours). The present invention relates to rock bolts that include an anchor at the leading end.

[0012] One form of prior art rock bolt comprises an anchor that includes grippers that are mounted for relative movement on a tapered mandrel so that during insertion of the anchor into a hole, the grippers can assume a reduced diameter on the mandrel (the insertion condition) and once the anchor has reached the activation position within the hole, the anchor can be activated to shift the mandrel relative to the grippers to an expanded and increased diameter (the anchor condition). The anchor is activated by pulling on the tendon that is connected to the mandrel, to pull the mandrel rearwardly relative to the grippers and to force the grippers into firm engagement with the wall of the hole.

[0013] In the above described form of prior art rock bolt, the grippers are biased towards the leading end of the anchor by a coil spring. The grippers can shift rearwardly on the mandrel against the bias as the anchor is pushed into the hole. This rearward shifting is beneficial, because a hole is usually drilled to be a close fit about the anchor and so the grippers will tend to scrape against the facing surface of the hole as the anchor is inserted. If the scraping load applied to the grippers is sufficient, progress of the anchor into the hole will be impeded or prevented. Accordingly, by facilitating shifting of the grippers to a smaller diameter against the bias of the coil spring, the scraping load can be reduced and the anchor can progress. The grippers are biased towards a larger diameter on the tapered mandrel so that when the anchor has reached its activation position within the hole, the grippers will be biased towards the leading end of the anchor and into initial engagement with the facing surface of the hole. The anchor is then ready for activation, whereby the grippers will be pressed into firmer engagement with the facing surface of the hole. The initial engagement of the grippers with the facing surface of the hole prevents the anchor from being pulled backwards in a direction out of the hole when the tendon is pulled to activate the anchor. This initial engagement gives the anchor sufficient purchase against the facing surface of the hole for the anchor to retain its position in the hole prior to the tendon being pulled to fully activate the anchor.

[0014] A potential difficulty with the anchor of the above described form of prior art rock bolt, is that the coil spring is exposed to grout within the hole as the anchor pushes through or into the hole and because the grout is flowable, it can enter into spaces between the coils of the spring, sometimes clogging the spring and affecting compression and expansion of the spring. This difficulty is reduced if the grout is more flowable, however installation preference is for thicker grout for several reasons, including the potential for quicker setting, reduced likelihood of the grout flowing out of the hole under gravity and higher compressive strength and greater durability once the grout sets. If the operation of the spring is reduced sufficiently, the grippers will not be able to shift relative to the mandrel sufficiently to assume a reduced diameter on the mandrel during insertion of the anchor into the hole, and / or the grippers will not be able to shift relative to the mandrel sufficiently to assume an increased diameter for initial engagement of the hole wall, prior to activation of the anchor.

[0015] The present invention has been developed to overcome or at least alleviate the above drawback of the prior art.Summary of the Invention

[0016] In one form of the invention, an anchor for a rock bolt is provided, in which the anchor is expandable between a hole insertion condition and a hole anchor condition. The anchor comprises a leading end and a trailing end, and a connector for connecting to a tendon. The anchor further comprises at least one gripper that is expandable outwardly from the insertion condition of the anchor to the anchor condition of the anchor for gripping the facing surface of a hole in which the anchor is installed. The at least one gripper is biased by a coil spring towards the leading end of the anchor. A protection shroud circumferentially surrounds an outside portion of the coil spring to protect a portion of the coil spring against ingress of grout.

[0017] An anchor according to the present invention provides protection for at least a section of the coil spring against grout entering or accessing that section of the coil spring. This means that the section of the coil spring about which the protection shroud extends should continue to operate to contract or expand even if other sections or the remaining section of the coil spring becomes inundated or invaded by the grout when it is wet and flowable, to reduce or prevent the inundated section from compressing or expanding. This allows the coil spring to continue to compress, albeit in a reduced section of the full length of the coil spring, when it is necessary for the grippers to assume a reduced diameter or contracted position and that advantageously allows the coil spring to continue to allow the anchor to progress into a hole and to push or urge the gripper into engagement with the facing internal surface of the hole once the anchor has reached its final destination within the hole.

[0018] The protection shroud can be positioned at any suitable position along the length of the coil spring. The protection shroud can be positioned at the leading end of the coil spring, at the trailing end, or intermediate the leading and trailing ends. Positioning the protection shroud at the leading end of the coil spring has advantages, in that the leading end of the coil spring can be substantially closed to ingress of grout and with the protection shroud at the leading end, as the anchor is pushed into a hole, the grout will tend to flow about the leading end and the protection shroud without any, or much ingress into the coils at the leading end. However, the protection shroud can be positioned elsewhere along the length of the coil spring with the protection shroud configured to resist entry of grout into that portion of the coil spring that the coil spring surrounds, or it may be acceptable for some ingress of grout into that portion of the coil spring that the coil spring surrounds, on the basis that the grout will not progress fully into the protection shroud and thus the protection shroud will still provide protection for a portion of the coil spring against ingress of grout. For example, the grout may clog at or just into the entrance into the protection shroud and thus may not progress into the protection shroud sufficient to prevent the coil spring from contracting or expanding within the protection shroud.

[0019] The protection shroud can be a close fit about the outside portion of the coil spring. Clearance between the inside surface of the protection shroud and the outer surface of the coils of the coil spring can be in the region of 0.5mm radially.

[0020] The leading and trailing ends of the coil spring correspond to the leading and trailing ends of the anchor and by this, it is meant that the leading end of the coil spring is closest to the leading end of the anchor and the trailing end of the coil spring is closest to the trailing end of the anchor. The anchor will usually have a longitudinal axis and the axis of the coil spring can be co-axial with the axis of the anchor.

[0021] The coil spring typically will be of constant diameter, ie cylindrical and the protection shroud can also be cylindrical and co-axial with the axis of the coil spring. The protection shroud can of course be of a different shape and may for example, be tapered outwardly towards the trailing end of the anchor, thereby tending to divert or push grout away from the coil spring as the anchor pushes through the grout.

[0022] The protection shroud can have any suitable lengthwise extent along the length of the coil spring. Where the protection shroud extends from the leading end of the coil spring towards the trailing end the protection shroud can extend for at least about 30% of the axial length of the coil spring. In alternative arrangements, the protection shroud can extend for at least about 50% of the axial length of the coil spring. The protection shroud could even extend the full length, or almost the full length of the coil spring.

[0023] The protection shroud can be mounted to the anchor relative to the coil spring in any suitable manner. In some arrangements, the protection shroud can be mounted to the coil spring, such as to the leading end of the coil spring. In some arrangements, the protection shroud can fit over the leading end of the coil spring to locate the protection shroud on the leading end of the coil spring. For example, the protection shroud can comprise one or more abutments against which the leading end of the coil spring abuts and which locate the protection shroud on the leading end. An abutment can comprise an inwardly extending annular flange that fits over the leading end of the coil spring, or one or multiple inwardly extending tabs could extend over the leading end of the coil spring.

[0024] In other arrangements, the protection shroud can comprise an annular channel, or the protection shroud can extend from an annular channel for the leading end of the coil spring to fit into for locating the protection shroud on the leading end.

[0025] An anchor according to the present invention comprises a coil spring. Coil springs having a spring constant in the order of 1.4n / mm and 1.9n / mm are considered appropriate. In the development of the present invention, coil springs having greater, or even much greater spring constants were trialled in order to overcome the resistance to compression and expansion when grout inundated or invaded the space between the coils of the coil spring. These coil springs having greater spring constants increased the cost of the anchor, as well as the weight and bulk of the anchor. Moreover, simply increasing the spring constant did not necessarily mean that the coil spring could overcome the resistance from grout inundation, unless a coil spring having a significantly large spring constant was adopted. However, such a coil spring would likely be unnecessary for many applications and therefore would add unnecessary cost, weight and bulk for most applications. The development of the protection shroud was therefore pursued and has been found to provide a solution to the problem of grout inundation, without the drawbacks associated with the use of coil springs having larger than often necessary spring constants.

[0026] The protection shroud can be formed of any suitable material. For example metal, such as steel metal plate could be used. However, the development to date has employed plastic as the material of the protection shroud. Plastic is cheap, easily formed, durable in a grout immersed environment and light weight. Example plastic material that is considered suitable for the protection shroud includes high-density polyethylene, reinforced nylon and unreinforced nylon.

[0027] The protection shroud can be a stand-alone component in that it can be a separate component to other parts of the anchor and assembled separately as part of the anchor. Alternatively, the protection shroud can be formed as part of another component of the anchor. The development to date has formed the protection shroud from plastic and integrally as part of another bracket component of the anchor.

[0028] In some forms of the present invention in which the protection shroud is formed as part of another component of the anchor, the anchor comprises a tapered mandrel on which the at least one gripper is mounted for relative movement between contracted and expanded conditions corresponding to the hole insertion condition and the hole anchor condition of the anchor, the mandrel being tapered between a larger diameter leading end and a smaller diameter trailing end corresponding to the leading and trailing ends of the anchor. In some forms of the anchor, the at least one gripper comprises multiple grippers, such as two grippers, but more preferably three grippers. Preferably, the two or three grippers are equidistantly spaced around the mandrel.

[0029] In the above forms of the anchor, the trailing end of the mandrel proximate the leading end of the coil spring and a bracket is mounted to the leading end of the coil spring, or to the trailing end of the mandrel. The bracket comprises an abutment associated with each gripper that is provided to limit movement of the gripper along the mandrel in the direction of the trailing end of the mandrel. The bracket further comprises the protection shroud. In some forms of the anchor, the protection shroud extends from the bracket at the leading end of the coil spring in a direction towards the trailing end of the coil spring. Alternatively, the protection shroud can connect to the bracket to extend from a portion of the coil spring spaced from the leading end of the coil spring, such as to extend from a position closer to or adjacent to the trailing end of the coil spring, or to extend from a position intermediate the leading and trailing ends.

[0030] The abutments of the bracket can be formed as arms or fingers. In some forms of the anchor, the protection shroud extends from the bracket at the leading end of the coil spring in a direction towards the trailing end of the coil spring and the arms extend in the opposite direction.

[0031] In a further development, the present invention provides for engagement between the arms or fingers of the bracket with each gripper that is more than abutting engagement. The arms or fingers of the bracket can thus by connected to the gripper or grippers against disconnection. This can be important if multiple grippers are provided and if, during insertion of the anchor into a hole, one of the grippers jams against the facing hole wall. In that circumstance, it may be necessary to withdraw the anchor a short distance to remove or dislodge the jam and advantageously, with this connection between the arms of the bracket and the grippers, reverse movement of the anchor and the bracket will withdraw the non-jammed gripper as well as the jammed gripper. This is beneficial because if the non-jammed gripper does not move in the reverse direction with the jammed gripper, as anchor is withdrawn, the mandrel will move in the reverse direction, so that the non-jammed gripper might move along the mandrel towards the larger diameter leading end, tending to increase grip against the hole wall and tending to retain the anchor against the withdrawal and maintaining the jammed gripper jammed.

[0032] In a different circumstance, as the anchor is being inserted into a hole, if one of the grippers engages the hole wall in a manner that it cannot continue to move forward (it engages a protruding rock for example), the bracket can continue to push against the non-jammed grippers and shift out of abutting connection with the jammed gripper. This leads to the anchor tilting about the jammed gripper and becoming jammed itself. However, with the arms of the bracket connected to the gripper or grippers against disconnection, the bracket cannot shift out of connection with the jammed gripper and so the anchor will not tilt and jam.

[0033] The arms or fingers of the bracket can be connected to the gripper or grippers against disconnection in any suitable manner. In some forms of the invention, the leading end of the arms or fingers are in pin connection with the trailing end of each gripper. The orientation of the pin of the pin connection can be generally tangential to the circumference of the mandrel, or it can be generally radial. Pin connection allows some movement between the arms or fingers of the bracket and the grippers as may occur as the grippers mover relative to the mandrel. The pin can thus form an axle about which relative rotation between the arms or fingers of the bracket and the grippers is facilitated.

[0034] The pin connection can be a pin that is separate to the arms or fingers of the bracket and to the grippers, or one of the arms or fingers of the bracket and the grippers can include a pin or pins that extends into an opening or openings in the other of the arms or fingers of the bracket and the grippers.

[0035] The pin can be fixed in place in any suitable manner. The pin can be a friction fit within at least one of the openings it extends through, or alternatively, the pin can be glued or brazed in place.Brief Description of the Drawings

[0036] In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which: Figure 1 is a perspective view of a prior art rock bolt. Figure 2 is an exploded view of the prior art anchor of the rock bolt of Figure 1. Figure 3 is a perspective view of a prior art gripper and bracket of the anchor of Figure 2. Figure 4 is a perspective view of an anchor according to a first embodiment of the present invention. Figure 5 is an exploded view of the anchor of Figure 4. Figure 6 is a perspective view of the bracket of Figures 4 and 5. Figure 7 is a perspective cross-sectional view of the bracket of Figure 6. Figure 8 shows the bracket of Figures 6 and 7 in connection with a pair of grippers. Figure 9 is a perspective view of a gripper according to one embodiment of the present invention. Detailed Description of the Drawings

[0037] Figure 1 is a perspective view of a prior art rock bolt.

[0038] The rock bolt 10 comprises an anchor 12, a tendon in the form of a cable 14 and a rock plate installation comprising a rock plate 16 and a barrel and wedge arrangement 18. The cable 14 is shown broken to indicate that it can be of any length.

[0039] It will be appreciated that the rock bolt 10 is intended to be installed in a hole that is drilled within a body of rock or a rock strata. The anchor 12 is provided at the leading end of the rock bolt 10 and is fed into the hole by bolting equipment in connection with a leading end of the cable 14. The cable 14 is fed from a cable reel. The anchor 12 is fed into the hole to be positioned usually at the inner end of the hole and the cable 14 extends rearwardly from the anchor 12. With the anchor 12 and the cable 14 installed in the hole, the anchor 12 can be initially activated by the bolting equipment pulling on the cable 14. With the anchor 12 activated and thus anchored within the hole, the cable 14 is also secured so that it can be severed at the open end of the hole, disengaging it from the bolting equipment and usually leaving about 300mm extending out of the opening of the hole. The bolting equipment can then move onto the next bolting location, while personnel and tensioning machinery can move into place to apply the rock plate assembly to the trailing end of the cable 14 and to then apply the operating or working tension to the cable 14. This process is highly advantageous, as personnel are prohibited from approaching the installed rock bolt if the cable of the bolt is loose and can fall out of the hole. The rock bolt 10 can initially secure the cable within the hole sufficiently to allow personnel to approach while the bolting equipment moves to the next upstream bolting location.

[0040] The rock plate 16 has a central opening through which the trailing end of the cable 14 extends and the barrel and wedge arrangement 18 is attached to the cable 14 to the side of the rock plate 16 shown in Figure 1.

[0041] The rock bolt 10 can be installed within an empty hole, or in a hole that has been filled with a cement grout or resin, so that the anchor 12 and the cable 14 pushes through the grout as it is installed within the hole.

[0042] The barrel and wedge arrangement 18 can be of a known form that attaches to the trailing end of the cable 14 and which grips the trailing end and bears against a facing surface of the rock plate 16. The barrel and wedge arrangement 18 is constructed with an outer sleeve 20 which accommodates inner wedges (not visible in Figure 1), in a manner that the cable 14 can be pulled through the wedges in the direction of arrow A, but which grips the cable 14 to prevent it from moving in the opposite direction. The barrel and wedge arrangement 18 thus allows the cable 14 to be tightened by pulling it in the direction of arrow A, which results in the arrangement 18 pressing the rock plate 16 into firm engagement against a facing rock strata.

[0043] Figure 2 is an exploded view of the anchor 12. The anchor 12 comprises a cap 24, a connector for connecting to a tendon in the form of wedges 26, a first spring 28, a body section, anchor body or mandrel 30, shells or grippers 32, a bracket 34, a second coil spring 36 and a tube 38.

[0044] To connect the cable 14 to the anchor 12, the leading end of the cable 14 extends through the anchor 12 and into the wedges 26. The leading end of the cable 14 can push into the wedges 26, but if the cable 14 is pulled in the opposite direction, the wedge 26 grips the leading end of the cable 14 and securely connects to it.

[0045] The wedges 26 are accommodated within the mandrel 30 and the proximal end of the cap 24 connects to the leading end of the mandrel 30 by screw thread connection. One end of the spring 28 bears against the cap 24, while the other bears against the wedges 26 so that when the leading end of the cable 14 is pushed into the wedges 26, the wedges 26 can push against the spring 28 to open and accept the leading end of the cable 14 and thereafter the spring 28 biases the wedges 26 into gripping engagement with the cable 14. That gripping engagement increases as the cable is pulled in the direction A of Figure 1.

[0046] The mandrel 30 tapers from the leading end 40 the trailing end 42. The bracket 34 fits to the trailing end 42 and includes three arms 44 that extend toward the leading end 40 as shown in Figure 1. There is one arm 44 for each of the grippers 32. As shown in Figure 3, the grippers 32 have a rear end 46 that includes a recess or slot 48 to accept or receive a leading end 52 of the arms 44. The slot 48 has an inner end 50 against which the leading end 52 of each arm 44 abuts.

[0047] The leading ends 47 of the grippers 32 also include a key 54 that is formed in a T- shape and that is in sliding connection with a complementary shaped keyway (not shown). The keyway is open at the leading end 40 of the mandrel 30 and is closed at the trailing end 42, so that the key 54 can be fitted to the keyway at the leading end 40 of the mandrel 30, but the key 54 cannot slide out of the keyway at the trailing end 42. The grippers 32 can thus slide longitudinally relative to the mandrel 30. Travel of the grippers 32 is prevented in the direction towards the trailing end 42 of the mandrel 30 either by reaching the end of the keyway at the trailing end 42, or upon abutment between the leading end 52 of the arms 44 with the inner end 50 of the slots 48. As will be apparent, the grippers 32 move away from the bracket 34 in a direction towards the leading end 40 of the mandrel 30 during expansion of the anchor 12 by the grippers 32 sliding longitudinally relative to the mandrel 30 by sliding movement of the key 54 within the keyway.

[0048] The present invention can be applied the anchor 12 as well as other anchors that employ a coil spring. Figures 4 and 5 show an anchor 60 that is very similar to the anchor 12 of the earlier figures and thus the anchor 60 comprises a cap 62, wedges 64, a first spring 66, a mandrel 68, shells or grippers 70, a bracket 72, a second coil spring 74 and a tube 76.

[0049] The anchor 60 operates in the same general manner as the anchor 12, in that, in accordance with Figure 1, a cable 14 can be pushed into the anchor 60 and gripped by the wedges 64. The anchor 60 can thereafter be pushed into a hole that is filled with grout and once the anchor reaches the inner end of the whole, the anchor 60 can be activated by pulling on the cable 14, to pull the mandrel 68 in a direction towards the opening of the hole, causing the grippers 70 to expand outwardly into firm gripping contact with the facing internal surface of the hole, thus anchoring the anchor 60 and the rock bolt within the hole.

[0050] As described earlier herein in relation to Figures 1 and 2, as the anchor 12 is pushed into a grout filled hole, grout can enter into the spaces between coils of the coil spring 36. This can prevent or at least limit compression and expansion of the coil spring 36 thus preventing or limiting allowable movement of the grippers 60 relative to the mandrel 30. The present invention has been developed in order to maintain the coil spring 36 operational during insertion of the anchor 12 into a hole.

[0051] In Figures 4 and 5, the bracket 72 is shown to be different from the bracket 34 of Figures 1 to 3. The bracket 72 includes a protection shroud 80 that is formed as a circular or cylindrical section that extends in a direction towards the trailing end 82 of the coil spring 74 that seats against the flange 84 of the tube 76. The protection shroud 80 therefore covers a portion of the coil spring 74 from the leading end 86 of the coil spring 74, so that the covered portion of the coil spring 74 is protected from ingress of grout between the coils of that covered portion as the anchor 60 is pushed into a grout filled hole. In Figure 4, the protection shroud extends for about 30% of the axial length of the coil spring 74. While the protection shroud 80 is shown as having a coverage of about 30% of the length of the coil spring 74, the protection shroud 80 could be longer or shorter depending on requirements.

[0052] Figure 6 shows the bracket 72 in isolation in perspective view, while Figure 7 shows the bracket in cross-sectional perspective view. It can be seen that the bracket 72 has three arms 88 and in the cross-sectional view, it can be seen that the protection shroud 80 either comprises an annular channel 90, or extends from the annular channel 90. The channel 90 accepts the leading end 86 of the coil spring 74 for locating or connecting the protection shroud 80 to the leading end 86. Advantageously, the connection between the leading end 86 of the coil spring 74 is very simple and the coil spring can be made to have a slight compression in the assembled arrangement of Figure 4, so that the leading end 86 of the coil spring 74 is always biased to engagement within the channel 90.

[0053] Returning to Figure 4, is the anchor 60 is pushed into a grout filled hole, the type add cap 62 will push through the grout and the grout will flow about the cap 62 and about the mandrel 68 and the grippers 70. Grout will then flow about the arms 88 before it reaches the protection shroud 80. Some grout will flow into the gaps between the arms 88 and therefore some grout may flow into any gaps existing between the leading end of the protection shroud 80 and the tube 76. However any gaps will be small and so it is not expected that grout ingress will be sufficient to inundate the coils within the protection shroud 80. Most of the grout will flow over the protection shroud 80 and will potentially inundate the exposed coils below the protection shroud 80, but advantageously, the coils within the protection shroud 80 should remain operational.

[0054] In the arrangement of the anchor 12 of Figure 1, there is abutment of the end surfaces of the arms 44 against the inner end 50 of the slots 48 in the grippers 32. This abutment is a pushing connection rather than a fixed connection. As shown in Figures 6 to 9, the arms 88 of the bracket 72 have distal ends 92 that incorporate openings 94. The openings 94 are provided to accept a pin 98 (see Figure 8 and Figure 5 as well) that extends through the openings 94 and through openings 100 in the trailing end 102 of the grippers 70. This pin connection securely fixes the grippers 70 to the arms 88 so that under circumstances such as described above, in which there would be the potential for a gripper 70 to disconnect from an arm 88, the pin connection prevents that disconnection.

[0055] It is to be noted that in the arrangement of Figure 8, distal ends 92 of the arms 88 extend into blind openings or pockets 104 in the grippers 70. Openings 100 extend through opposite walls of the openings 104 and it will be appreciated that the distal ends 92 are oriented so that the openings 94 align with the openings 100, so that a pin 98 can extend through the respective openings 100 and 94 to secure the distal ends 92 and thus the arms 88 to the grippers 70. This differs from the arrangement of the anchor 12, in which the grippers 32 have a rear end 46 that includes a recess or slot 48 to accept or receive a leading end 52 of the arms 44.

[0056] The pin can be fixed in place in any suitable manner. The pin can be a friction fit within at least one of the openings 100 for example. Alternatively, the pin can be glued in place, or brazed in place.

[0057] The pin connection shown in the figures shows the pins 98 oriented to extend generally radially relative to the longitudinal axis of the anchor 60. It will be appreciated that equally, the openings 94 could extend perpendicular to the direction shown in Figures 6 to 8 as long as the openings in the grippers were oriented in a similar direction for passage of a pin through both the grippers 70 and the arms 88.

[0058] Unless the context requires otherwise, where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other features, integers, steps or components, or group thereof.

[0059] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0060] Future patent applications may be filed in on the basis of or claiming priority from the present application. It is to be understood that the following claims are provided by way of example only, and are not intended to limit the scope of what may be claimed in any such future application. Features may be added to or omitted from the claims at a later date so as to further define or re-define the invention or inventions.

Examples

Embodiment Construction

[0037]Figure 1 is a perspective view of a prior art rock bolt.

[0038]The rock bolt 10 comprises an anchor 12, a tendon in the form of a cable 14 and a rock plate installation comprising a rock plate 16 and a barrel and wedge arrangement 18. The cable 14 is shown broken to indicate that it can be of any length.

[0039]It will be appreciated that the rock bolt 10 is intended to be installed in a hole that is drilled within a body of rock or a rock strata. The anchor 12 is provided at the leading end of the rock bolt 10 and is fed into the hole by bolting equipment in connection with a leading end of the cable 14. The cable 14 is fed from a cable reel. The anchor 12 is fed into the hole to be positioned usually at the inner end of the hole and the cable 14 extends rearwardly from the anchor 12. With the anchor 12 and the cable 14 installed in the hole, the anchor 12 can be initially activated by the bolting equipment pulling on the cable 14. With the anchor 12 activated and thus anchored ...

Claims

1. An anchor (60) for a rock bolt, the anchor (60) being expandable between a hole insertion condition and a hole anchor condition, the anchor (60) comprising: a. a leading end and a trailing end, and b. a connector for connecting to a tendon, c. at least one gripper (70) that is expandable outwardly from the insertion condition of the anchor (60) to the anchor condition of the anchor (60) for gripping the facing surface of a hole in which the anchor (60) is installed, the at least one gripper (70) being biased by a coil spring (74) towards the leading end of the anchor (60) to expand the gripper (70) outwardly, and d. a protection shroud (80) circumferentially surrounding an outside portion of the coil spring (74) to protect a portion of the coil spring (74) against ingress of grout.

2. An anchor (60) according to claim 1, the coil spring (74) having a leading end and a trailing end corresponding to the leading and trailing ends of the anchor (60) and the protection shroud (80) surrounding an outside portion of the coil spring (74) at the leading end of the coil spring (74).

3. An anchor (60) according to claim 2, the protection shroud (80) extending from the leading end of the coil spring (74) towards the trailing end of the coil spring (74) and extending for at least about 30% of the axial length of the coil spring (74).

4. An anchor (60) according to claim 2 or 3, the protection shroud (80) being mounted to the leading end of the coil spring (74).

5. An anchor (60) according to claim 4, the protection shroud (80) comprising one or more abutments against which the leading end of the coil spring (74) abuts.

6. An anchor (60) according to claim 4, the protection shroud (80) extending from an annular channel (90) within which the leading end of the coil spring (74) is located.

7. An anchor (60) according to any one of claims 1 to 6, the coil spring (74) having a spring constant in the order of 1.4n / mm and 1.9n / mm.

8. An anchor (60) according to any one of claims 1 to 7, the protection shroud (80) being formed of plastic, in particular high-density polyethylene, reinforced nylon or unreinforced nylon.

9. An anchor (60) according to any one of claims 1 to 8, the protection shroud (80) being cylindrical.

10. An anchor (60) according to any one of claims 1 to 9, the protection shroud (80) being a close fit about the outside portion of the coil spring (74), for example the clearance between the inside surface of the protection shroud (80) and the outer surface of the coils of the coil spring (74) being in the region of 0.5mm11. An anchor (60) according to any one of claims 2 to 6, further comprising a tapered mandrel (68) on which the at least one gripper (70) is mounted for relative movement between contracted and expanded conditions corresponding to the hole insertion condition and the hole anchor condition of the anchor (60), the mandrel (68) being tapered between a larger diameter leading end and a smaller diameter trailing end corresponding to the leading and trailing ends of the anchor (60), and the trailing end of the mandrel (68) being proximate the leading end of the coil spring (74), a bracket (72) mounted to the leading end of the coil spring (74) or to the trailing end of the mandrel (68), the bracket (72) comprising an abutment to limit movement of the at least one gripper (70) in the direction of the trailing end of the mandrel (68) and the bracket (72) further comprising the protection shroud (80) that extends from the leading end of the coil spring (74) in a direction towards the trailing end of the coil spring (74).

12. An anchor (60) according to claim 11, the bracket (72) being formed integrally from plastic, in particular high-density polyethylene, reinforced nylon or unreinforced nylon.

13. An anchor (60) according to claim 11 or 12, the abutment of the bracket (72) comprising an arm (88) and the leading end of the arm (88) being in pin (98) connection with a trailing end of the at least one gripper (70).

14. An anchor (60) according to claim 13, the trailing end of the at least one gripper (70) including a blind opening (104) into which the leading end of the arm extends (88), the pin (98) extending across the opening (104) and through the leading end of the arm (88).

15. An anchor (60) according to claim 14, the blind opening (104) having opposite walls and the opposite walls having aligned openings (100) through which the pin (98) extends and the pin (98) being a friction fit within at least one of the aligned openings (100).

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