AU2011295644A1 - Mechanical anchor for bolt - Google Patents

Abstract

An anchoring assembly (201) is disclosed for anchoring a bolt such as rock bolt within a borehole, including a cam member (202) mounted to pivot relative to the bolt from a closed position aligned with the bolt to an expanded position offset from the bolt to anchor the bolt within the borehole. The assembly may include a further expansion mechanism actuated by axial movement of the bolt, so that the cam mechanism provides initial tightening of the anchoring assembly and the further mechanism provides further tightening. Also disclosed is an anchoring assembly having an external expansion shell (226) having on or more ramp surfaces (231) which reacts to subsequent tensile loads on the rock bolt by expanding further against the borehole.

Description

WO 2012/027802 PCT/AU2011/001146 TITLE OF THE INVENTION MECHANICAL ANCHOR FOR BOLT CROSS-REFERENCES TO RELATED APPLICATIONS [00011 The present application claims priority from Australian Provisional Patent Application No. 2010903962 filed on 3 September 2010, and Australian Provisional Patent Application No. 2010905390 filed on 8 December 2010, the disclosures of which are incorporated herein by reference. BACKGROUND OF THE INVENTION 1. Field of the Invention 100021 The present invention relates to a mechanical anchor adapted to secure an elongate member, such as a bolt, within a borehole. The invention has particular application to rock bolts of the type typically used in mining or civil applications, and more particularly to self-drilling rock bolts, but is not restricted thereto. 2. Description of Related Art [00031 Rock bolts need to be anchored into boreholes to support the walls and roof of tunnels and mine roadways, often by using some form of mechanical anchor device. These mechanical anchor devices are forced against the inside surface of a borehole wall such that friction is created between the anchor device and the borehole wall so that the anchor device will anchor the rock bolt inside the borehole. These mechanical anchor devices are therefore often referred to as friction anchors. [00041 There are two main types of friction anchor used to secure a rock bolt in a borehole. The first type is where almost the whole length of the bolt is pressed against the borehole wall, and the friction between the bolt and the borehole wall secures the bolt in the borehole. Common rock bolts that use this type of friction anchor are the split set bolt by Ingersoll Rand, and the Swellex bolt by Atlas Copco.

I

WO 2012/027802 PCT/AU2011/001146 [00051 The second type of friction anchor bolt uses a substantially point anchor at the leading end or top end of the rock bolt. This type of point anchor device is typically an expansion shell type anchor. An expansion shell type anchor typically has two or more steel shells which are forced against the internal sides of the borehole wall to create a friction anchor against the rock surface of the borehole wall. The steel shells are forced outwards from the bolt and against the borehole wall by forcing a wedge between the shells. This wedge is typically pulled between the shells by a screw thread, whereby the leading end of the rock bolt is threaded and the wedge is also threaded such that rotation of the bolt causes the wedge to move along the thread on the bolt. As the bolt is rotated the wedge moves along the bolt between the shells and forces the shells outwards against the borehole wall thus anchoring the leading end of the bolt into the borehole. 100061 Typically the wedge has two planar inclined faces which contact two planar inclined faces on the inside of the shells. Typically the wedge moves backwards from the leading end of the bolt towards the trailing end or nut end of the bolt with the narrow end of the wedge facing backwards towards the nut end of the bolt. As the wedge is forced between the shells, the top of the shells are the first part of the shells to be forced outwards by the wedge. [00071 A disadvantage of expansion shell systems is that the expansion shells are designed to be a tight or close fit into a pre-drilled borehole such that the outside of the expansion shells catch on the borehole wall as they are pushed into the pre-drilled borehole so that the expansion shells and the wedge between them remain stationary as the rock bolt is rotated. 100081 Once the expansion shells cannot be expanded against the borehole wall any further, a nut on the bottom or trailing end of the bolt can then be tensioned up against the rock face. This nut may be a separate nut on a thread on the trailing end of the bolt, or may be a forged nut on the trailing end of the bolt and be an integral part of the bolt. As the nut is tensioned up against the rock face, a tensile force is generated in the rock bolt between the nut at the bottom of the bolt, and the expansion 2 WO 2012/027802 PCT/AU2011/001146 shell anchor at the top of the bolt. This type of expansion shell friction anchor is well known and is common in the mining industry. 100091 Typically in an expansion shell bolt, the wedge and shells are fitted over a solid steel bar to form the bolt such that the overall diameter of the bolt is much greater than the diameter of the main steel bar in the bolt. In practice, the diameter of the borehole drilled is just large enough to enable the expansion shells to be forced into the borehole, but small enough such that the expansion shells are just touching the borehole wall such that they do not rotate as the steel bar of the bolt is rotated. The inner planar faces of the shells are then contacting the leading part of the planar faces of the wedges such that the wedges do not rotate as the bar is rotated, and the wedges can then be pulled between the shells by the thread on the bar and through the wedge expansion washer. For example, an expansion shell bolt with a solid steel bar of 16mm in diameter would typically require a 30mm diameter borehole to accommodate the large diameter expansion shells. Solid steel bars of 20mm and 24mm in diameter would require boreholes of 35 and 45mm in diameter respectively to accommodate their respective large diameter expansion shells. Therefore the increase in borehole diameter over the bar diameter just to accommodate the large diameter expansion shells for 16mm, 20mm and 24mm diameter bars respectively, is typically 14mm, 15mm and 21mm. [00101 By having expansion shells and a wedge expansion washer mounted onto a steel bar necessitates the use of a borehole diameter that will accommodate the outer diameter of the shells. However, by keeping the bar diameter substantially the same along its entire length, and in particular where the wedge is screwed onto it, the tensile strength of the bolt is substantially the same along its entire length and there is no loss in tensile strength of the bolt where the expansion shells are located. For this reason known expansion shell bolts have a much larger overall diameter across the expansion shells, than across the main bar of the bolt. 100111 The large diameter borehole which is used to accommodate an expansion shell bolt can then be filled with cement grout or resin. If a grout tube is then fed into the bottom of the borehole, cement grout can then be pumped into the 3 WO 2012/027802 PCT/AU2011/001146 borehole to fill the annulus space between the bolt and the borehole wall such that the bolt can then be fully encapsulated with cement grout. [0012] Expansion shell bolts are sometimes referred to as being pre tensioned, because a tensile force can be generated in the bolt between the anchor point at the leading end of the borehole, and the nut at the trailing end of the rock bolt, prior to the grout or resin encapsulation. [00131 In some applications, an expansion shell bolt can also be installed with a resin cartridge. In this case, a borehole is drilled in the normal manner with a drill rod and drill bit, then a frangible resin cartridge is installed into the borehole. An expansion shell bolt is then pushed into the borehole behind the resin cartridge until the bolt pushes the resin cartridge to the leading end of the borehole. The expansion shell bolt is then pushed through the frangible resin cartridge which then ruptures releasing resin into the borehole. The bolt is then rotated to mix the resin and to expand the shells to anchor the bolt into the borehole. The resin then subsequently cures and hardens fixing the shells in their expanded position against the borehole wall. [00141 Such bolt installations require a relatively large volume of resin to completely fill the borehole, and in practice expansion shell bolts installed with resin cartridges are not fully encapsulated with resin, and the unencapsulated length of bolt can be subject to corrosion. [0015] If rock bolts are to be fully encapsulated with cement grout, then the cement grout is often pumped into the borehole either through a hollow bolt or hollow cable or through a separate grout tube which is inserted into the borehole. A grout pump is used to create sufficient pressure in the grout to enable it to flow through the hollow bolt or grout tube to surround the rock bolt and fully encapsulate the bolt with cement grout in the borehole. The cement grout is then allowed to cure and harden, and once the cement grout has hardened, it fully encapsulates and anchors the rock bolt in the borehole along its entire length. 4 WO 2012/027802 PCT/AU2011/001146 10016] Expansion shell bolts can be installed with or without resin cartridges, or with or without pumpable cement grout or pumpable resin. [00171 Self drilling rock bolts can be anchored and pre-tensioned in boreholes. Current self drilling rock bolts can be anchored and pre-tensioned by using a large diameter friction anchor device on the leading end of the bolt and then subsequently filling the borehole with cement grout or resin. However a disadvantage of such bolts is that they require the use of a large diameter borehole which necessitates the use of a large volume of cement grout or resin to fully encapsulate the bolt. In addition, such bolts often use small diameter bars to try and minimise the borehole diameter required, but this then has the disadvantage that the tensile strength of the bar and hence the bolt, will be limited. [00181 One disadvantage of using expansion shell type mechanical anchors with self drilling rock bolts is that the expansion shell assembly must be closed during the drilling cycle and not be subject to damage. Typically the expansion shell assembly has to be smaller in diameter than the borehole being drilled and stays in the closed position when rotating in the drilling rotation direction. However, when the self drilling rock bolt is rotated in the opposite direction the expansion shell assembly needs to expand inside the borehole. For this to occur, something has to prevent the expansion shell assembly from rotating relative to the bolt as the bolt is rotated in this direction. Typically an arm, or a lug, or a spring, or some other device is used to catch on the inside of the borehole wall to prevent the expansion shell assembly from rotating as the bolt is rotated in the opposite direction to the drilling direction. This arm or lug, or spring, or other device will often also catch on the inside of the borehole wall during the drilling cycle and be subjected to excessive wear as it catches and rubs against the borehole wall. In this case, the arm, or lug, or spring, or other device may then not catch on the borehole wall when the bolt is rotated in the opposite direction to the drilling direction. This is particularly the case in soft rock where the drilled borehole diameter may be several millimetres greater than the drill bit diameter, and also be greater than the diameter of the arm, or lug, or spring, or other device, after it has been subjected to wear and abrasion during the drilling cycle. 5 WO 2012/027802 PCT/AU2011/001146 Conversely, if the arm or lug or spring or other device is made very robust such that it will not wear away through abrasion during the drilling cycle, then the arm or lug or spring or other device may wear away a groove in the borehole wall, particularly in soft rock, such that the arm or lug or spring or other device may still not catch on the borehole wall when rotated in the opposite direction to the drilling direction. [00191 Consequently the use of expansion shell mechanisms with self drilling rock bolts is unreliable and they may not anchor the end of the self drilling rock bolt in the borehole. [00201 It is an object of the invention to provide a mechanical anchor arrangement which overcomes or ameliorates at least some of the above limitations of the prior art, or at least provides users with a choice. SUMMARY OF THE INVENTION 100211 In one form, the invention provides an anchoring assembly for anchoring a bolt within a borehole, comprising a cam member mounted to pivot relative to the bolt from a closed position aligned with the bolt to an expanded position offset from the bolt to anchor the bolt within the borehole. (00221 In one preferred form, the assembly includes an assembly body and leading end member comprising said cam member, the leading end member and anchoring assembly body being connected by an offset connector defining the offset pivot axis. [0023] The cam member may be adapted to remain in the closed position when the bolt is rotated in a first direction and to pivot to the expanded position when the bolt is rotated in a second direction. [0024] Further forms of the invention provide: [00251 a mechanical anchor system fixed to the leading end of a bolt or rock bolt or self drilling rock bolt that it does not significantly increase the overall outside diameter of the rock bolt such that the friction anchor device has a similar diameter to the main bar of the rock bolt; 6 WO 2012/027802 PCT/AU2011/001146 [00261 a mechanical anchor system comprising one or more cams that can rotate about a non-concentric bolt, or pin, or bar within the assembly; 100271 where the cams can rotate in one direction and remain in a closed position, but when they are rotated in the opposite direction the cams can be rotated into an expanded position; 100281 where the leading or front cam is rotated in one direction by the trailing or rear cam, but if the trailing or rear cam is rotated in the opposite direction, the trailing cam will not rotate the leading cam; 100291 where the bolt or pin or bar may be solid or hollow, and where this bolt is hollow, it can allow the passage of drilling fluids or grout or resin through the mechanical anchor assembly; [00301 where the external surfaces of the cams that contact the borehole wall are typically provided with teeth or ridges or deformations to maximise the friction between the cams and the borehole wall; [0031] a mechanical anchoring system comprising one or more cams whereby the cams will remain in a closed position if they are rotated in one direction, but if they are rotated in the opposite direction they will move sideways relative to each other into an expanded position and contact the borehole wall; [00321 a mechanical anchoring system whereby once the cams are rotated into their expanded position and a tensile force is applied to them, the cams will resist rotating back into their closed position thus maintaining a good anchorage in the borehole; 100331 a mechanical anchoring system whereby the cams can be expanded and locked onto the borehole wall with typically less than 180 degrees of rotation and where the external surfaces of the cams are provided with teeth or ridges or deformations to grip into the borehole wall. [00341 In a further form, the invention provides an anchoring assembly for anchoring a bolt within a borehole, comprising a first expansion mechanism adapted to actuate by rotation of the bolt to cause a first expansion of the anchoring assembly from a closed position to a first expanded position in which the anchoring assembly 7 WO 2012/027802 PCT/AU2011/001146 expands against the borehole, and a second expansion mechanism adapted to actuate by axial movement of the bolt to cause a second expansion of the anchoring assembly from said first expanded position to further tighten engagement of the anchoring assembly with the borehole. [0035] Preferably, the first expansion mechanism comprises a cam member mounted to pivot relative to the bolt upon said rotation of the bolt to actuate from a closed position aligned with the bolt to an expanded position offset from the bolt to anchor the bolt within the borehole, and the second expansion mechanism comprises a ramp mechanism actuated by axial movement of the bolt in the borehole. 10036] In a yet further form of the invention, there is provided an anchoring assembly for anchoring a bolt within a borehole in a rock strata, comprising an anchoring assembly body attached to the bolt and an expansion member adapted to contact an inner surface of the borehole, the expansion member and anchoring assembly body having co-operating ramp surfaces such that axial movement of the anchoring assembly body with tightening of the bolt causes expansion of the expansion member against the borehole, and wherein the anchoring assembly responds to additional tensile load on the bolt by movement of the rock strata following anchoring of the bolt in the borehole by further expansion of the anchoring assembly. 10037] Further forms of the invention include rock bolts incorporating the described anchoring assemblies, and methods of securing a rock bolt in a borehole utilising the rock bolts. 100381 In preferred embodiments, the present invention is used with self drilling rock bolts but is not so limited and could be used to anchor any solid or hollow bolts or bars or cables. 100391 Yet further forms of the invention will be apparent from the following description and are set out in the claims. BRIEF DESCRIPTION OF THE DRAWINGS 8 WO 2012/027802 PCT/AU2011/001146 100401 Further preferred embodiments of the invention will now be described with reference to the accompanying drawings, in which: 100411 Figure 1 is a schematic isometric view of a mechanical anchoring assembly having a cam mechanism in accordance with a first embodiment, with hidden details shown in dashed lines. 100421 Figure 2 is a schematic isometric view of a mechanical anchoring assembly of Figure 1. [00431 Figure 3 is a schematic end view of the mechanical anchoring assembly of Figure 1. 100441 Figure 4 is a schematic end view of a mechanical anchoring assembly showing the opposite end to Figure 3. [0045] Figure 5 is a schematic end view of the mechanical anchoring assembly shown in Figure 3, with the assembly in its closed position. [00461 Figure 6 is a schematic end view of the mechanical anchoring assembly shown in Figure 3 with the assembly in its expanded position. [0047] Figure 7 is a schematic isometric view of the anchoring assembly with the assembly in its closed position. 100481 Figure 8 is a schematic isometric view of the mechanical anchoring assembly with the assembly in its expanded position. [0049] Figure 9 is a schematic isometric view of the mechanical anchoring assembly with the assembly in its expanded position. [00501 Figure 10 is a schematic isometric view of a mechanical anchoring assembly according to a second embodiment, including a cam expansion mechanism and expansion shells. 9 WO 2012/027802 PCT/AU2011/001146 [0051] Figure 11 is a schematic exploded isometric view of the mechanical anchoring assembly of Figure 10. 100521 Figure 12 is a schematic end view of the trailing cam member of mechanical anchoring assembly of Figure 10. [00531 Figure 13 is a schematic end view of the leading cam member of the mechanical anchoring assembly of Figure 10. [00541 Figure 14 is a schematic end view of the mechanical anchoring assembly shown in Figures 12 and 13 viewed from the trailing end of the assembly and shown in the closed position a borehole. [0055] Figure 15 is a schematic sectional view of part of the trailing cam member shown in Figures 12 and 13, showing the expansion shell being forced into the borehole wall. 100561 Figure 16 is schematic isometric view of a mechanical anchoring assembly according to a third embodiment, including a cam expansion mechanism and a single expansion shell. 10057] Figure 17 is a schematic exploded isometric view of the mechanical anchoring assembly of Figure 16. 100581 Figure 18 is a longitudinal cross section of the anchoring assembly of Figures 16 and 17 when attached to a self-drilling rock bolt. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 100591 Figures 1 to 9 illustrate a mechanical anchoring assembly 1 according to a first embodiment, consisting of a leading cam member 2 and a trailing member 12 which are connected by a non-concentric pivot mechanism so the leading cam member 2 and the trailing member 12 can move between a closed position (Figures 1 to 5 and Figure 7) in which the two members are axially aligned to an 10 WO 2012/027802 PCT/AU2011/001146 expanded position (Figures 6, 8 and 9) in which the members are out of axial alignment. [00601 The pivot mechanism consists of an internal connector member in the form of connecting bolt 22 (Figures 1, 5 and 6) in aligned bolt holes 5 and 15 of the respective members which are parallel to but not concentric with the longitudinal axis of the assembly 1. Bolt hole 5 of the leading cam member may be threaded 6 for attachment of the bolt 22. [0061] As seen in Figure 3 - a rear end view of the trailing member 12 - the trailing member 12 has a concentric hole 16 on its trailing end, threaded to attach the cam 12 to the end of a self drilling rock bolt (not shown). Figure 3 also shows the non concentric hole 15 to accommodate the connecting bolt 22 (not shown). 100621 As seen in Figure 4 - a front end view of the leading cam member 2 - the leading cam member 2 has a concentric hole 7 on its leading end, threaded to attach the drill bit of the self drilling rock bolt (not shown). Figure 4 also shows the non-concentric hole 5 to accommodate the connecting bolt 22 (not shown). [00631 The cam members 2, 12 have respective passageways 4, 14 to allow the removal of drill cuttings (not shown) from operation of the self drilling rock bolt when the self drilling rock bolt is drilling a borehole. In the illustrated embodiments these passageways take the form of flat portions on the exterior of the leading and trailing members which will form a gap between the anchor assembly and the borehole for escape of the drill cuttings. [00641 The leading cam member 2 and trailing member 12 each has one or more external ribs or teeth 3, 13 to enhance friction when forced against a borehole wall (not shown), as further described below. The ribs 3 and 13 may extend fully or partly around the circumference of the two members. 100651 The cam members have respective drive surfaces 9, 19, operation of which will be described later with reference to Figures 5 to 9. 11 WO 2012/027802 PCT/AU2011/001146 [00661 The leading end of the leading cam member 2 may have a fully or partially chamfered end face 8. The trailing end of the trailing member 12 may also have a fully or partially chamfered end face 18. [0067] Figure 5 is a rear end view of the trailing member 12 attached to the leading cam member 2 with the assembly 1 in its closed position. Rotation of the trailing member 12 - applied by the rotation of the rock bolt (not shown) - in the direction of arrow 24a is transferred to the leading cam via contact of the drive surfaces 9 and 19, keeping keep the members 12 and 2 in the closed position. [00681 Figure 6 is the same view as Figure 5 but with the assembly in its expanded position. Rotation of the trailing member 12 - applied via the rotation of the rock bolt (not shown) - in the direction of arrow 24b will separate the drive surfaces 9 and 19 and thus not transfer the rotational force to the leading cam member 2, allowing relative rotation of the two members about the non-concentric bolt 22 and thereby causing lateral expansion of the anchor assembly. In practice, it will normally be the leading cam member 2 which remains static within the borehole, restrained by contact between the drill bit and the end of the borehole, and the trailing member 12 which rotates about the non-concentric bolt 22. [00691 Figures 7 to 9 illustrate three stages of operation of the anchor assembly. 100701 Figure 7 shows a first stage of operation, with trailing member 12 driven in the direction of arrow 24 during drilling of the borehole by the self-drilling rock bolt (not shown). As discussed above, this rotation is transferred to the leading cam member 2 via the drive surfaces 9 and 19, and thus the two members rotate together in direction 24a and remain in the closed position during drilling. 100711 Figure 8 shows a second stage, after drilling of the borehole in the direction 24a, the trailing member 12 rotated is rotated in the opposite direction (arrow 24b). Figure 8 shows that the drive surface 19 on the trailing member 12 has moved away from the drive face 9 on cam 2 as the trailing cam member 12 has been rotated in direction 24b. Trailing cam 12 rotates with respect to leading cam 2 about the non 12 WO 2012/027802 PCT/AU2011/001146 concentric axis of bolt 22 (not shown in Figure 8), to expand the assembly against the side walls of the borehole (not shown). [0072] Figure 8 more clearly illustrates contact faces 10 and 11 on cam member 2 which can press against contact faces 20 and 21 on cam member 12 to help apply axial thrust during the drilling operation. 100731 Figure 9 shows the mechanical anchor assembly 1 with the cam members 12 and 2 in their fully expanded position and a tensile force applied to the trailing cam member 12 in the direction of arrow 26 by tightening of the nut on the trailing end of the rock bolt (not shown). The expansion of the anchoring assembly 1 against the side walls of the borehole resist this tensile force (in direction of arrow 24c) so that the rock bolt is retained in the borehole. Figure 9 shows that some axial movement of leading cam 2 may occur in direction 24c and some slight separation may occur between leading cam 2 and trailing cam 12 as cam 12 rotates about the non-concentric axis of bolt 22 because the pitch of the thread on the connecting bolt 22 is designed to cause cam 2 and cam 12 to separate as the cams are being expanded (not shown). This is to ensure that the cam faces 10 and 11 do not tighten up and lock against cam faces 20 and 21 as cam 12 rotates and the connecting bolt 22 may rotate about its thread (not shown). [0074] The components of the anchor assembly 1 may be made of any suitably strong and durable material, for example steel or other metal or metal alloy or fibreglass or carbon fibre. 100751 In practice, the trailing member is fixed to the end of a self drilling rock bolt and a drill bit is fixed to the front end of the leading cam member. As the self drilling rock bolt is rotated in the drilling direction, the trailing cam member also rotates and the one way drive mechanism between the two cams causes the leading cam member to also rotate, thus causing the drill bit to rotate to drill the borehole. Water or other flushing fluid can be pumped through aligned passages in the two cam members and through the hollow connecting bolt to the drill bit where it flows out of 13 WO 2012/027802 PCT/AU2011/001146 the self drilling bolt assembly and flushes the drill cuttings away by flowing back down the annular space between the borehole wall and the bolt. [00761 Once the borehole has been drilled, the water is turned off and the drilling rotation is stopped. Then the bolt is rotated in the opposite direction. This causes the trailing member to rotate with the main bar of the rock bolt. However, the drill bit fixed to the front of the leading cam member catches on the borehole wall limiting rotation of the leading cam member. Moreover the leading cam member attached to the drill bit can easily be forced to remain stationary by simply applying axial thrust to the drilling machine such that the tip of the drill bit catches on the end of the borehole. This prevents the drill bit and the leading cam member from rotating. (00771 Consequently the trailing member then rotates with respect to the leading cam member about the non-concentric hollow connecting bolt between the leading cam member and the trailing cam member. Further rotation of the trailing member about the non-concentric bolt causes the outer surface of the trailing member to contact the borehole wall, and increasing rotation of the trailing member causes the opposite side of the leading cam member to contact the other side of the borehole wall, and both the trailing member and the leading cam are therefore forced into opposite sides of the borehole wall. 100781 Rotation of the bolt, and hence rotation of the trailing member, is continued until a pre-determined torque value has been reached. Typically this torque value would be determined by one or more shear pins in the drive nut on the trailing end of the self drilling rock bolt, and this would commonly be between 100 and 300Nm of torque. The greater the torque value applied to the cam members, then the greater the force applied to the cams to force them into the borehole wall and the greater the anchor capacity. 100791 Typically only 40 to 90 degrees of rotation of the trailing member with respect to the leading cam is required to fully anchor the members against the sides of the borehole. Once the members are anchored in the borehole, further 14 WO 2012/027802 PCT/AU2011/001146 rotation causes the shear pins in the nut on the trailing end of the self drilling rock bolt to fail and the nut can then be tensioned up against the rock face. 10080] A suitable nut arrangement is that described in Australian Provisional Patent Application No. 2010905286 filed 1 December 2010, the contents of which are incorporated herein by reference. [00811 If desired, the mechanically anchored rock bolt can then be fully encapsulated with grout or resin. [0082] Figures 10 to 15 illustrate a second embodiment of the invention, which employs a cam expansion mechanism generally similar in concept and operation to that of the first embodiment of Figures I to 9, but with an additional expansion shell mechanism also. Components performing similar functions to those of the previous embodiment are designated by similar reference numerals, but starting from 100. [00831 Figures 10 and 11 show a mechanical anchoring assembly 101 consisting of a leading cam member 102 and a trailing member 112 which forms the main body of the anchoring assembly, connected by an internal connecting bolt 122 offset from the axis of the assembly 101, in a manner similar to that described previously. [00841 As seen in Figure 11, in this embodiment the connecting bolt 122 has a central hole 132 and a female hex drive 133 to allow assembly, but the bolt could be solid. The connecting bolt 122 has an external thread 134 which screws into female threads in holes 105 (Figure 11) and 115 (Figure 12) inside the members 102 and 112. 100851 The trailing member 112 has a threaded hole 116 at its trailing end to receive a hollow connector 125 for attachment to the rock bolt (not shown). Alternatively the trailing member 112 could be fixed to the rock bolt (not shown) by any suitable method. 15 WO 2012/027802 PCT/AU2011/001146 10086] The leading end of the leading cam member 102 is adapted for attachment of a drill bit of a self-drilling rock bolt, as previously described. [00871 Operation of the cam mechanism of the anchoring mechanism is generally similar to that of the previously described embodiment, with rotation of the rock bolt and the trailing member 112 in the drilling direction driving rotation of the leading cam member 102 and its drill bit (not shown) by means of engaged drive surfaces 109 and 119 and retaining the assembly in its closed position, and with reverse rotation of the bolt and trailing member 112 causing expansion of the assembly against the borehole wall surface as previously described. [0088] In the embodiment of Figures 10 to 15, each of the trailing cam member 112 and the leading cam 102 additionally has respective expansion shells 126 fitted to its outside, to provide additional expansion of the anchoring assembly. The expansion shells are held in position around the cams by spring clips 127, located in grooves 128 around the outside of the shells 126. The shells 126 are prevented from rotating about the members 102 and 112 by projections 129 on the outer surfaces of the members. [00891 As best seen in Figures 11 and 15, the trailing cam member 112 has one or more ramp surfaces 130 on its outer surface. The leading cam 102 may have similar one or more ramp surfaces but these cannot be seen in Figure 11. [00901 The inner surfaces of the expansion shells 126 have one or more ramp surfaces 131 which are complementary in angle and pitch to those on the members 102 and 112. The outside surfaces of the shells 126 have a series of external ribs 103 or other friction-enhancing formations which are designed to enhance friction with the borehole wall (not shown) when the assembly is expanded against the borehole wall. 100911 Figure 12 is an end view of the trailing member 112 from the trailing end 136 (Figure 11), with its non-concentric hole 115 for the connecting bolt (not shown), and the expansion shell 126 being prevented from rotating with respect to the member by the projections 129. The drive keyway 119 is shown as a dotted 16 WO 2012/027802 PCT/AU2011/001146 line, as are the matching inclined faces 130 and 131 on the trailing member 112 and the shell 126. The threaded hole 116 for the connector 125 is also shown as a dotted line. [00921 Figure 13 is an end view of the leading cam 102 from the leading end 135 (Figure 11), with the non-concentric hole 115 for the connecting bolt 122 (not shown). The expansion shell 126 fits around the outside of the cam member 102 and is prevented from rotating with respect to the cam member by projections 129. The drive keyway 109 is shown which contacts against the keyway 119 on the trailing cam member (not shown in this view). The inclined or wedge type faces 130 and 131 on the cam member 102 and expansion shell 126 are visible as dotted lines. [0093] Figure 13 also shows water hole 137 through the leading cam member 102 for passage of flushing water. 10094] Figure 14 is a schematic end view of the anchoring assembly 101 viewed from the trailing end 136 (Figure 10), in its expanded position inside a borehole 138. The assembly 101 has been expanded by rotation of the trailing member 112 in direction 139 relative to the leading member 102, to bring the expansion shells 126 of the respective cam members into engagement with the inner surface of the borehole 138. It can be seen that shell 126 on the trailing member 112 bears against the borehole 138 at position 140, and shell 126 on the leading cam bears against the opposite side of the borehole 138 at position 141. 100951 Also visible in Figure 14 are the female hexagonal drive 142 of the cam connecting bolt 122 to facilitate assembly, and central hole 143 in the connecting bolt 122 to allow water or resin or grout to be pumped through the assembly 101. [00961 Figure 15 is a schematic sectional view of part of the trailing member 112 showing the expansion shell 126 being forced further against the borehole wall 138 as the trailing member 112 is pulled axially down the borehole 138 due to tensile load applied by tightening of the nut (not shown) of the rock bolt. The expansion shells 126, already pre-engaged to bear against the borehole wall 138 by actuation of the cam mechanism of the assembly 101 and having external ribs 103 for 17 WO 2012/027802 PCT/AU2011/001146 gripping the borehole surface, are therefore constrained by friction from moving axially along the borehole with the trailing cam member. The ramp surfaces 130, 131 of the cam member 112 and the shell 126 slide along one another as the trailing cam member 112 moves relative to the shell 126, causing further expansion of the assembly 101 and forcing the expansion shell outwards into the borehole wall. This further increases anchoring of the assembly, and therefore the rock bolt to which it is attached, in the borehole. [00971 It will be seen for example from Figure 15 that in the illustrated arrangement the ribbed outer surfaces of the expansion shells 126 expand outwards but remain generally parallel with the borehole wall and therefore contact with the borehole surface substantially along the whole of their length rather than just as a point contact. 100981 Further tensile force applied to the assembly, for example by shifting of the rock strata, will automatically cause further expansion of the expansion shell mechanism of the assembly 101 without manual intervention. [00991 The illustrated embodiment of Figures 10 to 15 therefore provides not only a quick initial securing mechanism for the rock bolt by means of the cam actuation, but further provides an 'active' anchoring mechanism whereby the frictional engagement of the anchoring assembly in the borehole increases with increasing axial tensile force on the rock bolt. [001001 Figure 15 also shows that the shell 126 on the trailing cam member 112 is not directly opposed by the other expansion shell 126 digging into the borehole 138 wall, because the shell 126 on the leading cam 102 (not shown in this Figure) is further along the borehole 138. The outward forces of the two shells 126 - which could cause tensile fracturing and failure of the borehole wall 138 - are therefore also offset, and therefore the likelihood of tensile fracturing of the borehole is reduced. [001011 Figures 16 to 18 illustrate a third embodiment of the anchoring assembly, generally similar in operation to the second embodiment of Figures 10 to 18 WO 2012/027802 PCT/AU2011/001146 15. Similar reference numerals are used for similar components to those previously described and illustrated, but starting with 200. [001021 Figure 16 is an isometric view of the anchoring assembly 201, and Figure 17 is an exploded view. Figure 18 is a longitudinal cross-section of the anchoring assembly 201 fitted to a leading end of a self-drilling rock bolt 260, and with a drill tip (body 261, tip 262) attached to the leading end of leading cam member 202. [00103] The anchoring assembly 201 has a leading cam member 202 pivotably connected by an offset hollow connecting bolt 222 with female hex drive 233 to the body of the assembly (trailing member 212) and with a keyway having mating drive surfaces 209, 219, all operating generally as described above in relation to the previous embodiments, in order to cause a first stage cam expansion of the anchoring assembly within the borehole 238 when the bolt 260 is rotated a part turn in the opposite direction from the drilling direction. 100104] The anchoring assembly differs from that of Figures 10 to 15 in the provision of a single expansion shell 226, on the trailing member 212 only, with the leading member 202 having fixed external ribs 203 instead. 1001051 The leading member 202 may have an exterior flat passageway portion 204 between the ribs 203, similar to the passageway 4 of the first embodiment, for allowing escape of drill cuttings and fluids. 1001061 On one exterior surface of the trailing member 212 is a ramp surface 230 adapted to cause expansion of the anchor with relative axial movement of the trailing member 212 and the expansion shell 226. The ramp surface 230 has a pair of angled slots 250 which receive re-entrant projections 251 on the inner surface 252 of the expansion shell 226 to allow the shell to track along the ramp surface 230. In one form, as illustrated, the projections 251 may be angled parallel to the angle of the ramp surface. In this way, the slots 250 are parallel with the projections 251 on the shell 226, such that the projections 251 will slide in the slots 250 while holding the shell 226 onto the trailing member 212. The shell 226 is therefore held onto the 19 WO 2012/027802 PCT/AU2011/001146 assembly while allowing the shell 226 to track along the ramp surface and replacing the need for the spring clips 127 of Figure 10. The shell 226 is therefore securely held onto the assembly during the drilling operation by the above projections 251 and slots 250. 1001071 Other projection and slot arrangements may be used, for example one or more re-entrant slots with matching projection shapes, such as dove-tailed, or Y- or T-shaped. [00108] Other arrangements for attaching the shell 226 to the body of the anchoring assembly may be used, and temporary attachments such as elastic band and/or shrink wrap plastic (not shown) may also be used to secure the shell onto the assembly during initial stages of handling, transportation and installation. 100109] The trailing end 254 of the shell 226 may have a wedged shape to nest in a similarly angled recess 253 in at the end of the ramp surface 230 when the expansion shell is fully retracted, to further secure the shell in place during the drilling operation. [001101 In use, the anchoring assembly 201 is attached to the leading end of a self-drilling rock bolt by the connector 225, with both the cam mechanism and expansion shell 226 in their fully retracted positions so that the anchoring assembly is of similar diameter to the rock bolt. A drill tip 261, 262 is screwed into the leading end of the leading member 202 of the assembly but may be fixed to the leading member 202 by any suitable method. [001111 The rock bolt with drill tip is brought against the surface to be drilled and is rotated in the drilling direction, typically in a counterclockwise direction, to cause the drill tip to drill the borehole 238. Meanwhile, a flushing liquid, typically water, is injected via communicating passageways in the hollow connector 225, trailing cam member 212 and via hollow connection bolt 222 to the end surface being drilled to flush away the cuttings and leaving via the gap between the rock bolt and the borehole. These passageways are best seen in Figure 18. 20 WO 2012/027802 PCT/AU2011/001146 1001121 After drilling has stopped, axial thrust is then applied to the bolt via the drilling machine so that the cutting tip frictionally engages the end of the borehole and prevents rotation of the leading cam member 202. [001131 Rotation of the bolt in the opposite direction by a part turn will cause the cam function of the anchor to actuate, forcing the ribbed surface of the leading cam member 202 against an inner surface of the borehole 238, and the still retracted expansion shell 226 on the trailing member 212 against a generally opposite inside surface of the borehole. [00114] In practice, when the cams are expanded in the borehole, a high rotational torque is applied to the bolt to force the ribs or teeth on the outside of both parts of the cam mechanism to grip into the borehole wall such that the expansion shell will not move axially in the next stage as tensile load is applied to the rock bolt. [001151 The nut at the bottom of the rock bolt is then tightened to apply tensile load, causing actuation of the expansion shell, the axial movement of the trailing cam member causing the expansion shell 226 to slide along the ramp surface and expand outwardly. As the expansion shell 226 is already pressed against the borehole by the cam mechanism, further movement of the shell 226 outwards into the borehole wall is very limited. Consequently, as the shell 226 is prevented from moving further outwards by the borehole wall, the shell 226 therefore prevents movement of the trailing cam member 212 axially down the borehole. Therefore only a small number of further turns of the nut may be required to achieve the required torque and fully tighten the rock bolt into the borehole. In addition, if the axial tensile load on the bolt increases due to subsequent rock movement, the shell 226 is forced further outwards into the borehole wall and therefore the shear strength between the borehole wall and the shell 226 increases. Consequently the anchor capacity of the invention increases as the applied axial load increases, and therefore the invention is an "active" mechanical anchor. 21 WO 2012/027802 PCT/AU2011/001146 [00116] Optionally, once the mechanical anchor is secured, grout or resin may be pumped through the bolt to fill the space between the bolt and the borehole and fully encapsulate the bolt with grout or resin. 100117] Thus, the embodiments of the invention allow self-drilling rock bolts to be installed and anchored quickly and to subsequently be fully grouted with resin or grout if desired. [001181 The illustrated embodiments have been illustrated and described as configured for left hand rotation for drilling a borehole and using right hand rotation for expanding the mechanical anchor assembly but is not so limited and could be used with the opposite rotation to that described. 1001191 In an unillustrated embodiment, the drill bit may be fixed to a separate cam at the leading end of the rock bolt, which is connected to a central cam, which in turn is connected to a trailing cam which is fixed to the rock bolt. In practice, this embodiment of the invention enables the drill bit cam to move sideways in the borehole relative to the central cam, such that the drill bit and the drill bit cam are not forced into the borehole wall as the cams are opened and expanded, and thus the drill bit and the drill bit cam does not restrict the central cam from being forced into the borehole wall. [001201 In a further unillustrated embodiment, and expansion mechanism similar to that of Figures 10 to 15 or Figures 16 and 17 may be used without a cam mechanism, or with a different pre-expansion mechanism. [001211 In this specification, the word "comprising" is to be understood in its "open" sense, that is, in the sense of "including", and thus not limited to its "closed" sense, that is the sense of "consisting only of'. A corresponding meaning is to be attributed to the corresponding words "comprise, comprised and comprises where they appear. 22 WO 2012/027802 PCT/AU2011/001146 1001221 Where the specification refers to a "drill bit" or to a "drill tip" it is to be understood that the invention includes all such variations and modifications of the above, including any device that can be use to drill a borehole in rock. [001231 Where the specification refers to a "cam" it is to be understood that such reference includes all such variations and modifications of a cam including any shaped member that can pivot or rotate about a non-concentric bolt, pin or rod or similar to expand laterally within the borehole. 1001241 Where the specification refers to a "closed position" or to "cams in their closed position" it is to be understood that the invention refers to the smallest diameter formed by the outside of two or more cams when they are assembled to form the mechanical anchor assembly. 100125] Where the specification refers to an "expanded position" or to "cams in their expanded position" it is to be understood that the invention refers to any diameter greater than the smallest diameter formed by the outside of two or more cams when they are assembled to form the mechanical anchor assembly. [001261 While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. It will further be understood that any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates. [001271 While the offset pivot mechanism disclosed in the preferred embodiments is a connecting bolt it is to be understood that the invention includes all such variations and modifications of a non-concentric bolt including any solid or 23 WO 2012/027802 PCT/AU2011/001146 hollow bolt or pin or rod which is axially non-concentric with respect to one or more cams and around which one or more cams can rotate. 1001281 Furthermore, it is to be understood that whilst the invention is described primarily as for use with self-drilling rock bolts, it may be used with other types or rock bolts and variants thereof, whether hollow or solid, including cable bolts and injection rods or tubes, and reference herein to "bolt" or "rock bolt" includes all such variations and modifications of the above including any long hollow elongate member including self drilling rock bolts. 24

Claims (25)

1. An anchoring assembly for anchoring a bolt within a borehole, comprising a cam member mounted to pivot relative to the bolt from a closed position aligned with the bolt to an expanded position offset from the bolt to anchor the bolt within the borehole.

2. An anchoring assembly according to claim 1, wherein said cam member is mounted to pivot about a pivot axis offset from a centre longitudinal axis of the bolt.

3. An anchoring assembly according to claim 2, wherein the pivot axis is defined by a connector member securing the cam member in the anchoring assembly.

4. An anchoring assembly according to claim 1, comprising an anchoring assembly body adapted for connection to the bolt, and a leading end member comprising said cam member, the leading end member and anchoring assembly body being connected by an offset connector defining said offset pivot axis.

5. An anchoring assembly according to claim 1, wherein the cam member is adapted to remain in the closed position when the bolt is rotated in a first direction and to pivot to the expanded position when the bolt is rotated in a second direction.

6. An anchoring assembly according to claim 5, including a drive arrangement adapted to drive rotation of the cam member with the bolt when the bolt is rotated in said first direction.

7. An anchoring assembly according to claim 6, further including means for hindering rotation of the cam member with the bolt when the bolt is rotated in the second direction so to cause pivoting of the cam member.

8. An anchoring assembly according to claim 7,wherein the bolt is a self-drilling rock bolt and the means for hindering rotation of the cam member comprises a drill tip of the self-drilling rock bolt which is attached to the cam member and is adapted to engage an end of the borehole to hinder rotation of the cam member. 25 WO 2012/027802 PCT/AU2011/001146

9. An anchoring assembly according to claim 1, wherein the rock bolt is a self drilling rock bolt, and wherein a drill tip of the rock bolt is mounted to said cam member.

10. An anchoring assembly according to claim 9, wherein the cam member and drill tip are adapted to rotate with the bolt when the bolt is rotated in a first drilling direction, and to pivot relative to the bolt to the expanded position when the bolt is rotated in a second direction.

11. An anchoring assembly according to claim 9, further comprising fluid passageways for passage of a flushing fluid.

12. A rock bolt adapted for anchoring within a borehole, including: a rock bolt member; a tightening nut; and an anchoring assembly according to claim 1

13. A rock bolt according to claim 12, being a self-drilling rock bolt, and further comprising a drill bit mounted on the anchoring assembly.

14. An anchoring assembly for anchoring a bolt within a borehole, comprising a first expansion mechanism adapted to actuate by rotation of the bolt to cause a first expansion of the anchoring assembly from a closed position to a first expanded position in which the anchoring assembly expands against the borehole, and a second expansion mechanism adapted to actuate by axial movement of the bolt to cause a second expansion of the anchoring assembly from said first expanded position to further tighten engagement of the anchoring assembly with the borehole.

15. An anchoring assembly according to claim 14, wherein said first expansion mechanism comprises a cam member mounted to pivot relative to the bolt upon said rotation of the bolt to actuate from a closed position aligned with the bolt to an expanded position offset from the bolt to anchor the bolt within the borehole. 26 WO 2012/027802 PCT/AU2011/001146

16. An anchoring assembly according to claim 14, wherein the second expansion mechanism comprises a ramp mechanism actuated by axial movement of the bolt in the borehole.

17. An anchoring assembly according to claim 16, wherein the ramp mechanism comprises an expansion member having at least one ramp surface, co-operating with a further ramp surface on the anchoring assembly to cause said second expansion.

18. An anchoring assembly according to claim 17, wherein the expansion member is an expansion shell on an outer surface of the anchoring assembly and adapted to contact the borehole surface.

19. An anchoring assembly according to claim 18, wherein the second expansion mechanism is adapted to respond to additional tensile load on the bolt following anchoring of the bolt in the borehole by expanding further.

20. A rock bolt adapted for anchoring within a borehole, including: a rock bolt member; a tightening nut; and an anchoring assembly according to claim 14.

21. A rock bolt according to claim 20, being a self-drilling rock bolt, and further comprising a drill bit mounted on the anchoring assembly.

22. An anchoring assembly for anchoring a bolt within a borehole in a rock strata, comprising an anchoring assembly body attached to the bolt and an expansion member adapted to contact an inner surface of the borehole, the expansion member and anchoring assembly body having co-operating ramp surfaces such that axial movement of the anchoring assembly body with tightening of the bolt causes expansion of the expansion member against the borehole, and wherein the anchoring assembly responds to additional tensile load on the bolt by movement of the rock 27 WO 2012/027802 PCT/AU2011/001146 strata following anchoring of the bolt in the borehole by further expansion of the anchoring assembly.

23. An anchoring assembly according to claim 22, wherein the expansion member is an expansion shell on an outer surface of the anchoring assembly body.

24. A rock bolt adapted for anchoring within a borehole, including: a rock bolt member; a tightening nut; and an anchoring assembly according to claim 22.

25. A rock bolt according to claim 20, being a self-drilling rock bolt, and further comprising a drill bit mounted on the anchoring assembly 28