Rock bolt

Abstract

A rock bolt includes a tube having a leading end and a trailing end. An expander mechanism is disposed within the tube near the leading end. An elongate bar is disposed within the tube and is connected at a first end with the expander mechanism and at a second end with an anchor arrangement positioned at the trailing end of the tube. The elongate bar is arranged to actuate the expander mechanism and remain connected between the expander mechanism and the anchor arrangement while the expander mechanism is actuated. The tube has a displaceable wall section at the leading end, which has a hinge end proximal the leading end connecting the displaceable wall section to the tube. The expander mechanism can be actuated to displace the displaceable wall section to rotate about the hinge end to shift the anchor end outwardly from the tube.

Claims

1. A rock bolt comprising: an elongate, circular tube, the tube having a leading end and a trailing end; an expander mechanism disposed within the tube in a region of the leading end; and an elongate bar or cable disposed longitudinally within the tube and in connection at or towards a first end of the bar or cable with the expander mechanism and in connection at or towards a second and opposite end of the bar or cable with an anchor arrangement positioned at the trailing end of the tube, the elongate bar or cable being actuatable to actuate the expander mechanism and to remain connected between the expander mechanism and the anchor arrangement when the expander mechanism is actuated, wherein the tube has at least one displaceable wall section in the region of the leading end the displaceable wall section having a hinge end proximal to the leading end connecting the at least one displaceable wall section to the tube, and side walls extending from the hinge end to an anchor end distal to the leading end the expander mechanism being actuatable to displace the at least one displaceable wall section to rotate about the hinge end to shift the anchor end outwardly from the tube.

2. The rock bolt according to claim 1, wherein the at least one displaceable wall section is formed integrally with the tube at the hinge end.

3. The rock bolt according to claim 2, wherein the at least one displaceable wall section is disconnected from the tube other than at the hinge end.

4. The rock bolt according to claim 1, wherein the at least one displaceable wall section is a section of wall of the tube that is separated from the surrounding tube by a groove or slot, so that the at least one displaceable wall section can be displaced outwardly from the tube wall.

5. The rock bolt according to claim 4, wherein the displaceable wall section is disconnected from the tube other than at the hinge end.

6. The rock bolt according to claim 1, wherein the hinge end of the at least one displaceable wall section includes a hinge portion that is connected to the tube and a free portion on either side of the hinge portion that is disconnected from the tube and that extends to the side walls of the at least one displaceable wall section.

7. The rock bolt according to claim 1, wherein the at least one displaceable wall section is separately connectable to the tube.

8. The rock bolt according to claim 1, wherein the at least one displaceable wall section comprises two displaceable wall sections at a same axial position of the tube and spaced apart about a circumference of the tube, such as and diametrically opposed.

9. The rock bolt according to claim 1, characterised by including wherein the at least one displaceable wall section comprises at least two displaceable wall sections axially spaced apart longitudinally along the tube.

10. The rock bolt according to claim 9, wherein the at least one displaceable wall section comprises a first group of displaceable wall sections is provided proximal the leading end of the tube and a second group of displaceable wall sections is provided axially spaced towards the trailing end of the tube.

11. The rock bolt according to claim 9, wherein the at least one displaceable wall section comprises a first pair of diametrically opposed displaceable wall sections provided proximal the leading end of the tube and a second pair of diametrically opposed displaceable wall sections provided axially spaced towards the trailing end of the tube.

12. The rock bolt according to claim 1, wherein the at least one displaceable wall section has a square or rectangular configuration.

13. The rock bolt according to claim 1, wherein the expander mechanism includes a mobile wedge and a displaceable wedge, the mobile wedge being connected to the elongate bar or cable and the displaceable wedge being associated with the inside of the at least one displaceable wall section, whereby actuation of the bar or cable is operable to shift the mobile wedge axially within the tube and to interact with the displaceable wedge to displace the at least one displaceable wall section to rotate about the hinge end.

14. The rock bolt according to claim 13, wherein the at least one displaceable wall section is restrained against rotation beyond a maximum rotation by a retainer that engages an inside surface of the tube when the at least one displaceable wall section has reached a point of maximum displacement to prevent further rotating movement of the at least one displaceable wall section.

15. The rock bolt according to claim 14, wherein retainer extends from a lower or bottom region of the displaceable wedge.

16. The rock bolt according to claim 1, wherein the tube includes a longitudinal split extending a length of the tube through the leading and trailing ends.

17. The rock bolt according to claim 16, wherein the at least one displaceable wall section comprises a pair diametrically opposed displaceable wall sections provided proximal the leading end of the tube.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which:

(2) FIG. 1 is a cross-sectional view of a rock bolt according to one embodiment of the invention with the rock bolt in a pre-deployed state.

(3) FIG. 2 is a cross-sectional view of the rock bolt of FIG. 1 with the rock bolt in a deployed state.

(4) FIG. 3 is a view of the displaceable wall section of the rock bolt of FIG. 1.

(5) FIG. 4 is a perspective view of the rock bolt of FIG. 2.

(6) FIG. 5 is an end view of the rock bolt of FIG. 2.

DETAILED DESCRIPTION

(7) FIG. 1 is a cross-sectional view of a rock bolt 10 according to one embodiment of the invention with the rock bolt in a pre-deployed state and ready for installation in a drilled bore or hole. The rock bolt 10 includes an elongate, generally circular tube 12 that has a leading end 14 and a trailing end 16. The length of the rock bolt 10 would ordinarily be in the order of about 2 m, and so the bolt 10 is shown in FIG. 1 with a break through the length of the tube 12.

(8) The tube 12 is formed with a gap or split along its full length (see the split 68 shown in FIG. 5 and described later herein) so that the rock bolt 10 is known as a split set as previously described. The split is not visible in FIG. 1 or 2. Thus, in normal operations where the rock strata can support a split set, the tube 12 would be percussion driven into a hole that has an inner diameter which is smaller than the outside diameter of the tube 12. The tube 12 would thus radially contract in diameter to fit into the hole and by that contraction, would frictionally engage the inner surface of the hole. The split set is held within the hole by that frictional engagement. In some forms, the present invention modifies the split tube 12 as described below to enable it to anchor within rock strata that does not have sufficient structural integrity to anchor by frictional engagement only. As would be apparent from the foregoing discussion, the present invention has been developed for installation of the rock bolt 10 in rock strata which is weak so that the frictional engagement normally employed by a split set does not appropriately anchor the rock bolt within the hole.

(9) The bolt 10 includes an expander mechanism 18 that includes a mobile wedge 20 that is threadably connected to the leading end 22 of an elongate rod 24. The rod 24 extends for substantially the full length of the tube 12, between the leading and trailing ends 14, 16 of the tube 12. The leading end 14 of the rod 24 is threaded and the wedge 20 is threadably connected to the leading end 22. The trailing end 16 of the rod 24 is formed as a nut 26 so that the nut 26 and the rod 24 are integrally connected. Rotation of the nut 26 rotates the rod 24 and by restraining the wedge 20 against rotation with the rod 24, the wedge 20 can be shifted on the threaded section 30 lengthwise of the rod 24.

(10) In a cable bolt, the wedge can be fixed to the leading end of the cable and the wedge can be shifted longitudinally within the tube by pulling or tensioning the trailing end of the cable. The trailing end of the cable can be anchored at the trailing end of the rock bolt by what is known as a barrel and wedge arrangement, which allows the cable to be pulled or tensioned in one direction and which clamps the cable against movement in the opposite direction.

(11) Returning to FIG. 1, the nut 26 bears against a washer 32 which in turn bears against a circular ring 34 that is welded to an outer surface of the tube 12. When the rock bolt 10 is installed in a hole, the ring 34 bears against a rock plate. This arrangement is shown in FIG. 2 in which the bolt 10 is shown installed within a hole H. In FIG. 2, the sleeve 36 in engagement with a rock plate 38 that bears against a facing surface 40 of the rock strata within which the bolt 10 is installed.

(12) The rock bolt 10 includes a pair of diametrically opposed displaceable wall sections 42 and 44. The wall sections 42 and 44 are shown in FIG. 1 coextensive with the tube 12, while in FIG. 2, they are shown displaced outwardly, embedded in the rock strata.

(13) A single displaceable wall section 42 is shown in FIG. 3 and that figure shows that the wall section 42 is formed to be generally rectangular so that the wall section 42 has a pair of generally parallel side walls 46 and a bottom edge 48. The wall section 42 is separated from the surrounding tube 12 by a groove or slot 50. The slot 50 can be cut into the tube 12 before the tube 12 is formed/rolled into its circular configuration. Thus, the groove 50 can be cut into a flat metal sheet or flat tube blank prior to the blank being rolled to form the tube 12. The groove 50 can be cut in any suitable manner, such as by laser, water jet or flame. The groove 50 can also be cut into a tube that has already been formed/rolled, by cutting or stamping.

(14) The wall section 42 remains connected to the tube 12 at a hinge end or section 52. The groove 50 include two inwardly depending free portions or groove sections 54 which terminate prior to meeting, so that the hinge section 52 is left in place and thus connects the wall section 42 to the adjacent part of the tube 12. The inwardly depending groove sections 54 are not essential, but the provision of the sections 54 reduces the effort required for the outward displacement of the wall section 42 from the coextensive position shown in FIG. 1, to the displaced position shown in FIG. 3. The sections 54 can be longer or shorter than shown in FIG. 3 to alter the effort required for the outward displacement of the wall section 42. If the sections 54 are shorter, then the effort increases, because the amount of metal between the wall section 42 and the tube 12 that needs to be bent for the wall section 42 to displace outwardly increases. Likewise, if the sections 54 are longer, the amount of metal between the wall section 42 and the tube 12 reduces and so the effort to bend the wall section 42 about the hinge section 52 reduces.

(15) As previously described, the rock bolt 10 has been developed for use in strata that is relatively weak, for example in strata that has been that has been consolidated with cement paste. The rock bolt 10 is intended to provide a more secure anchorage within the hole H (FIG. 2) within which the bolt 10 is installed, compared to traditional frictional rock bolts that anchor within a hole by virtue of frictional engagement with the facing walls of the hole. In contrast, the bolt 10 shown in the figures anchors within the hole H by displacement of the wall sections 42 and 44 outwardly to the position shown in FIG. 2, so that the wall sections 42 and 44 gouge into and become embedded in the surrounding rock strata and by that embedding, the bolt 10 is securely anchored within the rock strata. In particular, the bottom edge 48 of the wall sections 42 and 44 forms an anchor end of the sections 42 and 44 that tends to dig into the strata 58 immediately below it, thus resisting longitudinal movement of the bolt 10 within the hole H.

(16) The wall sections 42 and 44 are shifted between the coextensive position shown in FIG. 1 and the outwardly displaced position shown in FIG. 2 by movement of the mobile wedge 20 relative to fixed wedges 60 that are connected to or fixed to the inside surface of each of the wall sections 42 and 44. The fixed wedges 60 can be fixed to the inside surface of the wall sections 42 and 44 in any suitable manner, such as by welding, soldering, brazing, or by fastener fixing.

(17) Each of the fixed wedges 60 has an inclined wedge surface 62. The wedge surfaces 62 can be flat or planar, or they can be slightly concave or convex. The outside surface of the mobile wedge 20 is likewise inclined and has a profile to match the surface of the fixed wedges 60. As will be evident from the transition of the wall sections 42 and 44 between FIGS. 1 and 2, as the mobile wedge 20 is shifted along the threaded section 30 of the rod 24 in the direction of the trailing end 28 of the rod 24, the wall sections 42 and 44 are pushed outwardly, rotating about the hinge section 52 to reposition the bottom edge 48 of each wall section 42 and 44 into the adjacent rock strata 58. A perspective view of the rock bolt 10 showing the wall sections 42 and 44 displaced outwardly from the tube 12 in accordance with FIG. 2 is shown in FIG. 4.

(18) Thus, to displace the wall sections 42 and 44 outwardly, the nut 26 is rotated by a suitable driver, such as a hydraulic driver, so that the rod 24 rotates. The mobile wedge 20 is restrained against rotation with the rod 24 by the engagement of the inclined wedge surface 62 of the wedge 20 with the wedge surfaces 62 of the fixed wedges 60. The wedge 20 thus shifts longitudinally downwardly along the threaded section 30 from the upper position shown in FIG. 1 to the lower position shown in FIG. 2.

(19) As the wedge 20 shifts along the threaded section 30 of the rod 24, the wall sections 42 and 44 are simultaneously pushed or displaced outwardly. The effort to displace the wall sections 42 and 44 outwardly is the sum of the effort required to bend the metal of the tube 12 in the hinge section plus the effort required to displace the rock strata for the wall sections 42 and 44 to push into the rock strata.

(20) It may not be necessary for the wall sections 42 and 44 to be displaced to their maximum displacement as shown in FIG. 2. The rock strata may have sufficient integrity that it resists the wall sections 42 and 44 being displaced to the maximum displacement. Moreover, the rock bolt 10 may achieve some frictional anchorage by engagement between the outside surface of the tube 12 and the facing surface of the hole H. That frictional anchorage may vary along the length of the tube 12. However, the rock bolt 10 is intended to anchor within the hole H principally by the displaced wall sections 42 and 44 embedding in the rock strata and any additional anchorage achieved through frictional engagement with the facing surface of the hole H is beneficial to the security of the anchorage but is not relied on.

(21) The wedge 20 may therefore be driven to a position that is intermediate the upper position of FIG. 1 and the lower position of FIG. 2. The hydraulic drive may include a limiter that applies a maximum torque to the nut 26, so that once that maximum torque has been reached, no matter if the wedge 20 has not reached the maximum displaced position of the wall sections 42 and 44 shown in FIG. 2, the nut 26 is no longer rotated.

(22) It will be appreciated that regardless of the position to which the wedge 20 is driven on the threaded section 30 of the rod 24, the wedge 20 will remain in contact with the inclined wedge surfaces 62 of the fixed wedges 60 and thus will resist return movement of the wall sections 42 and 44 from the displaced position. While the wall sections 42 and 44 will not naturally return from the displaced positions because bending of the hinge section 52 is plastic and thus permanent, movement of the rock strata can push against the displaced wall sections 42 and 44 and so the continued contact between the wedge 20 and the fixed wedges 60 resists any inward pushing load and thus ensures that the wall sections 42 and 44 retain their displaced position.

(23) FIG. 5 is an end view of FIG. 4 taken from the leading end 14 of the tube 12. FIG. 5 thus shows the very top edge 64 of the tube 12, along with the short split 66 that is created in the flat tube blank so that the leading end 14 can be formed into a cone to assist entry of the leading end 14 into the opening of the hole H. FIG. 5 further shows the split 68 that extends along the full length of the tube 12 to form the rock bolt 10 as a split set as previously described.

(24) FIG. 5 illustrates the displaceable wall sections 42 and 44 in the displaced positions of FIGS. 2 and 4 and illustrates the continued connection between the wall sections 42 and 44 with the tube 12 at the hinge sections 52.

(25) Referring back to FIG. 2, in the displaced position of the displaceable wall sections 42 and 44, the bottom edge 48 or anchor end of the wall sections 42 and 44 has been pushed into the rock strata surrounding the tube 12. As shown in FIGS. 1 and 2, the wedges 60 have a bottom face 56 and as shown in FIG. 2, that face 56 is solid rather than open, which gives strength to the wedges 60 and gives them a greater area for contact with the rock strata in which they embed improving resistance to movement and removal of the rock bolt 10 from the hole H.

(26) The inclined wedge surfaces 62 continue beyond the bottom edge 48 of the wall sections 42 to form a retainer 70. The retainers 70 set the maximum angle of rotation of the wall sections 42 and 44 about the hinge sections 52. As shown in FIG. 1, prior to deployment of the wall sections 42 and 44, the retainers 70 are inside the tube 12 and extend to either side of the rod 24. This can occur because the retainers are curved and curve about the rod 24, or the retainers 70 can include a gap for the rod 24 to pass through. When the wall sections 42 and 44 have been displaced to the maximum displacement positions of FIG. 2, the retainers 70 shift to a position of engagement with the inside surface of the tube 12 directly below where the bottom edge 48 of the wall sections 42 and 44 is positioned the FIG. 1. It will be appreciated that once the retainers 70 engage against the inside surface of the tube 12, no further outward displacement of the wall sections 42 and 44 is possible. This is advantageous from the perspective of preventing over displacement of the wall sections 42 and 44. Over displacement would be problematic if the wall sections 42 and 44 were to displace to a position in which they could pass through a 90 rotation and thus experience a loss in the anchoring effect they provide, such as in the position shown in FIG. 2. This over displacement could occur for example, if the rock strata below the wall sections 42 and 44 were to shift and to drag the trailing end 16 of the tube 12 downwardly.

(27) The retainers 70 also provide additional benefits to the installation and operation of the rock bolt 10. When the retainers 70 engage against the inside wall of the tube 12, the mobile wedge 20 is prevented from further downward movement on the threaded section 30 of the rod 24. This gives installation personnel a tactile indication that the wall sections 42 and 44 have reached their maximum displaced position so that the installation personnel are aware that the rock bolt 10 has been appropriately deployed within the hole H. As indicated above, in the maximum displaced positions, the wedge 20 remains in contact with the inclined wedge surfaces 62 of the wedges 60, thus preventing inward return of the wall sections 42 and 44.

(28) The retainers 70 could be formed inboard of the position shown in FIGS. 1 and 2, so that they could extend from the bottom face 56 between the wall sections 42 and 44 and the inclined wedge surfaces 62 of the wedges 60 in order to change the maximum displaced position of the wall sections 42 and 44.

(29) The wedge 20 can be controlled in the maximum amount of travel it has relative to the rod 24 by terminating the threaded section 30. This is seen in FIG. 1 in which the rod 24 transitions from the threaded section 30 to a non-threaded bar at transition point 72. The rod 24 could be widened at the transition point 72 to provide an actual stop that the wedge 20 engages at the point of maximum travel.

(30) With reference to FIG. 5, it would be evident that a third displaceable wall section could be included in the tube 12 midway between the wall sections 42 and 44 and in line with the short split 66. A fourth wall section, opposite the third wall section, could not be included, as that section of the tube 12 is the longitudinal split 68. However, in rock bolt tubes that are not formed as split sets so that they do not employ a longitudinal split, a fourth wall section could be employed, so that the first pair of wall sections 42 and 44 would be accompanied by a second set of diametrically opposed wall sections, with the four wall sections equidistantly spaced apart. The wedge 20 could be arranged to cooperate with a third wall section, or a third and fourth wall section.

(31) It is also possible that additional wall sections could be formed in the wall of the tube 12 axially spaced beneath the wall sections 42 and 44, either directly beneath them, or displaced circumferentially to be offset from the upper wall sections. For this, the expander mechanism 18 would need to be modified, such as to include two or more axially spaced mobile wedges.

(32) 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.