AU2012201878B1 - Friction bolt - Google Patents

Abstract

A friction bolt 10 including an elongate tube 11 and an expander mechanism 14 within the tube. An elongate bar 19 extends within the tube between the expander mechanism 14 and an anchor 24. The expander mechanism 14 has an element 16 secured to the tube 11 and an element 15 secured to the bar 19. The element 16 has a first inclined face 31 and a second inclined face 33. The second face 33 is inclined at a greater angle to the face 31. The element 15 has a face for bearing engagement with an inside surface of the tube and a second face for bearing against the first and second faces 31 and 33 of the element 16.

Description

P/00/011 Regulation 3.2 AUSTRALIA Patents Act 1990 ORIGINAL COMPLETE SPECIFICATION STANDARD PATENT Invention Title: FRICTION BOLT Applicant: Sandvik Intellectual Property AB The following statement is a full description of this invention, including the best method of performing it known to me: 1 6067 SYC 2 FRICTION BOLT TECHNICAL FIELD The present invention relates to a rock bolt for use in rock strata for the purpose of stabilising the strata against fracture or collapse. The present invention is concerned principally with friction rock bolts which are known in the industry as "split sets" or "friction stabilisers". The basic form of this kind of rock bolt consists of a steel tube that is forced into a bore drilled into rock strata, so that the external surface of the tube frictionally engages the internal surface of the bore. Thus, the tube is frictionally anchored within the bore and by that anchoring, the rock strata is stabilised. The present invention relates to a particular form of this kind of rock bolt which is radially expandable, such as by a longitudinal split through the length of the tube and which is includes an internal expansion arrangement to promote radial expansion and thus to enhance the frictional engagement of the bolt with the internal surface of the bore. This form of rock bolt is known as an expansion rock bolt. BACKGROUND TO THE INVENTION Expansion rock bolts are installed by drilling a bore into the rock strata, inserting the rock bolt into the bore and expanding the expansion mechanism within the tube of the bolt. This method of insertion is relatively simple and is in contrast with other forms of rock bolts that employ resin or grout to anchor the rock bolt within the bore. In respect of resin anchored bolts, a resin cartridge is usually employed, which is required to be inserted into the bore prior to the bolt being inserted therein. Insertion of the resin cartridge is sometimes very difficult, because typically the tunnel walls extend to a significant height, so that access to bores into which the cartridge is to be inserted can be inconvenient. Additionally, the resin which is employed is relatively expensive and has a limited shelf life. Cement grouted rock bolts are less expensive than resin anchored bolts, but application of the cement is more cumbersome than that of the resin. Cement grouting requires cement mixing equipment, as well as pumping and delivery equipment, to deliver the mixed cement into the bore.

3 Resin or cement anchored rock bolts generally anchor in a bore to provide greater levels of rock reinforcement or stabilisation, because such bolts usually have a better bond between the bore wall and the resin or cement, compared to the frictional engagement of a friction rock bolt. However, the advantages of speed of installation and cost make friction rock bolts attractive in suitable environments. Expansion rock bolts include an elongate tube, which is split longitudinally, with an expander mechanism positioned within the tube, normally towards the leading end of the tube that is inserted first into the drilled bore in the rock wall. The expansion mechanism is usually in a collapsed or unexpanded condition as the tube is inserted into the bore and once the tube is properly positioned in the bore, the mechanism is actuated to expand against the internal surface of the tube, tending to expand the tube, by opening the longitudinal split. If the tube is already a tight frictional fit within the bore, expansion of the tube by the expander mechanism might be negligible or small, but there is nevertheless a benefit by the increased friction between the outside surface of the tube and the bore due higher normal forces imposed as a result of the expander mechanism. Conversely, where the bore has been drilled to a greater diameter than required, or the earth in which the bore has been drilled offers limited resistance to expansion, then the expansion achieved by the mechanism will be greater. Expansion mechanisms have a finite amount of expansion they can create in the tube. In one form of expansion mechanism, the expansion is created by a pair of wedges that can be made to move relative to each other and by that movement, create an expansion force against the internal surface of the tube. A difficulty with this form of expander is that if the relative movement is too great, the wedges can move out of contact, collapsing the expander mechanism and the expansion load can be lost, allowing the tube to contract radially. If that occurs, then the friction bolt might not be securely fixed within the bore and thus might not provide the structural support intended. In one particular form of expansion mechanism, a first wedge is fixed to the inside surface of the tube, such as by welding and a second wedge is movably mounted within the tube in proximity to the first wedge, so that the second wedge can be moved relative to the first wedge and by that movement, the second wedge can shift 4 radially outwardly against the internal surface of the tube creating the expansion load required. In the above form of expansion mechanism, the second wedge can be threadably mounted to one end of a bar within the tube and movement of the wedge can be by rotation of the bar to create axial movement of the second wedge relative to the first wedge. In this arrangement, the amount of movement of the second wedge longitudinally of the tube can be controlled by terminating the thread on the bar at the allowable point of maximum travel of the second wedge. Alternatively or in addition, the bar can include a crimp against which the second wedge can abut at the allowable point of maximum travel. However, the above arrangements for terminating travel of the second wedge do not always operate effectively. This is usually because the torque applied to the bar to move the second wedge relative to the first wedge is often so great in order to develop the expansion force required, that it is often also great enough to force the second wedge to deform and screw past the crimp even though he thread has ended. The provision of a stronger second wedge that will not deform is not a preferred solution given that any form of crimping applied to the bar can reduce the mechanical properties of the bar, including its ultimate tensile strength and its elongation. So the preference is to avoid crimping where possible. In addition, crimping of the bar can bend the bar and that can misalign the second wedge on the threaded portion of the bar and thus increase the friction in the threaded connection between the second wedge and the threaded portion, affecting the ability to move the second wedge relative to the first wedge. It is an object of the present invention to overcome or at least alleviate one or more of the drawbacks associated with prior art friction rock bolt arrangements. SUMMARY OF THE INVENTION According to the present invention there is provided a friction bolt, for frictionally engaging the internal surface of a bore drilled into a rock face, the friction bolt comprising; 5 an elongate, generally circular tube which is expandable radially, the tube having a leading end and a trailing end, and an expander mechanism disposed within the tube, for applying a load tending to expand at least a section of the tube radially, an elongate bar disposed longitudinally within the tube and in connection at or towards one end of the bar with the expander mechanism and in connection at or towards an opposite end of the bar with an anchor arrangement, the expander mechanism comprising a pair of expander elements, a first of which is secured relative to the tube and a second of which is secured to the elongate bar for movement relative to the first expander element, the first expander element having a first section defining a first face which is inclined upwardly in a direction toward the trailing end of the tube, the first section extending to a second section which defines a second face which is inclined at an angle to the first face so that the second face has a greater angle of inclination than the first face, the second expander element having a first face for bearing engagement with an inside surface of the tube and a second face for bearing against the first and second faces of the first expander element. In the operation of the friction bolt, bar is actuatable to expand the expander mechanism by moving of the second expander element relative to the first expander element. The orientation of the first and second faces of the first expander element is such that upon movement of the second expander element relative to the first expander element by bar actuation, the second expander element moves up the incline of the first face of first expander element in an expansion direction tending to expand the expander mechanism. In that movement, the second expander element bears against an inside surface of the tube to impose an expansion load on the tube. Further movement of the second expander element in the expansion direction brings the second expander element into bearing engagement with the second face of the first expander element, whereby further movement of the second expander element in the expansion direction is resisted. Accordingly, the present invention also provides a friction bolt, for frictionally 6 engaging the internal surface of a bore drilled into a rock face, the friction bolt comprising; an elongate, generally circular tube which is expandable radially, the tube having a leading end and a trailing end, an expander mechanism disposed within the tube for applying a load tending to expand at least a section of the tube radially, an elongate bar disposed longitudinally within the tube and in connection at or towards one end of the bar with the expander mechanism and in connection at or towards an opposite end of the bar with an anchor arrangement, the bar being actuatable to expand the expander mechanism, the expander mechanism comprising a pair of expander elements, a first of which is secured relative to the tube and a second of which is secured to the elongate bar and which is movable relative to the first expander element upon actuation of the bar, actuation of the bar being operable to move second expander element relative to the first expander element, to cause the expander mechanism to expand, the first expander element having a first section defining a first face against which the second expander element bears during relative movement, the first face being inclined in a direction so that the second expander element moves up the incline in an expansion direction tending to expand the expander mechanism as the bar is actuated, the first section extending to a second section which defines a second face which is inclined at an angle to the first face so that the second face has a greater angle of inclination than the first face, whereby the second expander element bears against an inside surface of the tube during movement relative to the first expander element in the expansion direction to impose an expansion load on the tube, and whereby movement of the second expander element relative to the first expander element in the expansion direction is resisted upon the second expander element coming into bearing engagement with the second face. The present invention also provides a method of operating a friction bolt according to the function of the friction bolt described above. A friction bolt according to the present invention can overcome problems associated with prior art expansion mechanisms, in particular relating to movement of the second expander element completely past the first expander element. Thus, the expander mechanism can be prevented from collapsing by movement of the second 7 expander element past the first expander element and by preventing collapse, the proper engagement between the friction bolt and the bore wall surface can be achieved. This has benefits particularly in relation to bores that have been over drilled, i.e. they have been drilled to a greater diameter than intended for the friction bolt being used, or which have been drilled within an earth or rock substrate that provides insufficient resistance to the rock bolt expansion, such as to allow the expansion to continue to the point at which the respective elements move past one another. By the present invention, the first expander element which is secured within the tube, includes first and second sections, with the second section being such as to resist movement of the second expander element beyond a particular point relative to the first expander element. By that resistance, the likelihood of the second expander element moving past the first expander element to a point at which the expander mechanism collapses, is either reduced or eliminated. The construction of the first expander element can take any suitable form to provide for the first and second faces being inclined relative to each other. In some forms of the invention, the first face of the first expander element can be formed at a substantially constant incline of between 3 to 100 relative to the longitudinal axis of the tube. In one form of the invention developed by applicant, the first face of the first expander element is disposed at an angle of 50 relative to the longitudinal axis of the tube. The second face of the first expander element can also be disposed at any suitable angle to provide the effect described above, that is to resist movement of the second expander element longitudinally of the friction bolt to further expand the expander mechanism, upon the second expander element coming into bearing engagement with the second face. By arranging the second face of the first expander element at a greater angle of incline than the first face, the orientation of the second expander element will be affected once the second expander element comes into bearing engagement with the second face. The second expander element will incline further relative to the longitudinal axis of the friction bolt and this will tend to misalign the second engagement element relative to the bar and by that misalignment, resistance to movement of the second expander element relative to the first expander element can be generated. In particular, some forms of the invention form a connection between the second expander element and the bar which is a threaded connection, 8 and the misalignment referred to above results in an increased friction between the threads of the engagement and that causes the resistance to movement of the second expander element relative to the first expander element. Effectively, the threads of the threaded engagement clash and the efficiency of the threaded connection is dramatically reduced so that the torque needed to move the second expander element increases significantly. Where the torque required to move the second expander element is greater than provided to rotate the bar, the bar will no longer be rotated and movement of the second expander element will cease. The second face of the first expander element can be disposed at an obtuse angle of between 1600 and 1750 relative to the first face of the first expander element and by forming the second face within this angular range, tests have shown that the resistance to movement of the second expander element relative to the first expander element can be achieved. The resistance increases as the angle decreases, but applicant has established that an obtuse angle of about 172*relative to the first face has an effect which is acceptable in practice to prevent the second expander element from continuing to move relative to the first expander element. Like the first face, the second face can have a substantially constant incline. In other forms of the invention, the second face of the first expander element can be disposed at an angle of between 90 and 100* relative to the first face, i.e. the second face is perpendicular to the first face or the obtuse angle between the faces is 1000. The angle between the first and second faces can be greater or lesser than the range above as required. The second section of the first expander element can be formed of two spaced apart sections each of which define a portion of the second face. These sections can be spaced apart laterally across the diameter of the tube. The spaced apart sections can be spaced apart by a recess which can be provided to accommodate at least a portion of the bar to which the second expander element is connected. In these arrangements, the bar can extend through the recess in the first expander element between the spaced apart sections of the second face to position the second expander element to overlie the first face of the first expander element. Whether the bar is fully or only partially accommodated within the recess will be dependent on the 9 height of the spaced apart sections and the depth of the recess. The recess can be located centrally between the two spaced apart sections. The recess described above can also extend into the first section of the first expander element and the bar can extend at least partially within that recess. The depth of the recess can decline towards the end of the first section remote from the second section. The recess can terminate ahead of the end of the first section, or can extend fully through the first section. In addition to the resistance provided by bearing engagement between the second expander element and the second face of the first expander element, in forms of the invention in which the bar and the second expander element are connected by threaded engagement, the threaded portion of the bar can be terminated in the region of the end of the second section of the first expander element remote from the first section. In these forms of the invention, the second expander element will meet resistance to further travel relative to the bar when it reaches the section of the bar at which the thread terminates, and that resistance will add to the resistance encountered through bearing engagement of the second expander element with the second face of the first expander element. The second expander element can have front and rear faces, whereby the front face faces the second face of the first expander element. That front face can be inclined complementary to the inclination of the second face for flush abutting engagement with the second face to enhance bearing engagement with the second face. BRIEF DESCRIPTION OF THE DRAWINGS 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 illustrates a friction rock bolt in longitudinal cross-section according to an embodiment of the invention. Figure 1A is a cross-sectional view through A-A of Figure 1. Figures 2 and 3 illustrate the friction rock bolt of Figure 1 in different stages of 10 expander mechanism expansion. Figure 4 illustrates the friction rock bolt of Figure 1 and shows the angles of inclination of the first and second faces of the first expander element. Figures 5 and 6 illustrate further embodiments of the invention. Figure 7 illustrates a first expander element according to an embodiment of the invention. DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a friction rock bolt 10 according to an embodiment of the invention. The bolt 10 includes an elongate generally circular tube 11 having a leading end 12 and a trailing end 13. Only the leading and trailing ends of the tube 11 is shown as the length of a typical rock bolt can be in the range of about one metre to about five metres. The tube 11 is split along its full length as shown in Figure 1A, to allow for expansion of the tube 11 radially. However, alternative arrangements to allow for the radial expansion for the tube 11 can be provided other than by the inclusion of a lengthwise split and such an alternative arrangement is disclosed in applicant's co-pending international application, published under publication WO/2010/104460, and reference is made to Figure 3 of that international publication. An expander mechanism 14 is disposed within the tube 11 towards the leading end 12 and comprises a pair of wedge or expander elements 15 and 16. The first wedge element 16 is secured to the internal surface 18 of the tube 11 by welding, while the second expander element 15 is secured to one end of a bar 19 disposed longitudinally within the tube 11. The expander element 15 is connected to the bar 19 by a threaded engagement, and Figure 1 illustrates the threaded portion 21 formed on the leading end of the bar 19. The trailing end 22 of the bar 19 extends to the trailing end 13 of the tube 11 and 11 through an end plate 23. A nut 24 is integrally formed as part of the bar 19, so that rotation of the nut 24 results in rotation of the bar 19. Other components at the trailing end 13 of the tube 11 include a ring 25 which is welded to the tube 11 and which in use abuts against a rock plate (not shown) to secure the rock plate against a rock wall surface and when the rock bolt 10 is under heavy load, the end plate 23 provides additional support to the ring 25 to resist load applied to the rock plate. Thus, the ring 25 is supported against failure by the end plate 23. An end fitting 27 is also located at the trailing end 13 of the tube 11 and is formed as a plug or bush, which operates to maintain the bar 19 concentric within the tube 11 and which frictionally engages the bar 19 so that axial movement of the bar 19 is resisted during insertion of the rock bolt 10 into a bore. This is important to ensure that the bar 19 does not move axially in a direction toward the trailing end 13 to result in premature engagement between the wedge elements 15 and 16, which might prevent radial contraction of the tube as it is inserted into the bore. Given that rock bolts are often inserted into a bore which has an internal diameter less than the external diameter of the bolt, the bolt must contract radially to facilitate insertion of the bolt into the bore. By maintaining the bar in the position shown in Figure 1, the wedge elements are maintained spaced apart and the tube 11 can contract as required during insertion. The components described above which are disposed at the trailing end 13 of the tube 11 need not be described further, as they are not of significant relevance to the present invention. Returning to the expander elements 15 and 16, the expander element 16 includes a first section 30 which defines a first face 31 and a second section 32 which defines a second face 33. Each of the faces 31 and 33 are of constant incline, however the angle of inclination of the second face 33 is greater than that of the first face 31. The element 15 also includes an inclined face 34 which is inclined at substantially the same angle as the first face 31 of the element 16. The element 15 is shown positioned towards the leading end 12 of the tube 11 at a position which the respective faces 31 and 34 are slightly spaced apart. In practice, it might be that these faces are actually in contact at the position shown in Figure 1, but regardless, the respective elements 15 and 16 are positioned relative to each other, to allow the 12 tube 11 to contract radially if necessary when being fitted into a bore. With reference to Figure 1a, it can be seen that the tube 11 includes a slot 35 and while this is not evident in Figure 1, the slot 35 extends the full longitudinal length of the tube 11, and allows the tube 11 to collapse radially inwardly. As indicated above, in Figure 1, the expander elements 15 and 16 are slightly spaced apart between the facing surfaces 31 and 34. In this position, the expander mechanism 14 is applying no expansion load against the internal surface 18 of the tube 11 to expand the tube 11 radially. Referring now to Figure 2, this shows the expander elements 15 and 16 in engagement, with the inclined surfaces 31 and 34 (see Figure 1) being in frictional sliding contact. Thus, the nut 24 has been rotated to rotate the bar 19, and by that rotation, the element 15 has shifted axially relative to the element 16, to bring the inclined face 34 of the element 15 into engagement with the first face 31 of the element 16. It is to be noted that the element 15 is restricted from rotating within the tube 11, so that rotation of the bar 19 results in axial movement of the element 15. It is to be understood that there can be some rotation of the element 15 when the bar 19 rotates, but upon a small amount of rotation, the element 15 will engage the element 16 and that will terminate rotation. Figure 2 shows the element 15 in the initial stages of axial movement relative to the element 16. Thus, the inclined surface 34 of the element 15 has just entered engagement with the first face 31 of the element 16 and continued rotation of the nut 24 will continue axial movement of the element 15 away from the leading end 12. As the element 15 shifts away from the leading end 12, it will be readily apparent that between the elements 15 and 16, an expansion load, tending to expand the tube 11 is applied by the expander mechanism 14. That expansion load can increase the friction that occurs between the tube 11 and the internal surface of the bore in which the rock bolt 10 is fitted, to firmly secure the bolt 10 within the bore. The amount of relative axial movement between the expander elements 15 and 16 depends on the amount of radial expansion that the tube 11 is allowed within a bore within which the bolt 10 is fitted. If the bore has been drilled to a greater diameter 13 than the outside diameter of the tube 11, or if the earth that the bore has been drilled into offers limited resistance to expansion, the axial travel of the element 15 relative to the element 16 will be greater than otherwise. It is important to ensure that the element 15 does not travel completely beyond the element 16, as that will remove any expansion load applied to the tube 11 and allow the tube to collapse radially and thus cause the bolt 10 to be insecurely held within a bore. In order to prevent complete travel of the element 15 beyond the element 16, the present invention provides that the element 16 includes the second section 32, in which the second face 33 is inclined at a greater angle to the longitudinal axis of the rock bolt 10 compared to the first face 31 of the first section 30. Figure 3 illustrates in exaggerated form, the expander mechanism in which the element 15 has travelled completely along the first face 31 of the element 16 and has now moved into bearing engagement on the second face 33 of the second section 32. It can be seen from Figure 3 that the element 15 has skewed out of axial alignment within the tube 11, and has rotated slightly anticlockwise, as a result of the leading end 36 of the element 15 now sliding in bearing engagement along the second face 33. While the arrangement is exaggerated in Figure 3, the change of orientation in the element 15 is such as to also tend to change the orientation of the trailing end 37 of the bar 19. However, it is difficult for the element 15 to actually bend the bar 19 and thus the change in orientation between the element 15 and the bar 19 is predominantly by a shift in the alignment of the threaded engagement between the element 15 and the threaded portion 21 of the bar 19. This results in a dramatic increase in the frictional engagement between the element 15 and the threaded portion 21. That dramatic increase in friction within the threaded engagement can cause the element 15 to lock onto the threaded portion 21 and thus to prevent or significantly resist further axial movement of the element 15 on the bar 19. The increase in friction will increase further as the leading end 36 of the element 15 climbs up the second face 33 of the element 16 and further misaligns the element 15 on the threaded portion 21. Thus, the further the element 15 moves axially relative to the second section 32, the greater the frictional engagement between the element 15 and the threaded portion 21 and the greater resistance to further axial movement of the element 15.

14 Appropriate selection of threaded connection between the element 15 and the threaded portion 21 is expected to ensure that once the element 15 reaches the second section 32 of the element 16, axial movement of the element 15 can be terminated. Moreover, the termination of movement can be influenced by the angle of inclination of the second face 22 relative to the first face 31. At present, the angle of inclination of the first face 31 is shown in Figure 4 relative to the longitudinal axis A of the bolt 10 as being approximately 50, while the angle of inclination of the second face 33 is approximately 10 0 relative to the longitudinal axis A. However, it is expected that the range of inclination for the first face 31 can be between 3 and 100, while the angle of inclination of the second face 33 can be between 100 and 200. The obtuse angle between the first and second faces can be between 160 to 1750. To further assist the restriction of movement of the element 15 relative to the element 16, the threaded portion 21 can be terminated in the region of an end of the second section 32 of the expander element 16 and in Figures 2 to 4, the threaded portion 21 terminates at the end 38. While it is possible that on continued rotation of the bar 19, the expander element 15 will continue to shift axially on the threaded portion 21 beyond the end 38, the absence of thread beyond the end 38 restricts that further axial movement. Figures 5 and 6 show alternative embodiments of the invention, and include only a section of a rock bolt 40 (Figure 5) and 60 (Figure 6) respectively. Referring to Figure 5, the rock bolt 40 has essentially the same construction as the rock bolt 10 shown in Figure 1 to 4, with the only variation being in the construction of the expander mechanism 41. Thus, shown in Figure 5 is a tube 42, which is elongate and split longitudinally, and a bar 43. The expander mechanism 41 comprises a first expander element 44 and a second expander element 45. The expander element 44 has essentially the same construction as the expander element 15 of the earlier figures. Thus, the element 44 includes a trailing end 46, a leading end 47, an inclined face 48 and an outer face 49, for engagement with the inside surface of the tube 42.

15 The second expander element 45 includes a first section 50 which has a first inclined face 51 and a second section 52, which has an abutment face 53. The face 53 is disposed substantially perpendicular to the lengthwise axis of the tube 42, so that the obtuse angle between the first and second faces is about 93 to 1000 based on the angle of the first face being 3 to 10* to the lengthwise axis of the tube 42. In the arrangement of Figure 5, rotation of the bar 43 causes axial movement of the expander element 44 towards the abutment face 53. Upon sufficient axial movement of the expander element 44, the leading end 47 will abut the abutment face 53 and by that abutment, further axial travel of the element 44 is resisted. In this arrangement, the provision of a gradual increase in the resistance of axial movement as found in the arrangement of Figures 1 to 4, is absent, as once the end 47 engages the face 53 significant resistance to further movement of the element 44 is encountered. Figure 6 illustrates a further embodiment of the invention, and is substantially the same as Figure 5, except in respect of the construction of the second section 65 of the second element of the expander mechanism 61. In Figure 6, a portion of a rock bolt 60 is illustrated, having an expansion mechanism 61, a tube 62 and a bar 63. The expander mechanism 61 comprises first and second expander elements 64 and 65 and apart from the construction of the second section 66, the other components of the bolt 60 are the same as the components of the bolt 40 of Figure 5. The second section 66 of the bolt 60 includes an inclined second face 67 that is set at an angle e of 90* to the inclined face 68 of the first section 69. In each of the Figure 5 and 6 embodiments, the leading ends 47 and 70 of the elements 44 and 64 are inclined complementary to the second faces 53 and 67 of the elements 45 and 65 for flush abutting engagement between the respective leading ends and faces. It will be seen in Figure 2 to 6 that the respective bars 19, 43 and 63 all extend through the stationary expander elements 16, 45 and 65. The extent to which the bar extends through the elements is dependent on the extent of the second sections of those elements and thus in Figures 2 to 4, there is only partial accommodation of 16 the bar 19 within the second section 32, whereas in Figures 5 and 6, there is substantially full accommodation of the bars 43 and 63 in the sections 52 and 66. Figure 7 illustrates an arrangement of an element of an expander mechanism, which is the stationary element equivalent to the element 16 of Figures 1 to 4, and shows the first section 30, the second section 32 and the respective inclined faces 31 and 33. The second section 32 is formed of a pair of spaced apart sections 32a and 32b and those sections are separated by a recess 75. The recess 75 is centred between the sections 32a and 32b and the recess extends from the second section 32 into the first section 30. The depth of the recess 75 and the extent to which it extends into the first section 30 is dependent on the height of the element 16 from the inner surface of the tube 11 in which it is fixed, along with the relative position of the bar 19 within the tube. The later arrangements of Figures 5 and 6 can include a similar arrangement to that shown in Figure 7, but clearly the second section 32 will change significantly in accordance with the second sections 52 and 66 of those embodiments. The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure.

Claims (19)

1. A friction bolt, for frictionally engaging the internal surface of a bore drilled into a rock face, the friction bolt comprising; an elongate, generally circular tube which is expandable radially, the tube having a leading end and a trailing end, and an expander mechanism disposed within the tube, for applying a load tending to expand at least a section of the tube radially, an elongate bar disposed longitudinally within the tube and in connection at or towards one end of the bar with the expander mechanism and in connection at or towards an opposite end of the bar with an anchor arrangement, the expander mechanism comprising a pair of expander elements, a first of which is secured relative to the tube and a second of which is secured to the elongate bar for movement relative to the first expander element, the first expander element having a first section defining a first face which is inclined upwardly in a direction toward the trailing end of the tube, the first section extending to a second section which defines a second face which is inclined at an angle to the first face so that the second face has a greater angle of inclination than the first face, the second expander element having a first face for bearing engagement with an inside surface of the tube and a second face for bearing against the first and second faces of the first expander element.

2. A friction bolt according to claim 1, the first expander element being fixed to the inside surface of the tube and the first face of the first expander element being at a substantially constant incline of between 3 and 100 relative to the longitudinal axis of the tube.

3. A friction bolt according to claim 1, the first expander element being fixed to the inside surface of the tube and the first face of the first expander element being at a substantially constant incline of 50 relative to the longitudinal axis of the tube.

4. A friction bolt according to claim 2 or 3, the second face of the first expander element being disposed at an obtuse angle of between 160 and 1750 relative to the first face of the first expander element. 18

5 A friction bolt according to claim 2 or 3, the second face of the first expander element being disposed at an obtuse angle of 1720 relative to the first face of the first expander element

6. A friction bolt according to claim 5, the second face having a substantially constant incline.

7. A friction bolt according to claim 2, the second face of the first expander element being disposed at an angle of between 90 and 100 0 relative to the first face.

8. A friction bolt according to claim 7, the second face being disposed at an angle of 90* to the first face.

9. A friction bolt according to claim 7, the second face being disposed at an angle of 1000 to the first face.

10. A friction bolt according to any one of claims 7 to 9, the second expander element having an inclined front face that is inclined at an angle for flush abutting engagement with the second face of the first expander element.

11. A friction bolt according to any one of claims 1 to 10, the second section being formed of two spaced apart sections which define the second face and which are spaced apart by a recess and the bar extending between the spaced apart sections at least partially within the recess.

12. A friction bolt according to claim 11, the recess being substantially centred between the two spaced apart sections.

13. A friction bolt according to claim 11 or 12, the recess extending into the first section of the first expander element and the bar extending at least partially within the recess in the first expander element.

14. A friction bolt according to any one of claims 1 to 13, the bar including a threaded end portion and the second expander element being threadably connected 19 to the threaded end portion, movement of the second expander element relative to the first expander element occurring by rotation of the bar.

15. A friction bolt according to claim 14, the thread of the threaded end portion terminating in the region of an end of the second section of the first expander element remote from the first section of the first expander element.

16. A friction bolt according to any one of claims 1 to 15, bar being actuatable to expand the expander mechanism by moving of the second expander element relative to the first expander element.

17. A friction bolt according to claim 16, the second expander element being threadably connected to the bar and movement of the second expander element relative to the first expander element being by rotation of the bar to cause the second expander element to shift axially along the bar.

18. A friction bolt according to any one of claims 1 to 17, the orientation of the first and second faces of the first expander element being such that upon movement of the second expander element relative to the first expander element by bar actuation, the second expander element moves up the incline of the first face of first expander element in an expansion direction tending to expand the expander mechanism and tending to expand the tube radially by bearing engagement against an inside surface of the tube, and whereby further movement of the second expander element in the expansion direction is resisted upon the second expander element coming into bearing engagement with the second face of the first expander element.

19. A friction bolt, for frictionally engaging the internal surface of a bore drilled into a rock face, the friction bolt comprising; an elongate, generally circular tube which is expandable radially, the tube having a leading end and a trailing end, an expander mechanism disposed within the tube for applying a load tending to expand at least a section of the tube radially, an elongate bar disposed longitudinally within the tube and in connection at or towards one end of the bar with the expander mechanism and in connection at or towards an opposite end of the bar with an anchor arrangement, the bar being actuatable to expand the expander mechanism, 20 the expander mechanism comprising a pair of expander elements, a first of which is secured relative to the tube and a second of which is secured to the elongate bar and which is movable relative to the first expander element upon actuation of the bar, actuation of the bar being operable to move second expander element relative to the first expander element, to cause the expander mechanism to expand, the first expander element having a first section defining a first face against which the second expander element bears during relative movement, the first face being inclined in a direction so that the second expander element moves up the incline in an expansion direction tending to expand the expander mechanism as the bar is actuated, the first section extending to a second section which defines a second face which is inclined at an angle to the first face so that the second face has a greater angle of inclination than the first face, whereby the second expander element bears against an inside surface of the tube during movement relative to the first expander element in the expansion direction to impose an expansion load on the tube, and whereby movement of the second expander element relative to the first expander element in the expansion direction is resisted upon the second expander element coming into bearing engagement with the second face.