AU2006252086B2 - Self-Drilling Anchor Bolt - Google Patents

Abstract

A self-drilling anchor bolt for the stabilising of strata; said anchor bolt including: 5 (a) an elongate steel rod or tube; (b) a drilling tip rigidly affixed at a distal end of said rod or tube; (c) a drive member rigidly affixed at a proximate end of said rod or tube; 10 and wherein rotation of said anchor bolt in a first direction drills a bore hole, and subsequent rotation of said anchor bolt in a second opposite direction causes expansion of said anchor assembly so as to anchor said anchor bolt in said bore hole. t.-.l - II I ii ii 0 iCi

Description

P/00/009 Regulation 3 2 AUSTRALIA Patents Act 1990 STANDARD SPECIFICATION Invention Title: SELF-DRILLING ANCHOR BOLT The invention is described in the following statement: Our Ref: 062050 -2 SELF-DRILLING ANCHOR BOLT The present invention relates to anchor bolt mechanisms for the stabilizing or control of strata such as in a mine or tunnel and, more particularly to such 5 mechanisms adapted for use in coal m ines and sometimes known as coal rib anchors.. BACKGROmDD Numerous types and configurations of anchor bolt or 10 roof anchors and coal rib anchors are known. A common object of such mechanisms is the provision of an economic device, capable of accepting high loads, easy to install within a minimum of time and a high degree of consistency of load capacity. 15 Typically, bolts are comprised of a length of rod or deformed bar threaded at least at one end (the proximal end) and provided with some means of securing the distal end at or near the end of a hole drilled into the stratum into which the bolt is to be placed. The proximal end is 20 generally provided with a support plate, washer and nut. Two principle categories of securing means are used to fix the distal end within the hole; chemical and mechanical.. Typically chemical systems require the insertion of a cartridge containing the chemical components 25 of a resin and catalyst into the hole after which the bolt is inserted and spun to break the cartridge and mix its 3 contents. The resin is then left for a predetermined interval of time to set so as to anchor the bolt in the hole after which the nut may be advanced on the proximal threaded end so as to bring the bolt into tension thereby 5 securing the area of stratum around the bolt. The insertion of the resin cartridge requires the hole to be clean; any material collapsing into the hole as the drill is withdrawn requires a time consuming clearing operation. This is a particular problem in coal rib 10 applications. Another problem with chemical anchor systems particularly in coal rib applications where wet drilling is mandatory, is that water collects in "bottom" holes which are angled downwardly. Water slows down the setting time of the resin mix and in some circumstances precludes use of a 15 resin mix or only permits use of a short cartridge. Mechanical steel systems are able to achieve little purchase particularly in coal stratum because of their inability to conform to any irregularities of the drilled hole. 20 A further disadvantage of many bolt arrangements is that two separate operations are required; firstly to drill suitable hole and secondly the insertion of the bolt. Especially in friable strata, the withdrawal. of the drill bit may cause the drilled hole to partially fill with loose 25 material, preventing in some cases the insertion of the -4 bolt until the material is cleared, causing yet a further increase in bolt setting time. The above discussion of background art is included to explain the context of the present invention. It is not to be taken as an admission that any of the documents or other material referred to was published, known or part of the common general knowledge in Australia at the priority date of any one of the claims of this specification. It is a desirable outcome present invention to address or at least ameliorate some of the above disadvantages. BRIEF DESCRIPTION OF INVENTION Accordingly, in a first broad form of the invention, there is provided a self-drilling anchor bolt for the stabilising of strata; said anchor bolt including: (a) an elongate steel rod or tube; (b) a drilling tip rigidly affixed at a distal end of said rod or tube; (c) an anchor assembly comprising at least one expander sleeve provided with an encapsulated nut retained in said sleeve, and wherein rotation of said anchor bolt in a first direction drills a bore hole, and subsequent rotation of said anchor bolt in a second opposite direction causes expansion of said anchor assembly so as to anchor said anchor bolt in said bore hole. Preferably, said anchor assembly is adapted to induce plastic flow of at least one element of said anchor -5 assembly so as to form a continuum of material between said rod and sides of said hole. Preferably, said strata is a portion of any one of a range of geological strata; said range including a coal 5 rib. Preferably, said elongate steel rod or tube is provided at said distal end with a threaded portion; said threaded portion handed in said second opposite direction. Preferably, said anchor assembly includes at least one 10 expander element and at least one expansion element. Preferably, said anchor assembly includes one expander sleeve and one expansion sleeve. Preferably, said anchor assembly included one expander sleeve and two expansion sleeves. 15 Preferably, said anchor assembly includes first and second expander sleeves and a pair of expansion leaves; said first and second expander sleeves and said expansion leaves interconnected by frangible connector elements. Preferably, said at least one expander element and said 20 at least one expansion element have an outer diameter not greater than the drilling diameter of said drilling tip.

Preferably, said rod or tube is provided with a projecting shoulder at a proximate end of said threaded portion; said at least one expansion sleeve and said at least one expander sleeve located between said drilling 5 tip and said projecting shoulder. Preferably, each of said at least one expansion element is in the form of a tubular expansion sleeve provided with at least one pair of opposing expansion slots; said slots extending from a distal end of said expansion 10 sleeve towards a proximal end of said expansion sleeve; said at least one pair of opposing slots extending for a proportion of the length of said expansion sleeve. Preferably, prior to use, each of said at least one expansion sleeve has an internal diameter adapted to 15 accept said threaded portion of said elongate steel rod or tube as a free sliding fit; said internal diameter extending from said proximal end of said expansion sleeve for a first portion of said length of said expansion sleeve. 20 Preferably, each of said at least one expansion sleeve has an internal generally conically outward tapering second portion increasing from said internal diameter to a diameter approaching said outer diameter of said at least one expansion sleeve at said distal end.

-7 Preferably, at least one said expander sleeve is located adjacent said drilling tip. Preferably, at least one said expansion sleeve is located adjacent said projecting shoulder. 5 Preferably, a first of said expander sleeves is located adjacent said drilling tip; a second of said expander sleeves is located adjacent said projecting shoulder, and wherein said pair of expansion leaves are located between said first and second expander sleeves. 10 Preferably, said first and second expander sleeves are each provided with a pair of wedge shaped portions; said wedge shaped portions adapted to force apart said pair of expansion leaves. Preferably, said at least one expander element and said 15 at least one expansion element are formed of injection moulded plastic. Preferably, said expander sleeve adjacent said drilling tip is provided with an encapsulated steel nut at a distal end of said expander sleeve; the thread of said 20 steel nut engaging with the thread of said threaded portion at said distal end of said elongate steel rod or tube.

Preferably, said expander sleeve adjacent said drilling tip is provided with a reaction pin projecting from said expander sleeve. Preferably, said reaction pin is a projecting end of a 5 spring wound around said threaded portion; said reaction pin projecting from said sleeve adjacent said encapsulated steel nut. Preferably, said reaction pin projecting from said expander sleeve is affixed to said encapsulated nut. 10 Preferably, prior to use, said expander sleeve has an internal diameter adapted to accept said threaded portion of said elongate steel rod or tube as a free sliding fit for that portion the length of said expander sleeve not taken up by said encapsulated threaded steel nut and said 15 spring. Preferably, said expander sleeve is provided with an external generally conically tapering section extending from a proximal end for a portion of the length of said expander sleeve; said tapering portion adapted to nest 20 within said internal generally conically outward tapering second portion of said at least one expansion sleeve. Preferably, said elongate steel rod or tube is provided at a proximal end with a fixed drive member.

9 Preferably, said elongated steel rod or tube is provided at said proximal end with a section of thread; said thread handed in said second opposite direction. Preferably, said drive member is a nut locked to said 5 section of thread by a shear pin; said shear pin adapted to shear at a predetermined torque applied to said nut relative said rod or tube so as to free said nut on said section of thread. Preferably, said nut is driven towards said distal end of 10 said anchor bolt when rotation is applied to said nut in said second opposite direction and said pin has sheared. Preferably, said elongate steel rod or tube is urged into said first rotation direction and said second opposite rotation direction by the application of a suitable 15 driver to said drive member. Preferably, said reaction pin is adapted to substantially prevent rotation of said at least one expander sleeve adjacent said drilling tip when said elongate steel rod or tube is rotated in said second opposite direction. 20 Preferably, rotation in said second opposite direction of said elongate steel rod or tube relative to said expander sleeve causes movement of said expander sleeve along said threaded portion away from said drilling tip.

- 10 Preferably, said movement of said expander sleeve forces an expansion of said at least one expansion element; said expansion forcing portions of said expansion element against the surrounding surface of said bore hole; said 5 expander sleeve consequently subject to deformation of internal and external surfaces. Preferably, said expansion approaches a limit defined by extent of deformation of said expander sleeve and said at least one expansion element; said expansion further 10 limited by limit of compressibility of said strata around said anchor assembly. Preferably, said deformation of said expander sleeve occurs in the form of plastic flow with the continued application of rotation by said driver to said drive 15 member; said deformation including the formation within said expansion slots of ridge-like protrusions from said external generally conically tapering section; said deformation further including the .forming of an internal thread for a portion of said internal diameter of said 20 expander sleeve. In a further broad form of the invention there is provided a method for stabilizing strata by the application of a self-drilling anchor bolt; said method including the steps of drilling said anchor bolt into said strata by rotation in a first direction to form a bore hole; said method further including providing for mechanically expanding portions of an anchor assembly of said anchor bolt by rotation of said anchor bolt in a 5 second opposite direction; and wherein said mechanically expanding portion includes at least an expander sleeve incorporating an encapsulated nut within said expander sleeve. Preferably, said method includes the further steps of 10 continuing to apply said rotation to induce maximal expansion within said hole of said expanding anchor assembly until rotation approaches stall due to constriction by said stratum and plastic flow of at least one of said expansion components. 15 Preferably, said anchor assembly includes plastic expander elements and expansion elements. Preferably, said plastic expander and expansion elements are injection moulded from any of a range of suitable plastics adapted to deform under compressive forces; said 20 range including polypropylene, polyethylene with or without glass fibre reinforcing. Preferably, said anchor assembly deforms to a point where at least an outer portion of said anchor assembly is embedded in walls of said bore hole; said deformation -12 including plastic flow of a portion of at least one of said plastic elements into a threaded portion of said elongate steel rod. In yet a further broad form of the invention, there is 5 provided a method for the anchoring of an anchor bolt within a hole drilled in .an area of strata; said method including the inducement of plastic flow by compression of anchor elements so as to form a continuum of compressed material between said bolt and the confines of 10 said hole as herein described and with reference to the accompanying drawings . BRIEF DESCRIPTION OF DRAWINGS Embodiments of the present invention will now be 15 described with reference to the accompanying drawings wherein: Figure 1 is a view of a self-drilling anchor bolt according to a first preferred embodiment of the invention, Figure 2 is a view of a self-drilling anchor bolt 20 according to a second preferred embodiment of the invention, Figure 3 is a partially sectioned side view of a portion of the self-drilling anchor bolt of figure 1, Figure 3A is a sectional view of a portion of the 25 self-drilling anchor bolts of figure 3, - 13 Figure 4 is a partially sectioned side view of a portion of the self-drilling anchor bolt of figure 2, Figure 5 is a view of the self-drilling anchor bolt of figure 1 approaching a final stage of a drilling operation, 5 Figure 6 is a view of the self-drilling anchor bolt of figures 1 and 5 approaching a point of maximum load capacity, Figure 7 is a sectional side view of a portion of the self-drilling anchor bolt of figure 6 with the threaded rod 10 removed (for clarity) after tension has been applied, Figure 8 is a first side view of a further embodiment of a self-drilling anchor bolt according to the invention, Figure 9 is a second side view of the anchor bolt of Figure 8, taken at right angles to the side view of Figure 15 8, Figure 10 is a side view of a proximate end portion after a first drilling phase and second anchoring phase prior to shearing of a shear pin of a further preferred embodiment of an anchor bolt, 20 Figure 11 is a side view of the proximate end portion of the anchor bolt of Figure 10 after the shearing of the shear pin, Figure 12 is a graph of the relationship between applied load and anchor displacement of the anchor bolts of 25 Figures 1 and 2.

- 14 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS First Preferred Embodiment With reference to figures 1 and 3, a self-drilling anchor bolt 10 according to a first preferred embodiment of 5 the invention includes an elongate steel rod or tube 15 provided with a threaded portion 12 at distal end 17, and anchor assembly 18. Anchor assembly 18 is seated against a projecting shoulder formed by a fixed nut 29 driven to the proximate end 13 of threaded portion 12. Also provided at 10 distal end 17 is a drilling tip 14 rigidly attached to rod or tube 15. Self-drilling anchor bolt 10 further includes a drive member or nut 21 rigidly affixed to proximal end 16 of steel rod or tube 15 as well as a support plate 19 and thrust washer 20. is Anchor assembly 18 in this first preferred embodiment includes an expansion sleeve 22 and an expander sleeve 23. Expansion sleeve 22 is provided with at least two diametrically opposed expansion slots 24 open at first end 25 and extending the greater portion of the length of 20 expansion sleeve 22. As may best be seen in the sectioned view of figure 3, expansion sleeve 22 is provided with an internal conically tapering mouth portion 26 adapted to mate with conically tapering end portion 27 of expander sleeve 23 25 Expander sleeve 23 is provided with captive hexagonal nut 28 so nested within the end of expander sleeve 23 that - 15 captive nut 28 cannot rotate relative to expander sleeve 23. Also captive within expander sleeve 23 and projecting from it, is a reaction pin 35. As shown in figures 3 and 3A, reaction pin 35 may take the form of a projecting end 5 of a spring 34 wound around threaded portion 12 and located adjacent nut 28. Alternatively as shown in figure 4, reaction pin 135 could be affixed in hexagonal nut 128. In at least one preferred form of the self-drilling anchor bolt of the present invention expansion sleeve 22 10 and expander sleeve 23 are formed of injection moulded plastic such as for example polypropylene, with elongate rod or tube 15, support plate 19, washer 20 and nuts 21, 28 and 29 of mild steel. Prior to use, the anchor assembly 18 is disposed along 15 threaded portion 12 of elongate rod 15 as shown in figures I and 3, with expansion sleeve 22 seated against fixed nut 29 and with conically tapered end portion 27 of expander sleeve 23 loosely nested just inside conically tapered mouth portion 26 of expansion sleeve 22. 20 With reference now to figure 5, at installation, a socket drive (not shown) is applied to the fixed nut 21 of the self-drilling assembled anchor bolt 10 and the bolt drilled into stratum 33 to form bore hole 32 until support plate 19 is in contact with external surface 24. 25 In the embodiments shown in the accompanying drawings, the configuration of the drilling tip, threaded portion 12 - 16 and projecting pin are arranged for the drilling action to be by clock-wise or right-hand rotation of the socket drive. It will be appreciated that the projecting pin 35 will be subjected to some reaction torque as the anchor 5 bolt is rotationally driven through the stratum and that the torque will be transferred to expander sleeve 23 and nut 28. However the thread of threaded portion 12 is a left-hand thread so that sleeve 23, nut 28 and reaction pin 35 are locked against drilling tip 14 and so are forced to 10 rotate with the clock-wise rotation of drive nut 21 and rod or tube 15. When the bore hole 32 has been drilled to depth so that support plate 19 is in contact with external surface 34, the clockwise rotation is arrested and the driving 15 socket set to reverse anticlockwise rotation. Again projecting pin 35 is subjected to torque (an increased torque due to its orientation) as it comes into contact with the surrounding stratum, but now with the rotation reversed nut 28 is free to rotate relative to threaded 20 portion 12 and, with the increased torque on pin 35, is substantially prevented from rotation within bore hole 32. The effect is that expander sleeve 23 is urged away from drilling tip 14 (as indicated by the arrow in figure 6) as left-hand threaded portion 12 rotates anticlockwise within 25 nut 28.

- 17 This movement of expander sleeve 23 towards proximal end 16 forces the conically tapered end portion 27 of expander sleeve 23 into the conically tapered mouth portion 26 of expansion sleeve 22. The end of expansion sleeve 22 5 is thereby forced outwardly and into contact with the walls of pre-drilled hole 32. As the forced entry of conically tapered end portion 27 progresses further into the end of expansion sleeve 22, expansion sleeve 22 is forced into the walls of bore hole 32 to the limit of compressibility of 10 the surrounding strata as may be seen in figure 6. As this limit is reached plastic deformation of the expander sleeve 23 commences as a result of the compressive forces brought to bear by the intruding expander sleeve, and progresses to the point where plastic flow has 15 substantially forced the material of expander sleeve 23 into all available space within the area of mating 37 of the two sleeves (figure 6) . In effect this forms a virtual continuum of compressed material between threaded portion 12 and the walls of bore hole 32 as best seen in figure 7. 20 This compression forces a degree of embedding of the outer deformed shape of the expansion sleeve 22 into the walls of the hole,. As can also be seen in figure 6, plastic flow includes the formation of ridging 38 as the material of conically tapered end portion of expander sleeve 23 is 25 deformed and flows into expansion slots 24.

-18 Plastic flow also occurs internally in expander sleeve 23 as can be seen in the sectioned view of the expansion sleeve 22 and expander sleeve 23 of figure 7, where the rod or tube 15 has been removed for clarity. Plastic has 5 deformed into the threaded portion 12 of rod 15 and this intrusion 39, together with the ridging 38 leads to a rapid rise in the torque required to be applied to drive nut 21. Consequently a point is reached where the socket drive approaches stall, unable to maintain the rotation against 10 the frictional forces built up in the deformed anchor assembly 18. In tests of the system the torque required to reach a maximum holding capacity of the anchor assembly in coal rib applications for a 27 mm hole was in the range of 160-200 N/m. As can be seen from the graphed result at 15 figure 8, the maximum applied load on the anchor bolt of this first preferred embodiment was of the order of 55 kN for a displacement of just over 30 mm. Second Preferred Embodiment In a second preferred embodiment of the invention as 20 shown in figures 1 and 4, in which like features are like numbered but with the addition of 100, an intermediate expansion sleeve 140 is interposed between expansion sleeve 122 and expander sleeve 123. Intermediate expansion sleeve 140 is similar in all respects to expansion sleeve 122 25 except that its end 141 is conically tapered in the manner of expander sleeve 123 so as to allow end 141 to nest in 19 the conically tapered mouth portion 126 of expansion sleeve 122. The process of installation of the bolt of this second embodiment is identical in every respect to that described 5 for the first embodiment so that after the bolt is drilled to depth to form bore hole 132 the socket drive applied to drive nut 121 is reversed as previously described. As before, the anticlockwise rotation of rod 115 draws expander sleeve 123 in towards intermediate expansion 10 sleeve 140 and in turn draws intermediate expansion sleeve 140 in toward expansion sleeve 122. Thus in this second preferred embodiment of the invention, there is a doubling of the area of expansion sleeves which is forced outwardly against the walls of bore 15 hole 132. External deformation in the formation of ridging now occurs on both expander sleeve 123 and intermediate expansion sleeve 140 and both these sleeves undergo plastic flow into the thread of rod 115. Similarly, ridging of expander sleeve 123 occurs into expansion slots 144 of 20 intermediate expansion sleeve 140 and of intermediate expansion sleeve 140 into the expansion slots 124 of expansion sleeve 122. By this means the holding force of the bolt is significantly increased as may be seen from the test result in figure 8 where for this embodiment of the 25 invention a maximum applied load of somewhat over 75 kN was achieved for a displacement of under 50 mm.

- 20 Expansion sleeves need not be limited to a maximum of two, thus in further .preferred embodiments of the invention three or more expansion sleeves may be employed. Bolts may be delivered to the site of application 5 fully pre-assembled. Bolts may be drilled into position and locked in their respective bore holes in a single setting operation requiring a single application of a socket driver, firstly drilling with the drive set to clockwise and then reversed to anticlockwise.. 10 As will be apparent from figures 5 and 6, the travel between the initial installed position of expander sleeve 23 relative to expansion sleeve 22 in fig-ure 5, and the fully engaged position of the two sleeves in figure 6, is relatively short. Thus installation is very rapid. is It will be apparent that although the embodiments above are described in terms of clockwise rotation for drilling and anticlockwise for locking, bolts and nut could be arranged with a right-hand thread, anticlockwise drilling tip and reoriented projecting pin, to achieve the 20 same effect with anticlockwise drilling and clockwise locking. Figure 10 shows a comparison of the amount of displacement for given loads for the single and double expansion sleeves of the first and second embodiments. 25 Third Preferred Embodiment - 21 In a further preferred embodiment of a self-drilling anchor bolt with anchor assembly with reference to Figures 8 and 9, anchor bolt 200 comprises an elongate steel rod or tube 215 provided with a somewhat larger diameter threaded 5 section 212 toward distal end 217. Provided at distal end 217 is a drilling tip 214 and at proximate end 216, a drive nut 221, both rigidly affixed to rod or tube 215. Elongate rod or tube 215 is provided with a left hand threaded section 212 towards distal end 217, with a nut 229 at the 10 thread run-out forming a projecting shoulder. In this embodiment, anchor assembly 218 (coextensive with threaded section 212) is made up of a number of elements arranged to form a segmented sleeve about the threaded section 212. Adjacent to the drilling tip 214 is a 15 first expander sleeve 223. The distal end of first expander sleeve 223 encapsulates a captive hexagonal nut (not visible in Figures 8 and 9), in the same manner as described for the first and second embodiments above and as shown in Figures 3 and 4. Also in the same manner as for 20 those embodiments, first expander sleeve 223 is provided with a projecting reaction pin 235. Located adjacent nut 229 is a second expander sleeve 230 which is provided with outwardly projecting reaction members 231. Both first expander sleeve 223 and second 25 expander sleeve 230 are provided with a pair of wedge shaped sections 225 and 227 respectively.

- 22 Located between first and second expander sleeves 223 and 230, are a pair of expansion leaves 240A and 240B, shaped with outer ends arranged so as to overlap the wedge shaped sections of the two expander sleeves, leaving gaps 5 244 between the separate elements of anchor assembly 218. Expander sleeves 223 and 230, and expansion leaves 240A and 240B are moulded as one unit from a suitable polymer, with small frangible interconnection elements in gaps 244 (not shown). This is to allow fitting of the anchor assembly 218 10 to the threaded section 212 (prior to attachment of the drilling tip) as one unit, and also to retain the separate expansion leaves in position during transport of the anchor bolt and the drilling phase of the bolt when in use. As described for the first and second embodiments 15 above, the bolt 200 is drilled into strata by the application of suitable drive source applied to drive nut 221 rotating the bolt 200 in a first clockwise or right hand direction. When the bolt is fully drilled into the stratum, such that plate 219 abuts the stratum wall, the 20 drive source is switched to anti-clockwise rotation. Reaction pin 235 substantially restricts the rotation of first expander sleeve so that rotation of the left hand thread within the encapsulated nut drives the nut and hence the expander sleeve away from the drilling tip. This forces 25 wedge shaped sections 225 against the distal end overlapping portions of the expansion leaves 240A and 240B, 23 and in turn forces the proximal end overlapping portions of the expansion leaves against the wedge shaped sections 227 of the second expander sleeve 230. As a result, expansion leaves 240A and 24DB are driven outwardly, fracturing the 5 friable connections between the leaves and expander sleeves, to engage with the sides of the bore hole drilled in the stratum. Fourth Preferred Embodiment In this further preferred embodiment, with reference 10 to Figures 10 and 11, an anchor bolt 215 again includes an elongate rod or tube 115 provided at a distal end, as described above, with a rigidly affixed drilling tip and anchor assembly (not shown in Figures 10 and 11) . In this embodiment however proximate end 216 is provided with a 15 short section of left hand thread 217 with drive nut 221 locked to the outer end of thread 217 by a shear pin 223. In use, a suitable drive tool (not shown) engages drive nut 221 and rotates the anchor bolt in clockwise direction to drill the bolt into the strata 229 until 20 support plate 219 contacts the strata surface 231 and the anchor bolt has been driven to depth. Again, as described above, the rotation of the drive tool is now reversed to anti-clockwise, causing the anchor assembly to expand against the sides of the bore hole. As 25 expansion increases, torque applied by the drive tool also increases to a predetermined maximum where resistance of - 24 rod or tube 215 to rotation causes pin 223 to snap, freeing drive nut 221 on the section of left hand thread 217. Anti-clockwise rotation of drive nut 221 on the left hand thread when rod or tube 215 is no longer rotating, 5 advances the nut towards the distal end of anchor bolt 200, driving support plate 219 hard against the surface of the strata and further increasing the anchorage of the bolt in the bore hole. 10 The above describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope and spirit of the present invention.

Claims (41)

1. A self-drilling anchor bolt for the stabilising of strata, said anchor bolt including: (a) an elongate steel rod or tube; (b) a drilling tip rigidly affixed at a distal end of said rod or tube; (c) an anchor assembly comprising at least one expander sleeve provided with an encapsulated nut retained in said sleeve, and wherein rotation of said anchor bolt in a first direction drills a bore hole, and subsequent rotation of said anchor bolt in a second opposite direction causes expansion of said anchor assembly so as to anchor said anchor bolt in said bore hole.

2. The anchor bolt of claim 1 wherein said anchor assembly is adapted to induce plastic flow of at least one element of said anchor assembly so as to form a continuum of material between said rod and sides of said hole.

3. The anchor bolt of claim 1 or 2 wherein said strata is a portion of any one of a range of geological strata; said range including a coal rib.

4. The anchor bolt of any one of claims 1 to 3 wherein said elongate steel rod or tube is provided at said distal end with a threaded portion; said threaded portion handed in said second opposite direction.

5. The anchor bolt of any one of claims 1 to 4 wherein said anchor assembly includes at least one expander element and at least one expansion element. -26

6. The anchor bolt of any one of claims 1 to 5 wherein said anchor assembly includes one expander sleeve and one expansion sleeve.

7. The anchor bolt of any one of claims 1 to 5 wherein said anchor assembly included one expander sleeve and two expansion sleeves.

8. The anchor bolt of any one of claims 1 to 5 wherein said anchor assembly includes first and second expander sleeves and a pair of expansion sleeves; said first and second expander sleeves and said expansion leaves interconnected by frangible connector elements.

9. The anchor bolt of any one of claims 5 to 8 wherein said at least one expander element and said at least one expansion element have an outer diameter not greater than the drilling diameter of said drilling tip.

10. The anchor bolt of any one of claims 6 to 8 wherein said rod or tube is provided with a projecting shoulder at a proximate end of said threaded portion; said at least one expansion sleeve and said at least one expander sleeve located between said drilling tip and said projecting shoulder.

11. The anchor bolt of any one of claims 5 to 10 wherein each of said at least one expansion element is in the form of a tubular expansion sleeve provided with at least one pair of opposing expansion slots; said slots extending from a distal end of said expansion sleeve towards a proximal end of said expansion sleeve; said at least one pair of opposing slots extending for a proportion of the length of said expansion sleeve. 5

12. The anchor bolt of claim 11 wherein, prior to use, each of said at least one expansion sleeve has an internal diameter -27 adapted to accept said threaded portion of said elongate steel rod or tube as a free sliding fit; said internal diameter extending from said proximal end of said expansion sleeve for a first portion of said length of said expansion sleeve.

13. The anchor bolt of claim 11 or 12 wherein each generally conically outward tapering second portion increasing from said internal diameter to a diameter approaching an outer diameter of said at least one expansion sleeve at said distal end.

14. The anchor bolt of any one of claims 6 to 13 wherein at least one said expander sleeve is located adjacent said drilling tip.

15. The anchor bolt of any one of claims 10 to 14 wherein at least one said expansion sleeve is located adjacent said projecting shoulder.

16. The anchor bolt of claim 10 wherein a first of said expander sleeves is located adjacent said drilling tip; a second of said expander sleeves is located adjacent said projecting shoulder, and wherein said pair of expansion leaves are located between said first and second expander 5 sleeves.

17. The anchor bolt of claim 16 wherein said first and second expander sleeves are each provided with a pair of wedge shaped portions; said wedge shaped portions adapted to 0 force apart said pair of expansion leaves.

18. The anchor bolt of any one of claims 5 to 17 least one expansion element are formed of injection moulded plastic. 5

19. The anchor bolt of any one of claims 14 to 18 wherein said expander sleeve adjacent said drilling tip is provided with the encapsulated nut at a distal end of said expander -28 sleeve; the thread of said nut engaging with the thread of said threaded portion at said distal end of said elongate steel rod or tube.

20. The anchor bolt of any one of claims 14 to 19 wherein said expander sleeve adjacent said drilling tip is provided with a reaction pin projecting from said expander sleeve.

21. The anchor bolt of claim 20 wherein said reaction pin is a projecting end of a spring wound around said threaded portion; said reaction pin projecting from said sleeve adjacent said encapsulated nut.

22. The anchor bolt of claim 20 wherein said reaction pin projecting from said expander sleeve is affixed to said encapsulated nut.

23. The anchor bolt of claim 21 wherein, prior to use, said expander sleeve has an internal diameter adapted to accept said threaded portion of said elongate steel rod or tube as a free sliding fit for that portion the length of said expander sleeve not taken up by said encapsulated threaded nut and said spring.

24. The anchor bolt of any previous claim wherein said expander sleeve is provided with an external generally conically tapering section extending from a proximal end for a portion of the length of said expander sleeve; said tapering portion adapted to nest within said internal D generally conically outward tapering second portion of said at least one expansion sleeve.

25. The anchor bolt of any one of claims 1 to 24 wherein said elongate steel rod or tube is provided at a proximal end 5 with a fixed drive member. -29

26. The anchor bolt of claim 25 wherein said elongated steel rod or tube is provided at said proximal end with a section of thread; said thread handed in said second opposite direction.

27. The anchor bolt of claim 26 wherein said drive member is a nut locked to said section of thread by a shear pin; said shear pin adapted to shear rod or tube so as to free said nut on said section of thread.

28. The anchor bolt of claim 26 or 27 wherein said nut is driven towards said distal end of said anchor bolt when rotation is applied to said nut in said second opposite direction and said pin has sheared.

29. The anchor bolt of any one of claims i to 28 wherein said elongate steel rod or tube is urged into said first rotation direction and said second opposite rotation direction by the application of a suitable driver to said drive member.

30. The anchor bolt of any one of claims 20 to 29 wherein said reaction pin is adapted to substantially prevent rotation of said at least one expander sleeve adjacent said drilling tip when said elongate steel rod or tube is rotated in said second opposite direction.

31. The anchor bolt of any one of claims 6 to 30 wherein rotation in said second opposite direction of said elongate 3 steel rod or tube relative to said expander sleeve causes movement of said expander sleeve along said threaded portion away from said drilling tip.

32. The anchor bolt of claim 31 wherein said movement of 5 said expander sleeve forces an expansion of said at least one expansion element; said expansion forcing portions of said expansion element against the surrounding surface of said -30 bore hole; said expander sleeve consequently subject to deformation of internal and external surfaces.

33. The anchor bolt of claim 32 wherein said expansion approaches a limit defined by extent of deformation of said expander sleeve and said at least one expansion element; said expansion further limited by limit of compressibility of said strata around said anchor assembly.

34. The anchor bolt of claim 33 wherein said deformation of said expander sleeve occurs in the form of plastic flow with the continued application of rotation by said driver to said drive member; said deformation including the formation within said expansion slots of ridge-like protrusions from said external generally conically tapering section; said deformation further including the forming of an internal thread for a portion of said internal diameter of said expander sleeve.

35. An anchor bold as herein described and with reference to the accompanying drawings.

36. A method for stabilizing strata by the application of a self-drilling anchor bolt; said method including the steps of drilling said anchor bolt into said strata by rotation in a first direction to form a bore hole; said method further including providing for mechanically expanding portions of an anchor assembly of said anchor bolt by rotation of said anchor bolt in a second opposite direction; and wherein said mechanically expanding portion includes at least an expander sleeve incorporating an encapsulated nut within said expander sleeve.

37. The method of claim 36 wherein said method includes the 5 further steps of continuing to apply said rotation to induce maximal expansion within said hole of said expanding anchor assembly until rotation approaches stall due to constriction -31 by said stratum and plastic flow of at least one of said expansion components.

38. The method of claim 36 or 37 wherein said anchor assembly includes plastic expander elements and expansion elements.

39. The method of claim 38 wherein said plastic expander and expansion elements are injection moulded from any of a range of suitable plastics adapted to deform under compressive forces; said range including polypropylene, polyethylene with or without glass fibre reinforcing.

40. The method of any one of claims 38 or 39 wherein said anchor assembly deforms to a point where at least an outer portion of said anchor assembly is embedded in walls of said bore hole; said deformation including plastic flow of a portion of at least one of said plastic elements into a threaded portion of said elongate steel rod.

41. A method for the anchoring of an anchor bolt within a hole drilled in an area of strata; said method including the inducement of plastic flow by compression of anchor elements so as to form a continuum of compressed material between said bolt and the confines of said hole as herein described and with reference to the accompanying drawings.