AU2004210565B2

AU2004210565B2 - Anchor Bolt

Info

Publication number: AU2004210565B2
Application number: AU2004210565A
Authority: AU
Inventors: Ghassan Skybey
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 2003-09-18
Filing date: 2004-09-10
Publication date: 2009-10-08
Anticipated expiration: 2024-09-10
Also published as: AU2004210565A1

Description

P/00/009 Regulation 3.2 AUSTRALIA Patents Act 1990 STANDARD SPECIFICATION Invention Title: ANCHOR BOLT The invention is described in the following statement: Our Ref: 042016 -2 ANCHOR BOLT The present invention relates to anchor bolts or roof anchor type mechanisms for the stabilizing or control of strata such as in a mine or tunnel and, more particularly 5 to such mechanisms adapted for use in coal mines and sometimes known as coal rib anchors. BACKGROUND 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insertion of the resin cartridge requires the hole to be clean; any material collapsing into the hole as the drill is withdrawn requires a time consuming clearing operation.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 It is an object of the present invention to address or at least ameliorate some of the above disadvantages. BRIEF DESCRIPTION OF INVENTION Accordingly, in one broad form of the invention, there is 25 provided an anchor bolt system for the stabilising of host material; said anchor bolt including an elongate rotatable -4 steel rod provided at a distal end with an anchor assembly adapted for expansion within the confines of a hole drilled into said host material so as to anchor said anchor assembly in said hole; said anchor assembly adapted to 5 induce plastic flow of at least one element of said anchor assembly so as to form a continuum of material between said rod and said confines of said hole. Preferably said host material is a portion of any one of a range of geological strata; said range including a coal 10 rib. Preferably said anchor assembly includes an expander sleeve and at least one expansion sleeve. Preferably said expander sleeve and said at least one expansion sleeve are formed of injection moulded plastic. 15 Preferably said expander sleeve and said at least one expansion sleeve have an outer diameter sufficiently smaller than said hole drilled in said strata so as to allow insertion of said anchor assembly into said hole as a free sliding clearance fit. 20 Preferably said elongate rotatable steel rod is provided at said distal end with a right hand threaded portion fitted with a steel nut positioned at the thread run-out end of said threaded portion; said steel nut providing a projecting shoulder to prevent movement of said expansion sleeve towards a proximal end of said elongate rotatable steel rod. Preferably said at least one expansion sleeve is in the 5 form of a tubular portion provided with at least one pair of opposing expansion slots extending from a distal end of said at least one expansion sleeve towards a proximal end of said at least one expansion sleeve for a proportion of the length of said at least one expansion sleeve. 10 Preferably said at least one expansion sleeve has prior to use an internal diameter adapted to mate with said threaded portion of said elongate rotatable steel rod as a free sliding fit for a first portion of said length of said at least one expansion sleeve extending from said proximal 15 end. Preferably 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 20 one expansion sleeve. Preferably said expander sleeve is provided with an encapsulated threaded steel nut at a distal end of said expander sleeve; the thread of said threaded steel nut engaging with the thread of said threaded portion of the -6 steel nut at said distal end of said elongate -rotatable steel rod. Preferably said expander sleeve has prior to use an internal diameter adapted to mate with said threaded 5 portion of said elongate rotatable steel rod as a free sliding fit for that portion the length of said expander sleeve not taken up by said encapsulated threaded steel nut. Preferably said expander sleeve is provided with an 10 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 generally conically outward tapering second portion of said at least one expansion sleeve. 15 Preferably said expander sleeve is provided with at least one pair of projecting lugs toward said distal end of said expander sleeve; said lugs projecting sufficiently beyond said external diameter of said expander sleeve so as to prevent rotation of said expander sleeve by intrusion into 20 the walls of said hole drilled in said strata. Preferably said elongate rotatable steel rod is provided at a proximal end with a right hand threaded portion, a support plate, thrust washer and a drive nut.

-7 Preferably said elongate rotatable steel rod is urged into clockwise rotation by the application of a suitable driver to said drive nut. Preferably clockwise rotation of said elongate rotatable 5 steel rod relative to said expander sleeve causes said expander sleeve to be drawn along said threaded portion towards said proximal end of said elongate rotatable steel rod. Preferably said expander sleeve forces an expansion of said 10 at least one expansion sleeve; said expansion forcing portions of said expansion sleeve against the surrounding surface of said hole drilled into said strata; said expander sleeve consequently subject to deformation of internal and external surfaces. 15 Preferably said expansion approaches a limit defined by extent of deformation of said expander sleeve and said at least one expansion sleeve; said expansion further limited by limit of compressibility of said strata around said anchor assembly. 20 Preferably deformation of said expander sleeve occurs in the form of plastic flow with the continued application of rotation by said driver to said drive nut; said deformation including the formation within said expansion slots of ridge-like protrusions from said external -8 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. In a further broad form, there is provided a method for the 5 stabilizing of a host material by the application of anchor bolts; said method including the steps of; (a) Providing anchor bolts; each one of said anchor bolts comprised of an elongate steel rod having an expanding anchor assembly including plastic 10 expansion components at a distal end and operating means at a proximal end, (b) Drilling a suitable hole in said host material adapted to allow insertion of one of said anchor bolts so as to place said distal end 15 toward an inner end of said hole with said support plate in contact with the surface of said host material at the entry of said hole, (c) Applying rotation to said operating means and said elongate steel rod so as .to cause 20 expansion of said anchor assembly, (d) Continuing to apply said rotation to induce maximal expansion within said hole of said expanding anchor assembly until rotation -9 approaches stall due to constriction by said stratum and plastic flow of at least one of said expansion components. Preferably said operating means include a portion of thread 5 engaging a drive nut, a thrust washer and a support plate. Preferably said plastic components are injection moulded from any of a range of suitable plastic adapted to deform under compressive forces; said range including polypropylene, polyethylene with or without glass fibre 10 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 hole; said deformation including plastic flow of a portion of at least one of said plastic 15 components into a threaded portion of said elongate steel rod. In a further broad form of the invention, there is provided a method for the anchoring of an anchor bolt within a hole drilled in an area of host material; said method including 20 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.

- 10 BRIEF DESCRIPTION OF DRAWINGS Embodiments of the present invention will now be described with reference to the accompanying drawings wherein: 5 Figure 1 is a view of an anchor bolt according to a first preferred embodiment of the invention when first installed in a hole drilled in a stratum of friable material. Figure 2 is a view of an anchor bolt according to a 10 second preferred embodiment of the invention when first installed in a hole drilled in a stratum of friable material. Figure 3 is a sectioned side view of a portion of the anchor bolt of figure 1. 15 Figure 4 is a sectioned side view of a portion of the anchor bolt of figure 2. Figure 5 is a view of the anchor bolt of figure 1 at the end of a first preparatory stage. Figure 6 is a view of the anchor bolt of figures 1 and 20 5 when approaching a point of maximum load capacity. Figure 7 is a sectional side view of a portion of the anchor bolt of figure 6 with the threaded rod removed after tension has been applied. Figure 8 is a graph of the relationship between 25 applied load and anchor displacement of the anchor bolts of figures 1 and 2.

- 11 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS With reference to figure 1, an anchor bolt 10 according to a first preferred embodiment of the invention 5 includes an elongate rotatable steel rod 15 threaded at both proximal end 16 and distal end 17, and anchor element 18. Anchor bolt 10 further includes support plate 19, thrust washer 20 and drive nut 21 assembled to proximal end 16 of steel rod 15. 10 Anchor assembly 18 in this first preferred embodiment is made up of expansion sleeve 22 and 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 15 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. 20 Expander sleeve 23 is provided with captive hexagonal nut 28 so nested within the end of expander sleeve 23 that captive nut 28 cannot rotate relative to expander sleeve 23. In at least one preferred form of the anchor bolt of 25 the present invention expansion sleeve 22 and expander sleeve 23 are formed of injection moulded plastic such as - 12 for example polypropylene, with elongate rod 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 threaded distal end 17 of elongate rod 15 as shown in 5 figures 1 and 3, with expansion sleeve 22' seated against a fixed nut 29 locked at the thread run-out 30 of threaded distal end 17 to provide a projecting shoulder and with conically tapered end portion 27 of expander sleeve 23 nested just inside conically tapered mouth portion 26 of 10 expansion sleeve 22. Turning again to figure 1, at installation the assembled anchor bolt 10 as so far described is inserted into a pre-drilled hole 32 in stratum 33 until support plate 19 is in contact with external surface 34. Any loose 15 material which may have fallen into the hole as the drill was withdrawn is simply pushed to the end of the hole which may be drilled a little deeper than required for this purpose. The diameter of pre-drilled hole 32 is just slightly 20 larger than the external diameter of anchor assembly 18. Thus for example in one particular preferred embodiment the outer diameter of anchor assembly 18 as inserted is 25 mm with the pre-drilled hole having a diameter of 27 mm. At least two diametrically opposed lugs 35 which 25 project from the surface of expander sleeve 23 are forced, during the insertion of the anchor bolt, to sufficiently -13 intrude into the surrounding stratum so as to provide initial resistance to any rotation of the anchor assembly. A suitable socket drive (not shown) is now engaged with drive nut 21 to initially pull elongate rod 15 5 outwardly from pre-drilled hole 32 until the drive nut 21 locks up against the thread. run-out 36 of proximal end 16 as can be seen in figure 5. This forces elongate rod 15 to also rotate with drive nut 21, clockwise as viewed from proximal end 16. Since expander sleeve 23 is prevented from 10 rotation within pre-drilled hole 32 by lugs 35, the effect is that expander sleeve 23 is drawn towards proximal end 16 by the interaction of the rotation of the threaded portion of distal end 17 of rod 15 within captive nut 28. This movement of expander sleeve 23 towards proximal 15 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 is thereby forced outwardly and into contact with the walls of pre-drilled hole 32. As the forced entry of conically 20 tapered end portion 27 progresses further into the end of expansion sleeve. 22, expansion sleeve 22 is forced into the walls of pre-drilled hole 32 to the limit of compressibility of the surrounding strata as may be seen in figure 6. 25 As this limit is reached plastic deformation of the expander sleeve 23 commences as a result of the compressive - 14 forces brought to bear by the intruding expander sleeve, and progresses to the point where plastic flow has substantially 'forced the material of expander sleeve 23 into all available space within the area of mating 37 of 5 the two sleeves (figure 6) . In effect this forms a virtual continuum of compressed material between rod 15 and the walls of hole 32 as best seen in figure 7. This compression forces a degree of embedding of the outer deformed shape of the expansion sleeve into the walls of the hole. As can 10 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 deformed and flows into expansion slots 24. Plastic flow also occurs internally in expander sleeve 15 23 as can be seen in the sectioned view of the expansion sleeve 22 and expander sleeve 23 of figure 7, where the threaded rod 15 has been removed for clarity. Plastic has deformed into the thread of rod 15 and this intrusion 39 together with the ridging 38 leads to a rapid rise in the 20 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 the frictional forces built up in the deformed anchor assembly. In tests of the system the torque required to reach a maximum 25 holding capacity of the anchor assembly in coal rib applications for a 27 mm hole was in the range of 160- 200 - 15 N/m. As can be seen from the graphed result at 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. 5 In a second preferred embodiment of the invention as 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 10 140 is similar in all respects to expansion sleeve 122 except that its end 141 is conically tapered in the manner of expander sleeve 123 so as to allow end 141 to nest in the conically tapered mouth portion 126 of expansion sleeve 122. 15 The process of installation of the bolt of this second embodiment is identical in every respect to that described for the first embodiment so that after the bolt is inserted into drilled hole 132 a socket drive is applied to drive nut as previously described. After the drive nut has locked 20 to rod 115 by running up against the thread run out 136, the rotation of rod 115 draws expander sleeve 123 in toward intermediate expansion sleeve 140 and in turn draws intermediate expansion sleeve 140 in toward expansion sleeve 122. 25 Thus in this second preferred embodiment of the invention, there is a doubling of the area of expansion -16 sleeves which is forced outwardly against the walls of 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 5 flow into the thread of rod 115. Similarly, ridging of expander sleeve 123 occurs into expansion slots 144 of 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 10 the bolt is significantly increased as may be seen from the test result in figure 8 where for this embodiment of the invention a maximum applied load of somewhat over 75 kN was achieved for a displacement of under 50 mm. Expansion sleeve's need not be limited to a maximum of 15 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 fully pre-assembled. After the drilling of the hole the bolt may be inserted without any further preparation and 20 the socket drive applied. 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 figure 5, and the fully engaged position of the two sleeves in figure 6, is 25 relatively short. Thus installation is very rapid.

- 17 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. Thus 5 for example, the proximal end of the bolt need not be threaded but may be fitted with a forged head or nut capable of accepting a rotational drive device. Similarly the fixed nut at the thread run-out at the distal end of the elongate rod may be replaced by a fixed collar for 10 example.

Claims

1. An anchor bolt system for the stabilising of host material; said anchor bolt including an elongate rotatable steel rod provided at a distal end with an 5 anchor assembly adapted for expansion within the confines of a hole drilled into said host material so as to anchor said anchor assembly in said hole; said anchor assembly adapted to induce plastic flow of at least one element of said anchor assembly so as to 10 form a continuum of material between said rod and said confines of said hole.

2. The anchor bolt system of claim 1 wherein said host material is a portion of any one of a range of geological strata; said range including a coal rib. 15

3. The anchor bolt system of claim 1 or 2 wherein said anchor assembly includes an expander sleeve and at least one expansion sleeve.

4. The anchor bolt system of claim 3 wherein said expander sleeve and said at least one expansion sleeve 20 are formed of injection moulded plastic.

5. The anchor bolt system of claim 3 or 4 wherein each of said expander sleeve and said at least one expansion sleeve have an outer diameter sufficiently smaller -19 than said hole drilled in said strata so as to allow insertion of said anchor assembly into said hole as a free sliding clearance fit.

6. The anchor bolt system of any one of claims 3 to 5 5 wherein said elongate rotatable steel rod is provided at said distal end with a right hand threaded portion fitted with a steel nut positioned at the thread run out end of said threaded portion; said steel nut providing a projecting shoulder to prevent movement of 10 said expansion sleeve towards a proximal end of said elongate rotatable steel rod.

7. The anchor bolt of any one of claims 3 to 6 wherein said at least one expansion sleeve is in the form of a tubular portion provided with at least one pair of 15 opposing expansion slots extending from a distal end of said at least one expansion sleeve towards a proximal end of said at least one expansion sleeve for a proportion of the length of said at least one expansion sleeve. 20

8. The anchor bolt of claim 5 or 6 wherein said at least one expansion sleeve has prior to use an internal diameter adapted to mate with said threaded portion of said elongate rotatable steel rod as a free sliding fit for a first portion of said length of said at - 20 least one expansion sleeve extending from said proximal end.

9. The anchor bolt of claim 8 wherein said at least one expansion sleeve has an internal generally conically 5 outward tapering second portion increasing from said internal diameter to a diameter approaching said outer diameter of said at least one expansion sleeve.

10. The anchor bolt system of any one of claims 6 to 9 wherein said expander sleeve is provided with an 10 encapsulated threaded steel nut at a distal end of said expander sleeve; the thread of said threaded steel nut engaging with the thread of said threaded portion of the steel nut at said distal end of said elongate rotatable steel rod. 15

11. The anchor bolt system of claim 10 wherein said expander sleeve has prior to use an internal diameter adapted to mate with said threaded portion of said elongate rotatable steel rod as a free sliding fit for that portion the length of said expander sleeve not 20 taken up by said encapsulated threaded steel nut.

12. The anchor bolt system of any one of claims 9 to 11 wherein said expander sleeve is provided with an external generally conically tapering section extending from a proximal end for a portion of the -21 length of said expander sleeve; said tapering portion adapted to nest within said internal generally conically outward tapering second portion of said at least one expansion sleeve. 5

13. The anchor bolt system of any one of claims 10 to 12 wherein said expander sleeve is provided with at least one pair of projecting lugs toward said distal end of said expander sleeve; said lugs projecting sufficiently beyond said external diameter of said 10 expander sleeve so as to prevent rotation of said expander sleeve by intrusion into the walls of said hole drilled in said strata.

14. The anchor bolt of any one of claims 1 to 13 wherein said elongate rotatable steel rod is provided at a 15 proximal end with a right hand threaded portion, a support plate, thrust washer and a drive nut.

15. The anchor bolt system of claim 14 wherein said elongate rotatable steel rod is urged into clockwise rotation by the application of a suitable driver to 20 said drive nut.

16. The anchor bolt system of claim 15 wherein clockwise rotation of said elongate rotatable steel rod relative to said expander sleeve causes said expander sleeve to -22 be drawn along said threaded portion towards said proximal end of said elongate rotatable steel rod.

17. The anchor bolt of any one of claims 2 to 16 wherein said expander sleeve forces an expansion of said at 5 least one expansion sleeve; said expansion forcing portions of said expansion sleeve against the surrounding surface of said hole drilled into said strata; said expander sleeve consequently subject to deformation of internal and external surfaces. 10

18. The anchor bolt of claim 17 wherein said expansion approaches a limit defined by extent of deformation of said expander sleeve and said at least one expansion sleeve; said expansion further limited by limit of compressibility of said strata around said anchor 15 assembly.

19. The anchor bolt of claim 18 wherein deformation of said expander sleeve occurs in the form of plastic flow with the continued application of rotation by said driver to said drive nut; said deformation 20 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 - 23 portion of said internal diameter of said expander sleeve.

20. A method for the stabilizing of a host material by the application of anchor bolts; said method including the 5 steps of; (a) Providing anchor bolts; each one of said anchor bolts comprised of an elongate steel rod having an expanding anchor assembly including plastic expansion components at a distal end and 10 operating means at a proximal end, (b) Drilling a suitable hole in said host material adapted to allow insertion of one of said anchor bolts so as to place said distal end toward an inner end of said hole with said 15 support plate in contact with the surface of said host material at the entry of said hole, (c) Applying rotation to said operating means and said elongate steel rod so as to cause expansion of said anchor assembly, 20 (d). 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 - 24 stratum and plastic flow of at least one of said expansion components.

21. The method of claim 20 wherein said operating means include a portion of thread engaging a drive nut, a 5 thrust washer and a support plate.

22. The method of claim 20 or 21 wherein said plastic components are injection moulded from any of a range of suitable plastic adapted to deform under compressive forces; said range including 10 polypropylene, polyethylene with or without glass fibre reinforcing.

23. The method of any one of claims 20 to 22 wherein said anchor assembly deforms to a point where at least an outer portion of said anchor assembly is embedded in 15 walls of said hole; said deformation including plastic flow of a portion of at least one of said plastic components into a threaded portion of said elongate steel rod.

24. A method for the anchoring. of an anchor bolt within a 20 hole drilled in an area of host material; 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 - 25 the confines of said hole as herein described and with reference to the accompanying drawings. 5 DATED: 3 September 2004 10 Ghassan Skybey by his Patent Attorneys: WALL INGTON -DUMMR