WO2012015349A1

WO2012015349A1 - A rock bolt and an anchoring device

Info

Publication number: WO2012015349A1
Application number: PCT/SE2011/050755
Authority: WO
Inventors: John Horsch
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2010-07-30
Filing date: 2011-06-16
Publication date: 2012-02-02
Anticipated expiration: 2013-01-30
Also published as: ZA201300701B; AU2010206071A1; US20130129425A1; AU2010206071B2; CN103038448A

Abstract

A rock bolt (10) comprising an elongate shaft (11), and an anchoring device attached to the shaft having an expansion mechanism (15) which is operable to expand radially relative to the lengthwise extent of the shaft (11) to anchor the rock bolt (10) within a bore (40) drilled into a rock body (41). The anchoring device includes an annular band (45) which extends about the expansion mechanism (15) to resist expansion of the mechanism (15). The band is arranged so it can enter the bore (40) in which the bolt (10) is to be anchored in position about the expansion mechanism (15) and to maintain a resistance to expansion of the expansion mechanism (15) at least until the expansion mechanism (15) has substantially fully entered the bore (40). The band (45) can be a polymeric material such as a heat shrink polymeric material in tight fitting engagement about the expansion mechanism (15) so as to conform to the external shape of the expansion mechanism (15).

Description

A ROCK BOLT AND AN ANCHORING DEVICE

TECHNICAL FIELD

The present invention relates to rock bolts suitable for stabilization of rock walls and faces, such as for use in the underground mining and tunneling industry. The present invention has been developed for use with rock bolts that employ a mechanical expander which is used to anchor or assist anchoring the rock bolt in a bore into which the bolt has been installed. The present invention can be employed with rock bolts that are inserted into a pre-drilled bore or it can be employed with self drilling rock bolts.

BACKGROUND

Roof and wall support is vital in underground mining and tunneling operations. Mine and tunnel walls and roofs often consist of rock strata which requires reinforcement to prevent failure, such as fragmentation or collapse. Rock bolts are widely used for reinforcement purposes. In some forms of rock bolt, a bore is drilled into the rock wall and thereafter the rock bolt is inserted into the bore and is secured therein, such as by a resin or a cement grout. In other forms of rock bolt, a drilling tip is applied to the leading end of the bolt and the bolt itself is drilled into the rock wall. Once the bolt has been drilled to the desired depth, the bolt is secured within the bore, usually in the same manner as the first described rock bolt, i.e. with a suitable resin or cement grout.

Some forms of rock bolts include a mechanical anchor, usually at the leading end of the bolt, to either form the sole means of anchoring the rock bolt in the bore, or to provide a second form of anchoring, such as in addition to resin or cement grout. The mechanical anchor can include some form of expander that is expanded once the rock bolt has been inserted the desired depth in the rock wall. Applicant's co-pending International Patent Application WO 2008/06021 1 discloses such a rock bolt.

A difficulty with the use of an expandable mechanical anchor is maintaining the anchor contracted prior to the actual need for anchoring to take place, i.e. during storage and transport of the rock bolt and during insertion of the rock bolt into a pre- drilled bore, or during drilling of the bore if the rock bolt is a self drilling bolt. Applicant's co-pending International Patent Application WO 2008/06021 1 discloses the use of an annular band disposed about the expander portion of a mechanical anchor at the leading end of a self-drilling rock bolt to constrain the expander portion against expansion during transport and the commencement of drilling. The band extends about the anchor, which is rearward of the drilling tip and prevents it from expanding. The annular band is intended to engage against the facing surface of the rock wall or face immediately adjacent the bore which is drilled into the rock, so that the band does not enter the bore but rather, remains outside the bore and slips relative to the anchor as the anchor enters the bore with the rest of the rock bolt as the bolt drills into the rock. As the anchor slips relative to the band and enters the bore, the anchor continues to be constrained from expansion by engagement with the internal surface of the bore, so that continued restraint by the band is not required. In practice, the annular band has been provided as a relatively thick, rigid plastic ring. The thickness ensures the required engagement with the rock wall or face immediately adjacent the bore to cause the band to slip relative to the anchor as the anchor enters the bore and ensures that the band does not enter the bore because the outside diameter of the band is greater than the internal diameter of the bore.

While the use of the ring described above has benefits, it has been found that the ring can be dislodged in the early stages of rock wall drilling and before the anchor is within the bore. Dislodgement of the band can occur for example, during drilling through wire safety mesh which overlies a rock wall or face, or other mining or rock structures in the vicinity of the rock wall or face. Following dislodgement, the anchor can expand prematurely prior to complete entry into the bore, and that can result in breakage of the anchor.

It is an object of the present invention to overcome or at least alleviate one or more disadvantages associated with the prior art. SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, there is provided a rock bolt comprising an elongate shaft, and an anchoring device attached to the shaft having an expansion mechanism which is operable to expand radially relative to the lengthwise extent of the shaft to anchor the rock bolt within a bore drilled into a rock body, the anchoring device including an annular band which extends about the expansion mechanism to resist expansion of the mechanism, the band being arranged so it can enter the bore in which the bolt is to be anchored in position about the expansion mechanism and to maintain a resistance to expansion of the expansion mechanism at least until the expansion mechanism has substantially fully entered the bore.

The present invention also provides an anchoring device for a rock bolt which has an elongate shaft, the anchoring device including an expansion mechanism which is operable to expand radially relative to the lengthwise extent of the rock bolt shaft to anchor the rock bolt within a bore drilled into a rock body, the anchoring device including an annular band which extends about the expansion mechanism to resist expansion of the mechanism, the band being arranged so that it can enter the bore in which the bolt is to be anchored in position about the expansion mechanism and to maintain a resistance to expansion of the expansion mechanism at least until the expansion mechanism has substantially fully entered the bore.

The invention can provide for disintegration, either partial or full, of the band to thereafter permit expansion of the expansion mechanism to anchor the rock bolt into the rock body. Disintegration can be by way of tearing, shredding, rupturing or melting for example. Advantageously, these forms of disintegration can occur during insertion of the rock bolt into a bore, for example so that the action of insertion causes the disintegration. Alternatively, disintegration can be made to occur once the bolt has been inserted into the bore, either partially or fully.

In other forms of the invention, the band can remain in place about the expansion mechanism as that mechanism is expanded. Thus, the invention includes a band that resists expansion of the expansion mechanism during any of storage and transport of the rock bolt, and during installation of the rock bolt into a bore, but which allows expansion of the expansion mechanism under an expansion load which is applied upon the rock bolt reaching the desired depth of penetration into the rock body. That expansion load can be a load which is applied by the drive arrangement which drives the rock bolt into the rock body and can be a load which is applied in a manner different to the load which drives the rock bolt into the rock body. Thus, the load applied by the band to resist expansion of the expansion mechanism can be high enough to prevent expansion during any of storage and transport of the rock bolt, and during installation of the rock bolt into a bore, but which is less than that applied to expand the expansion mechanism once installed. In this form of the invention, the band can be elastic or stretchable to allow the expansion mechanism to be expanded.

The band can be formed of any suitable material and can have any suitable dimensions. In some forms of the invention, the band is a close fit to or about the expansion mechanism and in these forms, the band can be a tight fit. In some forms of the invention, the band can be sufficiently tight and/or of a suitable material such that the band grips the expansion mechanism against slipping relative to the expansion mechanism during insertion of the rock bolt into a bore. This is highly desirable to prevent the band from slipping off the anchor during transport of the rock bolt or the anchor from the place of manufacture or storage, to the point at which the rock bolt is attached to drive machinery for insertion into a rock body. The band can be a sufficiently tight fit, and/or of a sufficiently thin wall thickness and/or of a sufficiently flexible or malleable material, to conform to the external shape of the expansion mechanism, including at least partially entering one or more recesses, openings, spaces, voids or depressions formed in the external surface of the expansion mechanism.

The band can be formed from a polymeric material which can be tightly fitted to the expansion mechanism. The band can be an elastic material that can be expanded to position the band about the expansion mechanism and thereafter allowed to contract to engage the expansion mechanism for resisting its expansion. Alternatively, the band can be a material that can contract such as by the application of heat. Thus, the material can be a tube which is heat shrinkable, such that the tube prior to shrinking can be of a diameter greater than the external surface of the expansion mechanism for ease of fitting to the expansion mechanism and once properly positioned, heat can be applied to the tube to shrink it into tight engagement with the expansion mechanism. Application of the heat can advantageously, be as simple as by a hand held heat gun. Thus, the band can be of a polymeric material, preferably thin, that has been elastically contracted, for example by heat shrinking, into tight fitting engagement about the expansion mechanism. The wall thickness of the material is expected to be less than 2mm, preferably about 1 mm. However greater or lesser wall thicknesses can be employed, and factors which determine this include the material of the band, the abrasiveness of the rock to be drilled and whether the bolt is self drilling. Other factors can also have an influence.

The band can take other forms and can include for example, paper, plastic or fabric adhesive tape, string, other forms of strapping. What is required is that the band be able to be applied about the expansion mechanism so as to be able to enter the bore into which the bolt is being inserted, and to allow the expansion mechanism to expand when required. The invention can be employed with both rock bolts and self drilling rock bolts. In self drilling rock bolts, the resistance to expansion of the expansion mechanism can be relieved be through frictional engagement of the band with the facing walls of the bore being drilled. The band can be made to disintegrate through that frictional engagement. Thus, the band can be formed so that the action of drilling relieves the resistance to expansion, such as by disintegration, but not before the expansion mechanism of the anchor has substantially fully entered the bore. It is acceptable that the band commence disintegration as the expansion mechanism enters the bore, but the band is required to maintain a resistance to expansion of the expansion mechanism until the expansion mechanism has substantially fully entered the bore.

The band can be made to disintegrate as soon as or around the time the expansion mechanism has substantially fully entered the bore or it can be made to disintegrate later, such as when the rock bolt travels to the desired depth of penetration at which it is to be anchored. For example, the band could be made to survive the drilling or insertion of the rock bolt into the rock body, but afterwards, the rock bolt could be made rotate or vibrate or otherwise move within the bore in order to cause the band to disintegrate. In relation to a self drilling rock bolt, the band can commence disintegration as the rock bolt drills into the rock body, as long as it does not disintegrate sufficiently to allow the expansion mechanism to expand prior to the expansion mechanism substantially fully entering the bore. Thus, the band can commence disintegration as the rock bolt drills into the rock body but survive to an acceptable extent to remain operable until the expansion mechanism has substantially fully entered the bore. Likewise, in relation to a non-drilling rock bolt, the band can commence disintegration as the bolt enters the previously drilled bore, such as by engagement of the band with the facing surface of the bore, or by the bolt being rotated, vibrated or otherwise moved within the bore.

The invention can include facility for rupturing the band when necessary. Rotation or vibration as discussed above can be employed. Thus, the drive arrangement which is used to drive the rock bolt into the bore can also be made to rotate the rock bolt at a suitable speed to cause the band to rupture, or the drive arrangement can be used to vibrate the rock bolt to rupture it, or rotation and vibration can be employed. Alternatively, the anchoring device can include a rupturing arrangement to rupture the band. This might simply comprise expanding the expansion mechanism. Alternatively, other methods of rupturing the band can be employed.

The band can be a single band applied to the expansion mechanism. Alternatively, a pair of bands can be employed. More than two bands can be employed as necessary. These can be spaced apart lengthwise of the expansion mechanism and/or be in overlapping relationship. Overlapping bands can allow an outer band to protect an inner band from rupturing prematurely.

The invention has particular application to rock bolts disclosed in Applicant's copending International Patent Application WO 2008/06021 1 which comprise first and second ends, a shaft extending between the ends, and an anchoring device extending along a first part of the shaft adjacent the first end, the anchoring device comprising a mandrel, and at least one expansion element overlaying the mandrel, wherein the at least one expansion element is displaced radially outwardly on a predetermined relative movement between the mandrel and the at least one expansion element, wherein the at least one expansion element is joined to a connector to form an anchor assembly, said anchor assembly being keyed to the mandrel, and said anchor assembly comprising a relative rotation actuator which is active during rotation of the anchoring device. A band applied to the above form of rock bolt can be of the kind that ruptures progressively as the bolt is inserted into the bore, or it could be of a kind that remains in place about the expansion mechanism but does not prevent expansion of the mechanism under the exertion of an expansion load. The band could have a first condition in which it resists expansion of the expansion mechanism, and a second condition in which it at least partially disintegrates to allow the expansion mechanism to expand. The band can be formed to take the second condition when the expansion mechanism of the anchoring device fitted to a rock bolt has at least substantially fully entered the bore in which the rock bolt is to be anchored. The band can be formed to take the second condition by frictional rubbing of the band against a facing surface of a bore into which the rock bolt is installed, or by any other suitable mechanism as herein described. The band need not take the second condition, if the band is of the kind described earlier that will allow expansion of the expansion mechanism under a suitable expansion load without full or partial disintegration.

In a rock bolt or an anchoring device according to the invention, the band can have an axial length of between 50 and 125mm, and including about 100mmor 75mm.

The present invention also provides a method of installing a rock bolt of any one of the forms of rock bolt discussed above including drilling a bore into a rock body to the desired depth of penetration into the rock body, inserting the rock bolt and expanding the expansion mechanism.

In the above form of method, the rock bolt can be a self drilling rock bolt so that the method steps of drilling a bore into a rock body and inserting the rock bolt into the bore are conducted simultaneously as the self drilling rock bolt drills the bore.

Because of the applicability of the rock bolt of International Patent Application WO 2008/06021 1 to the present invention the disclosure of that application is fully incorporated herein by cross-reference.

BRIEF DESCRIPTION OF THE DRAWINGS

It is convenient to hereinafter describe embodiments of the present invention with reference to the accompanying drawings. The particularity of the drawings and the related description is to be understood as not superseding in generality of the preceding broad description of the invention.

Figure 1 illustrates a rock bolt according to one embodiment of the invention.

Figure 2 is an exploded view of the leading end portion of the rock bolt of Figure 1 .

Figure 3 is an assembled view of the leading end of the rock bolt of Figure 1 . Figure 4 is a cross-sectional view of the leading end of the rock bolt of Figure 1 shown partially inserted into a bore drilled in a rock body.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a rock bolt 10, which includes an elongate shaft 1 1 which has first and second ends 12 and 13. The shaft 1 1 includes a rolled thread 14, which is applied to the shaft 1 1 for the purpose of improving anchoring of the shaft 1 1 within a bore, when the anchoring is at least partially made by the injection of resin or grout.

The rock bolt 10 includes an anchor comprising an expansion mechanism 15 at the first end 12. The expansion mechanism 15 is fixed to the first end 12 via a thread 16. In other embodiments of the invention not shown in the drawings, the expansion mechanism can be located further toward the second end 13.

The rock bolt 10 also includes a drill tip 17, which is threadably connected to the shaft 1 1 and renders the bolt 10 a self-drilling bolt. Thus, the bolt 10 can be driven to rotate and by virtue of the drill tip 17, the bolt can drive a bore into a rock body which can subsequently accommodate the bolt 10. The benefits of self-drilling rock bolts are set out in Applicant's International Patent Application WO2008/06021 1 as not requiring a separate drilling assembly for drilling a bore. However, it should be appreciated that while a self-drilling rock bolt is shown in the drawings, the invention also applies to a rock bolt which is not self-drilling, i.e. which does not include the drill tip 17.

The expansion mechanism 15 is illustrated in exploded view in Figure 2 and with reference to that figure, the mechanism 15 comprises a mandrel 20, an expansion element 21 and a connector 22. The connector 22 includes openings 24 which receive pins 25 which extend from one end of the expansion element 21 , while legs 26 of the connector 22 are received within recesses 27 of the mandrel 20. By the above arrangement, rotational movement of the mandrel 20 relative to the expansion element 21 is prevented, while the pin connection of the expansion element 21 to the connector 22 forms a hinge which allows the respective elements 28 and 29 of the expansion element 21 to move outwardly to engage the internal surface of a bore drilled in a rock body. Outward movement of that kind occurs as the mandrel 20 moves axially relative to the expansion element 21 and the elements 28 and 29 ride upwardly on the includes surfaces 30 of the mandrel 20. For a more detailed discussion of the operation of the expansion mechanism 15, reference to Applicant's International Patent Application WO2008/06021 1 can be made.

The drill tip 17 includes a threaded shaft 23 for receipt within a bore formed in the end 24 of the shaft 1 1 . The thread direction is formed to tighten the threaded shaft 23 within the bore as the bolt 10 is rotated for drilling into a rock body

Figures 3 and 4 show the first end 12 of the rock bolt 10, with the expansion mechanism 15 in a collapsed or non-expanded condition. Figure 4 shows the arrangement of Figure 3 in cross section inserted within a bore 40 which has been drilled in a rock body 41 by the bolt 10. The bore 40 is only partially drilled in Figure 4 as the bore 40 is only at the depth of the commencement of the thread 14.

Each of Figures 1 to 4 illustrate an annular band 45, which is employed for the purpose of resisting expansion of the mechanism 15 until the expansion mechanism 15 has substantially fully entered the bore 40..

The annular band 45 is shown as a single piece band, which extends circumferentially about the expansion mechanism 15 and which extends axially about a significant lengthwise portion of the expansion element 21 . The band thus operates to resist radially outward movement of the elements 28 and 29, for example as might tend to occur during high speed rotation of the bolt 10 to drill into the rock body 41 . As shown in Figure 3, the annular band 45 is a sufficiently tight fight about the expansion mechanism 15, that it conforms to or takes the external shape of the portions of the mandrel 20 and the elements 28 and 29 against which it bears. To produce this fit, the band 45 can be elastic, or it can be a heat shrink fit, such that the band has a larger diameter prior to fitting to the rock bolt 1 0 and once fitted in position, is heated which causes the band to shrink and to conform to the external surface of the expansion mechanism 15 about which it has been positioned. A suitable form of heat shrink tubing is produced by Cabac, under their product code XLP Heatshrink-Thin Wall. The Cabac heatshrink tubing product XLP38, has a pre-shrink diameter of 38.1 mm and a post-shrink diameter of up to 19.1 mm. While the band 45 is shown as a single piece band, the invention contemplates a pair of bands applied to the expansion mechanism 15 in a spaced apart relationship, or three or more bands. In addition, overlapping bands can be employed.

In the form of the invention illustrated in Figures 1 to 4, applicant intended that the annular band 45 would survive drilling of the bolt 10 for the depth of the bore 40 that was required for the expansion mechanism 15 to substantially fully enter the bore 40. Thus, applicant intended that the band 45 would not disintegrate prior to the expansion mechanism 15 substantially fully entering the bore 40. It was expected that some disintegration of the band 45 would take place during initial drilling into the rock body 41 , however applicant intended that the band would retain sufficient integrity, despite some disintegration, as to resist expansion of the expansion mechanism 15 until the expansion mechanism 15 had substantially fully entered the bore 40, after which, the internal surface of the bore 40 would resist expansion. Testing of the invention has successfully taken place in relation to the above Cabac product with the following dimensions:

1 ) 2 x 50mm band sections were fitted tightly about the expansion mechanism side by side and they shredded completely during drilling of the rock bolt into a rock body but after the expansion mechanism had fully entered the bore drilled into the rock body.

2) a 1 x 75mm band section was fitted tightly about the expansion mechanism and it had partially shredded after the expansion mechanism had fully entered the bore, but through that partial shredding the band became free of the expansion mechanism sufficiently to allow the expansion mechanism to be expanded.

3) a 1 x 100mm band section was fitted tightly about the expansion mechanism and shredded completely free from the expansion mechanism after the expansion mechanism had fully entered the bore.

4) a 1 x 125mm band section was fitted tightly about the expansion mechanism and it had partially shredded after the expansion mechanism had fully entered the bore, but through that partial shredding the band became free of the expansion mechanism sufficiently to allow the expansion mechanism to be expanded.

Returning to the figures, as discussed earlier, Figure 4 illustrates the rock bolt 10 having been partially drilled into the rock body 41 . It can be seen that the rock bolt 10 has penetrated the rock body 41 only to the end of the start of the threaded section 14, so that a significant portion of the rock bolt 10 is still to be drilled in to the rock body 41 . In Figure 4, the band 45 is shown intact and without any extent of rupture. While Figure 4 is a schematic illustration only, it is expected that the band 45 will have at least partially ruptured and, more likely, significantly ruptured at the position of the bolt 10 in the rock body 41 shown in Figure 4. The band 45 is selected in dimension and material characteristics, so that complete rupture, or rupture sufficient for the expansion mechanism 15 to expand, will not occur until the expansion mechanism 15 has substantially fully entered the bore 40. As previously indicated, the invention also contemplates that the band 45 will remain intact when the rock bolt 10 arrives at the desired penetration into the rock body 41 . In that arrangement, it is intended that the expansion mechanism 15 can expand the band 45, and either through that expansion rupture the band 45, or, leave the band intact, but expand as necessary to engage the bore surface 40 for anchoring of the rock bolt 10 within the bore 40. That is, the band will not apply sufficient resistance to expansion of the expansion mechanism 15, to prevent that mechanism from being expanded even though the band remains in tact about the mechanism. The benefit of the Cabac heatshrink product referred to above, or similar products provided by other suppliers, is that the band can easily be applied to the expansion mechanism 15 and contracted about the expansion mechanism 15 by simple application of heat from a suitable heat gun. Alternatively, a plurality of bolts could be loaded into a suitable oven or furnace for shrinking the heatshrink tubing. The assembly of the band to the expansion mechanism is thus simple but effective in maintaining the expansion mechanism against expansion during storage and transport of a rock bolt, and during installation of the rock bolt into a bore formed in a rock body. However, the heatshrink tubing has the added advantage of being able to shred and thus disintegrate either progressively during insertion into a bore, or drilling of a bore, or by rotating or vibrating the rock bolt upon the bolt reaching its desired penetration level. The invention thus provides advantages in reducing or eliminating the destruction of expansion mechanisms as can occur if an expansion mechanism expands prematurely during insertion into a bore, but the cost of the bolt is not increased dramatically, nor is the bolt assembly time.

The disclosures in Australian patent application No. 2010206071 , from which this application claims priority, are incorporated herein by reference. It is to be appreciated that the invention is not restricted to use with form of bolt shown in the figures. Thus, the invention has potential use in both self drilling and non-self drilling rock bolts, and in rock bolts in which the expansion mechanism differs from that shown in the drawings. 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

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1 . A rock bolt comprising an elongate shaft, and an anchoring device attached to the shaft having an expansion mechanism which is operable to expand radially relative to the lengthwise extent of the shaft to anchor the rock bolt within a bore drilled into a rock body, the anchoring device including an annular band which extends about the expansion mechanism to resist expansion of the mechanism, the band being arranged so it can enter the bore in which the bolt is to be anchored in position about the expansion mechanism and to maintain a resistance to expansion of the expansion mechanism at least until the expansion mechanism has substantially fully entered the bore.

2. A rock bolt according to claim 1 , the band being of a polymeric material that is in tight fitting engagement about the expansion mechanism.

3. A rock bolt according to claim 2, the band being of a heat shrink polymeric material in tight fitting engagement about the expansion mechanism so as to conform to the external shape of the expansion mechanism.

4. A rock bolt according to claim 1 , the band being of a paper, plastic or fabric adhesive tape, string, or strapping.

5. An anchoring device according to any one of claims 1 to 4, the band having a first condition in which it resists expansion of the expansion mechanism, and a second condition in which it at least partially disintegrates to allow the expansion mechanism to expand, the band being formed to take the second condition when the expansion mechanism of the anchoring device fitted to a rock bolt has at least substantially fully entered the bore in which the rock bolt is to be anchored.

6. A rock bolt according to any one of claims 1 to 5, the band having an axial length of up to about 125mm.

7. A rock bolt according to any one of claims 1 to 5, the band having an axial length of up to about 100mm.

8. A rock bolt according to any one of claims 1 to 5, the band having an axial length of up to about 75mm.

9. A rock bolt according to any one of claims 1 to 5, the band having an axial length of up to about 50mm.

10. A rock bolt according to any one of claims 1 to 9, the band comprising at least a pair of bands spaced apart axially.

1 1 . A rock bolt according to claim 10, the pair of bands each having an axial length of up to about 50mm.

12. A rock bolt according to any one of claims 1 to 1 1 , the band having a wall thickness of about 1 mm.

13. A rock bolt according to any one of claims 1 to 9, the band comprising at least a pair of bands in overlapping relationship.

14. A rock bolt according to any one of claims 1 to 13, comprising first and second ends, a shaft extending between the ends, and the anchoring device extending along a first part of the shaft adjacent the first end, the expansion mechanism comprising a mandrel, and at least one expansion element overlaying the mandrel, wherein the at least one expansion element is displaced radially outwardly on a predetermined relative movement between the mandrel and the at least one expansion element, wherein the at least one expansion element is joined to a connector to form an anchor assembly, said anchor assembly being keyed to the mandrel, and said anchor assembly comprising relative rotation actuator means active during rotation of the anchoring device.

15. A rock bolt according to any one of claims 1 to 14, the rock bolt being a self drilling rock bolt.

16. An anchoring device for a rock bolt which has an elongate shaft, the anchoring device including an expansion mechanism which is operable to expand radially relative to the lengthwise extent of the rock bolt shaft to anchor the rock bolt within a bore drilled into a rock body, the anchoring device including an annular band which extends about the expansion mechanism to resist expansion of the mechanism, the band being arranged so that it can enter the bore in which the bolt is to be anchored in position about the expansion mechanism and to maintain a resistance to expansion of the expansion mechanism at least until the expansion mechanism has substantially fully entered the bore.

17. An anchoring device according to claim 16, the band being of a polymeric material that is in tight fitting engagement about the expansion mechanism.

18. An anchoring device according to claim 17, the band being of a heat shrink polymeric material that is in tight fitting engagement about the expansion mechanism so as to conform to the external shape of the expansion mechanism.

19. An anchoring device according to claim 16, the band being of a paper, plastic or fabric adhesive tape, string, or strapping.

20. An anchoring device according to any one of claims 16 to 19, the band having a first condition in which it resists expansion of the expansion mechanism, and a second condition in which it at least partially disintegrates to allow the expansion mechanism to expand, the band being formed to take the second condition when the expansion mechanism of the anchoring device fitted to a rock bolt has at least substantially entered the bore in which the rock bolt is to be anchored.

21 . An anchoring device according to claim 20, the band being formed to take the second condition by frictional rubbing of the band against a facing surface of a bore into which the rock bolt is installed.

22. A method of installing a rock bolt, the rock bolt comprising an elongate shaft, and an anchoring device attached to the shaft having an expansion mechanism which is operable to expand radially relative to the lengthwise extent of the shaft to anchor the rock bolt within a bore drilled into a rock body, the anchoring device including an annular band which extends about the expansion mechanism to resist expansion of the mechanism, the band being arranged to enter the bore in which the bolt is to be anchored in position about the expansion mechanism and to maintain a resistance to expansion of the expansion mechanism at least until the expansion mechanism has substantially fully entered the bore, the method including drilling a bore into a rock body to the desired depth of penetration into the rock body, inserting the rock bolt and expanding the expansion mechanism.

23. A method of installing a rock bolt according to claim 22, the band being of a polymeric material that is in tight fitting engagement about the expansion mechanism.

24. A method of installing a rock bolt according to claim 23, the band being of a heat shrink polymeric material in tight fitting engagement about the expansion mechanism.

25. A method of installing a rock bolt according to claim 22, the band being of a paper, plastic or fabric adhesive tape, string, or strapping.

26. The method of any one of claims 22 to 25, the rock bolt being a self drilling rock bolt so that the method steps of drilling a bore into a rock body and inserting the rock bolt into the bore are conducted simultaneously as the self drilling rock bolt drills the bore.