AU2012231763A1 - Inflatable friction bolt - Google Patents

Abstract

An inflatable friction bolt (101) comprises a friction bolt leading portion (101A), friction bolt central portion (101B) and friction bolt trailing portion (101C). The friction bolt leading portion (101 A) has a surface feature (106) or features along its length configured to promote interlocking of the friction bolt leading portion (101 A) with a curable anchoring medium (156) encapsulating the friction bolt leading portion (101 A) in use. The friction bolt central portion (101B) is defined by an inflatable body (102). The friction bolt central portion (101B) is radially expandable upon application of fluid pressure to an interior of the body (102). The friction bolt trailing portion (101C) has an enlarged head (107).

Description

WO 2012/126042 PCT/AU2012/000273 INFLATABLE FRICTION BOLT Technical Field The present invention relates to strata control in civil engineering and mining operations and in particular relates to an inflatable friction bolt. Background of the Invention A current method of stabilising the roof or wall of an underground mine or other underground excavation involves the use of a class of rock bolts known as friction bolts or friction rock stabilisers. These types of rock bolts rely on friction between the body of the friction bolt and the wall of a bore hole drilled into the rock face to retain the friction bolt within the hole. One form of friction bolt, commercial examples of which are known as the "Swellex@" bolt or "Omega@" bolt, is an inflatable friction bolt. Referring to Figures 1 and 2 of the accompanying drawings, a typical inflatable friction bolt 1, in the form of an Omega@ bolt, comprises an inflatable elongate body 2 and an enlarged head 4 (often referred to as a ferrule) mounted on the trailing end 2b of the body and a leading ferrule 3 mounted on the leading end 2a of the body 2. Referring particularly to Figure 2, the body 2 has a hollow generally horse-shoe or "Ll" cross section between the leading and trailing ferrules 3, 4. The leading and trailing ferrules 3, 4 are welded to the body 2 at the extreme ends of the body 2 and act to constrain the cross-section of the body 2 toward the leading and trailing ends 2a, 2b. In use, the friction bolt I is inserted into a bore hole drilled into the rock face of the strata to be supported, with the diameter of the bore hole being slightly greater than the diameter of the leading ferrule 3 and central portion of the body 2. A washer plate (not depicted) is mounted on the body 2 adjacent the flared leading end 4a of the trailing ferrule 4. The friction bolt I is driven into the bore hole such that the washer plate engages the rock face and the flared leading end 4a of the trailing ferrule 4 engages the washer plate. Water is then charged into the hollow body 2 via a charging port 5 formed in the side wall of the trailing ferrule 4 that extends through the outer wall of the body 2 so as to communicate with the hollow interior 6 of the body 2. Charging of the hollow interior of the body 2 results in the central portion of the body 2 bulging, plastically deforming so as to provide an interference fit of the central portion of the body 2 within the bore hole. This interference fit provides frictional resistance between the friction bolt and wall of the bore hole, retaining the friction bolt within the bore hole and enabling load transfer between WO 2012/126042 PCT/AU2012/000273 2 the rock strata and the friction bolt 1. The washer plate distributes axial loads carried by the friction bolt 1, transferred by the trailing ferrule 4, across the rock face. Object of the Invention It is the object of the present invention to provide an improved inflatable friction bolt, or at least to provide a useful alternative to current inflatable friction bolts. Summary of the Invention In a first aspect, the present invention provides an inflatable friction bolt comprising: a friction bolt leading portion having a surface feature or features along its length configured to promote interlocking of said leading portion with a curable anchoring medium encapsulating said leading portion in use; a friction bolt central portion defined by an inflatable body, said central portion being radially expandable upon application of fluid pressure to an interior of said body; and a friction bolt trailing portion having an enlarged head. Typically, said friction bolt leading portion includes a leading ferrule mounted on a leading end of said body to constrain said leading end of said body against radial expansion. In one or more embodiments, said surface feature(s) helically extends along said friction bolt leading portion. In a preferred form, said surface feature(s) is defined by a wire extending along said friction bolt leading portion and fixed in relation to said body. In one or more embodiments, said wire extends over a leading region of said body. Typically, a leading end region of said helical wire is secured to said leading ferrule. In one or more embodiments, said wire helically extends over said leading region of said body. In another form, said wire extends substantially linearly along said leading region of said body without being fixed to said body, allowing said wire to be twisted about said body. In another form, said friction bolt leading portion comprises an extension bar extending from a leading end of said body.

WO 2012/126042 PCT/AU2012/000273 3 In one form, said surface(s) is defined by a wire extending along said extension bar. In another form, said wire helically extends along said extension bar. In an alternate form, said friction bolt leading portion includes a sleeve secured to, aid extending over, a leading region of said body. Typically, said surface feature(s) comprises one or more thread-like deformations formed in an exterior surface of said sleeve, In preferred forms, said friction bolt trailing portion has a plurality of drive surfaces adapted to engage complementary surfaces of a rotatable drive for rotating said friction bolt. In one or more embodiments, said friction bolt trailing portion includes a trailing ferrule mounted on the trailing end of said body to constrain said trailing end of said body against radial expansion. In a preferred form, said enlarged head comprises a drive nut mounted on said body adjacent a leading end of said trailing ferrule and defining said drive surfaces. - In one or more embodiments, said drive nut is provided with a substantially semi-spherical leading end surface configured to directly engage a washer plate in use. In an alternate form, said friction bolt trailing portion further comprises a washer mounted adjacent a leading end of said drive nut, said washer having a substantially semi spherical leading end surface configured to directly engage a washer plate in use. In another form, said friction bolt includes a drive element in the form of a regular prism defining said drive surfaces, said drive element being fixed to, and extending rearwardly from, said trailing ferrule, said trailing ferrule forming said enlarged head. In a second aspect, the present invention provides an inflatable friction bolt comprising: a friction bolt leading portion configured to be point anchored within a bore hole in use; a friction bolt central portion defined by an inflatable body, said friction bolt central portion being radially expandable upon application of fluid pressure to an interior of said body; and a friction bolt trailing portion having an enlarged head and a plurality of drive surfaces adapted to engage complementary surfaces of a rotatable drive for rotating said friction bolt.

WO 2012/126042 PCT/AU2012/000273 4 In one or more embodiments, said friction bolt trailing portion includes a trailing ferrule mounted on the trailing end of said body to constrain said trailing end of said body against radial expansion. In a preferred form, said enlarged head comprises a drive nut mounted on said body adjacent a leading end of said trailing ferrule and defining said drive surfaces. In one form, said drive nut is provided with a substantially semi-spherical leading end surface configured to directly engage a washer plate in use. In an alternate form, said friction bolt trailing portion further comprises a washer mounted adjacent a leading end of said drive nut, said washer having a substantially semi spherical leading end surface configured to directly engage a washer plate in use. In another form, said friction bolt includes a drive element in the form of a regular prism defining said drive surfaces, said drive element being fixed to, and extending rearwardly from, said trailing ferrule, said trailing ferrule forming said enlarged head. In a third aspect, the present invention provides a method of securing a rock strata having a rock face, said method comprising: drilling a hole in said rock face into said rock strata; inserting an inflatable friction bolt into said bore hole; anchoring a leading portion of said friction bolt in an upper end portion of said bore hole; engaging an enlarged head of a trailing portion of said friction bolt with a washer plate mounted on said friction bolt and engaging said washer plate with said rock face; and applying fluid pressure to the interior of an inflatable body of said friction bolt, thereby radially expanding a central portion of said friction bolt to engage the wall of said bore hole. Typically, anchoring said leading portion of said friction bolt comprises: inserting a two-component resin filled cartridge having a frangible casing into said upper end portion of said bore hole prior to inserting said friction bolt; rotatably driving and thrusting said friction bolt into said cartridge, thereby puncturing said casing and mixing said two-component resin; and allowing said two-component resin to cure.

WO 2012/126042 PCT/AU2012/000273 5 Brief Description of the Drawings Preferred embodiments of the present invention will now be described, by way of examples only, with reference to the accompanying drawings wherein: Figure 1 is a front elevation view of a prior art inflatable friction bolt; Figure 2 is a cross-sectional view of the inflatable friction bolt of Figure 1 taken at section 2-2; Figure 3 is a front elevation view of an inflatable friction bolt according to a first embodiment; Figure 4 is a perspective view of the friction bolt of Figure 3; Figure 5 is a perspective view of the drive nut of the friction bolt of Figure 3; Figure 6 is a cross-sectional front elevation view of the drive nut of Figure 5; Figure 7 is a perspective view of the friction bolt of Figure 3 with a washer plate mounted thereon; Figure 8 is a partially cross-sectioned view of a bore hole in a rock face with a resin cartridge inserted therein; Figure 9 is a partially cross-section view of the bore hole of Figure 8 with the friction bolt of Figure 3 ready for insertion; Figure 10 is a partially cross-section view of the bore hole of Figure 8 with the friction bolt of Figure 3 inserted therein; Figure 11 is a partially cross-section view of the bore hole of Figure 8 with the friction bolt of Figure 3 full installed therein; Figure 12 is a front elevation view of an inflatable friction bolt according to a second embodiment; Figure 13 is a perspective view of the friction bolt of Figure 12; Figure 14 is a front elevation view of an inflatable friction bolt according to a third embodiment; Figure 15 is a perspective view of the friction bolt of Figure 14; Figure 16 is an enlarged fragmentary perspective view of the friction bolt of Figure 14, particularly depicting the trailing end portion thereof; Figure 17 is a front elevation view of an inflatable friction bolt according to a fourth embodiment; Figure 18 is a perspective view of the friction bolt of Figure 17; Figure 19 is a front elevation view of an inflatable friction bolt according to a fifth embodiment; Figure 20 is a perspective view of the friction bolt of Figure 19; WO 2012/126042 PCT/AU2012/000273 6 .Figure 21 is a front elevation view of an inflatable friction bolt according to a sixth embodiment; Figure 22 is a perspective view of the friction bolt of Figure 21; Figure 23 is a front elevation view of an inflatable friction bolt according to a seventh embodiment; Figure 24 is a perspective view of the friction bolt of Figure 23. Figure 25 is a perspective view of an inflatable friction bolt according to an eighth embodiment; Figure 26 is a perspective view of the friction bolt of Figure 25 with the wire helically twisted; Figure 27 is a perspective view of an inflatable friction bolt according to a ninth embodiment; and Figure 28 is a perspective view of the friction bolt of Figure 27 with the wire helically twisted. Detailed Description of the Preferred Embodiments An inflatable friction bolt 101 according to a first embodiment is depicted in Figures 3 through 11. Firstly referring to Figures 3 and 4, the friction bolt 101 is based on the basic form of an Omega@ bolt, discussed above. The friction bolt 101 has a friction bolt leading portion 101A configured to be point anchored within a bore hole, as will be discussed further below, and a friction bolt trailing portion 101C provided with a plurality of drive surfaces adapted to engage complementary surfaces of a rotatable drive for rotating the friction bolt 101 as will also be discussed further below. A friction bolt central portion 101B is defined by an inflatable body 102, typically formed of high manganese steel. The body 2 has the same hollow generally horse-shoe or "0" cross section as that depicted in Figure 2. The friction bolt central portion 101B is radially expandable upon application of fluid pressure to the interior of the body 102. As with the standard Omega@ bolt, the friction bolt leading portion 101 A includes a steel leading ferrule 103 mounted on the leading end of the body, here by swaging, to constrain the cross-section section of the body 102 at the leading end against radial expansion. Similarly, the friction bolt trailing portion 101C includes a steel trailing ferrule 104 mounted on the trailing end of the body 102, again by swaging, to constrain the cross section of the body 102 at the trailing end from radial expansion. A charging port 105 is formed in the side wall of the trailing ferrule 104 and communicates with the interior of the body 102 to enable fluid pressurisation of the interior of the body 102.

WO 2012/126042 PCT/AU2012/000273 7 The friction bolt leading portion 101 A is adapted to be point anchored by way of a surface feature along its length that is configured to promote interlocking of the friction bolt leading portion 101A with a curable anchoring medium, such as a two-component resin or cement grout, encapsulating the friction bolt leading portion 101 A in use as will be further discussed below. In the first embodiment, the surface feature is defined by a helical wire 106 helically extending along the friction bolt leading portion 101 A. The helical wire 106 is fixed in relation to the body 102, here by being secured to the leading ferrule 103 by welding. The helical wire 106 is welded to the leading ferrule 103 rather than directly to the body 102 so as not to weaken the body 102. In the configuration depicted, the helical wire 106 extends rearwardly from the leading ferrule 103 over a leading region of the body 102. The helical wire 106 and anchoring medium restrains the leading region of the body 102 against radial expansion and thus the radially expandable central portion 101 B is effectively only defined by that part of the inflatable body 102 not encapsulated by the helical wire 106 and anchoring medium. For a typical 2.4 m long friction bolt 101, the helical wire 106 (and friction bolt leading portion 10 1A) would typically extend along the leading 0.5 to I m length of the friction bolt, providing for point anchoring of the friction bolt leading portion 101A. In the context of this specification, and as is well understood in the art, the term "point anchoring" refers to anchoring of the friction bolt along a discrete region of the bolt (that may extend over a notable length of the bolt as noted above, rather than a discrete "point"). In the configuration depicted in Figures 3 and 4, the friction bolt trailing portion 101C includes a drive nut 107 mounted on the body 102 adjacent the flared leading end 104a of the trailing ferrule 104. The drive nut 107 is typically welded to the trailing ferrule 104, but may otherwise be welded directly to the body 102. Welding the drive nut 107 to the trailing ferrule 107 is preferred so as not to weaken the body 102. The drive nut 107, depicted in greater detail in Figures 5 and 6, is of hexagonal form, defining six drive surfaces 108 adapted to engage complementary internal surfaces of the socket of an installation dolly so as to rotate the friction bolt 101 during installation, as will be discussed below. The drive nut 107 forms an enlarged head of the friction bolt 101 and is provided with a substantially semi-spherical leading end surface 109 that is configured to directly engage a washer plate 154 in use, as depicted in Figure 7. Referring to Figures 5 and 6, the drive nut 107 is also provided with an annular recess 110 that is sized to receive the flared leading end 104a of the trailing ferrule 104, thereby providing for load transfer between the trailing ferrule 104 and nut, 107 without having the trailing ferrule 104 WO 2012/126042 PCT/AU2012/000273 8 tending to peel back under load in the case where the drive nut 107 is welded to the trailing ferrule 104 rather than directly to the body 102. If the drive nut 107 were secured directly to the body 102, the trailing ferrule 104 could be eliminated, so long as an alternate charging port were provided. Referring now to Figures 8 through I1 a rock strata 150 having a rock face 151 may be secured utilising the friction bolt 101 described above by first drilling a bore hole 152 in the rock face 151 into the rock strata 150 in the usual manner. Referring to Figure 8, a two-component resin filled cartridge 153 having a frangible casing is then inserted into the bore hole 152 and lodged in the upper end portion of the bore hole 152. Referring to Figure 9, a washer plate 154 is then assembled onto the friction bolt 101 such that the rim 155 of an aperture extending through the washer plate 154 engages the leading end surface 109 of the drive nut 107. The friction bolt 101 is then inserted into the bore hole 152, with the friction bolt leading end portion 101A leading. The friction bolt 101 is inserted into the bore hole 152 by way of an installation dolly with the drive nut 107 received within the socket of the installation dolly with the drive surfaces 108 of the drive nut 107 engaging the complementary internal surfaces of the socket. Referring to Figure 10, as the friction bolt 101 is inserted into the bore hole 152, it is thrust into the cartridge 153 and at the same time rotatably driven by the socket of the installation dolly. The advancing friction bolt leading portion 101A punctures the casing of the cartridge 153, with rotation of the friction bolt 101 assisting with mixing of the two-component resin 156. The helical wire 106 is particularly effective in mixing the resin 156 and, due to the helically extending nature of the helical wire 106, acts to pump the resin 156 toward the upper end of the bore hole 152, thereby reducing the prevalence of any air bubbles or the like within the resin 156 and enhancing mixing of the resin 156. When the friction bolt 101 is fully inserted, the washer plate 154 is engaged with the rock face 151, thereby enabling transfer of loads between the rock face 151 and enlarged head defined by the drive nut 107. The semi-spherical leading surface 109 of the drive nut 107 allows for misalignment of the washer plate 154 with the friction bolt (that is, when the washer plate is not perpendicular to the friction bolt). Such misalignment may arise from irregularities in the rock face 151 or from the rock face 151 not being perpendicular to the bore hole 152. In the case of such misalignment, the rim 155 of the washer plate 154 will still engage the leading surface 109 of the drive nut 107 about its entire circumference. Once mixing of the resin 156 is complete, rotation of the friction bolt 101 ceases and the resin 156 is allowed to cure. Once the resin 156 is cured (typically in a matter of seconds) the friction bolt leading end portion 101A forms a point anchor securing the friction bolt WO 2012/126042 PCT/AU2012/000273 9 101 A within the bore hole 152. The surface feature defined by the helical wire 106 promotes interlocking of the friction bolt leading portion 101 A with the resin, as compared to a smooth and regular external surface which would be at risk of pulling through the resin upon application of a tensile load to the friction bolt 101. In place of the helical wire 106, a surface feature or features could alternatively be formed by deforming the external surface of the leading region of the body 102. Referring to Figure 11, fluid pressure is applied to the interior of the body 102 of the friction bolt 101 by charging the interior with water via the charging port 105 in the usual manner. The application of fluid pressure gradually expands the region of the body 102 located in the friction bolt central region 101 B, between the restrained leading region of the body 102 and the drive nut 107 which acts together with the trailing ferrule 104 to restrain the trailing end of the body 102 against radial expansion. The completed friction bolt installation provides the benefits of resin point anchoring and frictional anchoring provided by radial compression of the friction bolt central portion 101 B against the wall of the bore hole 152. On occurrence of a dynamic event in the rock strata, or a rock burst, the friction bolt 101 will provide tensile resistance by way of the point anchoring as well as frictional resistance by way of the radial expansion of the friction bolt central portion 101B, thereby permitting the elongation or movement of the friction bolt 10 1 as the rock strata moves. In the event of a fault line extending across the friction bolt 101 in the event of a rock strata fracture, the resin point anchoring of the friction bolt leading portion 101A will secure the free portion of rock strata below the fault line, even in the absence of any significant length of the friction bolt central portion 101 B providing frictional resistance above the fault line. A friction bolt 201 according to a second embodiment is depicted in Figures 12 and 13. The friction bolt 201 of the second embodiment is identical to the friction bolt 101 of the first embodiment, apart from the configuration of the drive nut 207. Accordingly, all features of the friction bolt 201 that are common with the friction bolt 101 are provided with the same reference numerals in the accompanying drawings. In the friction bolt 201, the drive nut 207 is in the form of a standard hexagonal nut defining six drive faces 208. The drive nut 207 is again welded to the flared leading end 104a of the trailing ferrule, or may alternately (but less preferably) be welded directly to the body 102. Rather than forming the drive nut 207 with a semi-spherical leading surface, a separate dome washer 211 having a substantially semi-spherical leading surface 212 is mounted on the body 102 adjacent the drive nut 207. The leading surface 212 of the dome washer 211 acts in the same manner as the leading surface 109 of the drive nut WO 2012/126042 PCT/AU2012/000273 10 107 of the friction bolt 101 of the first embodiment, engaging the rim 155 of the aperture extending through the washer plate 154, allowing for misalignment of the washer plate. 154 with the friction bolt 101 resulting from irregularities in the rock face 151 and/or non alignment of the bore hole 152. The dome washer 211 transfers loads between the drive nut 207 and the washer plate 154 such that the drive nut 207 effectively indirectly engages the washer plate 154. Given that the dome washer 211 is not required to transfer torque loads to the body 102 during rotation of the rock bolt, there is no need to secure the dome washer 211 to the body 102 or drive nut 207, although it may be convenient to do so, typically by welding, so as to retain the dome washer 211 in place prior to installation. The friction bolt 301 is installed in the same manner as described above in relation to the friction bolt 101. A friction bolt 301 according to a third embodiment is depicted in Figures 14 to 16. The friction bolt 301 of the third embodiment is again largely identical to the friction bolt 101 of the first embodiment and, accordingly, features of the friction bolt 301 that are identical to features of the friction bolt 101 are again provided with the same reference numerals in the accompanying drawings. The friction bolt 301 eliminates a drive nut adjacent the trailing ferrule 104 and instead has a drive element 307 fixed to and extending rearwardly from the trailing end 104b of the trailing ferrule 104. The drive element 307 is in the form of a regular prism, here a rectangular prism, defining four drive surfaces 308 that engage the internal surfaces of a complementary socket on the installation drive dolly to rotate the installation bolt 301 during installation. In the absence of the drive nut, the trailing ferrule 104 forms the enlarged head engaging the washer plate 154 to transfer loads between the rock face 151 and friction bolt 301. The flared leading end 104a of the trailing ferrule 104 may directly engage the rim 155 of the washer plate 154. Alternatively, to allow for misalignment of the washer plate 154 and to inhibit peelback of the flared leading end 104a of the trailing ferrule 104, a dome washer, particularly of the form disclosed in Australian Patent Application No. 2009201251, the entire contents of which are incorporated herein by cross-reference, may be disposed between'the trailing ferrule 104 and washer plate 154 in use. The friction bolt 301 is installed in the same manner as described above in relation to the friction bolt 101, except that the socket of the installation dolly engages the drive element 307. A friction bolt 401 according to a fourth embodiment is depicted in Figures 17 and 18. The friction bolt 401 of the fourth embodiment is identical to the friction bolt 101 of the first embodiment, apart from the configuration of the friction bolt leading end WO 2012/126042 PCT/AU2012/000273 11 portion 40 IA. Accordingly, again features of the friction bolt 401 that are identical to the features of the friction bolt 101 are provided with the same reference numerals in the accompanying drawings. In the friction bolt 401, rather than having a helical wire welded to the leading ferrule 103 and extending back along the leading region of the body of the friction bolt, a helical wire 406 extends along an extension bar 413 extending forward from the leading end of the body 102. In particular, the extension bar 413 is welded to the leading end 103a of the leading ferrule 103, with the helical wire 406 being welded at each end to the extension bar 413. The extension bar 413 and helical wire 406 thus form the friction bolt leading end portion 401 A and the entire length of the body 102 between the leading ferrule 103 and drive nut 107 remains radially expandable, forming the friction bolt central portion 401B. Rather than providing a surface feature on the extension bar 413 in the form of the helical wire 406, a standard length of reinforcing bar, which is provided with a series of deformations along its length, could instead be utilised without any helical wire if so desired. The friction bolt 401 is installed in the same manner as described above in relation to the friction bolt 101. A friction bolt 501 according to a fifth embodiment is depicted in Figures 19 and 20. The friction bolt 501 of the fifth embodiment is identical to the friction bolt 401 of the fourth embodiment discussed above, except that the drive nut 107 has been eliminated. Given the similarity of the friction bolt 501 of the fifth embodiment to the friction bolt 401 of the fourth embodiment, features of the friction bolt 501 that are identical to the features of the friction bolt 401 are provided with the same reference numerals in the accompanying drawings. The friction bolt 501 is suitable for point anchoring of the friction bolt leading portion 401 A by cement grout encapsulation rather than two-component resin encapsulation as described above in relation to the installation of the friction bolt 101 of the first embodiment. As cement grout does not require mixing by rotation of the friction bolt, the drive nut 107 may be eliminated. The point anchoring of the friction bolt leading portion 401A may thus be achieved during installation of the friction bolt 501 by either pre- or post-grouting the friction bolt leading portion 401 A, thereby encapsulating the friction bolt leading portion 401A, anchoring the friction bolt leading end portion 401A within the upper end of the bore hole 152 upon setting of the cement grout. The surface feature defined by the helical wire 406 again promotes interlocking of the friction bolt leading portion 401 A with the cement grout. In the absence of the drive nut, the trailing ferrule 104 again engages the washer plate 154 either directly or indirectly via a dome WO 2012/126042 PCT/AU2012/000273 12 washer during installation so as to transfer loads between the friction bolt 501 and the rock face 151. Whilst the friction bolt 501 is particularly suitable for point anchoring by cement grout encapsulation, it is also envisaged that the friction bolt 501 may also be point anchored through the use of two-component resin encapsulation as described in relation to friction bolt 101 of the first embodiment. A friction bolt 601 according to a sixth embodiment is depicted in Figures 21 and 22. The friction bolt 601 of the sixth embodiment is again similar to the friction bolt 101 of the first embodiment and features of the friction bolt 601 that are identical to features of the friction bolt 101 are provided with the same reference numerals in the accompanying drawings. In the friction bolt 601, however, in place of a helical wire extending along the friction bolt leading portion, a sleeve 614 is secured to, and extends over, a leading region of the body 102. Typically, the sleeve 614 is welded to the leading ferrule 103. The sleeve 614 is provided with a helically extending surface feature along its length in the form of a threadlike deformation 615 formed in the exterior surface of the sleeve 614. Rather than a single continuous helical deformation 615 provided in the exterior surface, a series of separate deformations may alternatively be provided, again to promote interlocking of the friction bolt leading portion 601 A with resin when the friction bolt 601 is installed according to the procedure described above in relation to the friction bolt 101 of the first embodiment. As with the friction bolt 101 of the first embodiment, the sleeve 614 restrains a leading region of the body 102 against radial expansion, such that only that portion of the body 102 not encapsulated by the sleeve 614 will expand upon application of fluid pressure through the interior of the body 102 during installation. A friction bolt 701 according to a seventh embodiment is depicted in Figures 23 and 24. The friction bolt 701 is identical to the friction bolt 601 of the sixth embodiment, apart from elimination of the drive nut 107. Again, therefore, the features of the friction bolt 701 that are identical to those of the friction bolt 601 are provided with the same reference numerals in the accompanying drawings. The elimination of the drive nut 107 results in the friction bolt trailing portion being identical to that of the friction bolt 501 of the fifth embodiment, making the friction bolt 701 suitable for cement grouted anchoring in the same manner as the friction bolt 501 of the fifth embodiment. A friction bolt 801 according to an eighth embodiment is depicted in Figures 25 and 26. The friction bolt 801 of the eighth embodiment is identical to the friction bolt 201 of the second embodiment, apart from the configuration of the wire 806 and the addition of a resin dam 816. Accordingly, all features of the friction bolt 801 that are WO 2012/126042 PCT/AU2012/000273 13 common with the friction bolt 201 are provided with the same reference numerals in the accompanying drawings. In the friction bolt 801, the wire 806 is welded to the leading ferrule 103. However, rather than helically extending over the leading region of the body 102, the wire 106 extends substantially linearly along the leading region of the body 102 as depicted in Figure 25. As shown in Figure 25, the wire 806 may effectively be partially received in the longitudinally extending recess defined by the horse-shoe section of the body 102. As with the first through third embodiments, the wire 806 is secured to the leading ferrule 103 only, and is not fixed directly to the body 102. A resin dam 816 is mounted on the leading region of the body 102 so as to inhibit the flow of resin beyond the leading region of the body 102 in use. The resin dam 816 is typically swaged or crimped onto the body 102, fixing it in place. It is envisaged that the resin dam 816 may also be applied to the first through third embodiments described above to inhibit the passage of the two-component resin beyond the leading region of the body 102. In the arrangement depicted in Figure 25, the wire 806 extends beyond the resin dam 816 and is tucked under the resin dam 816, prior to swaging the resin dam 816, so as to restrain the free trailing end portion of the wire 806. The friction bolt 801 is installed in the same manner as that described above in relation to the friction bolt 101 of the first embodiment. Whilst the friction bolt 801 is rotated to mix the two-component resin 156, the resistance provided by the two component resin 156 applies a load on the wire 806 which results in the wire 806 being twisted around the leading region of the body 102, as depicted in Figure 26. This helical twisting action of the wire 806 tends to draw the trailing end of the wire 806 through the resin dam 816 and towards leading ferrule 103. Continued rotation of the friction bolt 801 further enhances the mixing of the two-component resin 156 by virtue of the now helically deformed wire 106 twisted about the body 102. A friction bolt 901 according to a ninth embodiment is depicted in Figures 27 and 28. The friction bolt 901 of the ninth embodiment is identical to the friction bolt 801 of the eighth embodiment, apart from the configuration of the wire 906 and the resin dam 916. All features of the friction bolt 901 common with the friction bolt 801 are thus provided with the same reference numerals. In the friction bolt 901, the resin dam 916 is not swaged or crimped onto the body 102, but is loosely mounted on the body 102. The wire 906 is welded both to the leading ferrule 103 and to the resin dam 916. Again, the wire 906 is not fixed directly to the body 102. During resin mixing, the wire 906 again tends to twist about the leading WO 2012/126042 PCT/AU2012/000273 14 region of the body 102, which results in the loosely mounted resin dam 916 moving along the body 102 towards the leading ferrule 103, as depicted in Figure 28. Back pressure from the two-component resin 156 acting on the resin dam 916 as it moves along the body 102 will assist in preventing the wire 906 from overtwisting. Rather than providing for point anchoring of the friction bolts described above by resin or cement grout encapsulation, it is also envisaged that the friction bolts may be modified so as to be point anchored by mechanical means such as a known mechanical expansion shell mounted on the friction bolt leading portion. In such an arrangement, the surface feature(s) promoting interlocking with a curable anchoring medium would be replaced with a feature to co-operate with the mechanical means. In particular, for a mechanical expansion shell a thread would be provided on the friction bolt leading portion to engage the thread of the expansion shell. The drive nut 107 or drive element 307 would then be used to rotate the friction bolt and threadingly advance the friction bolt relative to the expansion shell, expanding the same into engagement with the wall of the bore hole. A person skilled in the art will appreciate the various features of the embodiments described above can be readily interchanged and other modifications made without departing from the spirit of the friction bolt described.

Claims (27)

1. An inflatable friction bolt comprising: a friction bolt leading portion having a surface feature or features along its length configured to promote interlocking of said friction bolt leading portion with a curable anchoring medium encapsulating said friction bolt leading portion in use; a friction bolt central portion defined by an inflatable body, said friction bolt central portion being radially expandable upon application of fluid pressure to an interior of said body; and a friction bolt trailing portion having an enlarged head.

2. The friction bolt of claim 1, wherein said friction bolt leading portion includes a leading ferrule mounted on a leading end of said body to constrain said leading end of said body against radial expansion.

3. The friction bolt of claim 1, wherein said surface feature(s) helically extends along said friction bolt leading portion.

4. The friction bolt of claim 2, wherein said surface feature(s) is defined by a wire extending along said friction bolt leading portion and fixed in relation to said body.

5. The friction bolt of claim 4, wherein said wire extends over a leading region of said body.

6. The friction bolt of claim 5, wherein a leading end region of said wire is secured to said leading ferrule.

7. The friction bolt of claim 6, wherein said wire helically extends over said leading region of said body.

8. The friction bolt of claim 6, wherein said wire extends substantially linearly along said leading region of said body without being fixed to said body, allowing said wire to be twisted about said body.

9. The friction bolt of claim 1, wherein said friction bolt leading portion comprises an extension bar extending from a leading end of said body. WO 2012/126042 PCT/AU2012/000273 16

10. The friction bolt of claim 9, wherein said surface feature(s) is defined by a wire extending along said extension bar.

11. The friction bolt of claim 10, wherein said wire helically extends along said extension bar.

12. The friction bolt of claim 1, wherein said friction bolt leading portion includes a sleeve secured to, and extending over, a leading region of said body.

13. The friction bolt'of claim 12, wherein said surface feature(s) comprises one or more thread-like deformations formed in an exterior surface of said sleeve.

14. The friction bolt of claim 1, wherein said friction bolt trailing portion has a plurality of drive surfaces adapted to engage complementary surfaces of a rotatable drive for rotating said friction bolt.

15. The friction bolt of claim 14, wherein said friction bolt trailing portion includes a trailing ferrule mounted on the trailing end of said body to constrain said trailing end of said body against radial expansion.

16. The friction bolt of claim 15, wherein said enlarged head comprises a drive nut mounted on said body adjacent a leading end of said trailing ferrule and defining said drive surfaces.

17. The friction bolt of claim 16, wherein said drive nut is provided with a substantially semi-spherical leading end surface configured to directly engage a washer plate in use.

18. The friction bolt of claim 16, wherein said friction bolt trailing portion further comprises a washer mounted adjacent a leading end of said drive nut, said washer having a substantially semi-spherical leading end surface configured to directly engage a washer plate in use. WO 2012/126042 PCT/AU2012/000273 17

19. The friction bolt of claim 15, wherein said friction bolt includes a drive element in the form of a regular prism defining said drive surfaces, said drive element being fixed to, and extending rearwardly from, said trailing ferrule, said trailing ferrule forming said enlarged head.

20. An inflatable friction bolt comprising: a friction bolt leading portion configured to be point anchored within a bore hole in use; a friction bolt central portion defined by an inflatable body, said friction bolt central portion being radially expandable upon application of fluid pressure to an interior of said body; and a friction bolt trailing portion having an enlarged head and a plurality of drive surfaces adapted to engage complementary surfaces of a rotatable drive for rotating said friction bolt.

.21. The friction bolt of claim 20, wherein said friction bolt trailing portion includes a trailing ferrule mounted on the trailing end of said body to constrain said trailing end of said body against radial expansion.

22. The friction bolt of claim 21, wherein said enlarged head comprises a drive nut mounted on said body adjacent a leading end of said trailing ferrule and defining said drive surfaces.

23. The friction bolt of claim 22, wherein said drive nut is provided with a substantially semi-spherical leading end surface configured to directly engage a washer plate in use.

24. The friction bolt of claim 22, wherein said friction bolt trailing portion further comprises a washer mounted adjacent a leading end of said drive nut, said washer having a substantially semi-spherical leading end surface configured to directly engage a washer plate in use.

25. The friction bolt of claim 21, wherein said friction bolt includes a drive element in the form of a regular prism defining said drive surfaces, said drive element WO 2012/126042 PCT/AU2012/000273 18 being fixed to, and extending rearwardly from, said trailing ferrule, said trailing ferrule forming said enlarged head.

26. A method of securing a rock strata having a rock face, said method comprising: drilling a hole in said rock face into said rock strata; inserting an inflatable friction bolt into said bore hole; anchoring a leading portion of said friction bolt in an upper end portion of said bore hole; engaging an enlarged head of a trailing portion of said friction bolt with a washer plate mounted on said friction bolt and engaging said washer plate with said rock face; and applying fluid pressure to the interior of an inflatable body of said friction bolt, thereby radially expanding a central portion of said friction bolt to engage the.wall of said bore hole.

27. The method of claim 26, wherein anchoring said leading portion of said friction bolt comprises: inserting a two-component resin filled cartridge having a frangible casing into said upper end portion of said bore hole prior to inserting said friction bolt; rotatably driving and thrusting said friction bolt into said cartridge, thereby puncturing said casing and mixing said two-component resin; and allowing said two-component resin to cure.