AU2014203249A1 - Rock bolt - Google Patents

Abstract

A rock bolt (100) for fully resin encapsulated installation in a bore hole (181) has an elongate bar (101) longitudinally extending between a bar leading end (102) and bar trailing end (103). A first wire (110) helically extends about a first bar portion (109) located toward the bar leading end (102). A second wire (120) helically extends about a second bar portion (119) toward the bar trailing end (103). The rock bolt (100) is configured to provide a debonded bar portion (129) between the first bar portion (109) and the second bar portion (119). The debonded bar portion (129) is debonded from resin (141) encapsulating the rock bolt (100) in use, at least upon application of a predetermined service load to the bar (101). 1(01 (00 160 % log ' AV t a -rZO

Description

1 ROCK BOLT Field [0001] The present invention relates to strata control in civil engineering and mining operations, and in particular relates to a rock bolt for securing the roof or wall of a mine, tunnel or other ground excavation. Background [0002] One known method of stabilising the wall or roof of an underground mine is to secure a rock bolt into a bore hole drilled in to the face of the rock to be stabilised. Rock bolts are formed with an elongate load bearing element, commonly formed of a rigid steel bar. [0003] A known method of installing such a rock bolt involves first drilling a bore hole into the rock face. A sausage-like two-component resin filled cartridge is then inserted into the bore hole, followed by the rock bolt which pushes the resin filled cartridge towards the blind end of the bore hole. The rock bolt is then rotated by the installation rig which also thrusts the rock bolt upwardly whilst it is rotating to mix the resin components and shred the frangible cartridge casing, pushing it towards the blind end of the bore hole. Various means have previously been proposed to be formed with, or mounted on, the leading end portion of the rigid bar to assist in mixing of the resin components and/or assisting in anchoring the rock bolt within the resin. Rotation of the rock bolt is then stopped for a few seconds to allow the resin to cure. [0004] In one form of installation, the resin only encapsulates the leading end portion of the rigid bar, thereby forming a point anchor. In such an installation the rock bolt may be tensioned by way of a drive nut mounted on a threaded trailing end portion of the bar and which bears against a plate washer that engages the rock face adjacent the bore hole opening. For additional load transfer and corrosion protection, it is known to post-grout the annular cavity about the rigid bar extending between the resin encapsulated leading end portion and the bore hole opening. According to another previously proposed installation configuration, the entire length of the rigid bar within the bore hole may be resin encapsulated.

2 Summary of Invention [0005] In a first aspect, the present invention provides a rock bolt for fully resin encapsulated installation in a bore hole, said rock bolt comprising: an elongate bar longitudinally extending between a bar leading end and a bar trailing end; a first wire helically extending about a first bar portion of said bar located towards said bar leading end; and a second wire helically extending about a second bar portion of said bar located towards said bar trailing end; wherein said rock bolt is configured to provide a debonded bar portion of said bar between said first bar portion and said second bar portion, said debonded bar portion being debonded from resin encapsulating said rock bolt, in use, at least upon application of a predetermined service load to said bar. [0006] In a preferred form, said first and second wires are helically wound in a common direction of helical winding. [0007] In a preferred form, said first wire has a greater helical pitch than said second wire. [0008] In a preferred form, said first and second wires are welded to said bar. [0009] In a second aspect, the present invention provides a rock bolt for fully resin encapsulated installation in a bore hole, said rock bolt comprising: an elongate bar longitudinally extending between a bar leading end and a bar trailing end; a first wire helically extending about a first bar portion of said bar located towards said bar leading end; and a resin dam extending about a second bar portion of said bar located towards said bar trailing end, said resin dam being configured to inhibit passage of resin beyond said resin dam towards said bar trailing end, in use; wherein said rock bolt is configured to provide a debonded bar portion of said bar between said first bar portion and said second bar portion, said debonded bar portion being debonded from resin encapsulating said rock bolt, in use, at least upon application of a predetermined service load to said bar.

3 [0010] In a preferred form, said resin dam comprises a second wire helically extending about said second bar portion. [0011] In a preferred form, said rock bolt further comprises a debonding sleeve mounted on said bar over said debonded bar portion, said debonding sleeve debonding said debonded bar portion from resin encapsulating said rock bolt, in use. [0012] In an alternate form, said debonded bar portion is provided with a smooth outer surface configured to debond from resin encapsulating said rock bolt, in use, upon application of the predetermined service load to said bar. [0013] In one specific form, said smooth outer surface is provided with a surface coating to promote debonding from resin encapsulating said rock bolt, in use. [0014] In a preferred form, said first and second bar portions are provided with surface protrusions configured to interlock with resin encapsulating said rock bolt, in use. [0015] In a preferred form, said bar has a threaded trailing end bar portion located between said second bar portion and said bar trailing end, said rock bolt further comprising a threaded drive nut mounted on said threaded trailing end bar portion. [0016] In a preferred form, a leading end of said first wire projects outwardly from the helix defined by said first wire so as to form a projection for shredding a resin cartridge casing during installation. [0017] In a particular preferred form, said projection is bent so as to extend towards a trailing end of said first wire. [0018] In a third aspect, the present invention provides a method of installing any one of the rock bolts defined above, said method comprising the steps of: drilling a bore hole with a blind end into a rock face to be stabilized; inserting a two-component resin filled cartridge having a frangible casing into said bore hole; inserting said rock bolt into said bore hole with said bar leading end leading; thrusting said rock bolt towards said blind end whilst rotating said rock bolt; 4 puncturing said frangible casing and allowing said resin to flow along said bar whilst being mixed by said first and second wires; and stopping thrusting and rotation of said rock bolt, allowing said resin to cure. [0019] In a preferred method, said rock bolt is rotated in a direction opposite to the direction of helical winding of said first and second wires. Brief Description of Drawings [0020] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein: [0021] Figure 1 is a fragmentary front elevation view of a rock bolt according to a first embodiment; [0022] Figure 2 is a fragmentary partly sectioned front elevation view of the rock bolt of Figure 1; [0023] Figure 3 is a first isometric view of the rock bolt of Figure 1; [0024] Figure 4 is a second isometric view of the rock bolt of Figure 1; [0025] Figure 5 is a partially cross-sectioned front elevation view of a partially completed rock bolt installation utilizing the rock bolt of Figure 1; [0026] Figure 6 is a partially cross-sectioned front elevation view of a completed rock bolt installation utilizing the rock bolt of Figure 1; [0027] Figure 7 is a front elevation view of a rock bolt according to a second embodiment; [0028] Figure 8 is a fragmentary front elevation view of a rock bolt according to a third embodiment; [0029] Figure 9 is a front elevation view of a rock bolt according to a fourth embodiment; [0030] Figure 10 is a front elevation view of a rock bolt according to a fifth embodiment; 5 [0031] Figure 11 is a front elevation view of a rock bolt according to a sixth embodiment; and [0032] Figure 12 is a partially cross-sectioned front elevation view of a completed rock bolt installation utilizing the rock bolt of Figure 11. Description of Embodiments [0033] Referring to Figures 1 to 4, a rock bolt 100 has an elongate load bearing element in the form of a rigid bar 101 which longitudinally extends between a bar leading end 102 and a bar trailing end 103. The bar 101 may be of any of various known forms used in rock bolting applications. The bar will typically be formed of steel and here has a coarse left-handed thread 105 that is hot rolled into the bar 101 along its length. Here the thread 105 extends over a threaded trailing end bar portion 104 of the bar 101 and along the remainder of the length of the bar 101. [0034] The bar 101 typically has a nominal diameter of between 12 and 30 mm, with common nominal diameters being 16, 20 and 24 mm. The bar 101 will typically have a length of the order of 1.8 to 2.4 m, but this may vary to suit the particular application. [0035] In the arrangement depicted, an end fitting in the form of a hexagonal threaded drive nut 106 and dome washer 107 is mounted on the threaded trailing end portion 104, with the drive nut 106 threadingly engaging the thread 105 of the threaded trailing end bar portion 104. A standard plate washer 108 is mounted on the rock bolt 100, engaging the dome washer 107 in a known manner. [0036] The drive nut 106 will typically be fixed in relation to the bar 101 by way of a locking means that is configured to fail upon application of a predetermined torque during the installation process. This allows the drive nut 106 to advance along the threaded trailing end portion 104 of the bar 101 upon application of torque exceeding the predetermined torque during post-tensioning of the rock bolt 100, as will be discussed further below. In the configuration depicted, the locking means is in the form of a shear pin 106a that locks the drive nut 106 to the bar 101. The locking means could alternatively be in the form of a slightly deformed thread of the threaded trailing end portion 104 of the bar 101. In another alternate form, the locking means could be in the form of a disc mounted in the trailing end of the drive nut 106 and configured to prevent the bar 101 from passing through the trailing end of the drive nut 106 until application of 6 a torque exceeding the predetermined torque, at which the disc ruptures. The locking means may also take any other suitable form. [0037] A first wire 110 helically extends about a first bar portion 109 of the bar 101 located towards the bar leading end 102. In the arrangement depicted, the first wire 110 extends to the bar leading end 102. The wire 110 extends from a first wire leading end 111 to a first wire trailing end 112. The first wire 110 is typically formed of steel and, in the arrangement depicted, has a diameter of about 3.15 mm although wire diameters of up to about 6.3 mm or greater may also be suitable for some applications. The first wire 110 helically extends in a direction opposing the intended direction of rotation of the rock bolt 100 during installation. Accordingly, for a standard left-handed installation rig, the first wire 110 will helically extend in a right handed direction as depicted in the accompanying drawings, and in an opposing direction to the left-handed coarse thread 105 formed on the bar 101 (particularly on the threaded trailing bar portion 104). In one example, the first wire 110 extends over a length of about 500 mm. The first wire 110 will typically extend over a length of between 300 mm and 1000 mm and between 3 and 20 revolutions. [0038] In the arrangement depicted, the first wire 110 is fixed to the first bar portion 109 by welding, here being welded towards the first wire leading and trailing ends 111, 112 and partway along the length of the first wire 110. Alternatively, the first wire leading end 111 may be secured in a slot formed in the bar leading end 102. In a still further alternative, particularly suitable for applications with high tensile steel bars which might otherwise be weakened through inadvertent heat treatment of the bar during a welding process, the first wire trailing end 112 may be fixed to the bar 101 by way of a ferrule that is crimped onto the bar 101. A person skilled in the art will appreciate other suitable means for securing the first wire 110 to the bar 101. [0039] In the arrangement depicted, the first wire leading end 111 projects outwardly from the helix defined by the first wire 110, so as to form a projection 113, best depicted in Figure 4, which is useful in shredding the resin cartridge casing during installation as will be described below. In the embodiment depicted, the projection 113 is bent so as to extend towards the first wire trailing end 112. This assists in preventing the projection 113 from catching on the bore hole side wall during installation.

7 [0040] With the rock bolt 100 being intended for full resin encapsulation along its length, the first wire 110 serves three basic purposes, being to mix the two-component resin during the installation process, to pump the resin towards the blind end of the bore hole during installation and to assist in anchoring the first bar portion 109 within the resin upon the application of tensile load to the rock bolt 100 in service. [0041] In one example, the first wire 110 has a helical pitch of about 75mm. The helical pitch of the first wire 110 will typically be between 50 mm and 100 mm. [0042] A second wire 120 helically extends about a second bar portion 119 of the bar 101 located towards the bar trailing end 103, forward of the threaded trailing end bar portion 104. The second wire 120 extends from a second wire leading end 121 to a second wire trailing end 122. The second wire 120 is typically formed of steel and, in the arrangement depicted, has a diameter of about 3.15 mm although wire diameters of up to about 6.3 mm or greater may also be suitable for some applications. The second wire 120 will typically have the same diameter as the first wire 110. The second wire 120 typically helically extends in the same direction as that of the first wire 110, being in the direction opposing the intended direction of rotation of the rock bolt 100 during installation. Accordingly, for a standard left-handed installation rig, the second wire 120 will helically extend in a right-handed direction as depicted in the accompanying drawings. The second wire 120 will typically extend over a length of between 100 mm and 500 mm, although it is envisaged that, when the second wire is employed merely to act as a resin dam, that it may extend over a shorter length, such as about 50 mm. For long rock bolts, where it is desired to lock the second bar portion 119 over an extended length, that the second wire 120 may have lengths of up to about 800 mm. The second wire 120 will typically extend over at least 3 revolutions. [0043] In the arrangement depicted, the second wire 120 is fixed to the second bar portion 119 by welding, here being welded towards the second wire leading and trailing ends 121, 122 and partway along the length of the second wire 120. In an alternative, particularly suitable for applications with high tensile steel bars which might otherwise be weakened through inadvertent heat treatment of the bar during a welding process, the second wire leading and trailing end 121, 122 may be fixed to the bar 101 by way of ferrules crimped onto the bar 101. A person skilled in the art will appreciate other suitable means for securing the second wire 120 to the bar 101.

8 [0044] With the rock bolt 100 being intended for full resin encapsulation along its length, the second wire 120 serves the same three basic purposes as the first wire 110, being to mix the two component resin during the installation process, to pump the resin towards the blind end of the bore hole during installation and to assist in anchoring the second bar portion 119 within the resin upon the application of tensile load to the rock bolt 100 in service. [0045] The second wire 120 may have a helical pitch approximately the same as that of the first wire 110 or alternatively, and more preferably have a helical pitch less than that of the first wire 110. The helical pitch of the second wire 120 will typically be between 10 mm and 75 mm, and more typically between 25 mm and 50 mm. [0046] The rock bolt 100 is configured to provide a debonded bar portion 129 of the bar 101 between the first bar portion 109 and the second bar portion 119. In the first embodiment depicted in Figures I to 4, the debonded bar portion 129 is defined by the region of the bar 101 covered by a debonding sleeve 130 mounted on the bar 101 between the first and second bar portions 109, 119. As will be further described below, the debonding sleeve 130 debonds the debonded bar portion 129 from resin encapsulating the rock bolt 100 in use. The debonding sleeve 130 may be formed of any suitable material which enables the debonded bar portion 129 to be separated from encapsulating resin, and will typically be formed of a plastics material, such as low density polyethylene. The debonding sleeve 130, and accordingly the debonded bar portion 129, will typically have a length of the order of 1000 mm, and will typically have lengths of between 700 mm and 1300 mm, depending upon the length of the rock bolt 100. [0047] Installation of the rock bolt 100 will now be described with reference to Figures 5 and 6. A bore hole 181 is first drilled into the rock face 180. A two-component resin filled cartridge 140 is then inserted into the bore hole 181. The rock bolt 100, with the plate washer 108 mounted on the bar 101 in front of the dome washer 107, is then inserted into the bore hole 181 with the bar leading end 102 leading. The rock bolt 100 is thrust towards the blind end 182 of the bore hole 181, utilizing a standard rock bolt installation rig, thereby pushing the resin filled cartridge 140 against the bore hole blind end 182 and rupturing the frangible casing of the cartridge 140. [0048] Whilst the installation rig thrusts the rock bolt 100 towards the bore hole blind end 182, it also rotates the drive nut 106, here in an anticlockwise direction, thereby rotating the entire 9 rock bolt 100 in a direction opposing the direction of helical winding of the first and second wires 110, 120. The projection 113 at the first wire leading end 111 pierces and shreds the casing of the cartridge 140 as the rock bolt 100 is rotated and advanced and the first bar portion 109, and particularly the first wire 110, actively mixes the two components of the resin. As the resin 141 flows down over the debonding sleeve 130 and about the second bar portion 119, the second wire 120 will further mix the two components of the resin 141. With the first and second wires 110, 120 helically extending in an opposing direction to the direction of rotation of the rock bolt 100, the resin 141 is actively pumped towards the bore hole blind end 182. In arrangements where the second wire 120 has a shorter helical pitch than the first wire 110, the shorter pitch will provide an enhanced pumping effect to assist in better consolidating the resin. Thrusting and rotation of the rock bolt 100 is then ceased, allowing the resin 141 to cure for a few seconds. [0049] After the resin 141 has cured, the drive nut 106 is driven by the installation rig at an increased torque that is equal to or in excess of the predetermined torque at which the shear pin 106a fails. The torque applied to the drive nut 106 then threads the drive nut 106 along the threaded trailing end bar portion 104. Continued driving of the drive head 106 bears the drive nut 106 against the dome washer 107, which in turn bears against the plate washer 108 and in turn the rock face 181, thereby resulting in tensioning of the bar 101. In a particularly preferred installation method, the two-component resin filled cartridge 140 contains two separate resins, with a relatively fast setting resin at the top of the cartridge 140 used to point anchor the first bar portion 209, and a slower setting resin at the bottom of the cartridge used to encapsulate the second bar portion 119. In this configuration, the rock bolt 100 will be pretensioned once the first, faster setting resin has cured, anchoring the first bar portion 109, but prior to the second, slower setting resin curing. This enables elongation of the second bar portion 119 and debonded bar portion 129 within the second, slower setting resin during the pretensioning process. The separate fast and slow setting resins could alternatively be housed in separate cartridges. [0050] In the completed installation, depicted in Figure 6, the first and second bar portions 109, 119 are firmly anchored within the resin 141, whilst the debonded bar portion 129 is debonded from the resin 141 by virtue of the debonding sleeve 130. As a result, in the event of any movement or fracture of unstable rock the debonded bar portion 129 is able to yield over its full length, effectively "slipping" within the encapsulating resin 141, allowing the bar 101 to absorb movement of the rock over the debonded bar portion 129. This can be contrasted against an 10 installation where the bar remains bonded to the resin along its entire length such that the bar must endeavor to absorb any movement locally at the failure plane of the rock over a very short distance, often resulting in catastrophic failure of the bar. [0051] A rock bolt 200 according to a second embodiment is depicted in Figure 7. The rock bolt 200 is of an identical configuration to the rock bolt 100 of the first embodiment, particularly including a first wire 110, second wire 120, debonding sleeve 130, drive nut 106, and dome washer 107. The rigid bar 201, however, is of an alternate form to the bar 101 of the rock bolt 100 of the first embodiment. Here the bar 201 has the first and second bar portions 209, 219 formed with ribbed protrusions 205 to assist load transfer with the encapsulating resin, and a threaded trailing end bar portion 204 with a left-handed thread rolled into the bar 201 for receipt of the drive nut 106 which has a mating thread. The debonded bar portion 229, located between the first and second bar portions 209, 219 has a smooth outer surface. The ribbed protrusions 205 formed on the first and second bar portions 209, 219 are formed by a cold working process, particularly cold rolling. The cold working process hardens and increases the yield strength of the first and second bar portions 209, 219, whilst leaving the debonded bar portion 229 in its original softer and more ductile form. As a result, upon loading of the rock bolt 200 beyond the yield strength of the debonded bar portion 229, the debonded bar portion 229 will yield without yielding of the first and second bar portions 209, 219, allowing the first and second bar portions 209, 219 to remain firmly anchored within the resin. [0052] A rock bolt 300 according to a third embodiment is depicted in Figure 8. The rock bolt 300 is identical to the rock bolt 200 of the second embodiment, but omits the debonding sleeve 230. In this arrangement, the smooth outer surface of the debonded bar portion 229 provides the necessary debonding of the debonded bar portion 229 from the resin encapsulating the rock bolt 300 in use, upon application of a predetermined service load to the bar 201 which exceeds the shear bond strength between the resin and the smooth outer surface of the debonded bar portion 229. Accordingly, whilst when initially installed, the debonded bar portion 229 may be relatively lightly bonded to the encapsulating resin, the resin readily debonds from the debonded bar portion 229 upon the application of a predetermined service load. Such a load may result from movement or fracture of the rock that is resisted by yielding deformation of the debonded bar portion 229 in a similar manner to that described above in relation to the first embodiment. It is also envisaged that a surface coating, such as a low-friction paint surface coating, may be applied to the debonded bar portion 229 to further promote debonding of the debonded bar 11 portion 229. Suitable surface coatings include low-friction, lubricating paints such as polyolefin based paints. [0053] A rock bolt 400 according to a fourth embodiment is depicted in Figure 9. The rock bolt 400 is of an identical configuration to the rock bolt 300 of the third embodiment, except that the rigid bar 401 is a plain bar with a smooth surface along its length, apart from the threaded trailing end bar portion 404, thus omitting the ribbed protrusions 205 of the bar 201 of the rock bolt 300 of the third embodiment. [0054] A rock bolt 400 according to a fifth embodiment is depicted in Figure 10. The rock bolt 400 is of an identical configuration to the rock bolt 100 of the first embodiment, but replaces the second wire 120 with an alternate second wire 420 having a helical pitch of less than that of the first wire 110. This will result in a reduced resistance and hence back pressure, on the first wire 110 as it is pushed through the bulk of the resin during installation, as compared to that of the second wire 420, thereby enabling a more rapid insertion of the rock bolt 400 through the resin into its final installed position than would be achieved with the first wire 110 having a helical pitch identical to that of the second wire 420. The increased pitch of the first wire 110 as compared to the second wire 420 will also reduce the pumping effect of the first wire 110 as the rock bolt 400 is rotated whilst the rock bolt 400 advances through the resin. The shorter helical pitch of the second wire 420 would provide a relatively greater resistance to the passage of the rock bolt 400 through the resin. However, given that the second wire 420 is located towards the bar trailing end 103, it will only need to pass through a relatively short length of the resin, such that the overall effect of an increased resistance would be minimal. The relatively shorter helical pitch of the second wire 420 will also increase the pumping effect of the second wire 420, to consolidate the resin more effectively and to effectively act as a resin dam, reducing the possibility of leakage of resin from the bore hole. [0055] A rock bolt according to a sixth embodiment is depicted in Figure 11. A rock bolt installation with the rock bolt 500 installed in a bore hole 181 formed in a rock face 180, using the same installation method as described above, is depicted in Figure 12. The rock bolt 500 is of an identical configuration to the rock bolt 100 of the first embodiment, except that, in place of the second wire 120, a resin dam 520 extends about the second bar portion 119 of the bar 101 towards the bar trailing end 103. The resin dam 520 may be of any of various forms. In the depicted embodiment, the resin dam 520 is in the form of a steel ring swaged or welded on to the 12 bar 101. The leading edge of the resin dam may be chamfered to ease insertion up the bore hole. The resin dam 520 may also incorporate a steel washer supported on the steel ring to more fully fill the annulus defined between the bar 101 and the bore hole wall. The resin dam 520 may also be formed of a plastic material. The resin dam 520, whilst not providing for pumping of the resin towards the blind end of the bore hole during installation, will still act to inhibit passage of resin beyond the resin dam towards the bar trailing end 103, and out of the bore hole 181. [0056] A person skilled in the art will appreciate other possible modifications and variations of the rock bolts described.

Claims (15)

1. A rock bolt for fully resin encapsulated installation in a bore hole, said rock bolt comprising: an elongate bar longitudinally extending between a bar leading end and a bar trailing end; a first wire helically extending about a first portion of said bar located towards said bar leading end; and a second wire helically extending about a second portion of said bar located towards said bar trailing end; wherein said rock bolt is configured to provide a debonded length of said bar between said first end portion of said bar and said second end portion of said bar, said debonded length being debonded from resin encapsulating said rock bolt, in use, at least upon application of a predetermined service load to said bar.

2. The rock bolt of claim 1, wherein said first and second wires are helically wound in a common direction of helical winding.

3. The rock bolt of either one of claims 1 and 2, wherein said first wire has a greater helical pitch than said second wire.

4. The rock bolt of any one of claims 1 to 3, wherein said first and second wires are welded to said bar.

5. A rock bolt for fully resin encapsulated installation in a bore hole, said rock bolt comprising: an elongate bar longitudinally extending between a bar leading end and a bar trailing end; a first wire helically extending about a first bar portion of said bar located towards said bar leading end; and a resin dam extending about a second bar portion of said bar located towards said bar trailing end, said resin dam being configured to inhibit passage of resin beyond said resin dam towards said bar trailing end, in use; wherein said rock bolt is configured to provide a debonded bar portion of said bar between said first bar portion and said second bar portion, said debonded bar portion being debonded from resin encapsulating said rock bolt, in use, at least upon application of a predetermined service load to said bar. 14

6. The rock bolt of claim 5, wherein said resin dam comprises a second wire helically extending about said second bar portion.

7. The rock bolt of any one of claims 1 to 6, wherein said rock bolt further comprises a debonding sleeve mounted on said bar over said debonded bar portion, said debonding sleeve debonding said debonded bar portion from resin encapsulating said rock bolt, in use.

8. The rock bolt of any one of claims I to 6, wherein said debonded bar portion is provided with a smooth outer surface configured to debond from resin encapsulating said rock bolt, in use, upon application of the predetermined service load to said bar.

9. The rock bolt of claim 8, wherein said smooth outer surface is provided with a surface coating to promote debonding from resin encapsulating said rock bolt, in use.

10. The rock bolt of any one of claims I to 9, wherein said first and second bar portions are provided with surface protrusions configured to interlock with resin encapsulating said rock bolt, in use.

11. The rock bolt of any one of claims 1 to 10, wherein said bar has a threaded trailing end bar portion located between said second bar portion and said bar trailing end, said rock bolt further comprising a threaded drive nut mounted on said threaded trailing end bar portion.

12. The rock bolt of any one of claims 1 to 11, wherein a leading end of said first wire projects outwardly from the helix defined by said first wire so as to form a projection for shredding a resin cartridge casing during installation.

13. The rock bolt of claim 12, wherein said projection is bent so as to extend towards a trailing end of said first wire.

14. A method of installing the rock bolt of any one of claims I to 13, said method comprising the steps of: drilling a bore hole with a blind end into a rock face to be stabilized; inserting a two-component resin filled cartridge having a frangible casing into said bore hole; inserting said rock bolt into said bore hole with said bar leading end leading; 15 thrusting said rock bolt towards said blind end whilst rotating said rock bolt; puncturing said frangible casing and allowing said resin to flow along said bar whilst being mixed by said first and second wires; and stopping thrusting and rotation of said rock bolt, allowing said resin to cure.

15. The method of claim 14, wherein said rock bolt is rotated in a direction opposite to the direction of helical winding of said first and second wires. DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON