AU2015101246A4 - Rock bolt fitting and assembly including same - Google Patents

Abstract

Abstract A rock bolt assembly is disclosed comprising a rock bolt having an axis and a shaft extending between opposite first and second ends spaced apart along the axis; and a fitting mounted to the rock bolt and operative to accommodate axial loading; the fitting comprising an inner member defining a passage through which the shaft locates, and a polymeric body moulded over the inner member, wherein the fitting is mounted to the rock bolt by way of a threaded connection between the inner member and the rock bolt shaft. c00 r-r4

Description

- 1 ROCK BOLT FITTING AND ASSEMBLY INCLUDING SAME Related Application The present application is a divisional application of Australian patent 2015100391, the contents of which are herein incorporated by cross reference. 5 Technical Field The present disclosure relates generally to rock bolts, and more specifically to a fitting for use on a rock bolt, and a rock bolt assembly including same. Background Art Rock bolt assemblies provide roof, wall and floor support. Roof and wall 10 support is vital in mining and tunnelling operations. Mine and tunnel walls and roofs consist of rock strata, which must be reinforced to prevent the possibility of collapse. Rock bolts include fittings which need to be able to accommodate significant loading to provide rock strata support. Fittings can be used as an end fitting to 15 abut the rock face and/or to tension the bolt or to receive attachments. In one form the fitting may be mounted by way of a threaded connection to the rock bolt shaft. Rotation of the fitting (to induce axial movement along the shaft) can be employed in tensioning the rock bolt. Fittings can also be used as an intermediate coupling to couple adjacent shafts or to tension the bolt. 20 In some applications, such as cuttable bolts where the bolts are destroyed during a mining operation on the strata support after their installation, it is suitable to make the fittings out of plastic. The above references to the background art do not constitute an admission that the art forms a part of the common general knowledge of a person of ordinary 25 skill in the art. The above references are also not intended to limit the application of the method and system as disclosed herein -2 Summary According to a first aspect, a rock bolt assembly is disclosed comprising: a rock bolt having an axis and a shaft extending between opposite first and second ends spaced apart along the axis; and a fitting mounted to the rock bolt and 5 operative to accommodate axial loading; the fitting comprising: an inner member defining a passage through which the shaft locates, and a polymeric body moulded over the inner member, wherein the fitting is mounted to the rock bolt by way of a threaded connection between the inner member and the rock bolt shaft. 10 In some embodiments, the thread profile is generally sinusoidal. In some embodiments, the fitting further comprises a torque transfer arrangement that is arranged to allow the fitting to impart torque to the shaft up to a threshold level under rotation of the fitting in a first direction, the torque transfer arrangement being arranged to fail at said threshold loading and 15 wherein when failed, the torque transfer arrangement does not inhibit the fitting from being able to move axially along the shaft under rotation in the first direction. In some embodiments, the torque transfer arrangement comprises one or more projections that extend from the polymeric body into the passage to abut the 20 shaft. According to a second aspect, disclosed is a fitting for a rock bolt having a shaft incorporating an external thread, the fitting having an axis and being arranged to be connected to a drive to impart rotation to the fitting about the axis, the fitting comprising a passage through which the shaft locates, an inner member 25 defining at least a portion of the passage and including an internal thread arranged to threadingly engage the external thread on the shaft, and a polymeric body being moulded over the inner member. In some embodiments, the material of the inner member has a higher material strength than the material of the body. In some embodiments, the inner -3 member is made from metal. In some embodiments, the inner member is operative to accommodate radial loading induced by axial loading of the fitting such that loading induced on the body is substantially axial. 5 In some embodiments, the inner member includes an abutment surface that extends radially in relation to the axis, and in use the abutment surface is operative to engage an internal surface of the body so as to inhibit separation of the body from the inner member. According to a third aspect, disclosed is a rock bolt assembly comprising a rock 10 bolt having an axis and a shaft extending between opposite first and second ends spaced apart along the axis, the shaft incorporating an external thread and a fitting according to the above aspect mounted on the shaft and arranged in use to tension the rock bolt when installed. In some embodiments the rock bolt is cuttable and made from, for example, 15 fibre-reinforced polymer. Brief Description of the Drawings Embodiments of the present disclosure will now be described with reference to the following drawings by way of example only, where: Fig. 1 is an exploded perspective view of an embodiment of a rock bolt 20 assembly including a fitting; Fig. 2 is an exploded perspective view of the fitting of Fig. 1; Fig. 3A is a plan view and Fig. 3B is a cross-sectional view through A-A of the embodiment shown in Fig. 1 in an assembled condition; and Fig. 4A is a plan view and Fig. 4B is a a cross-sectional view through A-A 25 of the embodiment shown in Fig. 1 in a tensioned condition. Detailed Description -4 The disclosed rock bolt assembly is suitable for use in hard rock applications as well as in softer strata, such as that often found in coal mines, and it is to be appreciated that the term "rock" as used in the specification is to be given a broad meaning to cover both these applications. The following description 5 relates to assemblies for reinforcement of rock strata through various bolting support mechanisms, including bolts bonding multiple layers or blocks together and tension placed across joints and bedding mobilising frictional resistance to rock movement. According to a first aspect, disclosed is a rock bolt assembly comprising: a rock 10 bolt having an axis and a shaft extending between opposite first and second ends spaced apart along the axis; and a fitting mounted to the rock bolt and operative to accommodate axial loading; the fitting comprising: an inner member defining a passage through which the shaft locates, and a polymeric body moulded over the inner member, wherein the fitting is mounted to the rock 15 bolt by way of a threaded connection between the inner member and the rock bolt shaft. To allow rock support to be achieved, the end of the rock bolt may be anchored mechanically to the rock formation by engagement of an expansion assembly on the end of bolt with the rock formation. Alternatively, the bolt may be 20 adhesively bonded to the rock formation with a resin bonding material inserted into the bore hole. Alternatively, a combination of mechanical anchoring and resin bonding can be employed by using both an expansion assembly and resin bonding material. According to the first aspect the fitting may be used in tensioning of the rock 25 bolt once it is installed. In this arrangement the fitting is arranged to rotate relative to the rock bolt shaft to allow it to translate axially along the shaft. The fitting (either directly or indirectly) is arranged to move into contact with the rock formation surrounding the bore hole. Once in contact with the rock formation, subsequent rotation of the fitting causes the bolt to be tensioned. 30 In some forms, the material of the inner member has a higher material strength -5 than the polymeric body. The material of the inner member may be stronger and stiffer than material than the polymeric body. For example, the inner member may be made from steel, copper, brass or carbon fibre which is able to accommodate load transfer from the rock bolt to allow for the inclusion of the 5 polymeric body without premature failure of the rock bolt. The body may be formed from any type of polymer such as a thermoset glass reinforced polymer (e.g., nylon). This arrangement is advantageous as the steel inner member accommodates the radial loading on the shaft of the rock bolt to prevent the polymer fitting from expanding under radial load which may 10 otherwise cause fracture of the body. In some forms, the threaded engagement between the inner member and the shaft of the rock bolt enables the fitting to accommodate the axial loading. Further, the thread profile may be any shape and pitch (e.g., the thread profile may be sinusoidal). In some forms, the inner member is operative to 15 accommodate radial loading induced by axial loading of the fitting such that loading induced on the body is substantially axial. Axial loading of the fitting occurs through the fitting being in forced engagement with the rock face (either directly or indirectly) on tensioning of the rock bolt. The inner member may also be operative to accommodate radial loading induced by axial loading of the 20 fitting such that loading induced on the body is substantially axial. In some embodiments, a torque transfer arrangement is provided that is arranged to allow the fitting to impart torque to the shaft up to a threshold level under rotation of the fitting in a first direction, the torque transfer arrangement being arranged to fail at said threshold loading and wherein when failed, the 25 torque transfer arrangement does not inhibit the fitting from being able to move axially along the shaft under rotation in the first direction. In embodiments where point anchoring of the rock bolt occurs (by a mechanical anchor and/or resin bonding), the torque transfer arrangement enables an operator to rotate the rock bold assembly in the bore to activate the mechanical 30 anchor and/or mix the resin before it has begun to set.

-6 Once the rock bolt assembly is anchored in the bore (either by using an expansion assembly or allowing resin to set or a combination of both), further rotational force applied to the rock bold assembly via the fitting causes the torque transfer arrangement to fail thereby allowing the fitting to rotate relative 5 to the shaft to thereby allow it to move axially along the shaft through the threaded connection to allow tensioning of the rock bolt. In some embodiments, the torque transfer arrangement comprises one or more projections that extend from the polymeric body into the passage to abut the shaft. In some forms the torque transfer arrangement forms at least part of a 10 wall of the polymeric body that is engaged by an end of rock bolt. In this embodiment, abutment of an end of the rock bolt on the wall of the polymeric body prevents relative rotation between the fitting and the shaft in one direction thereby allowing torque to be transferred from the fitting to the shaft . The torque transfer arrangement fails by the end of the rock bolt breaking through 15 the wall. The wall may be unitarily formed with the polymeric body or may be formed as a separate end cap that is received over an aperture in the polymeric body. In other embodiments, the torque transfer arrangement is another deformable or frangible part of the polymeric body, a shear pin that extends through the rock bolt into the fitting or adhesive between the rock bolt and the 20 fitting. In some embodiments, the inner member includes an abutment surface that extends radially in relation to the shaft, and in use the abutment surface is operative to engage an internal surface of the body so as to inhibit removal of the fitting from the shaft. However, the inner member may also be any suitable 25 shape, for example, a cylindrical member, a conical member, a hexagonal member a square or rectangular member, or a cylindrical member that is stepped or has a collar that extends radially in relation to the member anywhere along its length. In addition, the shaft of the rock bolt may be formed from fibre-reinforced 30 polymer. For example, the shaft may be manufactured from fibreglass, carbon- -7 fibre-reinforced polymer, or any type of fibre-reinforced-polymer including both natural and synthetic fibres. A fibre-reinforced polymer shaft is beneficial as it is cuttable without damaging mining equipment (as discussed above), and can be manufactured by continuous extrusion and then cut to size. Although, the 5 fitting is discussed primarily in relation to a rock bolt assembly in the form of a cuttable bolt, embodiments of the fitting may be used with either a rigid bolt or a cable bolt, and are not limited to a cuttable bolt. In a second aspect, disclosed is a fitting for a rock bolt having a shaft incorporating an external thread, the fitting having an axis and being arranged 10 to be connected to a drive to impart rotation to the fitting about the axis, the fitting comprising a passage in which the shaft locates, an inner member defining at least a portion of the passage and including an internal thread arranged to threadingly engage the external thread on the shaft, and a polymeric body being moulded over the inner member. 15 In some embodiments, the fitting further comprises a torque transfer arrangement that is arranged to allow the fitting to impart torque to the shaft up to a threshold level under rotation of the fitting in a first direction, the torque transfer arrangement being arrange to fail at said threshold loading and wherein when failed, the torque transfer arrangement does not inhibit the fitting from 20 being able to move axially along the shaft under rotation in the first direction. In some embodiments the torque transfer arrangement is a frangible part of the polymeric body such as a wall extending across the passage. According to a third aspect, disclosed is a rock bolt assembly comprising a rock bolt having an axis and a shaft extending between opposite first and second 25 ends spaced apart along the axis, the shaft incorporating an external thread and a fitting according to the above aspect mounted on the shaft and arranged in use to tension the rock bolt when installed. According to a third aspect, disclosed is a method of installing the rock assembly of the first aspect, and further comprisinga torque transfer -8 arrangement arranged to allow the fitting to impart torque to the shaft up to a threshold level under rotation of the fitting in a first direction, the torque transfer arrangement being arrange to fail at said threshold loading and wherein when failed, the torque transfer arrangement does not inhibit the fitting from being 5 able to move axially along the shaft under rotation in the first direction, the method comprising inserting the rock bolt assembly into a recess formed in a region surrounding a tunnel, anchoring the rock bolt assembly to the region, and applying torque to the fitting to cause the torque transfer arrangement to fail and thereafter rotating the fitting to cause axial movement of the fitting 10 relative to the shaft to enable the rock bolt to be placed under tension. Referring to the Figures disclosed is an illustrative embodiment of a rock bolt assembly 10. Referring to Fig. 1, disclosed is an embodiment of the rock bolt assembly 10 including a rock bolt 12 and a fitting 14 mounted to the rock bolt 12. The rock bolt 12 has an axis A and a shaft 16 extending between opposite 15 first 17 and second 18 ends spaced apart along the axis A. The fitting may be used as an end fitting which abuts the rock face, is able to tension the bolt, and is able to receive a drive to tension the bolt. In the illustrated form, the fitting 14 is an end fitting that is arranged to be connected to a drive (not shown) that is used to install the device. The fitting is 20 also arranged to abut the rock surface (either directly or indirectly) on installation. As such the fitting is required to accommodate significant loading (particularly axial loading) applied during both installation and tensioning of the bolt. The fitting is able to accommodate approximately 6 - 8 tonne load on the rock bolt. 25 The fitting 14 as shown is formed in a two part construction that includes a body 20 and an inner member 22. The body 20 is polymeric and is moulded over the inner member 22. As the body is moulded, it is able to be formed into a wide variety of shapes. Also by being polymeric it is able to be used in circumstances where the bolts are cut and passed through mining equipment 30 without damage to the equipment, which protects the equipment.

-9 In the illustrated embodiment, the body 20 is formed from a thermoset glass reinforced polymer (e.g. nylon) that is moulded over the steel inner member 22. It is understood that the body made be made from any mouldable plastic, such as any thermosetting plastic or thermosetting resin. 5 In the illustrated embodiment, the body 20 has a leading end 24 and a trailing end 26. The leading end 24 is convex to facilitate alignment of the body 20 in use in the rock bolt assembly. In some forms, the convex leading end 24 may be a dome-shaped end 28. In use, the rock bolt 12 is configured to be at least partially located in a bore formed in a rock substrate. The dome-shaped end 28 10 is partially located in the bore against the surface of the rock substrate, and increases in diameter extending from the leading end 24. The diameter of the bore is smaller than at least the maximum diameter of the dome-shaped end 28 to allow the body 20 to locate partially in the bore of the rock substrate. In other words, the dome-shaped leading end 28 abuts against the surface of the rock 15 substrate. The dome 28 is designed to form a spherical seating washer. In alternative non-illustrated embodiments, the rock bolt assembly may include a plate, for example, a volcano plate. The plate is located between the surface of the rock substrate and the leading end of the body. In this embodiment, the plate and the dome-shaped leading end are designed to facilitate alignment by 20 accommodating angled loading from the plate to the fitting for maximum load capacity. The trailing end 26 of the body is in the form of a drive receiving portion 30 that is arranged to receive the drive to impart rotary and/or axial drive to the rock bolt assembly 10. In the illustrated embodiment, the drive receiving portion 30 25 is hexagonal in cross-section, but may be any other non-circular shape profile. Alternatively, the driving receiving portion may be in the form of a recess formed in the end of the body to receive a suitable male drive. The trailing end 26 of the body is formed with an aperture 51 that is axially aligned with the rock bolt shaft axis A. A seat 52 is formed around the 30 perimeter of the aperture 51 in which a cap 50 is received and fixed. The cap -10 50 thus forms an end wall of the body 20. In the illustrated embodiment, the cap is formed as a integral component of the body and is connected to the body by a thin wall which is designed to fail. Varying the thickness of this wall allows for different threshold loads to be provided under which the wall will fail. 5 However, in other embodiments, the body may be formed with the end wall as a separate component that may be fixed in position by other means (for example a mechanical connection or adhesive). The cap 50 provides a torque transfer arrangement that allows the torque to be imparted to the shaft up until a threshold level through abutment of the end of 10 the shaft on the cap which prevents axial movement of the fitting relative to the shaft (in one direction). This arrangement is generally shown in Figs. 3A and 3B. On reaching the threshold level, the axial load induced through the thread under the threshold torque causes the cap to fail, thereby releasing the shaft end and allowing the fitting to move axially along the shaft under the continued 15 rotation. This arrangement is generally shown in Figs. 4A and 4B. This threshold torque is designed to be above loading encountered during insertion of the rock bolt into a recess or bore in a rock body or when the rock bolt is being rotated to anchor the rock bolt (by activating a mechanical anchor and/or mixing resin in the bore). Once the rock bolt is anchored to the rock 20 body, sufficient torque can be applied to the fitting to cause the cap 50 to break or detach from the body 20. The failing of the cap 50 then enables the rock bolt 12 to be placed under tension by applying further rotational forces to the fitting 14. Rotation of the fitting 14 in this situation will draw the rock bolt 12 through the fitting. The rock bolt is tensioned because its distal end is fixed in the rock 25 body and the fitting is in abutment with the surface of the rock body. Referring in particular to Figure 2, the cap 50 comprises a plurality of thicker triangular segments 54 divided by thinner portions 56 which extend radially from the center of the cap. The thinner portions 56 define lines of weakness along which the cap 50 can break to assist the cap breaking into pieces to 30 reduce build-up of caps within the socket of the tightening spanner.

-11 In other embodiments, either the torque transfer arrangement is not included or the torque transfer arrangment is in forms other than the end cap. For example, the torque transfer arrangement may be another deformable or frangible part(s) of the polymeric body such as one or more tabs, a shear pin 5 that extends through the fitting and into the rock bolt, a plug that locates within the passage of the inner member, or a portion of adhesive between the rock bolt and the polymeric body. Attachments may be used with the bolts, and when installed, may be used to hang mesh to inhibit crumbling and breaking rock from falling on workers. 10 During the development of a roadway or tunnel additional mining induced stress can break the rock surface about a tunnel, especially during the traction of the ore. The mesh may be required for the protection of the workers. The mesh can be fixed close to the rock surface by a secondary plate that is coupled to the body of the fitting. The secondary plate may be coupled by any suitable 15 means, for example, a threaded nut or fixed by any other means. Also, other embodiments of attachments may be used, such as an attachment to hang mining services (e.g. water or power lines). The body may be provided with an external threaded portion for the attachment to engage. The inner member 22 defines a passage 36 in which the shaft 16 locates. In 20 the illustrated embodiment, the inner member 22 includes an internal thread and is in threaded engagement with an external thread of the shaft 16. The shaft 16 includes a sinusoidal thread, but the thread profile may be any shape and pitch. As a result of the shape and pitch of the thread both axial and radial load is transferred to the fitting 14 through the shaft 16. The inner member 22 25 is operative to accommodate radial loading induced by axial loading to the fitting 14 such that loading induced on the body 20 is substantially axial. The inner member 22 is designed to provide radial confinement on the shaft 16 to inhibit the polymeric body 20 from expanding. In the illustrated embodiment, the shape and pitch of the thread profile is 30 coarse, which produces large radial forces on the inner member 22. The inner -12 member 22 is able to accommodate these large radial forces without shattering. As discussed above, the thread profile may be any shape or pitch provided it does not cause excessive radial loading on the inner member which would cause the inner member to fracture and failure instead of the axial loading of 5 the bolt. For example, the inner member may be formed from steel which, because of its material properties, is able to accommodate the loading transferred from the rock bolt. In some embodiments, the inner member 20 prevents the body 20 from expanding. This enables rock support to be achieved. 10 The material of the inner member 22 has a higher material strength than the polymeric body 20. The inner member 22 is made of a material that is able to withstand the load applied to the fitting while resisting failure. The shape and material of the inner member determines the maximum load the inner member is able to withstand without failing. The material strength of the inner member 15 not only refers to its load carrying capacity, but also its stiffness (i.e., its ability to resist deformation) and its stability (i.e., its ability to main maintain its original shape). The inner member has a high stiffness and stability and is able to restrict the radial stresses (or hoop stresses) induced by the thread of shaft without being permanently deformed. In the illustrated embodiment, the inner 20 member is formed from steel. The steel inner member 22 provides radial confinement on the thread of the shaft 16 to prevent the polymer body 20 expanding. For example, the combined steel inner member 22 with over moulded body 20 is able to achieve a 6- 8 tonne load without failing while minimising the amount of steel in a cuttable bolt. 25 To accommodate the transfer of the loading between the inner member 22 and the body 20, in the illustrated embodiment, the inner member 22 has an abutment surface 38 that extends radially in relation to the shaft 16. The abutment surface 38 engages an internal surface 40 of the body 20 so as to inhibit removal of the fitting 14 from the shaft 16. The abutment surface 38 acts 30 to inhibit the body 20 from de-bonding from the shaft 16 and the inner member 22. In other words, the engagement between the abutment surface 38 and the -13 internal surface 40 provides resistance to the axial forces and, in some embodiments, prevents the body 20 from sliding off the shaft 16 and the inner member 22. In the illustrated embodiment, the inner member 22 is cylindrical, but the inner 5 member may be any suitable shape. The abutment surface 38 is formed at a leading end of the inner member 22. However, the inner member may also be stepped to so that one or more abutment surfaces are located towards a trailing end of the inner member, or the inner member may have a collar having an abutment surface. The inner member may be hexagonal or a non-circular 10 shape to assist with locating of the inner member onto the shaft. As mentioned above the fitting with the polymeric body is ideally for use in cuttable bolts. When used in such applications the shafts are typically also made from a polymer. In particular, the illustrated shaft is made from fibreglass but may be made from any fibre-reinforced polymer (natural or synthetic), such 15 as carbon-fibre reinforced polymer. The combination of the polymeric shaft and body with a small steel insert is advantageous. Where the bolt 12 is being cut to remove the mined material, the steel inner member 22 is minimal enough to pass through cutting and transport equipment without damage to the equipment. The rock bolt and the body of the fitting both are made from 20 polymer which protects the equipment. The fitting 14 is also low profile in relation to the surface of the rock substrate, which also protects the mining equipment. In this regard, the fitting does not protrude excessively from the surface of the rock substrate. Shaft tails protruding into a mine tunnel are susceptible to damaging equipment or 25 equipment can hit and damage the ground support provided by the rock bolt assembly. Accordingly, embodiments of fittings and rock bolt assemblies are provided which allow for the transfer of torque and tensioning of rock bolts. Furthermore, in at least one form, the fitting is multifunctional and is suitable in combination 30 with cuttable bolts and for the attachment of related attachments.

-14 As will be understood, variations of the above described rock bolt assemblies can be made without departing from the scope of the claims. While the fittings and rock bolt assemblies have been described in reference to its preferred embodiments, it is to be understood that the works which have 5 been used are descriptive rather than limiting and that changes may be made without departing from its scope as defined by the claims. It is to be understood that a reference herein to a prior art document does not constitute an admission that the document forms part of the common general knowledge in the art in Australia or in any other country. 10 In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features 15 in various embodiments of the invention.

Claims (5)

1. A rock bolt assembly is disclosed comprising: a rock bolt having an axis and a shaft extending between opposite first 5 and second ends spaced apart along the axis; and a fitting mounted to the rock bolt and operative to accommodate axial loading; the fitting comprising: an inner member defining a passage through which the shaft locates, and 10 a polymeric body moulded over the inner member, wherein the fitting is mounted to the rock bolt by way of a threaded connection between the inner member and the rock bolt shaft.

2. A rock bolt assembly according to claim 1, further comprises a torque transfer arrangement that is arranged to allow the fitting to impart torque 15 to the shaft up to a threshold level under rotation of the fitting in a first direction, the torque transfer arrangement being arranged to fail at said threshold loading and wherein when failed, the torque transfer arrangement does not inhibit the fitting from being able to move axially along the shaft under rotation in the first direction. 20

3. A fitting for a rock bolt having a shaft incorporating an external thread, the fitting having an axis and being arranged to be connected to a drive to impart rotation to the fitting about the axis, the fitting comprising a passage in which the shaft locates, an inner member defining at least a 25 portion of the passage and including an internal thread arranged to threadingly engage the external thread on the shaft, and a polymeric body being moulded over the inner member. -16

4. A fitting according to claim 4, further comprises a torque transfer arrangement that is arranged to allow the fitting to impart torque to the shaft up to a threshold level under rotation of the fitting in a first direction, the torque transfer arrangement being arranged to fail at said threshold 5 loading and wherein when failed, the torque transfer arrangement does not inhibit the fitting from being able to move axially along the shaft under rotation in the first direction.

5. A rock bolt assembly or fitting according to claim 3 or 4, wherein the 10 torque transfer arrangement comprises one or more projections that extends from the polymeric body into the passage to abut the shaft.