AU2018101679B4

AU2018101679B4 - Rock bolt assembly

Info

Publication number: AU2018101679B4
Application number: AU2018101679A
Authority: AU
Inventors: Roland Christopher Walker
Original assignee: DSI Underground Australia Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 2017-12-14
Filing date: 2018-11-09
Publication date: 2019-06-13
Anticipated expiration: 2026-11-09
Also published as: AU2018101679A4

Abstract

ROCKBOLTASSEMBLY A rock bolt assembly (100) for temporary support of a tunnel or other ground excavation in a civil engineering application, said rock bolt assembly comprising: an elongate rod (110) formed of a fibre reinforced plastics material and extending between a rod leading end (111) and a rod trailing end (112); an end fitting mounted on said rod towards said rod trailing end, said end fitting (120) having a rod aperture for receiving said rod; and an elongate sleeve (130), said sleeve being mounted on said rod and extending from said end fitting toward said rod leading end, said sleeve and said rod together defining an annular sleeve cavity (131); wherein said end fitting is provided with one or more grout passages (125) communicating the exterior of said end fitting with said sleeve cavity for post grouting of said rock bolt assembly.

Description

ROCK BOLT ASSEMBLY

Field of the Invention [0001] The present invention relates to the field of strata control, and in particular relates to a rock bolt assembly for temporarily supporting the roof or wall of a tunnel, mine or other ground excavation. The invention is primarily intended for civil applications, but may also be utilised in mining applications.

Background of the Invention [0002] The roof and walls of road tunnels and other ground excavations in civil engineering applications are typically supported with the use of rock bolts installed into bore holes drilled into the rock strata. In such applications, there is often a need for temporary support in areas of the tunnel/excavation that may be further excavated after an initial excavation, as a sequence of tunnelling work progresses. Such multi-pass tunnelling situations may arise, for example, where two tunnels converge, or where progressive widening or profile shaping of the tunnel occurs. Rock bolts installed after the initial excavation are necessarily temporary in nature, and are sheared by the tunnelling equipment as further rock strata is removed in the subsequent excavation. Once excavation is complete, permanent rock bolts are installed.

Summary of Invention [0003] The present invention provides a rock bolt assembly for temporary support of a tunnel, mine or other ground excavation, said rock bolt assembly comprising:

an elongate rod formed of a fibre reinforced plastics material and extending between a rod leading end and a rod trailing end;

an end fitting mounted on said rod towards said rod trailing end, said end fitting having a rod aperture for receiving said rod; and an elongate sleeve, said sleeve being mounted on said rod and extending from said end fitting toward said rod leading end, said sleeve and said rod together defining an annular sleeve cavity;

wherein said end fitting is provided with one or more grout passages communicating the exterior of said end fitting with said sleeve cavity for post grouting of said rock bolt assembly.

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2018101679 09 Nov 2018 [0004] Typically, said rod has an external thread extending between said rod leading end and said rod trailing end.

[0005] In a preferred form, said rod extends through said end fitting.

[0006] In a preferred form, said elongate sleeve is formed from a plastics material.

[0007] In a preferred form, said rock bolt assembly further comprises an expansion shell anchor threaded onto said external thread of sad rod towards said rod leading end.

[0008] In a preferred form, said glass reinforced plastics material is fibreglass.

[0009] Typically, said end fitting comprises:

a first component secured to said sleeve and adapted to engage a plate washer; and a second component threaded onto said external thread of said rod between said first component and said rod trailing end, said second component being adapted to engage said first component and having an external drive surface for application of torque to said second component;

wherein said rod aperture extends through said first and second components.

[0010] In one form, said first component defines a concavity facing said second component and said second component is adapted to be at least partially received in said concavity, wherein said one or more grout passages is/are defined at an interface between said first and second components.

[0011] In an alternate form, said first component comprises a hollow body having a grout port communicating an exterior of said hollow body with the interior of said hollow body, said one or more grout passages being defined by said grout port and said interior of said hollow body; and said second component comprises a nut.

Brief Description of Drawings [0012] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings wherein:

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2018101679 09 Nov 2018 [0013] Fig. 1 is a front elevation view of a rock bolt assembly;

[0014] Fig. 2 is a right side elevation view of the rock bolt assembly of Fig. 1;

[0015] Fig. 3 is a partially cross sectioned front elevation view of the rock bolt assembly of Fig.

installed in a bore hole;

[0016] Fig. 4 is an enlarged fragmentary view of the leading portion of the rock bolt assembly of Fig. 1 with the expansion shell in the pre-expanded condition;

[0017] Fig. 5 is a fragmentary partial cross-sectioned view of the leading portion of the rock bolt assembly of Fig. 1 with the expansion shell in the expanded position and engaging a bore hole wall;

[0018] Fig. 6 is a fragmentary partially cross-sectioned view of the trailing portion of the rock bolt assembly of Fig. 1 with a modified form of drive nut; and [0019] Fig. 7 is a partially cross-sectioned front elevation view of a rock bolt assembly according to a second embodiment.

Description of Embodiments [0020] Referring to Figs. 1 and 2 of the accompanying drawings, a rock bolt assembly 100 according to a first embodiment has an elongate rod 110 formed of a fibre reinforced plastics material extending between a rod leading end 111 and a rod trailing end 112. An end fitting 120 is mounted on the rod 110 toward the rod trailing end 112 and has a rod aperture through which the rod 110 extends. An elongate sleeve 130 formed of a plastics material is mounted on the rod 110 and extends from the end fitting 120 toward the rod leading end 111. In the embodiment depicted, a standard expansion shell anchor 140 is mounted on the rod 110 between the sleeve 130 and the rod leading end 111.

[0021] The rod 110 is preferably formed of a glass reinforced plastics material and may typically have a diameter of between 20 mm to 35 mm, and will typically have a length of the order of 1.5 m to 6 m. The rod 110 is formed with an external thread 113 extending along its length between

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2018101679 09 Nov 2018 the rod leading end 111 and rod trailing end 112. The thread 113 is typically moulded into the exterior surface of the rod 110 whilst the resin of the glass reinforced plastics material is still curing, by feeding or rotating the rod 110 through a thread forming mould.

[0022] In the arrangement depicted, the sleeve 130 extends over the majority of the length of the rod 110, from the end fitting 120 to adjacent the expansion shell anchor 140 and, together with the rod 110, defines an annular sleeve cavity 131 for passage of cementitious grout. The sleeve 130 is provided with corrugations 132 to assist in anchoring the sleeve 130 with respect to cementitious grout that, following installation (as will be discussed below), fills the annular sleeve cavity 131 and a further annular cavity defined between the sleeve 130 and the wall of the bore hole within which the rock bolt assembly 100 is installed.

[0023] The expansion shell anchor 140 is of a known form, comprising a central anchor body

141 that is threaded on to the rod 110 adjacent the rod leading end 111 and a shell 142 mounted on the anchor body 141 and initially held in place by a wire spring 143. The anchor body 141 comprises a cylindrical threaded trailing anchor body portion 144 that is threaded on to the rod 110 and a tapered leading anchor body portion 145 defining laterally opposing cutouts. The shell

142 comprises a pair of opposing leaves 146 that are received in the cutouts of the leading anchor body portion 145. The leaves 146 each define a reverse tapered inwardly facing surface that engages the tapered outer surface of the cutout of the leading anchor body portion 145. In use (as will be discussed below), as the rod 110 is rotated, the anchor body 141 is drawn downwardly along the rod 110 and through the shell 142. The engaging tapered surfaces act to expand the leaves 146 radially outwardly (as shown in Figure 5), into engagement with the wall of a bore hole within which the rock bolt assembly 100 is installed (as will be discussed below). Drawing the rod 110 through the anchor body 110 also acts to lightly pretension the rod 110.

[0024] The end fitting 120 is typically formed of steel, although other materials may be used for example plastics materials, and comprises a first component 121 and a second component that, in the first embodiment, is in the form of a hexagonal drive nut 122. The first component 121 is secured to the sleeve 130 and comprises a hollow body 123 with a tube 124 fixed to the leading end of the hollow body 123. The tube 124 is mounted over, and secured to, the trailing end of the sleeve 130. The leading face of the hollow body 123, adjacent the tube 124, is adapted to engage a plate washer 150, as shown in Fig. 3, and as will be further discussed below. A grout port 125 extends through the side wall of the hollow body 123, communicating the exterior of the hollow

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2018101679 09 Nov 2018 body 123 with the interior 126 of the hollow body 123. The grout port 125 and the interior 126 of the hollow body 123, together with the annular passage between the tube 124 and the rod 110, define a grout passage communicating the exterior of the end fitting 120 with the sleeve cavity 131 for post grouting of the rock bolt assembly, as will be discussed below. The drive nut 122 is threaded on to the external thread 113 of the rod 110 between the first component 121 and the rod trailing end 112. The drive nut 122 engages the trailing end of the first component 121, via an anti-friction washer 127. The drive nut 122 defines six external drive surfaces 128 for receipt by a drive dolly of an installation rig for application of torque to the drive nut 122, as will be discussed below.

[0025] Installation of the rock bolt assembly 100 will now be described with reference to Figs. 3 to 5 of the accompanying drawings. A bore hole 200 is first drilled into the rock face 201 forming the wall or roof of the tunnel or other ground excavation in the usual manner. The rock bolt assembly 100 is then inserted into the bore hole 200 with the rod leading end 111 leading. For installation, the rock bolt assembly 100 may be mounted on a standard installation rig, as utilized with known permanent, post-groutable, mechanically anchored rock bolt assemblies of a similar form that utilise a high tensile strength steel rod, such as a rock bolt assembly known as the CT Bolt. In particular, the rock bolt assembly 100 may be mounted on a standard installation rig, with the drive nut 122 located in the installation dolly.

[0026] The rock bolt assembly 100 is advanced toward the blind end 202 of the bore hole 200, with a plate washer 150 mounted on the rock bolt assembly 100 adjacent the hollow body 123 of the first component 121 of the end fitting 120. With the rock bolt assembly 100 inserted into the bore hole 200, the installation rig rotates the installation dolly so as to apply torque to the drive nut 122 by way of the drive surfaces 128. During this initial driving of the drive nut 122, the rod 110 rotates with the drive nut 122 in a direction tending to advance the rod 110 through the anchor body 141 of the expansion shell anchor 140, here being in a standard left handed (anticlockwise) direction. With engagement of the plate washer 150 against the rock face 201, and engagement of the first component 121 against the plate washer 150, advancement of the rod 110 will be prevented, such that the rotation of the rod 110 with the drive nut 122 will result in the anchor body 141 of the expansion shell anchor 140 being drawn downwardly along the rod 110 toward the rod trailing end 112. The anchor body 141 is thus displaced relative to the expansion shell 142, which is held in place by friction between the leaves 146 and the wall 203 of the bore

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2018101679 09 Nov 2018 hole 200. The expansion shell anchor 140 thus expands from the initial configuration, as shown in detail in Fig. 4, to the expanded configuration, shown in Fig. 5, driving the leaves 146 into engagement with the bore hole wall 203, thereby point anchoring the rock bolt assembly 100 within the bore hole 200. Retracting the anchor body 141 down along the rod 110 also develops a degree of pre-tension in the rod 110.

[0027] To ensure that the rod 110 rotates with the drive nut 122 during initial rotation, to enable setting of the expansion shell anchor 140, the drive nut 122 may be temporarily secured to the rod 110 by way of a shear pin extending through the drive nut 122 and into the rod 110, with the shear pin failing upon application of a predetermined torque following setting of the expansion shell anchor. Alternatively, the drive nut 122 may be of a modified form, as depicted in Fig. 6 with a pin 129 or other form of detent extending across the aperture of the drive nut 122 adjacent its trailing end. Such a detent effectively forms a blind nut which would prevent the rod 110 from being drawn downwardly through the drive nut 122 during the initial rotation of the drive nut 122 for setting of the expansion shell anchor and initial pre-tensioning of the rod 110 by retraction of the anchor body 141 along the rod 110. It is also envisaged that friction between the internal thread of the drive nut and the external thread 113 of the rod 110 may be sufficient to rotate the rod 110 with the drive nut 122 during setting of the expansion shell anchor 140, obviating the need for any shear pin or pin 129.

[0028] Once the expansion shell anchor has been set, if desired, further torque may be applied to the drive nut 122, which will result in failure of any shear pin locking the drive nut 122 to the rod 110, or ejecting the pin 129 from the trailing end of the blind form of drive nut 122 shown in Fig. 6. Further application of torque will result in drawing the rod 110 through the drive nut 122, thereby further pre-tensioning the rod 110.

[0029] Following pre-tensioning, a grout hose is coupled to the grout port 125 and cementitious grout is injected through the grout passage defined by the grout port 125 and the interior 126 of the hollow body 123, into the annular cavity defined between the rod 110 and sleeve 130 and through the sleeve cavity 131 toward the expansion shell anchor 140. The cementitious grout then flows back down the annular cavity defined between the sleeve 130 and the bore hole 203. Once flow of cementitious grout from the opening of the bore hole 200 at the rock face 201 is identified, the delivery of grout is ceased.

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2018101679 09 Nov 2018 [0030] A rock bolt assembly 300 according to a second embodiment is depicted in Figure 7. The features of the rock bolt assembly 300 that are identical to the rock bolt assembly 100 of the first embodiment are provided with identical reference numerals. The rock bolt assembly 300 of the second embodiment is substantially identical to the rock bolt assembly 100 of the first embodiment, apart from the configuration of the end fitting 320.

[0031] The end fitting 320 comprises a first component 321 and a second component 332. The first component 321 is in the form of a trailing female portion 323 and a leading tubular portion 324 extending from the leading end of the female portion 323. The tubular portion 324 is mounted over, and secured to, the trailing end of the sleeve 130. The leading face of the female member 323, adjacent the tubular portion 324, is adopted to engage a plate washer 150. The trailing end of the female portion 323 defines a concavity 325 facing the second component 323. As shown in Figure 7, the second component 322 is adapted to be at least partially received in the concavity 325 and engaging the wall of the concavity 335. The second component 322 has a leading male portion 326 that is received within the concavity 325 and a trailing nut portion 327 defining drive surfaces 328 for the application of torque to the second component 322 by way of an installation dolly, in the same general manner as described above in relation to the rock bolt assembly 100 of the first embodiment. One or more grout passages are defined at the interface between the first and second components 322, 323, particularly formed as longitudinally extending recesses 329 extending along the outer face of the male portion 326 of the second component 323. This form of end fitting is of the same general form as that of a rock bolt assembly known as the DCP Bolt.

[0032] The rock bolt assembly 300 of the second embodiment is installed in substantially the same manner as the rock bolt assembly 100 of the first embodiment, as described above. After setting of the expansion shell anchor 140 and pre-tensioning of the rod 110 by the application of further torque to the nut portion 327 of the second component 322, post-grouting is carried out by injecting grout through the grout passages communicating the exterior of the end fitting 320 with the sleeve cavity 131 defined between the rod 110 and the sleeve 130.

[0033] Persons skilled in the art will appreciate other possible modifications and alterations to the rock bolt assembly described.

Claims

1. A rock bolt assembly for temporary support of a tunnel or other ground excavation in a civil engineering application, said rock bolt assembly comprising:

2. The rock bolt assembly of claim 1, wherein said rod has an external thread extending between said rod leading end and said rod trailing end.

3. The rock bolt assembly of claim 2, further comprising an expansion shell anchor threaded onto said external thread of sad rod towards said rod leading end.

4. The rock bolt assembly of any one of claims 1 to 3, wherein said glass reinforced plastics material is fibreglass.

5. The rock bolt assembly of any one of claims 1 to 4, wherein said end fitting comprises: a first component secured to said sleeve and adapted to engage a plate washer; and a second component threaded onto said said external thread of said rod between said first component and said rod trailing end, said second component being adapted to engage said first component and having an external drive surface for application of torque to said second component;

further wherein said rod aperture extends through said first and second components.