AU2013204178B2

AU2013204178B2 - A rock bolt assembly

Info

Publication number: AU2013204178B2
Application number: AU2013204178A
Authority: AU
Inventors: Gary Anthony Davey
Original assignee: DSI Underground Australia Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 2012-09-06
Filing date: 2013-04-12
Publication date: 2015-11-26
Anticipated expiration: 2033-04-12
Also published as: AU2013204178A1

Abstract

A rock bolt assembly (100) for installation in a bore hole (200) extending through a rock face (201) has an elongate load bearing member (101) longitudinally extending between a member leading end (101a) and a member trailing end (101b). An end fitting (120) is mounted on the load bearing member (101) towards the member trailing end (101b). The end fitting (120) is configured to engage a plate washer (160) in use for transferring load between the load bearing member (101) and the rock face (201) surrounding the bore hole (200). The end fitting (120) defines a grout delivery passage (135) for delivery of grout through the end fitting (120) to encapsulate a length of the load bearing member (101) in use. A debonding sleeve (150) is mounted on the load bearing member (101) between the end fitting (120) and the member leading end (101a) to at least substantially prevent the passage of grout between the sleeve (150) and the load bearing member (101). (7330988 1):PRW .12to (010 lo 1(04 14ah14 2c)

Description

1 A ROCK BOLT ASSEMBLY Technical Field [0001] The present invention relates to strata control in civil engineering and mining operations and in particular relates to rock bolts for securing the roof or wall of a mine, tunnel or other ground excavation. Background of the Invention [0002] Rock bolts are commonly utilised to secure the roof or walls of underground mines, tunnels and other ground excavations. Rock bolts comprise elongate load bearing members that may be in the form of a rigid bar or a flexible cable formed of multiple wires wound around a central wire. The flexible cable form of rock bolts are known as cable bolts. In one form of installation, a rock bolt is fixed into a bore hole drilled into a rock face by a mechanical or chemical anchor creating a point anchor at the leading (upper) end of the rock bolt and a grout, which is typically cementitious in form, encapsulating the rock bolt along its length. [0003] For mechanical anchor point anchoring, which is generally applicable to rigid rock bolts, the leading end of the rock bolt is inserted into the bore hole and point anchored into the upper end of the bore hole by way of an expansion shell mechanical anchor threaded onto the bolt leading end. Chemical anchors are applicable to both rigid rock bolts and cable bolts. Chemical anchors generally comprise a two-component resin filled cartridge having a frangible casing. The resin filled cartridge is inserted into the bore hole in front of the rock bolt. The rock bolt is rotated as it is thrust towards the top of the bore hole, thereby puncturing the frangible casing of the resin filled cartridge, and mixing the resin. The resin is allowed to set and thus point anchor the leading region of the rock bolt within the bore hole. [0004] When using either a chemical or mechanical anchor, once the point anchor is in place, rigid rock bolts are typically tensioned by way of a threaded end fitting threadingly mounted onto the trailing region of the rock bolt which bears against a plate washer which in turn engages the face of the rock surrounding the bore hole. Cable bolts are typically tensioned by way of a barrel and wedge assembly that bears against the plate washer. (7330988 1):PRW 2 [0005] The annular cavity defined between the rigid bar or cable bolt and the wall of the bore hole is then post-grouted by any of various mechanisms. The grout acts to provide for load transfer between the rock and the rigid bar or cable along an extended length of the rock bolt, rather than at the point anchor only. Grouting of the rock bolt also protects it from corrosion. Summary of the Invention [0006] In a first aspect, the present invention provides a rock bolt assembly for installation in a bore hole extending through a rock face, said rock bolt assembly comprising: an elongate load bearing member longitudinally extending between a member leading end and a member trailing end; an end fitting mounted on said load bearing member towards said member trailing end, said end fitting being configured to engage a plate washer in use for transferring load between said load bearing member and the rock face surrounding the bore hole, said end fitting defining a grout delivery passage for delivery of grout through said end fitting to encapsulate a length of said load bearing member in use; and a debonding sleeve mounted on said load bearing member between said end fitting and said member leading end to at least substantially prevent the passage of grout between said sleeve and said load bearing member. [0007] Typically, said debonding sleeve has a length of at least 250 mm and no more than 500 mm less than a length of said load bearing member. More typically, said debonding sleeve has a length of between 500 mm and 1500 mm. [0008] In preferred forms, said rock bolt assembly further comprises an elongate sheath extending from said end fitting over said debonding sleeve and towards said member leading end, said sheath defining an annular cavity with said load bearing member communicating with said grout delivery passage. [0009] In some embodiments, said load bearing member is a rigid bar. [0010] In preferred forms, said rock bolt assembly further comprises a mechanical anchor mounted on a leading region of said rigid bar, for point anchoring said leading region. In an alternate form, said rigid bar is configured for resin point anchoring of a leading region of said rigid bar. (7330988 1):PRW 3 [0011] In alternate embodiments, said load bearing member comprises a cable. [0012] In such alternate embodiments, said end fitting typically comprises a barrel and wedge fitting. Brief Description of the Drawings [0013] A preferred embodiment of the present invention will now be described, by way of an example only, with reference to the accompanying drawings wherein: [0014] Figure 1 is a fragmentary isometric view of a rock bolt assembly. [0015] Figure 2 is a fragmentary partially cross-sectioned isometric view of the rock bolt assembly of Figure 1. [0016] Figure 3 is a fragmentary partially cross-sectioned front elevation view of the rock bolt assembly of Figure 1. [0017] Figure 4 is an enlarged view of detail "A" of Figure 3. [0018] Figure 5 is an enlarged view of detail "B" of Figure 3. [0019] Figure 6 is an enlarged fragmentary view of the rock bolt assembly of Figure 1 depicting attachment of the debonding sleeve to the rigid bar. [0020] Figure 7 is a fragmentary partially cross-sectioned front elevation view of a rock bolt installation utilising the rock bolt assembly of Figure 1. Detailed Description of the Preferred Embodiments [0021] Referring firstly to Figures 1 to 5 of the accompanying drawings, a rock bolt assembly 100 comprises a rigid rock bolt having an elongate load bearing member which is in the form of a rigid bar 101 formed of steel material. The rigid bar 101 longitudinally extends between a leading end 101a and a trailing end 101b. The rigid bar 101 is of a standard configuration, having a threaded leading region 102, threaded trailing region 103 and a central region 104 extending along the majority of the length of the rigid bar 101 and having coarse thread-like deformations 105. The threaded configuration of the leading region 102 of the (7330988 1):PRW 4 rigid bar 101 provides for mounting of a mechanical anchor in the form of a standard expansion shell type mechanical anchor 110, which is threadingly mounted onto the leading region 102 of the rigid bar 101. For configurations utilising a chemical anchor in the form of a two-component resin filled cartridge to point anchor the leading region 102 of the rigid bar 101, the leading region 102 need not be threaded, but may be otherwise configured in a known manner to enhance mixing of the two-component resin and/or puncturing and shredding of the casing of the cartridge. In particular, the leading region 102 may be provided with surface features, such as a helical wire wrapped around the rigid bar 101, to enhance resin mixing. In such an application, a resin dam would typically be mounted on the rigid bar 101 to inhibit passage of resin from the leading region 102 down towards the trailing region 103. [0022] An end fitting 120 is mounted on the trailing region 103 of the rigid bar 101 towards the trailing end 101b. Referring specifically to Figure 5, the end fitting 120 is here in the form of a female component 121 and a male component 122, both of which are typically formed of steel. The female component 121 is in the general form of a cup, having a leading convexly curved outer face 123 formed as a body of revolution and configured to engage a plate washer as will be further discussed below. The outer face 123 of the female component 121 is provided with coupling means in the form of slots 124 (best depicted in Figure 1) for coupling the female component 121 to coupling pins of a grout delivery hose coupling (which is not depicted). The female component 121 is hollow, having an open trailing face 125. The inner wall 126 of the female component 121 defines the hollow interior 127 of the female component 121 which extends from the trailing face 125 to an opening 128 at the leading end of the female component 121, thereby defining a continuous opening through the female component 121 for passage of the rigid bar 101 and grout, as will be further discussed below. [0023] The male component 122 has a threaded aperture 129 extending along its length for threadingly mounting the male component 122 on the trailing region 103 of the rigid bar 101. The male component 122 has an enlarged leading head portion 130 with a convexly curved outer face 131, formed as a body of revolution. The head portion 130 is located within the hollow interior 127 of the female component 121 with the outer face 131 engaging the inner wall 126 of the female component 101 to transfer load therebetween. The male component 122 also has a trailing drive portion 132, defining a plurality of drive surfaces 133 for engagement with a drive socket to thread the male component 122 along the trailing (7330988 1):PRW 5 region 103 of the rigid bar 101. Here the drive portion 132 is specifically in the general form of a hexagonal nut. A rearwardly facing annular shoulder 134 is defined at the junction between the leading head portion 130 and trailing drive portion 132. A grout passage 135 extends through the head portion 130 from the shoulder 134 onto the outer face 131 adjacent the leading end of the male component 122, communicating with the hollow interior 127 of the female component 121. The grout passage 135 and hollow interior 127 of the female component 121 thus form a grout passage through the end fitting 120. Two or more grout passages 135 will typically be provided, radially spaced about the male component 122. An annular seal 136 is mounted in a recess formed in the inner wall 126 of the female component 121 and engages the outer face 131 of the head portion 130 of the male component 122, trailing the leading opening of the grout passage 135. The seal 136 acts to inhibit the backflow of grout out of the end fitting 120. Alternate forms of end fitting incorporating one or more grout passages may be utilised as desired. [0024] In the embodiment depicted, a steel grouting tube 140 is mounted on (or alternatively integrally formed with) the leading end of the female component 121 over the leading opening in the female component 121. A grouting sheath 141 formed of plastics material is mounted on the leading end of the grouting tube 140 and extends along the rigid bar 101, here to adjacent the leading portion 102 of the rigid bar 101. Here the grouting sheath 141 is provided with a series of corrugations 142 along its length to assist in keying into the grout in use. The grouting tube 140 and grouting sheath 141 together form a grouting sleeve, defining with the rigid bar 101 an inner annular passage 143 for the flow of grout along the rigid bar 101 to adjacent the leading region 102 of the rigid bar 101. [0025] To allow a portion of the rigid bar 101 to be debonded from the grout in use, a debonding sleeve 150 is mounted on the rigid bar 101 in the central region 104 between the end fitting 120 and the leading region 102 of the rigid bar 101, as best depicted in Figures 2, 3 and 4. Typically, the sleeve 150 will be mounted towards the centre of the rigid bar 101 and will preferably have a length of at least 250 mm, and more typically between 500 mm and 1500 mm. Preferably, the debonding sleeve 150 has a length that is not more than 500 mm less than the length of the rigid bar 101, so as to provide sufficient length of the leading region 102 for point anchoring of the rigid bar 101 and sufficient length of the trailing region 103 for location of the end fitting 120. In an example embodiment, the rigid bar 101 has a length of 2400 mm and the debonding sleeve 150 has a length of approximately 1000 mm. (7330988 1):PRW 6 The debonding sleeve 150 will typically be formed of plastics material and have a relatively tight fit over the rigid bar 101 so as to reliably inhibit, and substantially prevent, passage of grout between the debonding sleeve 150 and the rigid bar 101. The debonding sleeve 150 may be mounted on the rigid bar 101 by any suitable means. In one embodiment, as depicted in Figure 6, the ends of the debonding sleeve 150 are secured to the rigid bar 101 by way of a metallic tie wire 151 encircling each end of the debonding sleeve 150. The tie wire 151 will also serve to substantially seal or close any gap between each end of the debonding sleeve 150 and the rigid bar 101, further inhibiting the passage of grout. In the embodiment depicted, tape 152 or some other form of seal is applied over the tie wire 151 and the end region of the debonding sleeve 150 and adjacent portion of the rigid bar 101 to further seal or close any such gap. [0026] Referring to Figure 7, installation of the rock bolt assembly 100 will now be described. A bore hole 200 is drilled into the rock face 201 of the strata 202 to be secured in the usual manner. A standard domed plate washer 160 is mounted on the rock bolt assembly, engaging the outer face 123 of the female component 121 of the end fitting 120. The rock bolt assembly 100 is then inserted into the bore hole 202 with the expansion shell mechanical anchor 110 leading. With the rock bolt assembly 100 in place, the expansion shell mechanical anchor 110 is then activated by rotating the rigid bar 101 to draw the inner barrel component 111 of the expansion shell mechanical anchor 110 back along the threaded leading region 102 of the rigid bar 101, thereby expanding the leaves of the outer shell component 112 of the expansion shell mechanical anchor 110 in the usual manner. The expanded outer expansion shell component 112 engages the wall 203 of the bore hole 200, point anchoring the rock bolt assembly 100 within the bore hole 200. Rotation of the rigid bar 101 is achieved by rotatingly driving the drive portion 132 of the male component 122 of the end fitting 120. The male component 122 of the end fitting 120 will typically have already been threaded along the threaded trailing region 103 of the rigid bar 101 to the leading end of the threaded trailing region 103 during assembly of the rock bolt assembly 100 such that, during installation, rotation 101, driving of the male component 122 will be directly translated to rotation of the rigid bar 101. The threaded leading region 102 and threaded trailing region 103 will generally have like-handed threads (here left-handed threads) such that driving of the male component 122 in the counter-clockwise direction will keep the male component 122 engaged with the end of the threaded trailing region 103, providing rotation of the rigid bar 101 in the counter clockwise direction which will expand the expansion shell mechanical anchor 110. (7330988 1):PRW 7 [0027] Once the expansion mechanical anchor 110 is set, the rigid bar 101 is tensioned by further rotating the male component 122 of the end fitting 120 in the same direction, again rotatingly driving the drive portion 132. The rotation of the male component 122 tends to further drive the rigid bar 101 through the expansion shell mechanical anchor 110, which at this stage is fixed in position by engagement with the wall 203 of the bore hole 200. This has the effect of advancing the leading region 102 of the rigid bar 101 forwardly through the expansion shell mechanical anchor 110, tensioning the rigid bar 101. As the rigid bar 101 advances through the expansion shell mechanical anchor 110, the usual retaining clip 113 at the leading end of the expansion shell mechanical anchor 110, which holds the expansion shell mechanical anchor 110 together before it has engaged the wall 203 of the bore hole 200, is dislodged by the leading end 101a of the rigid bar 101. To allow the rigid bar 101 to be advanced through the expansion shell mechanical anchor 110, the bore hole 200 should be of a sufficient length to allow advancement of the leading end 101a of the rigid bar 101 beyond the expansion shell mechanical anchor 110. [0028] After tensioning of the rigid bar 101, a grout delivery hose coupling is coupled to the end fitting by way of the slots 124 formed in the female component 121 and grout is pumped through the grout delivery passages 135 formed in the male component 122. The grout flows through the grout passage 132, through the interior 127 of the female component 121 of the end fitting 120, up the inner annular passage 143 defined between the grouting tube 140, the grouting sheath 141 and rigid bar 101. The grout passes over the debonding sleeve 150, and further along the rigid bar 101 to the leading end 141a of the grouting sheath 141. As grout moves up the inner annular passage 143, air is expelled from the bore hole via an outer annular passage 204 defined between the bore hole wall 203 and the grouting sheath 141 and grouting tube 140 and out the bore hole opening. Once grout has reached the leading end 141a of the grouting sheath141, it flows back down the outer annular passage 204 towards the rock face 201. When evidence of grout escaping from the bore hole opening is noted, grouting is ceased and the grout delivery hose removed. The grout is then allowed to set. A length of the rigid bar 101 including at least the centre and trailing regions 104, 103 are thus encapsulated in the grout, with the grout being bonded to the rigid bar 101 in all regions apart from a debonded length that is covered by the debonding sleeve 150. Providing the debonded length of rigid bar 101 allows for deformation of the debonded region to accommodate ground movement and/or to absorb energy released by any dynamic rock event. (7330988 1):PRW 8 [0029] The same concept may be applied to cable bolt installations, mounting an equivalent debonding sleeve on the cable of a cable bolt between the leading region of the cable, which will typically be point anchored by way of a two-component resin filled cartridge chemical anchor, and the end fitting which will generally be in the form of a barrel and wedge assembly with provision for post-grouting. An example of suitable cable bolt assemblies that may have the debonding sleeve applied are described in International Patent Publication No. WO 2012/000016, the entire contents of which are incorporated herein by cross-reference. (7330988 1):PRW

Claims

1. A rock bolt assembly for installation in a bore hole extending through a rock face, said rock bolt assembly comprising: an elongate load bearing member longitudinally extending between a member leading end and a member trailing end; an end fitting mounted on said load bearing member towards said member trailing end, said end fitting being configured to engage a plate washer in use for transferring load between said load bearing member and the rock face surrounding the bore hole, said end fitting defining a grout delivery passage for delivery of grout through said end fitting to encapsulate a length of said load bearing member in use; and a debonding sleeve mounted on said load bearing member between said end fitting and said member leading end to at least substantially prevent the passage of grout between said sleeve and said load bearing member.

2. The rock bolt assembly of claim 1, wherein said debonding sleeve has a length of at least 250 mm and no more than 500 mm less than a length of said load bearing member.

3. The rock bolt assembly of claim 1, wherein said debonding sleeve has a length of between 500 mm and 1500 mm.

4. The rock bolt assembly any one of claims I to 3, wherein said rock bolt assembly further comprises an elongate sheath extending from said end fitting over said debonding sleeve and towards said member leading end, said sheath defining an annular cavity with said load bearing member communicating with said grout delivery passage.

5. The rock bolt assembly of any one of claims I to 4, wherein said load bearing member is a rigid bar.

6. The rock bolt assembly of claim 5, wherein said rock bolt assembly further comprises a mechanical anchor mounted on a leading region of said rigid bar, for point anchoring said leading region.

7. The rock bolt assembly of claim 5, wherein, said rigid bar is configured for resin point anchoring of a leading region of said rigid bar. (7330988 1):PRW 10

8. The rock bolt assembly of any one of claims I to 4,, wherein said load bearing member comprises a cable.

9. The rock bolt assembly of claim 8, wherein said end fitting typically comprises a barrel and wedge fitting.

10. A rock bolt assembly substantially as hereinbefore described with reference to the accompanying drawings. DYWIDAG-Systems International Pty Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON (7330988 1):PRW