AU722997B2

AU722997B2 - Yielding adapter for rock bolts

Info

Publication number: AU722997B2
Application number: AU59356/98A
Authority: AU
Inventors: Henry Alexander Stirling
Original assignee: DMHS RESOURCES Pty Ltd
Current assignee: Stirling Henry Alexander
Priority date: 1998-03-18
Filing date: 1998-03-18
Publication date: 2000-08-17
Anticipated expiration: 2018-03-18
Also published as: AU5935698A

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT a Name of Applicant: Actual Inventor Address for service is: DMHS RESOURCES PTY LTD HENRY ALEXANDER STIRLING WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Attorney code: WR Invention Title: "Yielding Adapter for Rock Bolts" The following statement is a full description of this invention, including the best method of performing it known to me:- -2- Title Device for yieldingly resisting a load" Field of the Invention This invention relates to a resistance device for yieldingly resisting a load imposed on an anchoring device such as a bolt anchor or a cable anchor. The invention also relates to an anchoring assembly incorporating such a resistance device.

Background Art Anchoring devices such as cable bolts and rock bolts are used to provide support for sections of rock in rock formations in underground mining and other tunnelling operations. Such anchoring devices comprise an anchoring shank having an S.inner end section adapted to be retained in an anchoring hole drilled into a face of the rock formation and an outer section to extend beyond the rock face for attachment to a bearing structure such as a bearing plate for bearing against the rock face to provide support therefor. The inner end section of the anchoring shank is retained in the anchoring hole by any suitable means such as by bonding with grout or resin.

Where the anchoring device is a cable bolt, the anchoring shank comprises a cable. Where the anchoring device is a rock bolt, the anchoring shank comprises a bolt.

While such anchoring devices perform satisfactorily in stable ground conditions, they can be deficient in ground conditions affected by seismic activity. If a seismic event does occur, loading on the anchoring device may increase, possibly to the extent of failure, leading to collapse of the rock section being supported by the anchoring device.

(a -3- It is against this background, and the deficiency associated therewith, that the present invention has been developed.

Disclosure of the Invention The present invention provides a resistance device for yieldingly resisting a load imposed on an anchoring device having an anchoring shank, said device comprising first and second members one of which is adapted for connection to said anchoring shank, the first and second members being adapted for engagement to each other to resist the load applied to the anchoring shank, and at least one of the first and second members being progressively deformable under the influence of said load to yieldingly resist said load.

The load to be yielding resisted is that load imposed on the anchoring device in excess of a prescribed magnitude. Typically, the prescribed load magnitude in excess of which the resistance device commences to offer yielding resistance is determined by characteristics of the resistance device.

Preferably, the second member is provided with a passage for receiving the first member for movement therealong, the first and second members being configured to resist movement of the first member along the passage upon :imposition of said load, wherein progressive deformation of said at least one of the first and second members permits progressive movement of the first member along the passage to yieldingly resist said load.

Preferably, one of the first and second members is configured to cause progressive deformation of the other of the first and second members upon movement of the first member along the passage. Such a configuration may be achieved by having said one member present a surface extending outwardly and rearwardly with respect to the direction of movement of the first member along the passage in the second member whereby the surface engages said other member to cause the progressive deformation.

-4- Preferably, the first member is the member adapted to be connected to the anchoring shank.

Preferably, the second member is the member adapted to undergo progressive deformation.

Preferably, the passage in the second member is defined by a cylindrical side wall section of the second member. The wall thickness of the side wall section and the material from which the side wall section is formed are several factors which determine the extent to which the load can be yieldingly resisted.

Conveniently, the first member is of a conical configuration, and in particular a frusto-conical configuration, with the smaller end thereof of a size which fits into the cylindrical passage of the second member and the larger end thereof of a size which does not so fit. In this way, the first member presents a tapering side wall surface which extends outwardly and rearwardly with respect to the direction of movement through the passage. The tapering side wall surface of the first 15 member bears on the cylindrical side wall of the passage as the first member moves along the passage, progressively expanding the cylindrical side wall outwardly to cause it to progressively deform and so yieldingly resist the load imposed on the anchoring device.

The invention also provides an anchoring assembly comprising an anchoring 20 device having an anchoring shank, and a resistance device as hereinbefore defined for yieldingly resisting a load imposed on the anchoring shank.

In one arrangement, the resistance device may be connected to the particular end section of the anchoring shank to be retained in an anchoring hole formed in a rock formation. With this arrangement, the resistance device is accommodated in the anchoring hole and is secured therein in any suitable way, such as by grout or resin, to anchor the end section of the anchoring shank to the rock formation.

In another arrangement, the resistance device may be adapted for connection to the particular end section of the anchoring shank extending outwardly of the anchoring hole in the rock formation. With this arrangement, the resistance device would be disposed between the anchoring shank and a bearing structure, such as a bearing plate, bearing against the adjacent face of the rock formation.

The latter arrangement has a particular advantage in that the resistance device is exposed and so can provide a visual indication of the extent to which yielding movement between the first and second members has occurred, thereby providing an indication of the extent of loading imposed on the anchoring assembly.

The invention also provides a cable bolt assembly comprising a cable bolt having an anchoring cable, and a resistance device as hereinbefore defined for yieldingly resisting a load imposed on the anchoring cable.

The invention also provides a rock bolt assembly comprising a rock bolt having 15 an anchoring bolt, and a resistance device as hereinbefore defined for yieldingly resisting a load imposed on the anchoring bolt.

The invention also provides an anchoring assembly comprising an anchoring *device having an anchoring shank, and a resistance device for yieldingly resisting a load imposed on the anchoring shank, the resistance device S° 20 comprising first and second members adapted for engagement with each other to resist the load applied to the anchoring shank, the first member being adapted for connection to the anchoring shank and the second member being provided with a passage for receiving the first member for movement therealong upon imposition of said load on the anchoring shank, the first and second members being configured to resist movement of the first member along the passage upon imposition of said load, wherein the second member is progressively deformable to permit movement of the first member along the passage and thereby yieldingly resist said load.

A t 1 4 ,6 -6- Brief Description-of the Drawings The invention will be better understood by reference to the following description of several specific embodiments thereof as shown in the accompanying drawings in which: Figure 1 is a perspective view of a resistance device forming part of an anchoring assembly according to a first embodiment; Figure 2 is a vertical cross-section of a tunnel roof in an underground mining operation showing the anchoring assembly according to the first embodiment in a normal condition prior to yieldingly resisting a load imposed thereon; Figure 3 is a view similar to Figure 2 with the exception that the anchoring assembly is shown in a condition in which there is yielding resistance to a load imposed thereon; and Figure 4 is a vertical cross-section of a roof in an underground mining operation showing an anchoring assembly according to a second embodiment installed therein.

Best Mode(s) for Carrying out the Invention Referring to Figures 1, 2 and 3 of the drawings, there is shown an anchoring assembly 10 according to a first embodiment for supporting a rock section 11 of a rock formation 13 above a tunnel 15 in an underground mining operation. The rock section 11 presents a rock face 16 to provide a roof for the tunnel. The anchoring assembly 10 is installed in a anchoring hole 17 drilled into the rock formation 13.

The anchoring assembly 10 comprises an anchoring cable 21 having an inner section 23 received and retained in the anchoring hole 17, and an outer section 25 extending outwardly of the anchoring hole 17 and beyond the rock face 16.

-7- The inner section 23 of the anchoring cable 21 is attached to a resistance device which is received and retained in the anchoring hole 17. The resistance device 30 is spaced inwardly from the open end of the anchoring hole 17 and is retained in position by grout 31 filling the section of the anchoring hole 17 between the resistance device 30 and the open end of the anchoring hole. A barrier tube 33 is positioned about that section of the anchoring cable 21 surrounded by the grout 31 to create a clearance space 35 between the anchoring cable 21 and the grout 31, as well as to prevent the grout from adhering to and fouling the anchoring cable.

The outer end section 25 of the anchoring cable 21 is operatively connected to a bearing structure 37 in the form of a bearing plate by way of an abutment member 39 secured to the anchoring cable 21. The abutment member 39 in this embodiment is in the form of a clamp which clampingly engages the anchoring cable 21 for rigid attachment thereto. The bearing plate 37 has an outer face 41 15 against which the abutment member 39 bears and an inner face 43 which bears against the rock face 16 in the region around the anchoring hole 17.

The resistance device 30 comprises a first member 51 and a second member 52.

The second member 52 is of cylindrical construction, comprising a cylindrical side wall 53 defining a central passage 55 of circular cross-section. The cylindrical side wall 53 has an outer face 57 and an inner face 59 both of cylindrical shape. The second member 52 has an end plate 61 closing one end *oo o.

of the central passage 55. The end plate 61 has a central aperture 63 therein through which the anchoring cable 21 can extend. The end plate 61 closes the passage 55 to prevent entry of grout 31 therein and to provide a bearing area for contact with the grout as best seen in Figures 2 and 3.

The central passage 55 is open at the other end to receive the first member 51.

The first member 51 comprises a body 63 of frusto-conical configuration, having an inner end 63, an outer end 65 and a tapering side wall 67. The side wall 67 tapers inwardly from the larger outer end 65 to the smaller inner end 63. The 'k -8inner end 63 is of a size which permits the first member 51 to partly enter the cylindrical passage 55 in the second member 53. The outer end 65 is of a size which prevents unrestricted movement of the first member 51 along the passage In this way, the smaller end 63 of the first member fits into the cylindrical passage 55 while the larger end 65 does not so fit.

The side wall 67 of the first member 51 presents a tapering surface which extends outwardly and rearwardly with respect to the direction of movement of the first member 51 through the passage 55 of the second member 53.

The inner end section 23 of the anchoring cable 21 is connected to the first member 51 through an abutment member 71 which bears against the outer face of the first member 51. The abutment member is in the form of a clamp for clampingly engaged onto the anchoring cable 21.

o In normal conditions, the anchoring assembly 10 assumes the condition shown in Figure 2 of the drawings where the first member 51 is partly received in the 15 passage 55 of the second member 52, with the anchoring cable 21 being under tensile loading so as to urge the bearing structure 37 into engagement with the rock face 16. In this way, the anchoring assembly 10 stabilises the rock section :13.

In the event of seismic activity, movement within the rock formation applies 20 outward pressure to the bearing plate 37 thereby applying further tensile loading •to the anchoring cable 21. In such circumstances, rather than the anchoring cable fracturing, the resistance device 30 provides a mechanism for yieldingly resisting the induced extra loading.

The resistance device 30 offers yielding resistance to the extra loading applied to the anchoring cable 21 by progressive deformation of the second member 52 to allow resisted movement of the first member 51 along the passage 55. The progressive deformation of the second member 52 is by outward swaging of the cylindrical side wall 53, as illustrated in Figure 3 of the drawings. The progressive deformation of the cylindrical side wall 53 regulates movement of the ~4,J -9first member 51 along the passage 55 in the second member 52, so providing yielding resistance to the load imposed on the anchoring cable 21.

With this arrangement, the anchoring cable 21 can be loaded to its accepted safety margin and thereafter the yielding resistance provided by the resistance device 30 can accommodate some additional (abnormal) tensile loading on the anchoring cable 21. In this way, the anchoring cable 21 may be saved from possible failure leading to collapsing of the rock section 11.

The wall thickness of the cylindrical side wall 53, the material from which the cylindrical side wall 53 is constructed, and the configuration of the first member 51 are some factors which determine the extent to which loading on the anchoring cable 21 can be yieldingly resisted.

o In the first embodiment shown in Figures 1 to 3 of the drawings, the anchoring assembly 10 employs a cable as the anchoring shank. It should be appreciated a bolt can be employed as the anchoring shank in other arrangements.

The second embodiment, which is shown in Figure 4 of the drawings, is directed S.to an anchoring assembly 10 in the form of a point anchor. In this arrangement, the resistance device 30 is located exteriorly of the anchoring hole 17. As with the first embodiment, the anchoring assembly 10 includes a cable anchor 21 *5o° having an inner section 23 and an outer section 25. In this embodiment, the 20 inner section 23 is retained in the anchoring hole 27 by way of a bonding agent a 81 such as resin or grout.

The resistance device 30 is positioned on the outer section 25 of the cable 21 so as to bear against the outer face 41 of the bearing plate 37. As with the first embodiment, additional (abnormal) loading applied to the anchoring cable 21, as a result of for example seismic activity, is accommodated yet yieldingly resisted by movement of the first member 51 along passage 55 of the second member 52.

I

The second embodiment has a particular advantage in that the resistance device is exposed and so can provide a visual indication of the extent to which yielding movement between the first and second members 51, 52 has occurred.

This provides an indication of the extent of loading imposed on the anchoring assembly.

From the foregoing, it is evident that the present embodiments each provide a simple yet highly effective arrangement for yieldingly resisting an abnormal load imposed on an anchoring device such as a bolt anchor or a cable anchor. The extent of the yielding resistance can be predetermined by appropriate selection of the characteristics of the first and second members. For example, the wall thickness around the passage 55 and the configuration of the passage are controlling factors, as is the configuration of the first member 51.

-It should be appreciated that the scope of the invention is not limited to the scope of the two embodiments described. For example, in the embodiments described, S 15 the first member 51 has been described and illustrated as being connected to the anchoring cable 21 by way of an abutment member 71 clamped on the cable 21.

In an alternative arrangement, the first member may incorporate the mechanism for direct attachment to the cable.

Throughout the specification, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A resistance device for yieldingly resisting a load imposed on an anchoring device having an anchoring shank, said device comprising first and second members one of which is adapted for connection to said anchoring shank, the first and second members being adapted for engagement to each other to resist the load applied to the anchoring shank, and at least one of the first and second members being progressively deformable under the influence of said load to yieldingly resist said load.

2. A resistance according to claim 1 wherein the second member is provided with a passage for receiving the first member for movement therealong, the first and second members being configured to resist movement of the first member along the passage upon imposition of said load, wherein S"progressive deformation of said at least one of the first and second members permits progressive movement of the first member along the 15 passage to yieldingly resist said load.

3. A resistance device according to claim 2 wherein one of the first and second members is configured to cause progressive deformation of the other of the first and second members upon movement of the first member along the passage. 20

4. A resistance device according to claim 3 wherein said one member present a surface extending outwardly and rearwardly with respect to the direction of movement of the first member along the passage in the second member whereby the surface engages said other member to cause the progressive deformation.

5. A resistance device according to any one of the preceding claims wherein the first member is the member adapted to be connected to the anchoring shank. I. -12-

6. A resistance device according to any one of the preceding claims wherein the second member is the member adapted to undergo progressive deformation.

7. A resistance device according to any one of claims 2 to 6 wherein the passage in the second member is defined by a cylindrical side wall section of the second member.

8. A resistance device according to any one of claims 2 to 7 wherein the first member is of a conical configuration with the smaller end thereof of a size which fits into the cylindrical passage of the second member and the larger end thereof of a size which does not so fit.

9. An anchoring assembly comprising an anchoring device having an anchoring shank, and a resistance device according to any one of the .preceding claims for yieldingly resisting a load imposed on the anchoring shank.

10. An anchoring assembly according to claim 9 wherein the resistance device is adapted for connection to the particular end section of the anchoring shank to be retained in an anchoring hole formed in a rock formation.

11. An anchoring assembly according to claim 9 wherein the resistance device is adapted for connection to the particular end section of the anchoring shank extending outwardly of the anchoring hole in the rock formation.

12. A cable bolt assembly comprising a cable bolt having an anchoring cable, and a resistance device according to any one of claims 1 to 8 for yieldingly resisting a load imposed on the anchoring cable.

13. A rock bolt assembly comprising a rock bolt having an anchoring bolt, and a resistance device according to any one of claims 1 to 8 for yieldingly I resisting a load imposed on the anchoring bolt. -13-

14. An anchoring assembly comprising an anchoring device having an anchoring shank, and a resistance device for yieldingly resisting a load imposed on the anchoring shank, the resistance device comprising first and second members adapted for engagement with each other to resist the load applied to the anchoring shank, the first member being adapted for connection to the anchoring shank and the second member being provided with a passage for receiving the first member for movement therealong upon imposition of said load on the anchoring shank, the first and second members being configured to resist movement of the first member along the passage upon imposition of said load, wherein the second member is progressively deformable to permit movement of the first member along the passage and thereby yieldingly resist said load.

15. A resistance device substantially as herein described with reference to the *eg0 °accompanying drawings. 15

16. An anchoring assembly substantially as herein described with reference to the accompanying drawings. Dated this day of DMHS RESOURCES PTY LTD Applicant "Wray Associates Perth, Western Australia Patent Attorneys for the Applicant