AU2021204317A1

AU2021204317A1 - Rock Bolt

Info

Publication number: AU2021204317A1
Application number: AU2021204317A
Authority: AU
Inventors: Adrian ALINGTON; David Maltby
Original assignee: Garock Pty Ltd
Current assignee: Garock Pty Ltd
Priority date: 2015-06-22
Filing date: 2021-06-24
Publication date: 2021-07-22
Also published as: AU2023203245A1; AU2016204239A1

Abstract

A rock bolt for supporting a rock body comprising an elongate multi-strand supporting cable. The supporting cable comprising a plurality of individual strand members wound or woven together along an elongate axis and is configured to be secured, at least in part, inside a borehole formed in the rock body. The rock bolt further comprises a yielding section comprising a collar connected to the supporting cable and an elongated support bar, wherein a lumen of the collar slidably receives the support bar. The rock bolt further comprises a flange assembly connected to the support bar, the flange assembly being configured to, at least in part, substantially abut a rock face of the rock body. When a movement of the rock face occurs, the support bar is caused to slide, at least in part, through the lumen thereby permitting the rock bolt to yield and govern the movement of the rock face.

Description

AUSTRALIA

PATENTS ACT 1990

COMPLETE SPECIFICATION

FOR A STANDARD PATENT (Original)

APPLICATION NO: LODGED: COMPLETE SPECIFICATION LODGED: ACCEPTED: PUBLISHED: RELATED ART:

NAME OF APPLICANT: Garock Pty Ltd

ACTUAL INVENTORS: Maltby, David; and Alington, Adrian

ADDRESS FOR SERVICE: LORD AND COMPANY, Patent and Trade Mark Attorneys, of PO Box 530, West Perth, Western Australia, 6872, AUSTRALIA.

INVENTION TITLE: "ROCKBOLT" DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S:

Australian Provisional Patent Application Number 2015902395 filed on 22 June 2015

The following Statement is a full description of this invention including the best method of performing it known to me/us:

TITLE "ROCK BOLT" FIELD OF INVENTION

[0001] The present invention relates to a rock bolt for use in supporting a rock body.

[0002] More particularly, but not exclusively, the present invention relates to a yielding cable rock bolt.

BACKGROUND

[0003] It is known to use a rock bolt for reinforcing a rock body in an underground, mining or civil engineering operation and for improving the safety of nearby personnel. Rock bolts are typically fitted into a borehole that has been pre-drilled into a rock body with one end of the bolt protruding from a rock face of the rock body. A thrust plate can then be mounted to the protruding end. The thrust plate is often used in combination with a support mesh and/or spray concrete that forms a net across the rock face so as to constrain or limit movement of the rock face in the event of a movement or failure of the rock body.

[0004] A rock bolt must be anchored deep within the rock body so that it can support the rock effectively and limit movements of the rock face. Often a rock bolt is secured within the borehole using a liquid cementous or resinous grout mixture that solidifies to lock the rock boltrigidly in position within the rock body.

[0005] One form of known rock bolt that is anchored in this manner is a cable rock bolt which comprises a metal elongate flexible supporting cable. It is also known to use a multi-strand cable rock bolt that comprises a plurality of individual metal strands woven or wound together to form an elongate cable. One or more flared bulbous portions are commonly disposed along the length of the multi-strand cable to vary a cross sectional dimension of the rock bolt and allow grout mixture to infiltrate easily into the rock bolt before setting. This increases the magnitude of a pull-out force that is required to dislodge the rock bolt in use.

[0006] Cable type rock bolts advantageously provide for a degree of flexure in the rock bolt allowing it, to an extent, to govern and withstand movements in the supported rock body during use. Problems still, however, often arise with known cable type rock bolts in dynamic rock conditions. Seismic and other earth movements, which may frequently take place during underground tunnelling and mining operations, may cause the rock face of a tunnel or excavated region to move and become less stable, thus placing significant load on rock bolts installed in the rock face. Rock failures may cause cable type bolts to undergo substantial tension, bend or twist, reducing their load bearing strength, and in extreme cases snap.

[0007} Cable type rock bolts are, in particular, susceptible to being damaged when shearing of the rock body occurs near to the rock face in dynamic rock conditions.

[0008] The present invention attempts to overcome, at least in part, the aforementioned disadvantages of previous cable type rock bolts.

SUMMARY OF THE INVENTION

[0009] According to one aspect of the present invention, there is provided a rock bolt for supporting a rock body, comprising: an elongate multi-strand supporting cable, the supporting cable comprising a plurality of individual strand members wound or woven together along an elongate axis and being configured to be secured, at least in part, inside a borehole formed in the rock body; a yielding section, the yielding section comprising a collar connected to the supporting cable and an elongated support bar, wherein a lumen of the collar slidably receives the support bar; and a flange assembly connected to the support bar, the flange assembly being configured to, at least in part, substantially abut a rock face of the rock body, whereby, when a movement of the rock face occurs, the support bar is caused to slide, at least in part, through the lumen thereby permitting the rock bolt to yield and govern the movement of the rock face

[0010] The collar may be substantially tubular and comprise a proximal end and a distal end, wherein the lumen of the collar extends from the proximal end to the distal end along a longitudinal axis of the collar.

[0011] The collar may further comprise a first crimped section where a cross sectional area of the collar and its lumen is reduced thereby increasing a fictional communication between an internal surface of the lumen and the support bar.

[0012] The support bar may have a proximal end and a distal end and a stop means disposed at its proximal end for limiting travel of the support bar through the lumen.

[0013] The stop means may comprise a flange formed at the proximal end of the support bar which, in use, abuts the internal surface of the lumen at the first crimped section when the support bar has travelled through the lumen to its maximum permitted extent.

[0014] The lumen may be configured to receive and frictionally retain the supporting cable substantially at the proximal end of the collar, thereby connecting the supporting cable to the collar by an interference fit.

[0015] The collar may also comprise a second crimped section where the cross sectional area of the collar and the lumen is also reduced, thereby increasing a frictional communication between the internal surface of the lumen and the supporting cable and, in turn, a strength of the interference fit.

[0016] A bushing means may be disposed inside the lumen sandwiched between the internal surface of the lumen and the supporting cable for increasing the strength and durability of the interference fit.

[0017] The bushing means may comprise a pair of opposed and substantially symmetrical complementary bush members.

[0018] Each complementary bush member may comprise a semi-cylindrical metallic member having a knurled outer surface and a profiled inner striated surface.

[0019] The flange assembly may consist of threaded portion disposed at a distal end of the support bar, a complimentary nut which threadedly engages with the threaded portion and a thrust plate that is slidably mountable onto thesupport bar for abutting the rock face.

[0020] The multi-strand cable may have one or more flared bulbous portions.

[0021] The supporting cable may be made of a metallic material, such as steel.

[0022] The supporting cable may further comprise a terminating end member.

[0023] The terminating end member may be a metal strip wrapped substantially around and swaged onto a circumferential surface of the supporting cable.

[0024] The terminating end member may, alternatively, be an anchoring means for anchoring the supporting cable inside the borehole.

[0025] The anchoring means may consist of a drive member swaged onto the supporting cable and a plurality of wedge members arranged substantially around the drive member wherein, in use, a movement of the supporting cable causes the drive member to push the wedge members apart and frictionally engage an internal surface of the borehole

[0026] The anchoring means may have a circumferential recess on an outer surface of the wedge members, the recess being configured to receive a fastening means for biasing the plurality of wedge members into a closed position.

BRIEF DESCRIPTION OF DRAWINGS

[0027] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0028] Fig. I shows an elevated side view of a rock bolt according to a preferred embodiment of the present invention;

[0029] Fig. 2(a) shows a perspective view of a bushing means of the rock bolt of Fig. I;

[0030] Fig. 2(b) shows a partial perspective view of the bushing means of Fig. 2(a);

[00311 Fig 3 shows an enlarged schematic side view of the yielding section of the rock bolt of Fig. 1;

[0032] Fig. 4(a) shows a side view of an anchoring means that may be used in embodiments of the rock bolt according to the present invention;

[0033] Fig. 4(b) shows a further side view of the anchoring means of Fig. 4(a);

[0034] Fig. 5(a) shows a partial schematic side view of the anchoring means of Fig. 4(a); and

[0035] Fig. 5(b) shows a partial schematic top view of an alternative anchoring means that may be used in embodiments of the rock bolt according to the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0036] Referring to Figure 1, there is shown a rock bolt I for supporting a rock body according to a preferred embodiment of the present invention.

[0037] The rock bolt I comprises an elongated supporting cable 3 that is configured to be secured, at least in part, inside a borehole formed in the rock body. The elongated supporting cable 3 is a multi-strand cable 4 having a plurality of individual strand members 5 wound or woven together along an elongate axis.

[0038] The rock bolt I further comprises a yielding section 7 comprising a collar 9 and an elongated support bar 11. A lumen 13 of the collar 9 slidably receives the elongated support bar I land, in use, a movement of a rock face of the rock body causes the elongated support bar 11 to slideat least in part, through the lumen 13 of the collar 9 thereby pennitting the rock bolt I to yield and govern the movement.

[0039] The collar 9 is substantially tubular and comprises a proximal end 15 and a distal end 17. The lumen 13 defines a longitudinal axis of the collar 9 and extends from the proximal end 15 to the distal end 17.

[0040) As is most clearly shown in Figure 3, the collar 9 has a first crimped section 19 where a cross-sectional area of the collar 9 and the lumen 13 is reduced. During the manufacturing process, the first crimped section 19 may be created by using, for example, a radial press machine, or equivalent cold pressing method, to exert a plurality of large inward forces radially about a circumference of the collar 9. This causes the collar 9 and the lumen 13 to undergo a substantial deformation causing their cross sectional area to reduce forming a stricture. The stricture substantially increases a frictional communication between an internal surface 20 of the lumen 13 and the elongated support bar I Iat the first crimped section 19.

[0041] The lumen 13 of the collar 9 is, further, arranged to receive and frictionally retain the elongated supporting cable 3 substantially at the proximal end 15 of the collar 9, thereby connecting the elongated supporting cable 3 to the yielding section 7 permanently.

[0042] The collar 9 comprises a second crimped section 23 where the cross-sectional area of the collar 9 and the lumen 13 are also reduced, thereby increasing a frictional communication between the internal surface 20 of the lumen 13 and the elongated supporting cable 3 and, in turn, the strength of the connection.

[0043] In embodiments of the present invention, a bushing means 25 may, optionally, be disposed inside the lumen 13 sandwiched between the internal surface 20 of the lumen 13 and the elongated supporting cable 3 for further increasing the strength and durability of the connection.

[0044] As shown in Figure 2(a), the bushing means 25, preferably, comprises a pair of substantially symmetrical complementary inserts 27 arranged opposite to one another.

[0045] Referring to Figure 2(b), each individual insert 29 comprises a semi cylindrical swaged insert 31 made from a metallic material. Each swaged insert 31 has a knurled outer surface 33 and a profiled inner striated surface 35.

[0046] During manufacture of the rock bolt 1, each swaged insert 31 is wrapped around and clamped to an end of the elongated supporting cable 3 before the elongated supporting cable 3 is placed into the lumen 13.

[0047] Each swaged insert 31, preferably, comprises a circumferential channel 36 adapted to receive a fastening means, such as a rubber O-ring or circlip, for example, to clamp each swaged insert 31 to the end of the elongated supporting cable 3 during installation.

[00481 The knurled outer surface 33 and profiled inner striated surface 35 of each swaged insert 31 each provide additional friction so that they grip securely, respectively, the internal surface 20 of the lumen 13 and the elongated support bar 11 when the second crimped section 23 is created when connecting the elongated support bar IIto the

yielding section 7 during manufacture.

[0049] As shown in Figure 1, the multi-strand cable 4. preferably, has one or more flared bulbous portions 37 and a terminating end member 39.

[0050] Each individual strand member 5 of the multi-strand cable 4 is made of a material that has a high degree of tensile strength and that is also ductile to provide for a degree of flexure of the cable 4. The cable 4 may, for example, be made of a metallic material such as steelstainless steel or iron.

[0051] In the embodiment shown in Figure 1, the terminating end member 39 comprises a metal strip 40 wrapped substantially around and swaged onto a circumferential surface of the elongate supporting cable 3.

[0052] As shown in Figure 3, the elongated support bar 11 comprises a proximal end 41 having a stop means 42 disposed at its proximal end 41 for limiting travel of the elongated support bar 11 through the lumen 13.

[0053] The stop means may comprise a flange 43 which, in use, abuts the internal surface 20 of the lumen 13 at the first crimped section 19 when the elongated support bar 11 has travelled through the lumen 13 to its maximum permitted extent.

[0054] The rock bolt I further comprises a flange assembly that is configured to, at least in part, substantially abut a rock face of the rock body. In the preferred embodiment that is shown in the Figures, the flange assembly consists of a threaded portion 45 disposed at a distal end 44 of the elongated support bar 11, a complimentary nut 46 which threadedly engages with the threaded portion 45 and a thrust plate (not shown) slidably mountable onto the elongated support bar 11 for abutting the rock face.

[0055J In use, a borehole is drilled into a rock body that needs supporting as is known in the art. The rock bolt I according to the present invention is then fitted into the borehole and a cementous or resinous grout mixture is applied to the borehole to anchor the rock bolt 1 to the rock body. The mixture fills the space between the rock bolt I and the borehole and, in particular, the spaces created by, and internal to, each flared bulbous portion 37. After the mixture has cured sufficiently, the thrust plate is slidably mounted onto the elongated support bar 11 which forns a flange for pressing against and supporting the rock face. The rock bolt 1 is then tensioned by attaching the nut 46 onto the elongated support bar 11 and tightening it.

[0056] As shown in Figure 1, a hemispherical seat 48 having a substantially rounded or tapered top end may also be, optionally, slidably mounted onto the elongatedsupport bar 11 and disposed between the thrust plate and the nut 46.

[0057] In use, when the nut 46 is tightened during installation of the rock bolt 1, the cylindrical seat 48 may freely rotate about, and travel along, the elongated support bar 11. The cylindrical seat 48 serves to evenly distribute and spread the pressure that would otherwise be placed on the thrust plate by the nut 46 thus allowing the thrust plate to travel more easily along the elongated support bar 1I when the apparatus is pre tensioned,

[0058] Further, the rounded or tapered top end of the cylindrical seat 48 enables the thrust plate to be secured to the rock face effectively in situations where the rock face surface is aligned at an angle that is not perpendicular to the rock bolt 1; for example, because the rock bolt 1 has been driven into the rock face at an angle. This also ensures that a uniform, evenly distributed force is applied to the thrust plate thereby allowing the rock bolt I to support the rock face effectively in these situations.

[0059] Once installed, mesh and spray concrete or similar means may also be used as known in the art.

[0060] Upon a rock body failure, creep or similar geological event whereby the rock face loses support and can move, a weight of the rock face is transferred to the thrust plate and, by extension, to the elongated support bar 11. Friction between the elongated support bar 11 and the collar 9 at the first crimped section 19 allows the elongated support bar 11 to slide in a controlled manner along the elongate length of the lumen 13 of the collar 9 according to the rock face weight transferred to the thrust plate. This allows the rock bolt I to yield thereby extending its ability to continue to support the rock face and provide a safe environment for persons present in the area following dynamic rock activity.

[0061] As shown in Figure 4(a), the terminating end member 39 used in the invention may, alternatively, comprise an anchoring means 51. The anchoring means 51 may be used to anchor the elongate supporting cable 3 within the borehole pre-drilled into rock body during installation of the rock bolt 1 in lieu of, or in addition to, thecementous or resinous grout mixture that may be used.

[0062] As shown in Figure 4(b), the anchoring means 51 may comprise a drive member 53 attached to the elongate supporting cable 3. The exemplary drive member 53 that is shown in Figure 4(b) comprises a frustoconical metallic member 55 swaged onto the elongate supporting cable 3.

[0063] The anchoring means 51 may further comprise a plurality of wedge members 57 arranged substantially around the drive member 53 each having a profiled outer striated surface 58.

[0064] Two wedge members 57 are used in the anchoring means 51 illustrated in Figures 4(a) and 4(b). However, it will be appreciated that a higher number of wedge members may be used. For example, three wedge members 57 may be used, as is used in the embodiment of the anchoring means 51 illustrated in Figure 5(b).

[0065] As shown in Figures 5(a) and 5(b), each wedge member 57 has a tapered inner surface 59. The arrangement of wedge members 57 defines a lumen 61 at the centre of the wedge members 57.

[0066] In use, when the nut 46 of the rock bolt1 is tightened during installation, the elongate supporting cable 3 will be drawn forcefully down through the borehole that has been pre-drilled into the rock body to be supported. This, in turn, causes the drive member 53 to be moved forcefully through the lumen 61 at the centre of the wedge members 57. Because of the tapered inner surface 59 of each wedge member 57, each wedge member 57 is pushed outwards radially causing each wedge member 57 to frictionally engage the internal surface of the borehole thereby anchoring the elongate supporting cable 3 into the borehole. The profiled outer striated surface 58 of each wedge member 57 improves the strength of the friction and resultant anchoring.

[0067] To facilitate use of the anchoring means 51 during installation of the rock bolt 1, each wedge member 57 may comprise a circumferential recess 63 on its outer surface that is configured to receive a fastening means, such as a rubber O-ring or circlip, for example, for biasing the plurality of wedge member 57 in a closed position while the rock bolt 1 is being fitted into the borehole

[0068] The anchoring means 51 may further comprise a spring 65 that abuts a stop member 67 swaged onto the elongate supporting cable 3. In use, the spring 65 ensures that the plurality of wedge member 57 remain disposed at a peripheral end of the elongate supporting cable 3 while the rock bolt 1 is being fitted into the borehole.

[0069] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

[0070] In the claims that 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" comprising" are 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 in various embodiments of the invention.

Claims

IL/_ CLAIMS

1. A rock bolt for supporting a rock body, comprising: an elongate multi-strand supporting cable, the supporting cable comprising a plurality of individual strand members wound or woven together along an elongate axis and being configured to be secured, at least in part, inside a borehole forced in the rock body; a yielding section, the yielding section comprising a collar connected to the supporting cable and an elongated support bar, wherein a lumen of the collar slidably receives the support bar; and a flange assembly connected to the support bar, the flange assembly being configured to, at least in part, substantially abut a rock face of the rock body, whereby, when a movement of the rock face occurs, the support bar is caused to slide, at least in part, through the lumen thereby permitting the rock bolt to yield and govern the movement of the rock face.

2, The rock bolt according to claim 1, wherein the collar is substantially tubular and comprises a proximal end and a distal end, and wherein the lumen of the collar extends from the proximal end to the distal end along a longitudinal axis of the collar

3. The rock bolt according to claim 1 or 2, wherein the collar further comprises a first crimped section where a cross-sectional area of the collar and its lumen is reduced thereby increasing a frictional communication between an internal surface of the lumen and the support bar.

4. The rock bolt according to any one of the preceding claims, wherein the support bar has a proximal end and a distal end and a stop means disposed at its proximal end for limiting travel of the support bar through the lumen.

5. The rock bolt according to claim 4, wherein the stop means comprises a flange formed at the proximal end of the support bar which, in use, abuts the internal surface of the lumen at the first crimped section when the support bar has travelled through the lumen to its maximum permitted extent.

6. The rock bolt according to any one of the preceding claims, wherein the lumen is configured to receive and frictionally retain the supporting cable substantially at the proximal end of the collar, thereby connecting the supporting cable to the collar by an interference fit.

7. The rock bolt according to claim 6, wherein the collar comprises a second crimped section where the cross-sectional area of the collar and the lumen is reduced, thereby increasing a fictional communication between the internal surface of the lumen and the supporting cable and, in turn, a strength of the interference fit between the supporting cable and collar.

8, The rock bolt according to claim 6 or 7, wherein a bushing means is disposed inside the lumen sandwiched between the internal surface of the lumen and the supporting cable for increasing the strength and durability of the interference fit.

9. The rock bolt according to claim 8, wherein the bushing means consists of a pair of opposed and substantially symmetrical complementary bush members.

10. The rock bolt according to claim 9, wherein each complementary bush member comprises a semi-cylindrical metallic member having a knurled outer surface and a profiled inner striated surface.

11. The rock bolt according to any one of the preceding claims, wherein the flange assembly consists of threaded portion disposed at a distal end of the support bar, a complimentary nut which threadedly engages with the threaded portion and a thrust plate that is slidably mountable onto the support bar forabutting the rock face.

12, The rock bolt according to any one of the preceding claims, wherein the supporting cable has one or more flared bulbous portions.

13. The rock bolt according to any one of the preceding claims, wherein the supporting cable is made of a metallic material.

14, The rock bolt according to any one of the preceding claims, wherein the supporting cable is made of steel.

15. The rock bolt according to any one of the preceding claims, wherein the supporting cable is made of stainless steel.

16. The rock bolt according to any one of the preceding claims, wherein the supporting cable further comprises a terminating end member.

17 The rock bolt according to claim 16, wherein the terminating end member comprises a metal strip wrapped substantially around and swaged onto a circumferential surface of the supporting cable.

18. The rock bolt according to claim 16, wherein the terminating end member consists of an anchoring means for anchoring the supporting cable inside the borehole.

19. The rock bolt according to claim 18, wherein the anchoring means consists of a drive member swaged onto the supporting cable and a plurality of wedge members arranged substantially around the drive member wherein, in use, a movement of the supporting cable causes the drive member to push the wedge members apart and frictionally engage an internal surface of the borehole.

20. The rock bolt according to claim 19, wherein the anchoring means has a circumferential recess on an outer surface of the wedge members, the recess being configured to receive a fastening means for biasing the plurality of wedge members into a closed position.