AU2017200155A1 - Rock bolt - Google Patents

Abstract

A rock bolt adapted for installation into a borehole for supporting a rock body. The rock bolt comprises an elongated body comprising a substantially arcuate wall defining a lumen, the lumen extending along a longitudinal axis between a first end and a second end of the body. A flexible tensioning tendon is disposed inside, and extends substantially through, the lumen. A wedge member is fixed to a first end of the tensioning tendon. A nut is releasably attachable to a second end of the tensioning tendon. In use, tightening the nut causes the wedge member to be drawn into the lumen of the body thereby urging the arcuate wall of the body outwardly and anchoring the rock bolt within the borehole. { 68 10, 20<K 281-

Description

2017200155 10 Jan 2017 APPLICANTS: NUMBER: FILED:

Garock Pty Ltd; M and J Mining (Pty) Ltd; VVK Engineering (Pty) Ltd

AUSTRALIA THE PATENTS ACT 1990

PROVISIONAL SPECIFICATION FOR THE INVENTION ENTITLED

ROCKBOLT

The present invention will be described in the following statement: ι 2017200155 10 Jan 2017

TITLE

“ROCK BOLT” FIELD OF INVENTION

[0001] The present invention relates to rock bolts for supporting rock bodies and, more particularly, to friction rock bolts.

BACKGROUND

[0002] It is known to use rock bolts to reinforce rock bodies in underground and civil engineering operations for improving safety of personnel located in nearby environments. Known rock bolts come in many different forms and are chosen based on various factors including the material and quality of the rock body to be reinforced and the amount of geological stress and movement common to particular rock bodies.

[0003] Known rock bolts consist of a metal pin that is placed into a borehole predrilled into the rock body to be reinforced. The rock bolt is fitted with one end 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 a 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] In order to reinforce the rock body, rock bolts are required to be anchored deep within the rock body so that the rock bolt can effectively support the rock and limit the movement of the rock face.

[0005] Known rock bolts anchor the rock face by a mechanical means of anchoring such as a rock bolt having a friction bolt configuration. Other means of anchoring a rock face can be used by more securely mounting the rock bolt in the borehole and thereby increasing a pull out force. These other means include use of chemical adhesion by the provision of a grout or resin which is applied to a borehole fitted with a rock bolt. The resin or grout is then cured to encase the rock bolt within the borehole. 2017200155 10 Jan 2017 2 [0006] Installation of known rock bolts can be costly and time consuming, particularly in the case of rock bolts using a chemical means of anchoring. These types of rock bolts must be installed into the borehole, the resin or grout then applied and left to cure for a period of time before the rock bolt can be tensioned. Installation, therefore, requires multiple passes by engineering personnel.

[0007] Problems arise in practise given the often large number of individual rock bolts fitted to any particular length of a rock body due to the duplication of time and expense of fitting rock bolts that require multiple passes for installation. Additional costs associated with resin cartridges or grout compounds these expenses.

[0008] Problems also often arise with known rock bolts in dynamic rock conditions. Seismic and other earth movements, which may frequently take place during underground tunnelling and mining operations, can cause a rock face of a supported rock body to move and become less stable, thus placing significant load on rock bolts installed in the rock face. Rock failures can cause bolts to undergo substantial tension, bend or twist, which reduces their load bearing strength and, in extreme cases, causes them to snap.

[0009] The present invention attempts to overcome, at least in part, the aforementioned disadvantages of previous rock bolts.

SUMMARY OF THE INVENTION

[0010] In accordance with one aspect of the present invention, there is provided a rock bolt adapted for installation into a borehole for supporting a rock body, comprising: an elongated body comprising a substantially arcuate wall defining a lumen, the lumen extending along a longitudinal axis between a first end and a second end of the body; a flexible tensioning tendon disposed inside, and extending substantially through, the lumen; a wedge member fixed to a first end of the tensioning tendon; and a nut releasably attachable to a second end of the tensioning tendon, 2017200155 10 Jan 2017 3 wherein, in use, tightening the nut causes the wedge member to be drawn into the lumen of the body thereby urging the arcuate wall of the body outwardly and anchoring the rock bolt within the borehole.

[0011] The tensioning tendon may comprise a plurality of peripheral wire strands wound about a central wire strand.

[0012] The peripheral wire strands of the tensioning tendon may be wound about the central wire strand in a helical configuration.

[0013] Each strand may be made of high tensile steel.

[0014] A thread may be ground into an external surface of the second end of the tensioning tendon, wherein the thread is complementary to an internal thread of the nut.

[0015] The nut may comprise a metal pin extending transversely across a threaded bore of the nut, the pin being configured to shear off from the nut when the nut is twisted by a sufficient amount during installation of the rock bolt.

[0016] The nut may be heat treated.

[0017] The wedge member may comprise a substantially tapered nose portion for facilitating insertion of the wedge member into the lumen of the body.

[0018] The wedge member may have a protuberance formed on its outer surface for limiting rotation of the wedge member about the longitudinal axis during installation of the rock bolt.

[0019] The protuberance may comprise an elongated fin formed on the outer surface of the wedge member.

[0020] The protuberance may comprise a pin formed on the outer surface of the wedge member.

[0021] The wedge member may have a hanging hook attached thereto. 4 2017200155 10 Jan 2017 [0022] A thrust plate may be secured to a lower end of the rock bolt for engaging and supporting a rock face of the rock body.

[0023] A cylindrical seat having a tapered top end may be disposed between the thrust plate and the nut.

BRIEF DESCRIPTION OF DRAWINGS

[0024] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [0025] Figure 1 is an elevated view of a rock bolt according to a preferred embodiment of the present invention; [0026] Figure 2(a) is an isolated view of the elongated body of the rock bolt of Figure l; [0027] Figure 2(b) is an isolated view of the tensioning tendon and wedge member of the rock bolt of Figure 1; [0028] Figure 3 is a partial enlarged view of an end of the tensioning tendon of the rock bolt of Figure 1; [0029] Figure 4(a) is a partial enlarged view of rock bolt of Figure 1 showing the tensioning tendon, cylindrical seat and nut in a partially assembled configuration; [0030] Figure 4(b) is a first enlarged perspective view of the nut of the rock bolt of Figure 1; [0031] Figure 4(c) is a second enlarged perspective view of the nut of Figure 4(b) shown with a shear pin installed therein; [0032] Figure 5 is a partial enlarged perspective view of an end of the tensioning tendon shown in Figure 3; [0033] Figure 6 is an alternative elevated view of a rock bolt of Figure 1 with a thrust plate installed thereon; and 5 2017200155 10 Jan 2017 [0034] Figure 7 is a partial elevated view of the wedge member of a rock bolt according to a further embodiment of the present invention, wherein the protuberance of the wedge member of the rock bolt comprises a metal fin.

DETAILED DESCRIPTION OF THE DRAWINGS

[0035] Referring to Figure 1, there is shown a rock bolt 10 for installation into a borehole for supporting a rock body, according to a preferred embodiment of the present invention.

[0036] The rock bolt 10 comprises an elongated body 12 comprising a contoured outer portion 14 that forms a substantially arcuate wall defining a lumen 16, the lumen 16 extending along a longitudinal axis between a first end 18 and a second end 20 of the body 12, and a flexible tensioning tendon 22 disposed inside, and extending substantially through, the lumen 16. The rock bolt 10 further comprises a wedge member 24 fixed to a first end 26 of the tensioning tendon 22, and a nut 28 releasably attachable to a second end 30 of the tensioning tendon 22. In use, tightening the nut 28 causes the wedge member 24 to be drawn into the lumen 16 of the body 12 thereby urging the arcuate wall of the body 12 outwardly and anchoring the rock bolt 10 within the borehole.

[0037] More particularly, the lumen 16 extends along a longitudinal axis of the body 12 between the first and second ends 18, 20 of the body 12. The wedge member 24 is affixed permanently to the first end 26 of the tendon 22, preferably by being swaged onto the tensioning tendon 22. The wedge member 24 comprises a substantially tapered nose portion 27 that facilitates insertion of the wedge member 24 into the lumen 16 of the body 12.

[0038] Referring to Figure 2(a), the outer portion 14 of the body 12 is formed, at least in part, by the substantially arcuate wall 32 formed about the lumen 16. A gap 34 is formed between opposed edges 36, 38 of the arcuate wall 32 and is disposed substantially along the longitudinal axis of the body 12.

[0039] The gap 34 provides for an amount of flexure of the arcuate wall 32 such that the edges 36, 38 may be moved closer to one another during a radial compression of the 6 2017200155 10 Jan 2017 body 12. A variation in the gap 34 corresponds with a change in an outer dimension of the arcuate wall 32 during fitting of the rock bolt 10 into a borehole which has a smaller internal diameter than a free standing outer dimension of the body 12, for example.

[0040] The resilient nature of the arcuate wall 32 ensures that the body 12 is biased toward an expanded position thereby urging the outer portion 14 into a radial expansion after a compressive installation process and thereby provides a source of frictional communication between the arcuate wall 32 and an inner surface of a borehole.

[0041] The body 12 may comprise any dimension of length and/or free standing outer diameter, however it will be appreciated that the dimensions of the rock bolt 10 will be substantially complementary to a receiving rock body borehole such that the rock bolt 10 may be forcefully inserted into the borehole.

[0042] During the forceful insertion, the arcuate wall 32 of the body 12 is compressed such that the opposed edges 36, 38 move closer to one another thereby yielding the gap 34. The resilient and tensile character of the body 12 results in an internally generated radially expanding force acting along the length of the body 12 and urging the body 12 into an interference fit with the borehole. It will be understood that a force acting in an orientation generally parallel with the longitudinal axis upon the body 12 of an installed apparatus 10 will be opposed by frictional force generated by the resultant radially expanding force.

[0043] The tensioning tendon 22 is disposed inside, and extends substantially through, the lumen 16 of the body 12. As shown in Figure 5, the tensioning tendon 22 comprises a flexible, multi-strand wire cable consisting of a plurality of high tensile peripheral wire strands 40 that are, preferably, wound in a twisted or helical configuration about a central wire strand 42. In the preferred embodiment that is illustrated in Figure 5, a total of six wire strands 40 are shown wound about the central strand 42. It will be appreciated, however, that an alternative number of wire strands may be wound about the central strand 42.

[0044] Each wire strand is made of a metallic material having a high degree of tensile strength and may be made of, for example, a steel material. 7 2017200155 10 Jan 2017 [0045] The tensioning tendon 22 further comprises a thread 44 ground into its external surface 46 at its second end 30. The thread 44 is formed by a grinding operation such as, for example, using one or more suitable rotary cutting discs. As best shown in Figures 4(a) and 4(b), the thread 44 is complemental to an internal thread 50 of the nut 28 to facilitate the releasable attachment of the nut 28 to the thread 44.

[0046] It will be appreciated that the process of grinding the thread 44 into the tensioning tendon 22 will remove some material from the tensioning tendon 22 and, hence, reduce its tensile strength. It is, therefore, preferable to make the thread 44 as shallow as possible. At the same time, it will also be appreciated that by making the thread 44 too shallow, it is possible to compromise the mechanical engagement achieved between the respective threads of the tensioning tendon 22 and nut 28. This problem is exacerbated by the fact that the high tensile wire strands 40 of the tensioning tendon 22 will be considerably harder than the normal mild steel of which conventional threaded nuts used in rock bolts are made, making it easier for the hard thread 44 of the tensioning tendon 22 to pull through the softer steel of the nut 28.

[0047] To solve this problem, the nut 28 is, therefore, heat treated and, preferably, case or through hardened in order to provide a hardening of the internal thread 50 such that the hardness of the internal thread 50 is equal to, or greater than, the hardness of the wire strands of the tensioning tendon 22 in which the thread 44 is ground.

[0048] In the preferred embodiment illustrated in the Figures, the thread 44 is aligned in the same direction as the lay of the wire strands 40 of the tensioning tendon 22, so that tightening of the nut 28 onto the tensioning tendon 22 tends to draws the wire strands 40 together.

[0049] In use, the rock bolt 10 may be fitted into a borehole using known forceful means, such as those provided by underground equipment including jumbo rigs and/or production drills, for example.

[0050] To install the rock bolt 10, the rock bolt 10 is positioned adjacent a borehole such that the body 12 and wedge member 24 are arranged to be received into the borehole. A force is applied to the rock bolt 10, preferably via the nut 28, thereby urging 8 2017200155 10 Jan 2017 the rock bolt 10 into the borehole and compressing the body 12. The rock bolt 10 is urged into the borehole until the body 12 is substantially received therein and the lower end of the rock bolt 10 substantially protrudes from the rock face.

[0051] A pre-tensioning step is then applied to the rock bolt 10 for activating a localised point anchor at the junction 52 between the body 12 and the wedge member 24. The pre-tensioning step involves tightening the nut 28 to a predefined tension causing the tensioning tendon 22 to be pulled downwards. A metal protuberance 53 formed onto the surface of the wedge member 24 abuts the opposed edges 36,38 of the body 12 and impedes rotation of the wedge member 24 as the nut 28 is tightened.

[0052] The protuberance 53 comprises a pin swaged or brazed onto the surface of the wedge member 24. As shown in Figure 7, in an alternative embodiment of the present invention the protuberance 53 comprises an elongated metal fin 72 swaged or brazed onto the surface of the wedge member 24.

[0053] Tightening the nut 28 urges the body 12 and the wedge member 24 to engage one another at the junction 52. For the purpose of verifying when the requisite torque and twisting movement has been applied to the nut 28, as shown in Figure 4(c) the nut 28 is a shear pin nut. This comprises a metal pin 54 arranged such that the pin 54 extends transversely across the threaded bore of the nut 28. The metal pin 54 is secured within two opposed grooves 56,58 formed into the base end of the nut 28. The pin 54 may be secured into the grooves 56,58 using a strong interference fit or by welding.

[0054] As the nut 28 is tightened during installation, it will be understood that the tensioning tendon 22 travels progressively through the thread 50 of the nut 28 towards the pin 54 until it bears against the pin 54. The pin 54 exerts a significant resistive force against the tensioning tendon 22 impeding further travel of the tensioning tendon 22 through the nut 28. Eventually, when the requisite torque has been applied to the nut 28, the pin 28 is caused to be sheared off and ejected away from the grooves 56,58, thereby indicating that the pre-tensioning step is complete.

[0055] Owing to the tapered nose portion 27 of the wedge member 24, when the nut 28 is tightened the wedge member 24 is drawn into the lumen 16 of the body 12 thereby 2017200155 10 Jan 2017 9 simultaneously urging the outer portion 14 outwardly and developing a point anchor with the borehole at the junction 52. The point anchor substantially increases the strength of the anchoring of the rock bolt 10 within the borehole.

[0056] As shown in Figure 6, a thrust plate 48 is fitted and secured over the lower end of the rock bolt 10 by known means for substantially engaging and supporting the rock face.

[0057] Mesh and/or spray concrete may also be used in conjunction with the rock bolt 10 as is known in the art.

[0058] In one embodiment of the invention, the rock bolt 10 additionally comprises a floating tapered cylindrical seat 60 disposed between the thrust plate 48 and the nut 28. As most clearly shown in Figure 4(a), a top end 62 of the cylindrical seat 60 is preferably tapered providing a substantially rounded surface that abuts a lower surface of the thrust plate 48.

[0059] In use, when the nut 28 is tightened during installation of the rock bolt 10, the cylindrical seat 60 may freely rotate about, and travel along, the longitudinal axis of the tensioning tendon 22. The cylindrical seat 60 serves to evenly distribute and spread the load that would otherwise be placed on the thrust plate 48 by the nut 28 when it is tightened. In this arrangement, the thrust plate 48 may move more easily along the longitudinal axis of the tensioning tendon 22 as the nut 28 is tightened during installation.

[0060] Further, the tapered top end 62 of the cylindrical seat 60 enables the thrust plate 48 to be secured to a rock face effectively in situations where the length of the rock bolt’s body 12 is aligned at an angle that is not substantially perpendicular to the rock face surface - for example, because the rock bolt 10 has been driven into a bore hole in the rock face at an angle. The rounded surface of the cylindrical seat 60 at its tapered top end 62 ensures that a uniform, evenly distributed force is applied to the thrust plate 48 thereby allowing the rock bolt 10 to support the rock face effectively in such situations. 2017200155 10 Jan 2017 ίο [0061] In one embodiment of the invention, a top end 68 of the wedge member 24 comprises a hook 70 which allows the rock bolt 10 to be hung conveniently from various structures during installation, transport and/or storage of the rock bolt 10.

[0062] Problems often arise with known rock bolts in dynamic rock conditions. Seismic and other earth movements, which may frequently take place during underground tunnelling and mining operations, may cause a rock face of a supported rock body to move and become less stable, thus placing significant load on rock bolts installed in the rock face. Rock failures may cause bolts to undergo substantial tension, bend or twist, reducing their load bearing strength, and in extreme cases snap.

[0063] In the present invention, the high tensile strength and flexibility that is provided by the tensioning tendon 22 advantageously ensures that the rock bolt 10 is able to adaptively withstand bending and other adverse forces that may act on the rock bolt 10 in dynamic rock conditions. The tensioning tendon 22 remains in tension and continues to support the rock face without cracking or otherwise being impaired.

[0064] The applicant has found, in particular, that the disclosed rock bolt 10 is advantageous in rock environments and underground mining installations where rock face shearing commonly occurs.

[0065] Further modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

[0066] In the preceding description of the invention and the following claims, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “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 (15)

1. A rock bolt adapted for installation into a borehole for supporting a rock body, the rock bolt comprising: an elongated body comprising a substantially arcuate wall defining a lumen, the lumen extending along a longitudinal axis between a first end and a second end of the body; a tensioning tendon disposed inside, and extending substantially through, the lumen, wherein the tensioning tendon is flexible; a wedge member fixed to a first end of the tensioning tendon; and a nut releasably attachable to a second end of the tensioning tendon, wherein, in use, tightening the nut causes the wedge member to be drawn into the lumen of the body thereby urging the arcuate wall of the body outwardly and anchoring the rock bolt within the borehole.

2. The rock bolt according to claim 1, wherein the tensioning tendon comprises a plurality of peripheral wire strands wound about a central wire strand.

3. The rock bolt according to claim 2, wherein the peripheral wire strands of the tensioning tendon are wound about the central wire strand in a helical configuration.

4. The rock bolt according to claim 2 or 3, wherein each strand is made of high tensile steel.

5. The rock bolt according to any one of the preceding claims, wherein a thread is ground into an external surface of the second end of the tensioning tendon, and wherein the thread is complementary to an internal thread of the nut.

6. The rock bolt according to any one of the preceding claims, wherein the nut comprises a metal pin extending transversely across a threaded bore of the nut, the pin being configured to shear off from the nut when the nut is twisted by a sufficient amount during installation of the rock bolt.

7. The rock bolt according to any one of the preceding claims, wherein the nut is heat treated.

8. The rock bolt according to any one of the preceding claims, wherein the wedge member comprises a substantially tapered nose portion for facilitating insertion of the wedge member into the lumen of the body.

9. The rock bolt according to any one of the preceding claims, wherein the wedge member has a protuberance formed on its outer surface for limiting rotation of the wedge member about the longitudinal axis of the body during installation of the rock bolt.

10. The rock bolt according to claim 9, wherein the protuberance comprises an elongated fin formed on the outer surface of the wedge member.

11. The rock bolt according to claim 9, wherein the protuberance comprises a pin formed on the outer surface of the wedge member.

12. The rock bolt according to claim 11, wherein the pin is swaged onto the outer surface of the wedge member.

13. The rock bolt according to any one of the preceding claims, wherein the wedge member has a hook attached thereto for hanging the rock bolt from a structure.

14. The rock bolt according to any one of the preceding claims, wherein a thrust plate is secured to a lower end of the rock bolt for engaging and supporting a rock face of the rock body.

15. The rock bolt according to any one of the preceding claims, wherein a cylindrical seat having a tapered topmost end is disposed between the thrust plate and the nut.