AU2021203871A1

AU2021203871A1 - Rock Bolt

Info

Publication number: AU2021203871A1
Application number: AU2021203871A
Authority: AU
Inventors: Adrian ALINGTON; David Maltby
Original assignee: Garock Pty Ltd
Current assignee: Garock Pty Ltd
Priority date: 2015-06-22
Filing date: 2021-06-10
Publication date: 2021-07-08
Also published as: AU2016204238A1; AU2023202198A1

Abstract

A rock bolt for supporting a rock body comprising an elongated body. The body comprises a contoured wall that defines, at least in part, a lumen passing through the body, an elongated support bar disposed inside the lumen of the body, the support bar having a proximal end and a distal end wherein a flange is disposed at the proximal end and the distal end is configured to have a thrust plate attached thereto and an elongated collar. The elongated collar is disposed, at least in part, inside the lumen of the elongated body and has a lumen, wherein the lumen of the collar slidably receives the support bar and the flange and has a stricture point where a cross sectional area of the lumen of the collar is reduced for increasing a frictional communication between the support bar and the collar at the stricture point. When a movement of a rock face of the rock body occurs, the rock face bears against the thrust plate causing the support bar and flange to travel through the lumen of the collar thereby permitting the rock bolt to yield and govern the movement, and whereby the stricture point stops the flange travelling through the lumen of the collar past the stricture point.

Description

ROCK BOLT CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is divided from Australian Patent Application 2016204238, the content of which is incorporated herein in its entirety by reference.

FIELD OF INVENTION

[0002] The present invention relates to a rock bolt for supporting a rock body and, more particularly but not exclusively, the invention relates to a yielding rock bolt.

BACKGROUND

[0003] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[0004] The following discussion of the background to the invention is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge of the person skilled in the art in any jurisdiction as at the priority date of the invention.

[0005] 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 rock bolt protruding from a rock face of the rock body. A thrust plate can then be mounted onto the protruding end which forms a flange that abuts the rock face. 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.

[0006] One form of known rock bolt is a friction rock bolt which comprises a friction means for anchoring the bolt in a borehole. The effectiveness of friction rock bolts can be impaired permanently 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. These rock failures can cause installed rock bolts to undergo substantial tension, bend or twist, reducing their load bearing strength, and in extreme cases snap.

[0007] It is, therefore, known to incorporate a yielding mechanism into a friction rock bolt in an effort to withstand dynamic rock conditions.

[0008] One form of known yielding friction type rock bolt comprises an elongated support bar and a resilient collar. The collar is disposed towards a proximal end of the rock bolt and is adapted to anchor the rock bolt inside the borehole. The collar has a lumen formed through its longitudinal axis that is adapted to receive slidably, and frictionally engage, the support bar. A thrust plate is secured to a distal end of the support bar that protrudes from the rock face once the rock bolt has been installed and abuts the rock face. In use, in the event of a movement of the rock face, the rock face exerts a load on the thrust plate causing the support bar to slide through the lumen of the collar thereby permitting the rock bolt to yield and govern the rock movement.

[0009] Yielding rock bolts of this design, whilst effective, require a borehole of substantial length to be pre-drilled into the rock face in order to allow the rock bolt to be installed and operate in use. This is because the yielding mechanism of the bolt will not work effectively unless a substantial length of the support bar is protruding from the top end of the rock bolt's collar to allow the support bar to travel through the collar by a sufficient amount when the rock bolt needs to yield. At the very least, the borehole must be drilled so that its length is equal to, or greater than, the length of the body of the rock bolt in addition to the part of the rock bolt's support bar that protrudes from its top end.

[0010] To minimise drilling time and resources required during installation, rock bolts must, ideally, be installed into a borehole that is of substantially the same length as the rock bolt. For the reasons explained above, however, this is not possible with current yielding rock bolt designs.

[0011] The present invention attempts to overcome, at least in part, the aforementioned disadvantages of previous yielding rock bolts.

SUMMARY OF THE INVENTION

[0012] According to one aspect of the present invention, there is provided a rock bolt for supporting a rock body, comprising:

an elongated body comprising a contoured wall that defines, at least in part, a lumen passing through the body; an elongated support bar disposed inside the lumen of the body, the support bar having a proximal end and a distal end, wherein a flange is disposed at the proximal end and the distal end is configured to have a thrust plate attached thereto; and an elongated collar that: is disposed, at least in part, inside the lumen of the elongated body, has a lumen, wherein the lumen of the collar slidably receives the support bar and the flange, and has a stricture point where a cross-sectional area of the lumen of the collar is reduced for increasing a frictional communication between the support bar and the collar at the stricture point, whereby, when a movement of a rock face of the rock body occurs, the rock face bears against the thrust plate causing the support bar and flange to travel through the lumen of the collar thereby permitting the rock bolt to yield and govern the movement, and whereby the stricture point stops the flange travelling through the lumen of the collar past the stricture point.

[0013] The flange may comprise a circumferential flange member swaged onto the support bar.

[0014] The collar may have a chock member formed on an outer surface of the collar, whereby the chock member frictionally engages a wall of the borehole to limit rotation of the collar and the support bar when the rock bolt is being installed into a borehole.

[0015] The distal end of the support bar may comprise a threaded portion configured to receive threadedly a complementary nut.

[0016] The collar may be tapered to form a flared portion wherein a diameter of the collar increases towards the flared portion, whereby when the nut is tightened during installation of the rock bolt into the borehole, the collar and flared portion are urged into the lumen of the body causing the proximal end of the body to expand radially and thereby restrain the rock bolt inside the borehole.

[0017] The contoured wall of the body may have a split section disposed at the proximal end of the body, the split section being configured to facilitate expansion of the body when the nut is tightened during installation of the rock bolt.

[0018] The contoured wall of the body may have a cross-sectional shape that is arcuate thereby providing that the body and the lumen are not completely enclosed.

[0019] The contoured wall of the elongated body may be shaped such that the contoured wall completely encloses the body and the lumen.

[0020] The rock bolt may further comprise a hemispherical seat having a tapered top end that is slidably mountable onto the support bar and is disposed between the thrust plate and the nut.

BRIEF DESCRIPTION OF DRAWINGS

[0021] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

[0022] Fig. 1 shows a yielding rock bolt as is known in the art;

[0023] Fig. 2 shows an elevated side view of a yielding rock bolt according to a preferred embodiment of the present invention;

[0024] Fig. 3 shows a further elevated side view of the rock bolt of Fig. 2, the rock bolt being shown from an opposite side;

[0025] Fig. 4 shows a partial perspective view of a proximal end of the rock bolt of Fig. 2; and

[0026] Fig. 5 shows a schematic side view of the rock bolt of Fig. 2.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] Referring to Fig. 1, there is shown a yielding rock bolt 10 as is known in the art. The rock bolt 10 comprises an elongated body 12 having a proximal end 14 and a distal end 16. The elongated body 12 comprises a contoured wall 18 that defines, at least in part, a lumen 20 passing through a longitudinal length of the body 12.

[0028] The rock bolt 10 further comprises an elongated support bar 22 disposed inside the lumen 20 of the elongated body 12. The support bar 22 has a proximal end 24 and a distal end 26 and spans the full length of the rock bolt 10.

[0029] The rock bolt 10 further comprises a collar 28 having a lumen 30 passing through the collar 28. The collar's lumen 30 has an interior wall 32 that is adapted to receive slidably the support bar 22. The interior wall 32 comprises a stricture point 34 where (as shown schematically in Fig. 1) a diameter of the collar's lumen 30 and interior wall 32 is reduced to substantially increase the co-efficient of friction between the interior wall 32 and the support bar 22 at the stricture point 34.

[0030] A stop means comprising a circumferential flange 36 is disposed substantially towards the proximal end 24 of the support bar 22 for limiting travel of the support bar 22 through the collar lumen 30.

[0031] The distal end 26 of the support bar 22 comprises a threaded portion 38 configured to receive threadedly a complementary nut 40.

[0032] To install the rock bolt 10, the rock bolt 10 is inserted forcefully into a borehole that has been pre-drilled into a rock face of the rock body that needs to be supported. This causes the contoured wall 18 of the body 12 to be compressed by the interior wall of the borehole thereby securing the rock bolt 10 within the borehole by interference fit. A thrust plate 42 (and, optionally, a press plate 44) is then attached to the support bar 22.

[0033] The nut 40 is then tightened which urges the support bar 22 and, by extension, the collar 28 towards the lumen 20 of the elongated body 12. In turn, this causes a wedge member 46 that is disposed between the collar 28 and the body 12 to be drawn into the lumen 20 of the elongated body 12. This, in turn, causes the proximal end 14 of the elongated body 12 to expand radially thus forming a point anchor 48 for further restraining the rock bolt 10 within the borehole. Mesh and spray concrete, or similar means, may then be additionally applied.

[0034] Once installed, in the event of a failure at the rock face, a substantial load is placed on the thrust plate 42. This, in turn, causes the support bar 22 to slide through the lumen 30 of the collar 28, overcoming the friction at the stricture point 34, thereby permitting the rock bolt 10 to yield and govern the rock movement. When the support bar 22 has travelled a sufficient distance through the lumen 30, the circumferential flange 36 abuts an outer edge of the lumen 30 which stops the support bar 22 from travelling any further and allows the rock bolt 10 to continue to support the rock face.

[0035] In order to allow the prior art rock bolt 10 to yield effectively in this manner, a section 50 of the support bar 22 must protrude substantially from the collar lumen 30 so that the support bar 22 is able to travel a sufficient distance through the collar's lumen 30. This requires the borehole to be drilled at a length that is substantially longer than the length of the rock bolt , which is an inefficient use of drilling time and resources.

[0036] Referring to Fig. 2, there is shown an elevated side view of a yielding rock bolt 52 according to a preferred embodiment of the present invention. The rock bolt 52 comprises an elongated body 54 having a proximal end 56 and a distal end 58.

[0037] The body 54 comprises a contoured wall 60 that defines, at least in part, a lumen 62 passing centrally through a longitudinal length of the body 54.

[0038] The contoured wall 60 has a cross-sectional shape that is, preferably, substantially arcuate thereby providing that the body 54 and its lumen 62 are not completely enclosed. It will be appreciated, however, that in alternative embodiments of the present invention, the contoured wall 60 may be shaped such that the body 54 and its lumen 62 are completely enclosed.

[0039] The rock bolt 52 further comprises an elongated support bar 64 disposed inside the lumen 62 of the body 54. The support bar 64 has a proximal end 66 and a distal end 68 and spans the full length of the rock bolt 52.

[0040] The rock bolt 52 further comprises an elongated collar 70. The collar 70 is manufactured from a hard, resilient material (preferably, a metallic material) and is disposed, at least in part, inside the lumen 62 of the body 54.

[0041] As most clearly shown in Fig. 4, the collar 70 comprises a lumen 72 formed through its entire longitudinal axis. The collar's lumen 72 has an interior wall 74 that is adapted to slidably receive the support bar 64.

[0042] As best shown schematically in Fig. 5, the collar 70 comprises a stricture point 76 where a cross-sectional area of the collar lumen 72 and interior wall 74 is reduced. During the manufacturing process, the stricture point 76 may be created by using, for example, a radial press machine, or equivalent cold pressing method, to exert large inward forces radially about a circumference of the elongated collar 70 at the stricture point 76. This causes the collar 70 and the collar's lumen 72 to undergo a substantial deformation causing their cross-sectional area to reduce forming a stricture. The stricture substantially increases a frictional communication between the interior wall 74 of the collar's lumen 72 and the support bar 64 at the stricture point 76.

[0043] Substantially towards the proximal end 66 of the support bar 64, there is disposed a flange which, in the Figures, is depicted in the form or a circumferential flange member 78 swaged onto the support bar 64.

[0044] Substantially towards the distal end 68 of the support bar 64, there is a threaded portion 80 that is adapted to receive threadedly a complementary nut 82.

[0045] Towards a proximal end of the collar 70, the collar 70 is tapered outwardly to form a flared portion 80 where a diameter of the collar 70 is increased. The collar 70 further comprises an elongated chock member 82 swaged onto its outer surface.

[0046] To install the rock bolt 52, the rock bolt 52 is inserted forcefully into a borehole that has been pre-drilled into a rock face of the rock body that needs to be supported. This causes the contoured wall 60 of the body 54 to be compressed by the wall of the borehole thereby securing the rock bolt 52 within the borehole by interference fit. The chock member 82 serves to frictionally engage the wall of the borehole thereby limiting rotation of the collar 70 and, by extension, the support bar 64, without materially limiting longitudinal movement of these components through the elongate length of the borehole.

[0047] A thrust plate (not shown) and, optionally, a press plate (not shown) is then attached to the support bar 64 as is known in the art. The nut 82 is then tightened in order to pre-tension the rock bolt 52.

[0048] As the nut 82 is tightened, this urges the support bar 64 and, by extension, the collar towards, and into, the lumen 62 of the elongated body 54. Due to the tapered flared portion 80 of the elongated collar 70, this, in turn, causes the proximal end 56 of the elongated body 54 to expand radially thus forming a point anchor 84 for further restraining the rock bolt 52 within the borehole.

[0049] Once the rock bolt 52 has been anchored, mesh and spray concrete, or similar means, may then be additionally applied.

[0050] The support bar 64 and circumferential flange member 78 are adapted such that, when the rock bolt 52 is required to yield in use, the support bar 64 and circumferential flange member 78 may travel through the collar's lumen 72 until the circumferential flange member 78 abuts the interior wall 74 of the collar's lumen 72 at the stricture point 76. This stops any further travel of the flange 78, and consequently the support bar 64, through the collar's lumen 72 past the stricture point 76, and the consequent ability of the rock bolt 52 to yield.

[0051] As shown in Fig. 3, the contoured wall 60 of the body 54 may comprise a split section 85 disposed at the proximal end 56 of the body 54, the split section 85 being configured to facilitate expansion of the body 54 at its proximal end 56 during the pre-tensioning step of installing the rock bolt 52.

[0052] In embodiments of the invention, a hemispherical seat 86 having a substantially rounded or tapered top end may also be, optionally, slidably mounted onto the support bar 64 and disposed between the thrust plate and the nut 82. When the nut 82 is tightened, the hemispherical seat 86 may freely rotate about, and travel along, the support bar 64. The hemispherical seat 86 serves to evenly distribute and spread the pressure that would otherwise be placed on the thrust plate by the nut 82 thus allowing the thrust plate to travel more easily along the support bar 64 when the apparatus is pretensioned.

[0053] Further, the rounded or tapered top end of the hemispherical seat 86 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 52; for example, because the rock bolt 52 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 52 to support the rock face effectively in these situations.

[0054] Once the rock bolt 52 has been fully installed, in the event of a failure at the rock face, a substantial load will be placed on the thrust plate. This, in turn, causes the support bar 64 to slide through the lumen 72 of the collar 70, overcoming the friction at the stricture point 76, thereby permitting the rock bolt 52 to yield and govern the rock movement.

[0055] When the rock bolt 52 yields in this manner, as disclosed above, the support bar 64 is adapted such that its proximal end 66 (including its circumferential flange member 78) may travel through the elongated collar's lumen 72 until the circumferential flange member 78 abuts the interior wall 74 of the collar's lumen 72 at the stricture point 76, at which point the rock bolt 52 will have yielded to its maximum permitted capacity.

[0056] The longitudinal length of the collar 70 is such that the collar 70 is disposed, at least in part, inside the lumen 62 of the body 54. In this arrangement, when the rock bolt 52 yields and the support bar 64 travels through the lumen 72 of the elongated collar 70, the proximal end 66 of the support bar 64 may travel, at least in part, through a section 88 of the collar's lumen 72 that is disposed within the lumen 62 of the elongated body 54 (as illustrated schematically in Fig. ).

[0057] The rock bolt 52 is, therefore, adapted such that its yielding mechanism may operate without the support bar 64 having to protrude out from the lumen 72 of the collar 70. It will be appreciated that this advantageously enables the rock bolt 52 to be installed in a borehole that is of substantially the same length as the rock bolt 52.

[0058] Significantly less drilling time and resources are, therefore, required during installation of the rock bolt 52.

[0059] 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.

[0060] Furthermore, throughout the specification, unless the context requires otherwise, the word "include" or variations such as "includes" or "including", 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.

IU

[0061] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

1. A rock bolt for supporting a rock body, comprising

an elongated body comprising a contoured wall that defines, at least in pail, a lumen passing through the body; an elongated support bar disposed inside the lumen of the body, the support bar having a proximal end and a distal end, wherein a flange is disposed at the proximal end and the distal end is configured to have a thrust plate attached thereto; and an elongated collar that: is disposed, at least in part, inside the lumen of the elongated body, has a lumen, wherein the lumen of the collar slidably receives the support bar and the flange, and has a stricture point where a cross-sectional area of the lumen of the collar is reduced for increasing a fictional communication between the support bar and the collar at the stricture point, whereby, when a movement of a rock face of the rock body occurs, the rock face bears against the thrust plate causing the support bar and flange to travel through the lumen of the collar thereby permitting the rock bolt to yield and govern the movement, and whereby the stricture point stops the flange travelling through the lumen of the collar past the stricture point.

2. The rock bolt according to claim 1, wherein the flange comprises a circumferential flange member swaged onto the support bar.

3. The rock bolt according to claim 1 or 2, wherein the collar has a chock member formed on an outer surface of the collar, whereby the chock member frictionally engages a wall of the borehole to limit rotation of the collar and the support bar when the rock bolt is being installed into a borehole.

4. The rock bolt according to any one of the preceding claims, wherein the distal end of the support bar comprises a threaded portion configured to receive threadedly a complementary nut.

5. The rock bolt according to any one of the preceding claims, wherein the collar is tapered to form a flared portion wherein a diameter of the collar increases towards the flared portion, whereby when the nut is tightened during installation of the rock bolt into the borehole, the collar and flared portion are urged into the lumen of the body causing the proximal end of the body to expand radially and thereby restrain the rock bolt inside the borehole.

6. The rock bolt according to any one of the preceding claims, wherein the contoured wall of the body has a split section disposed at the proximal end of the body, the split section being configured to facilitate expansion of the body when the nut is tightened during installation of the rock bolt.

7. The rock bolt according to any one of the preceding claims, wherein the contoured wall of the body has a cross-sectional shape that is arcuate thereby providing that the body and the lumen are not completely enclosed.

8. The rock bolt according to any one of claims I to 6, wherein the contoured wall of the elongated body may be shaped such that the contoured wall completely encloses the body and the lumen.

9. The rock bolt according to any one of the preceding claims, wherein the rock bolt further comprises a hemispherical seat having a tapered top end that is slidably mountable onto the support bar and is disposed between the thrust plate and the nut.