AU2013219190A1 - Rock bolt - Google Patents

Abstract

The present invention relates to a rock bolt for supporting a rock body. The rock bolt comprising a body having means for binding arranged to receive a grout mixture and permitting a grout mixture to pass through, at least in part, a portion of the body thereby increasing a pull out force required to dislodge the rock bolt from a bore hole in the rock body. The means for binding comprises a profiled outer surface such as a recess or groove formed in the outer surface. The, or each, recess or groove preferably has a helical configuration which extends substantially along a length of the body. In a preferred embodiment the rock bolt comprises a plurality of individual strands wound about a central core strand in a first direction, the helical configuration arranged to have a second orientation which is in a counter direction to the first orientation. Figure 2

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: Neville Hedrick David Maltby ADDRESS FOR SERVICE: LORD AND COMPANY, Patent and Trade Mark Attorneys, of PO Box 530, West Perth, Western Australia, 6872, AUSTRALIA. INVENTION TITLE: "ROCK BOLT" DETAILS OF ASSOCIATED PROVISIONAL APPLICATION NO'S: Australian Provisional Patent Application Number 2012903615 filed on 22 August 2012 TITLE "ROCK BOLT" FIELD [0001] The present invention relates to a rock bolt for use in supporting a rock body. BACKGROUND [0002] It is known to use a rock bolt to improve the structural integrity of a rock body and increase the personnel and environmental safety of underground works including mining and civil operations. Typically rock bolts are fitted into a pre-drilled bore hole in a rock face of a rock body, typically along a surface of an underground mine roof or wall for example. The rock bolt is fitted in order to support the rock face in the event of a sudden rock body fault or creep movement and thereby prevent or limit a collapse of the rock face and to support mesh which can be used to reinforce spray concrete for example. [0003] Often a rock bolt is secured within the bore hole using a liquid cementous or resinous grout mixture which solidifies to rigidly lock the rock bolt in position within the rock body. In a multi strand rock bolt it is also known to use one or more bulbous portions (also known as a bird cage) along a length of the rock bolt thereby varying a cross sectional dimension of the rock bolt as well as allowing grout mixture to infiltrate through the rock bolt before setting. This has the effect of increasing a magnitude of a pull-out force required to dislodge the rock bolt from the bore hole and thus improves the safety characteristics of the rock bolt in use. However the spiral configuration of a wound/woven rock bolt can to reduce the pull-out force as a torque is induced within the rock bolt leading to the rock bolt tending to 'unscrew' itself out of the bore hole when under load. [0004] The present invention attempts to overcome at least in part the aforementioned limitations of previous rock bolts. 2 SUMMARY [0005] The present invention relates to a rock bolt for use in supporting a rock body, the rock bolt having a body arranged to be substantially received within a rock body bore hole, the body having a length disposed between two peripheral end portions, wherein the rock bolt has means for binding arranged to receive a grout mixture and permitting the grout mixture to pass through, at least in part, a portion of the rock bolt body. [0006] Preferably the bolt comprises a plurality of individual strands directionally wound about a central core strand in a first orientation. [0007] Preferably the means for binding comprises a profiled outer surface disposed upon one or more respective individual strands. [0008] Preferably the profiled outer surface comprises a recessor groove, having a width and a depth, running about a circumference of each respective strand. [0009] Preferably the recess or groove has a helical configuration. [0010] In a preferred embodiment of the present invention, the profiled outer surface comprises a plurality of recessor grooves. [0011] Preferably each recessor groove is spaced apart by a dimension greater than the width of the recessor groove. [0012] In a preferred embodiment the helical configuration comprises a second orientation, the second orientation being of a counter direction to the first orientation. [0013] Preferably the means for binding surface extends substantially along the length of the rock bolt body. 3 BRIEF DESCRIPTION OF THE DRAWINGS [0014] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side view of a rock bolt in accordance with a preferred embodiment of the present invention; Figure 2 is a perspective end view of the rock bolt of Figure 1; Figure 3 is a sectional interpretation of the rock bolt of Figure 1 in use fitted in a rock body bore hole; Figure 4 is a perspective view of an alternative embodiment of the present invention; and Figure 5 is a perspective view of a still further alternative embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT [0015] Referring to the Figures, there is shown a rock bolt 10 for use in supporting a rock body 46 in underground operations such as mining or construction for example. The rock bolt 10 comprising a body potion 12 having a longitudinal length and peripheral first and second end portions 14,16. [0016] In use the first end portion 14 is arranged to enter the bore hole 42 (see Figure 3) and as such it preferably comprises tapered or pinched configuration as seen in Figures 1 and 5 to reduce the overall cross section of the rock bolt 10, at the first end portion 14 to assist fitting the rock bolt 10 to the bore hole 42. [0017] In the preferred embodiment of the present invention as shown in the Figure the rock bolt 10 body 12 comprises a plurality of individual strands 20 woven or wound about a central core strand 22. Preferably the strands 20,22 are formed from a metallic material having a high tensile strength with some ductile property characteristics such as iron or steel for example. Each individual strand 20 typically 4 comprises a substantially similar cross sectional shape and therefore has a substantially similar cross sectional area to each other individual strand 20. [0018] As can be seen in the Figure 3 the preferred embodiment has a total of six (6) individual strands 20 having a generally circular cross section and one single core strand 22 with each strand 20, 22 having substantially equal proportions. [0019] As seen in the Figures 1 and 2 the rock bolt 10 may further comprise one or more bulbous portions 18 as is known in the art. [0020] The present invention further comprises means for binding. In the preferred embodiment shown in the Figures the means for binding comprises a profiled outer surface 24 disposed upon each respective strand 20. Typically, as seen in the Figures the profiled outer surface 24 of each respective strand 20 comprises a recessor groove 26 formed thereon and which runs at least in part and preferably substantially and continuously along the length of the strand 20 over the length rock bolt 10 body 12. [0021] As can be seen in Figure 3 the groove 26 of the preferred embodiment of the present invention comprises a recessed surface 29 with upstanding side walls 27 defining a depth and width 31 of the groove 26 and providing a recessed passage running about a longitudinal axis of the strand 20. [0022] It should be understood that other configurations of the profiled outer surface 24 may also be used, such as a 'u' or 'v' shaped grooves 26, and the present invention is not limited to the substantially oblong configuration of the groove 26 herein described and illustrated in the Figures. Similarly, in alternative embodiments of the present invention the profiled outer surface 24 may comprise configurations having a raised portion (not shown) or alternatively a combination of a raised portion and recessed portion for example. [0023] It is to be understood that the image shown in Figure 3 may not represent the exact cross section of the rock bolt body 12 but serves to illustrate that the grooves 26 5 of the means for binding on any one individual strand 20 will be proximal with the adjacent individual or core strand 20, 22 at some point along the length of the body 12. Preferably there will be a plurality proximal junctions 43, where two grooves 26 overlap, along the length of the body 12. [0024] Typically the means for binding groove 26 of any respective individual strand 20 will complete a full 3600 rotation per 10-100 mm of axial or longitudinal length of the strand 20. [0025] Preferably each strand 20 will comprise a plurality of grooves 26 arranged to have a helical configuration as shown in Figures 1, 2, 4 and 5. Each groove 26 on a strand 20 is arranged to run about the circumference of a respective strand 20 and run substantially parallel with each other groove 26 on the respective strand 20 such that a length 27 of the outer surface is constantly space apart each groove (see Figure 4). [0026] The present invention is arranged such that the length 27 has a greater dimension than the width 31 of each groove 26. Thereby, the strands 20 may be wound about the core strand 22 such that the grooves 26 do not intermesh with one another and the recessed passage is substantially uninterrupted. It is an advantage of the present invention that in use the uninterrupted passage receives and accommodates a grout or cementous substance during installation of the rock bolt 10 for increasing a pull out force required to dislodge the rock bolt 10. [0027] The means for binding has a two fold advantage. Firstly it can provide a plurality of passages through which air may escape the bore hole 42 during an initial grouting procedure thereby improving a grout column integrity by reducing air voids within the bore hole 42 which are known to reduce the pull-out force of a rock bolt 10. It is to be understood that the viscosity of the grout mixture 40 whilst in its liquid state prior to setting must be suitable for substantially filling the grooves 26. Accordingly, it is envisaged that the present invention will primarily be used with an epoxy resin grout mixture 40 however other similar or cementous substances may also be used. 6 [0028] Secondly, the grooves 26 provide a plurality of substantially uninterrupted passages which the grout mixture 40 may fill thereby forming a plurality of restraining fingers comprising the grout mixture 40 entwining each respective individual strand 20. As the grooves 26 overlap at proximal junctions 43 with one another the restraining fingers may effectively become interlaced throughout the rock bolt 10. It is an advantage that this has the effect of increasing the pull-out force required to dislodge the rock bolt 10 from the bore hole. [0029] The rock bolt 10 body 12 comprises an outer portion 30 forming an effective rock bolt outer surface 32 along the length of the rock bolt 12. As can be seen in Figures 2, 4 and 5 the rock bolt outer portion 30 is formed by a plurality of partial outer surfaces 24 of the respective individual strands 20. As such and as shown in Figure 3 an axial cross sectional view of the rock bolt 10 illustrates the outer portion 30 is configured with a plurality of individual strands 20 abutting one another to form an effectively continuous outer surface 32. As can be seen in Figures 1, 2, 4 and 5 the wound or woven strand 20, 22 construction of the preferred embodiment of rock bolt 10 results in an outer portion 30 comprising a number of helical peaks 36 and helical troughs 38. [0030] The orientation of the individual strands 20 of the present invention is not critical and as such the individual strands 20 may be arranged with a clockwise or counter-clockwise orientation with respect to the first end 14 and the central core strand 22 which orientation comprises a first orientation of the present invention. [0031] However, it is preferable for the present invention that a second orientation of the groove 26 along an individual strand 20 profiled outer surface 24 run in a counter direction to the first orientation. Thus, the rock bolt seen in Figure 2 shows the individual strands 20 spiralling away from the first end portion 14 toward the second end portion 16 in a clockwise direction. According to the preferred embodiment the second orientation of the groove 26 in accordance with the present invention is arranged with a spiral configuration in a counter clockwise orientation. 7 [0032] It should be understood that the reverse configuration wherein the strands 20 are wound counter clockwise and the grooves 26 are formed clockwise would also provide functionality according to the preferred embodiment and as such is encompassed within the scope of the present invention. [0033] It is to be understood that the profiled outer surface 24 of the respective individual strands 20 provides a plurality of separate recesses spaced about the outer portion 30 which may be filled with a cementous substance or resinous grout 40 during installation of the rock bolt 10 within the bore hole 42. [0034] It should be further understood that the grooves 26 provide a passage for assisting the grout mixture 40 to infiltrate the rock bolt 10 body 12 and enter the crevices and voids 44 formed between the adjacent individual strands 20 and/or the central core strand 22 as illustrated in Figure 3. [0035] While the preferred embodiment of the present invention 10 discloses a core strand 22 free of means for binding it should be understood that alternative embodiments may comprise a central core strand 22 having a similar profiled outer surface 24. [0036] It is to be understood that the present invention is not limited to a rock bolt 10 having the wound or woven strand 20 type of construction and may equally be applied to alternative rock bolt configurations including rock bolts having an outer portion formed from a single and continuous wall (not shown) for example. [0037] In use, a bore hole 42 is drilled in a rock body 46 as is known in the art. A rock bolt 10 according to the present invention may be fitted into the bore hole 42 and a cementous or resinous grout mixture 40 applied to the bore hole 42 by fitting a hose into the bore hole 42 and retracting the hose as the bore hole 42 fills with the grout mixture 40. 8 [0038] As the liquid grout mixture 40 fills the bore hole 42 it surrounds the rock bolt 10 and enters into the means for binding thereby permeating the body 12 of the rock bolt 10 and expelling air from internal voids 44 as it does so. As the grout mixture 40 fills the one or more grooves 26 and hardens it forms one or more continuous fingers entwining about the individual strands 20. Each continuous finger (not shown) interlaces with the continuous finger of an adjacent strand to provide a plurality of helical fingers complementary to the grooves 26 of the means for binding. [0039] The second end portion 16 may have provision of a thrust plate and/or collar for abutting the rock body 46 as is known in the art. Similarly the rock bolt 10 may be spun and/or pre-tensioned during the grouting process or after installation as is required depending on the conditions of the rock body 46 and as is known in the art. [0040] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. 9

Claims (19)

1. A rock bolt, for use in supporting a rock body, the rock bolt comprises a body having an outer portion and a length disposed between two peripheral end portions, wherein the outer portion comprises means for binding arranged to provide an uninterrupted recessed volume for receiving a grout mixture and permitting the grout mixture to pass through, at least in part, a portion of the rock bolt body.

2. A rock bolt according to claim 1, wherein the means for binding comprises a portion of the outer portion having a profiled configuration.

3. A rock bolt according claim 2, wherein profiled configuration comprises a recess or groove disposed upon an outer surface.

4. A rock bolt according to claim 3, wherein the recess or groove comprises a helical configuration.

5. A rock bolt according to any one of the preceding claims, wherein the body comprises a plurality of individual strands wound about a central core strand, the plurality of strands being wound around the core strand with a first orientation.

6. A rock bolt according to claim 5, wherein each individual strand comprises respective means for binding.

7. A rock bolt according to claim 6, wherein respective means for binding is arranged to have a second orientation is arranged in a counter direction to that of the first orientation.

8. A rock bolt according to any one of claims 5 to 7, wherein the outer portion comprises a respective portion of each of the plurality of individual strands. 10

9. A rock bolt according to any one of claims 5 to 8, wherein the central core strand comprises means for binding.

10. A rock bolt according to any one of the preceding claims, wherein the uninterrupted volume enables air to be expelled from internal voids formed within the rock bolt.

11. A rock bolt according to any one of the preceding claims, wherein the body comprises a first peripheral end portion having a tapered configuration.

12. A rock bolt according to claim 5 wherein the body comprises six individual strands wound about a single core strand.

13. A rock bolt according to claim 3 wherein a cross sectional profile of the recess or groove comprises a substantially oblong configuration defined by a recessed surface and plurality of side walls.

14. A rock bolt according to claim 3 wherein a cross sectional profile of the recess or groove comprises a U or V shaped configuration.

15. A rock bolt according to claim 6, wherein the respective means for binding comprises a plurality of recesses or grooves spaced circumferentially about the respective individual strand.

16. A rock bolt according to any one of the preceding claims wherein the means for binding substantially extends along the length of the rock bolt body.

17. A rock bolt according to claim 5 wherein the body comprises one or more bulbous portions spaced along the length of the body, the bulbous portion being defined at least in part by a space separating the individual strands and the central core strand. 11

18. A rock bolt according to any one of the preceding claims wherein the rock bolt is adapted to receive or engage a mesh plate.

19. A rock bolt according to claim 3, wherein the outer portion is arranged such that each adjacent recess or groove is spaced apart by a dimension greater than a width of the recess or groove. 12