AU2015101969A4

AU2015101969A4 - Rock bolt

Info

Publication number: AU2015101969A4
Application number: AU2015101969A
Authority: AU
Inventors: David William Evans; Derek Colin Hird
Original assignee: DSI Underground Australia Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 2014-04-28
Filing date: 2015-04-27
Publication date: 2019-12-12
Anticipated expiration: 2023-04-27
Also published as: AU2015202157A1

Abstract

A rock bolt comprises a longitudinally extending bar (1) having a leading body (5) and a trailing threaded portion (4) for receipt of a drive nut. An exterior surface of the body (5) is defined by a generally cylindrical base surface (6) and an arrangement of ribs (7, 8, 9, 10) formed on, and radially protruding from the base surface (6). The arrangement of ribs includes sets of first and second circumferential ribs (7, 8) formed on opposing first and second sides of a central plane (P). The first and circumferential ribs (7, 8) are longitudinally spaced along the body (5) and are inclined at first and second acute angles respectively relative to a transverse axis (T). In one embodiment a first longitudinal rib (9) extends along a first line of intersection (P1) and separates the set of first circumferential ribs (7) from the set of second circumferential ribs (8). A maximum radial height of the first longitudinal rib (9) is less than a maximum radial height of each of the first and second circumferential ribs (7, 8). In another embodiment, in place of a first longitudinal rib (9), the base surface (6) is continuous across the lines of intersection (P1, P2) between the first and second circumferential ribs (7, 8).

Description

ROCK BOLT

Field [0001] The present invention relates to strata control in civil engineering and mining operations, and in particular relates to a rock bolt for securing the roof or wall of a mine, tunnel or other ground excavation.

Background [0002] One known method of stabilising the wall or roof of an underground mine is to secure a rock bolt into a borehole drilled into the face of the rock to be stabilised. Rock bolts are formed with an elongate load bearing element, commonly formed of a rigid steel bar.

[0003] A known method of installing such a rock bolt involves first drilling a borehole into the rock face. A sausage-like two-component resin filled cartridge is then inserted into the borehole, followed by the rock bolt which pushes the resin filled cartridge toward the blind end of the borehole. The rock bolt is then rotated as it is thrust upwardly to shred the frangible cartridge casing and mix the resin components. Thrusting and rotation of the rock bolt is then ceased, allowing the resin to cure, thereby point anchoring the leading end of the rock bolt toward the blind end of the borehole. The rock bolt is then pre-tensioned, typically by driving a drive nut along a trailing threaded portion of the rock bolt.

Summary of Invention [0004] In a first aspect the present invention provides a rock bolt comprising a longitudinally extending bar having a leading body and a trailing threaded portion for receipt of a drive nut, said rock bolt having a central longitudinal axis, a central plane in which said longitudinal axis lies and a transverse axis extending perpendicular to said central plane;

wherein an exterior surface of said body is defined by a generally cylindrical base surface and an arrangement of ribs formed on, and radially protruding from, said base surface, said arrangement of ribs comprising:

a set of first circumferential ribs each formed on a first side of said central plane, said first circumferential ribs being longitudinally spaced along said body and each extending (9967223_l):dah

2015101969 27 Apr 2015 from a first end adjacent a first line of intersection between said central plane and said exterior surface to a second end adjacent an opposing second line of intersection between said central plane and said exterior surface, each said first circumferential rib being inclined at a first acute angle relative to said transverse axis with the second end of the first circumferential rib being located between the first end of the first circumferential rib and a leading end of said bar;

a set of second circumferential ribs each formed on a second side of said central plane, said second circumferential ribs being longitudinally spaced along said body and each extending from a first end adjacent said first line of intersection to a second end adjacent said second line of intersection, each said second circumferential rib being inclined at a second acute angle relative to said transverse axis with the second end of the second circumferential rib being located between the first end of the second circumferential rib and said leading end of said bar; and a first longitudinal rib extending along said first line of intersection and separating said set of first circumferential ribs from said set of second circumferential ribs; further wherein a maximum radial height of said first longitudinal rib is less than a maximum radial height of each of said first and second circumferential ribs.

[0005] Typically, said first acute angle is at least substantially equal to said second acute angle.

[0006] Typically, said first and second acute angles are equal to about 16 degrees.

[0007] Typically, said maximum radial height of each of said first and second circumferential ribs is between 0.5 mm and 1.5 mm.

[0008] Typically, said maximum height of said first longitudinal rib is less than 0.5 mm.

[0009] Typically, said arrangement of ribs further comprises a second longitudinal rib extending along said second line of intersection and separating said set of first circumferential ribs from said set of second circumferential ribs, a maximum radial height of said second longitudinal rib being less than the maximum height of each of said first and second circumferential ribs.

[0010] Typically, said maximum radial height of said second longitudinal rib is less than 0.5 mm.

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2015101969 27 Apr 2015 [0011] Typically, said first circumferential ribs are longitudinally offset from said second circumferential ribs.

[0012] In a second aspect the present invention provides a rock bolt comprising a longitudinally extending bar having a leading body and a trailing threaded portion for receipt of a drive nut, said rock bolt having a central longitudinal axis, a central plane in which said longitudinal axis lies and a transverse axis extending perpendicular to said central plane;

a set of first circumferential ribs each formed on a first side of said central plane, said first circumferential ribs being longitudinally spaced along said body and each extending from a first end adjacent a first line of intersection between said central plane and said exterior surface to a second end adjacent an opposing second line of intersection between said central plane and said exterior surface, each said first circumferential rib being inclined at a first acute angle relative to said transverse axis with the second end of the first circumferential rib being located between the first end of the first circumferential rib and a leading end of said bar;

a set of second circumferential ribs each formed on a second side of said central plane, said second circumferential ribs being longitudinally spaced along said body and each extending from a first end adjacent said first line of intersection to a second end adjacent said second line of intersection, each said second circumferential rib being inclined at a second acute angle relative to said transverse axis with the second end of the second circumferential rib being located between the first end of the second circumferential rib and said leading end of said bar; and wherein said base surface is continuous across each of said first and second lines of intersection between each of the first and second circumferential ribs.

[0013] In a typical form, said base surface has a flattened strip extending along each of said first and second lines of intersection.

[0014] Typically, said first acute angle is at least substantially equal to said second acute angle.

[0015] Typically, said first and second acute angles are equal to about 16 degrees.

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2015101969 27 Apr 2015 [0016] Typically, said maximum radial height of each of said first and second circumferential ribs is between 0.5 mm and 1.5 mm.

[0017] Typically, said first circumferential ribs are longitudinally offset from said second circumferential ribs.

Brief Description of Drawings [0018] Preferred embodiments of the present invention will now be described, by way of examples, with reference to the accompanying drawings wherein:

[0019] Figure 1 is a front elevation view of a rock bolt according to a first embodiment;

[0020] Figure 2 is a right side elevation view of the rock bolt of Figure 1;

[0021] Figure 3 is a detailed fragmentary front elevation view of the rock bolt of Figure 1;

[0022] Figure 4 is a detailed fragmentary left side elevation view of the rock bolt of Figure 1;

[0023] Figure 5 is a cross-sectional view of the rock bolt of Figure 1 taken at section 5-5 of Figure 3;

[0024] Figure 6 is a partially cross-sectioned front elevation view of a rock bolt installation utilising the rock bolt of Figure 1;

[0025] Figure 7 is a detailed fragmentary front elevation view of a rock bolt according to a second embodiment;

[0026] Figure 8 is a detailed fragmentary left side elevation view of the rock bolt of Figure 7;

[0027] Figure 9 is a cross-sectional view of the rock bolt of Figure 7 taken at section 9-9 of Figure 7;

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2015101969 27 Apr 2015

Description of Embodiments [0028] Referring to Figures 1 to 5 of the accompanying drawings, a rock bolt comprises a longitudinally extending bar 1 that longitudinally extends from a bar leading end 2 to a bar trailing end 3. For ease of reference to various features of the rock bolt, the rock bolt is defined as having a central longitudinal axis L which lies in a central plane P. The rock bolt also has a transverse axis T that extends perpendicular to the central plane P.

[0029] The bar 1 has a trailing threaded portion 4 that extends from the bar trailing end 3. The threaded portion 4 is configured to receive a drive nut in the usual manner. The threaded portion 4 will typically have a length of the order of 150 mm although this may vary. The bar 1 also has a leading body 5 which here extends from the threaded portion 4 to the bar leading end 2. As best depicted in the detailed views of Figures 3 to 5, the body 5 has an exterior surface defined by a generally cylindrical base surface 6 and an arrangement of ribs 7, 8, 9, 10 formed on, and radially protruding from, the base surface 6. The arrangement of ribs 7, 8, 9, 10 is typically formed on the exterior surface by a hot or cold rolling operation on a plain steel bar.

[0030] The bar 1 typically has a nominal diameter of between 12 and 30 mm, with common nominal diameters being 16, 20 and 24 mm. In the particular embodiment depicted, the bar 1 has a nominal diameter of 24 mm which, following the roll forming process, provides the base surface 6 with a diameter of approximately 21.7 mm. The bar 1 will typically have a length of the order of 1.2 to 2.4 m, but this may vary to suit the particular application. In Figures 1 and 2, the rock bolt is depicted with an end fitting in the form of a hexagonal threaded drive nut 50 and dome washer 51 mounted on the threaded portion 4. A plate washer 52 is mounted on the bar 1, engaging the dome washer 51 in a known manner.

[0031] The arrangement of ribs comprises a set of first circumferential ribs 7 formed on a first side of the central plane P, a set of second circumferential ribs 8 formed on an opposing second side of the central plane P and first and second longitudinal ribs 9, 10.

[0032] The first circumferential ribs 7 are longitudinally spaced along the body 5. Typically the first circumferential ribs 7 are evenly longitudinally spaced and in the depicted embodiment are spaced by approximately 11.5 mm. Each first circumferential rib 7 extends from a first end 7a adjacent a first line of intersection Pl between the central plane P and the exterior surface of the (9967223_l):dah

2015101969 27 Apr 2015 body 5 to a second end 7b adjacent an opposing second line of intersection P2 between the central plane P and the exterior surface of the body 5. The first circumferential rib 7 is inclined at a first acute angle a relative to the transverse axis T. The first acute angle a is approximately 16 degrees in the preferred embodiment depicted, but may be modified as desired. Each first circumferential rib 7 is specifically inclined with an orientation such that the second end 7b of the first circumferential rib 7 is located between the first end 7a of the first circumferential rib 7 and the bar leading end 2.

[0033] The second circumferential ribs 8 are also longitudinally spaced along the body 5. Typically the second circumferential ribs 8 are evenly longitudinally spaced and in the depicted embodiment are also spaced by approximately 11.5 mm. Each second circumferential rib 8 extends from a first end 8a adjacent the first line of intersection Pl to a second end 8b adjacent the second line of intersection P2. The second circumferential rib 8 is inclined at a second acute angle, which will typically be equal to the first acute angle a, relative to the transverse axis T. Each second circumferential rib is again inclined in an orientation such that the second end 8b of the second circumferential rib 8 is located between the first end 8a of the second circumferential rib 8 and the bar leading end 2. The first and second circumferential ribs 7, 8 are longitudinally offset from each other in the depicted embodiment. It is also envisaged that the first and second circumferential ribs 7, 8 may be aligned.

[0034] The first longitudinal rib 9 extends longitudinally along the first line of intersection Pl and separates the set of first circumferential ribs 7 from the set of second circumferential ribs 8. The second longitudinal rib 10 extends longitudinally along the second line of intersection P2 and also separates the set of first circumferential ribs 7 from the set of second circumferential ribs 8.

[0035] The ribs 7, 8, 9, 10 are configured such that a maximum radial height of both the first and second longitudinal ribs 9, 10 is less than the maximum radial height of each of the first and second circumferential ribs 7, 8. The maximum radial height of each of the first and second circumferential ribs 7, 8 is typically between 0.5 mm and 1.5 mm, and more typically between 0.8 mm and 1.0 mm. In the specific embodiment depicted, the maximum radial height of each of the first and second circumferential ribs 7, 8 is approximately 1.0 mm. The radial height of the first and second circumferential ribs 7, 8 is substantially constant along the bulk of its length, tapering down to the same height as the first and second longitudinal ribs 9, 10 at the first and (9967223_l):dah

2015101969 27 Apr 2015 second ends 7a, 7b, 8a, 8b respectively. Each of the first and second circumferential ribs 7, 8 typically has a width of approximately 3.0 to 4.0 mm.

[0036] Each of the first and second longitudinal ribs 9, 10 typically has a radial height of less than 0.5 mm and, more preferably, less than 0.3 mm. In the embodiment depicted, each of the first and second longitudinal ribs 9, 10 has a height of approximately 0.5 mm. Each of the first and second longitudinal ribs 9, 10 will typically have a width of approximately 3.0 mm. It can be seen that the first longitudinal rib 9, together with the tapered first end 7a, 8a of each of the first and second circumferential ribs 7, 8 defines a flattened region of the exterior surface of the body 5, whilst the second longitudinal rib 10 together with the tapered second end 7b, 8b of each of the first and second circumferential ribs 7, 8 defines another flattened area of the exterior surface of the body 5.

[0037] Installation of the rock bolt of Figures 1 to 5 will now be described with reference to Figure 6. A borehole 101 is first drilled into a rock face 100. A two-component resin filled cartridge (not depicted) is then inserted into the borehole 101. The bar 1, with the drive nut 50, dome washer 51 and plate washer 52 mounted as discussed above, is inserted into the borehole 101, with the bar leading end 2 leading. The bar 1 is thrust toward the blind end 102 of the borehole 101 utilising a standard rock bolt installation rig, thereby pushing the resin filled cartridge against the borehole blind end 102 and rupturing the frangible casing of the cartridge, releasing resin 103. Whilst the installation rig thrusts the bar 1 towards the borehole blind end 101, it also rotates the drive nut 50. The drive nut 50 will be typically mounted on the threaded portion 4 by way of any of various known mechanisms which prevent relative rotation between the drive nut 50 and threaded portion 4 until the application of a predetermined torque. The rotation of the drive nut 50 thus rotates the bar 1. The ribs 7, 8, 9, 10 act to mix the resin 103 as it flows down the annular space between the body 5 of the bar 1 and the wall of the borehole 101. The present inventors have found that providing the ribs 7, 8, 9, 10 in the configuration described above, particularly having the first and second longitudinal ribs 9, 10 of a lesser height than the first and second circumferential ribs 7, 8, provides a particularly favourable balance between mixing of the resin 103 and retaining the resin 103 toward the borehole blind 102 over a limited length of the body 5 without excess longitudinal consolidating pressure acting on the resin 103 which may result in excess loss of resin into small cracks and voids in the strata.

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2015101969 27 Apr 2015 [0038] After mixing of the resin 103, the rotation of the drive nut 50 is ceased, allowing the resin

103 to cure. Following curing of the resin 103, which will typically occur in a matter of seconds, the drive nut 50 is further rotated by the installation rig, exceeding the predetermined torque required to advance the drive nut 50 along the threaded portion 4, thereby pre-tensioning the bar

1.

[0039] Rather than providing longitudinal ribs 9, 10 of a reduced height, it is also envisaged, and in fact preferred, to eliminate one or both of the first and second longitudinal ribs 9, 10, effectively providing longitudinal ribs of zero height. A modified form of rock bolt according to a second embodiment comprising a rigid bar Γ, is depicted in Figures 7 to 9. Figures 7 to 9 are equivalent to Figures 3 to 5, depicting the rock bolt of the first embodiment.

[0040] The rock bolt of the second embodiment depicted in Figures 7 to 9 is substantially identical to the rock bolt of the first embodiment depicted in Figures 1 to 5, apart from the absence of the first and second longitudinal ribs 9, 10. In the absence of the first and second longitudinal ribs 9, 10, the base surface 6 can be seen to be continuous across each of the first and second lines of intersection Pl, P2, between each of the first and second circumferential ribs 7, 8. In the second embodiment, the first and second ribs 9, 10 are replaced with first and second flattened strips 9’, 10’ of the base surface 6 that extend along the first and second lines of intersection Pl, P2 respectively. The radial height of each of the first and second circumferential ribs 7, 8 tapers down to zero at the first and second ends 7a, 8a, 7b, 8b. Accordingly, equivalent to in the first embodiment, the first and second flattened strips 9’, 10’ and tapered ends of the first and second circumferential ribs 7, 8 define a flattened region of the exterior surface of the body 5 Γ of the bar Γ.

[0041] A person skilled in the art will appreciate other possible modifications and variations to the rock bolts described.

Claims

1. A rock bolt comprising a longitudinally extending bar having a leading body and a trailing threaded portion for receipt of a drive nut, said rock bolt having a central longitudinal axis, a central plane in which said longitudinal axis lies and a transverse axis extending perpendicular to said central plane;

2. The rock bolt of claim 1 wherein said first acute angle is at least substantially equal to said second acute angle.

3. The rock bolt of claim 2 wherein said first and second acute angles are equal to about 16 degrees.

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2015101969 27 Apr 2015

4. The rock bolt of any one of claims 1 to 3 wherein said maximum radial height of each of said first and second circumferential ribs is between 0.5 mm and 1.5 mm.

5. The rock bolt of any one of claims 1 to 4 wherein said maximum height of said first longitudinal rib is less than 0.5 mm.

6. The rock bolt of any one of claims 1 to 5 wherein said arrangement of ribs further comprises a second longitudinal rib extending along said second line of intersection and separating said set of first circumferential ribs from said set of second circumferential ribs, a maximum radial height of said second longitudinal rib being less than the maximum height of each of said first and second circumferential ribs.

7. The rock bolt of claim 6 wherein said maximum radial height of said second longitudinal rib is less than 0.5 mm.

8. The rock bolt of any one of claims 1 to 7 wherein said first circumferential ribs are longitudinally offset from said second circumferential ribs.

9. A rock bolt comprising a longitudinally extending bar having a leading body and a trailing threaded portion for receipt of a drive nut, said rock bolt having a central longitudinal axis, a central plane in which said longitudinal axis lies and a transverse axis extending perpendicular to said central plane;

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2015101969 27 Apr 2015 a set of second circumferential ribs each formed on a second side of said central plane, said second circumferential ribs being longitudinally spaced along said body and each extending from a first end adjacent said first line of intersection to a second end adjacent said second line of intersection, each said second circumferential rib being inclined at a second acute angle relative to said transverse axis with the second end of the second circumferential rib being located between the first end of the second circumferential rib and said leading end of said bar; and wherein said base surface is continuous across each of said first and second lines of intersection between each of the first and second circumferential ribs.

10. The rock bolt of claim 9 wherein said base surface has a flattened strip extending along each of said first and second lines of intersection.

11. The rock bolt of either one of claims 9 and 10 wherein said first acute angle is at least substantially equal to said second acute angle.

12. The rock bolt of claim 11 wherein said first and second acute angles are equal to about 16 degrees.

13. The rock bolt of any one of claims 9 to 12 wherein said maximum radial height of each of said first and second circumferential ribs is between 0.5 mm and 1.5 mm.

14. The rock bolt of any one of claims 9 to 13 wherein said first circumferential ribs are longitudinally offset from said second circumferential ribs.