AU753104B2

AU753104B2 - Rock bolt anchor

Info

Publication number: AU753104B2
Application number: AU53498/99A
Authority: AU
Inventors: Mieczyslaw Rataj
Original assignee: Dywidag Systems International Pty Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 1998-10-07
Filing date: 1999-10-06
Publication date: 2002-10-10
Anticipated expiration: 2019-10-06
Also published as: AU5349899A

Description

S F Ref: 477691

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPEIFICATION FOR A STANDARD PATENT

ORIGINAL

113 fr.

Name and Address of Applicant: \ZW a. y c .c The ANI Corporation Limited Leyel 5, Merlin Centrc f 235 Pyrmont Strct V b 2 Pyrfment NSN-200

AUSTRALIA

Mieczyslaw Rataj Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Rock Bolt Anchor Actual Inventor(s): Address for Service: Invention Title: ASSOCIATED PROVISIONAL APPLICATION DETAILS [313 Application No(s) [33] Country PP6362

AU

[32] Application Date 07/10/98 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815 1 Rock Bolt Anchor Field of the Invention The invention relates to improvements in rock bolting, and in particular relates to an improved rock bolt anchor which enables installation of a rock bolt in a hole already filled with grout.

Background of the Invention The roofs in underground mines are secured using rock bolts installed in holes in the roof, with the upper end of the bolt inserted in the hole being secured to the rock by a chemical or mechanical anchor. A collar assembly at the lower end of the bolt engages the rock at the base of the hole to stabilise the roof. To improve load transfer between the bolt and rock, the hole is often filled with grout after the bolt has been installed. The g post-grouting operation is, however, very complicated and requires either a hollow bolt or breather tube attached to the bolt to provide a passage for expulsion of air from the hole in the rock as the grout is injected.

The post-grouting of holes is often completely forgotten during the rock bolting •installation process, or not perform effectively, and it is particularly difficult to control the quality of the post-grouting aspect of the rock bolt installation. Further, the through hole of a hollow bolt results in a thin side wall in the hollow bolt which is weak and thus prone to failure. A pre-grouting system whereby grout is injected into the hole before the rock bolt, with the rock bolt inserted into the hole through the grout, has been suggested.

"A pre-grouting system which has been introduced consists of a rock bolt with a slot and wedge arrangement. This slot and wedge arrangement does not, however, provide reliable anchorage strength, especially in weak rock. Another disadvantage of this system is the requirement to drill rock holes of a precise length such that the end of the hole will engage the wedge, pushing it into the cooperating slot of the bolt.

One form of mechanical anchor which has been utilised in a post-grouting system is known as an expansion shell. In this system a conical shell plug is threaded onto the end of the rock bolt, apex first. A pair of opposing shell leaves having a reverse taper as compared to the shell plug engage the plug on opposing sides thereof. A bail joins the narrow end of the tapered leaves and passes over the end of the bolt at the thick end of the shell plug. On installation of the bolt and expansion shell assembly into a rock bolt hole, the bolt is rotated such that the bolt will thread through the plug, exposing the [R:\LIBLL]08360.doc:GJG bolt end which engages the bail to drive the shell leaves along the tapered sides of the plug. The leaves thus move radially outwardly as a result of the taper and thereby wedge between the rock and shell plug. The conical form of the shell plug, however, prevents the expansion shell assembly from being used in a pre-grouting system, as the conical shell plug, which largely fills the cross section of the rock bolt hole, prevents grout in the rock bolt hole from being extruded past the shell assembly and out the hole, thereby largely preventing the bolt and shell assembly from being driven through the grout. The flat leading face presented by the shell assembly entering the hole further inhibits passage of the assembly through the grout.

Object of the Invention It is the object of the present invention to overcome or substantially ameliorate at least some of the above disadvantages.

Summary of the Invention There is disclosed herein an expansion shell plug for use with a bail and shell 15 leaves arrangement of a rock bolt expansion shell anchor assembly, said expansion shell plug comprising: a threaded hole extending longitudinally between first and second ends of said plug for receiving a threaded rock bolt, a pair of laterally opposing engagement surfaces tapering toward said plug first 20 end, and retaining means at said plug second end for retaining said bail with said shell leaves aligned with said engagement surfaces, wherein a profile of said expansion plug as viewed along the axis of said threaded hole has a generally elongated form with a maximum width measured in a direction extending between said engagement surfaces being greater than a maximum thickness in a perpendicular direction.

Preferably, said expansion shell plug further comprises a pair of opposing shoulder surfaces tapering from adjacent said engagement surfaces to said plug second end.

Typically, said retaining means comprises a pair of slots extending along said shoulder surfaces.

Preferably, said maximum width is at least double said maximum thickness.

[R:\LIBLL]08360.doc:GJG There is further disclosed herein a rock bolt expansion shell anchor assembly comprising: an expansion shell plug having a threaded hole extending longitudinally between first and second ends of said plug for receiving a threaded rock bolt, and a pair of laterally opposing engagement surfaces tapering toward said plug first end; and a pair of opposing tapered shell leaves joined at their respective narrow ends via a bail, said leaves having outwardly facing surfaces adapted to engage a rock bolt hole wall and inwardly facing surfaces adapted to engage said expansion plug engagement surfaces with said bail passing over said expansion plug threaded hole at said plug second end and engaging a retaining means provided at said plug second end to retain said shell leaves in alignment with said engagement surfaces, wherein a profile of said expansion plug as viewed along the axis of said **threaded hole has a generally elongated form with a maximum width measured in a 'direction extending between said engagement surfaces being greater than a maximum 15 thickness in a perpendicular direction.

Preferably a generally conical member is disposed centrally on said bail arm and pointing generally away from said leaves.

Preferably, said expansion shell plug further comprises a pair of shoulder surfaces tapering from adjacent said engagement surfaces to said plug second end.

Preferably, said maximum width is at least double said maximum thickness.

There is still further disclosed herein, in combination, said rock bolt expansion shell anchor assembly and a rock bolt threadingly received in said threaded hole.

Brief Description of the Drawings Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is an exploded perspective view of a rock bolt expansion shell anchor assembly and rock bolt.

Figure 2 is a perspective view of an alternate expansion shell plug of a rock bolt expansion shell anchor assembly.

Figure 3 is a side elevation view of a conical member for positioning on the bail a rock bolt expansion shell anchor assembly.

[R:\LIBLL]08360.doc:GJG Figure 4 is a front elevation view of a rock bolt expansion shell assembly according to a further embodiment engaged with a rock bolt.

Detailed Description of the Preferred Embodiments With reference to Figure 1, the expansion shell plug 2 of a first embodiment has a threaded hole 15 extending longitudinally between first and second ends 16, 17 of the plug 2 for receiving a threaded rock bolt 1. The plug 2 is provided with a pair of laterally opposing engagement surfaces 8, 9 which taper toward the plug first end 16. A pair of opposing shoulder surfaces 10, 11 extend from adjacent the end of the engagement surfaces 9, 8 respectively and taper toward the plug second end 17. Retaining means, here in the form of a pair of slots 13, 14 extending along the shoulder surfaces 10, 11, are provided at the plug second end 17 for retaining the bail 4 of a bail and shell leaves arrangement 18 as will be further discussed below.

The profile of the shell plug 2, as viewed along the axis of the threaded hole has a generally elongated form, with a maximum width measured in a direction extending between the engagement surfaces 8, 9 being greater than the maximum thickness in a perpendicular direction, measured between plug side wall surfaces 19, 20. Here the plug side wall surfaces 19 and 20 are flat, providing the plug with an elongated flat profile as opposed to the prior art conical expansion shell plugs which have a circular cross section.

Reducing the thickness of the plug profile as compared to the width, which will be generally fixed according to the size of rock bolt hole, reduces the overall cross sectional area of the shell plug.

It is preferred that the thickness of the profile, being the distance separating the side walls 19 and 20, is reduced at least such that the maximum width, measured between the ends of the engagement surfaces 8, 9 adjacent the shoulders 10, 11, is at least double the maximum thickness.

In an alternative embodiment of shell plug 2' as depicted in Figure 2, the plug side walls 19', 20' are contoured so as to minimise the cross sectional area of the profile of the shell plug 2'.

The bail and shell leaves arrangement 18, also depicted in Figure 1, is of a substantially conventional configuration, having a pair of opposed tapered shell leaves 3, joined at their respective narrow ends via a bail 4. The leaves have outwardly facing surfaces 21, 22 provided with serrations in the usual manner to engage a rock bolt hole wall when the assembly is installed. Inwardly facing surfaces 6, 7 of the leaves 3, 5 have R:LI B LL]08360.doc:GJG a contour matching that of the plug engagement surfaces 8, 9 in the usual manner to enable engagement with the expansion plug engagement surfaces 8, 9.

Prior to installation, the shell plug 2 is threaded onto the end of the threaded rock bolt 1 and the bail and shell leaves arrangement 18 located over the shell plug 2 with the shell leaves 3, 5 aligned with and engaging the shell plug engagement surfaces 8, 9. The bail 4 passes directly over the end of the bolt 1 in the threaded hole 15 at the plug second end 17. The angled sections 23, 24 of the bail 4 engage the slots 14, 13 provided in the plug shoulders 10, 11. Relative rotation of the bail and shell leaves arrangement 18 and plug 2 is thus inhibited, ensuring the shell leaves 3, 5 remain in alignment and engaged with the plug engagement surfaces 8, 9. The taper of the plug engaging surfaces 8, 9 and of the shell leaves 3, 5 will generally match in the usual manner, such that the outwardly facing surfaces 21, 22 of the shell leaves are disposed parallel to the axis of the threaded hole 15 and to the rock bolt hole wall.

The rock bolt 1 with the expansion shell anchor assembly is then inserted into a .15 rock bolt hole which has been filled with fresh grout. With the reduced thickness of the shell plug 2, grout displaced by the assembly can readily pass back down through the hole past the plug side wall surfaces 19, 20. The tapered shoulder surfaces 10, 11 of the plug allow for easier insertion of the assembly into the rock hole if there is any misalignment S•between the bolt 1 and the rock bolt hole, which is a regular occurrence due to displacement of the machine installing the rock bolt 1. The tapered shoulder surfaces 11 also provide less resistance through the grout than the equivalent flat surface provided on typical prior art shell plugs.

Additionally or alternatively, to enhance simple installation in the case of misalignment, and to reduce the resistance to penetration of the assembly through the grout, a conical member 12 may be attached to or integrally formed with the bail 4. Such a conical member would be located generally centrally of the bail and pointing in a direction generally away from the shell leaves 3, 5. If the conical member 12 is not formed with the bail 4, a possible method of attaching the conical member 12 is depicted in Figure 3. Here a clip member 25 is formed at the base of the conical member 12 for clipping on to the central section of the bail 4.

When the bolt and expansion shell anchor assembly have been fully inserted into the hole the bolt 1 is turned by turning a nut 3 which is located on the bolt 1 utilising a known mechanism providing resistance between the nut 3 and bolt 1, ensuring the bolt I turns with movement of the nut rather than the nut screwing on to the bolt. With the shell [R:\LIBLL]08360.doc:GJG leaves 3 at least lightly engaging the wall of the rock bolt hole, the shell plug 2 will be restrained from rotation and hence the rock bolt 1 will be screwed through the threaded hole 15, gradually protruding from the plug second end 17 and engaging the bail 4.

Further rotation of the bolt 1 will displace the bail and shell leaves assembly 18 further into the hole in the usual manner, driving the shell leaves 3, 5 along the plug engagement surfaces 9, 8 and thereby radially displacing the shell leaves 3, 5 to wedge between the rock wall and the plug 2 under action of the tapering of the leaves 3, 5 and engagement surfaces 8, 9.

An effective anchoring of the upper end of the rock bolt 1 is thus achieved, irrespective of the accuracy of the length of the rock bolt hole and avoiding the requirement for post-grouting of the hole.

A rock bolt expansion shell assembly according to a further embodiment is depicted in Figure 4. This assembly is arranged in the same general manner as the first embodiment except that the angled sections 123, 124 of the bail 104 and the tapered 15 shoulder surfaces 110, 111 of the plug 102 taper at a shallower angle, here approximately 300 to the longitudinal axis. This shallower taper angle presents a more streamlined leading portion of the assembly that can be more readily pushed through the fresh grout in S* the rock bolt hole.

In this embodiment, the tapered shoulder surfaces 110, 111 do not extend to such 20 a degree that they meet the plug second end 117 immediately adjacent the threaded hole 115 as per the first embodiment, and the angled bail sections 123, 124 extend beyond the shoulder surfaces 110, 111. Accordingly the bail 104 protrudes beyond the plug second end 117 prior to engagement with the bolt 101, typically by about 10 to 15 mm. The central section of the bail 104 arranged perpendicularly to the longitudinal axis has a width equivalent to that of the bolt 101 and is engaged thereby when the bolt is threaded through and beyond the threaded hole 115 as depicted in Figure 4. If desired, the conical member 12 of Figure 3 can be secured to the bail 104 to further streamline the leading portion of the assembly for passing through the fresh grout.

Various modifications to the form of the shell plug and shell bail and leaves arrangement will be apparent to the person skilled in the art. One such further modification would be a reduction in the width of the shell leaves, however the use of the standard form of bail and shell leaves arrangement has been found to be quite sufficient when combined with the reduced thickness plug.

[R:\LI BLL]08360.doc:GJG

Claims

1. An expansion shell plug for use with a bail and shell leaves arrangement of a rock bolt expansion shell anchor assembly, said expansion shell plug comprising: a threaded hole extending longitudinally between first and second ends of said plug for receiving a threaded rock bolt, a pair of laterally opposing engagement surfaces tapering toward said plug first end, and retaining means at said plug second end for retaining said bail with said shell leaves aligned with said engagement surfaces, wherein a profile of said expansion plug as viewed along the axis of said threaded hole has a generally elongated form with a maximum width measured in a direction extending between said engagement surfaces being greater than a maximum thickness in a perpendicular direction.

2. The expansion shell plug of claim 1, further comprising a pair of 15 opposing shoulder surfaces tapering from adjacent said engagement surfaces to said plug second end.

3. The expansion shell plug of claim 2, wherein said retaining means comprises a pair of slots extending along said shoulder surfaces.

4. The expansion shell plug of any one of claims 1 to 3, wherein said maximum width is at least double said maximum thickness.

A rock bolt expansion shell anchor assembly comprising: an expansion shell plug having a threaded hole extending longitudinally between first and second ends of said plug for receiving a threaded rock bolt, and a pair of laterally opposing engagement surfaces tapering toward said plug first end; and a pair of opposing tapered shell leaves joined at their respective narrow ends via a bail, said leaves having outwardly facing surfaces adapted to engage a rock bolt hole wall and inwardly facing surfaces adapted to engage said expansion plug engagement surfaces with said bail passing over said expansion plug threaded hole at said plug second end and engaging a retaining means provided at said plug second end to retain said shell leaves in alignment with said engagement surfaces, wherein a profile of said expansion plug as viewed along the axis of said threaded hole has a generally elongated form with a maximum width measured in a direction extending between said engagement surfaces being greater than a maximum thickness in a perpendicular direction. [R:\LIBLL]08360.doc:GJG

6. The anchor assembly of claim 5, wherein a generally conical member is disposed centrally on said bail arm and pointing generally away from said leaves.

7. The anchor assembly of either of claims 5 and 6, wherein said expansion shell plug further comprises a pair of shoulder surfaces tapering from adjacent said engagement surfaces to said plug second end.

8. The anchor assembly of claim 7, wherein said retaining means comprises a pair of slots extending along said shoulder surfaces, said bail being provided with angled sections adapted to engage said slots.

9. The anchor assembly of claim 8, wherein said angled sections extend beyond said shoulder surfaces such that said bail protrudes beyond said plug second end.

The anchor assembly of any one of claims 5 to 9, wherein said maximum width is at least double said maximum thickness.

11. In combination, a rock bolt expansion shell anchor assembly according to any one of claims 5 to 10 and a rock bolt threadingly received in said threaded hole.

12. An expansion shell plug for use with a bail and shell leaves arrangement of a rock bolt expansion shell anchor assembly, said expansion shell plug being substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawings.

13. A rock bolt expansion shell anchor assembly, substantially as hereinbefore described with reference to Figure 1 or Figures 1 and 3 of the accompanying drawings. Dated 1 October, 1999 The AN Corporatin Limited. Patent Attorneys for the pplicant/Nominated Persont SPRUSON FERGUSON fR:\LI BLL]08360.doc:GJG