DOUBLE-WEDGE ROCK BOLT

Abstract

A rock bolt includes a wedge-based expansion mechanism. The expansion mechanism includes a drive wedge arranged to expand an intermediate wedge upon tensioning of the rock bolt, wherein the intermediate wedge is arranged to expand a wedge device attached to an outer tube of the rock bolt. The use of the intermediate wedge enables greater expansion of the rock bolt.

Claims

1. A rock bolt comprising: a central rod; a tubular outer body provided around the central rod along at least a portion of a length of the central rod and; an expansion mechanism arranged for radially expanding the tubular outer body, wherein the expansion mechanism comprises; a first wedge means attached to the central rod; and a second wedge means attached to the outer body between the first wedge means and a trailing portion of the outer body, wherein the first wedge means and the second wedge means are configured such that the first wedge means is arranged to force the second wedge means radially outwards about a longitudinal axis of the rock bolt upon movement of the first wedge means in a first direction towards a trailing portion of the rock bolt to thereby radially expand the outer body, wherein the first wedge means includes a drive wedge attached to the central rod and an intermediate wedge provided around at least a portion of the drive wedge, between the drive wedge and the second wedge means, wherein the drive wedge and the intermediate wedge are configured such that the drive wedge is arranged to radially expand the intermediate wedge upon movement of the drive wedge in the first direction towards a trailing portion of the rock bolt, wherein first wedge means is thus arranged to force the second wedge means radially outwards with the radially expanded intermediate wedge.

2. The rock bolt according to claim 1, wherein the drive wedge is provided with first wedge surfaces, and wherein the intermediate wedge is provided with second wedge surfaces arranged for interfacing the first wedge surfaces of the drive wedge, wherein the first wedge surfaces are planar and wherein the second wedge surfaces are planar.

3. The rock bolt according to claim 1, wherein the drive wedge is provided with first wedge surfaces, and wherein the intermediate wedge is provided with second wedge surfaces arranged for interfacing with the first wedge surfaces of the drive wedge, wherein the first wedge surfaces have a first cross-sectional shape being constant along a length of each respective first wedge surface, wherein the second wedge surfaces have a constant second cross-sectional shape being constant along a length of each respective second wedge surface, and wherein the first cross-sectional shape fits with the second cross-sectional shape.

4. The rock bolt according to claim 3, wherein the first wedge surfaces have a constant cross-sectional shape perpendicular to the longitudinal axis of the rock bolt, and wherein the second wedge surfaces have a constant cross-sectional shape perpendicular to the longitudinal axis of the rock bolt.

5. The rock bolt according to claim 1, wherein the intermediate wedge is provided with one or more outer wedge surfaces having a tapering lead-in portion and a rear portion extending along the longitudinal axis of the rock bolt.

6. The rock bolt according to claim 5, wherein the rear portion is shaped such that when the intermediate wedge is fully expanded the rear portion is aligned with the lead-in portion.

7. The rock bolt according to claim 1, wherein the intermediate wedge is provided with one or more outer wedge surfaces tapered along a majority of a length of the intermediate wedge.

8. The rock bolt according to claim 1, wherein the drive wedge comprises includes at least one shoulder arranged for applying a driving force to the intermediate wedge to force the intermediate wedge in the first direction.

9. The rock bolt according to claim 8, wherein the shoulder is configured to enable the intermediate wedge to move relatively to the drive wedge from an unexpanded position to an expanded position, and configured to provide a stop surface preventing further relative movement of the intermediate wedge onto the drive wedge past the expanded position.

10. The rock bolt according to claim 1, wherein the intermediate wedge is made in one piece.

11. The rock bolt according to claim 1, wherein the intermediate wedge includes a plurality of wedge parts distributed about the longitudinal axis of the rock bolt.

12. The rock bolt according to claim 11, wherein the intermediate wedge comprises resilient retaining means configured to longitudinally align the wedge parts with respect to the longitudinal axis of the rock bolt and configured to allow the wedge parts to radially expand.

13. The rock bolt according to claim 12, wherein the retaining means includes one or more resilient circumferential bands extending about the longitudinal axis of the rock bolt and engaging respective corresponding recesses of the wedge parts.

14. The rock bolt according to claim 1, wherein the intermediate wedge is provided with a shoulder at its rear portion for limiting the axial movement of the intermediate wedge along the longitudinal axis of the rock bolt by engagement of the second wedge means.

15. The rock bolt according to claim 1, wherein the intermediate wedge and the drive wedge are configured such that at least a portion of the intermediate wedge upon being expanded by the drive wedge abuts the outer body to thereby radially expand the outer body upon further expansion of the intermediate wedge.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0039] FIG. 1 shows a prior art rock bolt.

[0040] FIGS. 2a-2b show a leading portion of a rock bolt according to a first embodiment of the present disclosure (central rod shown in dotted lines.

[0041] FIG. 2b shows the rock bolt in cross-section.

[0042] FIGS. 3a-3b show a first embodiment of the intermediate wedge of the rock bolt of FIGS. 2a-2b.

[0043] FIG. 3b show the intermediate wedge in cross-section.

[0044] FIG. 4 show an alternative embodiment of the intermediate wedge shown in FIGS. 3a-3b (multi-part embodiment with a resilient circumferential band to keep the parts aligned.

[0045] FIG. 5 shows an example of cross-sectional shapes of the interfacing wedge surface of the drive wedge and the intermediate member. Similar interfacing wedge surfaces may be provided between the intermediate member and the second wedge means.

[0046] FIG. 6 shows an alternative embodiment of the intermediate wedge provided with a shoulder for limiting its movement relative to the second wedge means along the longitudinal axis of the rock bolt.

[0047] FIGS. 7a-c show perspective views of an embodiment of the rock bolt with a full view in FIG. 7a, a section view in FIG. 7b and the section view with the central rod hidden in FIG. 7c.

[0048]

TABLE-US-00001 1 rock bolt 2 central rod 3 shoulder of intermediate wedge 4 tubular outer body 5 retaining means 6 first wedge means 7 second wedge means 8 drive wedge 9 intermediate wedge 10 first wedge surfaces 11 second wedge surfaces 12 shoulder of drive wedge 13 lead-in portion 14 rear portion 15 longitudinal axis of rock bolt 16 wedge parts 17 outer wedge surfaces 18 trailing portions 19 rear portion of intermediate wedge S1 first cross-sectional shape S2 second cross-sectional shape D first direction L1 shorter length of outer wedge surface of intermediate wedge L2 longer length of outer wedge surface of intermediate wedge

DETAILED DESCRIPTION

[0049] A rock bolt 1 according to an exemplary embodiment will hereinafter be described with reference to the appended drawings.

[0050] As shown in FIG. 2, the rock bolt 1 comprises a central rod 2, a tubular outer body 4 provided around the central rod 2 along at least a portion of the length of the central rod 2. The rock bolt 1 further comprises an expansion mechanism for radially expanding the tubular outer body 4. In this embodiment, the expansion mechanism is provided at a leading portion of the rock bolt 1 but in other embodiments the expansion mechanism could alternatively be provided further back along the length of the rock bolt 1. The leading portion of the rock bolt 1 is the portion of the rock bolt 1 first inserted in the bore upon installation of the rock bolt 1. The expansion mechanism comprises a first wedge means 6 attached to the central rod 2, and a second wedge means 7 attached to the outer body 4 between the first wedge means 6 and a trailing portion 18 of the outer body 4.

[0051] The first wedge means 6 and the second wedge means 7 are configured such that the first wedge means 6 is able to force the second wedge means 7 radially outwards about the longitudinal axis 15 of the rock bolt 1 upon movement of the first wedge means 6 in a first direction D towards the trailing portion 18 of the rock bolt 1 to thereby radially expand the outer body 4. The expansion is achieved by the mutually cooperating inclined wedge surfaces of the first and the second wedge means 6, 7 forcing the second wedge means radially outwards as the first wedge means and second wedge means are moved closed to each other about the longitudinal axis of the rock bolt 1.

[0052] According to the present disclosure, the first wedge means 6 comprises a drive wedge 8 attached to the central rod 2 and an intermediate wedge 9 provided around at least a portion of the drive wedge 8, between the drive wedge 8 and the second wedge means 7. The drive wedge 8 and the intermediate wedge 9 are configured such that the drive wedge 8 is able to radially expand the intermediate wedge 9 upon movement of the drive wedge 8 in the first direction D towards the trailing portion 18 of the rock bolt 1, wherein first wedge means 6 is thus able to force the second wedge means 7 radially outwards with the radially expanded intermediate wedge 9.

[0053] Although the first wedge means 6 is described as attached to the central rod 2, it is to be understood that it is only the drive wedge 8 of the first wedge means 6 that is attached to the central rod 2 and that the intermediate wedge 9 is movable relative to the central rod 2 but functionally associated with the drive wedge 8 so that they work together. In other words, the first wedge means 6 is anchored to the central rod 2.

[0054] The first wedge means 6 is expanded by moving the drive wedge 8 towards the trailing portion 18 of the rock bolt 1. Such movement is in this embodiment achieved by rotation of the central rod 2 achieved by rotating the blind nut shown in FIGS. 7a-c but in other embodiments (not shown in figures) the drive wedge 8 could alternatively be moved without rotating the central rod (i.e. without moving the drive wedge 8 relatively the central rod 2) by moving the central rod 2 towards the trailing portion 18 of the outer body 4, such as by using another type of nut allowing the nut to pull the central rod 2 upon rotation of the nut, i.e. not a blind nut.

[0055] The drive wedge 8 is provided with first wedge surfaces 10, and wherein the intermediate wedge 9 is provided with second wedge surfaces 11 for interfacing the first wedge surfaces 10 of the drive wedge 8. The first wedge surfaces 10 are planar and the second wedge surfaces 11 are planar. Here, planar is to be construed as having a portion extending in a respective plane, said portion being the portion of each respective wedge surface active for transmitting wedging force to the corresponding wedge surface of the other one of the first wedge surfaces 10 and the second wedge surfaces 11. Other portions of the drive wedge 8 and of the intermediate wedge 9 may be extend outside of the respective plane.

[0056] In alternative embodiments, instead of being planar the first wedge surfaces 10 may have a first cross-sectional shape S1 being constant along the length of each respective first wedge surface 10, wherein the second wedge surfaces 11 have a constant second cross-sectional shape S2 being constant along the length of each respective second wedge surface 11, and wherein the first cross-sectional shape S1 fits with the second cross-sectional shape S2. An example of such cross-sectional shapes S1, S2 are shown in FIG. 5, wherein the first wedge surfaces 10 have constant cross-sectional shape perpendicularly to the longitudinal axis of the rock bolt 1, and wherein the second wedge surfaces 11 have constant cross-sectional shape perpendicularly to the longitudinal axis of the rock bolt 1. The constant cross-sectional shape can for example define a planar surface or a surface with arcuate cross-sectional shape.

[0057] As shown in FIGS. 3a-3b, the intermediate wedge 9 is provided with one or more outer wedge surfaces 17 comprising a tapering lead-in 13 portion and a rear 14 portion extending along the longitudinal axis 15 of the rock bolt 1. The rear portion 14 is shaped such that when the intermediate wedge 9 is fully expanded the rear portion 14 is aligned with the lead-in portion 13 but may alternatively in other embodiments be shaped not to align with the lead-in portion 13. In yet an alternative embodiment, the intermediate wedge 9 is provided with one or more outer wedge surfaces 17 tapered along a majority of the length of the intermediate wedge 9. The length of the outer wedge surfaces 17 thus increases from a shorter length L1 to a longer length L2 upon expansion of the intermediate wedge 9, as shown in FIGS. 3a and 3b.

[0058] As shown in FIG. 3a, the drive wedge 8 comprises at least one shoulder 12 for applying driving force to the intermediate wedge 9 to force the intermediate wedge 9 in the first direction D. The shoulder 12 is configured to enable the intermediate wedge 9 to move relatively the drive wedge 8 from an unexpanded position to an expanded position, and configured to provide a stop surface preventing further relative movement of the intermediate wedge 9 onto the drive wedge 8 past the expanded position. If no such shoulder 12 is provided on the drive wedge 8, further expansion of the intermediate wedge 9 would be possible, thereby enabling further expansion of the second wedge means 7.

[0059] The intermediate wedge 9 is made in one piece but may alternatively in other embodiments, such as the one shown in FIG. 4, comprise a plurality of wedge parts 16 (two wedge parts in the FIG. 4 embodiment) distributed about the longitudinal axis 15 of the rock bolt 1. When made in one piece, the one piece could be made by any suitable manufacturing method, such as by molding or by attaching together multiple pieces such as by welding them to form one unitary piece.

[0060] When using a plurality of wedge parts 16, the intermediate wedge 9 may preferably comprise resilient retaining means 5 configured to longitudinally align the wedge parts with respect to the longitudinal axis of the rock bolt 1 and configured to allow the wedge parts 16 to radially expand. The retaining means comprises one or more resilient circumferential bands extending about the longitudinal axis 15 of the rock bolt and engaging respective corresponding recesses of the wedge parts 16, said resilient band(s) for example being O-rings.

[0061] In an alternative embodiment of the intermediate wedge 9 it is provided with a shoulder 3 at its rear portion for limiting the axial movement of the intermediate wedge 9 along the longitudinal axis 15 of the rock bolt 1 by engagement of the second wedge means 7.