ROCK BOLT INSTALLATION

Abstract

A rock bolt installation for a hole formed in a rock strata includes a cable bolt and a friction bolt disposed within the hole. The cable bolt can be embedded in grout, cement or resin. The cable bolt extends further into the hole than the friction bolt. The cable bolt and the friction bolt are disposed in an overlapping relationship within the hole and are connected structurally in the overlap to each other and to the internal wall of the hole.

Claims

1. A rock bolt installation comprising: a cable bolt and a friction bolt, the cable bolt and the friction bolt being arranged to be disposed within a hole formed in a rock strata, the cable bolt extending further into the hole than the friction bolt, wherein the cable bolt and the friction bolt are disposed in an overlapping relationship within the hole and are connected structurally in an overlap to each other and to an internal wall of the hole.

2. The rock bolt installation according to claim 1, wherein the cable bolt is embedded in grout, cement or resin.

3. The rock bolt installation according to claim 1, wherein the friction bolt is a rigid bolt or a flexible cable bolt.

4. The rock bolt installation according to claim 1, wherein a ratio of an extension of the friction bolt into the hole compared to an extension of the cable bolt into the hole, including the overlap between respective bolts being between 1/20 to of a total length of the hole or cable.

5. The rock bolt installation according to claim 4, wherein a cable of the cable bolt has a length of 4 m to 20, and wherein the friction bolt having has a length of 1 m to 4 m.

6. The rock bolt installation according to claim 1, wherein the overlap between the friction bolt and the cable bolt is at least equal to or greater than a critical embedment length.

7. The rock bolt installation according to claim 1, wherein a structural connection is provided by the grout interposed between the cable bolt and the friction bolt and the internal wall of the hole, or by the friction bolt clamping the cable of the cable bolt against the internal wall of the hole, or by a combination of the grout interposed between the cable bolt and the friction bolt and the internal wall of the hole and the friction bolt clamping the cable of the cable bolt against the internal wall of the hole.

8. The rock bolt installation according to claim 7, wherein the friction bolt clamps a cable of the cable bolt in a section of the overlap between the cable and friction bolts at a leading end of the friction bolt.

9. The rock bolt installation according to claim 8, wherein the friction bolt includes an expander mechanism at a leading end of a bar, rod or cable of the friction bolt, and wherein grout is disposed about the expander mechanism and in spaces between the hole and the bar, rod or cable of the friction bolt and in spaces between the friction bolt and the cable of the cable bolt.

10. The rock bolt installation according to claim 1, wherein the friction bolt includes an expander mechanism arranged to clamp against the internal wall of the hole, and wherein expander elements of the expander mechanism are shaped to accommodate a cable of the cable bolt so that the cable can extend past or through the expander mechanism in either axial direction within the hole.

11. The rock bolt installation according to claim 10, wherein the expander elements of the expander mechanism engage the cable of the cable bolt to clamp the cable to the internal wall of the hole.

12. The rock bolt installation according to claim 10, wherein the expander elements of the expander mechanism are arranged to accept or accommodate the cable of the cable bolt, the expander elements including a groove, slot or scallop for the cable to enter.

13. The rock bolt installation according to claim 1, wherein the friction bolt includes an expander mechanism is arranged to clamp against the internal wall of the hole, the expander elements of the expander mechanism including a serrated surface for engaging the internal wall of the hole.

14. The rock bolt installation according to claim 1, wherein the friction bolt is a rigid tube, and wherein the cable bolt extends through the tube, the tube being substantially filled with grout around the cable bolt, a wall of the tube including one or more internal deformations arranged for keying with the grout.

15. A rock bolt comprising: a tendon having a leading and trailing end; an expander mechanism disposed at the leading end; and an anchor mechanism disposed at the trailing end, the expander mechanism including expander elements that are expandible into engagement with an internal wall of a hole, the expander elements being arranged to accept or accommodate a cable of a cable bolt, wherein the expander elements include a groove, slot or scallop for the cable to enter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which:

[0053] FIG. 1 is a cross-sectional view of a rock bolt installation according to one embodiment of the invention.

[0054] FIG. 2 is a cross-sectional view through taken through the expander mechanism of the rock bolt installation of FIG. 1.

[0055] FIG. 3 is an end view of an expander element of the expander mechanism of the rock bolt installation of FIG. 1.

[0056] FIG. 4 is a cross-sectional view of a section of a rock bolt installation according to another embodiment of the invention.

[0057] FIG. 5 is a cross-sectional view of a rock bolt installation according to a second embodiment of the invention.

[0058] FIGS. 6 and 7 are cross-sectional views respectively through A-A and B-B of FIG. 5.

DETAILED DESCRIPTION

[0059] FIG. 1 is a cross-sectional view of a rock bolt installation 10 according to one embodiment of the invention. The installation 10 includes an elongate cable bolt 12 which is shown as a multi strand, single cable in FIG. 1. The cable bolt 12 can have any number of strands, or alternatively, it could be a single strand cable.

[0060] The cable bolt 12 is installed within a hole 14 that has been drilled into a rock body or rock strata 16 to a predetermined depth or length, for example to a depth of about 10 m. FIG. 1 illustrates only a short portion of the total length of the hole 14 along with only a short portion of the cable bolt 12. In practice, the cable bolt 12 would extend for substantially the full length of the hole 14.

[0061] The cable bolt 12 is anchored within the hole 14 by grout G. This will be described in more detail hereinafter, but the cable bolt 12 is formed as a single cable with no fittings at either end of the cable or along the length of the cable. Suitable fittings could be applied, such as will facilitate better anchoring or purchase of the cable bolt 12 within the grout G, while the cable of the cable bolt 12 could be formed with widened or expanded sections known as bulbs to likewise improve the anchor or purchase of the cable within the grout G within the hole 14. Suitable fittings are known in the art.

[0062] The installation 10 further includes a friction bolt 18 that extends adjacent to or in overlapping relationship with the cable bolt 12 and which has a shank 19 and leading and trailing ends 20 and 22. The trailing end 22 of the friction bolt 18 is adjacent the trailing end 24 of the cable bolt 12. The leading end of the cable bolt 12 is not visible in FIG. 1. The friction bolt 18 can be alternatively called a link bolt as it links to the cable bolt 12 via a structural connection as described below.

[0063] The friction bolt 18 has an expander mechanism 26 at the leading end 20, which is threadably connected to the threaded end 30 of the shank 19. The friction bolt 18 has a nut 28 at the trailing end 22. The nut 28 is a blind nut that is threaded onto the trailing end 22. In other embodiments, the nut 28 can be formed integrally with the end of the shank 19. The nut 28 is threaded onto the threaded end of the shank 19 until the end of the shank 19 engages the inner end of the opening in the nut 28, so that further rotation of the nut 28 rotates the shank 19. Rotation of the shank 19 will activate the expander mechanism 26.

[0064] A rock plate 32 is interposed between the nut 28 and the face 34 of the rock strata 16 into which the hole 14 is drilled. The rock plate 32 supports the rock strata 16 about the opening of the hole 14 and applies pressure against the face of the rock strata 16 as the nut 28 is rotated and the expander mechanism 26 is activated. As will be explained, load applied to the rock plate 32 will be transferred upwards via the friction bolt 18 and into higher strata above the friction bolt via the cable bolt 12. This transfer relies on the structural connection between the cable bolt 12 and the friction bolt 18, and the wall 15. While not illustrated, safety mesh can be secured broadly across the rock face by clamping the mesh between the nut 28 and the rock plate 32 of multiple friction bolts 18.

[0065] The expander mechanism 26 comprises a central wedge 36 and three leaves or elements 38. The expander mechanism is illustrated in FIG. 2 in end view and shows the three elements 38 spaced equidistantly about the central wedge 36. FIG. 2 also shows the bail 40 (which is also shown in FIG. 1) which overlies the top end of the threaded end 30 of the shank 19 and which has three arms that connect to the upper edges of the elements 38. The bail 40 is not connected to the central wedge 36. The bail 40 secures the elements 38 against movement along the longitudinal axis of the shank 19 and so the elements 38 are secured within the hole 14 at a generally constant axial position. The central wedge 36 is threadably connected to the threaded end 30 of the shank 19. The central wedge 36 can be restrained against rotation with the shank 19 simply by frictional engagement with the elements 38, or the central wedge 36 can be made non-circular with the elements 38 having complementary mating surfaces, including mating keyways. By rotating the nut 28 in the same direction that it threads onto the shank 19, the central wedge 36 can be shifted axially or longitudinally downwardly on the threaded end 30 relative to the elements 38 and by that movement, the elements can be forced radially into firm engagement with the wall 15 and with the cable bolt 12 as shown in FIG. 1.

[0066] It can be seen from FIGS. 1 and 2, that the cable bolt 12 and the friction bolt 18 are disposed within the hole 14 in adjacent, side-by-side or overlapping relationship. Also apparent from FIGS. 1 and 2, is that the hole 14 is filled with grout G which is shown by the random dotted pattern which is applied to the spaces or voids within the hole 14 that are otherwise not filled by the cable bolt 12 or the friction bolt 18.

[0067] The installation method is to first drill the hole 14 into the rock strata 16 and following that to pump the grout G into the hole. The grout G can be delivered by a grout hose that is fed to the back or inner end of the hole 14 and which is retracted as the grout G is progressively pumped into the full length of the hole 14. Following this, the cable bolt 12 can be fed into the hole 14. The cable bolt 12 would normally be fed from a storage reel which is attached to installation machinery. Once the cable bolt 12 has been installed within the hole 14, the friction bolt 18 can be installed. Installation machinery can be used to push the friction bolt 18 into the hole 14 and through the grout G to the point at which the friction bolt 18 is almost fully inserted into the hole 14. The installation of the friction bolt 18 can include percussion driving, to ensure grout flow fully about the bolt 18 and to the trailing end 22 of the bolt 18.

[0068] The nut 28 is then tightened, expanding the expander mechanism 26 and pushing the rock plate 32 firmly against the face 34 of the rock strata 16. At this stage, the friction bolt 18 is fully installed and operational and is providing reinforcement or ground support for the length of the friction bolt 18 between the expander mechanism 26 and the rock plate 32. That reinforcement or support is immediate and facilitates access to the tunnel or chamber in which the rock bolt installation 10 is made, by personnel and equipment. The cable bolt 12 is also fully installed, but is not operational until the grout G cures, which can be several days. Once the grout G has fully cured, the full length of the hole 14 is reinforced or supported.

[0069] In the rock bolt installation 10, the cable bolt 12 and the friction bolt 18 are connected structurally and in the embodiment illustrated, that structural connection is a combination of 1) the cured grout G that is interposed between the cable bolt 12 and the friction bolt 18, and the wall 15 of the hole 14 and 2) a clamping load applied by the elements 38 of the expander mechanism 26 against the wall 15, and by the element 381 (see FIG. 2) against the cable bolt 12 to clamp the cable bolt 12 against the wall 15 of the hole 14. However, it will be appreciated from the discussion earlier herein, that the structural connection could be facilitated through the grout G alone, or by the clamping load of the expander mechanism 26 of the friction bolt 18 alone.

[0070] The structural connection provided by the grout G is provided once the grout G has cured. Once the grout G has cured, it is a rigid and hard body within which the cable bolt 12 and the friction bolt 18 are embedded. By the rigid connection, load experienced by the friction bolt 18 can be transferred through the grout G to the cable bolt 12, so that reinforcement or ground support is extended upwardly from the friction bolt 18 to the cable bolt 12 and into what will likely be more stable rock strata. Accordingly, the grout G does not simply fill the spaces or voids within the hole 14 that are otherwise not filled by the cable bolt 12 or the friction bolt 18, but rather, the grout G structurally connects the hole 14 and the cable bolt 12 and the friction bolt 18 together.

[0071] The structural connection provided by the expander mechanism 26 acts in fundamentally the same way as the grout G, except that the structural connection is confined to the location of the expander mechanism 26 rather than extending the full length of the friction bolt 18. The expander mechanism 26 thus clamps against the cable bolt 12 and against the wall 15 of the hole 14. This is shown clearly in FIG. 2.

[0072] FIGS. 2 and 3 show the outer surfaces of the elements 38 as formed with concave recesses or scallops, so that the cable bolt 12 can be securely captured or accommodated for clamping against the wall 15. Each of the elements 38 includes a pair of recesses 42 so that the expander mechanism 26 does not need to be inserted into the hole 14 in a particular orientation for one of the recesses 42 to align with the cable of the cable bolt 12. Thus, as the expander mechanism 26 is expanded, the likelihood is high that the cable bolt will be received in one of the recesses 42. The use of the concave recesses 42 also tends to support the cable of the cable bolt 12 against distortion by the clamping load against the wall 15.

[0073] The concave recesses or scallops 42 can be of other shape or form and can be of greater radial depth in order to accept a greater amount of the cable bolt 12. The recesses 42 can also have a radial depth that is greater than the diameter of the cable bolt 12 so that the cable bolt 12 is received within a recess 42 but is not pressed or clamped against the wall 15. In that arrangement, the cable bolt 12 can be a close but lose fit within the recess 42.

[0074] One of the elements 38 is shown in isolation in FIG. 3 and this figure shows that the peaks 44 of the elements 38 on either side of the recesses 42 are serrated. These serrated peaks are provided to improve the grip with which the elements 38 engage the inside walls 15 and 64 of the holes 14 and 52 of FIGS. 1 and 4. The serrated peaks would replace the flat surfaces normally provided in expandible elements and the serrations will allow the peaks to dig into the wall of the holes in which the expander mechanism is inserted.

[0075] While the installation 10 is shown including a friction bolt 18 that includes a rigid shank 19 (formed as a bar or rod) the invention is also applicable to friction bolts employ cables rather than rigid bars or rods.

[0076] FIG. 4 shows an arrangement in which the friction bolt has a cable 50 instead of the rigid shank 19 of the friction bolt 18 of FIG. 1. In FIG. 4, the rock bolt installation includes a cable bolt 48 that is equivalent to the cable bolt 12 of FIG. 1, and so the cable bolt 48 comprises a cable that is embedded in grout with no fittings at either end of the cable or along the length of the cable. The cable bolt 50 is installed in overlapping or side-by-side relationship with the cable bolt 48, but the cable bolt 50 is formed as a friction bolt so that it has an expander mechanism at the leading end thereof (not shown in FIG. 4) that engages and clamps frictionally against the inside wall 64 of the hole 64 in the same manner as the expander mechanism 26 of the friction bolt 18, although the form of the expander mechanism employed with the cable bolt 50 will be different to the expander mechanism 26, as the cable bolt 50 does not have a threaded end on which the expander mechanism can be fixed. Persons skilled in the art will have knowledge of the type of expander mechanism that can be attached to the leading end of the cable bolt 50.

[0077] The respective bolts 48 and 50 are installed within the hole 52 and the trailing end 54 of the cable bolt 50 is secured against a rock plate 56 by an anchor 58 of an existing form, that comprises an outer barrel 60 and a pair of, or more likely three, inner wedges 62. Persons skilled in the art will understand that the trailing end 54 can be tensioned by pulling through the anchor 58, with the wedges 62 gripping the outside surface of the trailing end 54 to prevent return movement of the trailing end 54 in the reverse or opposite direction through the anchor 58.

[0078] In FIG. 4, the structural connection between the respective cable bolts 48 and 50 is by the cured grout G while there can be an additional structural connection if the expander mechanism of the cable bolt 50 clamps the cable bolt 48 against the wall 64 of the hole 52. The structural connections in the rock bolt installation of FIG. 4 are the same as the structural connections in the rock bolt installation 10 of FIGS. 1 and 2, despite the different use of a rigid bar friction bolt 18 in FIG. 1 as compared to a flexible cable friction bolt 50 of FIG. 4.

[0079] FIGS. 5 to 7 show an arrangement that employs a friction bolt that is a split tube 70. These types of friction bolt are relatively cheap and easy to install and so are preferred where the rock strata is appropriate for their use.

[0080] Before describing the FIGS. 5 to 7 arrangement, it is important to understand that a typical split tube has an outer diameter that is greater than the inner diameter of a hole that the tube is to be installed into and so the tube is forced to collapse radially on forced insertion into the hole. This means that the tube firmly engages the wall of the hole frictionally and forms a very tight connection with the hole wall for substantially the full length of the tube. The manner in which the tube engages the wall of the hole is different to friction bolt 18 of FIG. 1, which has the expander mechanism 26 at the leading end of the bolt 18 and so which only engages to hole wall at one relatively small region but under very high load.

[0081] Use of a split tube in the present invention poses difficulties. As previously explained, it is not realistic for a split tube to push into a hole with the cable of a cable bolt interposed between the wall of the hole and the outside surface of the tube, because 1) the cable would resist insertion of the tube 70, 2) the cable could cause the tube to buckle and prevent insertion in the hole, or 3) the cable could buckle and reduce the length of the engagement with the tube.

[0082] The present invention thus proposes that the cable be accommodated within the interior of the tube of the friction bolt. A problem to be overcome is to ensure that as the tube is pushed into the hole, it feeds about the cable bolt and that grout substantially fills the tube about the cable bolt to ensure that a suitable structural connection will be made by the grout between the cable bolt and the tube.

[0083] In FIG. 5, the friction bolt is a split tube 70 which is shown in longitudinal cross-section, having been pushed into the hole H through the grout G and about the cable 74 of the cable bolt 76. The tube 70 would be pushed into the hole H after the grout G has been injected into the hole H and after the cable 74 of the cable bolt 76 has been pushed into the hole H through the grout G.

[0084] The tube 70 engages a substantial portion of the circumference of the wall of the hole H over the major length of the tube 70. The tube 70 has a longitudinal split or gap 72 as shown in FIGS. 6 and 7. The gap 72 interrupts only a relatively small section of the circumference of the tube 70.

[0085] FIGS. 5 to 7 show that the tube 70 is filled with grout G. While the figures cannot represent actual field outcomes so that complete filing of the entire tube 70 cannot be guaranteed, the opening 78 of the tube 70 is of a width to facilitate entry of the cable 74 and the grout G into the interior of the tube 70, while the wall of the tube 70 includes internal deformations for keying to the grout G so that the grout G can connect more firmly to and grip the tube 70. In FIG. 5, the internal deformations comprise a plurality of longitudinally spaced circumferential indents or grooves 80 which form key or grip features for the grout G to key to or grip when the grout G has cured. The grooves 80 can be circumferential grooves that extend completely about the tube 70, or the grip features can alternatively be groove sections or nodules or other forms of inwardly extending or radial projections.

[0086] The grout G thus cures between the grooves 80 and the grout G is locked into place between the grooves 80, because the wider sections of grout G between the grooves 80 cannot be pulled past the inwardly extending grooves 80. The grout G connects with the cable 74 of the cable bolt 76 in the usual manner and with the inside of the tube 70 by keying with the grooves 80, while longitudinally beyond the opening 78 of the tube 70, the grout G connects with the cable 74 and with the facing wall of the hole H in the usual manner. By the provision of the internal deformations in the form of the grooves 80 and by ensuring the opening 78 of the tube 70 is sufficiently open, the tube 70 can be structurally connected with the cable 74 in the overlap between them and the tube 70 can be structurally connected to the wall of the hole H bv frictional engagement with the wall.

[0087] FIGS. 6 and 7 show cross-sectional views of the FIG. 5 arrangement and FIG. 6 shows that the grout G can flow into the spaces formed between the tube 70 and the wall of the hole H at the grooves 80. The grout G can thus enhance the connection between the tube 70 and the wall of the hole H. FIG. 7 shows that the opening 78 of the tube 70 has approximately the same inner diameter as that of the grooves 80 and that the leading end of the tube 70 is not completely folded in. This construction is intended to make the opening 78 large enough to minimise or at least reduce the difficulty with insertion of the tube 70 into the grout G and about the cable 74. Narrower openings would increase that difficulty.

[0088] The end of the tube 70 that protrudes from the hole H has a collar 82 fixed to the outside of the tube and in bearing engagement with a rock plate 84 that bears against the facing surface of the rock strata about the opening of the hole H. Persons skilled in the art will understand the operation of the collar 82 and the rock plate 84.

[0089] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.