AU2005203205A1 - A rock bolt - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant(s): Actual Inventor(s): Address for Service: Invention Title: Details of Associated Provisional Applications: INDUSTRIAL ROLL FORMERS PTY

LTD

David James FERGUSSON FRASER OLD SOHN Patent Attorneys Level 6, 118 Alfred Street MILSONS POINT NSW 2061 A ROCK BOLT Australian Patent Application No. 2004 904 113 Filed 23 July 2004 The following statement is a full description of this invention, including the best method of performing it known to us: 2945BJ-AU Field of the Invention The present invention relates to rock bolts having a cable tendon and to a method of fabricating such rock bolts.

Background Art Rock bolts maybe conveniently categorised into two categories depending upon the nature of the tendon of the bolt. In one category the tendon is a solid bar or rod. In the other category the tendon is a cable formed from individual wire strands.

Normally such strands are formed or twisted into a rope-like configuration so that the cable is in fact formed as a wire rope.

Cable tendons have the substantial advantage that the tendon is flexible and therefore long bolts maybe coiled up both for the purposes of transport from the factory to the mine, tunnel, or other engineering site and also for the purposes of transporting the bolt into the mine, etc to the intended location of installation. Such cable bolts are uncoiled at the location of installation.

A further advantage of cable tendons is that it has long been appreciated that by increasing the number of individual strands, the effective cross sectional area of the tendon can be increased, and thus the tensile strength of the rock bolt can also be increased. Furthermore, where the strands are all of the same size, then this increase in strength can be achieved without the need for a range of inventory sizes since a standard strand size is able to be utilised.

International Patent Application No. PCT/AU92/00369 (JJP Geotechnical Engineering Pty Ltd) published under WO 93/03256 discloses one such proposal for a rock bolt with a cable tendon. In this proposal, the cable is assembled in conventional fashion from the individual strands and then a thread is rolled onto, or cut into, the exterior of the cable or wire rope in order to enable a nut to be threadably engaged with the exterior strands of the wire rope. This proposal, which to the present applicant's knowledge has never been used commercially, suffers from the disadvantage that the rolling or cutting of the threads into the exterior strands of the cable, substantially weakens those strands and thus weakens the overall strength of the rock bolt.

2945BJ-AU t Furthermore, good keying between the wire rope and grout which surrounds the rope and adheres to the interior surface of the blind hole in which the rock bolt was installed, is required. In order to ensure adequate keying, it has been necessary to provide bulges in the strands at one or more locations, the bulged strands at such (Ni N 5 locations having the appearance of a birdcage. Considerable forces are required to bulge the strands of cable tendons and therefore a substantial amount of investment in capital equipment is required to successfully carry out such bulging. Furthermore, it Cc is not always known in advance where the most desirable locations for such bulges Sare since this may well depend upon the location and type of various kinds of rock strata through which the rock bolt is to pass.

The genesis of the present invention is a desire to substantially overcome, or at least ameliorate to some extent, the abovementioned disadvantages.

Summary of the Invention In accordance with a first aspect of the present invention there is disclosed a rock bolt having a cable tendon formed from a plurality of individual longitudinally extending strands, the number of strands being selectable to vary the tensile strength of the cable, wherein each of said strands has regular undulations, the trailing end of said rock bolt includes an interior former having a surface shaped to receive said undulations, said strands are spaced around the periphery of said former and a nut is threadably received on said bolt trailing end, said nut threadably engaging said strands and clamping same against said former.

In accordance with a second aspect of the present invention there is disclosed a method of fabricating a rock bolt having a cable tendon formed from a plurality of individual longitudinally extending strands, said method comprising the steps of: forming regular undulations in said strands, (ii) selecting the number of strands commensurate with the intended tensile strength of the rock bolt, (iii) spacing said undulating strands around the periphery of a former located at the trailing end of said rock bolt and having a surface shaped to receive said undulations, and 2945BJ-AU t (iv) threadably engaging a nut with said spaced undulating strands to clamp same against said former.

Brief Description of the Drawings N 5 Two embodiments of the present invention will now be described with reference to the drawings in which: Fig. 1 is an exploded perspective view of a rock bolt having a cable tendon in Cc accordance with a first embodiment, N Fig. 2 is side elevation of the installed cable of Fig. 1, Fig. 3 is a view similar to Fig. 1 but of a bolt of a second embodiment, and N Fig. 4 is a view similar to Fig. 2 but of the bolt of Fig. 3.

Detailed Description As seen in Figs. 1 and 2, the rock bolt 1 of the first embodiment has a leading end 2 and a trailing end 3. The rock bolt 1 also has a cable tendon 4 formed from a plurality of individual strands 6 each of which has a wavy appearance formed by creating regularly repeating undulations 7 which are preferably of a generally sinusoidal character. Thus the strands 6 maybe said to be crinkled or frizzed. The undulations 7 are easily formed by rolling the strands in known fashion. This does not reduce their cross-sectional area so the strands are not thereby weakened.

At the trailing end 3 a former 10 is provided the exterior surface of which is provided with a helical groove 11 which has a pitch of, say 10mm, and which is dimensioned to receive the undulations 7, which have a like pitch. Preferably the groove 11 is provided with seats 12 to each receive a corresponding strand 6.

The individual strands 6 are circumferentially arranged around the former and the undulations 7 are engaged with the helical groove 11. Then a nut 13 having an interior thread 14 is threadably engaged with the strands 6. In this process the strands 6 are clamped between the helical groove 11 of the former 10 and the nut 13.

Thus the strands 6 are retained in place within the corresponding seats 12 relative to the former 2945BJ-AU The former 10 is also provided with a breather passage 17 which extends right 0 Othrough the former 10 from one end to the other and which is mated to a breather tube 18 which extends along the length of the rock bolt 1. The breather tube 18 is preferably formed from polyethylene irrigation pipe, or similar such inexpensive (,i N 5 plastics tubing. The former 10 is also provided with a grout admitting passageway 19.

One or more transverse loops 9 (which can take the form of a plastics cable (N tie, a metal ferrule, or similar) are placed around the strands 6 so as to gather same together and thus maintain the strands 6 in a waisted or elongate form. It will be C 10 apparent to those skilled in the art that any number of (preferably regularly) spaced loops 9 can be provided.

At the leading end 2 of the rock bolt 1, an expansion anchor 22 is formed. A hollow frusto-conical tube 23 is fitted over the leading ends of the individual strands 6 which are formed around the leading end of the breather tube 18. Then the cone 23 is swaged to the strands 6. If desired, a short length of steel tubing (not illustrated) maybe slid over the leading end of the breather tube 18 to prevent the breather tube 18 being crushed during the swaging operation.

The remainder of the expansion anchor 22 is formed from a pair of tapered leaves 24 each of which is individually pivotably mounted to a ring 25. In conventional fashion the leaves 24 and ring 25 are retained on the cone 23 by means such as an expandable elastomeric band (not illustrated but conventional) which maintains the expansion anchor 22 in its initial unexpanded condition.

In order to install the rock bolt 1, the leading end 2 is inserted into a blind hole 28 which is slightly longer than the rock bolt 1 itself. An apertured plate 30 is located between the rock face 29 containing the blind hole 28 and the nut 13. The nut 13 is rotated on the strands 6 in order to advance the nut towards the leading end 2 thereby bringing the plate 30 into abutment with the rock face and placing the cable tendon 4 of the rock bolt I in tension. As a consequence, the cone 23 is drawn towards the nut 13, thereby expanding the leaves 24 and causing the expansion anchor 22 to grasp the interior of the blind hole 28. Once this happens, the expansion anchor 22 is securely anchored and further rotation of the nut 13 increases the tension on the cable tendon 4.

2945BJ-AU 'n After an appropriate degree of tension has been achieved, a grouting nozzle S(not illustrated but for example as disclosed in Australian Patent Application No. 2004 202 214 to the present applicants) is inserted in the grout admitting passageway 19 of the former 10 and viscous liquid grout is injected into the passageway 19 as indicated S 5 by arrow A in Fig. 2. As the grout is injected into the hole 28, air from within the hole is expelled by entering the leading end of the breather tube 18 as indicted by arrow B in Fig. 2. Progressively the hole 28 itself is filled with grout and then the Cc interior of the breather tube 18 is filled with grout until eventually grout emerges from Sthe breather passage 17. This indicates that both the hole 28 and the breather tube 18 are full of grout and therefore pumping of grout into the passageway 19 is N discontinued.

A number of important advantages result from the above described construction. Firstly, the undulations 7 provide good keying between the grout and the strands 6 and thus the need to bulge the cable tendon 4 is avoided.

Secondly, the undulating strands 6 may be cut to any length which a customer desires and thus customers are not obliged to select the length of the rock bolt from various standard lengths held in stock.

Thirdly, the number of strands can be varied in order to increase the tensile strength of the rock bolt. For example a rock bolt intended for a blind hole having a nominal diameter of 67mm may have, say, 5 to 7 individual strands 6, whereas a rock bolt 1 intended for a hole having a nominal interior diameter of 100mm may have, say, 20 individual strands 6. In the embodiment of Figs. 1 and 2 only four strands 6 are illustrated in Fig. 1 and the former 10 is illustrated with four seats 12. However, preferably the former 10 is fabricated with the same number of seats 12 as the intended maximum number of strands 6 and where a lesser number of strands 6 is used then some of the seats 12 remain unutilized.

Turning now to Figs. 3 and 4, a second embodiment of the present invention is illustrated and in which like parts to the first embodiment have a designation number increased by 100. Thus the rock bolt 101 of Figs. 3 and 4 has a leading end 102 and a 2945BJ-AU tn trailing end 103 and a cable tendon 104. As before, the individual strands 106 are Srolled to provide a wavy or undulating appearance formed by the undulations 107.

At the trailing end 103 a former 110 is provided with a helical groove 111 but r, 5 without any of the seats 12 of the previous embodiment. As before, the former 110 has a breather passage 117 and a grout admitting passageway 119. An apertured plate 130 and a nut 113 complete the trailing end 103. If desired, an elastomeric keeper Cc ring or rubber band 203 can be provided to keep the individual strands 106 in place ,i before the nut 113 is tightened.

At the leading end 102 of the rock bolt 101 an expansion anchor 122 is provided as before, but of a different construction. As is best seen Fig. 3, the expansion anchor 122 is formed from three leaves 124 each of which is mounted on a flexible arm 125. The leaves 124 surround a plug 123 which has a threaded interior and which is able to engage another former 210 which is provided with a longitudinally extending breather opening 217. A breather tube 118 extends between the two formers 110 and 210 and a second breather tube 218 extends beyond the second former 210.

An elastomeric ring 199 is used to maintain the leaves 124 in position prior to installation, as is conventional. One or more cable ties 109 are used to maintain the strands 106 bunched together, as before. The leading ends of the strands 106 are threadably engaged with both the second former 210 and the plug 123 as best seen in Fig. 4.

On installation, the leading end 102 is inserted into the blind hole 128 drilled in the rock or mineral face 129. Initial rotation of the nut 113 rotates the entire rock bolt 101. Thus the second former 210 rotates relative to the plug 123 which is drawn towards the trailing end 103 thereby expanding the leaves 124 which grip the interior of the hole 128 in conventional fashion. After the rock bolt 101 is thus anchored, continued rotation of the nut 113 moves the nut relative to the first former 110 and thereby progressively tensions the strands 106. Once a desired level of tension within the rock bolt 101 has been achieved, grouting takes place as before by injecting grout 2945BJ-AU t into the passageway 119 and allowing air to be expelled via the breather tubes 218 Sand 118 in sequence.

(Ni The foregoing describes only one embodiment of the present invention and 5 modifications, obvious to those skilled in the civil engineering arts, can be made thereto without departing from the scope of the present invention.

(Ni Cc For example, in order to better locate the strands 6, at spaced intervals along the rock bolt 1, a tube can be positioned. The breather tube 18 passes through the tube C 10 interior and the loop 9 holds the strands 6 against the tube. If the tube 9 is provided i with a helical groove 11 as provided on the former 10, then the loop 9 can be replaced by a small nut.

Similarly, other ways of connecting the leading ends of the strands to the expansion anchor 22 can be provided. For example, a tube with a helical groove similar to the former 10 can be provided and a nut used to clamp the leading end of the strands 6 against the tube. Alternatively, the leading end of the strands 6 can be hooked over the leading end of the cone 23 and crimped in place.

The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of'.

2945BJ-AU

Claims (12)

1. 2. The rock bolt as claimed in claim 1 and having at least one transversely N arranged loop extending around said strands to gather same together.
2. 3. The rock bolt as claimed in claim 1 or 2 and having an expansion anchor formed at, or adjacent, its leading end.
3. 4. The rock bolt as claimed in claim 3 wherein said expansion anchor includes a portion which mates with said undulations. The rock bolt as claimed in any one of claims 1-4 wherein said undulations are substantially sinusoidal in character.
4. 6. The rock bolt as claimed in any one of claims 1-5 and having a breather tube lying alongside said strands, extending substantially the length of said bolt, and communicating with said bolt trailing end via a passage extending through said former.
5. 7. The rock bolt as claimed in any one of claims 1-6 wherein said former includes a grout admitting passageway extending therethrough.
6. 8. The rock bolt as claimed in any one of claims 1-7 wherein said former includes a plurality of longitudinally extending seating grooves and each said strand is seated in a corresponding groove.
7. 9. A rock bolt substantially as herein described with reference to Figs 1 and 2 or Figs. 3 and 4 of the drawings. A method of fabricating a rock bolt having a cable tendon formed from a plurality of individual longitudinally extending strands, said method comprising the steps of: forming regular undulations in said strands, (ii) selecting the number of strands commensurate with the intended tensile strength of the rock bolt, 2945BJ-AU t (iii) spacing said undulating strands around the periphery of a former Slocated at the trailing end of said rock bolt and having a surface shaped to receive said undulations, and (iv) threadably engaging a nut with said spaced undulating strands to clamp same against said former.
8. 11. The method as claimed in claim 10 including the further step of: transversely locating at least one loop around said strands to gather Cc same together. N, 12. The method as claimed in claim 10 or 11 including the further step of: (vi) locating an expansion anchor at, or adjacent, the leading end of said N rock bolt.
9. 13. The method as claimed in any one of claims 10-12 including the further step of: (vii) providing a passage which extends substantially longitudinally through said former, (viii) locating a breather tube within said strands and extending substantially the length of said rock bolt, and (ix) terminating said breather tube so as to communicate with said passage.
10. 14. The method as claimed in any one of claims 10-13 including the further step of: providing a grout admitting passageway extending through said former. The method as claimed in any one of claims 10-14 including the step of: (xi) forming the undulations in said strands to be substantially sinusoidal.
11. 16. The method as claimed in any one of claims 10-15 including the further step of: (xii) creating longitudinally extending seating grooves in said former and seating each said strand in a corresponding one of said grooves.
12. 17. A method of fabricating a rock bolt, said method being substantially as herein described with reference to Figs. 1 and 2 or Figs. 3 and 4 of the drawings. 2945BJ-AU in Dated this 2 2 nd day of July 2005 SINDUSTRIAL ROLL FORMERS PTY LIMITED By FRASER OLD SOHN C Patent Attorneys for the Applicants iO t¢N 2945BJ-AU