Rock bolting system
The present invention discloses a tube (14) for rock bolts having either a cable tendon or a rod tendon. The tube is deformed to permit the tube to be coiled and yet also provide good keying between the tube and grout. In addition, a fitting (26, 46) for the rear end of the bolt is disclosed in which a grouting orifice (31) communicates with a cable passageway (34). Furthermore, the use of two or more cable anchors (57) at the far end of the bolt is disclosed where the bolt is intended to be used in poor ground conditions, such as sandstone.
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The present invention relates to rock bolts, whether the bolt tendon is formed from a flexible cable or a rigid rod, the grout delivery tube for such bolts, and the fabrication of such tubes.
BACKGROUND ARTRock bolts are widely used in civil engineering and mining applications to stabilise rock strata.
Essentially a blind hole or bore is drilled in the rock and a rock bolt having an anchor at its far end is inserted into the hole. The anchor is operated so as to grip the far end of the hole and secure the bolt in the hole. The bolt is surrounded by a tube and grout is pumped into the gap between the bolt and the tube. The grout passes down the tube until it reaches the anchor and then begins to flow back out of the hole between the interior of the hole and the exterior of the tube. The operator ceases to pump grout when the returning grout is observed escaping from the hole. The grout hardens and provides a force transmitting structure between the interior of the hole and the length of the rock bolt. In this way the steel bolt can react effectively against any movement in the surrounding ground.
OBJECT OF THE INVENTIONThe object of the present invention is to provide an improved tube, a cable bolt incorporating the tube, bolt fittings and fabrication techniques all of which together constitute an improved rock bolting system.
SUMMARY OF THE INVENTIONIn accordance with the first aspect of the present invention there is disclosed a tube for cable or rod bolt applications, said tube being extruded from plastics material and deformed beyond its yield point at a plurality of longitudinally spaced apart locations, along the length of the tube, each said deformation occurring in at least two different directions.
In accordance with the second aspect of the present invention there is disclosed a rock bolt having a tendon located within the above defined tube.
In accordance with a still further aspect of the present invention there is disclosed an end fitting for a rock bolt, said fitting comprising a barrel having a substantially flat front end, a rear end, a curved side wall, and a longitudinal axis, a cable passageway passing between said front and rear ends, and a grouting orifice extending from said front end into said cable passageway.
In accordance with a fourth aspect of the present invention there is disclosed a method of fabricating a tube for a rock bolt, said method comprising the step of radially deforming the side wall of said tube beyond its yield point in at least two different directions, at each of a plurality of longitudinally spaced locations.
In accordance with another aspect of the present invention there is disclosed a rock bolt for use in poor ground conditions, said bolt having a near end and a far end, anchor means at said far end to anchor the far end adjacent the base of a blind hole formed in said ground, and tension means at said near end to tension said bolt after said far end has been anchored, wherein said anchor means comprises at least two anchor devices, each known per se, and connected in series adjacent said far end.
In accordance with a still further aspect of the present invention there is disclosed a method of securing a rock bolt in poor ground conditions, said method comprising the steps of:
providing at least two anchor devices, each known per se, at the far end of said rock bolt,
inserting said rock bolt into a blind hole drilled in said ground,
activating all said anchor devices, and
tensioning said rock bolt.
Preferably, following tensioning of the rock bolt, the bolt is surrounded with grout.
BRIEF DESCRIPTION OF THE DRAWINGSThe prior art and the embodiments of the present invention will now be described with reference to the drawings in which,
As seen in
The purpose of small papillae 13 formed in the tube 4 is to provide a keying mechanism to enable longitudinal shearing forces to be transferred between the ground 9 and the tendon 2 by means of the grout 10.
Current methods of deforming the tube 4 involve processing the tube when it is hot and soft immediately after being formed and upon the tube exiting from the plastic extruder which creates the tube 4 from raw granular material. The tube in this soft and hot state enters another machine termed a “corrugator” which has a series of external moulds into which the tube is forced by compressed air from the inside, or vacuum applied from the outside, or both, so that the hot tube takes the shape of the moulds.
Such corrugators are known to produce corrugated plastic drainage pipe and corrugated swimming pool hose. Corrugated tube is known to be used in relation to rock bolts but suffers from a number of disadvantages. Firstly, the corrugating process is slow and therefore relatively expensive. Secondly, although the corrugated tubing has the advantage of being flexible and resistant to crushing, the geometry of corrugated tubing creates a number of disadvantages. In particular, the close corrugations, extending in an annular fashion relative to the axis of the tube, commonly trap air when the grout material is pumped therepast. These pockets of trapped air very substantially reduce the capacity of the tube to transfer mechanical loads. A similar problem is that the small amount of grouting material in the annular corrugations does not have the strength, because of its small mass and volume, to resist the shearing forces experienced in use. Therefore corrugated tube easily shears the grout from one annular deformation to the next.
In addition, the annular deformations of the corrugated tube catch on many types of objects during the installation procedure such as load plates, wire mesh, the parts of the installing machinery, and the like, all of which can lead to damage of the tube. If the corrugated tube is damaged the bolt can be uninstallable and/or unable to be grouted. This is because a hole in the tube will effectively “short circuit” the grouting procedure and result in grout not being delivered to the full length of the hole.
Whilst the known corrugated tube is flexible, and thus is able to be looped into a coil, the tube 4 of
The cost of the tube 4 is approximately three times the cost of similar tube (so called polytube made from high density polyethylene (HDPE)) used extensively in irrigation applications. It would therefore be desirable if this inexpensive tubing could be used for rock bolting applications.
Because the yielding zones 50 which create the bulges 17 are arranged in sequential fashion along the length of tube 14, these deformed patterns remain deformed and provide a mechanism to enable load transfer from the bolt to the surrounding ground via the grouting applied to both sides of the tube 14. In particular, the shape of the bulges 17 provide a number of advantages in that they reduce the occurrence of damage prior to, or during, installation. Similarly, the shape of the bulges 17 reduces the risk of air voids developing during the grouting operation.
Because the tube 14 thus deformed is able to be rolled into a coil, long lengths of rock bolt utilising steel cable as the rock bolt tendon, rather than solid steel rod, are able to be formed and also coiled prior to installation. This provides substantial advantages as regards packaging and handling of the bolts prior to installation. It also allows installation of long post grouted bolts in limited access areas.
In addition, the barrel 26 has a main passage 34 which includes a frusto-conical wedge 35 which acts a gripping mechanism for the cable 22. Thus the grouting passage 32 delivers grout above the cable gripping wedges 35 which hold the barrel 26 to the cable 22.
That is, after the hole in the ground has been drilled, the far end of the cable bolt 21 (not illustrated) is inserted into the hole and an anchor at the far end is activated so as to fix the far end of the bolt in the hole. Then the cable 22 can be placed under tension and the barrel 26 moved towards the far end until the barrel 26 comes into contact with a washer plate, or the like (not illustrated).
With the cable 22 thus tensioned, grout is able to be pumped through the grouting orifice 31 and grouting passage 32 into the interior of the polytube 14. The grout then travels along the length of the cable bolt 21, passes out the end of the polytube 14 and returns back towards the barrel 26 this time passing between the interior of the hole and the exterior of the polypipe 14.
It will be appreciated that the main passage 34 is not concentric with the cylindrical side wall 30 and thus at the near end of the cable bolt 1 the cable 22 is not concentric with the longitudinal axis of the tube 14.
The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention. For example, the bulges 17 in
In addition, the end fitting or barrel 26, 46 (in addition to being relatively inexpensive to manufacture) can also be used in a cable or rod bolt without the outer plastic tube 4, 14. In this arrangement a breather tube passes through the grouting orifice 31 and grouting passage 32 and then extends alongside the bolt to its far end. Under this arrangement grout is introduced between the bolt and hole and moves towards the far end of the hole but the air displaced by the grout is pushed out through the breather tube. Eventually the grout reaches the far end of the hole and then beings to fill the breather tube. The grouting process is stopped when the grout is seen returning through the breather tube.
Turning now to
Mounted on the cable 22 are a pair of spaced apart conventional shell anchors 53 such as those disclosed in Australian Patent Application No. 22992/02 which each include a restraining device in the form of a rupterable band 57. The anchors 53 are able to be expanded in known fashion by being spring loaded. In this way the two pivoted halves of the anchors 53 pivot outwardly to grip the interior of the surrounding blind hole 8.
The installation procedure is as follows. The rock bolt 51 is inserted fully into the blind hole 8. The spring expansion shells grip the sandstone surrounding the blind hole 8 with sufficient combined force to enable the cable 22 to be tensioned. Then the entire hole 8 is grouted in a single operation. The entire operation takes only a few minutes.
This is to be contrasted with the previous procedure where, following insertion of a rock bolt in poor ground, a sophisticated grout delivery system was used to grout only the far end of the rock bolt. Only after this grout had cured was the rock bolt tensioned. Then the remainder of the bolt was grouted. This prior art process took several weeks.
The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.
The term “comprising” (and its grammatical variations) is used in the sense of “having” or “including” and not in the sense of “consisting only of”.
Claims
1. A tube for rock bolts having either a cable tendon or a rod tendon, said tube being extruded from plastics material and deformed beyond its yield point at each of a plurality of longitudinally spaced apart locations extending along the length of the tube, said deformation at each said location occurring in at least two different directions.
2. The tube as claimed in claim 1 and deformed by inwardly directed compression.
3. The tube as claimed in claim 2 wherein at each said location said inwardly directed compression extends in two different directions making an angle with each other.
4. The tube as claimed in claim 3 wherein said angle iS substantially 90°.
5. The tube as claimed in claim 2 wherein at each said location said inwardly directed compression extends in three different directions.
6. The tube as claimed in claim 5 wherein the angle between said three directions is approximately 120°.
7. The tube as claimed in claim 1 and able to be looped into a coil.
8. The tube as claimed in claim 1 and fabricated from irrigation water supply tube.
9. The tube as claimed in claim 1 and fabricated from high density polyethylene (HDPE).
10. A rock bolt having a tendon located within a tube as claimed in claim 1.
11. The cable bolt as claimed in claim 10 wherein said tendon is formed from multi-strand steel cable and said bolt is looped into a coil.
12. An end fitting for a rock bolt, said fitting comprising a generally barrel-like shape having a front end, a rear end, a curved side wall and a longitudinal axis, and said fitting further having a tendon passageway extending between said front and rear ends, and a grouting orifice in said front end and leading into said cable passageway.
13. The fitting as claimed in claim 12 wherein said tendon passageway includes a cable anchor.
14. The fitting as claimed in claim 13 wherein said cable anchor includes a frusto-conical wedge.
15. The fitting as claimed in claim 12 wherein said front end is substantially domed.
16. The fitting as claimed in claim 12 wherein said front end is substantially flat.
17. The fitting as claimed in claim 1 wherein said rear end is substantially flat.
18. The fitting as claimed in claim 17 wherein said substantially flat rear end is substantially perpendicular to said longitudinal axis.
19. A method of fabricating a tube for a rock bolt, said method comprising the step of radially deforming the side wall of said tube beyond its yield point at each of a plurality of longitudinally spaced apart locations extending along the length of the tube, said deformation at each said location occurring in at least two different directions.
20. The method as claimed in claim 19 including the step of creating said deformation by inwardly directed compression.
21. The method as claimed in claim 20 including the step of: at each said location inwardly directing said compression in two different directions making an angle with each other.
22. The method as claimed in claim 21 wherein said angle is substantially 90°.
23. The method as claimed in claim 20 including the step of: at each said location inwardly directing said compression in three different directions.
24. The method as claimed in claim 23 wherein the angle between said three directions is approximately 120°.
25. A rock bolt for use in poor ground conditions, said bolt having a near end and a far end, anchor means at said far end to anchor the far end adjacent the base of a blind hole formed in said ground, and tension means at said near end to tension said bolt after said far end has been anchored, wherein said anchor means comprises at least two anchor devices, each known per se, and connected in series on said bolt adjacent said far end.
26. The rock bolt as claimed in claim 25 wherein said anchor devices comprise shell anchors.
27. A method of securing a rock bolt in poor ground conditions, said method comprising the steps of:
- providing at least two anchor devices, each known per se, at the far end of said rock bolt,
- inserting said rock bolt into a blind hole drilled in said ground,
- activating all said anchor devices, and
- tensioning said rock bolt.
28. The method as claimed in claim 27 wherein following tensioning of said rock bolt, said rock bolt is surrounded with grout.
Type: Application
Filed: Jun 20, 2003
Publication Date: May 4, 2006
Applicant: INDUSTRIAL ROLL FORMERS PTY LIMITED (SMITHFIELD)
Inventor: Jeffrey Fergusson (Glenorie)
Application Number: 10/518,340
International Classification: E21D 21/00 (20060101);