ZA200907142B

ZA200907142B - Rock Bolt

Info

Publication number: ZA200907142B
Application number: ZA200907142A
Authority: ZA
Inventors: Der Berg Bertrand Van
Original assignee: Aveng Africa Ltd
Priority date: 2008-10-17
Filing date: 2009-10-12
Publication date: 2010-06-30

Description

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BACKGROUND OF THE INVENTION :

[0001] This invention relates to a rock bolt which can be grouted in position. “Grout”, in this context, includes a settable material which hardens and bonds the oo rock bolt to a wall of a hole in which the rock bolt is placed. Examples of grouts are cementitious materials and resin-based materials.

[0002] When grouting takes place the grouting material, initially, is in liquid or fluid form. The grouting material can be mixed in situ, for example by using the rock bolt to break two or more capsules which contain constituents of the grouting material and which are thereafter mixed by rotating the rock bolt, or it can be placed by pumping the grouting material into a hole after the rock bolt has been inserted therein.

[0003] With each approach the grouting material substantially fills all open spaces in the hole and, in the process, causes air to be expelled from the hole.

To avoid the formation of air pockets inside the hole, a factor which could seriously reduce the strength of a bond between the rock bolt and the body of rock in which it is placed, it is necessary to provide a passage through which air can escape from the interior of the hole. A number of techniques have been proposed for this purpose. For example a shank of the rock bolt can be formed with an internal, longitudinally extending passage. This is an expensive solution which can be difficult, from a technical point of view, to implement. In another approach a small diameter flexible tube is attached to the shank of the rock bolt.

The tube has an internal passage which allows for air escape from the hole in

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: which the rock bolt is used. A drawback of this approach is that the tube can easily be damaged or detached from the rock bolt during storage, transport or . installation of the rock bolt, and care must be taken to avoid this type of event.

[0004] The invention aims to provide a rock bolt which addresses the afore- mentioned requirement in a cost-effective and reliable manner.

SUMMARY OF THE INVENTION

[0005] The invention provides a rock bolt which includes an elongate shank, at least one groove which extends longitudinally along the length of the shank in an outer surface of the shank, and a tubular sleeve which encloses the shank and the groove over at least a greater portion of the length of the shank.

[0006] Depending on the application the rock bolt may include a mechanical anchor at one end of the shank.

[0007] An opposing end of the shank can be threaded and a nut may be engaged therewith. The nut, in use, bears against a load distributing washer. The arrangement may be such that, if the nut is rotated in a first direction for example anti-clockwise, the nut and the shank are rotated in unison. However if the nut is rotated in an opposing direction, i.e. in a clockwise direction, the nut can threadedly advance along the shank. This objective may be achieved by forming an upset portion on the threaded end of the shank so that the nut is thereby prevented from threadedly unscrewing from the shank.

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[0008] The shank may include a plurality of keying or anchoring formations. The. shank may for example be made from rebar or a similar material.

[0009] The sleeve which encloses the shank may be formed so that keying or anchoring formations are defined by the sleeve, preferably in locations which coincide with keying or anchoring formations on the shank. The sleeve may for example be made from a plastics material which may be heat shrunk onto the shank so that the keying formations on the shank automatically form corresponding keying formations on the sleeve. Another possibility is to form the sleeve from a thin-walled metallic tube which, after being placed on the shank, is deformed for example by being passed through a roller or the like. In this way portions of the sleeve are urged towards the shank and keying formations on the shank, which stand proud on a surrounding surface of the shank, form similar formations in the deformed metal sleeve.

[0010] It is also possible to form the sleeve by wrapping a strip of a flexible band of suitable material in helical fashion onto the shank. The flexible band which autornatically substantially follows an outer contour of the shank and the sleeve thus automatically provides anchoring or keying formations which correspond to similar formations on the shank.

[0011] The groove may be of any appropriate size or shape. The groove should however not unduly reduce the strength of the shank. To ensure that air can effectively escape from an interior of a hole in which the rock bolt is used the

P21857/g shank may be formed with two or even more grooves. The grooves may be spaced from each other in a circumferential sense about the shank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention is further described by way of example with reference to the accompanying drawings in which: :

Figure 1 is a side-view of the rock bolt according to the invention installed in a hole in a rock face; and

Figure 2 is a view in cross-section of the rock bolt in Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENT

[0013] The accompanying drawings illustrate a rock bolt 10, according to the invention, installed in a hole 12 formed from a rock face 14 into a body of rock 16.

[0014] The rock bolt includes an elongate shank 20 formed from rebar or a similar material which carries a plurality of keying or anchoring formations.

Optionally an expanding mechanical anchor or similar device 22 is fixed to a leading end 24 of the shank. This aspect is conventional and for this reason is not further described herein. It is pointed out though that the use of a mechanical anchor allows the rock bolt, upon installation, immediately to take up a predetermined minimum load which can therefore be supplemented by a grouting process.

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[0015] An opposing end 26 of the shank has a threaded portion 28 and a nut 30 is threadedly engaged therewith. The thread is upset in a region 32 after the nut i has been engaged with the thread. A load-distributing washer 34 is engaged with the shank and bears against the nut and against the rock face 14.

[0016] The shank, in cross-section, has a generally circular orofile. In this example of the invention two elongate grooves 38 and 40, which diametrically oppose each other, are formed in an outer surface of the shank. Each groove extends longitudinally from one end of the shank to an opposing end. The grooves are formed using a suitable machining process. Thereafter a sleeve 44 is placed over the shank. The sleeve can be formed from any low cost deformable material. For example the sleeve can be formed from a flexible plastics material which, with the application of heat, shrinks onto the shank. As is shown in the insert drawing in Figure 1 this process causes keying or anchoring formations 48 in the shank to form corresponding raised formations 50 on the sleeve with regions 52 around each formation being set back. The formations 50 generally correspond in shape, size and number to the keying formations on the outer surface of the shank. Each groove is thus overlaid by a portion of the plastics material and is thereby transformed into an elongate passage.

[0017] The rock bolt can be used in different ways. The rock bolt shank can be used to break two or more capsules which contain constituents of a resinous material and which are previously placed in the hole. A tool, not shown, is engaged with the nut 30 and the nut is rotated in an anti-clockwise direction. Due to the upset portion 32 rotation of the nut in this direction causes rotation of the

P21857/ig shank 20 and in the process the constituents of the resin are mixed intimately. Air which might otherwise become trapped in the hole generally rises to a blind end

X 54 of the hole and then escapes through mouths of the grooves 38 and 40, at this end. The grooves, themselves, are not filled with the resin due to the protective effect of the sleeve 44. Once the resin has set the tool which is engaged with the nut is. rotated in a clockwise direction and the nut then advances along the thread 28. The nut bears against the washer 34 and the rock bolt shank is then tensioned.

[0018] It is also possible to expand the device 22 so that a mechanical anchor is immediately provided and, thereafter, to inject a settable material into the hole through a suitable aperture (not shown) provided, for example, in the load- distributing washer 34. As the settable material is injected into the hole air can escape from the blind end 54 through the grooves 38 and 40.

[0019] The use of a heat-shrinkable, plastic sleeve around the shank is preferred. Alternatively the sleeve could consist of a thin walled, low cost metallic material which is placed around the shank. The shank and sleeve are then passed through a set of rollers which deform the sleeve particularly in the regions of the shank which do not have anchoring formations. In this way corresponding anchoring formations are formed in the sleeve. Another possibility is to make use of an elongate strip or band of flexible material such as plastic tape. The tape is helically wound onto the shank and, as the tape is flexible, it substantially and automatically follows the contours of the shank thereby defining keying or anchoring formations.

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Claims

Page 8 co [0020] The sleeve is inexpensive and easy to use and its inclusion in the rock bolt adequately addresses the problems referred to in the preamble hereof. . CLAIMS I II I RR

1. A rock bolt which includes an elongate shank, at least one groove which extends longitudinally along the length of the shank in an outer surface of the shank, and a tubular sleeve which encloses the shank and the groove over at least a greater portion of the length of the shank. P21857/g

2. A rock bolt according to claim 1 which includes a mechanical anchor at one end of the shank.

3. A rock bolt according to claim 1 wherein an end of the shank is threaded : and a nut, which is engaged with the thread, bears against a load distributing washer, and wherein when the nut is rotated in a first direction, the nut and the shank are rotated in unison and wherein the nut, when rotated in an opposing direction, bears against the load distributing washer.

4. A rock bolt according to any one of claims 1 to 3 wherein the shank includes a plurality of keying formations.

S. A rock bolt according to any one of claims 1 to 4 wherein the sleeve is formed so that keying formations are defined by the sleeve.

6. A rock bolt according to any of claims 1 to 5 wherein the sleeve is made from a plastics material which is shrunk onto the shank so that keying formations on the shank automatically form corresponding keying formations on the sleeve.

7. A rock bolt according to any one of claims 1 to 5 wherein the sleeve is a thin-walled metallic tube which, after being placed on the shank, is deformed so that portions of the sleeve are urged towards the shank and keying formations on the shank, which stand proud on a surrounding P21857/lg .

: surface of the shank, form similar formations in the deformed metal sleeve. | w

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8. A rock bolt according to any one of claims 1 to 5 wherein the sleeve is formed by wrapping a flexible band in helical fashion onto the shank. .

9. A rock bolt according to any one of claims 1 to 8 which includes two of the grooves which are spaced from each other in a circumferential sense about the shank.

10. A rock bolt which includes an elongate shank with an outer surface in which is formed at least one longitudinally extending groove, a plurality of keying formations on the outer surface and a flexible plastics sleeve adhered to the outer surface and overlying the groove thereby to transform the groove into an elongate passage. Dated this 12" day of OCTOBER 2009. / 7 Le — McCALLUM, RADEMEYER & FREIMOND Patent Agents for the Applicant P21857/lg