AU742767B2

AU742767B2 - Rock bolt

Info

Publication number: AU742767B2
Application number: AU47612/97A
Authority: AU
Inventors: Theodore Daniel Swemmer
Original assignee: Hugotek Pty Ltd
Current assignee: Hugotek Pty Ltd
Priority date: 1996-12-09
Filing date: 1997-12-09
Publication date: 2002-01-10
Anticipated expiration: 2017-12-09
Also published as: AU4761297A

Description

P/00/OII Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention title: ROCK BOLT 0* a The following statement is a full description of this invention, including the best method of performing it known to us: Rock Bolt FIELD OF THE INVENTION This invention relates to rock bolts and more particularly to hollow tube bolts through which the bolts are grouted into a hole after location therein.

BACKGROUND TO THE INVENTION In this specification, where an item of knowledge is referred to or discussed, this reference or discussion is not an admission that the item of knowledge or any combination thereof was at the priority date part of common general knowledge or known to be relevant to an attempt to solve any problem with which this specification is concerned.

Tube bolts which consist of an elongated tubular tendon which is threaded at a first end for receiving a mechanical anchor of one type or another and at the other end for engaging a pre-tensioning arrangement are known. A problem with tube bolts of the above type is, however, that they have a significantly lower tensile strength than a standard solid rock 15 anchor tendon bar. For example the tensile strength of a standard solid tendon of diameter having m/20 threads is about twenty tons while a high strength tubular tendon with an m/20 thread has a tensile strength of only about ten or eleven tons. One method of °ooo• overcoming this limitation of tubular bolts is to use tubes of a larger diameter than the conventional 20mm to attain a tensile strength approximating that of the solid tendon bolts.

A difficulty in using larger diameter tubes is that the conventional expansion heads cannot be used on the larger diameter tubes and even if expansion heads were made to cater for the larger diameter tubes the heads would be cross-sectionally too large for use in standard bolt holes.

SUMMARY OF THE INVENTION A rock bolt according to the invention includes a tubular tendon having a co-axial threaded stud at one end which is of smaller cross-sectional dimension than the remainder of the tendon and with which an anchor head may threadedly be engaged and an aperture from the inside to the outside of the tendon tube through or adjacent the stud through which a liquid settable material may be pumped through the tendon and from the aperture into a hole in which the tendon is located, in use, to surround the tendon in the hole.

In a preferred form of the invention the stud is a length of the tendon tube which is reduced in diameter.

In another form of the invention the stud is a length of threaded bar which is fixed to an end of the tendon tube.

The aperture may pass axially through the stud. For example, in the form of the invention where the stud is a length of threaded bar which is fixed to an end of the tendon tube, the threaded bar may have an axial bore through it for grout escape as is the case with the totally tubular tendon.

Alternatively, the aperture may be a hole through the wall of the tendon tube adjacent the stud. For example, the tendon tube may be holed below the stud for grout escape from the tube.

In a further form, there is provided the rock bolt of the present invention in which a portion I of the length of the tendon tube from its end opposite the stud is threaded. In this case, the tendon tube between the stud and its threaded end may include one or more outwardly S 15 projecting anchor formations.

BRIEF DESCRIPTION OF THE DRAWING An embodiment of the invention is now described by way of example only with reference to the drawing which is a half-sectioned side elevation of the rock bolt of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The rock bolt of the invention is shown in the drawing to include an elongated tendon and anchor head 12, a tensioning nut 14 and a face washer 16.

The major portion 18 of the tendon tube 10, in this embodiment of the invention, has an outer diameter of about 27mm. The lower end of the portion 18 of the tendon tube is roll threaded to an outer thread diameter of 30mm. The upper portion 20 of the tendon tube is swaged down to an outer diameter of 20mm and has a length of about 125mm. It is important that in reducing the diameter of the portion 20 of the tube the wall thickness of that portion of the tube is not reduced to below that of the portion 18 of the tendon tube.

The reduced diameter portion 20 of the tendon is roll threaded to provide a stud for accommodating the threaded cone nut 22 of the anchor head 12. The upper end of the tendon tube portion 18 may in some applications include outwardly projecting anchor ormations 24 which may be pinched from the outer surface of the tube or may be welded ionto the tube.

The anchor head 12 is a conventional well known type of expansion head and includes the cone nut 22, expansion shells 26 and bale arms 28 to which the shell leaves 26 are attached. The cap which carries the bale arms is holed at 30 for grout escape from the bolt tendon.

In use the anchor bolt of the invention is used in exactly the same manner as conventional tube bolts by being located in a predrilled hole and spun until the anchor head shells are wedged outwardly by the nut 22 to anchor the head 12 firmly to the wail of the hole in which it is located. The nut 14 is then pulled up against the washer 16 with its upper face in the drawing bearing firmly on the rock face surrounding the bolt hole until the bolt is fully tensioned.

As with conventional 20mm tube bolts the bolt of the invention will have only an initial working load of only about 11 tons. However, after the bolt has been full column grouted in the conventional manner by pumping grout up through the tubular tendon into the hole S•the larger tube diameter of the portion 18 of the tendon becomes load bearing effective on S: 15 the curing of the grout to increase the load bearing capability of the bolt to between 16 and 18 tons.

The invention is not limited to the precise details as herein described. For example the anchor head 12 could be of any conventional type and not necessarily that shown in the oooo• drawing. The anchor formations on the portion 18 of the tendon could be any outwardly 20 projecting formations such as a rolled thread or ribs and could extend over the entire length ooooo of the portion 18 of the tendon down to its threaded end.

.ooooi S"Additionally, the portion 20 of the tendon could be provided by welding a suitably robust threaded tube or solid bar into the end of the larger diameter portion 18 of the tendon. In the case where a solid threaded bar is used to provide the tendon portion 20 at least one hole would need to be provided in the wall of the tube directly below the portion 20 for grout escape from the tendon in use. Also, in the event that the anchor head used on the bolt is of such a construction as to impede the passage of grout past it from the blind end of the hole towards the hole mouth, even the totally tubular bolt tendons could include one or more holes for grout escape from the tendon below the anchor head.

Claims

1. A rock bolt including a tubular tendon having a co-axial threaded stud at one end which is of smaller cross-sectional dimension than the remainder of the tendon and with which a suitable anchor head may threadedly be engaged and an aperture from the inside to the outside of the tendon tube through or adjacent the stud through which a liquid settable material may be pumped through the tendon and from the aperture into a hole in which the tendon is located, in use, to surround the tendon in the hole.

2. A rock bolt as claimed in claim 1 in which the stud is a length of the tendon tube which is reduced in diameter.

3. A rock bolt as claimed in claim 1 in which the stud is a length of threaded bar which is fixed to the tube at one of its ends.

4. A rock bolt as claimed in any one of claims 1 to 3 in which the aperture passes axially through the stud.

5. A rock bolt as claimed in any one of claims 1 to 3 in which the aperture is a hole through the wall of the tendon tube adjacent the stud. i

6. A rock bolt as claimed in any one of the above claims in which a portion of the length of the tendon tube from its end opposite the stud is threaded.

7. A rock bolt as claimed in claim 6 in which the tendon tube between the stud and its Q 20 threaded end includes one or more outwardly projecting anchor formations. HUGOTEK (PROPRIETARY) LIMITED 16 November 2001