AU754645B2

AU754645B2 - An improved bolt

Info

Publication number: AU754645B2
Application number: AU61241/00A
Authority: AU
Inventors: Christopher John Rainsford
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-10-04
Filing date: 2000-09-22
Publication date: 2002-11-21
Anticipated expiration: 2020-09-22
Also published as: AU6124100A; AU2002313905A1; AU2002313905A8

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT AN IMPROVED BOLT The following statement is a full description of this invention, including the best method of performing it known to me:

NUMBER:

DATE:

INVENTORS:

61241/00 22 September 2000 Christopher John Rainsford AN IMPROVED BOLT The present invention relates to a bolt adapted to be received in a bore hole in a rock face and relates particularly, although not exclusively, to such a bolt in the form of a rock bolt or cable bolt.

Rock bolts and cable bolts are well known items used in the mining industry and other applications requiring ground reinforcement and/or support. These bolts generally have a shaft which is inserted into a bore hole in a rock face and an end fitting which is secured to a part of the shaft protruding from the rock face. The end fitting may be used to form a fixing point in the rock face or the bolt may be used to hold together the rock to prevent it from collapsing. During the life of the rock bolt varying forces are applied to the end fitting which produces fatigue stresses in the bolt. Often these stresses can increase during the life of the bolt. The fatigue stresses can reach a point where the rock bolt fails and/or the end fitting detaches catastrophically from the rock bolt shaft.

The present invention seeks to provide an improved bolt which at least in part ameliorates the above mentioned problem and prolongs the life of the bolt.

C According to the present invention there is provided an improved bolt adapted to be received in a bore hole in a rock face comprising at least: A shaft for part insertion into the bore hole in the rock face, said shaft to be anchored in the bore hole; An end fitting associated with a part of the shaft outside the rock face; A securing means for securing the end fitting to part of the shaft outside the rock face; and A stress absorbing member, comprising of one or more elements, associated with the end fitting and with the rock face so as to absorb variations in the stresses applied to the end fitting during use Also according to the present invention there is provided A stress-absorbing member comprising of one or more elements for use with a bolt adapted to be received in a bore hole in a rock face, said bolt comprising a shaft for part insertion into the bore hole in the rock face and anchoring in the bore hole, an end fitting associated with a part of the shaft outside the rock face, and a securing means for securing the end fitting to the part of the shaft outside the rock face, wherein the said stress absorbing member comprising of one or more elements is adapted to be associated with the end fitting and with the rock face so as to absorb variations in the stresses applied to the end fitting during use of the bolt.

Preferably the stress-absorbing member is resistibly compressible. More preferably the stress absorbing member is resiliently compressible.

The present invention provides for the number and characteristics of each of the elements making up the stress absorptive member to be varied to take account of varied stress regimes within the rock matrix (rock mass).

Preferably the stress-absorbing member has a hole through each of the stress absorbing elements through which the shaft freely passes.

Preferably the stress-absorbing member includes an end plate at a first end. More preferably the stress absorbing member includes a second end plate at a second end opposite the first end.

Alternatively the end plates may be absent.

Preferably the bolt includes a washer disposed between the stress absorbing member and the rock face through which the shaft freely passes.

Preferably the bolt is a rock bolt. Alternatively the bolt is a cable bolt.

S: Preferably the securing means is a nut threadingly engagable with an end of the shaft. More i: "preferably the end plate is a washer.

2: Preferably the stress-absorbing member is pre stressed during installation of the bolt.

oSo In order to provide a better understanding a preferred embodiment of the present invention will now be described with reference to the accompanying drawings, in which: 23X Figure 1 is an upper perspective view of a preferred embodiment of a stress-absorbing member of the present invention; o. Figure 2 is a cross-sectional view of a preferred embodiment of a bolt in accordance with the present invention including the stress-absorbing member of figure 1; 0 30 Figure 3 is an upper perspective view of another preferred embodiment of a stress-absorbing member of the present invention; and SFigure 4 is a cross-sectional view of another preferred embodiment of a bolt in accordance with the present invention including the stress absorbing member of Figure 3 Referring to these figures, there is shown a rock bolt 30 for anchoring in a bore hole 24 in rock The face of the rock 20 is indicated as 22. The bolt 30 includes a shaft 32 which is inserted in the bore hole 24, but also has a part extending outside of the rock face 22. It can be seen that a washer 38 abuts the rock face 22 with the shaft 32 passing through the hole in the center of the washer 38. The stress absorbing member 10 includes a hole 16 passing through its length, which allows the shaft 32 to freely move longitudinally within the hole. A standard end fitting 34 abuts the other end of the stress absorbing member 10 with the shaft 32 passing through the hole in the standard end fitting 34. A securing means, in the form of a nut 36, threadingly engages the end of the shaft 32. The nut 36 abuts the other side of the standard end fitting 34. The stress-absorbing member 10 and washer are sandwiched between the nut 36 and the rock face 22. The nut may be tightened to partly compress and pre-stress the stress absorbing memberl0, and also to secure the standard end fitting 34, stress-absorbing member 10 and washer 38 hard against the rock face 22.

As can be seen in more detail in Figures 1 and 2, the stress-absorbing member 10/10A comprise of a single element, or a number of elements which form a cylinder 12/12A having a hole 16 passing through each cylinder along its length. At either end of the stress absorbing member 12 there is a non-compressible plate fused or adhered to either end of the cylinder. The individual elements making up the cylinder are made of a resistively compressible material and preferably a resiliently compressible material, such as dense rubber or polymer compound.

The end plates 14 are preferably in the form of metal washers. It is envisaged that other resiliently compressible materials may be used or the end plate may be absent. The compression and resilience characteristics of the compressible member may be selected depending on the actual application the bolt is to be used for. In some cases it may be more beneficial to have more resistive characteristics depending on the type of the rock and the stresses that the bolt will be subjected to.

.i Referring to Figures 3 and 4, the stress-absorbing member 10A is relatively shorter in length that Sthe stress-absorbing member 10 of Figure 1. Stress-absorbing member 10A may be relatively less A. 2 compressible than that of Figure 1. This type of stress-absorbing member 10A may be more "suited to an application where relatively less compression, but some stress absorption is desirable.

It is envisaged that the stress-absorbing member will provide an improvement to existing and new rock bolts and cable bolts as it will prolong the life of the bolt. As stresses increase the compression of the stress absorbing member will increase. The stress absorptive member will absorb increases in stresses applied to the bolt during the life of the bolt and thus prolong the Sbolt's'effective working life. It is envisaged that the stress-absorbing member may be retro fitted to existing bolts already in use or may be incorporated into any existing or new rock or cable bolt system.

Now that the preferred embodiment has been described, it will be apparent to the skilled addressee that modifications and variations can be made to the present invention without departing from the basic concept. Such as, the shape of the stress-absorbing member need not be cylindrical or even elongate; may be one or more elements making up the stress absorbing member; or the stress absorbing characteristics of the stress absorbing member may be varied to suit the actual application of the bolt. Such modifications are intended to be within the scope of the present invention, the nature of which is to be determined from the foregoing description.

Claims

1. A rock or cable bolt comprising a mechanism of non mechanical molecular shearing to assist energy absorption in rock bolts and cable bolts. A stress absorbing member which is made up of multiple contiguous elements constructed of resiliently and/or resistively compressible material, such as dense rubber or a polymer compound is designed to be used in conjunction with rock bolts or cable bolts as an additional element. The stress absorbing member will compress either permanently or reactively to absorb energy transferred through the rock face to the supporting device (rock bolt or cable bolt). Under the present invention, the stress absorbing member is used with a rock bolt or cable bolt which comprises of a shaft for part insertion and anchorage into a bore hole in a rock face, an end fitting associated with the part of the shaft outside of the rock face, and a securing means for securing the end fitting; wherein the said stress absorbing member is adapted to be associated with the end fitting and with the rock face so as to absorb variations in stresses applied to the end of the bolt during .use. The stress absorbing member will be constructed of multiple contiguous elements of S.resiliently and/or resistively compressible material, such as dense rubber or a polymer S.:i compound with the presence or absence of plates or washers (constructed of metal or other suitable materials) on each end of the stress absorbing member.

2. The rock bolt assembled whereby plates and washers may be present at each end of the stress absorbing member are constructed of metal.

3. Referring to claim one, use of the stress absorbing member may be incorporated into the application of any existing or new rock bolts or cable bolts, or may be retro fitted to existing bolts already in use.

4. The improved bolt substantially as herein described with reference to the accompanying S. drawings. Christopher John Rainsford 22 September 2000