AU5360600A

AU5360600A - Rock bolt

Info

Publication number: AU5360600A
Application number: AU53606/00A
Authority: AU
Inventors: Mieczyslaw Stanislaw Rataj
Original assignee: Ani Corp Ltd
Current assignee: DSI Underground Australia Pty Ltd
Priority date: 1999-08-24
Filing date: 2000-08-24
Publication date: 2001-03-01

Description

S&FRef: 519007

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name and Address of Applicant Actual Inventor(s): Address for Service: The ANI Corporation Limited Level 5, Merlin Centre 235 Pyrmont Street Pyrmont NSW 2009 Australia Mieczyslaw Stanislaw Rataj Spruson Ferguson St Martins Tower 31 Market Street Sydney NSW 2000 Invention Title: Rock Bolt ASSOCIATED PROVISIONAL APPLICATION DETAILS [33] Country [31] Applic. No(s) AU PQ2446 [32] Application Date 24 Aug 1999 The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5815c Rock Bolt Field of the Invention The present invention relates to improvements in rock reinforcement installations, and in particular relates to a rock bolt.

Background of the Invention Rock bolts have traditionally been installed in a rock formation by resin grouting. In this method, a plastic resin cartridge containing a two component resin is inserted into a pre-drilled borehole in the rock prior to insertion of the rock bolt. Forcing the bolt into the borehole while simultaneously rotating the rock bolt ruptures the plastic o casing of the resin cartridge or cartridges and mixes the resin components within the annular space formed between the bolt and the borehole wall.

To achieve maximum performance of the anchoring system it is important that the plastic of the resin cartridge is shredded into small pieces. Otherwise larger unshredded sections of the plastic container may contain some unmixed resin which may result in slip planes reducing the bolt anchorage strength. Since the plastic is being shredded in the annular space between the bolt and the borehole wall there are two conditions which contribute to make this operation successful. Firstly the annular space **°between the bolt and the borehole wall should be relatively small and secondly the bolt °should be configured to effectively shred the plastic resin cartridge.

The currently used bolting system has some limitations regarding both of these conditions. Currently available rock bolts are typically of constant diameter, and increasing this diameter will result in a thin annular space along the length of the bolt.

Installation of the bolt will be difficult as the resin must be extruded back along this annular space as the rock bolt is pushed into the end of the borehole. The currently available bolts are also relatively ineffective in shredding the plastic material of the cartridge as deformations formed on the surface of the bolt are relatively unsharp, having been formed by a hot-rolling process.

A crucial disadvantage of the presently available rock bolting systems is their limited anchorage capacity. Once a load which is sufficient to displace the bolt to some degree, known as the "peak pull-out load", has been achieved, the residual anchorage strength of the displaced bolt drops dramatically, enabling continued withdrawal of the bolt at a greatly reduced load such that the bolt provides effectively no reinforcement to the rock.

[R:\LIBLL]09940.doc:TCW:VJP Object of the Invention It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages.

Summary of the Invention In a broad form the present invention provides a rock bolt having a leading end portion with a cross-sectional area greater than that of a portion of said rock bolt adjacent said leading end portion, and a trailing end portion adapted to receive a rock plate.

Typically, said leading end portion cross-sectional area is greater than the crosssectional area of said bolt at substantially all locations along the remainder of the length io of said bolt.

Preferably, said rock bolt is tapered from said leading end portion to said adjacent portion.

oooo The rock bolt may also be reverse tapered from said adjacent portion to a bar S.portion of said rock bolt lying between said adjacent portion and the trailing end of said rock bolt.

Typically said rock bolt further has a sharpened projection or projections formed on and protruding from said leading end portion for shredding a plastic casing of a resin cartridge upon rotation of said rock bolt in a rock bolt hole.

Preferably, said sharpened projection(s) is/are formed by deformation of said 20 leading end portion.

Preferably, said sharpened projection(s) is/are formed by a cold rolling process.

S* Alternatively said sharpened projection(s) is/are formed by a forging process.

Preferably, said sharpened projection is in the form of a helical thread-like ridge.

Preferably, said trailing end portion is provided with a thread for receipt of a nut and a rock plate, said helical thread-like ridge being formed in the same direction as that of said trailing end thread.

Preferably, said leading end portion may be slotted.

In another broad form the present invention provides a method of forming a rock bolt comprising the steps of: forming a bar with a leading end portion having a cross-sectional area greater than that of a portion of said bar adjacent said leading end portion, and adapting a trailing end portion of said bar for reception of a rock plate.

[R:\LIBLL]09940.doc:Tcw:VJP Typically said bar is formed with said leading end portion cross-sectional area greater than the cross-sectional area of said bar at substantially all locations along the remainder of the length of said bar.

Preferably, said bar is formed with said greater leading end portion crosssectional area by deforming said bar.

Preferably, said bar is deformed by rolling said adjacent portion to a reduced cross-sectional area relative to said leading end portion.

Alternatively, said bar is deformed by slotting and expanding said leading end portion.

Typically said method further comprises the step of forming a sharpened projection or projections on said leading end portion so as to protrude therefrom.

Preferably, said sharpened projection(s) is/are formed by deformation of said leading end portion.

Preferably, said sharpened projection(s) is/are formed by cold rolling.

Alternatively, said sharpened projection(s) is/are formed by forging.

Brief Description of the Drawings A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a fragmentary front elevation view of a rock bolt.

Figure 2 is a fragmentary front elevation view of the rock bolt of 1iur installed in a rock bolt hole.

Figure 3 is a fragmentary front elevation view of an alternate rock bolt installed in a rock bolt hole.

Figure 4 is a front elevation view of a rock bolt during manufacture.

Figure 5 is a front elevation view of another alternate rock bolt.

Detailed Description of the Preferred Embodiments With reference to Figures 1 and 2, a rock bolt 1 according to a preferred embodiment of the present invention has a leading end portion 2 on which is formed a sharpened projection 3 (or multiple projections) for shredding the plastic casing of a resin cartridge (not shown) upon rotation of the rock bolt 1 in a rock bolt hole 100. The crosssectional area of the leading end portion 2 on which the projection(s) is/are formed is greater than that of the portion of the rock bolt adjacent to the leading end portion 2. That is, the diameter of the end portion itself, not of the projection formed thereon, is greater than that of the adjacent portion when both portions are cylindrical. In fact in this [R:\L1BLLIO9940.doc:TCW:VJP embodiment the leading end portion 2 cross-sectional area is greater than the crosssectional area of the entire bar portion 5 which extends along the remainder of the length of the bolt 1, apart from the trailing end portion 6 which is threaded for receipt of a nut and rock plate (as depicted in Figure The trailing end portion 6 need not necessarily be threaded to receive the rock plate and nut, but could have a head forged onto the end in place of the nut as is known to secure the rock plate.

The sharpened projection 3 is here in the form of a helical thread-like ridge. The continuous sharpened ridge is able to effectively cut through the plastic casing of a resin cartridge punctured by the rock bolt on insertion of the rock bolt into a rock bolt borehole 100. Multiple discrete projections could alternatively be utilised.

Most machinery utilised for installation of rock bolts are equipped to rotate the bolt with a clockwise or right hand rotation for mixing of resin from the plastic resin cartridge. It has previously been believed that it would be advantageous to arrange any •helix on the bolt in a left hand thread configuration so as to prevent resin being drawn Is down the rock bolt away from the end of the hole by the helix. Such a configuration, however, would also push plastic shredded from the cartridge casing towards the end of the hole rather than pulling it along the rock bolt 1 to expose it to the sharpened projection(s) 3 for shredding between the rock bolt and the wall of the rock borehole. Slip planes would result as discussed above. Accordingly, it is preferred that the helical thread-like ridge 3 be of a right hand configuration for such machinery so as to pull plastic of the cartridge down along the bolt leading end 1 for shredding between the helical thread-like ridge 3 and walls of the borehole 100. For installation machinery with S: a left handed rotation for mixing the resin, a left handed helical ridge should be employed.

To ensure the correct helical direction, the helical ridge 3 should be formed in the same direction as the thread 6 at the trailing end portion, as this will be formed in the same direction as the rotation of the installation machinery intended to be used.

A typical rock borehole has a diameter of the order of 27 millimetres, with the diameter of a typical rock bolt being approximately 22 millimetres. The bar portion 5 of the rock bolt 1 of the present embodiment may have an oval cross-section when formed by rolling (as will be discussed below), with a particular embodiment having a major axis diameter of about 22 mm and a minor axis diameter of about 20.5 mm. This compares with the typical diameter of the enlarged end portion of about 22 mm, providing an increased cross-sectional area as compared to the bar portion 5. The tip of the helical ridge 3 formed on the enlarged end portion 2 has an external diameter of approximately 24 millimetres, leaving a thin annular space having a depth of approximately [R:\LIBLL]09940.doc:TCW:VJP millimetres between the helical ridge 3 and the wall of the rock borehole 100. Reduction of the thickness of this annular space increases the efficiency of the shredding of the plastic. The enlarged end portion 2 typically has a length of about 30 to 50 millimetres, which has been found sufficient to effectively shred the plastic without providing excessive resistance to extrusion of the resin through the annular space as the rock bolt is pushed into the end of the hole 100.

The enlarged cross-sectional area of the end portion 2 as compared to the adjacent bar portion 5 importantly provides increased anchorage for the rock bolt 1. The column of mixed resin grout 7 anchoring the rock bolt 1 has a cross-sectional area at the adjacent bar portion 5 smaller than the cross-sectional area of the annular space between the enlarged portion 2 and the wall of the hole 100. Accordingly, once the peak pull-out load has been achieved and an initial displacement of the rock bolt 1 has resulted, the enlarged portion 2 is still supported by the resin grout 7, providing additional resistance to •pull-out of the bolt. The bolt 1 must be pulled through the grout 7 for failure of the bolt i. 15 installation. This improved anchorage can also be achieved without the sharpened projections 3, such as with a smooth enlarged end portion.

An alternative embodiment of the present invention is depicted in Figure 3. In this embodiment of the rock bolt 101, the bolt end portion 102 has a cross-sectional area larger than that of an adjacent portion 104 of the rock bolt. The leading end portion again typically has a diameter of about 22 mm compared to a diameter of about 19 mm at the adjacent portion 104. This rock bolt 101 is tapered from the leading end portion 102 to the adjacent portion 104, and is reverse tapered from the adjacent portion 104 to the constant :diameter bar portion 105. The leading end portion 102 is provided with a helical thread forming sharp projections 103 in a similar manner to the first embodiment. Whilst it is preferred that the diameter of the bar portion 105 is less than that of the leading end portion 102, such a relationship is not strictly necessary given that the reduced diameter portion 104 provides the additional anchorage for the grout and also provides an increased thickness annular space for extrusion of resin as the bolt is pushed into the end of the hole 100.

Formation of the tapered section 108 between the end portion 102 and the reduced diameter portion 104 increases the anchorage strength of the bolt, as when the bolt 101 is pulled and displaced, the tapered section 108 will progressively engage the annular portion of grout 107 directly below the tapered section 108, wedging the tapered section 108 against the grout. Formation of the reverse tapered section 109 between the reduced diameter portion 104 and the bar portion 105 of the bolt, as opposed to a step [R:\LIBLL]09940.doc:TCW:VJP change in diameter, will reduce the size of any void formed between the grout and the bolt when the bolt is displaced during attempted pull-out and will increase the load bearing capacity of the resin grout. The tapered and reverse tapered sections 108, 109 can be conical as depicted, or might alternatively each be formed in a truncated pyramid type configuration. The sharp edges defined between side surfaces of such truncated pyramids could assist in shredding plastic of the resin cartridge casing.

Whilst the reduced diameter 104 of the bolt adjacent the end portion 102 will reduce the tensile strength of the bolt, the minimum diameter 104 can be selected so as to still exceed the anchorage strength of the end portion 102. The length of the end portion 102 can be selected depending on the required anchorage strength and the tensile strength of the bar at the reduced diameter portion 104.

With reference to Figure 4, the rock bolts of the preferred embodiments of the present invention are formed by rolling a round bar between two dies 20, 21 to form a protruding pattern 10 on the surface of the bar during rolling in the usual manner. The S 15s bar is only rolled, however, in the central bar portion 5 of the bolt, with both the leading and trailing end portions being left blank. The pressure of the dies 20, 21 reduces the cross-section of the central rolled section, typically to an oval cross-section as discussed above. Accordingly, the leading end portion 2 will have a larger cross-sectional area than the rolled bar portion 5. The leading end portion 2 is then deformed by cold rolling to 20 form a helical thread-like ridge 3. The cold rolling process will form a sharpened ridge which will have a diameter larger than the diameter of the blank leading end portion 2 on which it was formed. The trailing end portion 6 of the bolt is threaded in the usual manner for receipt of a rock plate and nut. Alternatively, the trailing end 6 might be forged to provide a head against which a rock plate can bear once installed.

The sharp projection(s) could also be created by other methods, for example by hot or cold forging. The enlarged portion may be formed separately and secured by any of various methods to a blank bar of constant diameter.

With reference to Figure 5, the enlarged end portion 202 of an alternative bolt 201 could be provided by forming a slot or slots 211 in the leading end of the bolt 201.

The slot(s) can then be utilised to expand the end portion 202 by forcing a wedge or similar into the slot(s) 211. The expanded leading end portion 202 will then have a greater diameter than the adjacent unexpanded bar portion 205. During mixing of the resin from the resin cartridge, resin will flow into the slot 211 to prevent the opposing sections of the expanded end portion 202 from collapsing inwardly during pullout of the bolt.

[R:\LIBLL]09940.doc:TCW:VJP Other possible configurations and modifications will be appreciated by the person skilled in the art.

S

S.

[R:\LIBLL]09940.doc:TCW:VJP

Claims

1. A rock bolt having a leading end portion with a cross-sectional area greater than that of a portion of said rock bolt adjacent said leading end portion, and a trailing end portion adapted to receive a rock plate. s

2. The rock bolt of claim 1, wherein said leading end portion cross- sectional area is greater than the cross-sectional area of said bolt at substantially all locations along the remainder of the length of said bolt.

3. The rock bolt of either of claims 1 and 2, wherein said rock bolt is tapered from said leading end portion to said adjacent portion.

4. The rock bolt of claim 3, wherein said rock bolt is reverse tapered from said adjacent portion to a bar portion of said rock bolt lying between said adjacent portion and the trailing end of said rock bolt. *g

5. The rock bolt of any one of claims 1 to 4, further having a sharpened projection or projections formed on and protruding from said leading end portion for •15 shredding a plastic casing of a resin cartridge upon rotation of said rock bolt in a rock bolt hole.

6. The rock bolt of claim 5, wherein said sharpened projection(s) is/are °•formed by deformation of said leading end portion.

S7. The rock bolt of claim 6, wherein said sharpened projection(s) is/are formed by a cold rolling process.

8. The rock bolt of claim 6, wherein said sharpened projection(s) is/are formed by a forging process.

9. The rock bolt of any one of claims 5 to 8, wherein said sharpened projection is in the form of a helical thread-like ridge.

10. The rock bolt of claim 9, wherein said trailing end portion is provided with a thread for receipt of a nut and a rock plate, said helical thread-like ridge being formed in the same direction as that of said trailing end thread.

11. The rock bolt of any one of claims 1 to 10 wherein said leading end portion is slotted.

12. A method of forming a rock bolt comprising the steps of: forming a bar with a leading end portion having a cross-sectional area greater than that of a portion of said bar adjacent said leading end portion, and adapting a trailing end portion of said bar for reception of a rock plate. [R:\LIBLL]09940.doc:TCW:VJP 9

13. The method of claim 12 wherein said bar is formed with said leading end portion cross-sectional area greater than the cross-sectional area of said bar at substantially all locations along the remainder of the length of said bar.

14. The method of either of claims 12 and 13 wherein said bar is formed with said greater leading end portion cross-sectional area by deforming said bar.

The method of claim 14 wherein said bar is deformed by rolling said adjacent portion to a reduced cross-sectional area relative to said leading end portion.

16. The method of claim 14 wherein said bar is deformed by slotting and expanding said leading end portion. l0

17. The method of any one of claims 12 to 16 further comprising the step of forming a sharpened projection or projections on said leading end portion so as to protrude therefrom. •oil

18. The method of claim 17 wherein said sharpened projection(s) is/are :0 formed by deformation of said leading end portion. 15

19. The method of claim 18 wherein said sharpened projection(s) is/are formed by cold rolling. 0000

20. The method of claim 18 wherein said sharpened projection(s) is/are formed by forging.

21. A rock bolt substantially as hereinbefore described with reference to o•20 Figures 1 and 2, Figure 3 or Figure 4 of the accompanying drawings. 0900 Dated 23 August, 2000 6o* The ANI Corporation Limited Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON [R:\LIBLL]09940.doc:TCW:VJP