AU711823B3 - Rock anchor - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A PETTY PATENT Name of Applicant:

DITA

LIMITED

PRODUCTS (PROPRIETARY) Actual Inventor: Address for Service: KURT DIETER WOSTENFELDT CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

Invention Title: ROCK ANCHOR The following statement is a full description of this invention including the best method of performing it known to us:

TITLE

ROCK ANCHOR FIELD OF THE INVENTION This invention relates to a rock anchor which is particularly but not exclusively intended for use in rock bolting in underground mining and tunnelling operations and to an expansible anchor head for use with the anchor.

SUMMARY OF THE INVENTION A rock anchor according to the invention includes a tendon, an expansion head at or adjacent one end of the tendon which is made from a suitable plastics material, is externally cylindrical and has a tapered axial bore through it and carries on its external surface a plurality of radially extending flexible fins, and, a conical formation on the tendon which when pressed into the bore of the expansion head expands the head radially relatively to the tendon axis.

Further according to the invention the expansion head carries a plurality of circumferentially spaced slits which extend through its wall in the axial direction of the head with each second slit extending from a first end of the head to a position short of the second end and the slits between them extending from the second end of the head to a position short of the first end so that the slits between them define radially movable anchor wedges.

Conveniently, the conical formation on the tendon is tapered to the angle of taper of the anchor head bore. Preferably the formation is made from a plastics material and is attached in any suitable manner to the tendon.

The tendon may be a solid or hollow bar having a portion of its length opposite that at which the anchor head is located threaded. Alternatively, the tendon may be a cable.

The invention extends not only to the rock anchor but to the anchor head per se.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is now described by way of example only with reference to the drawings in which: Figure 1 is a side elevation of one embodiment of the rock anchor of the invention, Figure 2 is a sectioned side elevation of the anchor head of the Figure 1 rock anchor, Figure 3 is a plan view of the anchor head of Figure 2, and Figure 4 is a sectioned side elevation of the anchor head portion of a second embodiment of the rock anchor of the invention.

DETAILED DESCRIPTION The rock anchor of Figure 1 shown in the drawings to consist of a tendon 10 which is threaded over a portion of its length from 12 from its lower end and carries at its upper end and a conical formation 14 and an anchor head 16 which is slidably located on the tendon The formation 14 may be attached in any suitable manner to the tendon 10 but in this embodiment of the invention is fixed to the tendon by a dowel pin 17.

The conical formation and the anchor head are made from a suitable plastics material. The plastics material from which the anchor head is made could be nylon 56 which is 15% to 30% glass filled.

The anchor head 16 is more clearly shown in Figures 2 and 3 to consist of a body 18 which has a cylindrical outer surface and a conical bore 20 which passes axially through it. The bore is inwardly tapered from the upper end of the anchor head to its lower end with its angle of taper being complemental to that of-the formation 14. The walls of the anchor head are vertically slit by a first series of circumferentially spaced slits 22 which extend from the upper end of the anchor head to a position short of its lower end as is seen in Figure 2. Slits 24 of a second series are- situated between the slits 22 and extend from the lower end of the head to a position short of the upper end of the head to provide radially movable anchor wedges between alternate slits.

The tendon 10 includes a square or other noncircular washer 28 which is fixed by welding to the tendon. The underside of the anchor head body includes a recess 30 which surrounds the lower mouth of the anchor head bore 20 and which is complementally shaped to the washer 28.

The anchor head additionally includes flexible fins 32 which extend radially from the head with a circle which circumscribes the tips of the fins in Figure 3 being larger than the diameter of the hole in which the anchor head is to be used. The fins 32, in this embodiment of the invention, are shown to be parallel sided but are preferably tapered inwardly from a position along their length towards the head of the body 18, as illustrated in Figure 4, to simplify location of the anchor head in a drill hole.

The anchor head could additionally include downwardly and outwardly directed flaps 34 which are circumferentially spaced around the base of the anchor head to serve as flexible catches for engaging the wall of a drill hole when the anchor head is located in it at its position of use to inhibit withdrawal of the rock anchor from the hole.

In use, the anchor head portion of the rock anchor is fed into a predrilled hole by pressing the edges of the fins 32 up against the edges of the mouth of the hole and pressing the rock anchor towards the hole by means of the tendon while rotating it and so the anchor head 16 which is engaged with the washer 28. As the anchor head enters the hole the fins 28 will curl against the hole wall in the direction of rotation to enable the anchor head to be pressed into the hole to its desired location in the hole. The anchor head is located by the fins 32 and the flaps 34 adequately to hold the anchor head at that position and suitable pulling jack is then attached to the threaded end of-the tendon at the mouth of the hole and pulled downwardly from the position shown in Figure 1 to cause the conical formation to expand and firmly wedge lock the anchor head in that position in the hole. The hole surrounding the tendon 10 and at least portions of the anchor head may be grout or resin filled in the conventional manner and a face washer, a domed washer and a tension nut are located on the threaded end of the tendon which projects from the mouth of the hole and the rock anchor is tensioned in the hole, in the conventional manner, between the face washer and its anchor head prior to full curing of whatever settable material surrounds the rock anchor in the hole.

In the Figure 4 embodiment of the invention like reference numbers denote similar components to those described with reference to the rock anchor of Figures 1 to 3. The principal difference between the rock anchors of the two embodiments is that the cone 14 of the Figure 4 embodiment has a bore which passes through it with the lower portion of the bore being very slightly greater in diameter than the diameter of the tendon 10 and the portion of the bore above that being larger in crosssectional area and having a hexagonal cross-sectional shape. The upper end of the tendon is threaded and carries a nut 36 which is a neat sliding fit in the hexagonal portion of the cone bore. A spring is located between the upper surface of the washer 27 and the underside of the conical formation, as shown in Figure 4 to bias the cone 14 away from the washer 28.

The Figure 4 rock anchor is located in a predrilled hole as described with reference to Figure 1 with the exception being that when the anchor head 16 is located at its intended position in the drill hole the direction of rotation of the tendon is reversed to the direction in which it was rotated while being pressed into the hole to tend to uncurl the fins 28 and cause their edges to engage the side wall of the hole to hold the head in position and to prevent its rotation and simultaneously to rotate the tendon in the nut 36 to M -M 6 cause the nut to move downwardly on the tendon and so pull the conical formation 14 into the anchor head to expand it into firm wedge locking contact with the side wall of the hole. Although the spring between the nut and the conical formation 14 is useful in holding the conical formation extended from the anchor head 16 in applications where the anchor head is to be located at the blind end of the hole it may be omitted and the washer 28 could be moved upwardly on the tendon 10 to be located in the head recess 30 while the conical formation is in the extended position shown in Figure 4 while the tendon is rotated and pressed into the drill hole.

Claims (4)

1. A rock anchor including a tendon, an expansion head at or adjacent one end of the tendon and which has a tapered radial bore, the expansion head including a plurality of circumferentially spaced slits which extend through its wall in the axial direction of the head with each second slit extending from a first end of the head to a position short of the second end and the slits between them extending from the second end of the head to a position short of the first end so that the slits between them define radially movable anchor wedges, a conical formation on the tendon which when lo pressed into the bore expands the head relative to the tendon axis and the anchor wedges are radially moved to a wedge locking position.

2. The rock anchor of claim 1, wherein the expansion head carries on its external surface, a plurality of radially extending fins.

3. The rock anchor of claim 1, substantially as hereinbefore described with reference to Figures 1, 2 and 3 or Figure

4. DATED this 14th day of July 1999 DITA PRODUCTS (PROPRIETARY) LIMITED By their Patent Attorneys CULLEN CO. -I-"9