WO2018058156A2

WO2018058156A2 - Tension limiting rock anchor

Info

Publication number: WO2018058156A2
Application number: PCT/ZA2017/000009
Authority: WO
Inventors: Brendan Robert Crompton
Original assignee: Ncm Innovations (Pty) Ltd
Priority date: 2016-08-16
Filing date: 2017-08-15
Publication date: 2018-03-29
Also published as: WO2018058156A3

Abstract

The invention provides a cable anchor which includes a flexible elongate body which extends between a distal end and a proximal end and a tension limiting formation on the body which Is fixed at a predetermined distance from the distal end,

Description

TENSION LIMITING ROCK ANCHOR BACKGROUND OF THE INVENTION

[0001] This invention relates to a cable anchor which cannot be placed In tension unless properly installed within a rock hole of adequate depth.

[0002] A typical cable anchor assembly includes a flexible cable anchor of a standard length, having a distal end section to which is attached an anchoring means to anchor the distal end in a predriiled rock hole, and an opposed proximal end section which projects from the hole.

[0003] A barrel and wedge assembly, engaged with the proximal end section, provide a means to hoid tension cable anchor in tension, once placed in tension, to draw a faceplate on the proximal end section into load supportive contact with a rock face adjacent the rock hole.

[0004] The load support provided by the cable anchor is proportional to its length, thus the reason for standardising the length. However, optimal load support will not be provided by the cable anchor to the rock face if an installer fails to drill a hole of a depth adequate to receive the cable anchor in extension.

[0005] A problem arises when the installer, installing the cable anchor into a hole of insufficient depth, attempts to cover up this sub-optimal installation by removing the evidence, of excess length protruding from the hole after tensioning, by cropping the cable anchor.

[0006] The invention at least partially addresses the aforementioned problem. SUMMARY OF INVENTION

[0007] The Invention provides a cable anchor which includes a flexible elongate body which extends between a distal end and a proximal end and a tension limiting formation on the body which is fixed at a predetermined distance from the distal end. [0008] The distance is predetermined to cause the formation to abut against a post installation structure, engaged with the body on a proximal end section of the body to prevent the body from being drawn through the structure, in an attempt to place the body in tension within a rock hole, when the rock hole is of insufficient depth.

[0009] The post installation structure may be a faceplate, a load indicator or a barrel of a barrel and wedge system.

[0010] The limiting formation may be a ferrule or a lug attached to the body by, for example, welding or swaging.

[0011] Alternatively, the limiting formation may be made integral with the body by forming. [0012] The invention further provides a method of preventing a cable anchor from being installed in tension in a rock hole of insufficient depth, which cable anchor has a flexible body which extends between a distal end and a proximal end, which includes the steps of increasing the diameter of the body over a section of the body and spacing the section of increased diameter from the proximal at distance which is predetermined to cause the section to abut against a post installation structure on the body, preventing the body from being drawn through the structure before the body is placed in tension. [0013] The post installation structure may be a faceplate, a load indicator or a barrel of a barrel and wedge system.

[0014] The diameter of the body may be increased over the section by fixing a ferrule or a lug by, for example, swaging or welding.

[0015] Alternatively, the diameter of the body may be increased over the section by forming the body.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The invention is described with reference to the following drawings in which:

Figure 1 shows a cable anchor assembly correctly and optimally installed within a rock hole; and

Figure 2 shows a cable anchor assembly, with a cable anchor adapted in accordance with the invention, prevented from being correctly installed within a rock hole of insufficient depth.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0017] Figure 1 illustrates a rock anchor 10 which has an elongate cable body 12 which extends between a distal end 14 and an opposed proximal end 16.

[0018] The anchor 10 carries a mechanical anchor 18 at or towards the distal end. At a proximal end, a faceplate 20 and a barrel 22 and wedge 24 system is engaged to the body to complete a typical rock anchor installation, installed in a predrilled rock hole 26 in a rock face 28. [0019] The body 12 of the anchor is a standardised length. This length is predetermined to provide optimal load support by the installation to the rock face.

[0020] However to provide optimal support, the depth of the rock hole 26 must complement the length of the body 12 so that the body can extend, in tension substantially across the length of the rock hole, between the mechanical anchor 18 and the barrel and wedge system (22, 24).

[0021] To prevent the rock anchor 10 from being installed in tension in a rock anchor of insufficient depth, as illustrated in Figure 2, the rock anchor 10 of the invention carriers a lug or ferrule 30 which is engaged with the body 12 to a fixed point on the body. This fixed engagement is achieved by any suitable means such as, for example, by swaging. The lug is carried on the body at a predetermined distance, designated 32, from the proximal end 16 of the body.

[0022] This distance (32) is determined to cause the lug 30 to abut against a leading end 34 of the barrel 22, as illustrated in Figure 2A, preventing the body 12 from being tensioned by being drawn through the barrel and wedge system (22, 24), when the rock hole 26 is of insufficient depth. This is illustrated in Figure 2.

[0023] However, as illustrated in Figure 1, the distance is such that the lug is not caused to abut against the barrel if the rock hole 26 is of sufficient depth to allow the body 12 to be tensioned substantially across its length. [0024] With the lug 30 preventing tension of the cable bolt body 12, the faceplate 20 cannot be placed in load support contact with the rock face 28 and, on release of the body 12, dropping away from the wall and hanging on the body, as illustrated Figure 2B.

Claims

1 A cable anchor which Includes a flexible elongate body which extends between a distal end and a proximal end and a tension limiting formation on the body which Is fixed at a predetermined distance from the distal end.

2. A cable anchor according to claim 1 wherein the distance is predetermined to cause the formation to abut against a post installation structure, engaged with the body on a proximal end section of the body, to prevent the body from being drawn through the structure, in an attempt to place the body in tension within a rock hole, when the rock hole is of insufficient depth.

3. A cable anchor according to claim 2 wherein the post installation structure is a faceplate, a load indicator or a barrel of a barrel and wedge system.

4. A cable anchor according to any one of claims 1 to 3 wherein the limiting formation is a ferrule or a lug engaged with the body.

5. A cable anchor according to any one of claims 1 to 3 wherein the limiting formation is made integral with the body by forming.

6. A method of preventing a cable anchor from being installed in tension in a rock hole of insufficient depth, which cable anchor has a flexible body which extends between a distal end and a proximal end, which includes the steps of increasing the diameter of the body over a section of the body and spacing the section of increased diameter from the proximal end at a distance which is predetermined to cause the section to abut against a post installation structure on the body before the body is placed in tension.

7. A method according to claim 6 wherein the post installation structure Is a faceplate, a load indicator or a barrel of a barrel and wedge system.

8. A method according to claim 6 or 7 wherein the diameter of the body is increased over the section by fixing a ferrule or a lug to the body.

9. A method according to claim 6 or 7 wherein the diameter of the body is increased over the section by forming the body.