GB2284032A

GB2284032A - Bolt anchoring device

Info

Publication number: GB2284032A
Application number: GB9322893A
Authority: GB
Inventors: Nicholas William Midgley
Original assignee: LONGLEYS
Current assignee: LONGLEYS
Priority date: 1993-11-06
Filing date: 1993-11-06
Publication date: 1995-05-24
Anticipated expiration: 2013-11-06
Also published as: GB2284032B; GB9322893D0

Abstract

A bolt anchoring device includes an expandable sleeve 16 and a plug 18 which is press fitted within the trailing end of the sleeve 16. The plug 18 may be advanced by means of the bolt (not shown) within the sleeve 16 so as to cause the sleeve 16 to expand and grip the surfaces of a bore hole. Also claimed is an assembly including an expandable sleeve and a cartridge for curable bonding medium, and a method of anchoring a rock bolt into the bore hole. <IMAGE>

Description

BOLT ANCHORING DEVICE AND METHOD Field of the Invention This invention relates to a bolt anchoring device, of the type used to anchor a bolt in a bore hole. In particular the invention relates to the anchoring of rock bolts into mine roofs and walls and similar structures. The invention also relates to a method of anchoring a bolt, in particular a rock bolt, into a bore hole and also to an assembly consisting of the bolt anchor and a bolt to be anchored.

Background to the Invention The roofs and walls of underground structures such as mines often need to be reinforced. This is typically achieved by drilling a bore hole into the rock strata forming part of the roof or wall, to appropriate depth, and installing a rock bolt in the bore hole. The rock bolt is anchored in position in the bore hole and then tensioned to a desired torque, sufficient to support the wall or roof. In the majority of cases nowadays, the bolt is anchored in the bore hole by means of a suitable bonding agent such as a curable resin composition. Once the bore hole has been drilled, at least two resin cartridges are inserted into the bore hole and located at the closed end of the hole by means of a suitable retaining ring. The first cartridge to be inserted contains a relatively fast setting curable resin composition which typically takes less than 30 seconds to cure.The subsequent cartridge or cartridges contain a relatively slow setting resin composition which typically takes about 10 minutes to cure. A rock bolt, having a leading end which is adapted to be anchored in the bore hole and a threaded portion at its opposite end, is then driven into the bore hole with its threaded end protruding from the open end of the hole. A bearing plate, for example a washer, is positioned on the threaded end portion of the bolt and a tightening nut, adapted to engage with and run along the threaded end portion is also mounted on the threaded portion of the bolt.

The rock bolt is rotated whilst it is being driven into the bore hole. The leading end of the bolt punctures the cartridges containing the resin compositions, causing the release of the curable resin into the closed end of the bore hole and around the leading end of the bolt. The bolt is held in position in the bore hole for a period of time, typically up to 30 seconds, sufficient to allow the fast setting curable resin to harden and thus anchor the leading end of the bolt firmly in the bore hole. The bolt can then be tensioned, by tightening the nut against the bearing plate. The bearing plate itself bears against the outer surface of the wall or roof into which the bore hole has been drilled. During the next ten minutes or so, the slow setting resin composition cures and reinforces the anchoring of the bolt in the bore hole.

With modern mining techniques, the roof and walls of a mine are reinforced periodically typically by sets of eight rock bolts spaced apart by a fixed distance from previous and subsequent sets. Each set can take about 17 minutes to install and to save on labour costs, the bolts are all installed by one machine. Given that the machine must wait up to 30 seconds for the fast setting resin for each rock bolt to cure, it may spend up to 4 minutes for each set doing nothing but waiting. To increase productivity, the operator may be tempted not to wait long enough for the fast setting resin to cure and to begin torquing up the nut against the bearing plate too early. In the end, this is counterproductive, since it produces too many no bolts, ie bolts which pull out before the resin has set.It is an object of the present invention to obviate the need for fast setting curable resin and the associated waiting time.

This is achieved by replacing the fast setting resin cartridge with an anchoring sleeve and furnishing the leading end of the rock bolt with a thread which taps into the sleeve, causing the sleeve to be compressed between the rock bolt and the surfaces of the bore hole to anchor the rock bolt firmly in place.

However, with an anchor which takes the form of a simple sleeve, similar to a rawl plug (trade mark) domestic screw anchor, the problem may exist that the torque applied to the rock bolt causes the sleeve to rotate within the bore hole, thus preventing the thread on the leading end of the rock bolt from gaining a purchase and tapping into the sleeve. This problem is present with most applications in which an anchoring sleeve is used to anchor a bolt into a bore hole, such as with the domestic rawl plug (trade mark) discussed above, and is by no means limited to the anchoring or rock bolts.

It is a further object of the invention to provide a bolt retaining anchor which does not tend to spin as an attempt is made to tap in the bolt to be anchored.

Summarv of the Invention According to the invention there is provided an anchor for retaining a bolt within a bore hole comprising an expandable sleeve and a plug positioned within the trailing end of the sleeve, wherein the plug may be advanced within the sleeve so as to cause the sleeve to expand and grip the surfaces of the hole. The advantage of the anchor according to the invention is that it can be inserted into the bore hole with the sleeve in an unexpanded state.

Then, as the bolt is inserted into the hole and eventually contacts the plug, axial force on the bolt will cause the plug to begin to advance within the sleeve, which will preexpand the sleeve so that it grips the surfaces of the bore hole before the threaded leading end of the bolt begins to engage the sleeve. The sleeve, plug and bore hole will be so arranged that the grip of the pre-expanded sleeve will be sufficient to resist the torque imposed by the advancing bolt and therefore allow the thread to tap into the sleeve as required.

To aid in expansion it is preferred that the sleeve be axially split along its entire length. To aid in gripping the surfaces of the bore hole, it is preferred that the outside of the sleeve be provided with gripping profiles.

The gripping profiles may comprise one or more expandable rings, preferably split metallic rings surrounding the expandable sleeve. These metallic rings further improve the grip of the expandable sleeve on the surfaces of the bore hole, particularly in connection with the application of axial loads.

For convenience, it is preferred that the trailing end of the expandable sleeve includes a region of relatively large internal diameter as compared with the region of the sleeve towards its leading end. The plug may therefore be positioned in the region of relatively large internal diameter and only cause expansion of the sleeve as it is pushed into the region of relatively small internal diameter. Preferably, the transition between the relatively large and relatively small internal diameters is tapered, or the leading end of the plug is tapered, or both. This will enable the plug more easily to overcome the initial resistance against its entering the region of relatively small internal diameter.

A further advantage of the two regions of different diameters is that, as the plug begins to expand the region of relatively small internal diameter, it will in consequence also expand the region of relatively large internal diameter. When expanded, the diameter of the region of relatively small internal diameter will correspond with the diameter of the bolt to be inserted, discounting the raised portions constituted by the thread.

The region of relatively large internal diameter can be arranged such that, when it is expanded, it will clear the threads on the bolts to be anchored, thus preventing any torque from being exerted on the anchor until such time as the thread meets the region of relatively small internal diameter.

As is discussed above, the anchor according to the invention is suitable for use as replacement for fast setting resin in a rock bolting system. All that is required is the anchor and a cartridge of slow setting curable resin. Accordingly, the present invention extends to an assembly for anchoring a rock bolt within a bore hole including an anchor comprising an expandable sleeve and a cartridge of a curable bonding medium. The anchor is preferably as described above as being in accordance with the invention.

Preferably, the anchor and the cartridge are contained within a single package which is adapted to be inserted into a bore hole. In addition the assembly may include a retaining means, such as a retaining ring, adapted to retain the assembly within the bore hole, once inserted.

It will be understood that, according to the invention, the installation of a rock bolt will proceed as follows. First the anchor is inserted into the bore hole, followed by the resin cartridge and the retaining ring. These elements or any sub-combination of them may be inserted as a single assembly, so long as the anchor goes in first, the resin cartridge second and the retaining ring last. The rock bolt is rotated to drive it into the bore hole, and in being so driven, the leading end of the bolt punctures the cartridge containing the resin bonding agent, causing the release of the bonding agent into the bore hole. The bolt, having a threaded leading end, is then driven further into the bore hole so as to tap into the anchor, thereby firmly anchoring the bolt in place.The bearing plate and tightening nut may then immediately be tightened up against the wall or roof of the mine in which the bolt has been installed, since there is no need to wait for any fast setting resin to cure. This saves up to 30 seconds of installation time for each bolt.

A further advantage of the anchor and anchoring method according to the invention is that it is not necessary to have a separate nut on the trailing end of the bolt. The rock bolt may be provided with a standard bolt head which, as the bolt is tapped into the anchor approaches and eventually meets up with the roof or wall or the mine. A bearing plate can be positioned on the bolt before it is inserted into the bore hole and the bearing plate will then be tightened up to the mine roof or wall as the bolt is tapped into the anchor. The bolt can be torqued up immediately to the desired torque level with the torque being taken up by the anchor, rather than by the bolt itself.

Thus, the present invention also extends to a method of anchoring a rock bolt into a bore hole including: inserting firstly an anchor including an expandable sleeve and secondly a cartridge of curable bonding material into the bore hole; inserting a rock bolt having a threaded leading end into the bore hole; passing the leading end of the rock bolt through the cartridge so as to release the curable material contained therein; and applying to the bolt a torque sufficient to enable the threaded end to tap into and expand the expandable sleeve, thereby firmly anchoring the bolt in position.

As is mentioned above, the method may subsequently involve tightening a nut at the tailing end of the bolt against a bearing plate to the predetermined torque, or may simply involve torquing up the bolt such that a fixed head thereon tightens up against a bearing plate.

Naturally, in the method according to the invention, the anchor may be an anchor as is described above as being in accordance with the invention.

Brief Description of the Drawings The present invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 is a part-sectional view through the anchor; and Figures 2-4 illustrate the various stages during installation of a rock bolt using the anchor.

Figure 1 illustrates the anchor in isolation. The anchor 10 consists of a sleeve 16, divided from one to the other by a single split 36. The sleeve 16 may be formed from any suitable deformable material, such as nylon or other plastics. The exterior surface of the sleeve is provided with saw tooth shaped profiles, which are arranged to resist movement of the anchor in the direction opposite to its direction of insertion into the bore hole. Every third one of the saw tooth shaped profiles 22 is replaced with a circumferential groove 44, in which is seated a metallic ring 24. The rings 24 are, in section, trapezoidal and externally correspond in shape with the saw tooth profiles 22. However, the rings may be plain, chamfered or serrated, depending upon the nature of the material in which the anchor is to work.The rings may be formed from mild or carbon steel or spring steel, and, to aid their expansion and to assist in their position on the anchor in the first place, are also split.

At the leading end of the sleeve 16 is a region of relatively small internal diameter 26; at the trailing end is a region of relatively large internal diameter 28. The transition between the two diameters consists of a taper 30. Seated within the region of relatively large internal diameter 28 is a bullet shaped plug 18 formed of rigid material, such as acrylic or nylon or other rigid plastics material or metallic material. The plug is a a press fit into the region of relatively large internal diameter and has a tapered leading edge 32 which in connection with the taper 30 assists the passage of the plug 18 into the region of relatively small internal diameter 26.

Adjacent the trailing end of the sleeve 16 is a region of even larger internal diameter 46, into which the trailing end of the plug 18 projects. The diameter of this region 46 is a clearance diameter over the thread on the rock bolt and this region protects the plug 18 during transport and installation. The plug 18 projects into this region 46 so that the roof bolt can displace the plug 18 sufficiently to enable the anchor to be expanded and grip the hole before the thread on the bolt enters the region of relatively large internal diameter 28.

Figure 2 illustrates an anchoring assembly consisting of an anchor 10 and a resin cartridge 20 located in a bore hole in a rock substrate 38. In its unexpanded state, the anchor 10 is smaller in diameter than the bore hole and may therefore easily be inserted. Similarly, the cartridge 20 which may be included in a single package with the anchor 10, eg in a cellophane wrapping, is also inserted into the bore hole and the assembly is retained in place by a retaining ring (not shown). Typically, the anchor 10 will be approximately 6 inches in length. Next, a rock bolt 12, illustrated in Figure 3 is rotated to drive it into the bore hole. The bolt 12 punctures the resin cartridge 20, thus releasing the curable resin 42 into the bore hole.

Further advancement of the rock bolt 12 forces the resin 42 downwards into the annular region between the bolt 12 and the surfaces of the bore hole.

Once the leading end of the bolt 12 contacts the plug 18, the tapered leading edge 32 of the plug 18 rides up the taper 30 within the expandable sleeve, thus allowing the plug 18 to enter the region of relatively small internal diameter 26. As can be seen from Figure 3, expansion of the sleeve brings the lowest gripping ring 24a into contact with the surface of the bore hole and further expansion allows the ring to bite into the surfaces of the hole.

A consequence of the expansion of the trailing end of the anchor 10 is that the region of relatively large internal diameter 28 is also expanded. In its expanded state, this region is large enough to accommodate the thread 40 at the leading end of the rock bolt 12. Accordingly, the plug 18 can be advanced to such an extent that it lies entirely within the region of relatively small internal diameter 26 of the sleeve 16, before the thread 40 begins to tap into the sleeve 16. In this way, maximum expansion of the trailing end of the sleeve 16 is achieved without requiring any appreciable torque to be exerted on the sleeve. Thus, the trailing end of the anchor 10 is adequately fixed within the bore hole to resist the torque exerted by the bolt 12 as the thread 40 begins to tap into the sleeve.

As is shown, the diameter of the plug 18 is the same as the diameter of the bolt 12, disregarding the thread 40, which allows the bolt 12 to gain a good purchase on the anchor 10, but limits the increase in torque exerted on the anchor 10 as the thread 40 begins to tap in.

Figure 3 illustrates the rock bolt in its fully installed position. Each of the gripping rings 24 has bitten into the surfaces of the bore hole and the plug 18 has been driven right to the leading end of the anchor 10. During installation, when the plug 18 reaches the leading end of the anchor 10, a sudden increase in torque will be felt at the trailing end of the bolt. If the bolt is provided with a torque nut, for example a nut which is attached to the trailing end of the bolt 12 by a shear pin, the sudden increase in torque will be sufficient to free the torque nut which may then be tightened up against a bearing plate which in turn is tightened up against the wall or roof of the mine. The torque nut will typically be tightened to 160 Nm or torque, but it has been found that the anchor is capable of withstanding 270 Nm of torque and 5 tonnes of axial load.

From the above description, it can be seen that the present invention provides a simple, easy to use and inexpensive alternative to fast setting curable resin as a means for obtaining initial anchorage of a rock bolt in a bore hole.

It also provides a simple and effective anchor which tends to resist rotation as a bolt is tapped in.

Claims

1. An anchor for retaining a bolt within a bore hole comprising an expandable sleeve and a plug positioned within the trailing end of the sleeve, wherein the plug may be advanced within the sleeve so as to cause the sleeve to expand and grip the surfaces of the hole.

2. An anchor according to Claim 1 wherein the sleeve is axially split along its entire length.

3. An anchor according to Claim 1 or Claim 2 wherein the outside of the sleeve is provided with gripping profiles.

4. An anchor according to Claim 3 wherein the gripping profiles are in the form of one or more expandable rings.

5. An anchor according to Claim 4 wherein the expandable rings are in the form of split metallic rings surrounding the expandable sleeve.

6. An anchor according to any of the preceding claims wherein the trailing end of the expandable sleeve includes a region of relatively large internal diameter as compared with the region of the sleeve towards its leading end.

7. An anchor according to Claim 6 wherein the transition between the relatively large and relatively small internal diameters is tapered, or the leading end of the plug is tapered, or both.

8. An assembly for anchoring a rock bolt within a bore hole including an anchor comprising an expandable sleeve and a cartridge of a curable bonding medium.

9. An assembly according to Claim 8 wherein the anchor is as claimed in any of claims 1 to 7.

10. An assembly according to Claim 8 or 9 wherein the anchor and the cartridge are contained within a single package which is adapted to be inserted into a bore hole.

11. A method of anchoring a rock bolt into a bore hole including: - inserting firstly an anchor including an expandable sleeve and secondly a cartridge of curable bonding material into the bore hole; - inserting a rock bolt having a threaded leading end into the bore hole; - passing the leading end of the rock bolt through the cartridge so as to release the curable material contained therein; - and applying to the bolt a torque sufficient to enable the threaded end to tap into and expand the expandable sleeve, thereby firmly anchoring the bolt in position.

12. An anchor according to Claim 1 and substantially as described herein.

13. An anchor for retaining a bolt within a bore hole substantially as described with reference to the accompanying drawings.

14. An assembly according to Claim 8 and substantially as described herein.

15. An assembly for anchoring a rock bolt within a bore hole substantially as described with reference to the accompanying drawings.

16. A method according to Claim 11 and substantially as described herein.

17. A method of anchoring a rock bolt into a bore hole substantially as described with reference to the accompanying drawings.