ZA200304376B

ZA200304376B - Method and apparatus for adhesively anchoring tubular rock bolts.

Info

Publication number: ZA200304376B
Application number: ZA200304376A
Authority: ZA
Inventors: Neil Stewart Hunt
Original assignee: Celtite Pty Ltd
Priority date: 2001-11-23
Filing date: 2003-06-04
Publication date: 2004-08-12
Also published as: AUPR901601A0; WO2003044324A8; WO2003044324A1

Description

C0" WO 03/044324 PCT/AU02/01587

METHOD AND APPARATUS FOR

ADHESIVELY ANCHORING TUBULAR ROCK BOLTS

Background to the Invention

This invention concems, in one aspect, rock bolts used to stabilise the ground in civil engineering and mining operations. It has particular applicability to roof and wall stabilisation in underground hard rock mines.

Most rock bolts are made of solid steel bar although some are made of hollow steel bar and others are made from relatively light wall steel tubing. Hollow bar bolts have been used for self-drilling rock bolts, with the hollow core used as a conduit for supplying drilling fluid and resin bonding agent. Thin walled tubular bolts have been used particularly where they are caused to swell under hydraulic pressure to frictionally engage the hole in the rock along their length or where they have a tip with an expansion mechanism to frictionally engage the end of the hole in a point anchor manner. :

The present invention is particularly directed to the use of resin bonded rock bolts.

There are two general techniques for inserting resin into holes for affixing rock bolts therein. The most common method is to insert into the hole a cartridge or cartridges comprising the separated components of the resin in a frangible casing or casings, then insert the rock bolt and rotate it to rupture the cartridge and mix the resin components. The rotation is then stopped for a few seconds, during which time the resin cures, and the bolt is then tensioned. This method includes the following steps: 1. Inserting the resin cartridge into the hole in the rock. 2. Inserting the rock bolt and pressing it home to rupture the cartridge. 3. Rotating the rock bolt.

A significant problem in some situations is that there is insufficient mixing of the - resin components, often due to operator error. Another problem is the possibility of excess entrainment of air during the vigorous rotary mixing process can be exacerbated by fragments of the cartridge casing being wrapped around the bolt. The frangible casing can also itself be an inclusion which provides a weakness. All of these problems can result in the resin anchor having reduced strength.

A variation of the above first technique is to use such cartridges together with a rock bolt having a mechanical expansion anchor on its leading end as described in US patent no. 4,655,645. However there is a substantial cost penalty due to inclusion of the additional compenents in the expansion mechanism on the bolt. ] The second general technique for introduction of resin is to pump it into the hole, : usually through a longitudinal bore within the*bslt. UK patent application no. 2073283 describes a resin-anchored rock bolt having the form of a pipe or tube, where the adhesive is pumped into that end of the pipe which is at the working face. The components of the adhesive are mixed by a static mixer located inside the pipe adjacent the end of the pipe which is at the working face. The mixed resin is pushed along the pipe and out at the bottom (deep end) of the hole to affix the pipe to the rock. But such installation requires the coordinated manoeuvring of both resin injection equipment and bolt rotation equipment in the confined space of a mining tunnel and in practice this can often be a difficult and inefficient operation. Also, the technique results in a substantial quantity of adhesive effectively being wasted as it sets merely filling the pipe thereby having no effect in bonding the bolt to the surrounding rock.

There could be a substantial reduction in time, cost and ease of bolt installation if a i more streamlined installation process was available.

An aim of the present invention is to provide an alternative method and apparatus for supplying and mixing resin for rock bolting and an alternative rock bolt configuration incorporating such alternative apparatus.

Summary of the Invention

Accordingly, in one aspect the invention provides a method of stabilising a zone of rock comprising: (1) drilling a hole into the rock, said hole having a deep end deep in the hole and an opening end at a rock face where the drilling was started; (11) inserting a tubular rock bolt having a hollow bore into the hole whereby a first end of the rock bolt is towards said deep end of the hole and the second end of 10 . the rock bolt is towards said opening end of the hole; (iii) providing in the hollow bore an assembly comprising separate reservoirs * containing components of a multi-component reactive adhesive system; (iv) providing in the hollow bore a static mixer between said reservoirs and said first end of the rock bolt; (v) applying a force to said reservoirs to propel said components through the static mixer, whereby said components become intimately mixed together, and propelled out through said first end of the rock bolt, to then flow back along the hole outside the rock bolt ; and (vi) allowing the adhesive to set and thereby adhere the rock bolt within the hole.

An elongate member may be plunged into the bore to squeeze the reservoirs between the elongate member and the static mixer. The elongate member may transmit its force to the reservoirs by way of a load distributing cap positioned between the elongate member and the reservoirs.

The means for applying the force to the reservoirs may be a pressing member which forms a seal against the wall of the said core.

The reservoirs may take the form of one or more sausage-shaped frangible bags.

They may be ruptured by a sharp implement positioned between the reservoirs and the : mixer.

A rupturing body having a plurality of prongs may rupture the reservoirs. The adhesive components may flow through apertures in the rupturing body to enter the mixer.

The mixer, reservoirs and load distributing cap may be held within the bore, close to said first end, when the bolt is inserted into the hole. Altematively the mixer, reservoirs and load distributing cap may be inserted in the bore, from said second end, after the bolt has been placed into the hole. A cartridge containing all of the mixer, reservoirs and load distributing cap may be inserted into the bore. The rock bolt does not need to be and is preferably not rotated in the hole to mix the components of the adhesive system.

In another aspect the invention provides a tubular rock bolt comprising: (1) a first end adapted for insertion into a hole in the ground and a second end opposite said first end; : (1) a hollow bore within which is ‘housed an assembly comprising separate : reservoirs of components of a multi-component reactive adhesive system; (iit) a static mixer housed in said bore between said reservoirs and said first end of the bolt; (iv) a pressing member housed in said bore such that said reservoirs are housed between the pressing member and the static mixer, said pressing member forming a seal against the inside wall of the rock bolt, and wherein said pressing member is adapted to be pressed towards said first end of the rock bolt so that the reservoirs are thereby caused to rupture and their contents are forced through and thereby mixed within the static mixer before discharge of mixed adhesive from the first end.

The pressing member may comprise a load distributing cap having perforations therethrough to permit airflow during movement of the cap longitudinally of the bore.

A sharp implement, preferably having a plurality of prongs, may rupture the reservoirs. The sharp implement may have apertures whereby the adhesive components can flow through the implement to the mixer.

CT WO003/044324 PCT/AU02/01587

In a further aspect the invention provides a generally cylindrical cartridge adapted for insertion into the bore of a tubular rock bolt, said cartridge comprising:

A) means for storage of reactants, said storage means comprising separate 5 reservoirs of components of a multi-component reactive adhesive system, (1) a static mixer, (iil) means for pressing said reactants towards and through said mixer, and (iv) means for rupturing said reservoirs when said pressing means presses said reservoirs towards the mixer, said rupturing means being positioned between the reservoirs and the mixer.

The storage means, static mixer, pressing means and rupturing means may be held together by a heat sealed wrapping of layers of plastic film which may be a heat- shrink plastic film.

The pressing means may be a pressing means moveable relative to the rock bolt and is adapted to form a seal against the rock bolt.

Brief Description of the Drawings

In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings where: : Figure 1 is a cross section view of a rock bolt in accordance with a first embodiment of the invention shown inserted into a hole drilled into a rock face, together with an actuating plunger for use therewith;

Figure Z is an end view of the boit in Figure 1;

Figure 3 is a cross section view of a cartridge according to a second embodiment of the invention; and

Figure 4 is a cross section view through plane A-A in Figure 3.

For ease of explanation, components in the second embodiment have been identified in the Figures 2 and 3 using the same numbers as like components in the first embodiment.

Description of Examples of the Invention

Referring to Figures 1 and 2, the rock bolt 10 has a body formed of a straight length of steel tube 12. At one end, the trailing end, 14 is welded an outwardly extending flanged collar 16. The collar 16 is formed from solid round section steel rod bent into atoroid and is a neat fit over the outside of the tube 12. The collar 16 is welded flush to the end of the tube.

At the other end, the leading end, 20 of the bolt 10, the tube has a bevel or chamfer 18 on its outside edge 22 to facilitate easier insertion of the bolt into a hole § drilled from arock surface into a body of rock 6.

Held within the bore 24 at the insertion end (leading end) 20 of the bolt is an assembly 26 of components for storage, mixing and dispensing an adhesive which would, when installing the bolt, be used to retain the bolt in its respective hole in the rock.

Flush with the bolt leading end 20 is a static mixer element 28 which occupies the full cross section of the bore 24. Further into the bore is a sausage-shaped bag 30 containing reservoirs of components of a multi component reactive adhesive system.

The bag 30 is made from a plastics film tubing gathered and sealed with a clamp at each end to form an umbilicus 29 at each end of the bag. The bag 30 has two or more compartments, one compartment for each component in a reactive adhesive ) formulation. Two-part liquid epoxy adhesives or polyester adhesives are preferred, but three-part systems, or systems with even more parts, may be used. A suitable combination of components is that sold in Australia by Celtite Pty Ltd under the product names G7 resin anchor and G9 resin anchor.

CT WO003/044324 PCT/AU02/01587

Within the bore between the static mixer 28 and the bag 30 is a component 31 which serves as a bag rupturing and adhesive distributing device. The component 31 has a disc shaped body 32 axially aligned with the bolt bore 24 and occupying substantially the full cross section of the bore 24. The body disc 32 has extending from it in an axial direction a plurality of prongs 34 projecting towards the bag 30. The disc 32 also has an array of axial holes communicating between the opposite faces of the disc.

The rupturing and distributing component 31 may be made as, for example, a punched metal component or as a plastic moulding.

Positioned adjacent the other end of the bag 30 is a disc shaped end cap 36. This has a central bore 37 which accommodates the associated umbilicus 29 of the bag. The end cap 36 also carries, near its circumference, an array of perforations 42 extending between its opposite faces 43 and 44. The perforations 42 are designed to let air pass through the cap 36 as it is moved forward by the plunger 40 as described below.

To install the rock bolt 10 shown in Figures 1 and 2, a hole 8 is drilled into a mass of the rock 6 which is to be stabilised (which stabilisation may be to a depth of slightly greater than the length of the bolt 10). The bolt 10 is then fed into the hole 8 until the collar 16 contacts the rock surface 4 immediately surrounding the hole 8. A plunger 40 is then inserted into the bore 24 and the plunger tip 41 forced against the end cap 36 which in turn squashes the bag 30 against the prongs 34, rupturing the bag 30. The end cap 36 is a sliding fit within the bore 24. The adhesive components forming the contents of the reservoirs in the bag are forced through the apertures in the disc 32 into the static mixer 28 and are caused therein to intimately mix as they travel along the length of the mixer.

An inwardly directed flange or lip on the leading end 20 of the bolt prevents the mixer 28 from being expelled from the end 20.

The plunger 40 may be actuated in any convenient way but a suitable manner is to use a hydraulically powered mast or rig as used for installing expansion tip type mechanically anchored rock bolts. Such ngs are widely used in mines. The plunger

40 preferably does not form a seal with the bore 24 of the bolt. Instead, the seal preventing adhesive components from passing back along the plunger 40 is provided by the end cap 36 in contact with the bore 24 of the bolt. Adhesive is prevented from escaping through perforations 42 by the combination of their smaller diameter than the apertures in disc 32 and the casing of the then-ruptured bag forming an additional barrier.

The plunger 40 continues thrusting the end cap 36 towards the mixer 28 until substantially all the adhesive components have been pressed into the mixer 28. The mixed adhesive flows out of the leading end 20 of the bolt and, as the bottom 7 (or deep end) of the hole 8 in the rock is close by, the adhesive is forced ito fiow back along the hole 8 through the annular flow path 9 formed between the outside of the bolt 10 and the wall of the hole 8 where it comes to rest. The plunger 40 is then withdrawn from the bore 24. When the adhesive cures, it retains the bolt tightly within the hole. During the curing the bolt is preferably held with the collar 16 pressed hard in place against the rock at the hole opening.

Neither the bolt nor the plunger are rotated to provide mixing of the adhesive components.

The mixer remains in the bolt after the adhesive cures. When the plunger 40 is withdrawn from the bore 24, the mixer 28 is left full of the last of the adhesive, which cures there in due course.

Preferably the static mixer 28 is constructed of moulded plastics material. Many suitable designs are commercially available and an appropriate selection can be made by the skilled person. One suitable design would be that sold under the name Kenics by Chemineer. Such static mixers commonly split, rotate then recombine multiple small portions of the liquid adhesive flow and this achieves a significantly more uniform mixing of the adhesive components than is achieved by the rotation of rock bolts as practised in the prior art.

CT W003/044324 PCT/AU02/01587

The mixer 28, bag 30, disc 32, prongs 34 and disc 36 may be supplied to the end user pre-fitted inside the rock bolt tube or may be supplied as separate components for insertion into the tube by the end user. If the bag 30, with its contents, is supplied to the end user for separate installation, it is preferred that the mixer 28 is supplied firmly fitted to the bore 24 of the bolt in its operating position.

Alternatively the assembly 26 could be supplied to the end user as a pre-assembled cartridge 50 one form of which is shown in Figures 3 and 4. The cartridge 50 is inserted by the user into the bore 24 of a tubular rock bolt (not shown) not long before (or even after) the rock bolt is inserted into the hole drilled for it. The cartridge is a sliding fit into the bore.

The cartridge may comprise an assembly of the parts held together by either glue or a frangible wrapping of plastic film, or a combination of glue and wrapping. One preferred method of holding the parts together as a cartridge is to heat seal layers of plastic together. Heat-shrink wrapping of the assembly with a plastic film as generally used for heat-shrink wrapping would be suitable. Another preferred cartridge structure comprises the assembly of parts inserted into a rigid or semi-rigid thin-walled tubular container of plastics material which may then have an additional light-duty wrapping as protection from water ingress during storage. Any outer skin of film or the like may not need to be removed before a cartridge is used.

A semi-rigid casing 52 for the cartridge is shown in Figure 3. At its trailing end 54, beyond the disc-shaped end cap 36, the cartridge has a small cavity 38, open to the trailing end 54. The cavity 38 conveniently provides an accommodating guide for correct positioning of the tip 41 of the plunger 40. a The invention envisages the rock bolt optionally being of the sclf-drilling type (not : illustrated) where the tube drills its own hole by provision of a suitable cutting tip on its leading end 20. As the bore of the bolt would need to be kept clear for flushing during such a drilling operation, the cartridge 50 would be inserted afer the drilling operation is completed.

The bolt length, diameter and tube wall thickness may be chosen to suit the particular rock bolting performance desired. The bolt length would typically be in the range of 1 to 4 metres, the outside diameter typically in the range of 24 to 55 mm and the tube wall thickness typically in the range of 1 to 2 mm.

The bolt shown in Figures 1 and 2 has a smooth outer surface. It is convenient for such conventionally manufactured tube to be used as feedstock for manufacture of rock bolts according to the present invention. However rock bolts according to the invention may alternatively be made from tubing having an embossed or roughened outer surface or a pattern of ribs upstanding fram its outer cylindrical surface,

However the surface of the “inside” or bore 24 of the bolt is preferably smooth.

Bolts of the type described in relation to this invention are usually not intended to be tensioned by means of a nut engaged with a threaded end of the bolt, although there may be situations where a thread may be used. Instead the rock bolt is held with its head pressed hard against the exposed rock face immediately surrounding the hole while the adhesive cures. Preferably the head is also held against the exposed rock face at the time the adhesive is forced into the annulus between the bolt and the wall ofthe hole and is held in that manner until the adhesive has cured.

Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention.

For example, although the rupturing/distributing component 31 of the preferred embodiments have a plurality of prongs 34 to rupture the bag 30, the invention envisages the alternative use of a single prong or other rupture-facilitating device.

Also the prongs or other rupture-facilitating device may be a separate component to the apertured disc 32.

Also, although the preferred embodiments described have a static mixer portion 28 which occupies the full cross section of the bore, the invention may alternatively utilise a static mixer which occupies only part of the cross section. It will be appreciated that in such a situation it would be most desirable to have the contents of the bag 30 funnelled into the mixer with no bypassing of the mixer.

Although the plunger 40 is described as being a loose fit within the bore 24 of the bolt or the bore 25 of the cartridge, it may alternatively form a sealing fit with the bore.

It will be understood that where the word “comprise”, and variations such as “comprises” and ‘‘comprising”, are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that such prior art forms part of the common general knowledge of skilled persons in the art of rock bolting,

Claims

Claims

1. A method of stabilising a zone of rock comprising: so (i) drilling a hole into the rock, said hole having a deep end deep in the hole and an opening end at a rock face where the drilling was started; (11) inserting a tubular rock bolt having a hollow bore into the hole whereby a first end of the rock bolt is towards said deep end of the hole and the second end of the rock bolt is towards said opening end of the hole; (ii) providing in the hollow bore an assembly comprising separate reservoirs containing components of a multi-component reactive adhesive system; (iv) providing in the hollow bore a static mixer between said reservoirs and said first end of the rock bolt; (v) applying a force to said reservoirs to propel said components through the static mixer, whereby said components become intimately mixed together, and propelled out through said first end of the rock bolt, to then flow back along the hole outside the rock bolt ; and (vi) allowing the adhesive to set and thereby adhere the rock bolt within the hole.

2. A method according to claim 1 wherein an elongate member is plunged into the bore to squeeze the reservoirs between the elongate member and the static mixer.

3. A method according to claim 2 wherein the elongate member transmits its force to the reservoirs by way of a load distributing cap positioned between the elongate member and the reservoirs.

4. A method according to any one of the previous claims wherein the reservoirs take the form of one or more sausage shaped frangible bags. :

30S. A method according to any one of claims 2 to 4 wherein the reservoirs are - ruptured by a sharp implement positioned between the reservoirs and the mixer.

© WO 03/044324 PCT/AU02/01587

6. A method according to claim 5 wherein a rupturing body having a plurality of prongs ruptures the reservoirs and said adhesive components flow through apertures in said rupturing body to enter the mixer.

7. A method according to any one of claims 3 to 5 wherein the mixer, reservoirs and load distributing cap are held within the bore, close to said first end, when the bolt 1s inserted into the hole.

8. A method according to any one of claims 3 to 6 wherein the mixer, reservoirs and load distributing cap are inserted into the bore, from said second end, after the bolt has been placed into the hole.

9. A method according to claim 8 wherein a cartridge containing all of the mixer, reservoirs and load distributing cap is inserted into the bore.

10. A method according to any one of the previous claims wherein an outwardly extending collar affixed to said second end of the rock bolt is pressed hard against the rock during setting of the adhesive and until the adhesive is set.

11. A tubular rock bolt comprising: (i) a first end adapted for insertion into a hole in the ground and a second end opposite said first end, (1) a hollow bore within which is housed an assembly comprising separate reservoirs of components of a multi-component reactive adhesive system; (iii) a static mixer housed in said bore between said reservoirs and said first end of the bolt; (iv) a pressing member housed in said bore such that said reservoirs are housed between the pressing member and the static mixer, said pressing member : forming a sliding fit against the inside wall of the rock bolt, and wherein said pressing member is adapted to be pressed towards said first end of the rock bolt so that the reservoirs are thereby caused to rupture and their contents are forced through and thereby mixed within the static mixer before discharge of mixed adhesive from the first end.

12. A rock bolt according to claim 11 wherein the pressing member comprises a load distributing cap having perforations therethrough to permit airflow during movement of the cap.

13. Arock bolt according to claim 11 or 12 wherein said reservoirs of components take the form of one or more sausage-shaped frangible bags.

14. A rock bolt according to any one of claims 11 to 12 wherein between the reservoirs and the mixer is positioned a sharp implement adapted to rupture the [eServoirs.

15. A rock bolt according to claim 14 wherein the sharp implement has a plurality of prongs directed towards the reservoirs.

16. A rock bolt according to claim 15 wherein the sharp implement has apertures whereby the adhesive components can flow through the sharp implement from the reservoirs to the mixer.

17. A rock bolt according to any one of claims 11 to 16 wherein said pressing member includes means to permit airflow from one side of the pressing member to its other side as the pressing member slides within the bore.

18. A rock bolt according to any one of claims 11 to 17 wherein the mixer, reservoirs and pressing member are held within the bore close to said first end before - the bolt is inserted into the hole.

19. A generally cylindrical cartridge adapted for insertion into the bore of a tubular rock bolt, said cartridge comprising:

CT WO 03/044324 PCT/AU02/01587 (1) means for storage of reactants, said storage means comprising separate reservoirs of components of a multi-component reactive adhesive system, (if) a static mixer for mixing the reactants, (iif) means for pressing said reactants towards and through said mixer, and (iv) means for rupturing said reservoirs when said pressing means presses said reservoirs towards the mixer, said rupturing means being positioned between the reservoirs and the mixer.

20. A cartridge according to claim 19 wherein the mixer has a diameter substantially the same as the inside diameter of the rock bolt.

21. A cartridge according to claim 19 or 20 wherein the reservoirs take the form of one or more sausage-shaped frangible bags.

22. A cartridge according to any one of claims 19 to 21 wherein the rupturing means has a plurality of prongs directed towards the reservoirs.

23. A cartridge according to claim 22 wherein the rupturing means has apertures whereby the adhesive components can flow through the rupturing means from the reservoirs to the mixer.

24. A cartridge according to any one of claims 19 to 23 wherein the pressing means comprises a load distributing cap having a diameter substantially the same as the bore of the bolt.

25. A cartridge according to claim 24 wherein load distributing cap has , perforations therethrough to permit airflow therethrough during movement of the cap along said bore.

26. A cartridge according to any one of claims 19 to 25 wherein said storage means, static mixer, pressing means and rupturing means are held together by a heat sealed wrapping of layers of plastic film.