GB2073283A

GB2073283A - Rock bolting

Info

Publication number: GB2073283A
Application number: GB8103365A
Authority: GB
Original assignee: AMBERG INGBUERO AG
Current assignee: AMBERG INGBUERO AG
Priority date: 1980-02-12
Filing date: 1981-02-04
Publication date: 1981-10-14
Also published as: AU6691881A; NO810460L; IT8112431A0; ES8202894A1; FR2478193A1; FI810362L; SE8100922L; IT1168421B; ES499249A0

Abstract

A rock bolt (Fig. 1) is in the form of a pipe (11), which is spaced within a borehole (10) of greater diameter than the outer diameter of the pipe. Chemical anchoring material, for example a two-component adhesive, is pumped into the end of the pipe at the face (10a) of the working so as to pass along the inside of the pipe and at the inner end of the pipe to move outwards (10b) and back along the length of the pipe to fill the space between the pipe and the borehole. The anchoring material may be a two- component adhesive, and the components may be mixed by a pipe- like mixer(13) at the outer end (11a) of the pipe and having fixed guide walls (15) for causing a mixing motion of the components. For keeping the rock bolt pipe equally spaced from the wall of the bore hole before chemical anchoring, the pipe may have coil springs (20, 30) increasing in diameter along the length of the pipe. Fingered gripping means may be mounted within, to only partially obstructed, the inner end 11b of the pipe for gripping the wall of the borehole. <IMAGE>

Description

SPECIFICATION A rock bolt for strengthening the walls of an underground working Background of the Invention On making tunnels and other underground workings, it may be necessary for loose parts of the rock or for rock which is likely to be broken off from the face of the working to be fixed by rock bolts. Such rock bolts normaily take the form of single rods stretching as far as the end of specially made boreholes, at which end the rock bolt is fixed in position while at the outer end of the borehole, that is to say within the working, a washer or plate is fixed on the end of the bolt with nuts.If the rock bolt is not acted upon by any force or is only acted upon by a low degree of force, it may said to be a "slack rock bolt", while on the other hand, if the pulling force acting on the rock bolt is at a high level, it may be said to be a prestressed rock bolt.

In the case of a prestressed rock bolt, it is normal for the rock bolt only to be fixed at the inner end of the borehole furthest from the working, while the rest of the length of the rock bolt within the hole will be free. For making tunnels, in the case of which such rock bolts have to undertake their desired function for decades, such prestressed rock bolts may not be used because of the degree of corrosion so that, in such cases, use is best made of rock bolts, which are fixed to the rock right along the full length of the borehole. For this purpose, the borehole is completely filled with cement grout before driving in a steel rock bolt. A shortcoming in this respect is that the grouting mortar has to be highly fluid for gripping the keying and locking structures on the rock bolt.For this reason, such a rock bolt may not be put in position overhead or generally into boreholes which are upwardly sloping or upright.

In a further suggestion made in the prior art, cartridges with chemical anchoring material, as for example the two components (the adhesive and the curing substance) of a two-component adhesive material, are run into the borehole so that, on twisting the rock bolt and moving it inwards into the borehole, the two components are completely mixed. This form of chemical anchoring is, at the present-day, mainly used for prestressed rock bolts, in which it is only the end furthest from the working which is fixed in position. While, in theory, it would be possible for such an anchoring system to be used for slack rock bolts, the price would be overly high, because, as a first step, a great number of such cartridges would have to be used.

Short Outline of the Invention The present invention is with respect to a process for supporting and/or reinforcing the walls of underground workings, such as tunnels or mine roadways in hard rock which is likely to become broken or in soft rock such as earth, using pipes which are fixed in holes as rock bolts.

One purpose of the invention is that of designing a process, and a system for making use of the process, in the case of which a hollow bolt may be placed into an overhead borehole and in any desired direction. The invention is furthermore with respect to a system with such pipe rock bolts fixed in position.

For effecting these and other purposes, in the process of the invention, a borehole is produced with an inner diameter greater than the outer diameter of the pipe, the pipe is slipped into the borehole and fixed therein at its end furthest within the hole, and then a chemical anchoring material is run in through the pipe into the borehole for completely filling the space between the outer face of the pipe and the wall of the borehole. Because the pipe is fixed at its inner end (the end furthest from the working) in the borehole, it does not have to be otherwise supported on running the chemical anchoring material such as a two-component adhesive into the hole, and such filling with chemical anchoring material is made very much simpler.Because the chemical anchoring material or two-component adhesive takes up all the space within the pipe and the space between the pipe and the wall of the borehole, the rock bolt is fully safeguarded for its complete length within the borehole against corrosion. Because the full length of the pipe is fixed to the borehole wall, a very strong fixing structure is produced, which, in the case of the use, for example, of a pipe of glass fiber reinforced synthetic resin, will be stronger than steel.

Furthermore, such a system will be even more resistant to corrosion.

It is more specially useful for the process of the invention to be undertaken with a system having a mixer, without moving parts, which is placed in the pipe for causing complete mixing of the two components of the two-component adhesive when they are pumped in through the pipe.

Because of this, the two liquid components of the two-component adhesive may be pumped into an overhead pipe, using liquid supply pipes of the right design. On being pumped through the mixer, they will be mixed with each other right at the start of the pipe so that the completely mixed adhesive or chemical anchoring material will become so thick on being pumped through the pipe and then through the space between the pipe and the wall of the borehole, that there will be no danger of loss of adhesive through the adhesive's running out at the working end of the borehole.

As part of a further useful development of the invention, at least one coiled spring, in the form of a bell-like spacer, is placed on the pipe, for supporting it spaced and clear of the wall of the borehole, that is to say in a coaxial position. Such a coiled spring may furthermore be used forfixing the inner end of the pipe in the borehole.

In a form of the invention with a specially useful effect, such a support part has a gripping structure which has a foot designed to be locked in the inner pipe end, that is to say the end furthest in the borehole, and at least two fingers, which are symmetrical with respect to the axis and which, for being fixed against the wall of the borehole, are designed to be stretched out past the outer face of the pipe so that, after placing the empty pipe into the borehole, it is fixed by way of its inner end in the borehole by the gripping structure. It is useful if the gripping structure is designed as a stopper for at least partly shutting off the inner opening of the pipe, which, at its inner edge, has side openings. The useful effect produced here is that, on running the pipe into the borehole, no pieces of broken rock or the like may get into the pipe.

Furthermore, putting the gripping structure in position is very simple and it is strongly kept in position within the borehole.

On using the process of the invention, a rock bolt support system, for underground workings in mines and making tunnels, is produced which is characterized in that a pipe is fixed in a borehole, the outer diameter of the pipe being smaller than the inner diameter of the borehole, by the use of a synthetic resin or chemical anchoring material taking up the space between the pipe and the borehole wall. By using the rock bolt of the invention, the wall of a working under the ground, as for example in a mine, on driving a tunnel or, in the case of underground building works, is reinforced in the best possible way.As part of a more specially useful form of the invention, the pipe is made of glass fiber reinforced synthetic resin, this offering the useful effect that the walls of a working may be reinforced even before the working or tunnel for example is completed, using the rock bolts of the present invention without stopping any cutting away of material from the walls of the working later because glass fiber reinforced synthetic resin pipes may be readily cut through by rock cutting machines so that the rest of the pipe, still within the rock, may still be used for its desired function, that is to say reinforcing the wall of the working, after the working has been increased in size.

List of Figures A.detailed account will now be given of working examples of the invention to be seen in the figures.

Figure 1 is a lengthways section through the rock round a borehole having a rock bolt placed within it (as a first working example of the invention) with the top end of the rock bolt sectioned.

Figure 2 is a view of a supporting part in the form of a coiled or helical spring.

Figure 3 is a view of a spacer for keeping the pipe clear of the borehole wall, taking the form of a coiled spring.

Figure 4 is a view, on the same lines as Figure 1, of a second working example of the invention with a rock bolt pipe within a borehole.

Figure 5 is a perspective view of the mixer, without moving parts, used in the working example of Figure 4.

Figure 6 is a perspective view of the support part or keeper to be seen in Figure 4.

Detailed Account of Working Examples of the Invention The slack rock bolt of Figure 1 is made up of a stem in the form of a pipe 11 of any high-tensile material such as steel, fiber glass reinforced synthetic resin or the like. Pipe 11 is spaced to take up a middle position in borehole 10 at its inner end 1 Ob (that is to say the end furthest from the working) and at least furthermore at the outer end 1 0a. In the working example figured, for spacing and positioning the pipe coil springs 30 (see Figure 3) are used, whose smallest diameter, that is to say the diameter at the lower end 31, is at the most equal to the outer diameter of the pipe but, more specially, is somewhat smaller than it so that the coil spring 30, used for spacing purposes, is firmly gripped on pipe 11. At the other end 32, the diameter is at least equal to the diameter of the borehole 10.When such coil springs, acting as spacers, are so placed on the pipe 11 that the lower end 31, that is to say the end with the smaller diameter, is pointing towards the borehole end 1 Ob, when the pipe 11 has been placed in the borehole 10, it will be readily seen by the reader that, because of the spring's rubbing against the borehole wall, spring 30 will be pulled out and made longer, this producing openings between the turns of the spring. Such a coiled spring 30 for use as a spacer may for example be made of spring steel wire with a diameter of 2.5 mm. At borehole end 1 Ob there is a structure, which, in addition to spacing the pipe 11 equally on all sides from the inner wall of the borehole, has the function of locking pipe 11 in borehole 10 and stopping the pipe from slipping out of borehole 10 when acted upon by a force.As will be seen from Figure 2, such a structure may be made up of a coiled or helical spring 20 for keeping the pipe within the hole. At its one end 21, this spring has a diameter which is at the most equal to the diameter of pipe 11 and at its other end 22 has a diameter which is at least equal to the diameter of the borehole 10. The end 22 of coiled spring 20, used for keeping the pipe within the borehole, is outwardly bent for about 5 mm in its last part 23 where it takes the form of an outwardly running tail. At its lower end 21, the spring has a small diameter and at the top end 22 a great diameter.

For this reason, on placing the pipe or rod in position, the lower half of the coiled spring is pulled out forming openings. When the pipe 11 is acted upon by a force having a tendency of pulling it out of borehole 10, the coil spring 20, whose outwardly bent tail will be kept back by the rock because of its acting as a hook so that this spring 20 will have the function of keeping back the pipe within the borehole, because the top part of the spring will be forced together. Putting it differently, pipe 11 will be, to some degree, anchored in borehole 10.

At the outer pipe end 11 a there is a mixer 13 without moving parts within pipe 11. This mixer 13 is made up of a tube 14 having inner guide plates 15, which are out of line with each other so that, when a two-component adhesive, in the form of its separate parts (curing material B and adhesive material K) is pumped into the pipe, the two components will be mixed up because of turbulence caused by the guide plates 1 5.

Adhesive, acting as a chemical anchoring material, will be pumped into pipe 11 till the space between the borehole 10 and the outer wall of pipe 11 has been fully taken up.

At the present-day two-component adhesives may be made with, generally speaking, any desired viscosity so that, even with boreholes running up into the roof of the working vertically, there will be no run down and dripping of adhesive. In tests, a borehole was produced with a diameter of 41 mm in rock with a normal length, that is to say one of the order of 1.6 to 4 meters. A glass fiber reinforced synthetic resin pipe with fibers running in its length-direction was then slipped in to the borehole after a coiled spring 20 had been placed on the pipe end pointing to the back, for use as a keeper or fixing part as in Figure 2 and then, furthermore, a coiled spring 30 as a spacer (see Figure 3) was slipped over the pipe.A round pipe-like mixer 13, without moving parts, was placed in the pipe 11 and the two components of the adhesive pumped in separately, the adhesive being one marketed under the trade name of "Stucarit" by the Epple Company, Stuttgart. For every meter of pipe length, 1 liter of adhesive mix was pumped in with a pressure of about 120 bar. The pumping rate measured was about 5 liter of material a minute.

After a normal curing time, the pipe was acted upon by a pulling force of 37 metric tons, that is to say a force far greater than the fracture strength of a pipe designed on the same lines but made of steel. Such testing did not, as far as might be seen, seem to have any effect on, or make for any changes in, the rock bolt system.

The mixer 13 is best made of synthetic resin and is kept within the pipe permanently. In place of the coil spring 20 (Figure 2) for keeping the pipe within the rock, it is possible furthermore to make use of a leaf spring with legs springingly resting against the borehole wall. The only necessary function of such a spring is that of making certain that the axis of the pipe is at least roughly at the axis of the borehole and that there is nothing in the way of the motion of the liquid adhesive from the back to the front and furthermore that there is no danger of the pipe being forced out of the hole by the pressure of the adhesive at the end of the borehole.

For mechanically joining the coil springs 20 and 30 to the pipe 11, it is possible to have a screwthread 1 6 (only to be seen in part in Figure 1) in the outer face of the pipe.

The slack rock bolt of Figure 4 has a pipe 41, which, unlike pipe 11, has at its inner end 41 b a sidedoor-like opening 42, like the air outlet hole of a whistle, for the two-component adhesive. For locking the inner end 41 b of pipe 41 in borehole 10, in the case of this working example there is a gripper part 60, to be seen in more detail in Figure 6, which is made up of a band-like piece of spring steel 61 with a length being stamped out and bent outwards for forming a foot 62. The free end 63 of this foot 62 is hooked so that the foot may be locked within the space inside pipe 41.

Because the foot 62 is bent upwards, the rest of the parts of the spring part 61 takes the form of two parallel fingers 64. On the same lines, a band is stamped out of the other end of the spring part 61 so that the spring part 61 takes the form, in this case as well, of two parallel fingers 65, the same in design as fingers 64. The spring steel part 61 is made of such a length that fingers 64 and 65 go out past the outer face of pipe 41 by about the same amount, as is necessary for them to make for a gripping function when they are resting against the wall of the borehole 10.

When foot 62 is hooked into the inner end of pipe 41, it and the middle part of the spring steel part 61 will have the effect of stoppering and shutting off the greater part of the pipe crosssection so that, on slipping pipe 41 into its borehole 10, there will be little chance of broken stone or the like falling into the pipe, such broken stones being likely to be the cause of a decrease in strength of the two-component adhesive and in the chemical anchoring effect.

The diameter of borehole 10 will be such that, when the pipe 41 is equally spaced in borehole 10, the cross-section of the ring-like space between the borehole wall and the inner face of pipe 41 will be equal to the cross-section of the hollow within pipe 41 at the most. For this reason, on making the selection of the two-component adhesive such that, on coming from opening 42, it will have become stiff or viscous to a certain degree, it is possible to make certain that the pipe is kept equally spaced automatically by the twocomponent adhesive even without any coil springlike spacer 30.

To make certain that the two components of the two-component adhesive only become mixed together within the pipe 41, in the working example of Figure 4 the mixer 50, to be seen in perspective in Figure 5, is used, in which the pipe 54 has at its outer end a cover-like connection 51, sticking out so far past the outer edge of the pipe 54 that a collar 52 is formed, which, because of its resting against the outer edge of pipe 41, takes the form of a stop for limiting further motion of mixer 50 into pipe 41, this producing the useful effect that mixer 50 only has to be slipped into pipe 41 and not adhesively joined therewith.

This connection 51 has two openings 53 becoming narrower towards the pipe 54 and opening thereinto. Such openings 53 are used to take up the ends of two pipes 55 used for pumping the two components of the twocomponent adhesive, separately from each other, into the outer end of pipe 54. Because of this, it is possible to make quite certain that the two components of the two-component adhesive only come together inside the mixer 54, this making quite certain that the ends of the pipes 55 will not be stopped up by adhesive material, because the two components of the two-component adhesive will keep their liquid condition as long as they are not mixed with each other.

Claims

1. A method of fixing a rock bolt in rock, comprising making a borehole in the rock; placing in the borehole a hollow rock bolt in the form of a pipe having an outer diameter which is smaller than the diameter of the borehole; fixing the bolt in position at its inner end in the rock; passing a liquid anchoring material through the pipe into the borehole until the space between the outer wall of the pipe and the borehole is filled with the anchoring material for hardening them.

2. A method as claimed in claim 1, wherein the pipe is supported coaxially in the borehole while the anchoring material is being passed into the borehole.

3. A method as claimed in claim 1, wherein the anchoring material is a two-component adhesive whose two components are mixed at the start of the pipe.

4. A method as claimed in claim 3, wherein the two components are mixed in the pipe.

5. A rock bolting apparatus comprising a pipelike bolt having an outer and an inner end, and mixing means for mixing components of a liquid anchoring material when it is caused to flow through the mixing means from the outer to the inner end of the bolt, the mixing means being fixed at the outer end of the bort.

6. Apparatus as claimed in claim 5, wherein said mixing means if formed as a tube for guiding said anchoring material in an axial direction, said tube having interior guiding walls which are arranged out of line in said axial direction.

7. The apparatus as claimed in claim 5, wherein said mixing means is provided with a stop means, which extends radially over an edge formed by said outer end of said pipe-like bolt.

8. The apparatus as claimed in claim 7, wherein said stop means takes the form of a collar extending over and running round said edge of said outer end.

9. The apparatus as claimed in claim 7, wherein said stop means forms a plug means for shutting off said mixing means from the outside of said pipe-like bolt, said plug means extending radially over said edge of said outer end of said pipe-like bolt and having two holes for connection to two pipes for feeding different materials used for making said chemical anchoring material, said holes being provided for guiding said different materials separately into said mixing means.

10. The apparatus as claimed in claim 9, wherein said openings in said plug means become narrower towards said mixing means.

11. The apparatus as claimed in claim 9, wherein said plug means is in the form of a disk forming an outwardly running collar.

12. An apparatus as claimed in claim 5, wherein said pipe-like bolt being provided with at least one coiled spring becoming wider along the length of the pipe, said spring surrounding said pipe-like bolt for holding it coaxially within a borehole of a rock.

13. An apparatus as claimed in claim 5, wherein said pipe-like bolt being provided with a coiled spring surrounding its inner end and becoming wider along said pipe-like bolt for keeping said inner end of said pipe-like bolt within a borehole of a rock.

14. An apparatus for rock bolting the walls of an underground working by placing pipe-like bolts, each having an outer and inner end, in boreholes in rock and then chemically anchoring them in position, wherein at least one of said pipe-like bolts has a gripping means on its inner end to be placed furthest within said borehole, said gripping means having a foot means to be fixed within said inner end, and at least two finger means extending radially over an edge formed by said inner end for gripping the wall of said borehole.

15. The apparatus as claimed in claim 14, wherein said gripping means is designed as a stopper for shutting off the said inner end of said pipe-like bolt at least partly, said pipe-like bolt having a sidedoor-like opening adjacent said inner end.

16. The apparatus as claimed in claim 14, wherein said gripping means is made up of a band-like piece of spring steel forming said two finger means, from which a band is stamped for forming said foot means, said band being bent out of the plane of the piece of spring steel into the form of a hook.

17. The apparatus as claimed in claim 16, wherein by way of the stamped-out foot means two fingers are formed, which are parallel to each other on the one side of said foot means, while a part, positioned on the other side of said foot means, of the piece of spring steel is cut out in the same way as said foot means so that two further fingers, parallel to each other, are formed, all four fingers being pointed at outer ends thereof.

18. A rock bolt for bolting the walls of an underground working, the rock bolt having the form of a pipe, whose outer diameter is less than the inner diameter of an inner wall of a borehole in which it is placed, so that said rock bolt is surrounded by a space between said pipe and said inner wall of said borehole, said pipe being chemically anchored in said borehole by chemical anchoring material filling the inside of said pipe and said space.

1 9. The rock bolt as claimed in claim 18, wherein said pipe is made of glass fiber reinforced synthetic resin.

20. The rock bolt as claimed in claim 18, wherein said pipe has at least one spacer means for keeping the outer wall of said pipe at an equal distance from said inner wall of said borehole.

21. The rock bolt as claimed in claim 20, wherein said spacer means is made up of at least one coiled spring becoming wider along the pipe.

22. The rock bolt as claimed in claim 20, wherein an outer surface of said pipe is threaded for mechanically joining said spacer means with said pipe.

23. The rock bolt as claimed in claim 18, wherein an outer end of said pipe, opposite to an inner end placed furthest in said borehole, has a mixing means with fixed parts for guiding, and thereby mixing, two chemical materials for forming said chemical anchoring material.

24. The rock bolt as claimed in claim 23, wherein said mixing means is provided with a plug means extending over an edge formed by said outer end of said pipe, said plug means having two openings running into said mixer.