GB2169050A

GB2169050A - Anchor bolt and method of application thereof to associated structure

Info

Publication number: GB2169050A
Application number: GB08529612A
Authority: GB
Inventors: Paul Radmall
Original assignee: DOWTY GROUP SERVICES
Current assignee: DOWTY GROUP SERVICES
Priority date: 1984-12-15
Filing date: 1985-12-02
Publication date: 1986-07-02
Also published as: GB8529612D0; GB8431720D0; AU5048385A; ZA859215B

Abstract

An anchor bolt 1, which is formed by a drill intended permanently and substantially wholly to remain in a drilling immediately after that drilling has been made, is provided with a cutting head 2 at one end portion thereof and is basically of non-circular cross-sectional shape for at least the major part of its length. The bolt may be further provided with a longitudinal passage 7 which is suitably in communication with orifice means 10, 11 disposed in the bolt adjacent the cutting edges 4, 5 of the head, for the introduction of a settable substance. <IMAGE>

Description

SPECIFICATION Anchor bolt and method of application thereof to associated structure This invention relates to anchor bolts, suitable for permanent retention in a drilling, for example in a concrete or like structure or, alternatively, in a mine for connecting rock strata together. In the latter case in particular each such bolt resists relative movements in said structure thereby avoiding local collapse of the strata in for example the roof of the mine. Such anchor bolts form a means for keeping open mine galleries and other excavations in the face of rock movement to which those galleries and other excavations are often subjected. Thus the anchor bolts resist the loosening of the rock layers from their otherwise rigid formation about the galleries and other excavations.Hence collapse of the mine roof in particular is considerably delayed by the bracing of those layers to the more solid rock adjacent thereto which is afforded by the deep penetration of the anchor bolts into the rock structure.

Hitherto such anchor bolts have been inserted in suitable drillings formed in the associated structure, in some cases the bolts being so expanded as to ensure that they are reliably retained in those drillings.

In certain cases however the drill used to drill the hole is itself permitted to remain in the drilled hole after the drilling operation, so that the drill then forms the anchor bolt. Here the drill so remaining in the hole is locked in place by grout and is of circular cross-section, being provided with ridges of helical or other form, or with disc-shaped protuberances in order better to connect the rock strata together.

It is the object of this invention to provide an improved anchor bolt and an improved method of applying it to associated structure.

According to this invention an anchor bolt, which is formed by a drill intended permanently and substantially wholly to remain in a drilling immediately after that drilling has been made, is provided with a cutting head at one end portion thereof and is basically of noncircular cross-sectional shape for at least the major part of its length.

Preferably said anchor bolt is further provided with a longitudinal passage which is suitably in communication with orifice means disposed in the bolt adjacent the cutting edge or edges of said cutting head.

The said part of said bolt of non-circular cross-sectional shape may be provided with a plurality of members which protrude from the lengthwise surface thereof.

Preferably said anchor bolt may be of elliptical cross-sectional shape for at least the major part of its length.

Also according to this invention there is provided a method of so using an anchor bolt in accordance with any of the next four preceding paragraphs that it is caused to form said drilling and then permitted to remain in the drilling, whereupon a settable substance in a fluid state is introduced into voids formed between said bolt and the wall of the drilling so that when, after a predetermined time, that substance has set, the bolt is locked against any further rotation or axial movement in said drilling.

During the formation of said drilling said cutting head may be assisted in its cutting action by liquid jets caused to discharge from said head, the velocity of said jets being sufficiently high as to contribute substantially -to the drilling operation.

The said method may include the steps of (a) locating the anchor bolt on the surface of the associated structure to be drilled by the use of a spreading plate and a guide box which engages said spreading plate, (b) loading said anchor bolt against said structure by means of a drive head, (c) supplying liquid under pressure to the interior of said anchor bolt whereby said liquid jets are discharged from said cutting head, and, simultaneously, rotating said anchor bolt through the intermediary of said drive head, (d) stopping rotation of said anchor bolt and cutting off the supply of said liquid under pressure when the anchor bolt has penetrated said structure by a desired amount, and permitting said anchor bolt to remain in said structure, (e) with said drive head still engaging said anchor bolt, introducing said settable substance in a fluid state into said voids between said anchor bolt and said wall of said drilling under pressure, and maintaining that pressure for a predetermined time for complete filling, or substantially so, of said voids, and, (f) disconnecting said drive head from said anchor bolt and disengaging said guide box from said spreading plate.

The settable substance may be introduced into said voids by way of the interior of said guide box which in turn opens to said voids by way of an opening in said spreading plate.

The said method may further include the step of slowly rotating said anchor bolt during said introduction of said settable substance so that the constituents of that substance are adequately mixed in order to achieve satisfactory setting thereof.

The settable substance may be of resinous type comprising a base material and another material which forms a hardener for the base material. The hardener, at least, may initially be contained in capsules.

The base material may be for example a polyester resin and the hardener may be benzoyl peroxide.

Also according to this invention apparatus, suitable for use in a method in which an anchor bolt formed by a drill basically of noncircular cross-sectional shape for at least the major part of its length is caused permanently and substantially wholly to remain in a drilling immediately after that drilling has been made, includes a guide box for initially locating said anchor bolt on the surface of the structure in which the drilling is to be made, a drive head which is engageable with the anchor bolt at its end remote from said surface, a device for supporting said guide box and said drive head, means for adjusting the position of said guide box, means for adjusting the position of said drive head and supply means for supplying a settable substance by way of said guide box LO voids formed between said anchor bolt and the wall of said drilling.

Further supply means may be provided for supplying liquid under pressure by way of said drive head to the interior of said anchor bolt.

The guide box and the drive head may each be carried by a respective link means pivotally-mounted on said device and in this case said link means may be pivotally adjusted by actuator means, the arrangement of link means affording necessary alignment between said drive head and guide box. The said actuator means may be carried by said device and be hydraulically-operable.

The said device may comprise a wheeled or tracked vehicle.

The said supply means and said further supply means may be carried by said device.

The guide box may engage said surface through the intermediary of a spreading plate which itself has an aperture through which said anchor bolt passes, the outer face of said spreading plate being engageable by a flange carried by the outer end portion of said anchor bolt to limit the depth of penetration of the anchor bolt into the associated structure.

By the invention the drilling and fixing operations for an anchor bolt are combined into one semiautomatic and thus relatively rapid process.

One way of carrying out the invention is described in detail below with reference to drawings which illustrate only one specific embodiment, in which: Figure 1 is a perspective view of a rock drill which is utilisable also as an anchor or roof bolt, Figure 2 is a typical cross-section of the rock drill shown in Figure 1, Figure 3 is a side elevation of a support vehicle from which the rock drill shown in Figures 1 and 2 is caused to penetrate rock structure, Figure 4 is an enlarged cross-sectional view of part of the apparatus shown in Figure 3 before drilling of the rock structure takes place, and Figure 5 is another enlarged cross-sectional view of a greater part of the apparatus shown in Figure 3 with the rock drill penetrating rock structure as far as possible.

The rock drill 1 shown in the drawings is of elliptical cross-section and includes a cutting head 2 at its upper end. This drill is formed from a thick-walled tube of circular cross-section which is changed into its elliptical crosssectional shape by forging and at the same time is provided with a plurality of axiallyspaced radially-outwardiy directed protrusions 3 for a portion of its length. The cutting edges 4, 5 of head 2 are also formed by forging while at its lower end the drill is suitably upset to provide a flange 6 of waisted profile disposed a short distance from that end. A passage 7 formed in the drill 1 opens into two branch passageways 8, 9 which themselves terminate in orifices 10, 11 at the upper face of head 2 adjacent the cutting edges 4, 5.The drill is of such material and is subjected to such heat treatment as to provide sufficient hardness for the cutting edges to withstand the drilling of only one hole into, in this embodiment, a mine roof.

It is intended that jets of water issuing from orifices 10, 11 assist the cutting action of the drill, the return path for the water containing drilling debris being provided by spaces 12, 13 formed between the elliptical profile of the drill and the circular cross-sectional shape of the hole 14 produced by the drill, as shown in Figure 2.

It is also intended that when the drill has penetrated the mine roof structure sufficiently far, the drill remains permanently and substantially wholly in the drilling thus to form an anchor or roof bolt which is locked in the drilling by a settable resinous substance which is suitably injected into spaces or voids 12, 13 as later described.

With reference now to Figure s 3 to 5, a wheeled vehicle 16 is provided which carries link means 17, 18 pivotally-mounted at 19, 20 respectively thereon, supply means 21 which is capable of delivering water at high pressure through flexible pipe 22 and supply means 23 which is capable of delivering a settable resinous substance through flexible pipe 24.

The upper link means 17 is adjustable about its pivotal connection 19 by an hydraulic actuator 25, while the lower link means 18 is adjustable about its pivotal connection 20 by an hydraulic actuator 26. Link means 1 7 is pivotally-connected at 27 to a guide box 28 and link means 1 8 is pivotally-connected at 29 to a drive head 30.

The guide box 28 is, on operation of actuator 25, urged upwardly towards the surface 31 of the mine roof structure 32 and is caused to bear against that surface through the intermediary of a spreading plate 33 of corrugated spring steel.

The drive head 30 is, on operation of actuator 26, also urged upwardly towards surface 31, axially loading the rock drill 1 against the mine roof structure 32, and the drill, in passing through the aperture 34 in plate 33, being located as positionally required on the surface 31. Simultaneously, a fluid connection is automatically made between the drive head and drill.

To commence drilling of the roof structure water at high pressure is first discharged from pipe 22 into passage 7 of the drill through a channel 35 and through a fail-safe coupling 36 provided between the frusto-conical spindle 37 and the drill, this water issuing as jets from orifices 10, 11 at high velocity. With axial load maintained by drive head 30, drill 1 is rotated by an hydraulic motor 38 which is supplied with pressure liquid through conduit means 39 and which drives spindle 37 of drive head 30. The high velocity water jets assist the cutting edges 4, 5 of the drill in their drilling of hole 14.

During drilling water containing drilling debris which passes downwardly through spaces 12, 13 and past the waisted portions of flange 6 is extracted through ports 40 in guide box 28 and pipe 41 by a vacuum pump (not shown) carried by vehicle 16.

Drilling continues until the depth of hole 14 is such that flange 6 comes into engagement with plate 33. Simultaneously frusto-conical spindle 37 seats in the opening 42 of guide box 28 as shown in Figure 5. The engagement of flange 6 with plate 33 is sensed by the system and, automatically, rotation of the drill is caused to cease and the supply of water under pressure to passage 7 is cut off.

This passage is then suitably and automatically vented to atmosphere.

The next stage in the process is to lock drill 1 in place in drilling 14 by injecting the settable resinous substance supplied by means 23 into spaces 12, 13, so that the drill forms an anchor bolt. The substance is of two-part type, consisting of a polyester resin base and a hardening agent in the form of benzoyl peroxide. This resinous substance is packaged in plastic tubes (not shown) for safe handling, the hardener being contained in capsules disposed in the polyester resin base within the tubes. Hydraulic power suitably provided in vehicle 16 is applied directly within each plastic tube by way of a slave piston.

When the tube is pressurised the contents thereof are discharged through pipe 24 into a resin injection port 43 in the guide box 28.

This port includes a filter element 44 which comprises a screen having a plurality of sharpedged holes the diameter of each of which is slightly less than that of each capsule. As the contents of the tube are forced through the screen the capsules are ruptured by contact with the sharp edges of the holes so that the hardener therein is released and mixes with the polyester resin base downstream of the screen. The mixture then passes upwardly past the waisted portion of flange 6 into spaces 12, 13, air in those spaces being vented to atmosphere by way of passageways 8, 9 and passage 7. During this resininjection stage drill 1 is rotated slowly to ensure even distribution and mixing of the polyester resin base and hardener.When the spaces 12, 13 are full, the consequent rise in resin pressure is sensed and caused automatically, by way of suitable means (not shown), to terminate the resin injection and to effect stopping of the slow drill rotation.

The drill is thereafter maintained stationary for a few seconds until the resin mixture sets and then the guide box and drive head are lowered from the mine roof to enable the equipment to be moved on to the next required anchor bolt location.

Although in the embodiment above described with reference to the drawings the drill/anchor bolt is of elliptical cross-sectional shape, in other embodiments of the invention the drill/anchor bolt may be of other suitable non-circular cross-sectional shape at least for the major part of its length, for example of triangular cross-section, of rectangular crosssection, of star cross-section or suitably scalloped cross-section, all of which shapes afford good locking of the drill/anchor bolt with respect to its drilled hole when said substance so injected into the said spaces between it and its drilled hole has set. Whatever its noncircular cross-sectional shape the drill/anchor bolt may be helically grooved lengthwise thereof to facilitate the passage of material removed by drill operation to the exterior of the drilled hole.Such helical grooving may extend for the entire length of the drill/anchor bolt, or alternatively for a substantial part thereof, and may comprise a single helical groove or alternatively a suitable number of helical grooves in excess of one.

Again, although in the embodiment above described with reference to the drawings the settable substance used is in the form of a mixture of a polyester resin base and benzoyl peroxide, in alternative embodiments of the invention any other suitable substance may instead be used for example an epoxy resin and an associated hardener.

Further, although in the embodiment above described with reference to the drawings the anchor bolt is applied to a mine roof, in alternative embodiments of the invention it may instead and with advantage be applied to other rock structures, to concrete or reinforced concrete structures or to any other drillable structures where it is required that once the drilling has been made the drill should permanently and substantially wholly remain in situ, for example for ieinforcement of the associated structure, or for any other reason.

Finally, although in the embodiment above described with reference to the drawings the capsules containing the hardener are ruptured as they are forced through the screen of a filter device, in alternative embodiments of the invention the arrangement may not include such a filter device and in this case the cap sules may pass with the base material into the spaces 12, 13 where they become ruptured upon engagement therewith by the slowly-rotating drill. Continued slow-rotation of the drill ensures satisfactory mixing of the base material and hardener. On stopping of the drill the mixture rapidly sets to lock the drill in place in the drilled hole.

Claims

1. An anchor bolt, which is formed by a drill intended permanently and substantially wholly to remain in a drilling immediately after that drilling has been made, said anchor bolt being provided with a cutting head at one end portion thereof and being basically of non-circular cross-sectional shape for at least the major part of its length.

2. An anchor bolt as claimed in claim 1, said bolt being further provided with a longitudinal passage which is suitably in communication with orifice means disposed in said bolt adjacent the cutting edge or edges of said cutting head.

3. An anchor bolt as claimed in either claim 1 or claim 2, wherein said part of said bolt of non-circular cross-sectional shape is provided with a plurality of members which protrude from the lengthwise surface thereof.

4. An anchor bolt as claimed in any one of the preceding claims, wherein said bolt is of elliptical cross-sectional shape for at least the major part of its length.

5. A method of so using an anchor bolt, as claimed in any one of claims 1 to 4, that said bolt is caused to form said drilling and is then permitted to remain in the drilling, whereupon a settable substance in a fluid state is introduced into voids formed between said bolt and the wall of the drilling so that when, after a predetermined time, that substance is set, the bolt is locked against any further rotation or axial movement in said drilling.

6. A method as claimed in claim 5, wherein during the formation of said drilling said cutting head is assisted in its cutting action by liquid jets caused to discharge from said head, the velocity of said jets being sufficiently high as to contribute substantially to the drilling operation.

7. A method as claimed in claim 6, said method including the steps of (a) locating the anchor bolt on the surface of the associated structure to be drilled by the use of a spreading plate and a guide box which engages said spreading plate, (b) loading said anchor bolt against said structure by means of a drive head, (c) supplying liquid under pressure to the interior of said anchor bolt whereby said liquid jets are discharged from said cutting head, and, simultaneously, rotating said anchor bolt through the intermediary of said drive head, (d) stopping rotation of said anchor bolt and cutting off the supply of said liquid under pressure when the anchor bolt has penetrated said structure by a desired amount, and permitting said anchor bolt to remain in said structure, (e) with said drive head still engaging said anchor bolt, introducing said settable substance in a fluid state into said voids between said anchor bolt and said wall of said drilling under pressure, and maintaining that pressure for a predetermined time for complete filling, or substantially so, of said voids, and, (f) disconnecting said drive head from said anchor bolt and disengaging said guide box from said spreading plate.

8. A method as claimed in claim 7, wherein said settable substance is introduced into said voids by way of the interior of said guide box which in turn opens to said voids by way of an opening in said spreading plate.

9. A method as claimed in either claim 7 or claim 8, and further including the step of slowly rotating said anchor bolt during said introduction of said settable substance so that the constituents of that substance are adequately mixed in order to achieve satisfactory setting thereof.

10. A method as claimed in claim 9, wherein said settable substance is of resinous type comprising a base material and another material which forms a hardener for the base material.

11. A method as claimed in claim 10, wherein said hardener, at least, is initially contained in capsules.

12. A method as claimed in either claim 10 or claim 11, wherein said base material is a polyester resin and the hardener is benzoyl peroxide.

13. Apparatus, suitable for use in a method in which an anchor bolt formed by a drill basically of non-circular cross-sectional shape for at least the major part of its length is caused permanently and substantially wholly to remain in a drilling immediately after that drilling has been made, including a guide box for initially locating said anchor bolt on the surface of the structure in which the drilling is to be made, a drive head which is engageable with the anchor bolt at its end remote from said surface, a device for supporting said guide box and said drive head, means for adjusting the position of said guide box, means for adjusting the position of said drive head and supply means for supplying a settable substance by way of said guide box to voids formed between said anchor bolt and the wall of said drilling.

14. Apparatus as claimed in claim 13, wherein further supply means is provided for supplying liquid under pressure by way of said drive head to the interior of said anchor bolt.

15. Apparatus as claimed in either claim 13 or claim 14, wherein the guide box and the drive head are each carried by a respective link means pivotally-mounted on said device.

16. Apparatus as claimed in claim 15, wherein said link means is pivotally adjusted by actuator means.

17. Apparatus as claimed in claim 16, wherein said actuator means is carried by said device and is hydraulically-operable.

18. Apparatus as claimed in any one of claims 13 to 17, wherein said device comprises a wheeled or tracked vehicle.

19. Apparatus as claimed in any one of claims 13 to 18, wherein said supply means and said further supply means are carried by said device.

20. Apparatus as claimed in any one of claims 13 to 19, wherein said guide box engages said surface through the intermediary of a spreading plate which itself has an aperture through which said anchor bolt passes, the outer face of said spreading plate being engageable by a flange carried by the outer end portion of said anchor bolt to limit the depth of penetration of the anchor bolt into the associated structure.

21. An anchor bolt substantially as hereinbefore described with reference to the accompanying drawings.

22. A method of using an anchor bolt substantially as hereinbefore described with reference to the accompanying drawings.

23. Apparatus substantially as hereinbefore described with reference to the accompanying drawings.