AU6807200A - A strata bolting apparatus and method - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant: SPRINGVALE COAL PTY LTD A.C.N. 052 096 769 Invention Title: A STRATA BOLTING APPARATUS AND METHOD 4 b* *4 4 The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 A STRATA BOLTING APPARATUS AND METHOD Field of the Invention The present invention relates to a method and apparatus for bolting rock strata in underground mining applications. It should be remembered, however, that the invention has broader use in all manner of excavation and strata stabilisation situations.

Background Art Apparatus and methods for bolting rock strata are known in the art to provide ways of stabilising the strata in mines and in civil and hard rock excavation situations.

For example, these devices are used to provide a level of pretension to the roof rock in the workings of an underground mine. However, the known techniques require complex installation methods and materials, and in use are not always particularly successful.

Usually these devices comprise long cable tendons (nominally 4-8m in length, some with a 'birdcage' or .0 portion of the cable where the strands are separated and 20 protruding), which are spun by external means into a predrilled hole to firstly anchor and then longitudinally pretensioned, and then the tendons are fully grouted or sealed into place by some means. The difficulty with most pretensioned tendon devices is that they are not able to be post-grouted. One reason for the difficulty in postgrouting is the need to provide a breather tube to allow air to flow from the upper end of the hole cavity simultaneously as grout is pumped from the bottom of the hole upward in order to fill the hole and seal the tensioned tendon in place. A bolt which is spun into a resin cartridge to provide its initial anchor will normally destroy any externally attached breather tube located in the drill hole, making this an unreliable system. A postgrouting system which pumps grout upward from the hole opening can also often be problematic as the hole needs to be well sealed by a collared end cap against leaks.

39924 3 Some pre-tensioning and post-grouting apparatus and techniques are known. For example, a birdcaged tendon fitted with an internal breather tube has been used by being spun into a drill hole and then tensioned. The grouting comprises standard grout pumped upward from the base of the hole as air exits via the tendon itself.

Usually these devices fail as the grout leaks from the hole before sealing can occur. Similarly, rigid hollow steel bolts can be screwed together to allow them to reach the desired length in the drill hole. They may be anchored in the hole using a mechanical anchor and accordingly pretensioned. The grouting of the hole is achieved by utilisation of the tubular bolt section to pump the grout into the hole or alternatively for it to act as a breather tube.

In a further alternative example, a tendon is spun into a hole (of typically 28mm in diameter) passing through several chemical anchor cartridges. The cartridges contain resin of different setting speeds, arranged so that the 20 uppermost one is able to set most quickly, thus allowing the bolt to be anchored for pre-tensioning, and the lower cartridges very slow setting to enable the bolt to be e longitudinally pre-tensioned prior to hardening of the resin. A resin-encapsulated tendon is produced. The problem with this system is often that the hole is not always filled over its entire length with the tendon as it is often not possible to consistently push the tendon through that amount of resin or past more than two cartridges.

A further, less preferred alternative device is a birdcaged cable bolt tendon which is pushed into the hole (of typically 52mm diameter) and fully grouted but without the anchor system to allow any longitudinal pretension to be applied. The sealing of the collar in this case is simplified because it is not inhibited by any external pretensioning apparatus, but the usefulness of this device 39924 4 is limited.

There has been little attempt to devise an improved apparatus for bolting rock strata in order to improve these factors as well as facilitating the insertion and post tension encapsulation of rock bolts in a simple and rapid fashion.

Summary of the Invention The present invention provides apparatus for insertion into a longitudinal cavity for stabilisation of the substrate strata comprising: a longitudinal element fitted with one or more radial protrusions located on or around a first end of the oo eo longitudinal element; and a conduit element insertable into the cavity from the direction of a second end of the longitudinal element and extendable into the cavity when the longitudinal element is placed in the cavity; whereby in use the longitudinal element can be placed 2* in the cavity and sealed into the cavity at the first end 20 by a bonding substance and subsequently sealed at the second end of the of the longitudinal element by a bonding *.*substance which is passed into the cavity by means of the conduit element.

Preferably a divider element is mounted to the longitudinal element and located at a position on the longitudinal element such that the divider element divides the first end fitted with the radial protrusions from the second end of the longitudinal element and wherein the divider element has an outer dimension at most equivalent to the dimension of the longitudinal cavity when the longitudinal element is placed therein.

Preferably a capping element is positionable at the second end of the longitudinal element and at the entry of the longitudinal cavity through which both the longitudinal element and conduit element are passed in use.

Preferably the longitudinal element is a cable tendon.

39924 5 More preferably the cable tendon is a multi-strand cable and the radial protrusions are the outwardly stretched and separated strands of the cable.

Preferably the divider element is positioned orthogonally to the longitudinal element. More preferably the divider element is a substantially circular plate element.

Preferably the conduit element is a tube positionable against an inner wall of the cavity. Alternatively the conduit element is a tube or tubular cavity provided within the longitudinal element.

Preferably the capping element comprises one or more o domed plates with a hole or holes therein to allow both the cable tendon and conduit element to be passed through it in use.

In a further aspect, the invention provides a method for affixing a longitudinal element into a longitudinal cavity for stabilisation of the substrate strata comprising the steps of: placing a quantity of bonding substance into the longitudinal cavity; mrpassing a longitudinal element, fitted with one or Smore radial protrusions located on or around a first end of the longitudinal element, into the cavity and causing the longitudinal element to move into the bonding substance in the cavity in order to achieve anchorage of the longitudinal element; inserting a conduit element into the cavity from the direction of a second end of the longitudinal element when the longitudinal element is placed in the cavity; and introducing sealing grout mixture through the conduit element and into the cavity in order to affix the longitudinal element.

Preferably the method further comprises the step of applying a force to cause the longitudinal element to rotate and to cause the radial protrusions to mix with and 39924 6 disperse the bonding substance into the first end of the cavity in order to achieve anchorage of the longitudinal element at that end.

Preferably the method further comprises the step of mounting a divider element at a position on the longitudinal element such that the divider element divides the first end fitted with the radial protrusions from a second end of the longitudinal element.

Preferably the method further comprises the step of applying an external force in order to longitudinally tension the anchored longitudinal element prior to the introduction of the sealing grout mixture.

Preferably the method further comprises the step of positioning a capping element at the second end of the longitudinal element and at the entry of the longitudinal cavity, through which the longitudinal element is passed in use.

Preferably the grout is introduced into the region between the divider element and the capping element.

In a further aspect, the invention provides a method for affixing a longitudinal element into a longitudinal cavity for stabilisation of the substrate strata comprising the steps of: placing a quantity of a bonding substance into the longitudinal cavity in order to anchor the longitudinal element; and subsequently introducing sealing grout mixture into the remainder of the cavity in order to affix the longitudinal element.

Preferably the bonding substance is a chemical resin.

Brief Description of the Drawings Notwithstanding any other forms which may fall within the scope of the present invention, preferred forms of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a side schematic view of one embodiment 39924 7 of a strata bolting device in accordance with the invention.

Modes for Carrying out the Invention Referring to the drawings, apparatus 10 is shown for insertion into a longitudinal cavity 12 for stabilisation of a rock substrate 14 which comprises a longitudinal multi-strand cable tendon 16 fitted with three radial protrusions 18 or 'birdcages' formed from the outwardly stretched and separated strands of the cable 16. When the cable 16 is inserted into the cavity 12 these protrusions 18 are located on the end of the cable 16 innermost the 4 cavity 12. The cable 12 also optionally has a circular plate element 20 fitted to it, located so as to divide the end of the cable 12 fitted with the birdcages from the other end nearest to the opening 22 of the cavity 12. The plate 20 has an outer diameter equivalent to the internal diameter of the cavity 12.

After the cable 16 is inserted into cavity 12, a conduit tube 24 is inserted into the cavity 12 also from the cavity opening 22, extending up to be near the plate The tube 24 can either be positioned against an inner wall of the cavity 12 as shown, or in another embodiment as a tubular cavity provided within cable 16 itself (not shown). A cap 26 for cavity 12 is positioned over cavity opening 22 and is comprised of two domed plates with three holes drilled in it to allow the cable tendon 16 and tube 24 to be passed through and provide an inspection hole 28.

In use the apparatus 10 provides a means of affixing a cable tendon 16 into a longitudinal drill hole cavity 12 (typically 55mm in diameter) for stabilisation of a rock substrate 14. In previous practice, resin anchoring has not been used in a 55mm diameter drill hole, and, rather, a hole of tapering diameter down to 28mm at the innermost end has been required to allow normal resin cartridges to anchor a cable tendon. One application of the apparatus is to stabilise the roof of workings in an underground mine by 39924 8 grouting the cable into a drill hole after installation.

Pre-tensioning of the cable 16 is also a possible feature of the method before post-grouting. This produces a fully encapsulated ground support cable tendon 16. Typically these are 8m long but can be of any length. This apparatus and method would find particular application in coal mines but could equally be applied to harder rock strata applications. The follow up grouting only improves the reinforcement value of the tendon.

The method involves placing cartridges or other containers of a bonding substance such as a chemical resin into the cavity 12 and then passing the cable 16 into the cavity. The cartridges of resin are held in place by the plate 20 in the region of the cable closest to the birdcage protrusions. The end of cable 16 protruding from cavity 12 and cap 26 is then connected by link 30 to an external drive (not shown) located outside of the cavity 12 in order to apply a force to cause the cable tendon 16 to rotate.

The birdcage protrusions 18 mix with and disperse the fast- 20 setting chemical resin into the uppermost end of the cavity 12 above the plate 20 in order anchor the cable 16 at that end. The resin retention plate 20 was added to the tendon S"to assist keeping the resin in the birdcage 18 area during the mixing and setting of the resin, although this plate feature is not essential if a particularly viscous resin is used to bond the cable tendon 16.

If no pretensioning of the cable 16 is required, the method then simply involves the insertion of the tube 24 into the cavity 12 through the cap 26 via the cavity opening 22. The tube 24 outlet 29 is positioned close to the plate 20 in the region of the cavity 12 between the plate 20 and the cap 26 and sealing grout mixture is introduced through the tube and into the cavity 12 in order to affix the cable 16 in position. Grout fills the cavity 12 from the top downward.

If cable 16 is required to be pre-tensioned prior to 39924 9 affixing, in order to provide rock strata stabilisation, a further external force is applied to confer longitudinal tension to the anchored cable 16 before grouting commences.

Tube 24 typically has a 12mm internal diameter which is sufficient to allow it to fit in the radial gap between the cable 16 and the wall of cavity 12 in a drill hole as small as 55mm diameter. Use of such constant diameter drill holes as a standard can dramatically reduce the amount of time involved in drilling holes of various diameters to produce tapered holes in which to incorporate other previously known cable anchoring techniques.

The type of grout used is able to be pumped downward oo from the outlet 29 of tube 24 without the need for a breather tube. Advantageously, the grout used has nil slump properties which means the collar of the cap 26 does not have to be sealed. The inspection hole 28 in cap 26 allows the grout to be forced out of the hole 28 as a visible test of a completely grouted cavity.

S Whilst the invention has been described with reference 20 to preferred embodiment it should be appreciated that the invention can be embodied in many other forms.

In the claims that follow and in the summary of the S"invention, except where the context requires otherwise due to express language or necessary implication, the words "comprised" or "comprising" are used in the sense of "including", i.e. the features specified may be associated with further features in various embodiments of the invention.

39924

Claims (19)

1. Apparatus for insertion into a longitudinal cavity for stabilisation of the substrate strata comprising: a longitudinal element fitted with one or more radial protrusions located on or around a first end of the longitudinal element; and a conduit element insertable into the cavity from the direction of a second end of the longitudinal element and extendable into the cavity when the longitudinal element is placed in the cavity; whereby in use the longitudinal element can be placed in the cavity and sealed into the cavity at the first end by a bonding substance and subsequently sealed at the second end of the of the longitudinal element by a bonding substance which is passed into the cavity by means of the conduit element.

2. Apparatus as claimed in claim 1 wherein a divider element is mounted to the longitudinal element and located at a position on the longitudinal element such that the divider element divides the first end fitted with the radial protrusions from the second end of the longitudinal element and wherein the divider element has an outer dimension at most equivalent to the dimension of the longitudinal cavity when the longitudinal element is placed therein.

3. Apparatus as claimed in claim 1 or claim 2 wherein a capping element is positionable at the second end of the longitudinal element and at the entry of the longitudinal cavity through which both the longitudinal element and conduit element are passed in use.

4. Apparatus as claimed in any of the preceding claims wherein the longitudinal element is a cable tendon.

Apparatus as claimed in claim 4 wherein the cable tendon is a multi-strand cable and the radial protrusions are the outwardly stretched and separated strands of the cable. 39924 11

6. Apparatus as claimed in claims 2 to 5 wherein the divider element is positioned orthogonally to the longitudinal element.

7. Apparatus as claimed in claim 6 wherein the divider element is a substantially circular plate element.

8. Apparatus as claimed in any one of the preceding claims wherein the conduit element is a tube positionable against an inner wall of the cavity.

9. Apparatus as claimed in any one of claims 1 to 7 wherein the conduit element is a tube or tubular cavity provided within the longitudinal element.

10. Apparatus as claimed in any one of claims 3 to 9 wherein the capping element comprises one or more domed ".'o.plates with a hole or holes therein to allow both the cable tendon and conduit element to be passed through it n use.

11. A method for affixing a longitudinal element into a longitudinal cavity for stabilisation of the substrate strata comprising the steps of: placing a quantity of bonding substance into the longitudinal cavity; mrpassing a longitudinal element, fitted with one or Smore radial protrusions located on or around a first end of the longitudinal element, into the cavity and causing the longitudinal element to move into the bonding substance in the cavity in order to achieve anchorage of the longitudinal element; inserting a conduit element into the cavity from the direction of a second end of the longitudinal element when the longitudinal element is placed in the cavity; and introducing sealing grout mixture through the conduit element and into the cavity in order to affix the longitudinal element.

12. A method as claimed in claim 11 further comprising the step of applying a force to cause the longitudinal element to rotate and to cause the radial protrusions to 39924 12 mix with and disperse the bonding substance into the first end of the cavity in order to achieve anchorage of the longitudinal element at that -end.

13. A method as claimed in claim 12 further comprising the step of mounting a divider element at a position on the longitudinal element such that the divider element divides the first end fitted with the radial protrusions from a second end of the longitudinal element.

14. A method as claimed in claim 12 or claim 13 further comprising the step of applying an external force in order to longitudinally tension the anchored longitudinal element prior to the introduction of the sealing grout ""mixture.

15. A method as claimed in claim 14 further comprising the step of positioning a capping element at the second end of the longitudinal element and at the entry of the longitudinal cavity, through which the longitudinal element is passed in use.

16. A method as claimed in claim 15 wherein grout is 20 introduced into the region between the bonding substance and the capping element.

17. A method for affixing a longitudinal element into a longitudinal cavity for stabilisation of the substrate strata comprising the steps of: placing a quantity of a bonding substance into the longitudinal cavity in order to anchor the longitudinal element; and subsequently introducing sealing grout mixture into the remainder of the cavity in order to affix the longitudinal element.

18. A method as claimed in claims 11 to 17 wherein the bonding substance is a chemical resin.

19. Apparatus for insertion into a longitudinal cavity for stabilisation of the substrate strata as herein described with reference to the accompanying drawings. A method for affixing a longitudinal element into a 39924 13 longitudinal cavity for stabilisation of the substrate strata as herein described with reference to the accompanying drawings. Dated this 19 t h day of October 2000 SPRINGVALE COAL PTY LIMITED By their Patent Attorneys GRIFFITH HACK *0 4 «o ooo o* 39924