AU2007216933A1

AU2007216933A1 - A rock bolt

Info

Publication number: AU2007216933A1
Application number: AU2007216933A
Authority: AU
Inventors: Peter Harold Craig; Timothy Joseph Gaudry
Original assignee: FCI Holdings Delaware Inc
Current assignee: FCI Holdings Delaware Inc
Priority date: 2006-09-25
Filing date: 2007-09-21
Publication date: 2008-04-10

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION Standard Patent Applicant(s): Jennmar Corporation Invention Title: A ROCK BOLT The following statement is a full description of this invention, including the best method for performing it known to me/us: -2- A ROCK BOLT TECHNICAL FIELD The present invention relates to rock bolts suitable for use in the mining and tunnelling industry to provide rock and wall support. The invention is suitable for use in hard rock applications as well as in softer strata, such as that often found in coal mines, and it is to be appreciated that the term "rock" as used in the specification is to be given a broad meaning to cover both these applications.

BACKGROUND

Roof and wall support is vital in mining and tunnelling operations. Mine and tunnel walls and roofs consist of rock strata, which must be reinforced to prevent the possibility of collapse. Rock bolts are widely used for consolidating the rock strata.

In conventional strata support systems, a bore is drilled into the rock by a drill rod, which is then removed and a rock bolt is then installed in the drilled hole and secured in place typically using a resin or cement based grout. The rock bolt is tensioned which allows consolidation of the strata by placing that strata in compression. The rock bolt is typically formed from a steel rod.

To allow the rock bolt to be tensioned, the end of the bolt may be anchored mechanically to the rock formation by engagement of an expansion assembly on the end of bolt with the rock formation. Alternatively, the bolt may be adhesively bonded to the rock formation with a resin bonding material inserted into the bore hole.

Alternatively, a combination of mechanical anchoring and resin bonding can be employed by using both an expansion assembly and resin bonding material.

A mechanically anchored rock bolt typically includes an expansion assembly threaded onto one end of the bolt shaft and a drive head for rotating the bolt. A plate is positioned between the drive head and the rock surface. The expansion assembly generally includes a multi-prong shell supported by a threaded ring and a plug threaded onto the end of the bolt. When the prongs of the shell engage with rock -3- "surrounding a bore hole, and the bolt is rotated about its longitudinal axis, the plug threads downwardly on the shaft to expand the shell into tight engagement with the rock thereby placing the bolt in tension between the expansion assembly and the mine rock surface.

When resin bonding material is used, it penetrates the surrounding rock O formation to adhesively unite the rock strata and to hold firmly the rock bolt within I the bore hole. Resin is typically inserted into the bore hole in the form of a two component plastic cartridge having one component containing a curable resin composition and another component containing a curing agent (catalyst). The two component resin cartridge is inserted into the blind end of the bore hole and the mine rock bolt is inserted into the bore hole such that the end of the mine rock bolt ruptures the two component resin cartridge. Upon rotation of the mine rock bolt about its longitudinal axis, the compartments within the resin cartridge are shredded and the components are mixed. The resin mixture fills the annular area between the bore hole wall and the shaft of the mine rock bolt. The mixed resin cures and binds the mine rock bolt to the surrounding rock.

SUMMARY OF THE INVENTION According to a first aspect of the invention there is provided a rock bolt comprising: an elongate shaft configured to be located in a bore formed in a rock substrate; and indicia on a predetermined portion of the shaft to indicate that a predetermined length of the shaft is in the bore when the indicia is aligned with a reference member.

When the resin cartridge is shredded upon insertion and rotation of the rock bolt, the shredded cartridge can interfere with the resin and catalyst mixing. Poor mixing results in an inferior cured resin and results in poor bond strength between the bolt and bore hole wall. In addition a phenomenon of"glove fingering" may occur when the plastic film that forms the cartridge lodges in the bore hole proximate the surrounding rock thereby interrupting the mechanical interlock desired between the resin and bore hole wall.

-4- An advantage of the rock bolt according to the above aspect is that by controlling the depth of insertion of the rock bolt into the bore, the likelihood of interference by the shredded cartridge to bonding of the rock bolt in the bore can be reduced.

Optionally, the reference member is the surface of the rock substrate adjacent bore opening. Alternatively, the reference member is an outer surface of a support plate disposed on the shaft and arranged to bear against a surface of the rock strata.

Optionally, the rock bolt comprises a drive head disposed at a proximal end of the shaft and arranged to attach the bolt to a drilling assembly. The reference member may be mounted to the drilling assembly.

The indicia may comprise a single marking, or alternatively may comprise a series of graded markings representing a plurality of said predetermined lengths of the shaft in the bore, or further alternatively may comprise a band of predetermined width representing the predetermined length of the shaft in the bore and tolerances therefore.

The shaft may be rigid and may be formed from a steel rod. The rock bolt may comprise indicia to indicate the grade of steel of the steel rod. The rod may be profiled. The indicia to indicate a predetermined shaft length may comprise the indicia to indicate steel grade. This will reduce the number of physical indicia on the shaft.

The shaft may comprise bonding elements. The bonding elements may comprise raised portions in the shaft surface.

Optionally, the rock bolt comprises: an abutting device slidably mounted on the shaft and adapted to abut a portion of the substrate adjacent the bore opening; and a holder near or at a proximal end of the shaft for preventing the plate from being removed from the shaft at its proximal end.

The shaft may comprise a threaded portion at its proximal end for threaded engagement with the plate and/or the holder.

The indicia may be provided by a luminous substance.

According to a second aspect of the present invention there is provided a rock bolt system comprising: a container containing a bonding substance therein and configured to be inserted in a bore formed in a rock substrate, the bore being arranged to be of a predetermined length; a rock bolt having an elongate shaft configured to be located in the bore and having indicia on the shaft; wherein the bolt is inserted in the bored after insertion of the container and the indicia is arranged to provide a visual guide to facilitate correct placement of the bolt and the container in the bore.

Optionally the indicia indicates that a predetermined length of the shaft is in the bore wherein the indicia indicates that a predetermined length of the shaft is in the bore when the indicia is adjacent a reference member.

The reference member may be the surface of the rock strata adjacent to bore opening or may be an outer surface of a support plate disposed on the shaft and arranged to bear against a surface of the rock strata.

Optionally, the indicia is capable of being associated with a plurality of containers of differing length and is arranged to provide a visual guide to facilitate correct placement of the bolt and any one of the associated containers in the bore.

The indicia may include a plurality of components each associated with a respective one of the plurality of containers of different lengths. Optionally, the container is formed from a plurality of cartridges.

The indicia may comprise a single marking. Alternatively, the indicia comprises a series of graded markings representing a plurality of said predetermined lengths of the shaft in the bore. Further, alternatively the indicia may comprise a band of predetermined width representing the predetermined length of the shaft in the bore and tolerances therefore.

Optionally, the bonding substance is a two-part resin, each of said two-parts being kept separate in the container.

Optionally, the depth of the bore is about 100 to 150 mm less than a total length of the shaft. Optionally, the length of the container together with the length of the shaft from its distal end to the indicia is approximately equal to the depth of the bore.

-6- SAccording to another aspect of the present invention there is provided a method for installing a rock bolt, comprising the steps of: drilling a bore of a predetermined depth into a rock substrate; inserting a container containing a bonding substance therein into the bore; e¢3 C€ 5 inserting a rock bolt shaft into the bore, the shaft having indicia on a O predetermined portion thereof; Susing the indicia as a visual guide to insert the bolt a predetermined distance O into the bore; and Sperforming a predetermined action on the bolt when the bolt is inserted the predetermined distance in to the bore.

Optionally, the indicia indicates that a predetermined length of the shaft is in the bore when the indicia is adjacent a reference member.

Optionally, the reference member is the surface of the rock strata adjacent the bore opening.

Alternatively, the reference member may be an outer surface of a support plate disposed on the shaft and arranged to bear against surface of the rock strata.

Optionally, the rock bolt shaft further comprises a drive head disposed at a proximal end of the shaft and arranged to attach the bolt to a drilling assembly to the bolt in the bore.

Optionally, the predetermined action comprises rotating the shaft for a predetermined time period to fracture the container and to mix the bonding substance within the container.

Optionally, the method further comprises the step, after the mixing step, of allowing the bonding substance to set.

Optionally, the bonding substance is a two-part resin, each of said two-parts being kept separate in the container, and which are mixed together to set during the mixing step.

Optionally, the method comprises a step of stopping rotating of the holder when a rotator used to rotate the holder stalls.

Optionally, the setting step is performed for 10-80 seconds and preferably for 12 to 60 seconds.

-7- SOptionally, the mixing step is performed for 7 to 15 seconds and preferably to 12 seconds.

C Optionally, the rock bolt system for the mixing step performed for 1 to seconds and preferably for 2 to 4 seconds.

¢€3 The method may comprise the step, once a predetermined length of the shaft is in the bore, of stopping the inserting step.

BRIEF DESCRIPTION OF THE DRAWINGS Preferred embodiments of the invention will now be described, by way of example only and where like reference numerals denote like parts, with reference to the accompanying drawings in which: Figure 1 illustrates a side elevation of a preferred embodiment of a rock bolt; Figures 2 to 7 illustrate different steps for installing the rock bolt of Figure 1 into a substrate; and Figure 8 is a side elevation of an alternative embodiment of a rock bolt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 1, a preferred embodiment is a rock bolt 10 for use in a system for supporting walls and/or roofs of mining shafts. The rock bolt 10 comprises a rigid elongate shaft 12 preferably manufactured from steel, however may be made from other suitable materials depending on the application. For example, the shaft 12 may be manufactured from other hard or hardened metals or polymeric materials. The shaft 12 comprises bonding elements in the form of raised portions 13 for improving a bond between the shaft 12 and the bonding substance which is described in more detail below. In this embodiment, the shaft 12 is profiled.

Indicia in the form of a band 14 is on a predetermining portion of the shaft 12 and is described in more detail below. A drive head nut 16 is disposed at a proximal end 18 of the shaft 12 and is arranged to be connected to a drilling rig (described below). An abutting device in the form of a tensioner 22 is threadedly mounted on a -8threaded portion 24 of the shaft 12 at its proximal end 18. The tensioner 22 comprises the drive head nut 16, a washer 22a, plate 22b and a dome ball 22c. The drive head nut 16 acts as a holder to prevent the tensioner 22 from being removed from the shaft's proximal end 18. A second indicia 19 is present to indicate to a user the shaft's 12 grade of steel, where different steel grades are used in different applications, such as in different types of rock substrates. For example, one grade may be mild steel of 300MPa yield, while another grade may be extra high tensile steel of 600MPa yield. Alternatively, the second indicia 19 may be in the form of a resin indicator marking provided on the shaft 12 to indicate to an operator the type of resin to be used with the particular rock bolt 10. The length of the shaft 12 may also be indicated on the shaft's distal end. A typical range of lengths may be from 200cm.

The rock bolt 10 will now be described in conjunction with a rock bolt system embodiment and a use thereof. As illustrated in Figure 2, a drilling rig 26 is provided at the surface 28 of a substrate in the form of a mine shaft roof 30. The drilling rig 26 is used to drill a bore 32 into the mine shaft roof 30 using a drill bit 34, to a predetermined depth, typically of 100 to 150mm shorter than the length of the shaft 12. This ensures that a portion (100-150mm) of the shaft 12 extends from the bore 32 when the shaft 12 is fully inserted in the bore 32. The tensioner 22 lies on this extended shaft portion.

The drill bit 34 is then removed from the bore 32 and a container 36 inserted therein, as illustrated in Figure 3. The container 36 contains a bonding substance in the form of a two part resin, each part of which is kept separate from the other while in the container 36.

The rock bolt 10 is then inserted into the bore 32 after the container 36, as illustrated in Figure 4, with the drilling rig 26 connected to the drive head nut 16. The shaft is then pushed axially against the container 36 in the bore 32. When the band 14 on the shaft 12 is aligned with a reference member in the form of an outer surface of the support plate 42 of the drilling rig 26, rotation of the shaft 12 is commenced by the drilling rig while the shaft 12 is continually moved axially into the bore 32. The width of the band 14 represents a tolerance for the amount of the length of shaft -9required to be inserted into the bore 32 prior to rotation thereof. The pressure of the distal end 44 of the rotating shaft 12 against the container 36 is such that the container is then fractured. The shaft 12 is then continually moved axially up through the fractured container and its continued rotation mixes the two components of the resin.

The time taken from the beginning of the rotation of the shaft 12 until the shaft is fully inserted into the bore 32 is preferably 10 to 12 seconds. Depending on the type of resin used, this time may be in the range of 7 to 15 seconds. Once the shaft 12 is fully inserted into the bore (Figure rotation of the shaft is maintained for a further 2 to 4 seconds. The rotation of the shaft 12 is then stopped and the shaft is maintained in its position in the bore 32 for a further 12 to 60 seconds, in which time the two mixed components of the resin are allowed to set (Figure 6) to bond the shaft 12 to the bore 32. As illustrated in Figure 7, once the allotted time has passed for the resin to set, the tensioner 22 is rotated by the drilling rig 26, forcing the tensioner 22 against the surface 28 of the mine shaft roof The drive head 38 is continually rotated until the drill motor of the drilling rig 26 stalls. Rotation of the tensioner against the surface 28 provides a tensile force along the shaft 12. This in turn, as described above with respect to the prior art, provides a compressive force on the rock substrate 46 surrounding the shaft 12 and bore 32. Once the drill motor has stalled, and therefore the rotation of the tensioner 22 is complete, the drilling rig 26 is removed from the mine shaft.

As will be understood, variations of the above described rock bolt 10 and its use thereof can be made without departing from the scope of the appended claims.

For example, in the alternative embodiment of the rock bolt 10 illustrated in Figure 8, the indicia may comprise series of graduated markings 14 which signify different lengths of the shaft from its proximal end 18 to the marking in question. This can be useful where either different known length containers are used for providing the bonding resin to the bore 32 or to allow flexibility in how deep a bore may be drilled.

Also, instead of employing a band 14 (or graduated markings 14') and a second indicia for indicating the grade of steel of the shaft 12, only one indicia may be provided to serve both purposes. For example, the indicia may be in the form of a band as described above, but adapted to indicate the grade of steel of the shaft 12. For example, the band may indicate both a tolerance of the amount of length of the shaft 12 to be inserted in the bore 32 and also be coloured to indicate the steel grade of the shaft.

In alternative arrangements, the resin may be provided in a plurality of containers of differing length and the indicia, whether it be in the form of a band 14 with respect to the first mentioned embodiment or the graduated markings 141 described above with respect to the alternative embodiment, is arranged to indicate to an operator the depth of penetration of the shaft into the bore required for the given resin containers for the use. The indicia may provide a visual guide to facilitate correct placement of the rock bolt 10 and any one of the plurality of containers in the bore 32. In an alternative arrangement, the indicia is fluorescent to improve visibility thereof in a dark environment such as a mine shaft.

In other alternative arrangements, the reference member can be the surface of the rocks strata adjacent the bore opening, or the reference member may be mounted to the drilling assembly.

While the invention has been described in reference to its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made to the invention without departing from its scope as defined by the appended claims. For example, whereas the preferred embodiments have been described with reference to mining applications, it will be understood that it is not limited to this application. Also, whereas the preferred embodiment has been described with reference to a mine shaft roof, it will be understood that it could also be applied to a sidewall or base/floor.

Claims

1. A rock bolt comprising: an elongate shaft configured to be located in a bore formed in a rock substrate; and indicia on a predetermined portion of the shaft to indicate that a predetermined length of the shaft is in the bore when the indicia is aligned with a reference member.

2. The rock bolt of claim 1, wherein the reference member is the surface of the rock strata adjacent the bore opening.

3. The rock bolt of claim 1, wherein the reference member is an outer surface of a support plate disposed on the shaft and arranged to bear against a surface of the rock strata.

4. The rock bolt of any one of the preceding claims, further comprising a drive head disposed at a proximal end of the shaft and arranged to attach the bolt to a drilling assembly.

5. The rock bolt of claim 4, wherein the reference member is mounted to the drilling assembly.

6. The rock bolt of any one of the preceding claims, wherein the indicia comprises a single marking.

7. The rock bolt of claims 1 to 5, wherein the indicia comprises a series of graded markings representing a plurality of said predetermined lengths of the shaft in the bore.

8. The rock bolt of claims 1 to 5, wherein the indicia comprises a band of predetermined width representing the predetermined length of the shaft in the bore -12- and tolerances therefore.

9. The rock bolt of any one of the preceding claims, wherein the shaft is formed from a steel rod.

The rock bolt of claim 9, comprising indicia to indicate the grade of steel of the steel rod.

11. The rock bolt of claim 10, wherein the indicia to indicate a predetermined shaft length comprises the indicia to indicate steel grade.

12. The rock bolt of claim 9, 10 or 11, wherein the rod is profiled.

13. The rock bolt of any one of the preceding claims, wherein the shaft comprises bonding elements for improving a bond between the shaft and a bonding substance between the shaft and a surface of the bore.

14. The rock bolt of claim 13, wherein the bonding elements comprise raised portions on the shaft surface.

The rock bolt of any one of the preceding claims, comprising: an abutting device slidably mounted on the shaft and adapted to abut a portion of the substrate adjacent the bore opening; and a holder near or at a proximal end of the shaft for preventing the plate from being removed from the shaft at its proximal end.

16. The rock bolt of claim 15, wherein a shaft comprise a threaded portion at its proximal end for threaded engagement with the plate and/or the holder.

17. The rock bolt of any one of the preceding claims, wherein the indicia is provided by a luminous substance. t -13-

18. A rock bolt system comprising: a container containing a bonding substance therein and configured to be inserted in a bore formed in a rock substrate, the bore being arranged to be of a 5 predetermined length; a rock bolt having an elongate shaft configured to be located in the bore and having indicia on the shaft; wherein the bolt is inserted in the bored after insertion of the container and the N, indicia is arranged to provide a visual guide to facilitate correct placement of the bolt and the container in the bore.

19. The rock bolt system of claim 18, wherein the indicia indicates that a predetermined length of the shaft is in the bore when the indicia is adjacent a reference member.

The rock bolt system of claim 19, wherein the reference member is the surface of the rock strata adjacent the bore opening.

21. The rock bolt system of claim 19 or claim 20, wherein the reference member is an outer surface of a support plate disposed on the shaft and arranged to bear against a surface of the rock strata.

22. The rock bolt system of any one of claims 18 to 21, further comprising a drive head disposed at a proximal end of the shaft and arranged to attach the bolt to a drilling assembly to the bolt in the bore.

23. The rock bolt system of any one of claims 18 to 22, wherein the indicia is associated with a container of specific length and is arranged to provide a visual guide to facilitate correct placement of the bolt and the associated container in the bore.

24. The rock bolt system of any one of claims 18 to 22, wherein the indicia is -14- capable of being associated with a plurality of containers of differing length and is arranged to provide a visual guide to facilitate correct placement of the bolt and any one of the associated containers in the bore.

25. The rock bolt system of claim 24, wherein the indicia includes a plurality of components each associated with a respective one of the plurality of containers of different lengths.

26. The rock bolt system of any one of claims 18 to 25, wherein the container is formed from a plurality of cartridges.

27. The rock bolt system of any one of claims 18 to 26, wherein the indicia comprises a single marking.

28. The rock bolt system of any one of claims 18 to 26, wherein the indicia comprises a series of graded markings representing a plurality of said predetermined lengths of the shaft in the bore.

29. The rock bolt system of any one of claims 18 to 26, wherein the indicia comprises a band of predetermined width representing the predetermined length of the shaft in the bore and tolerances therefore.

The rock bolt system of claims 18 to 29, wherein the shaft is formed from a steel rod.

31. The rock bolt system of claim 30, comprising indicia to indicate the grade of steel of the steel rod.

32. The rock bolt system of claim 31, wherein the indicia to indicate a predetermined shaft length comprises the indicia to indicate steel grade.

33. The rock bolt system of any one of claim 30, 31 or 32, wherein the rod is profiled.

34. The rock bolt system of any one of claims 18 to 33, wherein the shaft comprises bonding elements for improving a bond between the shaft and the bonding substance between the shaft and a surface of the bore.

The rock bolt system of claim 34, wherein the bonding elements comprise raised portions on the shaft surface.

36. The rock bolt system of any one of claims 18 to 35, comprising: an abutting device slidably mounted on the shaft and adapted to abut a portion of the substrate adjacent the bore opening; and a holder at or adjacent a proximal end of the shaft for preventing the plate from removal from the shaft at its proximal end.

37. The rock bolt system of claim 36, wherein the holder is adapted to be rotated on the shaft to force the plate against the portion of the substrate adjacent the bore opening.

38. The rock bolt system of any one of claims 18 to 37, wherein the shaft is configured to fracture the container in the bore when rotatably forced upon the container.

39. The rock bolt system of claim 38, wherein the shaft is configured to be rotated to mix the bonding substance from the fractured container when the shaft is rotated.

The rock bolt system of any one of claims 18 to 39, wherein the bonding substance is a two-part resin, each of said two-parts being kept separate in the container. -16-

41. The rock bolt system of any one of claims 18 to 40, wherein the depth of the bore is about 100 to 150 mm less than a total length of the shaft.

42. The rock bolt system of any one of claims 18 to 41, wherein the length of the container together with the length of the shaft from its distal end to the indicia is approximately equal to the depth of the bore.

43. A method for installing a rock bolt, comprising the steps of: drilling a bore of a predetermined depth into a rock substrate; inserting a container containing a bonding substance therein into the bore; inserting a rock bolt shaft into the bore, the shaft having indicia on a predetermined portion thereof; using the indicia as a visual guide to insert the bolt a pretermined distance into the bore; and performing a predetermined action on the bolt when the bolt is inserted the predetermined distance in to the bore.

44. The method of claim 43, wherein the indicia indicates that a predetermined length of the shaft is in the bore when the indicia is adjacent a reference member.

The method of claim 44, wherein the reference member is the surface of the rock strata adjacent the bore opening.

46. The method of claim 44, wherein the reference member is an outer surface of a support plate disposed on the shaft and arranged to bear against surface of the rock strata.

47. The method of any one of claims 43 to 46, further comprising a drive head disposed at a proximal end of the shaft and arranged to attach the bolt to a drilling assembly to the bolt in the bore. -17-

48. The method of any one of claims 43 to 47, wherein the predetermined action comprises rotating the shaft for a predetermined time period to fracture the container and to mix the bonding substance within the container.

49. The method of claim 48, comprising the step, after the mixing step, of allowing the bonding substance to set.

The method of claim 48 or claim 49, wherein the bonding substance is a two- part resin, each said two-parts being kept separate in the container, and which are mixed together to set during the mixing step.

51. The method of claim 49 or claim 50, wherein the rock bolt comprises an abutting device slidably mounted on the shaft and a holder threadedly mounted at or adjacent a proximal end of the shaft for preventing the plate from being removed from the shaft at the shaft's proximal end, and wherein the method comprises the step, after the bonding substance is set, of rotating the holder toward the bore such that the holder forces the plate against the portion of the substrate adjacent the bore opening.

52. The method of claim 51, comprising the step of stopping rotating of the holder when a rotator used to rotate the holder stalls.

53. The method of any one of claims 49 to 52, wherein the setting step is performed for 10-80 seconds and preferably for 12 to 60 seconds.

54. The method of any one of claims 48 to 53, wherein the mixing step is performed for 1 to 5 seconds and preferably for 2 to 4 seconds.

The method of any one of claims 43 to 54, wherein the inserting step is performed for 7 to 15 seconds and preferably 10 to 12 seconds.

56. The method of any one of claims 43 to 55, wherein the depth of the bore is -18- about 100 to 150 mm less than a total length of the shaft.

57. A rock bolt, a rock bolt system, or a method of installing a rock bolt substantially as herein described with reference to the accompanying drawings.