AU5199801A

AU5199801A - Rock bolt assembly

Info

Publication number: AU5199801A
Application number: AU51998/01A
Authority: AU
Original assignee: ABTROV Pty Ltd
Current assignee: ABTROV Pty Ltd
Priority date: 2000-06-21
Filing date: 2001-06-19
Publication date: 2002-03-21

Description

Our Ref:7617900 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Address for Service: Abtrov Pty Limited Unit 4 4 Metro Court Gateshead New South Wales 2290 Australia DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Rock bolt assembly Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 r i'l~ -L P\WPDOCS\DYSpedA7466143.doc-1 5 hn 2001 -1- ROCK BOLT ASSEMBLY The present invention relates generally to rock bolt assemblies and more particularly though not exclusively to integrated drilling rock bolt assemblies.

Rock bolts are used to improve the stability and maintain the load carrying capability of strata (such as, for example, rock strata) in the region of underground excavations. Rock bolts are tensioned to impose a compression load to the rock surface at the time of installation. Tensioned rock bolts can fail as a result of shifts in the rock strata.

These strata shifts can be in the form of inclined shifts as well as downward pressure.

Such movement on the actual wedge of a roof bolt can bring about failure due to the wedge being dislodged which brings about the loss of bolt tension, therefore giving a false impression that the strata is still held in a controlled safe state. Also with conventional roof bolts that are point anchored by various methods, eg. tapered wedge, expansion shell, or chemical set, the bolt is point anchored then by applying torque via the nut to the roof bolt plate this creates a clamp force to the strata and in turn causes the roof bolt to be tensioned via the bolt's resistance to stretch. As an example, if one applied a tensioning load of 18 tons to a 20 ton capacity roof bolt there now needs only a two ton strata incursion load to bring about a bolt failure. It will be appreciated that because the bolts are in a prestressed condition, the forces required to cause the rock bolt to fail are significantly less than if the bolt was in an preloaded compressed state prior to tensioning S the strata.

25 An object of the present invention is to provide an improved rock bolt assembly which improves the capabilities of the rock bolts characteristics so as to withstand the stresses that are causing premature failure of rock bolts coupled with the ability to monitor and apply a controlled uniformed compression force to the strata.

According to the present invention there is provided a rock bolt assembly for use in strata control, the rock bolt assembly including an outer tubular body when in use is i i, -l r; .L ri 1- :\WPDOCM DYSWpeci©\7466143.do-15 June 200 -2adapted to be disposed within a hole in the strata, anchoring means at one end portion of the tubular body, an actuator operable in response to relative axial movement between the actuator and the anchoring means to cause the anchoring means to secure the tubular body within the hole in the strata, an inner member extending through the tubular body, a first force applicator operable to apply a tensile force to the inner member and a compressive force to the outer tubular body, and a second force applicator operable to act on the tubular body to transfer the compressive force applied by the first force applicator.

In one preferred form, the anchoring means includes one of the end portions of the tubular body the end portion having longitudinal relieving slots therein which are adapted to allow the ease of flaring the end portion of the tubular body. The arrangement is such that the actuator causes the tubular body to flare urging outwardly into locking engagement with the surrounding strata. Preferably, anchoring is effected as a result of relative axial movement between the tubular body and the anchoring means.

In one form, the actuator may comprise an actuating element which is at least partially receivable within the aforementioned one end of the tubular body. Preferably, "the actuating element includes a cylindrical parallel to cone wedge like portion which upon relative axial movement between wedge like portion and the tubular body urges the flaring in the slot relieved area outwardly and into locking engagement with the surrounding strata.

wow•• The wedge like portion may be generally frustoconical in shape and the actuating element further include a generally cylindrical portion which has a cross sectional 25 dimension which approximates that of the inner cross sectional dimension of the tubular member.

The inner member may in one form, include an elongated body portion secured to or integral with the actuating means and at the other end have a threaded portion.

Preferably, the inner member may include a flexible cable or a high tensile rod or like section between the actuating means and the threaded portion.

i"x-i i i i' -i i _ili l.WPDOCSOYSW7ic7466143.doc-15 Jmc 2001 -3- In one preferred embodiment, the first force applicator includes a nut which is receivable on the threaded portion of the inner member, the nut including a bearing surface which is adapted to abut against the outer end of the tubular member. The arrangement is such that tightening of the nut causes the inner member to be tensioned and at the same time anchors in the strata and applies a compressive force to the tubular body.

The second force applicator may include a nut which is adapted to cooperate with a threaded portion at the other end of the tubular body. The second nut acts independently of the first nut so that when tightened it transfers the compressive force in the tubular body previously applied to it by the first force applicator.

The assembly may further include a drilling element located adjacent the aforementioned one or inner end of the tubular body and operatively connected thereto so as to transmit torque and prevent relative displacement between the drilling element and the tubular body whereby the drilling element is adapted to bore a hole in the strata upon the rotational movement together of the drilling element and the tubular body. The operative connection is subsequently operable in an anchoring mode to permit relative axial displacement between the drilling element and the tubular body in response to a 20 predetermined threshold axial force component applied to the tubular body. Preferably, the drilling element is operatively connected to or forms part of the actuating means.

S'In a preferred form, the cylindrical portion of the anchoring member is operatively connected to the tubular body by fractuable connection so as to temporarily connect to the 25 inner surface of the tubular body. Under the predetermined axial load conditions the fractuable connection is subsequently broken to initiate the anchoring mode whereby the S•so divided anchoring elements are driven into expanding engagement with the anchoring actuator thereby force flaring outwardly to engagement with the surrounding strata. The cylindrical portion may for example, be lightly swaged by the tubular body.

P'\WPDOCSDYSospcci¢\7466143.doc-1 June 2001 -4- In order to enable a clearer understanding of the invention, drawings illustrating an example embodiment, and in those drawings Figure 1 is a sectional side elevation of a rock bolt assembly according to the present invention; Figure 2 is an end view of the assembly shown in Figure 1, looking from the outer threaded end; Figure 3 is a similar view to Figure 4 showing the inner end of the bolt assembly in an anchored position; and Figure 4 is a side elevation of the complete assembly shown in Figures 1 to 3 in an anchored tensioned state.

Referring to the drawings there is shown a rock bolt assembly generally indicated at 10 for use in the stabilising of a strata 60, the rock bolt assembly 10 includes a tubular body 12 which in use is disposed within a hole 62 in the strata 60. (See Figure The tubular body 12 is in the form of a steel tube having an inner end 13 and an outer end 14.

S" 20 The outer end 14 of the tube has a threaded portion Anchoring means 16 is disposed at the inner end portion of the tubular body. The S' anchoring means 16 is defined by the inner end 13 of the tubular body 12 which has longitudinal relieving slots 17 therein which are adapted to promote the flaring of the end portion of the tubular body. The arrangement is such that the flaring at 18 is urged outwardly into locking engagement with the surrounding strata An actuator 20 is operable in response to relative axial movement between the actuator 20 and the anchoring means 16 to cause the anchoring means to secure the tubular body within the hole 62 in the strata 60. As shown, the actuator 20 includes a parallel portion 24 which is lightly swaged by the outer tube 12 which is received within the i i -I i-~i r ?-I;1I~L-rrii P:\WPDOCS\DYS ecdc\7466I43.doc-15 Jue 2001 aforementioned one end of the tubular body and has a wedge shaped portion 23 which upon relative axial movement between the wedge shaped portion 23 and the tubular body 12 urges the flaring 18 outwardly into locking engagement with the surrounding strata The wedge shaped portion 23 is generally frustoconical in shape and there is also a cylindrical portion 24 having a cross sectional dimension which approximates that of the inner cross sectional dimension of the tubular body. Grooves 25 are formed in the outer surface of the actuator 20 to allow access for water during drilling and grout for encapsulation. The cylindrical portion 24 is lightly swaged by the outer tube 12.

An inner member 30 extends through the tubular body 12 and is secured to or integral or swaged with the actuator 20 at one end and at the other end an integrated swaged externally threaded portion 34. The coupling section is in the form of a flexible cable or any high tensile rod or tube or the like section.

The assembly includes a first force applicator 40 in the form of a nut 42 which is receivable on the threaded section 34 of the inner member 30. The nut includes a bearing surface 43 which is adapted to locate and abut against the threaded end of the tubular member 12. The arrangement is such that tightening of the nut causes the inner member to be tensioned and at the same time it applies a compressive force to the tubular body.

Apertures 45 in the nut 42 provide access for water for flushing and cooling whilst drilling or for chemical or grout medium as required for full encapsulation.

go The second force applicator 46 may include a nut 47 which is adapted to cooperate with a threaded portion 15 of the tubular body. The second nut 47 acts independently of 25 the first nut 42 so that when tightened against 49 a plate it applies a compression force to the strata 60 and coincidingly to 12 the tube a tensile force acting to try to overcome the preload compression created by the nut 42 which in turn urges the frustoconical wedge 23 to further engage anchoring means 16 causing a consistent reinforcement to the point anchor in the strata hole 62.

'P:\WPDOCSIDYS~specie\1466I43.doolS5 Jo 2001 -6- In the embodiment shown, the assembly further includes a drilling element located adjacent the inner end of the tubular body 12. The drilling element forms part of the actuator 20 and is arranged to transmit torque and prevent relative displacement between the drilling element and the tubular body whereby the drilling element is adapted to bore a hole in the strata upon conjoined rotational movement of the drilling element and the tubular body. As described earlier the connection is subsequently operable in an anchoring mode to permit relative actual displacement between the drilling element and the tubular body in response to a predetermined threshold axial force component applied to the tubular body. Flutes 54 are arranged to direct the tailings out of the hole during the drilling operation.

The cylindrical portion 24 of the actuator member 20 is operatively connected to the tubular body by fractuable connection so as to temporarily connect to the inner surface of the tubular body. Under the predetermined axial load conditions the fractuable connection is subsequently broken to initiate the anchoring mode whereby the flaring of the slot relieved area 18 are forced outwardly into engagement with the surrounding strata.

"The operation of the rock bolt assembly will hereinafter be described. Firstly, with the cylindrical portion 24 of the actuator 20 lightly swaged by the inner surface of the tubular body 12 a hole is drilled in the strata using the drilling element 50. Once the hole has been drilled to the required depth nut 42 is rotated so as to place the inner member in tension and draw the actuator 20 in the direction of the tubular body 12. The force S created is sufficient to break the lightly swaged connection between cylindrical portion 24 and the tubular body 12 so that the relative movement between the wedge shaped portion 25 23 and the tubular body 12 causes movement and flaring of the flaring 18 outwardly into locking engagement with the hole 62 in surrounding strata 60 thereby creating an integrated point anchor which becomes pretensioned whilst simultaneously pre-load compressing the outer tube 12. This is effected prior to applying a compression load to the strata 60 via the torquing of the nut 47 on the plate 49 to compress the strata 60 with the strata 60 now clamp force tensioned. The situation with the now set roof bolt combines the strength of the inner member 30 with the outer tube 12 where by when a -ILh -x~C i-r, rr-, *,ii rt;-i-i i~i- ,i iir -i I ~-i P:\WPDOCS\DYS~spniV7466143.dm-l5 June 2001 -7strata 60 incursion load occurs it will promote further engagement flaring 18 of the already pre-tensioned point anchor, in turn offering a combined maximum resistance to the incurred load. If the torque applied to the nuts 42 and 47 is noted it is possible to be able to return to these roof bolts and re-check the torque at any given time and be able to record any incursion load therefore giving the indication of more bolts required to hold up the strata thereby creating a safer work environment for underground workers.

Finally, it is to be understood that the inventive concept in any of its aspects can be incorporated in many different constructions so that the generality of the preceding description is not to be superseded by the particularity of the attached drawings.

Various alterations, modifications and/or additions may be incorporated into the various constructions and arrangements of parts without departing from the spirit or ambit of the invention.

S

I.

Claims

1. A rock bolt assembly for use in strata control, the rock bolt assembly including an outer tubular body when in use is adapted to be disposed within a hole in the strata, anchoring means at one end portion of the tubular body, an actuator operable in response to relative axial movement between the actuator and the anchoring means to cause the anchoring means to secure the tubular body within the hole in the strata under a predetermined anchor load by an inner member extending through the tubular body, a first force applicator operable to apply a tensile force to the inner member and a compressive force to the outer tubular body to a predetermined threshold prior to applying a clamp force to the strata, and a second force applicator operable to act on the tubular body to transfer the compressive force applied by the first force applicator.

2. A rock bolt assembly according to claim I wherein the anchoring means includes one of the end portions of the tubular body the end portion having longitudinal relieving slots therein which are adapted to allow the ease of flaring the end portion of the tubular *."body. 20

3. A rock bolt assembly according to claim 1 or claim 2 wherein said actuator includes an actuating element which is at least partially receivable within the aforementioned one end of the tubular body, the actuating element including a cylindrical parallel to cone wedge like portion which upon relative axial movement between wedge like portion and the tubular body urges the flaring in the slot relieved area outwardly and into locking engagement with the surrounding strata.

4. A rock bolt assembly according to claim 3 wherein said wedge like portion is frustoconical in shape and the actuating element further includes a generally cylindrical portion which has a cross sectional dimension which approximates that of the inner cross sectional dimension of the tubular member.

P:\WPDOCS DYSkspcci¢\7466143,d-15 Jle 2001 -9- A rock bolt assembly according to any preceding claim wherein said inner member includes an elongated body portion secured to or integral with the actuating means and at the other end have a threaded portion, the inner member includes a flexible cable or steel rod or tube, composite or like section between the actuating means and the threaded portion.

6. A rock bolt assembly according to any preceding claim wherein the first force applicator includes a nut which is receivable on the threaded portion of the inner member, the nut including a bearing surface which is adapted to locate and abut against the outer end of the tubular member.

7. A rock bolt assembly according to any preceding claim wherein the second force applicator includes a nut which is adapted to cooperate with a threaded portion at the other end of the tubular body, the second nut acting independently of the first nut so that when tightened it transfers the compressive force in the tubular body previously applied to it by the first force applicator and by tensioning the strata transfers the preload tension on the S. outer tube bolt portion that is within the strata hole.

8. A rock bolt assembly according to any preceding claim wherein further including a 20 drilling element located adjacent the aforementioned one or inner end of the tubular body and operatively connected thereto so as to transmit torque and prevent relative displacement between the drilling element and the tubular body whereby the drilling element is adapted to bore a hole in the strata upon the rotational movement together of the drilling element and the tubular body, the operative connection being subsequently 25 operable in an anchoring mode to permit relative axial displacement between the drilling element and the tubular body in response to a predetermined threshold axial force component applied to the tubular body, the drilling element being operatively connected to or forming part of the actuating means. 'P:\WPDOCS\DYS\spcie\7466143.doc-19 lune 2001

9. A rock bolt assembly according to any preceding claim wherein said cylindrical portion of the anchoring member is operatively connected to the tubular body by fractuable connection so as to temporarily connect to the inner surface of the tubular body.

10. A rock bolt assembly substantially as hereinbefore described with reference to the accompanying drawings. Dated this 19t day of June, 2001. ABTROV PTY LIMITED By their Patent Attorneys DAVIES COLLISON CAVE *o t 1..