US20110070035A1 - Self drilling rock bolting - Google Patents

Abstract

The present invention relates to self drilling rock bolting. In particular, the invention concerns both a drilling apparatus for rock bolting, and a rock bolt for use with the drilling apparatus. The drilling apparatus comprises within it a fluid injector having an upper part that mates with a self-drilling rock bolt for boring a hole. The injector includes three fluid inlets, three fluid outlets in the upper part, and three fluid conduits extending from respective inlets to respective outlets. The self drilling rock bolt comprises an elongate body having a leading end with a cutting tip, and around the tip a thread with a coarse pitch. The bolt also has a trailing end with an integral collar for fluid connection to a channel that extends axially through the body of the rock bolt to the leading end. Above the collar is a thread with a fine pitch. In other aspects the invention concerns a system comprising the drilling apparatus in combination with a rock bolt and a method for rock bolting using the system. The invention has application, but not exclusively, to rock bolting to stabilise the roof and walls of underground coal mines.

Description

FIELD OF THE INVENTION
• The present invention relates to self drilling rock bolting. In particular, the invention concerns both a drilling apparatus for rock bolting, and a rock bolt for use with the drilling apparatus. In other aspects the invention concerns a system comprising the drilling apparatus in combination with a rock bolt and a method for rock bolting using the system. The invention has application, but not exclusively, to rock bolting to stabilise the roof and walls of underground coal mines.
BACKGROUND OF THE INVENTION
• Self drilling rock bolts are known for providing a single drilling and securing function. This negates the need to drill a hole, withdraw the drill bit and subsequently insert a bolt into the hole.
• An existing method of securing a rock bolt to a coal strata is to drill a hole in the coal strata using a drill mast with a drill bit attached thereto. After the hole has been bored and the drill bit retracted, the drill bit is removed from the drill chuck. A rock bolt is then inserted into a drive dolly which forms an adapter between the bolt and a chuck. A resin capsule is then inserted into the bored hole. The bolt is then loaded into the bore hole, and the bolt causes the resin capsule to rupture. The bolt is then rotated to promote mixing and dispersion of the resin. Once the resin has set, a nut on the end of the bolt is rotated and the nut comes into abutment with the collar of the hole. The interaction between the collar of the borehole and the nut places a tensile loading on the stem of the bolt. Accordingly, the strata adjacent to the bolt is compressively loaded, thereby locally stabilising the strata.
• A disadvantage with the above described bolting method is that it is a multi stage, and is thus time consuming operation. The complicated nature of this bolting installation technique also requires significant manual handling, which results in slow bolt installation cycle times.
• One known self drilling rock bolting system uses a hollow bar. A passage through the centre of the bar serves as a flow path for water to flush rock cuttings out of the bore hole. The passage is also used for the ingression of a cementious grout for subsequently securing the bolt to the adjacent wall of the borehole. The cementious grout is generally supplied in a secondary process. Accordingly, this system also suffers from being time consuming.
• A known single stage self drilling rock bolt system is manufactured by Hilti Corporation. This system utilises a hollow bar with a chemical resin capsule housed in the centre of the bar. Water for flushing drill cuttings is also permitted to travel through the inside of the bar in a separate annulus leading to the drill tip. In this system, after the hole boring has been completed, water is injected into the cavity containing the resin capsule. The water ruptures the resin capsule, forcing resin through a hole in the tip of the bar to the bore hole. The resin then sets, bonding the bolt to the rock strata.
• The equipment used in the Hilti system is based upon conventional drilling equipment, with the addition of the water injection function to disperse the resin. A disadvantage with this system is that the resin capsule may prematurely rupture during transportation, or during the boring process, prior to completion of the boring process. A further disadvantage is that the bolts have a limited shelf life on account of the expiration of the resin capsule.
• Other known self drilling rock bolt systems use a mechanical expansion shell, similar to a Dynabolt™. The expansion of the shell is affected by the tightening of a nut, against the collar of a hole. The bored hole is then filled with cementious grout to prevent corrosion, and to assist in the load transfer of the supported strata. A disadvantage this type of system is that the bolt is grouted in a secondary process, requiring the use of grouting equipment that is separate from the drilling equipment. This increases the installation cycle times and the labour required to install the bolts.
SUMMARY OF THE INVENTION
• In a first aspect the invention is a drilling apparatus for rock bolting with a self-drilling rock bolt, comprising within it a fluid injector having an upper part that mates with a self-drilling rock bolt inserted into the drilling apparatus for boring a hole. The injector includes three fluid inlets, three fluid outlets in the upper part, and three fluid conduits extending from respective inlets to respective outlets.
• In use water, resin and catalyst are pumped through respective conduits at selected times, and enter a channel in the rock bolt. Mixing of the catalyst and the resin only occurs after they have entered the rock bolt, and as a result there is reduced risk of the drilling apparatus becoming blocked with prematurely hardened resin.
• The system may further comprise a hydraulically driven pump to pump water to a first fluid inlet. It may also comprise pumps to pump resin and catalyst to second and third fluid inlets. The pumps may operate to provide different resin and catalyst flow rates. In addition they may provide precise differential control, to allow different resin catalyst mix ratios for different bolting conditions.
• The upper part of the injector is insertable within a fixed collar of the rock bolt to make a fluid tight mating between them.
• In a second aspect the invention is a self drilling rock bolt, comprising an elongate body having a leading end with a cutting tip, and around the tip a thread with a coarse pitch.
• The bolt also has a trailing end with an integral collar to form a fluid connection to a channel that extends axially through the body of the rock bolt to the leading end, and above the collar a thread with a fine pitch. In use a nut is threaded onto the fine pitch and engaged with a drill which operates to drive the nut along the fine pitch thread to abut against the collar during boring. After boring, reversal of the drill drives the nut away from the collar.
• The channel within the rock bolt may open in the cutting tip of the bolt.
• The channel within the rock bolt may incorporate a fluid mixer within it. The fluid mixer may comprise a flow restriction.
• In another aspect the invention is a rock bolting system comprising a combination of the drilling apparatus and a rock bolt.
• In a further aspect the invention is a method of using the system for rock bolting, comprising the steps of:
• Attaching a rock bolt to the drilling apparatus for drilling, such that the nut on the rock bolt is secured in the drilling apparatus against rotation, and the upper part of the injector mates with the fluid connection of the rock bolt in a fluid tight manner.
• Then operating the drilling apparatus to bore a hole such that rotation of the rock bolt drives the nut against the collar.
• And simultaneously pumping water through a first fluid inlet of the injector, through the respective conduit and out, and into the channel in the rock bolt to exit the leading end of the bolt.
• When the hole has been completely bored, operation of the drilling apparatus and pumping of the water are ceased before pumping resin and catalyst through respective second and third fluid inlets of the injector, through the respective second and third conduits, out of respective second and third fluid outlets and into the channel in the rock bolt, where they are mixed before exiting the leading end of the bolt. The resin then hardens to bond the rock bolt to the surrounding strata.
• A further step in the process then involves operation of the drilling apparatus, in the opposite direction to the direction used to bore the hole, to push the nut into abutment with the opening of the bore hole and to compressively load a local region of strata.
• The drilling apparatus is then separated from the rock bolt and removed from the site of the boring and securing operation. The drilling apparatus may then be reloaded with a further bolt and the process is repeated as required.
BRIEF DESCRIPTION OF THE DRAWINGS
• An example of the present invention will now be described with respect to the accompanying drawings, in which:
• FIG. 1 is a schematic diagram of a rock bolt installation system in a detached configuration and showing some of the interior detail.
• FIG. 2 is a schematic diagram of a rock bolt installation system in a use configuration and showing some of the interior detail.
BEST MODE OF THE INVENTION
• FIG. 1 depicts a rockbolt installation system10 for securing arock bolt20 to a strata, such as a coal strata. Thesystem10 includes hydraulically operateddrilling apparatus30.
• Thedrilling apparatus30 is selectively operable in both clockwise and anticlockwise rotational directions.
• Therock bolt20 has aleading end21 with a cuttingtip22 and a trailingend23. The leadingend21 is threaded and has a coarse pitch. Part of the trailingend23 is also threaded but has afine pitch24. The trailingend23 of therock bolt20 also includes a fixedcollar27. Anut25 is threadingly engageable with thefine pitch24 of the rock bolt above thecollar27. Thenut25 which has a polygonal profile that mates with thechuck31 ofdrill30.
• When thenut25 is rotated toward the trailingend23, it comes into abutment with thecollar27, as shown inFIG. 1. This abutment prevents thenut25 from moving further toward the trailingend23.
• Therock bolt20 has an internal centralfluid flow channel40 formed therein which extends between openings in theleading end21 and withincollar27 at the trailingend23. A static mixer is located within the flow channel. The mixer is in the form of aflow restriction41.
• Thedrilling apparatus30 includes within it aninjector50. Theinjector50 haswater inlet51 to receive water from awater pumping system61 or water source.Injector50 also has aresin inlet52 to receive resin from aresin pumping system62. And, acatalyst inlet53 to receive catalyst from acatalyst pumping system63. Theresin pumping system62 andcatalyst pumping system63 use pumps which are resistant to the aggressive chemical nature of the resin. Thesepumping systems62 and63 permit different resin and catalyst flow rates to be provided, with precise differential control, to allow different resin catalyst mixes for different bolting conditions.
• Theupper end57 of theinjector50 is insertable within the fixedcollar27 of therock bolt20. The connection between theprojection57 and thecollar27, when the projection is inserted into the skirt, is fluid tight.
• The operation of thesystem10 will now be described with reference toFIG. 2. Within drill30 awater flow conduit71 carries water betweeninlet51 and theupper end57 ofinjector50. Likewise flowconduits72 and73 extend from theresin52 andcatalyst53 inlets to carry resin and catalyst to the upper end ofinjector50. Since the resin is unable to harden until it comes into contact with the catalyst, by providing separate fluid flow conduits for the resin and the catalyst, the risk of the injector head becoming blocked with hard resin is significantly reduced.
• When arock bolt20 is to be installed into a strata, such as a mine roof, the trailingend23 of therock bolt20 is inserted into thechuck31 of thedrill motor30, such that thenut25 is seated within the chuck and secured thereto. In this position theupper end57 of theinjector50 is inserted within thecollar27 of therock bolt20.
• The cuttingtip22 of therock bolt20 is then placed against thecoal strata80 and thedrill motor30 is rotated in an anticlockwise direction. Thenut25 abuts against thecollar27 preventing therock bolt20 from longitudinal movement relative to the chuck. By simultaneously applying anticlockwise rotation and thrust against the coal strata, the cuttingtip22 of therock bolt20 starts to bore a hole within the strata.
• During the boring operation, thewater pumping system61 or source delivers water into theconduit71 of theinjector50. The water passes axially through theinjector50 and out of itsupper end51 before entering into the trailingend23 of therock bolt20. The water passes throughchannel40 in therock bolt20 and exits from thetip22 where it assists in dispersing drill cuttings away from the cuttingtip22 of therock bolt20, and out of the bore hole. Thecoarse thread21 adjacent to thetip22 of therock bolt20 assists with clearing of the rock cuttings, and this improves load transfer between the bolt and the strata after bonding.
• When the hole has been completely bored rotation ofchuck31 is ceased. The resin andcatalyst pumping systems62 and63 are then used to deliver the resin throughconduit72 and a catalyst throughseparate conduit73. The resin and catalyst pass throughinjector50 and enter into the trailingend23 of therock bolt20. While passing throughchannel40 the resin and catalyst are no longer separated from each other, and thestatic mixer41 interrupts the flow of the resin and the catalyst, thereby promoting mixing of the catalyst and the resin into a single homogeneous fluid .
• The homogenous mixture of resin and catalyst then exits fromtip22 and fills the space between therock bolt20 and theadjacent strata80. The resin quickly sets and hardens, bonding therock bolt20 to thestrata80.
• Thenut25 is then rotated clockwise so that it moves axially along thefine thread24 of the trailingend23 of therock bolt20. This movement separates thenut25 fromcollar27 and pushesnut25 firmly into abutment against the opening of the bore hole.
• By further rotating thenut25 in a clockwise direction, thenut25 starts to place therock bolt20 into tension. Since therock bolt20 is now bonded to thestrata80, a local region of the strata is compressively loaded. This loading secures the roof of the mine and reduces the risk of a roof collapse in that area.
• Thechuck31 is then released from therock bolt20 anddrill30 is removed from the site of the boring and securing operation. Thedrill30 and chuck31 are then reloaded with afurther bolt20 and the process is repeated as required.
• Although the invention has been described with reference to a specific example, it will be appreciated by those skilled in the art that many variations and modifications are possible. For instance, the rock bolt may be secured to the drill in many different ways, such as by using a threaded connection, a frictional interference such as an expanding collet chuck, or another suitable engagement.
• Also, instead of a static mixer, many other mechanisms could be employed which promotes non-laminar flow of fluid s passing therethrough, and hence mixing to create a homogeneous fluid .

Claims (17)

1. A drilling apparatus for rock bolting with a self-drilling rock bolt, comprising within it a fluid injector having an upper part that mates with a self-drilling rock bolt inserted into the drilling apparatus for boring a hole; wherein the injector includes three fluid inlets, three fluid outlets in the upper part, and three fluid conduits extending from respective inlets to respective outlets.

2. A drilling apparatus according toclaim 1 wherein, in use, water, resin and catalyst are pumped through respective conduits at selected times, and enter a channel in the rock bolt.

3. A drilling apparatus according toclaim 1, further comprising a pump to pump water to a first fluid inlet, and pumps to pump resin and catalyst to second and third fluid inlets.

4. A drilling apparatus according toclaim 3, wherein the pumps operate to provide different resin and catalyst flow rates.

5. A drilling apparatus according toclaim 3, wherein the pumps provide precise differential control, to allow different resin catalyst mix ratios for different bolting conditions.

6. A drilling apparatus according toclaim 1, wherein the upper part of the injector is insertable within a fixed collar of the trailing end of the rock bolt to make a fluid tight mating between them.

7. A self drilling rock bolt, comprising an elongate body having a leading end with a cutting tip, and around the tip a thread with a coarse pitch; the bolt also has a trailing end with an integral collar for fluid connection to a channel that extends axially through the body of the rock bolt to the leading end, and above the collar a thread with a fine pitch.

8. A self drilling rock bolt according toclaim 7, wherein, in use, a nut is threaded onto the fine pitch and engaged with a drill which operates to drive the nut along the fine pitch thread to abut against the collar during boring.

9. A self drilling rock bolt according toclaim 8, wherein after boring, reversal of the drill drives the nut away from the collar.

10. A self drilling rock bolt according toclaim 7, wherein the trailing end of the rock bolt incorporates a collar that, when installed in the chuck makes a fluid tight connection to an upper part of an injector within the drill.

11. A self drilling rock bolt according toclaim 7, wherein the channel within the rock bolt opens in the cutting tip of the bolt.

12. A self drilling rock bolt according toclaim 7, wherein the channel within the rock bolt incorporates a fluid mixer within it.

13. A self drilling rock bolt according toclaim 12, wherein the fluid mixer comprises a flow restriction.

14. A rock bolting system comprising:

a drilling apparatus for rock bolting with a self-drilling rock bolt, comprising within it a fluid injector having an upper part that mates with a self-drilling rock bolt inserted into the drilling apparatus for boring a hole; wherein the injector includes three fluid inlets, three fluid outlets in the upper part, and three fluid conduits extending from respective inlets to respective outlets. a combination of the drilling apparatus and a rock bolt; and,

a self drilling rock bolt, comprising an elongate body having a leading end with a cutting tip, and around the tip a thread with a coarse pitch; the bolt also has a trailing end with an integral collar for fluid connection to a channel that extends axially through the body of the rock bolt to the leading end, and above the collar a thread with a fine pitch.

15. A method of using the system for rock bolting according toclaim 14, comprising the steps of:

attaching a rock bolt to the drilling apparatus for drilling, such that the nut on the rock bolt is secured in the drilling apparatus against rotation, and the upper part of the injector mates with the fluid connection of the rock bolt in a fluid tight manner;

then operating the drilling apparatus to bore a hole such that rotation of the rock bolt drives the nut against the collar;

and simultaneously pumping water through a first fluid inlet of the injector, through the respective conduit and out, and into the channel in the rock bolt to exit the leading end of the bolt.

16. A method according toclaim 15 wherein, when the hole has been completely bored, operation of the drilling apparatus and pumping of the water are ceased before pumping resin and catalyst through respective second and third fluid inlets of the injector, through the respective second and third conduits, out of respective second and third fluid outlets and into the channel in the rock bolt, where they are mixed before exiting the leading end of the bolt.

17. A method according toclaim 15, comprising a further step of operating the drilling apparatus in the opposite direction to the direction used to bore the hole, to push the nut into abutment with the opening of the bore hole and to compressively load a local region of strata.

Images