Patent Publication Number: US-2011070035-A1

Title: Self drilling rock bolting

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 rock bolt installation system  10  for securing a rock bolt  20  to a strata, such as a coal strata. The system  10  includes hydraulically operated drilling apparatus  30 . 
     The drilling apparatus  30  is selectively operable in both clockwise and anticlockwise rotational directions. 
     The rock bolt  20  has a leading end  21  with a cutting tip  22  and a trailing end  23 . The leading end  21  is threaded and has a coarse pitch. Part of the trailing end  23  is also threaded but has a fine pitch  24 . The trailing end  23  of the rock bolt  20  also includes a fixed collar  27 . A nut  25  is threadingly engageable with the fine pitch  24  of the rock bolt above the collar  27 . The nut  25  which has a polygonal profile that mates with the chuck  31  of drill  30 . 
     When the nut  25  is rotated toward the trailing end  23 , it comes into abutment with the collar  27 , as shown in  FIG. 1 . This abutment prevents the nut  25  from moving further toward the trailing end  23 . 
     The rock bolt  20  has an internal central fluid flow channel  40  formed therein which extends between openings in the leading end  21  and within collar  27  at the trailing end  23 . A static mixer is located within the flow channel. The mixer is in the form of a flow restriction  41 . 
     The drilling apparatus  30  includes within it an injector  50 . The injector  50  has water inlet  51  to receive water from a water pumping system  61  or water source. Injector  50  also has a resin inlet  52  to receive resin from a resin pumping system  62 . And, a catalyst inlet  53  to receive catalyst from a catalyst pumping system  63 . The resin pumping system  62  and catalyst pumping system  63  use pumps which are resistant to the aggressive chemical nature of the resin. These pumping systems  62  and  63  permit different resin and catalyst flow rates to be provided, with precise differential control, to allow different resin catalyst mixes for different bolting conditions. 
     The upper end  57  of the injector  50  is insertable within the fixed collar  27  of the rock bolt  20 . The connection between the projection  57  and the collar  27 , when the projection is inserted into the skirt, is fluid tight. 
     The operation of the system  10  will now be described with reference to  FIG. 2 . Within drill  30  a water flow conduit  71  carries water between inlet  51  and the upper end  57  of injector  50 . Likewise flow conduits  72  and  73  extend from the resin  52  and catalyst  53  inlets to carry resin and catalyst to the upper end of injector  50 . 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 a rock bolt  20  is to be installed into a strata, such as a mine roof, the trailing end  23  of the rock bolt  20  is inserted into the chuck  31  of the drill motor  30 , such that the nut  25  is seated within the chuck and secured thereto. In this position the upper end  57  of the injector  50  is inserted within the collar  27  of the rock bolt  20 . 
     The cutting tip  22  of the rock bolt  20  is then placed against the coal strata  80  and the drill motor  30  is rotated in an anticlockwise direction. The nut  25  abuts against the collar  27  preventing the rock bolt  20  from longitudinal movement relative to the chuck. By simultaneously applying anticlockwise rotation and thrust against the coal strata, the cutting tip  22  of the rock bolt  20  starts to bore a hole within the strata. 
     During the boring operation, the water pumping system  61  or source delivers water into the conduit  71  of the injector  50 . The water passes axially through the injector  50  and out of its upper end  51  before entering into the trailing end  23  of the rock bolt  20 . The water passes through channel  40  in the rock bolt  20  and exits from the tip  22  where it assists in dispersing drill cuttings away from the cutting tip  22  of the rock bolt  20 , and out of the bore hole. The coarse thread  21  adjacent to the tip  22  of the rock bolt  20  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 of chuck  31  is ceased. The resin and catalyst pumping systems  62  and  63  are then used to deliver the resin through conduit  72  and a catalyst through separate conduit  73 . The resin and catalyst pass through injector  50  and enter into the trailing end  23  of the rock bolt  20 . While passing through channel  40  the resin and catalyst are no longer separated from each other, and the static mixer  41  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 from tip  22  and fills the space between the rock bolt  20  and the adjacent strata  80 . The resin quickly sets and hardens, bonding the rock bolt  20  to the strata  80 . 
     The nut  25  is then rotated clockwise so that it moves axially along the fine thread  24  of the trailing end  23  of the rock bolt  20 . This movement separates the nut  25  from collar  27  and pushes nut  25  firmly into abutment against the opening of the bore hole. 
     By further rotating the nut  25  in a clockwise direction, the nut  25  starts to place the rock bolt  20  into tension. Since the rock bolt  20  is now bonded to the strata  80 , 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. 
     The chuck  31  is then released from the rock bolt  20  and drill  30  is removed from the site of the boring and securing operation. The drill  30  and chuck  31  are then reloaded with a further bolt  20  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 .