Abstract:
The present invention relates to rock bolts which may be used in mining applications. The rock bolt of this invention includes a mechanical anchoring arrangement to facilitate retaining the rock bolt in a borehole, and also a drill bit to enable self drilling of the rock bolt. Rotation of the rock bolt about an axis of the rock bolt in a first direction causes the drill bit to drill into rock and to create a borehole to receive the rock bolt. Subsequently, rotation in the opposite direction actuates a mechanical anchoring arrangement to anchor rock bolt.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a rock bolt and particularly, but not exclusively, to rock bolts which may be used in mining applications. 
     BACKGROUND OF THE INVENTION 
     Rock bolts for supporting structures e.g. roofs of passageways in mines are well known. There are many different types of rock bolts. A rock bolt generally consists of an elongate shank (length will generally depend upon the material which the rock bolt is intended to secure) having a distal end (the end which in use is fixed furthest within the rock), or “head end”, and a proximal end (the end, in use, which is closest to the surface of a rock and, in many cases, may actually project from the rock surface), or “tail end”. 
     Rock bolts are fixed in elongate boreholes (not much wider or even slightly less in width than the rock bolt) which is drilled in the rock. In use, a bearing plate is secured at the tail end of a rock bolt fast against the rock surface. The rock bolt and bearing plate assembly operate to support the rock. Many rock bolts may be used to support structures. For example, in mines rock bolts may be used to support passageways. 
     Installation usually requires drilling of the borehole by using a drill rig and a drill steel (a long steel rod with a drill bit on the end). The drill steel is then removed from the borehole. Resin (or “grout”) is inserted into the borehole, then the rock bolt itself is inserted and tightened up against the bearing plate. 
     Some rock bolts incorporate point anchoring mechanisms, which can be manipulated post insertion of the rock bolt to mechanically interfere with walls of the borehole in order to firmly secure the rock bolt. 
     The conventional procedure for installing rock bolts can be relatively time consuming in the context of efficient mine operation. It requires a number of separate tasks (affixing the drill steel, drilling the borehole, removing the drill steel, inserting the resin and rock bolt, securing the rock bolt) which require time and a significant amount of labor. In a mining situation, where it is important that mining shafts, passageways, etc be created quickly (as this directly affects the economic operation of the mine), this is a disadvantage. Further, the drill steel and drill bit are consumables which add to the cost of installing rock bolts. 
     “Self drilling” rock bolts are known. These generally incorporate a drill bit as part of or connected to the head end of the rock bolt, the tail end being attachable to a drill rig in order to drill the borehole. Once the hole is drilled, the rock bolt is retained in the hole. Whilst self drilling rock bolts have the advantage of speed of application, grouting can be difficult and there are no provisions for any point anchoring mechanism to firmly secure the rock bolt. 
     SUMMARY OF THE INVENTION 
     In accordance with a first aspect, the present invention provides a rock bolt, the rock bolt including a mechanical anchoring arrangement and a drill bit to enable self drilling. 
     An advantage of at least an embodiment of the invention is that a self drilling rock bolt is provided which can also be mechanically point anchored. 
     In an embodiment, the mechanical anchoring arrangement and drill bit are arranged such that rotation of the rock bolt about an axis of the rock bolt in a first direction causes the drill bit to drill into rock (or other substrate) and create a borehole to receive the rock bolt. Subsequently, rotation in the opposite direction actuates the mechanical anchoring arrangement to point anchor the rock bolt. 
     In an embodiment, a tail end of the rock bolt is formed with an end fitting which is moveable axially with respect to the rock bolt after the rock bolt has been secured in the borehole, in order to allow for further take up. This may be useful in heavily fractured rock which can be compressed, for example. In an embodiment, the end fitting provides an engagement surface for a drill rig and is not axially moveable with respect to the rock bolt during drilling. In this embodiment, the end fitting may include a break out mechanism which breaks when the rock bolt is secured in the borehole, subsequently enabling axial movement. The end fitting may be a threaded nut mounted on a co-operating threaded tail end of the rock bolt. In an embodiment, instead of a break out mechanism, a fixed stop or thread deformation may prevent rotation of a nut when the borehole is being drilled. 
     In an embodiment, the mechanical anchoring arrangement includes an expansion assembly including an expansion shell and a co-operating chuck. In operation, the chuck and expansion shell are arranged to move relative to each other, co-operating surfaces sliding over each other and resulting in expansion of the expansion shell so that walls of the expansion shell abut against walls of the borehole and secure the rock bolt mechanically. In an embodiment, the expansion shell is arranged to rotate with the rock bolt during the drilling operation. In an embodiment, outer walls of the expansion shell include protrusions to aid mechanical interference with the borehole walls. In an embodiment, the protrusions are arranged in spiral formation to facilitate fluid and leavings flow during drilling. 
     In an embodiment, the mechanical anchoring arrangement is provided at one end (the head end) of the rock bolt. In some prior art, a mechanical anchoring arrangement includes a sleeve extending nearly the entire end of the rock bolt. This is not the case of this embodiment of the present invention, which only requires the head end of the rock bolt to mount a mechanical anchoring arrangement. In an embodiment where the mechanical anchoring arrangement includes an expansion shell, the expansion shell is mounted at the head end of the rock bolt. 
     In an embodiment, the drill bit is mounted to an end of the rock bolt and operates as a stop to prevent the chuck and expansion shell from moving off the rock bolt end. In an embodiment, the stop may comprise a surface which facilitates non seizure of the chuck. A co-operating surface (with the stop) of the chuck may also be arranged to facilitate non-seizure. 
     In an alternative embodiment, the drill bit is mounted by the chuck of the mechanical anchoring arrangement. The chuck in this embodiment includes a recess within which is seated the end of the rock bolt, for relative axial motion with respect to the chuck. A stop on the end of the rock bolt prevents the chuck from moving off the rock bolt during drilling. 
     In an embodiment, an axially extending central passageway is provided through the rock bolt to enable introduction of a cementatious material to the borehole, for grouting. 
     In accordance with a second aspect, the present invention provides a method of installing a rock bolt in accordance with a first aspect of the invention, including the steps of: 
     rotating the rock bolt in a first direction to drill a borehole in a substrate in a self drilling operation; and 
     rotating the rock bolt in a second, opposite direction, in order to secure the mechanical anchoring arrangement in the borehole. 
     In an embodiment, the method includes the further step of post grouting by injecting cementatious material into the borehole. In an embodiment, where the rock bolt has an axial passageway extending within it, the cementatious material may be injected by way of the axial passageway. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the present invention will become apparent from the following description of embodiments thereof, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  is a view from one side of a rock bolt in accordance with a first embodiment of the present invention; 
         FIG. 2  is a detail of a head end of the rock bolt of  FIG. 1 ; 
         FIG. 3  is a detail of a tail end of the rock bolt of  FIG. 1 ; 
         FIG. 4  is a side view of a rock bolt in accordance with a second embodiment of the present invention; 
         FIG. 5  is a detail of a head end of the rock bolt of  FIG. 4 ; 
         FIG. 6  is an exploded view from the side of a rock bolt in accordance with the embodiment of  FIGS. 1 to 3 ; 
         FIG. 7  is an exploded view from the side of the head end of the rock bolt of the embodiment of  FIGS. 4 and 5 ; 
         FIG. 8A  and  FIG. 8B  are details of an alternative embodiment of a tail end arrangement for the rock bolt in accordance with an embodiment of the present invention, and 
         FIG. 9  is a detail of a head end for a rock bolt in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     A first embodiment of the present invention will now be described with reference to  FIGS. 1 to 3 . 
     A rock bolt, generally designated by reference numeral  1  includes a distal, head end  2 , and a proximal, tail end  3 . A shank  4  extends between the head end  2  and tail end  3 . The head end  2  includes a mechanical anchoring arrangement  5  which, in this example embodiment, includes a co-operating chuck  6  and expansion shell  7 . The head end  2  is also provided with a drill bit  8  to enable self drilling. In this example embodiment, the drill bit  8  is mounted at the distal end of the rock bolt  1 . 
     The mechanical anchoring arrangement  5  will now be described in more detail. Towards the head end  2 , a shank  4  of rock bolt  1  is threaded with screw threads  9 . The threaded portion  9  extends up to the drill bit  8 . The drill bit  8  comprises a drilling tip  10  at the distal end of the rock bolt and a base forming a stop  11  where the threaded portion  9  meets the drill bit  8 . 
     The mechanical anchoring arrangement  5  includes an expansion shell  7  and chuck  6 . The expansion shell  7  in this example, has longitudinally extending leaves  12 ,  13  (note only two are shown in the drawings but there are three leaves). Note that the number of leaves on the expansion shell  7  could vary. For example, the leaves could vary from two to four. The leaves  12 ,  13  are arranged to move outwardly on expansion of the expansion shell  7  and are formed with a plurality of external protrusions  14  which assist in gripping the sides of the borehole to secure the rock bolt  1  in place. The expansion shell  7  also includes a bore  15  for sliding engagement with the threaded portion  9 . An abutment member in the form of a threaded nut  16  is mounted on the threaded portion  9  and operates to prevent the expansion shell  7  from sliding further towards the tail end  3 . 
     The chuck  6  has a threaded bore (not shown) for threaded engagement with the threaded portion  9 . Rotation of the rock bolt  1  relative to the chuck  6  thus causes axial motion of the chuck  6  along the threaded portion  9 . The chuck  6  includes tapered surfaces in sliding keying engagement with complementary surfaces on the extension leaves  12 ,  13 , such that axial motion of the chuck  6  towards the tail end  3  relative to the expansion shell  7  will cause the leaves  12 ,  13  to diverge outwardly and grip the walls of the borehole. The chuck also includes projections  17  which extend into slots  18  formed between the leaves  12 ,  13  and prevent relative rotation of the chuck  6  and expansion shell  7  with respect to each other. 
     Stop  11  formed by the base of the drill bit  8  prevents chuck  6  and expansion shell  7  from moving over the head end of the rock bolt  1 . 
     The protrusions  14  are in a spiral formation, to assist with the flow of fluid during drilling, and aid in clearance of filings/cuttings. The spiral runs in the opposite direction to the thread form i.e. right hand spiral for left hand thread. 
     The tail end  3  of the bolt  1  will now be described in more detail with reference in particular to  FIGS. 1 and 3  The tail end includes a further threaded portion  19  which, in this embodiment, is threaded in the same direction (left hand) as the threaded portion  9 . A ball washer  20 , washer  21  and threaded nut  22  are mounted on the further threaded portion  19 . In use, the ball washer abuts a mounting plate (not shown), which, when the rock bolt is installed, is hard up against the rock face. 
     The nut includes a torque break out mechanism  23 . The nut  22  is therefore initially fixed relative to the threaded portion  19  and can be gripped by the spanner of a drill rig for rotation of the rock bolt for installation. Subsequently, when the mechanic anchoring arrangement is anchored, the torque break out mechanism  23  may be broken to allow the nut  22  to rotate relative to the threaded portion  19  to enable additional thread take up, for example, in heavily fractured rock which can therefore be compressed and partings closed. 
     Installation of a rock bolt  1  in accordance with the embodiment of  FIGS. 1 to 3  will now be described. 
     A drill rig and spanner is attached to the rock bolt by way of the tensionable nut  22 . Drilling into the rock substrate is implemented by rotating the rock bolt in the clockwise direction (in this embodiment. It will be appreciated that a reverse threaded arrangement may be rotated in the anticlockwise direction). As drilling proceeds, the expansion shell  7  may resist rotation as it abuts the walls of the borehole, and this will result in relative anticlockwise rotation of the expansion shell  7  and chuck  6  relative to the rock bolt  1 . This will cause the chuck  6  to travel along the threaded portion  9  towards the head end of the rock bolt where it will abut the flat  11 . Once flat  11  is engaged by the chuck  6  then the expansion shell  7  and chuck  6  will continue to rotate in the drilling direction with the rock bolt  1 . 
     Once the rock bolt  1  has created a borehole of the desired length, drilling in the forward direction is ceased and rotation in the reverse direction (anticlockwise in this embodiment) is applied by the drill rig. By virtue of the anticlockwise motion of the threaded portion  9 , the chuck  6  will now move towards the tail end  3 . As the chuck  6  moves along the threaded portion  9 , the tapered surfaces in sliding keying engagement with the complementary surfaces on the extension leaves  12 ,  13 , cause the expansion shell  7  to expand outwardly. The protrusions  14  on the external surfaces of the leaves  12 ,  13  engage the walls of the borehole and mechanically secure the rock bolt  1  in place. 
     Once the expansion shell tightens in the borehole, continued rotation in the anticlockwise direction causes the break out mechanism  23  to break and the nut  22  to rotate relative to the further threaded portion  19 , in order to tighten up against the washer  21 , ball washer  20  and mounting plate (not shown). This is particularly useful where additional thread take up is required in heavily fractured rock which can be compressed and partings closed. The threaded end  24  of the rock bolt  1  remaining provides a protruding section which may be used to allow secure attachment of grout hose for post grouting applications. 
     A grout hose for injecting cementateous material may then be placed over the threaded end  24  so that cementateous material can be injected via the passageway  25  extending axially in the rock bolt  1 . Holes (not shown) in the chuck  6  allow the cementateous material to flow into the borehole and down to the plate. 
     Alternatively, grout can be pumped up between the section between the borehole and the outer circumference of the rock bolt. The hollow centre of the bolt is used as a breather tube to allow air to escape as grout fills the voids. 
     A further embodiment of the present invention will now be described with reference to  FIGS. 4 and 5 . The rock bolt  100  includes some features which are the same as the rock bolt of  FIGS. 1 to 3 . These features have been allocated the same reference numerals and no further description will be given. The main differences between the embodiment of  FIGS. 4 and 5  and embodiment of  FIGS. 1 to 3 , is in the head end  2  and tail end  3  of the rock bolt  100 . 
     Referring firstly to the head end  2  of the rock bolt  100 , although the expansion shell  7  is of the same configuration as the expansion shell  7  of the  FIGS. 1 to 3  embodiment, the chuck  101  is of a different configuration. In this embodiment, the chuck  101  directly mounts the drill tip  102  on the periphery of a extension portion  103  of the chuck  101 . The extension portion  103  surrounds a centre hole  104  extending within the chuck  101 . The chuck  101  includes tapered surfaces in sliding key engagement with complementary surfaces of the extension leaves  12 ,  13 , and also includes projections  17  which extend into slots  18  formed between the leaves  12 ,  13  and prevent relevant rotation of the chuck  101  and expansion shell  7  with respect to each other. 
     In this embodiment however, threaded portion  9  does not end in a stop supporting a drill bit. Instead, a fixed stop  105  is mounted at the end  106  of the threaded portion  9  extending within the centre hole  104 . During drilling operation, this prevents the chuck  101  from moving off the end of the threaded portion  9 . A shoulder  107  formed at the base of the centre hole  104  abuts the fixed stop  105  to prevent movement of the chuck  101  past the stop. 
     The tail end  3  of the rock bolt  100  is formed without any threaded portion. Instead, the tail end  3  includes a drive end in the form of a forged end portion  108  for engagement by the drill rig for drilling. Washer  21  and Ball washer  20  are slideably mounted on the shank  4  of the rock bolt  100 . A hole (not shown) to suit a water spickett is also provided in the forged end  108 . 
     In operation of this embodiment, drill rig engages the forged end  108  and rotates the rock bolt  100  in the drilling direction (in this case clockwise). The drill tip  102  is larger than the expansion shell diameter and operates directionally opposite to what is required to expand the shell. 
     On commencement of rotation in the clockwise direction, the chuck  101  will rotate relative to the threaded end  9  and will move along the threaded end  9  until the shoulder  107  meets the fixed stop  105 . The drill bit  102  will then rotate with the drill rig, resulting in drilling of a borehole for the rock bolt  100 . 
     On completion of the borehole, drill rotation is then applied in an anticlockwise direction. This causes the chuck  101  to move along the threaded end  9  away from the fixed stop  105  and causes expansion of the expansion shell  7  until the protrusions  14  grip the sides of the borehole and the rock bolt  100  is fixed in place. 
     The centre hole  104  in the chuck  101  allows the bolt end  106  to move into the void during tightening, and provides over drill. This allows tightening of end  108  compressing the rock, closing partings in the ground, etc. This allows tightening of the bolt without any tails left hanging from the wall. This is an important feature for bolting in the ribs/wall where personnel can walk and machines often hit and damage bolt tails. 
     As with the embodiments of  FIGS. 1 to 3 , post grouting can be implemented utilising the axial passageway  25 . 
     As an alternative to break out arrangement or forged end of the rock bolt, an arrangement such as that shown in  FIG. 8A and 8B  may be utilised at the tail end of the rocks in accordance with the embodiments described above. A threaded nut  200  is mounted at the tail end of the rock bolt. On rotation in a drilling direction, the nut  200  rotates towards the proximal end of the rock bolt where a press deformation  201  prevents travel passed the deformation  201 . On completion of drilling of the borehole, and on reverse rotation of the rock bolt, the nut disengages from the deformation end and operates as discussed in relation to the embodiment of  FIG. 1 . 
     Instead of a crimp deformation, a welded ring may provide a stop to prevent the nut  200  from moving off the rock bolt during drilling. The nut  200  is a reversing nut. 
     Other arrangements for preventing motion of the nut during drilling and allowing motion after drilling may be employed. 
     In the preceding embodiments, the surfaces of the stop  11  and  105  are planar, as are corresponding abutting surfaces of the chucks in those embodiments. In some circumstances, this could potentially lead to seizure, as drilling forces may cause seizing of the chuck against the stop which would prevent opening of the expansion shell during reverse rotation, or make it more difficult. Referring to  FIG. 9 , in a further embodiment, in arrangement where the abutting chuck surface  210  and stop surface  211  do not make planar contact, but instead contact only particular areas (e.g.  212 ) may be utilised in order to facilitate non seizure. Other arrangements of surfaces may be utilised to facilitate non seizure and this embodiment is not limited to the arrangement shown in  FIG. 9 . 
     In the above embodiments, the projections which interfere with the walls of the boreholes ( 14 ) are arranged in spiral formation. Although this is advantageous, the present invention is not limited to spiral formation projections. The projections may be non-spiral. The projections may be in any form which engages with the walls of the borehole. 
     It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.