Abstract:
Disclosed is a cable anchor assembly including: a cable anchor body longitudinally extending between leading and trailing ends; a tensioning device with an outer member having first and second ends and a threaded through passage between the ends and an inner member which threadedly engages the threaded passage of the outer member and fixedly attached to the cable anchor body at or towards the trailing end; a faceplate engaging the cable anchor body between the leading end and the tensioning device. In use, with the cable anchor body inserted in a borehole and anchored therein, the faceplate positioned against a rock face and the first end of the outer member abutting the faceplate, the outer member is rotatable relative to the inner member, causing the inner member to move within the passage towards the second end of the outer member, drawing on the cable anchor body, tensioning the body.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a tensionable cable anchor assembly and to a tensioning device for same. The tensionable cable anchor is suitable for use in mining and tunnelling to provide rock and wall support. 
       BACKGROUND OF THE INVENTION 
       [0002]    A cable anchor is installed in a rock hole, by anchoring a distal end of the anchor within the hole. Then, to an end section protruding from the rock hole, a barrel and wedge assembly is attached or pre-attached. The cable anchor is then typically tensionably applying a tensioning force to this end section, to place the anchor body in pre-tension. Thereafter, the barrel is wedged against a faceplate to hold the body in pre-tension. 
         [0003]    The distal end of the cable anchor can be mechanically anchored within the rock hole. Alternatively, the distal end can be anchored with a grout or resin. 
         [0004]    The anchor process includes first inserting an adhesive containing capsule into the rock hole, followed by the cable anchor. Then, the cable is spun about its longitudinal axis, by engaging a suitably adapted drive means to a protruding or proximal end of the cable anchor. Once the capsule is torn to release its adhesive content, the drive means is removed and a tensioner attached. The tensioner tensions the cable anchor, now fixed in the rock hole by the hardened adhesive, and held in tension by the pre-attached barrel and wedge system. The tensioner is then detached and most of the end section of the anchor, which protrudes past the barrel and wedge, is cropped to prevent it from being safely taken off. 
         [0005]    The process described above is disadvantageous in that a number of devices are used which have to be attached and removed from the cable anchor. 
         [0006]    The disadvantage with this process is that, not only is the tensioning and cropping equipment is heavy and therefore difficult and cumbersome to elevate to the hanging wall of an excavation, where typically cable anchors are installed in a mining environment. 
         [0007]    Also, it is difficult to have control over the length of cable anchor body that is cropped. The length of protruding cable is an important indication of proper cable installation. 
         [0008]    To ensure that an installed cable anchor provides sufficient support to the rock mass within which it is installed, a predetermined length of the cable anchor must be inserted into the rock hole to extend, in tension, the length of the hole. If the hole is insufficiently deep, a cable anchor installed in this hole will have a longer protruding end section. 
         [0009]    However, should a mine worker wish to cover up the fact that the rock hole is of insufficient depth, and the installed cable anchor of inadequate support, he merely has to crop the protruding end section after tensioning. 
         [0010]    The invention at least partially solves the aforementioned problems. 
       SUMMARY OF INVENTION 
       [0011]    In a first aspect, the invention provides a cable anchor assembly which includes: 
         [0012]    a cable anchor body which longitudinally extends between a leading end and a trailing end; 
         [0013]    a tensioning device which includes an outer member having a first end and a second end and a threaded passage which extends through the member between the ends and an inner member which threadedly engages with the threaded passage of the outer member and which is fixedly attached to the cable anchor body at or towards the trailing end; 
         [0014]    a faceplate engaged with the cable anchor body between the leading end and the tensioning device; 
         [0015]    wherein, in use, with the cable anchor body inserted in a borehole and anchored therein, the faceplate positioned against a rock face and the first end of the outer member abutting the faceplate, the outer member is rotatable relatively to the inner member to cause the inner member to move within the passage towards the second end of the outer member, drawing on the cable anchor body to place the body in tension. 
         [0016]    The cable anchor body may be mechanically or adhesively anchored with the borehole. 
         [0017]    To mechanically anchor the cable anchor body within the borehole, the cable anchor assembly may include a mechanical anchor engaged with the anchor body at or towards its leading end. 
         [0018]    The outer member may have a barrel-like body. 
         [0019]    The outer member may be domed at the first end to provide a spherical seat to the faceplate. 
         [0020]    The outer member may be adapted to engage with a rotatable part of a torquing apparatus, such as, for example, a rotatable socket of a torque gun. 
         [0021]    The inner member may have a cylindrical body which extends between a distal end and a proximal end. 
         [0022]    The inner member may have a tapered bore which tapers towards the distal end and which is sized to receive the cable bolt. 
         [0023]    The tensioning device may include a wedge element which is adapted for insertion in the bore of the inner member between the cable anchor body and a wall of the bore to wedge the cable anchor within the bore. 
         [0024]    The inner member may be adapted to engage with a stationary part of the torquing apparatus, such as, for example, a stationary shaft of a torque gun. 
         [0025]    The invention provides, in another aspect, a tensioning device for a cable anchor which includes an outer member having a first end, a second end and a threaded passage which extends through the member from the first end to the second end, and an inner member which is sized to fit within, and which threadedly engages with, the threaded passage of the outer member and which is adapted to fixedly attach to the anchor. 
         [0026]    The outer member may have a barrel-like body. 
         [0027]    The outer member may be domed at the first end to provide an abutment surface to an abutting faceplate. 
         [0028]    At the second end, the outer member may be adapted to engage with a rotatable drive part of a torquing apparatus such as a torque gun. 
         [0029]    The inner member may have a cylindrical body which extends between a distal end and a proximal end. 
         [0030]    The inner member may have a tapered bore which tapers towards the distal end and which is sized to receive the cable anchor body. 
         [0031]    The tensioning device may include a wedge element which is adapted to be received in the bore of the inner member. 
         [0032]    In use of the tensioning device, when the cable anchor is received through the bore and the inner member is caused to move relatively to the outer member within the threaded passage towards the second end, the tapered bore is urged against the wedge element to wedge the cable anchor within the bore. 
         [0033]    At the proximal end, the inner member may be adapted to engage with a stationary shaft of the torquing apparatus. 
         [0034]    The tensioning device may include a locking means to lock the inner member to the outer member to ensure that the inner member and outer member rotate in unison. The locking means may be, for example, a shear pin or the like. When the shear pin breaks, the inner member or outer member can rotate independently of one another. 
         [0035]    The invention extends to a method of tensioning a cable anchor within a rock hole, which cable anchor includes a cable anchor body which longitudinally extends between a leading end and a trailing end, a tensioning device which includes an outer member having a first end and a second end and a threaded passage which extends through the member between the ends and an inner member which threadedly engages with the threaded passage of the outer member and which is fixedly attached to the cable anchor body at or towards the trailing end, wherein the cable anchor is inserted into a rock hole and anchored within the hole, characterised in that the outer member is rotated relatively to the inner member, whilst retained in a constant position relatively to the rock hole, to cause the inner member to move within the threaded passage away from the rock hole thereby to place the bolt in tension. 
         [0036]    The invention further provides a method of anchoring a cable anchor within a rock hole, which cable anchor includes a cable anchor body which longitudinally extends between a leading end and a trailing end, a tensioning device which includes an outer member having a first end and a second end and a threaded passage which extends through the member between the ends and an inner member which threadedly engages with the threaded passage of the outer member and which is fixedly attached to the cable anchor body at or towards the trailing end, the method including the steps of: 
         [0000]    a) inserting the cable anchor into a predrilled rock hole, behind a capsule containing an adhesive material;
 
b) spinning the anchor, by actuating the inner member and the outer member of the tensioning assembly to rotate in unison, to break the capsule to release and mix the adhesive material and, once the adhesive material has hardened;
 
c) tensioning the anchor, by actuating the outer member to rotate relatively to the inner member to cause the inner member to move longitudinally relatively to the outer member.
 
         [0037]    Preferably, the inner member is engaged with the cable anchor body at the trailing end. 
         [0038]    The inner member and the outer member may be caused to rotate in unison by preventing the inner member from moving relatively to the outer member. 
         [0039]    Preventing movement of the inner member relatively to the outer member may be achieved by locking the inner member to the outer member. 
         [0040]    The inner member and the outer member may be locked together by a locking means. The locking means may be, for example, a shear pin. When the shear pin breaks, the inner member or the outer member can rotate independently of the other member. 
         [0041]    In step (b), the inner and outer members may rotate, in unison, in a first rotational direction. 
         [0042]    In step (c), the outer member may rotate relatively to the inner member in the first rotational direction or in an opposed second rotational direction. 
         [0043]    With the tensioning assembly being of the kind described above, the outer member may be rotated, independently, in the second rotational direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0044]    The invention is described with reference to the following drawings in which: 
           [0045]      FIG. 1  is a view in elevation of a tensioning device in a cable anchor assembly in accordance with a first embodiment of the invention; 
           [0046]      FIG. 2  illustrates, in longitudinal section, an inner component of the tensioning device of  FIG. 1 ; 
           [0047]      FIG. 3  illustrates, in perspective, the tensioning device and cable bolt of  FIG. 1 ; 
           [0048]      FIG. 4  is an exploded view of the components of the tensioning device of  FIG. 1 ; 
           [0049]      FIG. 5  illustrates, in perspective, a partially sectioned tensioning device in use engaged with actuating components of a torque gun; 
           [0050]      FIGS. 6A and 6B  illustrate, in longitudinal section, the tensioning device of  FIG. 1  engaged with the cable bolt which is inserted into a rock hole, before activation and in an activated tensioning state respectively; 
           [0051]      FIG. 7  is a view in perspective of a cable anchor and tensioning device assembly for use in a method of the invention: 
           [0052]      FIGS. 8A and 8B  diagrammatically illustrate the cable anchor assembly of  FIG. 7 , inserted in a rock hole in a pre-tensioned state; 
           [0053]      FIG. 9  diagrammatically illustrates the cable anchor of  FIG. 7  in a tensioned state; and 
           [0054]      FIGS. 10A and 10B  diagrammatically illustrate a cable anchor assembly in accordance with a second embodiment of the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0055]    With reference to  FIGS. 1 to 6 , a tensioning device  10  in a cable anchor assembly according to a first embodiment of the invention, is described for use with a cable bolt  11  for supporting walls of a mining excavation or the like. The device  10  is configured for use with the cable bolt  11 , which bolt typically comprises a plurality of helically wound high tensile steel wire strands providing a flexible cable bolt body. 
         [0056]    With particular reference to  FIG. 4 , the tensioning device  10  includes an outer barrel-like nut  12 , an inner barrel  14  and a washer  16 . The nut  12  has a first end  18  and an opposed second end  20  and a threaded passage  22  which extends between the ends. 
         [0057]    The inner barrel  14  is cylindrically shaped and complementary sized to locate within the passage  22  in use. The outer surface  24  of the barrel  14  is threaded to engage with the complementary threads of the passage  22 . The barrel  14  has a leading end  26  and an opposed trailing end  28 . Between these ends, a bore  30  extends which, as illustrated in  FIG. 2 , tapers towards the leading end. 
         [0058]    The tensioning device  10  also includes a truncated conical wedge element  32  which tapers in a corresponding manner to the taper of the inner barrel bore  30 . Thus, in use, the wedge element  32  fits within the bore about the cable bolt  28  as illustrated in  FIG. 2 . 
         [0059]    The washer  16  provides a leading end spherical seat  34  which is presented to, and abuts, a faceplate  36  when in use. The washer  16  further prevents the tensioning device  10  from pulling through a hole in an associated faceplate when in use. Opposed to the spherical seat  34 , the washer  16  is concave, providing a recess  35  for receipt of the first end  18  of the outer nut  12 . For ease of explanation, the washer  16  is not illustrated in subsequent Figures nor described hereafter. 
         [0060]    In tensioning a cable bolt  11  within a predrilled rock hole  38 , as illustrated in  FIGS. 6A and 6B , the cable bolt  11  must be fixed within the rock hole  38  by any suitable means which is not shown in these figures. Often this is achieved mechanically with the bolt  11  having a mechanical anchor that is engaged with the bolt at one end and which is actuatable to fix the cable to the walls of the rock hole. 
         [0061]    Alternatively, the bolt  11  can be adhesively anchored within the rock hole  38  in a method described below. In a grouted or adhesively anchored application, a resiliently deformable bung  40  is often associated with the cable bolt  11 , engaged with the bolt  11  in a pre-assembly ahead of the tensioning device  10 . When the bolt  11  is inserted in the rock hole  38 , the bung  40  is at least partially inserted to seal a mouth of the rock hole from egress of a grout or adhesive material that is introduced through a conduit  42  in the bung  40 . 
         [0062]    The cable bolt  11  and tensioning device  10  pre-assembly is assembled by locating the faceplate  36  on the bolt  11 , behind the bung  40 , on a trailing end portion  44  of the bolt, followed by the washer  16 . The inner barrel  14  trails the washer  16 , passed over the trailing end  44  of the bolt  11 . The wedge element  32  then is inserted into the tapered bore  30 , between the bore  30  and the bolt  11 , to wedge the barrel  14  to the bolt  11 . Finally, the nut  12  is threadedly engaged with the barrel  14  by threadedly receiving the barrel within the passage  22 . 
         [0063]    When the pre-assembly is inserted in the rock hole  38 , the faceplate  36  abuts a rock face  46 , with the tensioning device  10  accessible to an operator, projecting from the hole  38  attached to the trailing end portion  44  of the bolt  11 . 
         [0064]    A specially adapted torque gun is used to actuate the tensioning device  10  to tension the cable bolt  11  between an inner anchor point or location, within the rock hole  38  and an outer anchor point, which is defined at the point at which the inner barrel  14  attaches to the bolt  11 . The gun can be driven hydraulically, pneumatically, mechanically, electronically and can be designed to be driven by, for example, a rock drill. Only the connecting parts  48  of the gun that engage with the tensioning device  10  are illustrated in  FIG. 5 . 
         [0065]    The connecting part  48  includes an outer rotating socket  50  which engages with the outer nut  12  at its first end  18 . The first end is adapted on an outer surface with a plurality of recessed formations  52  to which the socket  50  engages, each radially spaced from the others. In this example, the recessed formations are arched but they can be of any suitable shape, for example, hex-shaped. This feature is illustrated in  FIGS. 3 and 4 . An inner locking shaft  54  of the gun engages the inner barrel  14  at its trailing end  28  to hold the barrel stationary to reciprocate against the torque imparted on the outer nut as more fully described below. At the trailing end, the barrel  14  is formed with a plurality of recessed concave formations  56  on an inner surface leading to the bore  30  to which the shaft  54  engages. 
         [0066]    Actuating the gun causes the socket  50  to rotate imparting torque on the outer nut  12 . As the nut abuts the faceplate  36 , as illustrated in  FIGS. 6A and 6B , it rotates without moving in a direction axial to the axis of the cable bolt  11 . However, within the outer nut, the inner barrel  14 , which is prevented from rotating with the nut by the locking shaft  54  (which, whilst preventing rotation, is able to slide freely up and down in the axial direction to compensate for an activation stroke to be described below), moves relatively to the nut as a consequence, threadedly drawn through the passage  22  from the first end  18  towards the second end  20 . This action is illustrated in  FIGS. 6A and 6B . By this action, the barrel  14  pulls the end of the bolt  11  to which it is attached, axially outwardly of the hole  38  to tension the bolt  11  between this outer attachment point and the inner attachment point. In a counteractive force, the bolt  11  pulls on the wedge element  32  enhancing the wedging action. 
         [0067]    The degree to which the cable bolt  11  is placed in tension in this manner can be represented by the distance the inner barrel  14  travels from a starting point, at the head of the nut  12 , as illustrated in  FIG. 6A , to an end point, projecting and trailing from the nut  12  at the opposed end as illustrated in  FIG. 6B . This activation distance, or stroke, is designated X on  FIG. 6B . 
         [0068]    As a matter of practicality, the locking interface of the locking shaft  54  can be designed to allow the gun to couple and then hang from the tensioning device  10  during tightening to free the operator&#39;s hands. 
         [0069]    The tensioning device  10  as part of the cable anchor assembly described above, can be used in a method of anchoring the cable anchor within a rock hole  38 . This method is now described with reference to  FIGS. 7 to 10 . 
         [0070]    The cable anchor  11  has a flexible elongate body, comprising of a plurality of helically wound high tensile steel wires, which extends between a distal end  60  and an opposed proximal end  62 . 
         [0071]    The cable anchor  11  includes a plurality of paddle formations, respectively designated  64 A and  64 B, preferably positioned towards the distal end  60 . These paddle formations are formed by bird caging sections of the cable anchor by teasing the wires from inter-wound engagement with one another to separate along these sections and bow outwardly to form “a bird cage”. These paddle formations are there to enhance the mixing of an adhesive resin as will be more fully described below. However, these formations  64 A and  64 B do not limit the scope of the invention and are a preferable inclusion to the cable anchor  11 . 
         [0072]    At the proximal end  16 , the tensioning device  10  is provided. The device is as described above. However, an addition to the inner barrel  14  is a plurality of radially spaced formations  65  which laterally project from the barrel  14  at its trailing end  28 . 
         [0073]    In use of the cable anchor  11  (the paddle formations  18  not shown for simplicity of illustration) in accordance with a first step of this method as illustrated in  FIG. 8A , a capsule  66 , having a wall of a frangible material, containing an adhesive material  71 , is inserted into a predrilled rock anchor hole  38 , in advance of the anchor bolt  11 . The anchor bolt, optionally, has a retaining formation  68  formed and attached to its distal end  60 . This retaining formation  68  engages with the resin containing capsule and assists in retaining the capsule position within the hole once the cable anchor  11  is inserted behind the capsule  66  into the rock hole  38 . 
         [0074]    After the bolt  11  is inserted, the outer nut  12  of the tensioning device  10  is rotated in a first rotational direction, as indicated by a directional arrow in  FIG. 8A  by engaging the rotation chuck of the torque gun (not shown), to move downwardly towards the proximal end  62  of the anchor body, over the inner barrel  14 . This action is not torque inducing, with no consequent rotation of the inner barrel  14  or the anchor bolt  11 . This is a first pre-positioning step to interlock the outer nut  12  with the inner barrel as described below. 
         [0075]    Once the second end  20  of the outer nut  12  reaches the trailing end  28  of the inner barrel  14  and engages with the formations  65  (as illustrated in  FIG. 8B ), the inner barrel  14  and the outer nut  12  are effectively interlocked to cause both these components of the tensioning device  10  to rotate in unison and, as the inner barrel  14  is fixed to the body of the cable anchor  11 , also the cable anchor about its longitudinal axis. 
         [0076]    This spinning causes fingers  70  of the retaining formation  46  to puncture and sever the walls of the resin capsule  66  to release the adhesive content  71  into the annular space  72  between the cable anchor  11  and the walls of the rock hole  38 . Mixing of the adhesive content  71  is enhanced by the paddle formations  64 A and  64 B. 
         [0077]    Once the adhesive material  71  hardens within at least a distal end section of the rock hole  38 , at least an end section  74  of the cable anchor body  11  is fixed within the rock hole  38 . Thereafter, further spinning of the anchor  11  is prevented. 
         [0078]    At this point, the direction of rotation of the rotation socket (not shown in  FIGS. 8 and 9  for ease of illustration) of the torque gun is reversed, and the outer nut  12  is caused to rotate in a second rotational direction (indicated with a directional arrow in  FIG. 9 ) i.e. in the opposite direction. At the same time the locking shaft  54  of the torque gun engages with the inner barrel  14  to prevent the barrel  14  rotating. 
         [0079]    With the inner barrel  14  prevented from rotating with the outer nut  12 , and the outer nut  12  held in a fixed position relatively to the rock hole  38 , abutting the faceplate  36 , further rotational drive will cause the inner barrel to move relatively to the nut, drawn longitudinally outwardly (illustrated with a directional arrow on  FIG. 9 ), pulling the cable anchor  11  with it and placing the anchor in tension. 
         [0080]    In a second embodiment of the invention, illustrated in  FIGS. 10A and 10B , the tensioning device  10 A includes a shear pin  76  which penetrates both the outer nut  12  and the inner barrel  14  to lock the outer nut to the inner barrel. The shear pin is analogous to the formations  65  in function. 
         [0081]    Thus, when the torque gun is engage with device  10 , the device and the cable anchor  11  rotate in unison, initially in the first rotational direction. 
         [0082]    The spinning anchor  11  ruptures the resin capsule  66 , releasing the adhesive content  71  which hardens, after mixing, and secures at least the end section  74  of the anchor in the rock hole, as illustrated in  FIG. 10B . 
         [0083]    With the anchor  11  now prevented from spinning, and with further application or rotational drive, either in the first or the second rotational direction, a load is imposed on the shear pin  76  which eventually causes the pin to break, unlocking the outer nut  12  from the inner barrel  14 . Now with the inner barrel  14  prevented from rotating as described above, the outer nut can rotate, independently of the barrel, with the effect that the barrel  14  is pulled through the nut  12 , as the nut  12  is held in position by interaction with the faceplate  36 , in a longitudinal outward direction, placing the anchor  11  in tension (this tension is illustrated with a bidirectional arrow on  FIG. 10B ).