Background to the Invention Rock bolts take many shapes and sizes. One popular type of rock bolts used in underground mines is the chemical anchor rock bolt. A typical chemical anchor rock bolt is a solid steel bar having protruding ribs on the surface and a thread and nut at one end.

Installation of such a rock bolt comprises four steps : (i) drilling a suitable hole in the ground to be supported, (ii) inserting a two-pack resin capsule in the hole, (iii) inserting the bolt into the hole and spinning the bolt in order to pierce the resin capsule and mix the resin, and (iv) tightening a nut on the threaded portion after the resin is cured in order to tension the bolt and apply a compressive force to the surrounding ground.

When chemical anchor rock bolts were first introduced, it was common practice to forge a small square head on the bolt at the threaded end. To mix the resin, the bolt would be spun using a square socket fitted onto the square head. That socket would then be removed as the resin hardened. A hexagonal nut would then be fitted over the square head and onto the bolt thread and spun up tight using a socket larger than that used on the square end.

Over the past two decades techniques have been developed to increase efficiency by removing the need to change sockets and thus steps (iii) and (iv) above are completed on a drill rig continuously without changing its position. This is achieved by using a nut that is designed to lock onto the rock bolt until a high torque is reached, and thereafter turn freely on the bolt thread. This enables the nut to be rotated and hence spin the bar at a low torque to mix the resin. When the resin is set, attempting to turn the nut increases the torque sufficiently that the nut will no longer be pinned to the bar, but can rotate freely and be tightened.

The nut can be pinned to the bar by a number of methods. In US patents 5, 352, 065 and 5, 443, 332 for example a stopping washer is pressed or adhered in the nut at one end. The washer prevents the bolt end moving through the nut at low torques, but at high torques, a large axial force is generated which breaks the stopper washer from the nut. A similar approach has also been used that has a resin plug in the end of the nut rather than the metal washer. Both of these approaches leave metal or resin plugs behind after installation which can block the drive sockets used on the bolt installation equipment.

Another technique has a pin inserted through the nut into the bar and the pin is designed to shear at a given torque. While this method works well at low torques, at higher torques it has a tendency to result in thread damage. Another method has been to produce threads with a bulge in them that only allows the nut to pass after a given torque is reached.

All of these systems suffer from limitations, and there are a number of problems that can arise if the breakaway torque is not accurately controlled. If the breakaway torque is too low, then the nut can spin on the bolt before the resin is properly mixed and/or the bolt is properly positioned. This lower limit to the torque range is difficult to predict as the torque to mix the resin varies significantly with the straightness of the hole, resin condition and mixing time. The torque can also increase if the bolt rubs on other roof support components, such as plates or mesh, during installation. This results in a bolt partially installed into the roof which then needs to be removed or bent out of the way and another roof bolt installed. If the breakaway torque is too high, then the drill rig may not be able to overcome the nut-bolt bond/resistance to tighten the nut. Also, at high breakaway loads the structural integrity of the resin can be damaged due to the high torque. Increasing the resin set time can reduce this damage, but this will slow the roof bolt installation. A high breakaway torque also produces higher stresses in the installation equipment.

Thus there is a relatively small window for the required nut breakaway torque and, given the variability in manufacture and mine conditions, some bolts are not correctly installed.

With the increased use of higher strength, larger diameter roof bolts, the difference between the minimum torque required, and the maximum torque that can be applied by the installation equipment is getting smaller and so these problems will increase.

In US patent 3, 940, 941 Libert et al proposed a dual-turn method to install roof bolt. A discontinuity is pressed or deformed onto the bolt threads after the nut is screwed to the bolt. When the nut is driven in one direction, the nut runs along the thread until it hits the discontinuity and entrains the bolt to rotate to mix the resin. Once the resin is cured, the

nut is rotated in the opposite direction to tighten the bolt. However the discontinuity damages the threads and prevents a further nut being run fully onto the exposed thread in order to retain a hook or bracket or the like.

The object of the present invention is to provide a new rock bolt with its installing device to overcome the aforementioned shortcomings of the current bolt installing systems.

Summary of the Invention Accordingly, in one aspect the present invention provides a method of rock bolting comprising : - drilling a hole in a rock structure to be supported ; - inserting into the hole the components of a setting resin ; - inserting into the hole a rock bolt such that it has a threaded end protruding from the hole and its other end is in contact with the resin components ; - providing a nut matingly engaged with said thread ; - engaging a rotation tool with the nut and with a drive means on the bolt and rotating both nut and bolt together in a first direction in order to mix the resin components in the hole ; - allowing the resin to set ; - reversing the direction of rotation of the tool to cause disengagement of the tool with the drive means on the bolt and cause the nut to spin along the thread towards the rock ; and - continuing to turn the nut in said reverse direction in order to tension the bolt.

Preferably the disengagement of the tool from the drive means on the bolt is accomplished by retraction of a pawl component of the tool from engagement with a notch on the bolt. Preferably when the tool is rotated in the first direction the pawl engages a notch running transverse to the thread so causing the bolt to rotate whereas when the tool is rotated in the reverse direction the pawl rides along the thread crest without causing the bolt to rotate.

Preferably the resin components are contained in separate compartments in a capsule when inserted into the hole. Preferably the thread on the bolt continues to the end face of said threaded end. Preferably the portion of the bolt in contact with the resin carries raised ridging aligned helically on the bolt with the same handedness as that of said thread.

In another aspect the invention provides a rock bolt for use in ground support having an insertion end for inserting into a hole drilled in rock and having a threaded portion at the other end for engagement with a corresponding nut, the threads adjacent the end face of the

threaded end being interrupted by a notch running transverse to the thread. Preferably the notch has two walls extending from the end face of the threaded portion and running parallel to the major axis of the bolt, one said wall being substantially radial of the bolt and the other being close to tangential.

In another aspect the invention provides a rock bolt and nut assembly, the bolt having an insertion end for inserting into a hole drilled in rock and the other end threaded for engagement with a corresponding nut, the threads adjacent the threaded end face being interrupted by a notch running transverse to the thread. Preferably the notch has two walls extending from the end face of the threaded portion and running parallel to the longitudinal axis of the bolt, a first of said walls being substantially radial of the bolt and the second of said walls being substantially orthogonal to said first wall. Preferably said second wall is substantially tangential to a circle which is centred on the longitudinal axis of the bolt and which is between 60% and 90%, and is more preferably approximately 75%, of the bolt diameter.

In another aspect the invention provides a tool for installing a rock bolt, the tool having a pawl portion adapted to engage and rotate the bolt in a first direction when the tool is rotated in said first direction, and to ride over the bolt without rotating the bolt when the tool is rotated in the reverse direction, and a socket portion for engaging and driving a nut in said reverse direction onto the bolt in order to tension the bolt.

The present invention provides a notched rock bolt and its installing device. The bolt is notched at the thread end and the torque required for mixing the resin is applied directly to the bolt using this notch rather than being applied via the nut. The installing device includes a socket to hold the bolt and tighten the nut, a pawl (which may be termed a cam or driving key) to exert torque to the bolt by engaging with the notch on the bolt and springs to hold the key in the notch. The notch and the key are designed so that when the socket is rotated in one direction, the bolt and socket are engaged via the notch and rotate in the same direction. Therefore, the resin can be mixed and the maximum torque available from the drill rig can be used if required.

Once the resin is cured, the socket is rotated in the opposite direction. The bolt will disengage with the socket, so that only the nut is rotated to tighten the bolt. The torque required for this is a very small initially as there is no restriction to the nut winding on the thread. For this new bolt and driver system, no special breaking nut is needed. Also the bolt to bolt variation in resin mixing torque is of no concern as it does not influence when the nut might move up along the bolt.

Brief Description of the Drawings In order that the invention may be more fully understood there will now be described, by way of example only, preferred embodiments and other elements of the invention with reference to the accompanying drawings where : Figure 1 is a discontinuous partial cutaway view of a rock bolt and its installing device according to the present invention during their application in mine roof bolting ; Figure 2 is an isometric view of the threaded end of a preferred rock bolt used in the invention and having a notch machined at its end ; Figure 3 shows a cutaway section through a preferred bolt-installing device and its engaged nut and bolt ; and Figure 4 shows section A-A indicated on Figure 3.

Detailed Description of the Preferred Embodiment Figure 1 shows a rock bolt 5 being installed into a predrilled hole 3 in rock 1 by a drill/bolter rig 12. The bolt 5 has a threaded end 14 and an insertion end 15. Where the bolt is not threaded it carries raised ribs or ridging 54 on its surface and these follow a left- handed helical path. The hole is preloaded with a chemical capsule 2 in which liquid resin and its hardener are enclosed in separate compartments of the capsule. A bearing plate 4 is held against the roof by the frame 6 of the rig 12 and this plate may bear directly against the rock 1 or roof support mesh (not shown). The frame 6 may sit on any mobile equipment such as a continuous miner or shearer or can be a stand alone unit. The frame 6 carries a drill header 9 which can rotate in both clockwise and counter clockwise directions around its driving shaft. A standard hexagon nut 7 with a left-hand thread is engaged with the threaded end 14. A hexagon socket dolly 8 mounted on the header embraces the nut 7 which can be freely run along the thread by rotation of the dolly.

In the embodiments shown in the Figures, both bolt 5 and nut 7 have left handed threads and the rib pattern ridging 54 on the rock bolt 5 is also left handed. Accordingly a right handed or clockwise rotation of the bolt is preferred to mix the resin. This is because anticlockwise rotation would tend to pump the resin downwards along the bolt by a screw action.

The bolt 5 the end of which is shown in Figure 2 carries a longitudinal rib 55 in addition to the circumferential ribs 54. The bolt carries a notch 51 extending from the end face 18 of the threaded end along the bolt for a distance of approximately the diameter of the bolt.

The notch has a wall 56 set approximately radially to the bolt, a wall 57 set at right angles to the wall 56 and tangential to a circle of about 75% of the bolt diameter, and an end wall 58 which slopes obliquely to the longitudinal axis of the bolt. Being longitudinal to the bolt axis, the walls 56 and 57 cut transversely through the ridges and valleys of the thread.

The notch 51 intersects the end face 18 at two straight edges 52 and 53. The notch 51 can be easily machined by feeding a rotated cutter parallel to the bolt axis. The notch edge 52 is positioned along the bolt's radial direction to minimise the contact stress for any given bolt driving torque.

The preferred tool 8 for installing the notched bolt is shown most clearly in Figures 3 and 4. The view of Figure 3 follows a cutaway along stepped line B-B shown in Figure 4. The nut 7 is preferably supplied to the end user pre-installed on the bolt 5 with part of the thread extending through the nut as shown in Figure 3. A specially designed pawl or key 84 is used to drive the bolt, with the bolt notch acting as a drive means. The pawl 84 can slide in a rectangular aperture which passes through the wall of the socket tool 81. Two springs 83 bias the pawl 84 to engage with the notch 51 when the bolt is rotated to align the notch with the pawl. The springs 83 are axially retained by a shell 82, which also protects the springs and the pawl from damage and the ingress of dirt. The shell 82 is attached to the socket tool 8 by screws 85. The comer 841 of the pawl, where the pawl meets the bolt first, is chamfered, so that the bolt can be easily inserted into the central hole 812 of socket 81 without necessarily aligning the bolt notch with the pawl 84. Once the bolt is inserted in the hole 812, the pawl 84 can automatically engage the notch 51 if the socket 81 is rotated clockwise relative to the bolt 5 or the bolt is rotated counter clockwise relative to the socket. Figures 3 and 4 show such engagement.

Comer 844 of the pawl 84 is also chamfered to allow the pawl to disengage from the bolt notch when the socket 81 is rotated counter clockwise as shown in Figure 4. There are two holes 842 on pawl 84 to seat the springs 83. The pawl also has a step 843 near its outermost face to prevent the pawl from moving too deeply into the tool.

The installation of a rock bolt according to the invention and having a left hand thread on its nut involves the following stages. When the socket 81 is driven in a clockwise direction, the pawl 84 will automatically engage to the notch 51 to drive bolt 5 in a clockwise direction and this motion of the bolt serves to mix the resin. When the socket 81

is then driven in a counter clockwise direction, the pawl 84 will ride out of the notch to disengage the socket 81 with the bolt 5, so that the nut 7 can be rotated around the bolt 5. The nut 7 moves up along the bolt until it contacts the bearing plate 4 and the bolt 5 is tightened.

In operation, the socket tool 81 is first fitted onto a drill driver (not shown) by engaging the driver into socket 813. Installation of the bolt then takes the following steps : (1) Drill a hole in a rock structure.

(2) Insert a resin capsule into the hole.

(3) Thread the bolt 5 through the nut 7 until most of notch 51 extends from the nut as shown in Figure 3. This step may be done by the bolt manufacturer prior to supply.

(4) Engage the nut 7 and bolt together into the socket 81 and (optionally) rotate the bolt clockwise to engage the notch 51 with the pawl 84.

(5) Insert the bolt into the hole in the rock by raising the header 9, of the drill/bolter rig.

(6) Rotate the socket in the clockwise direction to mix the resin. This can be done simultaneously with step (5) to save time.

(7) Allow the resin to set.

(8) Reverse the socket rotation direction to tighten the nut. This can be automatically done by the header control system or manually done by monitoring the hydraulic (or pneumatic) pressure of the header.

(9) Stop tool rotation when the bolt is tightened to the desired torque.

It will be appreciated that in some situations it may be more convenient to insert the bolt into the hole in the rock before the socket 81 is engaged with the nut.

The rock bolt would normally be manufactured from commercially available reinforcing bar. Many rib patterns are used on such bars. Some rib patterns require a definite rotating direction to mix the resin. If the rotation is in the wrong direction the angle of the ribs tends to pump the resin out of the hole. If the reinforcing bar requires clockwise turning to mix the resin, the threads on the bolt 5 and in nut 7 should be left handed, which is the case for the preferred bolt described with reference to Figures 1 through 4. If the reinforcing bar does not require a definite rotating direction to mix the resin, the turning direction of the bolt thread can be designed according the user requirement. If right handed threads are used, the position of notch 51 and pawl 84 should be mirrored vertically to that shown in Figure 4.

With this notched rock bolt of the present invention and its rotary tool for installation, no special nuts are needed. The operator does not need to worry about the early breaking of a special nut and different nuts with different breaking-off torques need not be ordered nor stocked. The resin mixing and nut tightening can be automated by slightly modifying existing control systems for drill rigs or bolters, or manually done by monitoring the pressure of the fluid which drives the equipment.

Whilst the above description includes the preferred embodiments of the invention, it is to be understood that many variations, alterations, modifications and/or additions may be introduced into the constructions and arrangements of parts previously described without departing from the essential features or the spirit or ambit of the invention.

For example it is not essential for a left hand threaded bar as described above to have a left handed helical form to the rib pattern on the bar used to manufacture the rock bolt, or for a right hand threaded bar to have a right handed helical form to the rib pattern on the bar.

Instead the rib pattern may be non-handed so that it would not have a preferred rotation direction to mix the resin.

It will be also understood that where the word"comprise", and variations such as "comprises"and"comprising", are used in this specification, unless the context requires otherwise such use is intended to imply the inclusion of a stated feature or features but is not to be taken as excluding the presence of other feature or features.