BACKGROUND OF THE INVENTION

[0001] This invention relates to a rock bolt which is suitable for use in the reinforcement of rock.

[0002] As used herein "rock" includes rock strata, a cementitious body or similar hard materia!.

[0003] The provision of support in an underground mining excavation is of paramount important. Such support must be provided in cost-effective manner.

[0004] Support structures such as hydraulically or mechanically extensible steel jacks, elongate wooden supports, mat packs, mechanically actuated or grouted rock bolts or cable anchors, and bags or tubes which are filled with a settable material, have all been used to provide support.

[0005] In narrower excavations mechanical ground anchors or rock bolts have not found widespread acceptance because of space limitations. It is difficult to drill vertical holes, up to two meters long, for steel anchors in a confined space. Reliance must be placed on extension drilling techniques with coupling rods. The installation of steel anchors is also problematic. A steel anchor should have a length which is about twice the height of the stope which is to be supported and must therefore be constructed from several short sections which are bolted together using extension sleeves at the time of installation. An example of this approach is disclosed in AU 2005 204239. [0006] A polyester resin is commonly used to anchor a steel shank in a hole. The volume of resin which is needed to fill an annular space in a hole, around a bolt shank, can be high and the resin is expensive. Moreover, if the quantity of resin is large, then the bonding strength of the resin could be reduced and the steel anchor might not be able to carry its designed load. It is also difficult to assess the quality of the installation because the shank must be rotated, at the time of installation, to break the resin capsules and to mix the resin. Inadequate or excessive rotation adversely affects the shear strength of the resin.

[0007] A nut which is engaged with a protruding threaded end of the shank is tightened against a face plate which is engaged with the shank and which bears against the rock face. The protruding end of the shank remains exposed. This is undesirable because the protruding shank can severely restrict movement of men and machinery in a shallow excavation.

[0008] It is an object of the invention to provide a rock bolt which can be constructed in various lengths, according to requirement, and which addresses the aforementioned factors.

SUMMARY OF THE INVENTION

[0009] The invention provides a rock bolt component which includes an elongate rod which has a body with opposed first and second ends and, at the first end, a set of first locking formations and wherein at least one of the locking formations has a undercut surface which is transverse to a longitudinal axis of the rod. [0010] Each locking formation may be in the form of a rib and a respective recess may be positioned between each adjacent pair of ribs.

[0011] As used herein "undercut" implies that the respective formation is only engageable with a complemental formation in a similar rod with a sliding action in which one rod is moved transversely to a longitudinal axis of the other rod.

[0012] Preferably the undercut iocking formation is such that when a complemental formation on a second rod is engaged therewith there is a natural tendency for the rods to be longitudinally aligned with each other. This may be achieved by forming the undercut surface with an arcuate or V-shape when viewed from one side (not in cross section).

[0013] The rod may include a set of second locking formations at the second end. The second formations may be complemental to the shape of the first locking formations.

[0014] An objective is that if the first formations on a first component are engaged with the second formations on a second component a joint which is thereby established between the components is able to transfer tensile stress in excess of a predetermined minimum and the maximum width of the joint (in a direction which is transverse to a longitudinal axis of the joint) should not be meaningfully greater than the width or diameter of the body of either component.

[0015] In one form of the invention the first formations are undercut formations which are arcuate with respect to a longitudinal axis of the rod. Each formation may be a rib which is flanked by opposed recesses and which has opposed side walls which are inclined to a longitudinal axis of the body so that an outermost surface of the rib is wider than a base of the rib.

[0016] The first formations may be axially displaced from one other at the first end.

[0017] As the second formations are complemental in shape to the first formations the aforementioned features, relating to the first formations, appiy with equal effect to the second formations.

[0018] A surface of the body may include mixing or anchoring formations of any suitable type.

[0019] In a variation of the invention the component includes an anchoring formation or mechanism at one end of the rod. This formation or mechanism can be of any suitable form. In one embodiment a wedge arrangement is used which, when activated, expands or increases the effective cross-sectional dimension of this end of the rod.

[0020] The invention also provides a rock bolt which includes at least first and second rock bolt components, each rock bolt component being of th ie aforementioned kind, wherein the first formations of the first component are engaged with the second formations of the second component by moving one component laterally relatively to a longitudinal axis of the other component. The lateral movement may take place in a straight line or alternatively with an arcuate motion. [0021] The rock bolt may include a third rock bolt component, of the aforementioned kind, which is engaged in a similar manner to what has been described, to the second component. The process may be repeated to increase the overall length of the rock bolt.

[0022] Due to the undercut nature of the locking formations it is possible for torque to be transferred from one component to another component, for example for mixing a grout or resin.

[0023] A tubular sleeve may be threadedly engaged with the second end of the first rock boit component.

[0024] The sleeve may include a formation which is engageable with an external tool so that the sleeve can be rotated in a first direction or in a second direction which opposes the first direction.

[0025] An end of the sleeve, remote from the first rock bolt component, may be engagable with a load-distributing washer.

[0026] The invention also provides a rock bolt which includes a first component which has a body with a first end and a second end, a tubular sleeve which is threadedly engaged with the second end, a lock which allows for the transfer of torque between the first component and the sleeve so that the sleeve and the first component can be rotated, in unison, in a first direction, and which allows the sleeve to be rotated relatively to the first component in a second direction which is opposite the first direction, and a second component which is axially aligned with the first component, the two components including complementary interengaged tensile load and torque-transferring undercut formations at abutting ends.

[0027] The sleeve which is engaged with the first component is preferably connected to a load-transferring washer.

[0028] The undercut formations of the first and second components may be interengaged with one another by moving one component transversely to a longitudinal axis of the other component. This movement may be in a straight line but preferably is along an arcuate path.

[0029] The invention also provides a method of extending the length of a shank of a rock bolt which includes a first component with an elongate body and a plurality of tensile load and torque-transferring undercut formations at one end of the body, the method including the step of engaging tensile load and torque-transferring undercut formations at an end of a second component with the formations on the first component.

[0030] Once the shank is inserted into a hole n a rock body the wall of the hole ensures that the formations remain engaged with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The invention is further described by way of examples with reference to the accompanying drawings in which:

Figure 1 is a side view of a rock bolt according to one form of the invention;

Figure 2 shows the rock bolt of Figure 1 in cross section; Figure 3 is a side view on an enlarged scale of a joint which is being made between two adjacent components in the rock bolt of Figure 1;

Figure 4 is a view on an enlarged scale and in cross-section of one end of the rock bolt in Figure 1;

Figure 5 is a view on an enlarged scale and in cross-section of a joint between two adjacent components in the rock bolt;

Figures 6 shows the rock bolt in the process of installation;

Figure 7 illustrates an upper end of the rock bolt;

Figures 8 and 9 are similar to Figures 5 and 6 respectively, illustrating a variation of the invention; and

Figure 10 is similar to Figure 4, illustrating a variation of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] Figure 1 of the accompanying drawings illustrates from one side a rock bolt 10 according to the invention which includes a first component 12 and a number of additional components 14. As will become apparent from the following description the components 14 are substantially identical except for one uppermost component (in Figure 1) designated 14A.

[0033] The number of components which can be included in the rock bolt can be varied according to requirement.

[0034] The rock bolt is shown from one side and in cross-section in Figure 2. [0035] The component 12, also partially shown in enlarged cross-section in Figure 4, has an elongate body 16 with a first end 18 and a second end 20. The body, externally, has a number of fluted formations 22, see Figure 1 , which assist with resin or grout mixing and which also act as retention or keying formations, when the rock bolt is installed.

[0036] The first end 18 is formed with a first plurality of formations 24 which are shown on an enlarged scale and in cross-section in Figure 5 and in Figure 6. The formations are irregular in shape but, generally speaking, are undercut. In this example of the invention the formations can be categorised as two ribs 24A and 24B respectively and two slots 24C and 24D respectively. The rib 24A has a flat outer surface 26 which is substantially parallel to longitudinal axes 28 and 28A of the components, and sloping walls 28 and 30 respectively with surfaces which taper towards each other away from the flat outer surface 26. These features give the rib an undercut nature.

[0037] The slot 24C has a flat base 32 and is bounded by the wall 30 on one side and by a wali 34 which is substantially at a right angle to the longitudinal axes 28 and 28A.

The rib 24B has a flat outer face surface 36 and is flanked by the wall 34 and a wall 38 with a surface which slopes away from the surface 36 so that this rib, too, is undercut. The slot 24D has a flat base 40 which is bounded by the sloping wall 38 and an opposed wall 42.

[0038] The component 14 which is adjacent the component 12 has a first end 40 and a second end 46. The second end, shown in enlarged detail and in cross-section in Figure 5 is configured with a plurality of formations 48 which conform in cross-sectional shape to the formations 24. Due to the undercut nature of the ribs and slots it is evident that the formations 48 are only engageable with the formations 24 if one set of formations is moved transversely to the longitudinal axes 28 and 28A so that the formations can be interengaged with a sliding action with each other.

[0039] Figure 3 is a view which is displaced by 90°, about the axes 28 and 28A, relative to the view in Figure 5. The component 12 is shown in dotted outline at a position at which the component is aligned with the component 14, and in solid outline at a position at which the longitudinal axis 28 of the component 12 is inclined to the longitudinal axis 28A of the component 14. The formations 24A to 24D extend transversely to the longitudinal axis 28. There are two possibilities in this connection. If the sides of the ribs and slots (30, 34, 38 and 42) are each at a right angle to the longitudinal axes 28 and

28A then one component is moved linearly transversely to the other component in order to cause interengagement of the complemental ribs and slots. On the other hand, as is shown in Figure 3, the surfaces 30, 34, 38 and 42 can each lie on an arc which is centred on the longitudinal axis 28. With this arrangement it is only possible to engage the formations on one component with the compiemental formations on the other component if, as shown, one component is initially inclined relatively to the other. The engagement process is then one in which (in the drawing) the component 12 is moved along an arcuate path, relatively to the other component, as is indicated by means of a curved arrow 50 in Figure 3, until the components are axially aligned.

[0040] The arcuate formations and movement hold a number of benefits. Firstly if a tensile force is applied to the interengaged components, whether by mechanical means or due to gravity, there is an automatic tendency for the components to align longitudinally with each other. Secondly, the components cannot be disengaged from each other simply by moving one component laterally relatively to another component. This means that when the components are installed in a hole in a body of rock, as is shown in Figure 6, that the components remain interengaged with each other. There is no need for a retention device e.g. a tube to keep the components interengaged. Also the joint is such that it is capable of transmitting torque. A third factor is that the pivoting type movement required to couple one component to another is advantageous in limited space conditions, for example a narrow slope, for the components are only fully axially aligned with each other as they are pushed into a hole in the rock body.

[0041] The end 40 of the component 14 has formations 52 which are identical in all material respects to the formations 24 except that when the formations 46 are engaged with the formations 24 the formations 52 face in an opposing direction to the formations 24.

[0042] The second end 20 of the component 12 is shown in enlarged cross-section in Figure 4. The second end has a threaded shank 64 which projects from the remainder of the body 16. A tubular sleeve 68 has an internal thread 70 at one end 72. A locking wire 74 acts between the threaded shank 64 and the threaded section 70.

[0043] An opposing end of the sleeve 68 has an enlarged flared section 76 which abuts a rim 78 of a load-distributing washer 80 which has a central hole 82 through which the sleeve extends. A drive formation 84 is formed internally on the projecting flared section 76.

[0044] The component 14A which is at an end of the rock bolt 10 which is remote from the load-distributing washer 80 has an inner end 88 which carries formations 90 which are similar to the formations 24. An outer end 92 of the body 94 of the component 14A is split in an axial sense by a longitudinally extending slot 96, see Figure 7. An elongate wedge member 98 has a leading end 100 which is inserted into the slot 96 so that sides of the wedge member are frictionally engaged with opposing sides of the slot. Figure 2 shows the assembled rock bolt in cross-section and Figure 6 shows the rock bolt on an enlarged scale and installed in a hole 102 formed in a body of rock 104 from a rock face 106.

[0045] The rock bolt 10 is readily assembled on site. The component 14A with the wedge member 98 is inserted into the hole 102 but with the end 88 projecting slightly from the hole. An adjacent component 14 is then connected to the component 14A essentially in the manner shown in Figure 3 i.e. by tilting the member 14 relatively to a longitudinal axis of the member 14A and then with a sideways, slightly arcuate motion causing the undercut formations at abutting ends of the components to engage with each other. Once the interengagement has been effected the component 14 is moved into the hole and the component 14A is advanced towards an end of the hole.

[0046] The joint between the two components is then moved into the hole 102. It is not possible for the components to disengage from each other once the joint is in the hole for this can only take place if one component is moved on an arcuate path relatively to the other - a process which is not possible when the interengaged ends of the components are inside the hole. Due to the centralizing action of the arcuate formations one component is not materially offset laterally to an adjacent component and, when the components are tensioned, any offset is effectively diminished. [0047] The process continues in this way with the effective length of the rock bolt 10 being extended according to requirement by the addition of subsequent components 14.

[0048] The last component to be added to the assembly is the component 12 which carries the load-distributing washer 80. The component 12 and washer 80 are delivered to an installation site in an assembled state. The threaded shank 64 is screwed home fully into the sleeve 68 so that the sleeve protects the thread on the shank against damage. Initially the washer is displaced from the rock face 106. The hole 102 is drilled to a length which ensures that a leading end 108 of the wedge member 98 abuts an end 110 of the hole 102. It is therefore possible to set the rock bolt, in a mechanical sense, by applying an impact force to the protruding end 76 in order to drive the components axiaiiy into the hole 102. The wedge member 98 is then driven into the slot 96 and the end 92 of the component 14A is thereby expanded in a radial sense.

[0049] Prior to the aforementioned process one or more resin or grout capsules, not shown, are inserted into the hole 102. As the rock bolt is pushed home the wedge member and leading end 92 of the component 14A penetrate the capsules and the constituents of the capsules are released into the hole 102. A tool, not shown, is engaged with the formations 84 at the protruding end 76 of the tubular member 68. This tool is activated to rotate the bolt inside the hole so that the constituents of the capsules are thoroughly mixed and to ensure that the mixture is dispersed along the length, and on the outer side, of the rock bolt. Thereafter the actuation process referred to is initiated in order to set the bolt mechanically. The resin or grout mixture, as the case may be, is then allowed to set to establish a bond between an outer surface of the rock bolt and a wall of the hole. This bond is enhanced by the fluted formations 22 on an outer surface of the body of each component.

[0050] Torque can be transferred in an anti-clockwise direction from the sleeve 68 to a remainder of the rock bolt by virtue of the locking wire 74 which prevents the sleeve from unscrewing from the threaded shank 64. Once the settable material (resin or grout) has set the tool is reengaged with the formations 84 and the sleeve 68 is rotated in a clockwise direction. The sleeve can then advance in a threaded manner along the shank 64 and, in the process, the distributing washer 80 is compressed against the rock face 106 and the bolt is stressed in an axial direction. The direction of the thread on the shank, and hence on the sleeve, is exemplary only for a right hand thread may conventionally prevail in some countries and a left hand thread in other countries.

[0051] The mechanical setting provides immediate support and the settable material, once set, provides permanent support.

[0052] It is evident from an inspection of the accompanying drawings that the length of the rock bolt can be extended, as necessary, by the use of additional components 14 according to requirement.

[0053] Once the rock bolt has been installed the load-distributing washer 80 and the end 76 of the sleeve 68 are effectively flush with the rock face 106 and do not, in themselves, present an obstruction to the movement of men or machines in the excavation in question.

[0054] The formations which are used to interconnect adjacent components to each other are formed using conventional milling techniques. These formations can be varied in size and number according to requirement. Figure 8, which is similar to Figure 5, illustrates interengaged formations 124 and 146 at abutting ends 118 and 146 respectively of modified components 112 and 114 respectively. A comparison of Figure 5 with Figure 8 shows that the formations 124 and 148 are each in the nature of a dove tail whereas in Figure 5 one set of formations has flat sides which are at a right angle to the longitudinal axes 28 and 28A. The dove tail arrangement shown in Figure 8 is slightly more difficult to machine than the arrangement shown in Figure 5. However in both instances positive locking is assured and, as stated, there is no need for a retention member to encircle a joint to ensure that the components remain interengaged with each other. In effect, the wall of the hole in the rock acts as a sleeve which encircles the joint which is then supported by the wall of the hole and the surrounding grout.

[0055] Figure 9 is similar to Figure 6 and shows the components 112 and 114 in a rock bolt 10A. A leading end of the rock bolt does not have the wedge structure shown in Figure 7. In this case the rock bolt is grouted or fixed by means of a resin in piace and thereafter is tensioned by advancing the threaded sleeve 68 which is located at a mouth of the hole 102 at the rock face 106.

[0056] It is also possible for the leading end of the rock bolt to carry a mechanically actuated expansion shell assembly of a kind which is known in the art. The invention is not limited in this regard.

[0057] Figure 10 shows another variation of the invention. In this instance a resiliency compressible element 184, made for example from a rubber block, lies on an inner surface 186 of the washer 80. The rubber element has a central passage 188 through which the tubular sleeve 68 passes.

[0058] The rock bolt shown in Figure 10 is used in a similar manner to what has already been described herein. When the sleeve 68 is rotated in a clockwise direction, in order to tension the rock bolt, the sleeve advances in a threaded manner along the shank 64 and in the process the element 184 is compressed. This stresses the rock bolt in an axial direction.