1 METHOD FOR FIXING A CABLE OR TENDON The present application is a divisional application from Australian Patent Application No. 2008303063 filed on 25 September 2008 the entire disclosure of which is incorporated herein by reference. FIELD OF THE INVENTION The invention relates generally to a method of grouting an elongate cavity adapted to locate a strata cable or tendon. BACKGROUND OF THE INVENTION In underground mining and strata control, bolting is generally recognised as the primary support system. Bolting usually involves grouting of a rock bolt within a bolt hole formed in the strata of an underground mine. The bolt is commonly tensioned using a 2-speed resin capsule so that the strata surrounding the bolthole is held in compression. This technique has been extended to cables or tendons where generally a barrel and wedge fitting is attached to the cable and is tensioned using hydraulically actuated equipment. The typical practice for post-grouting to achieve full encapsulation involves: (i) Clamping or clipping an air return tube or hose along the length of the cable or tendon; (ii) Filling the annulus space surrounding the cable or tendon with grout from the bottom up and venting air from the enclosed upper space of the hole via the air return tube or hose. The grout is typically pumped into the hole via a port provided in a strata plate which surrounds the opening to the hole. The cable or tendon may also require bulbing to improve its anchor strength due to the larger hole to fit the air return tube. SUMMARY OF THE INVENTION According to one aspect of the invention there is provided a method of grouting an elongate cavity adapted to locate a strata cable or tendon, the method comprising the steps of: inserting a capsule having an outer membrane and containing grout or resin 2 lengthwise into the cavity; advancing the cable or tendon within the cavity thereby laterally displacing the capsule, the cable or tendon having a cutting tool being shaped asymmetric and including an oblique surface attached to an end of the cable or tendon; and rupturing the displaced capsule by cutting or piercing it with a cutting edge defined by the oblique surface of the cutting tool. According to another aspect of the invention there is provided a method of grouting an elongate cavity adapted to locate a. strata cable or tendon, the method comprising the steps of: inserting a capsule having an outer membrane and containing grout or resin lengthwise into the cavity; advancing the cable or tendon within the cavity thereby laterally displacing the capsule, the cable or tendon having one end shaped asymmetric including an oblique surface; and rupturing the displaced capsule by cutting or piercing it with a cutting edge defined by the oblique surface of the cable or tendon. Preferably the capsule is one of multiple capsules inserted into the cavity Preferably the capsule includes an outer membrane containing the grout or resin and the step of laterally displacing the capsule involves advancing the cable or tendon within the cavity pushing the membrane aside with the oblique surface. BRIEF DESCRIPTION OF THE FIGURES In order to achieve a better understanding of the nature of the present invention preferred embodiments of the various aspects relating to installation of a strata support cable or tendon and the cable or tendon itself will now be described, by way of example only, with reference to the accompany figures within which: Figure 1 shows a schematic partial X-ray elevational view of a tensioning device for a strata support cable or tendon according to one embodiment of the invention; Figure 2 shows a schematic partial X-ray elevational view of a typical barrel & wedge type tensioning member being adapted for the methodology of another embodiment of the invention; Figure 3 is cross-sectional view A-A through the tensioning member and cable shown in 3 figure 1; and Figure 4 is a cross sectional view B-B through figure 2; Figure 5 is a schematic illustration of an end of a strata support cable or tendon shaped according to an embodiment of another aspect of the invention; Figure 6 is a schematic illustration of a cutting or piercing tool of an embodiment of yet another aspect of the invention detachably attached to an end of a strata support cable or tendon; Figure 7 is various views of the cutting head of the cutting or piercing tool of Figure 6; and Figure 8 shows a side view of a tensioning member with a non-detachable threaded portion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figure 1 shows one embodiment of a tensioning device, generally indicated by the reference numeral 10 through which a strata support cable 12 or tendon passes. The cable 12 is installed into an elongate cavity drilled into a geological strata (not shown). The tensioning device 10 includes a tensioning member 14 which has a central elongate bore 16. The elongate bore 16 is adapted to receive the strata support cable 12, and preferably has a slightly larger diameter than the cable 12. In this embodiment, the tensioning member 14 has a threaded portion 18 for threaded engagement with an actuator member or relatively large nut 20. This embodiment of the tensioning member 14 also includes a wedge assembly 22 for securing the cable 12 or tendon to the tensioning member 14 to prevent the cable 12 or tendon pulling through the elongate bore 16. A fluid inlet 24 is defined by a transverse aperture 26 in a sidewall of a head of the tensioning member 14. The aperture 26 is threaded and the inlet 24 opens into the elongate bore 16. When the cable 12 passes through the elongate bore 16 a fluid passageway 28 is formed in the annulus between the cable 12 and the tensioning member 14. Thus, the fluid inlet 24 formed in the tensioning member 14 opens into the annular fluid passageway 28. In use, the fluid inlet 24 allows injection of a preferably thixotropic grout or resin (shaded regions of figures) into the elongate cavity of the geological structure surrounding the cable or tendon 12. This post grouting is via the annular fluid passageway 28 that runs along the length of 4 the tensioning member 14, and out of an opening 29 at a distal end of the tensioning member 14. The cable 12 or tendon is in the form of wire rope and comprises a plurality of steel strands or wires, such as 30 in figure 3, rendering the cable 12 permeable to air. One or more of the strands or wires 30 can be wound or braided, whereas others can be straight. Because air is less viscous than the grout or resin the cable is substantially more permeable to the air than the grout or resin. Thus, the cable 12 or tendon includes a plurality of internal air vents or interstitial passageways 32 between the strands or wires as shown in figure 3. The passageways 32 are oriented generally longitudinally of the cable or tendon 12 and are generally shaped in the form of a helix. As shown in figure 3, on injection of the grout or resin into the elongate cavity (filling from the bottom up) the air that is displaced by the grout or resin is exhausted from the cavity through the cable 12 or tendon itself via one or more of the passageways such as 32. This means that the use of a breather tube or air return tube or hose (of the prior art) is not necessary. Furthermore the multiplicity of interstitial passageways 32 is advantageous because some of the interstitial passageways may be blocked by, for example, the grout or resin. In this circumstance, air from the cavity can still be exhausted via the unblocked interstitial passageways. The threaded fluid inlet 24 permits attachment of a non-return valve coupled to a conduit, hose or pipe fitting 33 conducting the grout or resin from a grout or resin supply separate from the tensioning device 10. In the preferred embodiment of the method, the elongate cavity is in a pre-grouting step partly loaded or filled with capsules containing grout or resin. The capsules are broken with the advancing cable 12 or tendon to release the resin or grout which sets to secure a distal end of the cable 12 or tendon within the cavity. After this pre-grouting or anchoring step the cable 12 or tendon is tensioned by rotating the nut 20 around the thread portion 18 which drives a strata or volcano plate 34 against the strata to compress it about the cavity. An intermediate domed washer and bearing assembly 36 is located between the nut 20 and the volcano plate 34. Operation and construction of the tensioning device 10 is otherwise described in some detail in the applicant's international patent application no. PCT/AU2007/01141 the disclosure of which is incorporated herein by way of reference. Of particular relevance to this present application is the disclosure of two different configurations in which the threaded portion is integrated with the tensioning member. Figure 1 shows a configuration where the threaded portion 18 is detachable from the 5 tensioning member 14. Figure 8 shows another configuration where the threaded portion 180 is non-detachable from the tensioning member 140. The two configurations are otherwise substantially identical and either configuration can be used in place of the other. Specifically, the tensioning member 140 also has a fluid inlet 240 defined by a transverse aperture 260 in a sidewall of a head of the tensioning member 140. Figure 2 shows a typical tensioning device 100 of the barrel and wedge type of the prior art. For ease of reference and to avoid repetition, like components of this embodiment and that of figure 1 have been designated with an addition "0". The strata or volcano plate 340 of this embodiment includes a threaded opening 102 for attachment of the pipe fitting 330. The device 100 otherwise includes the dome-shaped barrel 104 and wedge assembly 220 for securement of the cable or tendon 120. In this embodiment and as best shown in figure 4 the device 100 is adapted to allow post grouting and air venting via the interstitial air passageways 320 of the cable or tendon 120, in a similar manner to the previous embodiment. Figure 5 shows three (3) views of an embodiment of an end of a strata support cable or tendon 50 according to another aspect of the invention. The cable or tendon 50 has its end shaped asymmetric for laterally displacing and thereafter cutting or piercing of a resin or grout capsule located within a cavity drilled into a geological strata (not shown). In this example the cable 50 is cut at an acute angle to define three (3) cutting edges 54, 55 & 56 terminating at a rounded tip 52, and an oblique surface or asymmetric wedge 57. Figure 6 illustrates an embodiment of a cutting or piercing tool 60 according to yet another aspect of the invention. The tool 60 comprises cutting means in the form of a cutting head 62 which is shaped asymmetric and adapted to laterally displace and thereafter cut a resin or grout capsule located within a cavity drilled into a geological strata (not shown). Figure 7 illustrates different views (perspective view, front view and side view) of the cutting head 62 shown in Figure 6. The cutting head 62 is generally cylindrical and truncated at an acute angle to define a pair of oblique surfaces 64 & 66 together defining a cutting edge 67 terminating at a rounded tip 68. The cutting head 62 is formed integral with mounting means in the form of a threaded spigot 70. The tool 60 also comprises a coupling element in the form of internally threaded socket 72 being configured to provide threaded attachment for the tool 60 to the cable or tendon 73 via the threaded spigot 70. The tool may be fabricated of hard plastic, metal or any other suitable material. The asymmetric shaped cable or tendon 50 or the cutting or piercing tool 60 allows the cable 6 or tendon to be pushed through the resin capsule easier. The tendon 50 or tool 60 pushes the resin capsule to the side and avoids concertina of the capsule or sausage packaging lining the hole and forming a glove about the tendon 50. This means that it may be possible to include multiple resin capsules in the cavity or hole to achieve better pre-grout encapsulation. The tendon 50 may also be advanced into the cavity for the majority of its length without rotation. This means that the exposed length of tendon 50 on rotation of the tendon 50 is minimised. In some applications this use of multiple resin capsules may eliminate or lessen the need for post-groutings. In another embodiment of the method, one or more capsules each having an outer membrane containing resin are inserted lengthwise into the cavity. The capsule membrane is then ruptured by inserting a cable or tendon 12 into the cavity, the end of the cable 12 having a penetration tool such as 50 or 60 attached or formed therein. The tool has an oblique surface or asymmetric wedge, such as 57 or 67, that pushes the membrane to one side of the cavity as the tool 50, 60 and cable 12 are advanced into it. This prevents the concertina or collapse of the membrane before the tool which would form an impassable plug blocking further advance of the cable 12 into the cavity. The rounded tip 52, 68 of the tool 50, 60 aids in the penetration of the tool 50, 60 deep into the cavity containing elongate resin capsules. Once a sufficient length of cable 12 has been inserted, the cable 12 can be rotated to promote the final advance of the cable 12 into the cavity and break up the membrane. The cavity diameter and depth is typically around 30 millimetres and 10 metres respectively, and the capsule is typically sausage-like with a diameter and length that are typically around 24 millimetres and 1 metre respectively. Now that a preferred embodiment of the present invention has been described in some detail it will be apparent to those skilled in the art that the tensioning device and method of installing a strata support cable or tendon have at least the following advantages: 1. There is no longer a need for the traditional air return tube or hose and cable bulbing and therefore there are cost savings both in terms of labour and materials for the assembly and installation; 2. The hole or elongate cavity drilled into the geological strata need not be sized or sufficiently large to accommodate the air return tube or hose, and can therefore be drilled faster; 3. The smaller hole size reduces the need for cable bulbing to compensate for the reduced pull out strength in the larger holes; 7 4. The post-grouting procedure is simplified by exclusion of the return tube or hose and venting via the cable or tendon itself; 5. There is no need to protect the breather or air return tube of the prior art from damage or blocking up from the initial pre-grouting and anchoring steps; 6. In the event that some of the interstitial passageways are blocked, the multiplicity of the interstitial passageways allows air to be exhausted from the cavity via the unblocked interstitial passageways; and 7. The asymmetric shaped cable or tendon or cutting tool displaces the capsule packaging increasing the anchorage strength of the tendon. 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. For example, although the tensioning device of this embodiment is preferably fabricated from steel, any suitable material such as plastic or alloy would suffice. The tensioning device may also provide for a different porting or grout/resin entry point to that described. The cutting or piercing to is not limiting to the shape described but may extend to other asymmetric shapes and configurations. The steel strands of the braided cable or tendon may be fabricated of other materials such as plastics. The present embodiments are, therefore, to be considered in all respects as illustrated and not restrictive.