WO2004063530A1

WO2004063530A1 - Strata control method and apparatus

Info

Publication number: WO2004063530A1
Application number: PCT/AU2004/000020
Authority: WO
Inventors: Neil Stewart Hunt; Roland James Shaw; Grant Whitbourn
Original assignee: Celtite Pty Ltd
Priority date: 2003-01-09
Filing date: 2004-01-09
Publication date: 2004-07-29
Also published as: AU2003900074A0

Abstract

A tendon support assembly (10) for supporting a rock formation (6). A first end (12) of the assembly (10) is adhesively fastened in a borehole (2) drilled from a rock face (4) into the rock formation (6) and its second end (14) is fastened at the rock face (4). The tendon support assembly (10) has cables (16, 17, 18) extending side by side along the length of the assembly. In one form, the assembly (10) has spacers (26) spaced along the length of the assembly, holding the cables (16, 17, 18) away from each other, and a flexible tube (28) extending from the second end and supported by the spacers. In another form, the assembly (10) has an end cap (20) to which an end of each of the cables (16, 17, 18) is fastened and which has an aperture (44) therethrough, and means (70) for injecting a multi-component reactive adhesive through the aperture (44).

Description

Strata Control Method and Apparatus

Field of the Invention

This invention concerns the manufacture and use of support systems incorporating ^■ cables used to stabilise the ground in civil engineering and mining operations. It has particular applicability to roof stabilisation in underground mines.

Background to the Invention

Supporting ground and strata in civil engineering and mining has traditionally been done with soil nails, rock bolts, and cables. Situations and conditions arise in underground mines where supports are required which have a length greater than the height of the mining excavation. The use of cable as a tendon support in such operations allows the bolt to be bent as it is fed into its hole and thus long support lengths may be utilised.

Tendon supports are usually installed point anchored by a resin-based adhesive. To install a tendon support in the usual manner, firstly a borehole is drilled into the rock strata to be supported. A capsule, containing the components of a multi-component resin-based adhesive, is inserted into the borehole and then the cable bolt is pushed into the hole which in turn pushes the resin capsule to the back (otherwise called the blind end or deep end) of the hole. The tendon is inserted to its full extent in the hole and ruptures the resin capsule. The tendon is then rotated, typically via a mixing dolly which engages the exposed end of the tendon, and is mounted on the same drilling machine used to drill the borehole in the rock. Whilst rotating the tendon, thrust is also applied pushing the deep end of the tendon through the resin and mixing the resin. The rotation is stopped, the dolly is removed, and the resin allowed to cure, thus anchoring the end of the tendon at the deep end of the borehole. The strength of such a system relies upon the bond strength between the resin and the deep (or far) end of the tendon and the bond strength between the resin and the rock wall of the borehole.

If a pre-tensioned post-grouted tendon is required, a grout tube and breather tube are then inserted into the borehole alongside the tendon. These tubes have to be pushed far enough along the length of the tendon so as to ensure the remaining free length of tendon is fully encapsulated with grout. When the tubes are in place, suitable fastening fittings are attached to the exposed end of the tendon and a pretension is then applied to the tendon. The tendon is fastened in its tensioned state at the rock face and the tensioning equipment is removed. The free space in the borehole is then filled with grout via the grout tube.

The borehole in the above described example has a diameter significantly larger than the diameter of the tendon to be installed in order to have clearance to push into place the grout tube(s) and breather tube(s) alongside the tendon in the hole. This means that a substantial quantity of grout is required to fill the hole. Also there is a substantial time and labour requirement to undertake all the above described steps sequentially.

There is a need for an alternative cable bolting system which minimises the borehole diameter for any given tensile load requirement and also reduces the number and difficulty of the steps required to be performed to install a cable bolt.

There is also a demand for a high capacity, pretensionable, and post groutable tendon support. Such a support could be achieved by using in the conventional manner a single cable of larger diameter than presently used. However the load capacities of existing tensioning equipment would need to be upgraded and non standard fixing hardware provided for. Alternatively the higher capacity could be achieved by using a plurality of conventionally sized cables laid in parallel to each other in the borehole. This would allow the use of standard sized cable tensioning equipment and fastening hardware items but, with such a configuration, it is not possible mix the resin by rotating the cables in the conventional manner because they would have a tendency to wind together, and thus jam, in the hole.

An aim of the present invention is to provide a tendon support assembly made from cable, and a method of installation, which overcome or at least reduces the above described difficulties.

Summary of the Invention

Accordingly, in a first aspect the invention provides a tendon support assembly for supporting a rock formation, said tendon support assembly comprising:

(a) a first end adapted for insertion into a borehole drilled from a rock face into the rock formation and for fastening to the rock within the borehole, (b) a second end distal from said first end and adapted for fastening at the rock face,

(c) a plurality of cables extending side by side along the length of the assembly,

(d) a plurality of spacers, spaced along the length of the assembly, each said spacer holding the cables away from each other, and

(e) a flexible tube extending from said second end and supported by the spacers.

The flexible tube preferably extends from said second end to short of said first end. The tube preferably passes through a hole formed in each of the spacers. The flexible tube preferably passes through the centre of each said spacer. The spacers may hold the cables away from the tube. Preferably a circumferential clamp intermediate of an adjacent pair of said spacers holds the cables in contact with and surrounding the tube. The cables may all be affixed at said first end to an end cap. The end cap preferably has a hole therethrough, preferably a single hole centrally positioned, for passage of anchoring resin in use.

The cables may pass through and be affixed to a barrier plate which is spaced from the end cap and which is without a hole or holes for passage of anchoring resin therethrough.

Preferably the wire strands in each cable are spread or bulbed in the region between the end cap and the barrier plate.

Preferably the flexible tube extends along the tendon support assembly from said second end to between the barrier plate and that spacer closest the barrier plate.

The tendon support assembly may also include a multi-compartment dispenser containing the components of a multi-component reactant adhesive, the dispenser having its dispensing nozzle inserted within said hole through the end cap. Preferably the nozzle has attached to it a tubular static mixer which extends into the region between the end cap and the barrier plate.

In a second aspect the invention provides a method of stabilising a rock formation comprising:

(a) drilling a borehole into the rock formation to be stabilised,

(b) inserting into the borehole a first end of an assembly comprising: (i) a tendon having a plurality of cables extending side by side along the length of the tendon, and (ii) a plurality of spacers, spaced along the length of the assembly, supporting said cables relative to each other,

(c) causing a multi-component reactive adhesive to be mixed and dispensed around the tendon at said first end of the assembly,

(d) allowing the adhesive to set to thereby fasten said first end of the tendon to the rock in the hole, (e) tensioning the tendon and fastening it at the rock face,

(f) injecting a grout into the borehole through a tube which extends along the assembly and which is supported by each of the spacers, and

(g) allowing the grout to set.

In a third aspect the invention provides a tendon support assembly for a rock formation comprising:

(a) a first end adapted for insertion into a borehole drilled from a rock face into the rock formation and for adhesively fastening to the rock within the borehole,

(b) a second end opposite said first end and adapted for fastening at the rock face,

(c) a plurality of cables extending side by side along the length of the assembly, (d) at said first end, an end cap to which the end of each of the cables is fastened and which has an aperture therethrough, (e) spaced from said end cap but near said first end, an obstructing member adapted to at least substantially fill the cross section of the borehole and through which said cables pass, and (f) means for injecting a multi-component reactive adhesive through said aperture and into the space between the end cap and the obstructing member.

The aperture is preferably located centrally through the end cap. The obstructing member may have the form of a circular plate (which may hereinafter be called a barrier plate) and preferably has no open hole therethrough.

Preferably the wire strands in each cable are spread or bulbed in the region between the end cap and the obstructing member. Preferably the tendon support assembly has a plurality of spacers spaced along the length of the assembly, the cables pass through the spacers and each spacer holds the cables away from each other. Preferably a flexible tube extends along the assembly from said second end to between the obstructing member and that spacer closest the obstructing member.

In a fourth aspect the invention provides a method of stabilising a rock formation comprising:

(a) drilling a borehole into the rock formation to be stabilised, said borehole having an opening at the rock face and a blind end within the rock formation,

(b) inserting into the borehole a first end of a tendon support assembly, said assembly comprising:

(i) a tendon having a plurality of cables each extending for the length of the tendon, (ii) at said first end, an end cap to which each of the cables is fastened and which has an open aperture therethrough, (iii) spaced from said end cap, but near said first end, an obstructing member through which said cables pass, and (iv) a multi-compartment dispenser containing the components of a multi-component reactant adhesive, the dispenser having a dispensing nozzle inserted through said aperture, (c) thrusting the tendon deep into the borehole to compress the dispenser against the blind end of the borehole to thereby cause the adhesive components to be dispensed through the aperture in the end cap to at least substantially fill the volume in the borehole between the end cap and the obstructing member, (d) allowing the adhesive to set, and

(e) tensioning the tendon and fastening it at the rock face.

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 shows a discontinuous elevation view of a tendon support assembly according to one embodiment of the present invention;

Figure 2 shows an elevation view of the region around a first end of the tendon support assembly prior to its installation as shown in Figure 1 ; Figure 3 shows the other end of the tendon support assembly in Figure 1;

Figure 4 is a section view shown through C-C indicated on Figure 2;

Figures 5 and 6 are respectively a plan view and elevation view of one of the components shown in Figures 2 and 3,

Figure 7 is a perspective view of portion of the assembly in Figure 2; Figure 8 is a cut away side view of some of the components in Figure 7;

Figure 9 is an alternative arrangement to that shown in Figure 8;

Figures 10 and 11 are respectively a cross section and plan view of a component shown in Figure 7;

Figures 12 an 13 are respectively a cross section and plan view of an alternative configuration for the component shown in Figures 10 and 11 ;

Figures 14 and 15 are respectively a plan and elevation view of another component of the assembly shown in Figure 7;

Figures 16, 17 and 18 are respectively a plan view and two elevation views of an alternative configuration for the components shown in Figures 14 and 15; Figure 19 is a cross section view of a component used in some embodiments of the invention for storage and dispensing of reaction adhesive materials; and

Figure 20 is a cross section of a dolly utilised for installing the assembly shown in Figure 1.

Description of the Preferred Embodiment and Other Examples of the Invention

Referring to Figure 1, a tendon support assembly 10 has a first end 12 which is inserted in a borehole 2 drilled from a rock face 4 into a rock formation 6. The tendon support assembly 10 comprises a tendon 15 and an adhesive dispenser 70.

The borehole 2 has an opening 5 at the rock face 4 and a blind end 7 wihin the rock formation 6. The first end 12 of the assembly is fastened by resin adhesive 8 to the blind end 7 of the borehole. The second end 14 of the assembly 10 is fastened at the rock face 4 and the tendon 15 is tensioned. Grout 9 fills the remainder of the borehole.

As more clearly seen in Figures 2 to 4, tendon 15 has three steel cables 16, 17 and 18 which extend for the length of the tendon 15 from an end cap 20 to through and beyond a circular bearing plate 22. The construction of each cable has a central core wire around which is wound 6 other wires.

The tendon support assembly is made to the length necessary for its particular application. It would typically be between two and four metres long but may be of any length as required.

Close to the first end 12 but spaced from the end cap 20 is a circular barrier plate 24. Spaced along the assembly between the barrier plate 24 and the bearing plate 22 are spacer frames 26 at a spacing of approximately 500mm.

Plan and elevation views of a spacer 26 are shown as Figures 5 and 6. The spacer is moulded from nylon and has a rounded-cornered triangular frame-like or skeletal-like structure formed as three rings 27 equi-spaced around a fourth ring 30 all bounded by a peripheral band 31, the band 31 taking the shape of a rounded-cornered triangle. The cables 16, 17 and 18 pass through respective rings 27.

A flexible tube 28 extends along the length of the assembly from the second end 14 through the bearing plate 22 and through each spacer frame 26 until its outlet 29 shortly before the barrier plate 24. The tube 28 fits neatly through the central ring 30 in each spacer 26.

The cables 16, 17 and 18 are spaced from each other and from the tube 28 at each spacer 26. Half way between each spacer 26 a tie wire 32 is tightly wrapped around the cables 16, 17 and 18 to form a circumferential clamp which presses the cables hard against the tube 28 to give the configuration shown in Figure 4. Figures 2 and 3 show only the end regions of the tendon support assembly 10. There would in most circumstances also be additional replications of central segments having a spacer 26, lengths of cables 16, 17 and 18, tube 28 and a tie wire 32.

The cables 16, 17 and 18 are not fastened to the spacer 26 other than by the cables passing through the rings 27, so the spacer 26 is free to slide to a limited extend on the cable. Such sliding is limited by the effect of the tie wires 32 clamped around the assembly but the sliding is sufficient to allow the assembly 10 to be easily bent as it is fed into its borehole in use.

At the second end 14 of the tendon support assembly 10 each cable 16, 17 and 18 carries a conventional barrel and wedge cable fastening assembly 34 the configuration of which is known to those skilled in conventional prior art cable bolts. The barrel and wedge assemblies 34 are' used to fasten each cable as it is tensioned in use.

The configuration of the tendon 15 between the barrier plate 24 and the end cap 20 can be best seen in Figures 7 and 8. A ferrule 40 (omitted in Figure 8 for clarity) is clamped around each cable close to its end to prevent the end of the cable from fraying during the manufacturing process. The ends 36, 37 and 38 of the cables 16, 17 and 18 are welded 47 into holes 44 which pass through the end cap 20 and which are evenly spaced around the central aperture 42 in the end cap 20. Although there are four holes through the end cap 20, three of them are filled with cable ends while only one 42 is open. Detailed views of the end cap 20 are shown in Figures 10 and 11.

The cables 16, 17 and 18 pass through corresponding holes 45 in the barrier plate 24 and are fastened there by grub screws 46. Detailed views of the barrier plate 24 are also shown in Figures 14 and 15. Between the ferrules 40 and the barrier plate 24, the cables 16, 17 and 18 are expanded out so that the constituent wires 41 in each form a cage type structure 48 known in the cable bolting field as a Garford bulb. The cables are not expanded in this manner elsewhere in the tendon assembly.

When the tendon is in use, the end cap 20, the barrier plate 24 and the surrounding walls of the borehole form a chamber which in this specification is called the fastening chamber 49.

Between the expanded cage structures 48 and the barrier plate 24 a neoprene rubber disc 23 threaded onto the cables. The rubber disc 23 has three holes to accommodate the three cables respectively. The disc 23 is not shown in Figure 7 to assist clarity, but it is shown in Figure 8. The diameter of the rubber disc 23 is somewhat greater than the diameter of the barrier plate 24 such that the disc 23 contacts the wall of the borehole around its full periphery. Typical dimensions for a nominal 70mm diameter borehole would be to have a 65mm diameter barrier plate and a 75mm diameter rubber disc.

An alternative configuration to the end cap 20 is shown as the end cap 50 in Figures 9, 12 and 13. For this the cables 16, 17 and 18 are retained in blind holes 51 by grub screws 52 instead of the welds 47 used with the end cap 20.

An alternative construction of the barrier plate is shown in Figures 9, 16, 17 and 18. That version of the barrier plate 54 is split along lines 56, 57 and 58 into three portions 62, 63 and 64 which may then be clamped around the cables by means of socket headed bolts 60. One of the cables 16 is clamped between two portions 62 & 63, another cable 17 is clamped between two portions 63 & 64 respectively, while the third cable 18 is clamped between all three portions 62, 63 and 64. A ferrule 40 is clamped around each cable close to its end to prevent the end of the cable from fraying during the manufacturing process. Attached to the end cap 20 is an adhesive container/dispenser 70. The container 70 is shown in detail in Figure 19. It has the general form of a large syringe and contains in separate compartments 72 and 74 two components of a reactive resin mix. The compartments are coaxial within the container 70. The container 70 is constructed of a rigid plastic material. The central chamber 72 contains the catalyst and the annular chamber 74 contains the mastic component, there being ten times the volume of mastic than the catalyst. One end of the cartridge has two seals, an inner seal 71 for the catalyst and an annular outer seal 73 for the mastic. A double acting piston or plunger 75 pushes the seals 71 and 73 through the chambers 72 and 74 respectively, expelling the contents of the chambers simultaneously through a nozzle 76. A suitable dispenser of suitable adhesive is that sold by Exchem PLC in the United Kingdom under the name and code RESIFIX 3PLUS 46814A1

The nozzle 76 of the dispenser 70 carries an external thread 77 onto which is screwed a static mixer 78 having the form of a semi-flexible elongate tube containing a multitude of flow splitting and recombining channels. A suitable mixer is the KWM10 model static mixer from Ritter GmbH.

The nozzle 76 is held within the aperture 42 in the end plate of the tendon assembly and the static mixer 78 extends along the central axis of the fastening chamber 49 between the caged portions 48 of cables until at its outlet, it is close to the barrier plate 24. At least most of the mixer 78 is thus between the end cap 20 and the barrier plate 24.

When installing the support assembly in a borehole, the mixed contents of the dispenser 70 are discharged from the mixer 78 into the fastening chamber 49. The capacity of the dispenser 70 is approximately 20% more than the free volume of the fastening chamber 49 so any excess adhesive squeezes between the rock wall of the borehole and the peripheral face 21 of the end cap 20. A little adhesive might squeeze between the rock and the barrier plate 24 but this is largely prevented by the rubber disc 23 forming a seal. The pressure exerted on the disc 23 by the adhesive filling the fastening chamber causes the disc 23 to press hard against the barrier plate 24.

The relatively close fit of the end cap 22 to the wall of the borehole improves the likelihood that the fastening chamber 49 becomes completely filled with adhesive and that the adhesive therefore makes maximum possible contact with the wall of the borehole to which it is intended to fasten. Inclusion of the disc 23 is optional although preferable but, even if not included, the relatively small gap between the barrier plate 24 and the wall of the borehole improves the likelihood that the fastening chamber 49 is completely filled.

The mixing dolly 80 shown in Figure 20 has a socket 81 sized to accept simultaneously the ends of all three cables 16, 17 and 18. The socket has a tapered entry 82, a cylindrical main body 84, and a tapered blind end 86 at its driven end. The length of the socket 81 sets the length of the tail of the tendon which is allowed to remain protruding from the rock face. The correct length of tail is required in order to provide sufficient room to fit on the appropriate barrels and wedges while not leaving excess protruding. Such excess would be detrimental in a mine operation and the correct (minimum) tail length will maximise clearance and minimise snagging during later operations in the mine.

To install the assembly as described above, the borehole 2 of suitable length is predrilled from the rock face 4 in the conventional fashion. The hole diameter is a clearance fit for the end cap 20 and barrier plate 24. No further gap is required for tubing. The operator screws a static mixer 78 to the nozzle 76 of a dispenser 70 and feeds the mixer 78 and nozzle 76 through the central aperture 42 in the end cap 20. The nozzle/mixer is a friction fit in the aperture 42 which serves to retain the dispenser in position. The first end 12 of the assembly 10 including the dispenser 70 is then carefully inserted into the hole and the assembly 10 is pushed in after it. The tendon support assembly 10 is pushed into place first by hand, then by a drilling or bolting machine. To connect to the bolting machine, the three cable ends at the second end 14 of the tendon assembly 10 are fed into a socket 81 in a mixing dolly 80 which is mounted on a bolting machine. The machine presses the dolly forward and the assembly is thereby further pushed into the hole. Thrust only is applied to the assembly. It is not rotated.

When the first end of the assembly 10 reaches the blind end 7 of the borehole, the plunger 75 in the dispenser 70 is pressed inwards by contact with the blind end of the borehole. This forces the two components of the adhesive from the dispenser 70 through the nozzle 76, then through the static mixer 78, and into the fastening chamber 49. The plunger 75 can be seen extended (before activation) in Figure 2 whereas it is depressed in Figure 1.

The dispenser contains approximately 20% more adhesive than the capacity of the fastening chamber and the excess adhesive oozes between the peripheral edge of the end cap and the wall of the hole. The resin is fully cured within about one minute and then the dolly 80 is removed. The bearing plate 22 is slid onto the free ends of the three cables and each of the cables is then individually tensioned and fastened with a conventional barrel and wedge fastening assembly. Grout is then pumped through the central tube 28 which extends into the hole to close to the barrier plate 24 and, when the operator detects that the hole has been filled, the grout insertion equipment is removed and the grout allowed to set. The tube 28 is allowed to remain in the hole 2.

The above described arrangement provides a relatively high capacity anchoring system. Each of the cables in the assembly may be conventional 15.2mm diameter cable having a capacity of 3 x 25 tonnes giving 75 tonnes in total. If three 18.5mm diameter cables are used, each having a capacity of 40 tonnes, a 120 tonne capacity system would result.

If, as an alternative to the configuration of spacers 26 described above, spacers are configured as discs unperforated other than for the holes to accommodate the cables and central tube, they would serve to provide a greater resistance to the outward flow of the grout so that it greatly reduces the incidence of voids occurring between the strand and the grout.

The tendon assembly may be easily bent around tight radii which is important in low seam heights and other confined areas in mines.

In its broadest aspect, the present invention does not necessarily utilise grout when installing the tendon. However the use of grout does have several advantages, namely it provides resistance to corrosion, enhances the load transfer of the bolt, improves the stiffness of the system, and increases resistance to both horizontal and vertical stresses.

The construction of the tendon along most of it length is such that the spacers provide a large diameter for good load transfer to the grout. Having the position of each of the cables vary from close to the outer edge of the spacers to hard against the grout tube also improves the load transfer from each cable to the grout.

The use of the spacers and the ties also confers an additional degree of longitudinal rigidity on the tendon so that the thrust, whereby the resin is dispersed into the fastening chamber, may be transmitted through the tendon without it buckling.

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 instead of the tie wires 32 in some of its embodiments, the invention may instead utilise any other suitable type of circumferential clamp such as for example a crimped metal band, a rubber ring or a ring of heat shrink plastic shrunk into place. Also, although the tendon support assemblies described in the examples have three cables, the invention anticipates embodiments having two cables, or four or five cables for example. Also the cables may be of any suitable construction.

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.

Claims

1. A tendon support assembly for supporting a rock formation, said tendon support assembly comprising: - a first end adapted for insertion into a borehole drilled from a rock face into the rock formation and for fastening to the rock within the borehole,

- a second end distal from said first end and adapted for fastening at the rock face, a plurality of cables extending side by side along the length of the assembly, - a plurality of spacers, spaced along the length of the assembly, each said spacer holding the cables away from each other, and

- a flexible tube extending from said second end and supported by the spacers.

2. A tendon support assembly according to claim 1 wherein the flexible tube extends from said second end to short of said first end.

3. A tendon support assembly according to claim 1 or 2 wherein the flexible tube passes through a hole formed in each of the spacers.

4. A tendon support assembly according to claim 3 wherein the flexible tube passes through a hole in the centre of each said spacer.

5. A tendon support assembly according to any one of the previous claims wherein the spacers hold the cables away from the tube.

6. A tendon support assembly according to any one of the previous claims wherein a circumferential clamp intermediate of an adjacent pair of said spacers holds the cables in contact with the tube.

7. A tendon support assembly according to any one of the previous claims wherein the cables are affixed at said first end to an end cap.

8. A tendon support assembly according to claim 7 wherein the end cap has a hole therethrough for passage of anchoring resin in use.

9. A tendon support assembly according to any one of the previous claims wherein the cables pass through, and are affixed to, a barrier plate which is spaced from the end cap.

10. A tendon support assembly according to claim 9 wherein the wire strands in each cable are spread or bulbed in the space between the end cap and the barrier plate.

11. A tendon support assembly according to claim 9 or 10 wherein the flexible tube extends along the tendon support assembly from said second end to between the barrier plate and that spacer closest the barrier plate.

12 A tendon support assembly according to any one of claims 9 to 11 wherein the barrier plate has no hole for passage of anchoring resin therethrough.

13. A tendon support assembly according to claim 8 and including a multi- compartment dispenser containing the components of a multi-component reactant adhesive, the dispenser having its dispensing nozzle inserted within said hole through the end cap.

14. A tendon support assembly according to claim 13 wherein the nozzle has attached to it a tubular static mixer most of which is positioned between the end cap and the barrier plate.

15. A tendon support assembly according to any one of claims 8, 10, 11, 13 or 14 wherein said hole for passage of anchoring resin through the end cap is centrally positioned in the end cap.

16. A method of stabilising a rock formation comprising: drilling a borehole from a rock face into the rock formation to be stabilised, inserting into the borehole a first end of an assembly comprising: - a tendon having a plurality of cables extending side by side along the length of the tendon, and - a plurality of spacers, spaced along the length of the assembly and supporting said cables relative to each other, causing a multi-component reactive adhesive to be mixed and dispensed around the tendon at said first end of the assembly,

- allowing the adhesive to set to thereby fasten said first end of the tendon to the rock in the hole,

- tensioning the tendon and fastening it at the rock face,

- injecting a grout into the borehole through a tube which extends along the assembly and which is supported by each of the spacers, and

- allowing the grout to set.

17. A tendon support assembly for a rock formation comprising: a first end adapted for insertion into a borehole drilled from a rock face into the rock formation and for adhesively fastening to the rock within the borehole,

- a second end opposite said first end and adapted for fastening at the rock face,

- a plurality of cables extending side by side along the length of the ^■ assembly,

- at said first end, an end cap to which the end of each of the cables is fastened and which has an aperture therethrough, spaced from said end cap but near said first end, an obstructing member adapted to at least substantially fill the cross section of the borehole and through which said cables pass, and - means for injecting a multi-component reactive adhesive through said aperture and into the space between the end cap and the obstructing member.

18. A tendon support assembly according to claim 17 wherein the aperture is located centrally through the end cap.

19. A tendon support assembly according to claim 17 or 18 wherein the obstructing member has the form of a circular plate.

20. A tendon support assembly according to any one of claims 17 to 19 wherein the wire strands in each cable are spread or bulbed in the region between the end cap and the obstructing member.

21. A tendon support assembly according to any one of claims 17 to 20 wherein the tendon support assembly includes a plurality of spacers spaced along the length of the assembly, the cables pass through the spacers and each spacer holds the cables away from each other.

22. A tendon support assembly according to any one of claims 17 to 21 and including a multi-compartment dispenser containing the components of a multi- component reactant adhesive, the dispenser having its dispensing nozzle inserted within said aperture through the end cap.

23. A tendon support assembly according to claim 22 wherein the nozzle has attached to it a tubular static mixer most of which is positioned between the end cap and the obstructing member.

24. A method of stabilising a rock formation comprising: - drilling a borehole into the rock formation to be stabilised, said borehole having an opening at the rock face and a blind end within the rock formation, - inserting into the borehole a first end of a tendon support assembly, said assembly comprising:

- a tendon having a plurality of cables each extending for the length of the tendon, - at said first end, an end cap to which each of the cables is fastened and which has an open aperture therethrough,

- spaced from said end cap, but near said first end, an obstructing member through which said cables pass, and

- a multi-compartment dispenser containing the components of a multi- component reactant adhesive, the dispenser having a dispensing nozzle inserted through said aperture,

- thrusting the tendon deep into the borehole to compress the dispenser against the blind end of the borehole to thereby cause the adhesive components to be dispensed through the aperture in the end cap to at least substantially fill the volume in the borehole between the end cap and the obstructing member,

- allowing the adhesive to set, and

- tensioning the tendon and fastening it at the rock face.