EP2861826B1

EP2861826B1 - An anchor mechanism and a cable rock bolt

Info

Publication number: EP2861826B1
Application number: EP13731305.2A
Authority: EP
Inventors: Mieczyslaw Rataj
Original assignee: Sandvik Intellectual Property AB
Current assignee: Sandvik Intellectual Property AB
Priority date: 2012-06-18
Filing date: 2013-06-11
Publication date: 2017-07-26
Anticipated expiration: 2033-06-11
Also published as: AU2013203198A1; WO2013189785A3; MX348788B; PE20150219A1; CN104379871A; EP2861826A2; MX2014014854A; WO2013189785A2; CN104379871B; CL2014003409A1; AU2013203198B2

Description

Technical Field

The present invention relates to rock bolts suitable for stabilization of rock walls and faces, such as for use in the underground mining and tunnelling industry. The present invention concerns cable rock bolts that employ a flexible cable and a mechanical expander at the leading end of the cable, which is used to anchor or assist anchoring the rock bolt in a bore into which the bolt has been installed.

Background of Invention

The following discussion of the background to the invention is intended to facilitate an understanding of the invention. However, it should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was published, known or part of the common general knowledge as at the priority date of the application.
Rock bolts for use in underground mining include solid bar rock bolts and cable rock bolts. Solid bar rock bolts employ a rigid bar or rod and because the bar is rigid, the maximum length of the rock bolt is determined by the position and orientation in which it is to be installed and the dimensions of the space in the area installation. For example, if the rock bolt is to be installed in the roof of a mine tunnel perpendicular to the floor of the tunnel, then the length of the bolt can be no longer than the height of the tunnel.
In contrast, because cable rock bolts employ a flexible cable rather than a solid bar, cable rock bolts have the benefit that the length of the bolt can be greater than the dimensions of the space in the area of installation because the cable can be fed into a bore from a direction not aligned with the bore. Advantageously, the length of a cable rock bolt can be significantly greater than the height of the mine tunnel and in many circumstances, many times greater than the height of the tunnel.
A typical cable bolt installation involves drilling a bore into the wall of the mine, such as a 10m bore and then inserting the cable into the bore. A cement grout is then pumped into the bore about the cable to secure the cable within the bore. As part of the grouting process and before grout is pumped into the bore, a grout tube is often inserted just into the bore at the end proximate the mine wall and the bore is sealed or closed at that end with a fast curing grout about the cable and the grout tube. Grout can then be pumped into the bore through the grout tube. However, as the grout enters the bore, the air it displaces must be evacuated from within the bore. For this, a small diameter plastic tube can be attached to the cable of the cable bolt and the tube can extend completely to the inner end of the bolt, providing an exhaust passage for the displaced air. Other examples of cable bolts and their methods of installation are shown in the documents AU 2006 201 823 A1 , US 4 160 615 A and US 2 970 444 A . A first problem with a cable bolt installation of the above kind is that the process itself is cumbersome and time consuming, but more importantly, the cable bolt provides no wall reinforcement or support until the cement grout cures. This can take up to 2 days and thus the cable rock bolt provides limited or no support in that time. In addition, this type of cable bolt requires a separate operation to fit the rock plate and any other associated fittings to the trailing end of the cable as well as to tension the cable, given that these activities cannot be undertaken until complete curing of the grout has occurred. This can involve delays of one or two days. In many mining environments, work within the mine cannot continue until the cable bolts have been fully installed to provide the required support.
In solid bar rock bolts, mechanical expanding anchors can be used to anchor the leading or inboard end of the bolt to the inboard end of the bore. These mechanical anchors normally employ a threaded connection with the solid bar, so that rotation of the solid bar can create a relative axial movement between the bar and the anchor which is used to expand the anchor against the facing internal surface of the bore. By that expanding movement, the anchor grips the facing surface frictionally and anchors the inboard end of the solid bar within the bore.
An expanding anchor of the above kind which is used with solid bar rock bolts is not suitable for use with cable bolts. The threaded connection which is used with a solid bar rock bolt is not available with a flexible cable, and nor is it practical to rotate the cable to generate the required axial movement.
A mechanical anchor has been employed in cable rock bolts in the past, and in those installations, the anchor is fitted to the cable by a wedge arrangement. The wedge arrangement includes a wedge which is swaged to the cable, or otherwise fixed in place, and expander elements are positioned adjacent to the wedge, but axially toward the open end of the bore. Thus, as the cable is fed into a bore, the wedge enters the bore ahead of but followed closely by the expander elements. There is normally a slight overlap between the wedge and the expander elements.
The expander elements are attached to the cable, but in a manner to allow for axial movement relative to the cable, so that when required, the elements can move axially relative to and over the wedge to expand. To maintain the position of the elements adjacent to the wedge, a coil spring can be used to bias the elements into initial engagement with the wedge. The coil spring can bear at one end against the expander elements and at the other end against a stop or abutment swaged onto the cable at a position spaced from the expander elements. The biasing load applied to the expander elements is low and only sufficient to maintain the position of the expander elements relative to the wedge during installation of the cable rock bolt into a bore.
Accordingly, as the cable is fed into a bore, the wedge and expander elements remain together but no expansion takes place. While the expander elements will tend to scrape against the facing bore wall surface during installation, which will tend to shift the expander elements away from the wedge, the bias of the spring resists that movement. However, when the cable has reached its final position within the bore, a pull load applied to the cable moves the wedge axially relative to the expander elements and forces the expander elements to expand into frictional engagement with the bore wall. The cable is pulled until such time as the engagement between the expander elements and the wall is sufficient to anchor the leading end of the cable in place.
The pull load applied to the cable is usually in the order of 10 tonne. Once the required load has been applied to the cable so that the expansion of the anchor is complete and the cable is fully tensioned, the opposite or trailing end of the cable which extends outside the bore can be fixed in place to prevent return axial movement of the cable to maintain the applied tension in the cable.
The above form of cable rock bolt can be supplied in pre-cut cable lengths and with the mechanical anchor fixed to one end of the cable. Once the mechanical anchor has been activated, the cable bolt is then grouted into position. Thus, a grout tube is inserted into the open end of the bore and the bore end is sealed at that end with a fast curing grout. The grout can then be pumped into the bore through the grout tube and a plastic tube can be employed for exhausting air from within the bore as described above.
A major problem with cable bolts of the above kind is that they are manufactured off-site and so are supplied in fixed lengths only and with the mechanical expander anchor already attached to one end. This means that the cable bolt length cannot be customised to suit the drilled bore on site. The mine operators must buy the cable bolts at set lengths and drill bores to suit those lengths when stabilising a mine wall. Moreover, as discussed above, where it is necessary to allow the cement grout to cure before the installation procedure is finished, the installation process is cumbersome and time consuming.
More recently, cable rock bolts are now being installed by machine. In this form of installation, a bore is drilled first and then cement grout is pumped into the bore and the cable is then inserted into the bore. The cable is stored on a reel cassette in an installation machine. When the cable has been inserted fully into the bore, it can be cut close to the open end of the bore leaving a small amount of cable outside the bore, approximately 300mm in some installations, for attachment of a rock plate and tensioning device. However, the rock plate and the tensioning devices cannot be attached for at least 24 hours, to allow the cement grout to cure at least partially.
Thus, machine installation of cable bolts can allow different length bolts to be installed, but the installation still suffers from the same problems as discussed above, whereby attachment of end fittings to the cable bolt occurs as second operation once there has been partial or full curing of the cement grout. AU2006201823 discloses a cable bolt, which comprises a multi-strand tendon formed with one or more bulbs and a mechanical anchor assembly at one end thereof, the anchor assembly being arranged to grip mechanically with the interior of a bore hole. In mining, where movement of the rock surface is undesirable, cable bolts are used to stabilize the rock surface against collapse. There is provided a mechanical anchor assembly, which enables the securing of the cable bolt in a bore hole in a rock surface.
It is an object of the present invention to overcome or at least alleviate one or more disadvantages associated with the prior art.

Summary of Invention

According to the present invention there is provided, an expander mechanism for a cable bolt, as defined in claim 1. The present invention also provides a cable bolt including an elongate flexible cable as defined in claim 13. The present invention further provides a method for installing a cable bolt as defined in claim 14. An advantage of the expander mechanism of the present invention is that it can be connected to one end of a cable bolt at the site of installation, i.e. within a mine. Thus, the cable bolt does not need to be formed or assembled away from the site, but rather, a bore can be drilled in a mine wall, and a suitable length of cable can be selected to form the rock bolt, and the expander mechanism can then be attached to the leading end of the cable length that is selected. The present invention thus provides for flexibility in the length of the cable bolt which is not otherwise available in prior art cable bolts of the kind described above.
The present invention is also highly applicable to machine installation of cable bolts, where the cable is stored on a reel cassette. Advantageously, in this form of machine installation, the expander mechanism can be formed to be non-cylindrical, which allows the cylindrical bore into which the cable is installed to first be filled with cement grout and thereafter, the cable and the expander mechanism attached to the leading end of the cable can be pushed into the bore through the grout with the grout flowing about the expander mechanism. That is, by the expander mechanism being formed as non-cylindrical, space is available for grout to flow about the expander mechanism so that the expander mechanism can be pushed into the bore, despite the bore being filled with grout.
In addition, a cable bolt according to the invention can be fitted with a rock plate and thereafter tensioned, immediately after insertion into a grout filled bore hole by machine installation. By this installation, there is no need for a separate fitting on a later day of a rock plate and tensioning of the cable, and most importantly, the cable bolt can immediately provide the required ground support. Once the cement grout cures, the structural support provided by the cable bolt will merely be enhanced, as the full length of the cable will be bonded to the facing rock.
Where the present invention applies to a cable bolt installed by machine installation, after the cable has reached a desired position within the bore, the cable is cut, leaving a small amount of cable extending out of the bore to which a tension device is attached. In this arrangement, the length of the cable is directly related to the depth of the bore and is selected on site.
Installation of a cable bolt according to the invention by machine, particularly with the bore hole pre-filled with cement grout, can provide significant efficiencies in the installation process and significant cost reductions. These advantages arise given that the cable bolt can be installed in a single stage process, rather than the prior art process requiring a first installation stage followed by a second tensioning stage. Moreover, the invention allows the length of the cable bolt to be customised on site.
An expander mechanism according to the present invention can be supplied as an independent unit for use at a mine site, such as by machine installation. Thus, in the form in which the expander mechanism is not already attached to a cable, the gripper elements can be loosely housed within the housing until such time as a cable is inserted into the housing. The gripper elements themselves can be secured together circumferentially in a manner that allows the gripper elements to slide together axially relative to the housing and to shift apart upon axial movement in the second direction to increase the diameter of the central bore, and to shift together in the opposite first direction, to reduce the diameter of the central bore. An elastic O-ring can be employed for that purpose and the O-ring can be located in a circumferential groove formed in the outer surface of the gripper elements.
Alternative to loose housing of the gripper elements within the housing is to provide a bias which tends to shift the gripper elements in the first direction and into engagement, sliding engagement for example, with the internal surface of the housing. The bias can be provided in some forms of the invention by a coil spring that acts between the housing and the facing ends of the gripper elements. The housing can have a suitable spring engagement structure such as an end wall, or one or more abutments that the spring can engage. The spring can be aligned axially with the axis of the gripper elements.
As a cable is inserted into the housing, it will engage a leading end of the gripper elements for entry into the central bore defined by those elements. Typically the central bore will be of a smaller diameter than the diameter of the cable prior to the cable being inserted into the central bore. Thus, when a cable is inserted into the housing, the end of the cable will tend to push against the leading end of the gripper elements tending to move then axially in the second direction, so as to allow the gripper elements to separate radially to increase the diameter of the central bore and to allow the cable to enter the central bore. To facilitate entry of the cable end into the central bore, the gripper elements can define a bevelled or chamfered entry that the leading end of the cable can push into as it is inserted into the housing to cause the gripper elements to separate radially. Thus, each gripper element can have a bevelled or chamfered front end or edge about the central bore which can also assist to guide the cable end into the central bore. The housing of the expander includes an axial extension which extends from the rear end of the housing in the first direction and which includes an abutment remote from the rear end of the housing. The biasing arrangement which acts between the housing and the expander elements, acts in compression between the abutment of the axial extension and the expander elements. The biasing arrangement can comprise a coil spring.
The axial extension can be formed as a tube, which is connected to the rear end of the housing and which extends fully about the cable, or partly about the cable. The axial extension could be tubular but be split lengthwise for example into a plurality of separated extension portions. A pair of opposed extension portions could form the axial extension and those portions could be connected by one or more rings along the length of the portions. The axial extension can include a flange for forming the abutment and the flange can be formed remote from the rear end of the housing, such as at a distal end of the axial extension. In some forms of the invention, the flange can simply be a flared end of the tube.
In the above forms of the invention, attachment of a cable to the expander mechanism can be by inserting the cable through the axial extension and into the housing, and then into the central bore of the gripper elements. Where the axial extension is formed by a tube or extension portions, the tube and the gripper elements should be coaxial when the cable is inserted into them.
The axial extension can be formed as an integral part of the housing, or it can be connected to the part of the housing that houses the gripper elements, such as by a threaded, soldered, brazed or welded connection.
The use of a biasing arrangement which acts between the housing and the expander elements to bias the expander elements in the second direction, allows the expander elements to shift forward and back relative to the housing as the expander mechanism is inserted into a bore. That movement is required to accommodate normal variations in the diameter of the bore that occur when the bore is drilled, by allowing the diameter of the expander mechanism to vary in diameter responsive to variations in the bore diameter. Thus, where the bore reduces in diameter, the expander elements can shift in the first direction against the bias to reduce the outer diameter of the expander mechanism so the expander mechanism can move past the section of reduced diameter bore and then the expander mechanism can return in the second direction once the bore diameter increases in diameter.
This duplicates what has been said above.
An expander mechanism according to the present invention can have any number of expander elements. In some forms of the invention two expander elements are provided on diametrically opposite sides of the expander mechanism. In other forms of the invention, three or four expander elements can be provided. In most forms of the invention, the expander elements are spaced apart equidistantly about a central axis of the mechanism.
A support plate or member can be provided against which the expander elements can abut to limit axial movement of the expander elements relative to or away from the housing in the first direction. Where the support plate or member extends across the path that a cable takes through the expander mechanism, the plate or member can include an opening through which the cable can be inserted. The same opening can accommodate the axial extension in the forms of the invention in which the housing includes an axial extension.
The biasing arrangement which acts between the housing and the expander elements can be made to act between the housing and the support plate or member and in those forms of the invention in which the housing includes an axial extension, a coil spring can be made to act conveniently between an abutment or flange of the axial extension and the support plate or member.
The housing can be closed at the front end thereof to form an end wall. Advantageously, by closing the housing at the front end, the cable which is inserted into the expander mechanism is prevented from extending fully through the expander mechanism. By this arrangement, the end of the cable pushes against the closed front end of the housing when the cable is fed into a bore and thus the cable pushes the expander mechanism forward into the bore. By this arrangement, it is not necessary for the expander mechanism to otherwise grip the cable as it is inserted with the cable into the bore.
The front end of the housing can be formed as a closed structure, or the housing can include an opening which is closed by a closure member, such as a cap or plug for example. Where the front end of the housing is formed closed, the gripper elements can be inserted into the housing through the opening which is provided through the rear end of the housing. In alternative arrangements, where an opening is provided in the front end of the housing, the gripper elements can be inserted through the front end prior to closure with a closure member. Other elements that might be housed within the housing can also be inserted through the front or rear ends depending on the construction of the housing, and this includes the biasing arrangement, for example the coil spring, which acts against the housing and the gripper elements discussed above.
The closure member can be fixed in place relative to an opening formed in the front end of the housing in any suitable manner. Suitable arrangements include fixing the closure member by threaded connection, welding, brazing, soldering or crimping. It will be appreciated that whether the housing is formed with a closed front end, or whether it is formed with an opening that is closed by a closure member, it is intended that once the gripper elements are placed within the housing, that they are housed against release from the housing. By this arrangement, the expander mechanism can be manufactured and sent to a mine site with the gripper elements already positioned within the housing and ready to accept the end of a cable. By this arrangement, mine personnel can easily attach an expander mechanism to the end of a cable simply by inserting the cable into the housing which will automatically cause the cable end to enter the central bore defined by the gripper elements. The process is simple and does not require skilled personnel. In addition, no tools are required and no assembly of the expander mechanism is required on site. It is simply a matter of pushing the cable into the expander mechanism and holding the expander mechanism in place until the cable has entered the central bore of the gripper elements.
In some forms of the invention, the expander elements and the housing can be interlocked axially, so that the expander elements can move axially relative to the housing, but are substantially prevented from circumferential movement relative to the housing. This interlocking arrangement can provide benefits particularly for machine installation, because occasionally, the cable which is uncoiled from the reel of the installation machinery rotates slightly. This rotation can shift the expander elements relative to the housing to position them at a position which is not conducive to proper operation. Thus, interlocking between the expander elements and the housing which allows the required relative movement axially between the expander elements and the housing, but which restricts circumferential movement, can maintain the expander elements properly positioned relative to the housing despite any cable rotation.
While the interlock between the expander elements and the housing can take any suitable form, in some forms, an axially extending tongue and groove arrangement can be provided, whereby one of the expander elements and the housing includes a tongue component or components and the other of the expander elements and the housing includes a groove or grooves.
Where the expander mechanism of the invention is used for machine installation, the expander mechanism can be formed non-cylindrical in cross-section, to allow the anchor mechanism to push into a cylindrical bore which is filled with grout. Because the bore which is drilled into the mine wall will be cylindrical, a non-cylindrical cross-section of the expander mechanism will allow space about the expander mechanism for grout to flow past the expander mechanism as the expander mechanism is pushed into the bore. While the non-cylindrical cross-sectional shape of the expander mechanism can be any suitable shape, in some forms of the invention, the expander elements form a pair of diametrically opposite convex bore engaging surfaces for engaging the surface of a bore wall and side walls of the expander mechanism that extend between the bore engaging surfaces are spaced apart a distance which is less than the distance of the spacing between the bore engaging surfaces. The side walls can be straight or linear or otherwise shaped, such as curved. In some forms of the expander mechanism, the cross-section of the expander mechanism through the expander elements is somewhat oval shaped, with curved ends connected by relatively straight sides. Variations on this shape can be adopted, but for maximum grout flow, a major reduction in the cross-sectional area of the expander mechanism compared to the diameter of the bore is desirable.

Brief Description of Drawings

In order that the invention may be more fully understood, some embodiments will now be described with reference to the figures in which:

Figure 1 is a cross-sectional view of a cable bolt according to one form of the invention.
Figure 2 is a cross-sectional view of the expander mechanism of the cable bolt of Figure 1.
Figure 3 is a cross-sectional view taken through AA of Figure 1.
Figure 4 is a cross-sectional view of an alternative arrangement to the view of Figure 3.
Figure 5 is a cross-sectional view of an alternative expander mechanism according to the invention.

Detailed Description

With reference to Figures 1 and 2, there is illustrated an expander mechanism 10 and in Figure 1, the mechanism 10 is shown attached to the leading end of a cable 11. The cable 11 in Figure 1 is shown broken between the expander mechanism 10 and a tensioning device 12. The actual length of the cable 11 can be from 2m to 15m, although shorter or longer lengths are possible.
With reference first to Figure 2, the expander mechanism 10 includes a plurality of cable gripper elements 13 which can be seen in cross-section in each of Figure 3 and 4. The gripper elements 13 are each identical to one another and are formed as segments of a circle, and are dimensioned so that when the gripper elements 13 firmly grip the outside surface of the cable 11 as shown in Figure 1, gaps G (see Figure 3) between facing edges of the elements 13 remain.
As seen in Figures 1 and 2, the gripper elements 13 define a central bore 14 into which the leading end 15 of the cable 11 can be inserted. Figure 1 shows the leading end 15 inserted into the central bore 14, while Figure 2 shows the central bore 14 empty and ready for receipt of the leading end 15.
The gripper elements 13 are housed within a housing 16. The housing 16 defines an internal space which is conical and so has an inclined internal surface or wall 17. The surface 17 is inclined complementary to facing surfaces or walls 18 of the gripper elements 13. This arrangement enables for inclined sliding engagement between the surface 17 and the facing walls 18 of the respective housing and gripper elements, and the arrangement is that movement of the gripper elements 13 relative to the housing 16 in a first direction DF reduces the diameter of the central bore 14, whereas movement of the gripper elements 13 in a second and opposite direction DS allows the diameter of the central bore 14 to increase. The gripper elements 13 are biased in the first direction DF by a coil spring 20 which acts between the forward end wall 21 of the housing 16 and facing ends 22 of the gripper elements 13.
The expander mechanism 10 further includes a plurality - two in this case - of expander elements 25 which are positioned for sliding engagement against the outer surface 26 of the housing 16. Like the inclined sliding engagement which is available between the gripper elements 13 and the inclined surface 17 of the housing 16, the expander elements 25 have an internal inclined surface 27 which has an inclination suitable for sliding engagement against the outer surface 26 of the housing 16. The arrangement is such that axial movement of the housing 16 relative to the expander elements 25 in the first direction DF tends to shift the expander elements 25 radially outwardly, whereas relative axial movement in the second and opposite direction DS allows the expander elements 25 to shift radially inwardly.
Thus, the expander mechanism 10 allows for relative movement between the gripper elements 13 and the housing 16, and between the housing 16 and the expander elements 25. The provision of these two forms of relative movement will be described later herein in relation to the advantages they provide for installation of cable bolts into a bore drilled in a mine wall.
Describing the expander mechanism 10 further, the housing 16 includes an axial extension in the form of a tube 30 that is connected to the rear end 31 of the housing 16 by way of a threaded, brazed, soldered or welded connection. Alternatively, the tube 30 can be formed integrally with the housing 16. The tube 30 is connected to the internal surface of an opening 32 which is formed in the rear end 31 of the housing 16 and in Figure 1, it can be seen that the cable 11 extends through both the tube 30 and the opening 32.
It will be readily appreciated that while a tube 30 is shown in the figures, the tube could be alternative to that illustrated, and could, for example, comprise a circular band for connection to the opening 32, such as by threaded engagement or welding, and two elongate elements which extend from the band in the direction DF and which extend to an abutment of any suitable form. Other arrangements are possible and within the scope of the present invention.
The tube 30 defines a flange 33 at the distal end of the tube 30, or at the end of the tube 30 remote from the rear end 31 of the housing 16. The flange 33 forms an abutment against which a coil spring 34 can act. The coil spring 34 forms part of a biasing arrangement, which acts between the housing 16 (of which the tube 30 is one part) and the expander elements 25 which tends to bias the expander elements 25 in the second direction DS relative to the housing 16. Thus, as illustrated in Figures 1 and 2, the coil spring 34 acts in compression. The invention also covers arrangements in which the biasing arrangement acts in tension.
The opposite end of the coil spring 34 acts against a support plate 35 which abuts against the rear ends 36 of the expander elements 25. The support plate 35 includes an opening 37 through which the tube 30 extends. By providing abutting contact between the support plate 35 and the expander elements 25, the expander elements 25 can expand radially outwardly, i.e. they can shift radially relative to the plate 25.
In Figure 2, a sleeve 38 is shown extending about the outside the expander elements 25. That sleeve 38 is applied to the expander mechanism 10 following its assembly, to maintain the expander elements 25 in the position shown in Figure 2. The sleeve 38 can be removed for insertion of the expander mechanism 10 into a bore in a mining wall, or it can disintegrate as part of the installation process. The sleeve can be a rubber, an elastic plastic, a metal band or other suitable material.
With reference to Figure 2, it can be seen that in absence of a cable having been inserted into the expander mechanism 10, that the gripper elements 13 are positioned adjacent the rear end 31 of the housing 16 under the influence or load of the biasing spring 20. Moreover, the expander elements 25 have only a small overlap at their front ends 39 with the outer surface 26 of the housing 16. In contrast, in Figure 1, the leading end 15 of the cable 11 has been inserted into the expander mechanism 10 and the mechanism 10 as attached to the cable 11 has been inserted into a bore 40 which has been drilled into a mine wall 41. In the Figure 1 arrangement, the cable grippers 13 have moved in the direction DS within the housing 16. Movement in that direction has increased the diameter of the central bore 14 of the gripper elements 13 to allow the leading end 15 of the cable 11 to be accommodated within the central bore 14. Moreover, the expander elements 25 are shown in Figure 1 in a position of significant overlap with the outer surface 26 of the housing 16.
In the position shown in Figure 1, the cable gripper elements 13 are in firm gripping connection with the leading end 15 of the cable 11. The surfaces of the gripper elements 13 that form the central bore 14 are shown to be serrated in Figures 1 and 2, and that enhances the grip made between the leading end 15 of the cable 11 and the gripper elements 13.
Likewise, the outer surfaces 42 of the expander elements 25 are serrated for enhancing the frictional grip between the elements 25 and the facing surface of the bore 40.
The manner in which the transition occurs between the expander mechanism as shown in Figure 2 and as installed in Figure 1 will now be described.
To attach the leading end 15 of the cable 11 to the expander mechanism 10, a very simple process is necessary, which requires no special tooling skill. All that is necessary is that the leading end 15 be fed into the tube 30, so that it enters the housing 16. Upon that entry, the very forward end of the cable 11 will engage the gripper elements 13 and as shown in Figures 1 and 2, those ends 43 are chamfered so as to help to locate the leading end 15 relative to the gripper elements 13 to enter the bore 14.
Further feeding of the cable 11 into the expander mechanism 10 will force the gripper elements 13 to shift in the direction DS against the biasing influence of the coil spring 20 and because the leading end 15 of the cable 11 is bearing against the chamfered ends 43 of the gripper elements 13, the gripper elements 13 will be forced radially outwardly, to increase the diameter of the central bore 14. The gripper elements 13 can slide against the inclined side wall 17 as they move in the direction DS.
The diameter of the cable 11 will determine how much shifting movement of the gripper elements 13 is required in the direction DS for the central bore 14 to increase in diameter sufficient for the cable end 15 to enter the central bore 14. A typical amount of movement will be in the order of 5 to 30mm.
The leading end 15 will eventually enter into the central bore 14 and once it engages the forward end 21 as shown in Figure 1, further feeding of the cable 11 into the expander mechanism 10 ceases. The expander mechanism 10 is now connected to the leading end 15. As will be readily apparent, that connection process has been extremely simple. The expander mechanism 10 is not anchored to the leading end 15 but is connected to the leading end.
The cable 11 can now be feed into the bore 40 of Figure 1. The leading end 15 of the cable 11 pushes the expander mechanism 10 into the bore by its engagement with the forward end 21. As the feed occurs, the outer surface 42 of the expander elements 25 might scrape against the wall of the bore 40. That scraping movement can shift the expander elements 25 in the direction DF, but the arrangement of the tube 30 and the coil spring 34 maintains the expander elements 25 in an overlapping position with the outer surface 26 of the housing 16, while still allowing easy insertion of the expander mechanism 10 into the bore 40. The amount of movement of the expander elements 25 depends on how closely fitted the expander mechanism 10 is within the bore 40, or in other words, it depends on the relative dimensions of the external diameter of the expander mechanism 10 relative to the diameter of the bore 40.
When the expander mechanism 10 and cable 11 have been pushed to the final position as shown in Figure 1, the cable 11 can be tensioned through the tensioning device 12, which requires a pull load to be applied to the cable 11 in the direction DF. That pull load is applied to the trailing end 46 of the cable 11 and causes the gripper elements 13 to shift relative to the housing 16 in the direction DF so as to reduce the diameter of the central bore 14 and thus to firmly engage the leading end 15. Moreover, the pull load will tend to pull the housing 16 relative to the expander elements 25 in the direction DF to radially expand the expander elements 25 against the surface of the bore 40 and to grip that surface. The pull load that is applied can be in the region of 10t and by that load, each of the leading end 15 and the surface of the bore 40 is firmly gripped and thus the cable 11 is firmly anchored at the inner end of the bore 40. The tensioning device 12 can then be shut off, and this can occur simply by a "barrel and wedges" arrangement comprising the barrel 44 and wedges 45, which grip the trailing end 46 of the cable 11 against a rock plate 47, which fits over the open end of the bore 40. Once the tensioning device 12 has been shut off, the cable bolt comprising the expander mechanism 10, the cable 11 and the tensioning device 12 is now firmly anchored and providing structural support for the mine wall 41.
The present invention as illustrated in the figures is suitable for use with manual installation, or machine installation. With machine installation, the process can include filling the bore 40 with a cement grout prior to installing the cable bolt. For that, the expansion mechanism 10 can be formed to have a non-circular shape, so that when the expander mechanism 10 is pushed into the grout filled bore, gaps on one or either side of the mechanism 10 allow grout to flow past the mechanism 10 so that the mechanism 10 can enter the bore as required. With reference to Figures 3 and 4, the wall of the bore 40 is shown in broken outline, and it can be seen that a space S exists on either side of the mechanism 10 between a pair of diametrically opposite convex bore engaging surfaces 50 of the expander elements 25. It is to be appreciated that the side walls 51 are shown completely flat and straight and that in practice, this is unlikely to be the case. Nevertheless, the side walls 51 extend between the surfaces 50 to allow the spaces S to exist within the bore 40 on either side of the expander mechanism 10.
Figures 3 and 4 additionally illustrate an interlock which exists between the housing 16 and the expander elements 25. The interlock comprises an axially extending tongue 52 of the housing 16 and an axially extending groove 53 of the expander elements 25. This can be reversed if required.
Figure 4 shows substantially the same arrangement as that in Figure 3, apart from the interlocking arrangement which differs from Figure 3. Thus, Figure 4 shows an interlocking arrangement comprising a tongue 54 of the housing 16 and a groove 55 of the expander elements 25. The surface 56 from which the tongues 54 extend is inclined in Figure 4, whereas it is straight in Figure 3. In other respects, there is no difference between the arrangement in Figure 4 compared to Figure 3.
Figure 5 illustrates a slightly different expander mechanism to that of Figure 2. In Figure 5, components which are the same as Figure 2 have the same reference number plus 100. Thus, the expander mechanism 100 includes a sleeve 138, expander elements 125, a tube 130 and gripper elements 113.
The housing 110 differs slightly to the housing 16 of the earlier figures and will form the subject of the following discussion. In Figure 5, the housing 110 includes an opening 111 at the leading end 112 thereof which, in Figure 5, is shown closed by a closure member 113. The closure member 113 is shown fixed in place in the opening 111 by a crimp 114, but the closure member 113 could alternatively be welded, brazed, soldered, threaded or otherwise secured into the position shown.
The advantage of the arrangement shown in Figure 5 is that the opening 111 can be employed to insert the gripper elements 113 and the spring 120 into the housing 110. Once those components have been inserted and any other components required to be inserted, the closure member 113 can be installed and can be fixed in place by crimping or other mechanism as discussed above. The closure member also provides significant support against radial collapse of the housing 110 when the tensioning load is applied to the cable 11 and the expander elements 25 move radially outwardly against the inclined surfaces 26.
Figure 5 also shows an O-ring 115 within a circumferential groove for holding the gripper elements together within the housing 110. The same arrangement could be applied to the gripper elements 13 of the earlier figures.
The alternative to the arrangement in Figure 5 is the arrangement shown in Figure 2, whereby the components within the housing 16 are inserted through the opening 32 in the rear end 31. However, as shown in Figure 5, the opening 111 can be larger than the opening 32, so allowing for easier insertion of the components into the housing 110.
The invention described herein is susceptible to variations, modifications and/or additions other than those specifically described and it is to be understood that the invention includes all such variations, modifications and/or additions which fall within the spirit and scope of the present disclosure.
Throughout the description and claims of this specification the word "comprise" and variations of that word, such as "comprises" and "comprising", are not intended to exclude other additives, components, integers or steps.

Claims

An expander mechanism (10) for a cable bolt, including
a plurality of cable gripper elements (13) arranged to define a central bore (14) into which a cable (11) can be inserted,
a housing (16) which houses the gripper elements (13),
the housing (16) and the gripper elements (13) having facing inclined surfaces (26) for inclined sliding engagement so that axial sliding movement of the gripper elements (13) relative to the housing (16) in a first direction reduces the diameter of the central bore (14) and axial sliding movement of the gripper elements (13) in a second and opposite direction increases the diameter of the central bore (14),
a plurality of expander elements (25) arranged for sliding engagement against an outside surface of the housing (16), the sliding engagement being such that movement of the housing (16) in the first direction relative to the expander elements (25) tends to shift the expander elements (25) radially outwardly,
the housing (16) having front and rear ends, an opening being provided through the rear end through which a cable (11) can be inserted for insertion into the central bore (14) of the gripper elements (13),
a biasing arrangement (34) acting between the housing (16) and the expander elements (25) biasing the expander elements (25) in the second direction relative to the housing (16), characterised by the housing (16) including an axial extension (30) which extends from the rear end of the housing (16) in the first direction and includes an abutment (33) remote from the rear end of the housing (16), the biasing arrangement (34) acting in compression between the abutment (33) and the expander elements (13).
An expander mechanism (10) according to claim 1, the amount of axial sliding movement of the gripper elements (13) relative to the housing (16) being between 5 and 30mm.
An expander mechanism (10) according to claim 1 or 2, the gripper elements (13) being biased in the first direction.
An expander mechanism (10) according to claim 3, the gripper elements (13) being biased in the first direction by a coil spring (20) that acts between the housing (16) and facing ends of the gripper elements (13).
An expander mechanism (10) according to any one of claims 1 to 4, the gripper elements (13) being secured together circumferentially in a manner that allows the gripper elements (13) to slide together axially relative to the housing (16) and to shift apart upon axial movement in the second direction to increase the diameter of the central bore (14) and to shift together upon axial movement in the first direction to reduce the diameter of the central bore (14).
An expander mechanism (10) according to claim 1, the biasing arrangement comprising a coil spring (34).
An expander mechanism (10) according to claim 1 or 6, the axial extension comprising a tube (30) connected to the rear end of the housing (16) and extending about the cable (11), the tube (30) including a flange (33) forming the abutment and the flange (33) being formed remote from the rear end of the housing (16).
An expander mechanism (10) according to any one of claims 1 to 7, the front end of the housing (16) being closed and the front end of the housing (16) including an opening which is closed by a closure member (113)..
An expander mechanism (10) according to claim 8, the closure member (113) being threaded, welded or crimped into the opening to close the opening.
An expander mechanism (10) according to any one of claims 1 to 9, the expander mechanism (10) being non-cylindrical in cross section.
An expander mechanism (10) according to claim 10, the expander elements (25) forming a pair of diametrically opposite convex bore engaging surfaces (50) for engaging a surface of a bore wall and a pair of side walls extending between the bore engaging surfaces (50), the distance between the bore engaging surfaces (50) being greater than the distance between the side walls.
A cable bolt including an elongate flexible cable having leading and trailing ends and an expander mechanism (10) according to any one of claims 1 to 11 attached to the leading end of the cable (11).
A cable bolt including;
an elongate flexible cable having leading and trailing ends,
an expander mechanism (10) assembly according to claim 1 attached to the leading end of the cable (11) such that movement of the housing in the first direction relative to the expander elements (25) tends to shift the expander elements (25) radially outwardly to grip a facing wall surface of a bore.
A method of installing a cable bolt, including:
drilling a bore into a rock wall,

attaching an expander mechanism (10) according to any one of claims 1 to 19 to a leading end of a cable (11), by inserting the leading end through the opening in the rear of the housing (16) and into the central bore (14) of the gripper elements (13),

at least substantially filling the bore with grout and feeding the cable (11) into the bore,

upon the cable (11) reaching a desired position within the bore, applying tension to the cable (11) tending to shift the gripper elements (13) in the first direction to grip the cable (11) and tending to shift the housing (16) relative to the expander elements (25) in the first direction to shift the expander elements (25) radially outwardly into engagement with the bore wall so as to anchor the leading end of the cable (11) within the bore (14).
A method according to claim 14, the method including cutting the cable (11) from a larger length of cable upon the cable (11) reaching a desired position within the bore (14).