WO2015013740A1

WO2015013740A1 - A grouted friction rock bolt

Info

Publication number: WO2015013740A1
Application number: PCT/AU2014/000754
Authority: WO
Inventors: Gary Davison
Original assignee: GAZMICK Pty Ltd
Current assignee: GAZMICK Pty Ltd
Priority date: 2013-07-29
Filing date: 2014-07-28
Publication date: 2015-02-05
Anticipated expiration: 2016-01-29
Also published as: AU2014295889B2; AU2014295889A1

Abstract

A rock bolt for the stabilisation of earthen formations such as the roof or side walls of an underground mine or above ground rock cut and/or method of installation thereof, comprising a hollow elongate body portion having an opening extending parallel to the longitudinal axis of the body portion, and an elongate closure member aligned to substantially cover said opening, the closure member having apertures located periodically along its length.

Description

A GROUTED FRICTION ROCK BOLT FIELD OF THE INVENTION

[0001] The present invention relates generally to the stabilisation of earthen formations such as the roof or side walls of an underground mine or above ground rock cut. It also relates generally to devices used to anchor, secure or stabilise earthen formations.

[0002] The present invention relates particularly to the anchoring of rock bolts in earthen formations and reduction of known difficulties associated with such devices.

[0003] Further, the present invention provides a cartridge and method of installation of rock bolts that reduces known difficulties associated with inserting filling material into rock bolts and installation of such filled devices. 0004] It will be convenient to describe the present invention in relation to man-made underground structures such as tunnels, however it should be appreciated that the present invention is not so limited and can be used to stabilise both above ground and underground earthen structures, whether man-made or naturally occurring. Furthermore, vvhiie it will also be convenient to describe the present invention with reference to the mining industry, it should be appreciated that the present invention is not limited to mining applications and can be used by other industries such as civil engineering and geotechnical engineering.

BACKGROUND OF THE INVENTION

[0005] The discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain related art problems by the inventor and, moreover, any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention, it should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein. [0006] ft is to be appreciated that any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the present invention. Further, the discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain related art problems by the inventor. Moreover, any discussion of materia! such as documents, devices, acts or knowledge in this specification is inciuded to explain the context of the invention in terms of the inventor's knowledge and experience and, accordingly, any such discussion should not be taken as an admission that any of the material forms part of the prior art base or the common general knowledge in the relevant art in Australia, or elsewhere, on or before the priority date of the disclosure and claims herein.

[0007] Rock bolts and dowels have been used for many decades to support earthen formations for mining and civil engineering.

[0008] Where used herein the term 'rock bolt' is intended to refer to any elongate anchor for location in drill holes to stabilise rock excavations and may alternately be known by names such as 'friction stabiliser rock bolt', 'roof-bolt', 'friction stabiliser' or 'split-set' bolt. Rock bolts transfer load from the unstable exterior of an earthen formation, to the confined and much stronger interior of the rock mass.

[0009] Traditional rock bolts generally consist of steel rods with a mechanical or chemical anchor at one end and a face plate and nut at the other end. In a more recent version, well known 'split set' rock bolts have an elongate tube is generally of circular or C- shaped cross-section and having a longitudinal channel or groove along the entire length of the tube. Split set rock bolts are usually installed into a hole drilled into an earthen formation using an impact tool.

[0010] Rock bolts essentially rely on two physical parameters to provide load support, namely: (i) strength - particularly tensile strength and so some degree, shear strength, and (ii) friction or transmitted friction between the rock bolt body, or some part of it and the rock.

[0011] In the "spilt set' variation, the diameter of the drill hole is slightly less than the outer diameter of the elongate tube, so that during installation, the elongate tube is subject to radial compressive force. The compressive force causes the channel or groove to at least partly close, reducing the diameter of the tube to fit the diameter of the hole. This ensures that there is at least some frictional engagement between the elongate tube and the earthen formation.

[0012] Strength is relatively simple to achieve but friction is more difficult, especiall for 'split sets'. Rock bolts of the prior art principally rely on mechanical coupling devices, grout, and the spring effect of the C section split set described above and resistance to deformation of a steel section.

[0013] Some commercially available rock bolts are manufactured in a range of diameters, each diameter having a different recommended load carrying capacity. When they are inserted into drill holes, they are distorted to the shape of the drill hole/drill hole wall by application of pushing force or by application of water under high pressure. In order to achieve suitable distortion under pressure, yet maintain high tensile strength it is necessary to use thin walled tubes of expensive steel.

[0014] Split set rock bolts used in underground mines are typically about 2.4 metres long, and have an uncompressed diameter of approximately 46mm. This diameter of rock bolt would typically be installed in a drill hole having a nominal diameter of 43.5mm. However the actual diameter of the hole will vary along its length between approximately 43 and 46 mm. In particular, the diameter of the drill hole can vary markedly where the drill hole passes through unstable areas, or soft rock that crumbles, or areas where rocks dislodge from the side of the drilled hole. Figure 1 graphically illustrates this variance.

[0015] Hence if a 46mm rock bolt is installed into an approximately symmetrical drill hole the width of the channel or groove in the tube will vary with the diameter of the drill hole, conforming to variations in the drill hole diameter. The elongate tube of the rock bolt will be squeezed by the earthen wall of the hole where the diameter is less than 46mm giving good frictional engagement. A "spilt set' rock bolt having a tube of 46mm diameter, installed in this manner, can develop friction of approximately 4 tonnes per metre of embedment. However, the rock bolt tube will have less radial reactive force and lower friction in regions where the diameter of the drill hole is greater than 45 mm. [0016] Filler: For short term applications, rock bolts are generally left ungrouted. However for more permanent applications, high load areas, or in rock in which corrosive groundwater is present, the space between the bolt and the surrounding earth can be partially or completely filled with a filler such as cement or resin grout. Grouting changes a rock bolt from a ductile object into a stiff object and locks it in place creating a higher friction than is normally achieved. Shear strength is also increased in post grouted "spilt sets" the grout subsequently sets locks in the variable diameter of the boit caused by the variable diameter of the rockbolt hole and bonds to the rock .also increasing friction.

[0017] It is known that by providing a grout internally to the rock bolt, after the rock bolt is embedded into the hole, the support capacity of the rock bolt can be, depending upon the rock type, increased to approximately 12-16 tonnes per meter of embedment. The grout, once set, substantially reduces any subsequent radial deformation of the rock bolt that may occur as a result of the rock bolt being subject to increased forces by movement of surrounding material. Further, any load acting to dislodge or force the rock bolt out of the hole will be resisted as the load attempts to force larger diameter portions of the rock bolt body through narrower portions of the hole in which it is installed. Generally, grouting a friction rock bolt substantially increases the load carrying capacity of that rock bolt.

[0018] However, there are problems associated with the grouting of rock bolts. It can be difficult to pump grout into a drill hole such that the grout travels the entire length of the rock bolt tube. Often air is trapped inside the drill hole and cannot be vented to make way for the flow of grout. Also, rock bolts are often inserted into the vertical drill holes in mine roofs. If grout of low viscosity or slow setting time is used it can tend to fall out of the drill hole under the action of gravity.

[0019] The confined area of a mine tunnel also presents difficult working conditions that make it necessary to install rock bolts in two steps. In the first step the holes are drilled and the rock bolts inserted. Then, due to the limited working space the drilling crew retire and remove their drilling equipment to make way for the large size pumping equipment. In the second step the pumping crew bring their pumping equipment into the tunnel to pump grout into the drill holes. [0020] The two-step approach to installing and grouting rock bolts has the disadvantage of causing delays as the two separate crews bring in and remove equipment. There can also a requirement for separate drilling and grouting crews. The two-step process is considered costly, cumbersome and time consuming.

[0021] Some examples of prior art rock bolts are illustrated, in cross section, in Figures 2a, 2b, 2c and 2d.

[0022] US reissue patent Re 30,2.56 (Scott) discloses a rock bolt similar to that illustrated in Figure 2a. The rock bolt consists of a tube with a slot defined by edges 5 and 6 which are separate prior to installation. During the installation process, in those parts of a hole which are narrower than the nominal diameter of the rock bolt, the edges 5 and 6 are forced together (as shown by arrow 7). if portions of the hole are very narrow, the edges 5 and 6 will butt together and thus restrict any further radial compression of the rock bolt. This would make installation of the rock bolt very difficult or in some cases impossible, it has also been found in practice that the edges 5 and 6 and the inner and outer surface area are relatively exposed to water (from underground seepage) and over time the rock bolt will tend to rust and fail.

[0023] US patent 4,012,913 (Scott) discloses a rock bolt similar to that illustrated in Figure 2b. The rock bolt has offset edges 8 and 9 which are separated prior to installation. During the installation process, in the narrower parts of the hole, the edges 8 and 9 will be moved past each other as shown by arrow 10. However, this deformation causes further problems after installation as with further radial compression, the external surface area of the rock boit reduces thus decreasing the area which the surrounding material has the ability to develo a frictional force to act upon the rock bolt. Radial compression of a rock bolt of this type subsequent to installation can result in premature disiodgement of the rock bolt which is unsafe.

[0024] If this type of rock bolt is installed in a roof section of an underground mine, and sufficient load is applied to the rock bolt, say by a portion of the roof weakening and applying extra load to the rock bolt acting to dislodge the rock bolt, then just as the rock bolt exhibits compression and expansion as it is inserted into the hole, equally and conversely, the rock bolt can expand and compress as it is forced out of a hole under the toad of the mine roof section, in other words, the applied load may dislodge the rock bolt from the hole, with the rock bo!t deforming in the direction of arrow 10 as the rock bolt is forced out of the hole and passes the narrower parts of the hole. As a result, it is generally considered that the effective bond strength due to friction between surrounding material and rock bolts of this type is relatively low.

[0025] A further problem with rock bolts of this type is a problem referred to as 'tangential gap'. Figure 2c illustrates this problem. Figure 2c is a representation of the part of Figure 2b "Compressed" marked "A". As previously mentioned, as the rock bolt is installed in a hole, edges 8 and 9 are moved passed each other. However, proximate the edge 8, there is always a gap 10b (referred to as the tangential gap) which is formed as a result of the rock bolt wa!l 9 moving inwardly of the rock bolt wall 8.

[0026] The gap is formed between the rock bolt wall 9 and the hole wall 10a, This gap reduces the overall frictional engagement of the rock bolt with the earthen formation into which the rock bolt is installed as there is no frictional engagement along the portion of the rock bolt proximate the gap 10b.

[0027] US patent 5,297,900 (Witzand) discloses a rock bolt similar to that illustrated in Figure 2d. The rock bolt has edges 12 and 13 that are separated prior to installation. The rock bolt has a V shaped portion extending substantially along the entire length of the rock bolt. The V shaped portion is described as providing greater frictional resistance to movement between the bolt and the mine roof as compared with slotted rock bolts (as illustrated in Figures 2a and 2b).

[0028] During the installation process, in those parts of a hole which are narrower than the nominal diameter of the rock bolt, the edges 12 and 13 are forced together (as shown by arrow 14). As occurs in the rock bolt of Figure 2a, if portions of the hole are very narrow, the edges 12 and 13 will butt together and thus prevent any further circumferential deformation of the rock bolt. This would make installation of the rock bolt very difficult or in some instances impossible. It has been also found in practice that many parts of the 'V^* shape remain open and exposed to the earthen hole wall and are thus relatively exposed to water (from underground seepage) and over time the rock bolt will tend to rust and fail. [0029] The V shaped portion, being internal to the rock boit, is considered to inhibit the flow of grout as it is pumped internally along the length of the rock bolt. Further, it is difficuit to insert grout externaiiy a!ong the rock bolt proximate the V shaped portion which is desirable in order to reduce the likelihood of further radial compression of the rock bolt subsequent to installation.

[0030] International patent application WO 03/014517 (Davison) describes a rock bolt of the type illustrated in Figures 3a and 3b. The rock bolt comprises an elongate body portion, having an eiongate opening that can be covered by an elongate closure member, thus reducing the likelihood of a cartridge inside the body portion becoming ensnared on the internal wall of a drill hol during insertion of the rock bolt. It is an object of the present invention to alleviate at least one of the problems associated with the prior art.

SUMMARY OF THE INVENTION

[0031] An object of the present invention is to improve the speed and efficiency with which a rock bolt may be located and secured in a drill hole.

[0032] A further object of the present invention is to improve the retention and load capacity of a rock bolt in a drill hole.

[0033] A further object of the present invention is to alleviate at least one disadvantage associated with the related art.

[0034] It is an object of the embodiments described herein to overcome or alleviate at least one of the above noted drawbacks of related art systems or to at least provide a useful alternative to related art systems.

[0035] In a first aspect, the present invention provides a rock bolt for earthen stabilisation, the rock bolt comprising: a hollow elongate body portion having an opening extending parallel to the longitudinal axis of the body portion, and an elongate closure member aligned to substantially cover said opening and extending adjacent an inner wall of the body portion, wherein the closure member has apertures located periodically along its length.

[0036] In a second aspect, the present invention provides a method of installing a rock bolt, the method including the steps of: a. drilling a hole in the earthen region to be stabilised, b. introducing a filler inside the elongate body portion, and c. locating the rock bolt of the present invention in the drill hole wherein part of the filler exudes through one or more of the apertures.

[0037| Typically the drill hole has a diameter that is less than the diameter of the rock bolt to be installed.

[0038] Other aspects and preferred aspects are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention.

[0039] Throughout this specification the term 'filler' is a substance such as grout, cement and/or filler. The term 'filler' is intended to include 'expanding substances of any kind and/or expanding fillers' which are substances that can be introduced to a rock body in a fluid or mud like form and subsequently expand and transition to a solid form. The expanding filler is usually inserted into the rock bolt fluid or mud like form having been activated and requires a period of time to 'set' or 'cure' thereby transitioning to a solid form.

[0040] Furthermore, the word 'rock bolt' is used to mean any form of earth stabiliser, rock stabiliser, tubular pin, anchoring device or a device which serves to facilitate stability of naturally occurring or man-made earthen formations. The earthen formations may include, for example, mining tunnels, open cut mining sites, transport tunnels forming part of a road or rail system, cuttings or cliffs. [0041] The closure member may be separate from the rock bolt body portion or may be affixed to the body portion. In any event, the opening in the body portion should allow compression and deformation of the rock bolt body portion when subject to a sufficient compressive force such as will generally occur during installation of the rock bolt into a bored hole in an earth or rock structure

[0042] In a preferred embodiment, the rock bolt body portion is a substantially cylindrical tube with a slot extending along the entire length of the tube, the slot being parallel to the longitudinal axis of the tube.

[0043] In another embodiment, the closure member is a sleeve segment of substantially the same length of the rock bolt body and affixed along one of the sleeves longitudinal edges to the inner wall of the rock bolt body such that the sleeve substantially covers the slot whilst allowing the slot to partially close upon application of a sufficient radial compressive force to the rock boit body. In this embodiment, the sleeve segment is shaped to conform with the shape of the internal wall of the rock bolt body and resides within the body portion. This embodiment is particularly useful in instances where filler material is inserted into the rock bolt body before installation of the rock bolt into a drill hole.

[0044 Conforming the shape of the closure member to the shape of the inner wall of the rock bolt body in the vicinity of the opening has the added advantage of the closure member acting to guide the edges of the opening toward each other when a compressive force is applied and as deformatio of the rock bolt body occurs.

[0045] In essence, it has been found that the closure member provides a means by which, upon circumferential compression of the rock bolt, the surface area of the body portion in contact with the surrounding earthen material does not decrease to the same extent as compared with some prior art arrangements. It has also been found that the closure member provides a means by which filler material is largely retained in the rock bolt but some part of the filler may be allowed to seep out, in effect Venting' the filler from the rock bolt caused by pressure applied to the rock bolt from the surrounding earth and/or from within the rock bolt due to the type of filler material used in the rock bolt. The vented filler may exude into any void between the closure member and the rock, and preferably adhering to the rock as well The apertures located periodically along the length of the closure may be of any convenient dimensions. In a particularly preferred embodiment the apertures are circular or oval in shape. Preferably, the conformation and/or number of apertures is predetermined to ensure that a required amount of filler exudes through the apertures into th space between the rock bolt and walls of the drill hole. Preferably, the amount of fixative exuded is proportional to the forces, particularly compressive forces imposed on th rock bolt as it is inserted in the drill hole.

[0046] The exuding of filler from the interior of the rock boit, through the apertures has a number of advantages including provision of extra adhesion between the rock bolt and the dri!! hole wall to reduce slippage. The filler squeezed out through the apertures can also fill voids between the rock bolt and drill hole wall. By contrast the rock bolts of the prior art prevent escape of filler.

[0047] The filler may exude through the apertures during and/or after the rock bolt is located in the drill hole.

[0048] The filler may be provided in the form of a cartridge that can be located in the body of the rock bolt. The cartridge may for example contain filler in a bag of fluid permeable material, the bag being shaped to substantially conform to the internal dimensions of a rock bolt body. There is preferably some clearance between the externa! dimensions of the bag and the internal dimensions of rock bolt body to enable relatively easy insertion of the cartridge into a rock bolt body before installation into the rock bolt hole.

[0049] Preferably, the filler material is grout that is activated, (and the setting process commenced) by exposure to a fluid such as water. Preferably, the cartridge is immersed in a reservoir of activating fluid prior to placement of the cartridge into a rock bolt of the type according to the present invention, in another embodiment, the cartridge is placed into a rock bolt according to the present invention to form a rock bolt assembly and the assembly is immersed in a reservoir of activating fluid prior to insertion of the rock bolt assembly into the hole. [0050] In a particularly preferred embodiment of the invention, the closure member of the rock boft assembly is an integral part of the cartridge. In this embodiment, the closure member is adhered to the external surface of a cartridge, installation of the cartridge according to this embodiment into a rock bolt body effects simultaneous installation of a cartridge and a closure member.

[0051] Preferably, the closure member adhered to the external surface of the cartridge is shaped to conform to the shape of the internal wall of the rock bolt body in the vicinity of the opening. In the instance where the opening is a slot and the rock bolt is a substantially cylindrical tube, the closure member is preferably a sleeve segment which is adhered to the external surface of the cartridge. Further, the sleeve segment, in addition to the apertures may additionally include one or more protuberances on its surface for location within the slot (ie between the edges of the slot) of the rock bolt body.

[0052] The protuberances act to retain the closure member in position covering the opening along the longitudinal surface of the rock bolt body during insertion of the rock bolt into a hole. Of course, the protuberance should not protrude beyond the external notional diameter of the rock bolt body portion otherwise the protuberance would be likely to catch upo the wall of the hole as the rock bolt is installed.

[0053] In essence, embodiments of the present invention stem from the realization that it would be advantageous to have small amounts of filler exuded from the interior of a rock bolt to any void space existing between the rock bolt and drill hole wail. This is in contradistinction to rock bolts of the prior art that were configured to prevent leakage of filler from the interior or the rock bolt to the exterior, or alternatively, unrestrained escape of filler from the interior of the rock bolt.

[0054] Advantages provided by the present invention comprise the following:

• increased adhesion between a rock bolt and surrounding rock, thus increasing the toad capacity of the rock bolt;

♦ controlled release of filler from the interior of the rock bolt to the exterior; • filler readily can be introduced to the region between the rock bolt and drill hole wall without the need for specialized equipment;

• voids adjacent the rock bolt can be filled with filler, improving retention of the rock bolt in a drill hole and meaning less reliance on close conformance between the rock bolt and drill hole diameters;

• overall increase ability to mobilize the fall tensile strength and shear strength of the rock bolt as compared with rock bolts of the prior art;

• the ability to introduce filler to the rock bolt in one pass;

« the ability of the filler material once activated inside the bolt to "lock" the shape and dimensions of the bolt thus increasing the friction between the bolt and the rock; and

• filling all voids in the bolt and between the bolt and the rock thus increasing the shear strength of the installed bolt.

[0055] Further scope of applicability of embodiments of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure herein will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Further disclosure, objects, advantages and aspects of preferred and other embodiments of the present application may be better understood by those skilled in the relevant art by reference to the following description of embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the disclosure herein, and in which: • Figure 1 is a graph illustrating the possible variation of hole diameter along the length of a bored hole in an earthen formation;

• Figures 2(a), 2(b), 2(c) and 2(d) are cross sectiona! illustrations of examples of prior art rock bolts;

» Figures 3(a) is a cross sectional view of a rock bolts according to the prior art and Figure 3(b) is a perspective view of the rock bolt of Figure 3(a);

• Figure 4 is a perspective view of one embodiment of a rock bolt of the present invention; and

• Figure S is a perspective view of one embodiment of a rock bolt of the present invention.

DESCRIPTION

[0057] Figure 1 is a graph of rock bolt diameter (mm) along the length (m) of the rock boit. The graph illustrates how the diameter of a drill hole can vary markedly where the driil hole passes through unstable areas, or soft rock that crumbles, or areas where rocks dislodge from the side of the drilled hole. For example, if a 46mm rock bolt is installed into an approximately symmetrical drill hole the width of the channel or groove in the tube will vary with the diameter of the driil hoie, conforming to variations in the driil hoie diameter. The elongate tube of the rock boit wiil be squeezed by the earthen wali of the hoie where the diameter is less than 46mm giving good frictional engagement.

[0058] Some examples of the cross secfionai shape of hollow rock bolts of the prior art are illustrated in Figures 2a, 2b, 2c and 2d.

[0059] Figure 2b illustrates a rock boit that has offset edges 8 and 9 which are separated prior to installation. During the installation process, in the narrower parts of the hoie, the edges 8 and 9 will be moved past each other as shown by arrow 10. However, this deformation causes further problems after installation as with further radial compression, the externa! surface area of the rock bolt reduces thus decreasing the area over which the surrounding material has the ability to develop a frictional force to act upon the rock bolt. Radial compression of a rock bolt of this type subsequent to installation can result in premature dislodgement of the rock bolt which is unsafe,

[0060] Figure 2c illustrates another problem associated with these rock bolts and referred to as 'tangential gap'. Figure 2c is a representation of the part of Figure 2b "Compressed" marked "A". As the rock bolt is installed in a hole, edges 8 and 9 are moved passed each other. However, proximate the edge 8, there is always a gap 10b (referred to as the tangential gap) which is formed as a result of the rock bolt wail 9 moving inwardly of the rock bolt wall 8.

[0061] The gap is formed between the rock bolt wall 9 and the hole wall 10a. This gap reduces the overall frictional engagement of the rock bolt with the earthen formation into which the rock boit is installed as there is no frictional engagement along the portion of the rock bolt proximate the gap 10b.

[0062] Figure 2d depicts another type of rock bolt of the prior art. This rock bolt has edges 12 and 13 that are separated prior to installation. The rock bolt has a V shaped portion extending substantially along the entire length of the rock bolt The V shaped portion is described as providing greater frictional resistance to movement between the bolt and the mine roof as compared with slotted rock bolts (as illustrated in Figures 2a and 2b).

[0063] During the installation process, in those parts of a hole which are narrower than the nominal diameter of the rock bolt, the edges 12 and 13 are forced together (as shown by arrow 14). As occurs in the rock bolt of Figure 2a, if portions of the hole are very narrow, the edges 12 and 13 will butt together and thus prevent any further circumferential deformation of the rock bolt. This would make installation of the rock bolt very difficult or in some instances impossible, it has been also found in practice that many parts of the V shape remain open and exposed to the earthen hole wall and are thus relatively exposed to water (from underground seepage) and over time the rock bolt will tend to rust and fail. The V shapes portion can also inhibit the flow of grout as it is pumped internally along the length of the rock bolt. [0064] Figure 3(a) illustrates in cross section, one embodiment of a rock bolt according to the prior art. In the embodiment illustrated, the body portion 15 has a generally cylindrical shape and an elongate gap defined by edges 24 and 25, The cover 28 overlaps the edges 24 and 25 and the overlap could extend over only a small part of the length of the body portion 15, or extend intermittently along the length of the body portion 15. Several protuberances or bosses 23 are located along the length of the cover. The are more clearly visible in Figure 3(b) which provides a perspective view of the rock bolt.

[0065] Figure 4 illustrates, in perspective view, a section of a rock bolt according to the present invention for earthen stabilisation, having a holiow elongate body portion 15 having an opening extending parallel to its longitudinal axis. The elongate closure member 28 is aligned to substantially cover the opening and extending adjacent an inner wail of the body portion, parallel with the edges 24, 25 of the gap of the bod portion 15. The closure member 28 has apertures 30 located periodically along its length.

[0066] Figure 5 illustrates, in perspective view, a section of a rock bolt according to another embodiment of the present invention. In this embodiment bosses 23 and apertures 30 located periodicall along the entire length of the closure member 28.

[0067] The rock bolts of the present invention as depicted in Figures 4 and 5 are typically filled with a bulk or packaged filler. The bulk filler is typically pumped into the rock bolt. Packaged fillers are typically in the form of cartridges or bags that are loaded into the interior of the rock bolt and then ruptured to release the contents.

[0068] Fillers are often supplied in porous cartridges that are shaped so thai they can be pushed along the interior of the rock bolt. For example, the cartridge is porous to water, and upon contact with water (either before or after it is located in the rock bolt) the filler in the cartridge starts to cure.

[0069] Alternatively the cartridges may contain a first chemical component and a second chemical component which react together to form the filler. The cartridges typically need to be ruptured to bring the first and second chemical components into contact and mixed to facilitate reaction. [0070] Typically installation of the rock bolt would comprise the steps of (a) drilling a hole in the earthen region to be stabilised, (b) introducing a filler inside the elongate body portion. And (c)) locating the rock bolt of the present invention in the drill hole, and (c). Bulk filler will typically flow out of the apertures as it is being pumped into the rock bolt. Packaged filler will typically flow out of the apertures when the cartridges are ruptured.

[0071] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that th above described embodiments are not to limit the present invention unless specified, but rather should construed broadly within the spirit and scope of the invention as defined in the appended claims. Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

1. A rock bolt for earthen stabilisation, the rock bolt comprising: a hollow elongate body portion having an opening extending parallel to the longitudinal axis of the body portion, and an elongate closure member aligned to substantially cover said opening and extending adjacent an inner wall of the body portion, wherein the closure member has one or more apertures.

2. A rock boft according to claim 1 , wherein the rock bolt body is a substantially cylindrical tube and the opening is a slot extending the entire length of the body, the elongate closure member having apertures located periodically along its length.

3. A rock bolt according to any one of the preceding claims wherein the closure member is a sleeve segment with one of the longitudinal edges of the sleeve segment being affixed to the internal wall of the rock bolt body and the other longitudinal edge remaining free to move relative to the rock bolt body thus allowing the opening to close upon application of a sufficient compressive force whilst retaining the sleeve segment in a position relative to the opening to substantially cover the opening.

4. A rock bolt according to any one of the preceding claims wherein the closure member is shaped to substantially conform with the shape of the inner wall of the rock bolt body in the vicinity of the opening.

5. A method of installing a rock bolt, the method including the steps of: a. drilling a hole in the earthen region to be stabilised, b. introducing a filler inside the elongate body portion, and c. locating the rock bolt of claim 1 in the drill hole wherein part of the filier exudes through one or more of the apertures.

6. A method according to claim 5 wherein the filler is packaged filler and comprises at least one cartridge that is exposed to activating fluid to activate setting of the filler material prior to the cartridge being placed in the rock bolt.

7. A method according to claim 5 wherein the filler is a bulk filler and is pumped into the rock bolt before the rock bolt is installed into the hole in the rock.

8. A method according to any one of claims 5 to 7 wherein the apertures are sized to exude a predetermined amount of filler compared to a compressive force applied to the rock bolt.

9. A method according to any one of claims 5 to 7 wherein the number of apertures are predetermined to exude a requisite amount of filier compared to a compressive force applied to the rock bolt.