SE543164C2 - Dynamic friction rock bolt having an elongated support member, an elongated collar, and a localised anchor - Google Patents

Abstract

A ground support apparatus (10) for use in supporting a rock body comprising an elongated support member (50), an elongated collar (100) and a localised anchor means. The localised anchor means is adapted to substantially restrain the apparatus (10) within a borehole formed within the rock body. The elongated collar (100) comprises a lumen (115) that receives the elongated support member (50) and, additionally, comprises a flange assembly that, at least in part, substantially abuts a rock face of the rock body. In use, a movement of the rock body causes the elongated collar (100) to travel, at least in part, along the elongated support member (50) thereby permitting the apparatus (10) to yield and govern the rock body movement.

Description

DYNAMIC FRICTION ROCK BOLT HAVING AN ELONGATED SUPPORT MEMBER, ANELONGATED COLLAR, AND A LOCALISED ANCHOR FIELD OF INVENTION [000l] The present invention relates to a ground support apparatus for use in ground support in mining, tunnelling and civil engineering operations. id="p-2"

[0002] More particularly, the present invention relates to a dynamic friction rock bolt.BACKGROUND[0003] It is known to use a ground support apparatus such as a rock bolt for reinforcing a rock body in an underground or civil engineering operation for improvingsafety of personnel located in nearby environments. Known rock bolts come in manydifferent forrns and are chosen based on Various factors including the material andquality of the rock body to be reinforced and the amount of geological stress and movement common to particular rock bodies. id="p-4"

[0004] Known rock bolts consist of an elongate member that is placed into a boreholepredrilled into the rock body to be reinforced. The rock bolt is fitted with one end protruding from a rock face of the rock body. A thrust plate can then be mounted to theprotruding end. The thrust plate is often used in combination with a support mesh and/or a spray concrete that forrns a net across the rock face so as to constrain or limit movement of the rock face in the event of a movement or failure of the rock body. id="p-5"

[0005] In order to reinforce the rock body, known rock bolts are required to beanchored deep within the rock body so that the rock bolt can effectively support the rock and limit the movement of the rock face. id="p-6"

[0006] Known rock bolts anchor the rock face by a mechanical means of anchoringsuch as a rock bolt having a friction bolt configuration or using a wedge member forexample. Other means of anchoring a rock face can be used by more securely mountingthe rock bolt in the borehole and thereby increasing a pull out force. These other means include use of chemical adhesion by the provision of a grout or resin which is applied to a borehole which is fitted with a rock bolt. The resin/grout is then cured and encases the rock bolt within the resin/grout within the borehole. id="p-7"

[0007] Installation of known rock bolts can be costly and time consuming,particularly in the case of rock bolts having chemical means of anchoring as the rock boltmust be installed into the borehole, the resin or grout applied and then left for a period oftime before the rock bolt can be tensioned after the chemical means have curedsuff1ciently. These types of installation methods require multiple passes for a complete installation of a rock bolt. id="p-8"

[0008] Problems arise in practise given the often large number of individual rockbolts f1tted to any particular length of a rock body due to the duplication of time andexpense of f1tting rock bolts that require multiple passes for installation. Additional costs associated with resin cartridges or grout compounds these expenses. id="p-9"

[0009] Further, it known to incorporate yielding mechanisms in rock bolt designs thatare adapted to govem a relative movement between the bolt and the rock body beingsupported, thereby permitted the bolt to withstand and accommodate a degree of rock body failure or movement. Such rock bolt designs are not, however, adapted to withstandshearing of the rock body that may occur near to the rock body's face in dynamic conditions. [00l0] Further, known rock bolts do not provide any means that enable mining andtunnelling engineers to determine easily when a rock body failure has actually taken place. [00l l] The present invention attempts to overcome at least in part the aforementioned disadvantages of previous ground support apparatus and methods.SUMMARY OF THE INVENTION id="p-12"

[0012] In accordance with a first aspect of the present invention, there is provided aground support apparatus for use in supporting a rock body, the apparatus comprising an elongated support member, an elongated collar and a localised anchor means, wherein: the localised anchor means is adapted to substantially restrain the apparatus within a borehole formed within the rock body; the elongated collar comprises a lumen that receives the elongated supportmember; the elongated collar also comprises a flange assembly that, at least in part,substantially abuts a rock face of the rock body; and in use, a movement of the rock body causes the elongated collar to travel, at leastin part, along the elongated support member thereby perrnitting the apparatus to yield and govem the rock body movement. id="p-13"

[0013] The lumen of the elongated collar may have a yielding section where adiameter of the lumen is less than a diameter of at least one other section of the lumenfor increasing frictional communication between the lumen and the elongated support member at the yielding section. id="p-14"

[0014] The flange assembly may comprise: a nut that threadedly engages with a complementary threaded portion disposed on anexterior surface of the elongated collar; and a thrust plate disposed between the nut and the rock face and which substantially abuts the rock face. id="p-15"

[0015] The flange assembly may additionally comprise a substantially cylindrical seatdisposed between the nut and the thrust plate. id="p-16"

[0016] The nut may be a locking nut. id="p-17"

[0017] The apparatus may additionally comprise an elongated body having a firstend, second end and a contoured outer portion defining, at least in part, a lumen, whereinthe elongated support member and the elongated collar each extend, at least in part, through the lumen of the elongated body. id="p-18"

[0018] The outer portion may comprise a substantially arcuate wall formed about the lumen of the elongated body. id="p-19"

[0019] The arcuate wall may comprise a gap that is formed between opposed edges of the arcuate wall and is disposed substantially along a longitudinal axis of the elongated body. id="p-20"

[0020] The outer portion may be adapted such that it undergoes radial compressionand frictionally engages an inner surface of the borehole when the apparatus is inserted into the borehole. id="p-21"

[0021] The localised anchor means may comprise a resilient collar non-releaseablyattached to the elongated support member, wherein the resilient collar substantially abutsthe first end of the elongated body and, during installation of the apparatus into theborehole, a movement of the elongated support member causes the resilient collar totravel, at least in part, inside the lumen of the elongated body and displace outwardly the contoured outer portion thereby anchoring the apparatus in the borehole.[0022] The resilient collar may comprise a nose portion and tail portion. id="p-23"

[0023] The nose portion may comprise a section that is substantially knurled forincreasing frictional communication between the nose portion and the lumen of the elongated body during installation of the apparatus.BRIEF DESCRIPTION OF DRAWINGS id="p-24"

[0024] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: id="p-25"

[0025] Figure l shows a front eleVation View of a ground support apparatus according to a preferred embodiment of the present invention; id="p-26"

[0026] Figure 2 shows a front eleVation View of the ground support apparatus of Figure l in a partially assembled state; id="p-27"

[0027] Figure 3 shows an enlarged side View of the top end of the ground support apparatus of Figure l; id="p-28"

[0028] Figure 4 shows a side eleVation view of the lower end of the ground support apparatus of Figure 1 in a first partially assenibled state; id="p-29"

[0029] Figure 5 shows an enlarged side view of the lower end of the ground support apparatus of Figure l in a second partially assenibled second; id="p-30"

[0030] Figure 6 shows a partial enlarged perspective view of the lower end of the ground support apparatus of Figure 1; and id="p-31"

[0031] Figure 7 shows a cross-sectional View of the ground support apparatus of Figure 1 following a rock failure.

DETAILED DESCRIPTION OF THE DRAWINGS id="p-32"

[0032] Referring to Figures 1 and 2, there is shown a ground support apparatus 10 according to a preferred enibodinient of the present invention. id="p-33"

[0033] The apparatus 10 coniprises a first portion 12 and a second portion 14. Thefirst portion 12 coniprises an elongated body 20 having an outer portion 17 that defines alunien 19. The lunien 19 extends along a longitudinal axis of the elongated body 20 and is disposed between a first end 22 and a second end 24 of the elongated body 20. id="p-34"

[0034] The first portion 12 of the ground support apparatus 10 further coniprisesfrictional nieans and, as can be seen in the Figures, the frictional nieans is defined, at least in part, by the outer portion 17 of the elongated body 20. id="p-35"

[0035] The outer portion 17 coniprises a resilient niaterial shaped coniplenientary to aborehole into which, in use, the apparatus 10 is to be installed. The elongated body 20resenibles or coniprises a friction rock bolt configuration wherein the outer portion 17 coniprises a substantially arcuate wall 26 substantially forrned about the lunien 19. id="p-36"

[0036] A gap 28 is forrned between opposed edges 30, 32 of the arcuate wall 26. Itwill be understood that the gap 28 provides for an aniount of flexure of the wall 26 suchthat the edges 30,32 niay be nioved closer to one another during a radial conipression of the elongated body 20. The variation in the gap 28 corresponds with a change in an outer diniension of the arcuate wall 26 during fitting of the apparatus 10 to a borehole which has a snialler internal dianieter than a free standing outer diniension of the elongated body 20, for example. id="p-37"

[0037] The resilient nature of the elongated body 20 ensures that the gap 28 is biasedtoward an expanded position thereby urging the elongated body 20 into a radial expansion after a compressive installation process and thereby provides a source offrictional communication between the arcuate wall 26 and an inner surface of the borehole. id="p-38"

[0038] The elongated body 20 of the preferred embodiment of the present inventionmay comprise any dimension of length and/or free standing outer diameter, however it will be appreciated that the dimensions of the apparatus l0 will be substantiallycomplementary to a receiving rock body borehole such that the first portion l2 may be forcefully inserted into the borehole. id="p-39"

[0039] During a forceful insertion, the wall 26 of the elongated body 20 iscompressed such that the opposed edges 30,32 move closer to one another therebynarrowing the gap 28. The resilient and tensile material of elongated body 20 acts toprovide a resultant intemally generated radially expanding force acting along the lengthof the elongated body 20 and urging the elongated body 20 into an interference fit withthe borehole. It will be understood that a force acting in an orientation generally parallelwith the longitudinal axis upon the first portion l2 of an installed apparatus l0 will beopposed by the frictional force generated by the radially expanding force. id="p-40"

[0040] It is also an advantage of the present invention that there is no pull ringrequired on the elongated body 20. Known friction rock bolts comprise a pull ringwelded to a peripheral end of the rock bolt for limiting travel of the rock bolt into theborehole and for assisting in removing the rock bolt from the borehole. Known pull ringsare welded about a circumference of the rock bolt and can be counterproductive to thefunction of the rock bolt in that they operate to resist compressive or expansive urges developed in the bolt. [004l] The second portion 14 of the apparatus l0 is arranged to at least abut and preferably engage the first portion 12. The second portion 14 comprises a localised anchor means consisting of a resilient collar 42 having a lumen 44 passing therethrough, the collar lumen 44 being adapted to receive a support means therethrough. id="p-42"

[0042] The support means preferably comprises a solid and continuous elongatedsupport member 50 made from a resilient metal material having a high degree of tensilestrength. The elongated support member 50 comprises a top end 54 and a bottom end 52and extends substantially through the complete elongated length of the apparatus 10. id="p-43"

[0043] The elongated support member 50 is disposed inside the lumen 44 of theresilient collar 42 and is non-releasably attached therein using a secure fastening method.Preferably, the elongated support member 50 is fastened inside the lumen 44 perrnanently by a welding process (not shown). id="p-44"

[0044] Altematively, the intemal surface of the lumen 44 preferably comprises athreaded section (not shown) that engages with a complimentary threaded sectiondisposed on the extemal surface of the elongated support member 50 towards its top end54 (not shown). In this arrangement, during manufacture of the apparatus 10 the collar42 is screwed tightly onto the elongated support member 50 with sufficient torque suchthat the collar 42 is attached to the elongated support member 50 non-releasably. id="p-45"

[0045] Towards the first end 22 of the elongated body 20, there is provided anelongated collar 100 disposed, at least in part, inside the lumen 19 of the elongated body20. As most clearly shown in Figures 2 and 4, the elongated collar 100 is, preferably,substantially cylindrical in shape and is manufactured from a resilient material having high tensile strength such as, for example, steel. id="p-46"

[0046] An outer surface of the elongated collar 100 is substantially in contact with aninterior surface of the outer portion 17 of the elongated body 20. The co-efficient of friction between the two surfaces is, however, sufficiently low such that, in use, theelongated collar 100 is able to travel smoothly along the longitudinal length of the lumen 19 defined by the outer portion 17. id="p-47"

[0047] The elongated collar 100 extends through to the lower end of the apparatus 10 and substantially protrudes from its lower end. id="p-48"

[0048] As shown in Figure 6, the elongated collar 100 is hollow and comprises alumen 115 that passes through the longitudinal length of the elongated collar 100. Theelongated support member 50 is disposed inside the lumen 115 and extends through towards a bottom end of the elongated collar 100. id="p-49"

[0049] Also, disposed towards the bottom end of the elongated collar 100, there isfurther provided a flange assembly. The flange assembly consists of a substantiallythreaded portion 110 disposed on the exterior surface of the elongated collar 100 whichalso extends towards the lower end of the apparatus 10. The flange assembly, further,consists of a complementary nut 55 (preferably, a locking nut, as customarily used in theart) that threadedly engages with the threaded portion 110. The nut 55 is preferablydimensioned to be complementary to installation equipment, such as a jumbo rig forexample. As shown in Figures 1 and 2 (omitted in all other Figures), the flange assembly, further, consists of thrust plate 62 that is disposed between the nut 55 and arock face of the rock body to be supported and which substantially abuts the rock face. id="p-50"

[0050] Disposed towards the top end of the elongated collar 100, there is provided ayielding section 70. During manufacture of the apparatus 10, the elongated supportmember 50 is guided into the lumen 115 of the hollow elongated collar 100. The elongated collar 100 is then compressed at the yielding section 70, using a radial pressmachine or equivalent cold pressing method. This causes the elongated collar 100 toundergo a substantial deformation and, as shown schematically in Figure 1, causes the radius of the lumen 115 to reduce at the yielding section 70 forrning a stricture. id="p-51"

[0051] The stricture that is formed increases considerably the co-eff1cient of frictionbetween the interior wall of the lumen 115 and the surface of the elongated supportmember 50 disposed therein at the yielding section 70. This results in an extremely strong interference fit between the elongated support member 50 and the elongated collar100 at the yielding section 70. This interference fit provides that the elongated collar 100 is not able slide along the elongated support member 50 unless a considerable force is applied to the support member 50 relative to the elongated collar 100. id="p-52"

[0052] The flange assembly may additionally comprise a cylindrical seat 61 disposedbetween the thrust plate 62 and the nut 55. As shown in Figures 1, 2, 4 and 5, the top end of the cylindrical seat 61 is tapered providing a substantially rounded surface. In use,when the nut 55 is tightened during installation of the apparatus the cylindrical seat 61may freely rotate about, and travel along, the threaded section 110 of the elongated collar 100. id="p-53"

[0053] The cylindrical seat 61 serves to evenly distribute and spread the load thatwould otherwise be placed on the thrust plate 62 by the nut 55 thus allowing the thrustplate 62 to move more easily along the longitudinal axis of the apparatus 10 as theapparatus is pre-tensioned during installation. Further, the tapering at the top end of thecylindrical seat 61 enables the thrust plate 62 to be secured to a rock face effectively insituations where the rock face surface is aligned at an angle that is not perpendicular tothe elongate length of the elongated body 20; for example, because the apparatus 10 hasbeen driven into the rock face at an angle. The rounded surface of the cylindrical seat 61at its tapered end ensures that a uniforrn, evenly distributed force is applied to the thrustplate 62 in these situations thereby allowing the apparatus 10 to support the rock faceeffectively. id="p-54"

[0054] The apparatus 10 may be f1tted to a borehole using known forceful means suchas those provided by underground installation equipment, including jumbo rigs and/orproduction drills for example. The apparatus 10 is arranged with the thrust plate 62 f1ttedover the threaded portion 110 of the elongated collar 100, followed by the cylindrical seat 61 and then the nut 55. id="p-55"

[0055] The apparatus 10 is positioned adjacent a borehole such that the collar 42 andthe second portion 14 is inside the borehole. A force is then applied to the apparatus 10,preferably via the nut 55, urging the apparatus 10 into the borehole and compressing thefriction means of the first portion 12. The apparatus 10 is urged into the borehole until the elongated body 20 is substantially received therein and the bottom end 52 of the elongated support member 50 substantially protrudes from the rock face. id="p-56"

[0056] A pre-tensioning step is then applied to the apparatus 10 for activating the localised anchor means and developing a point anchor 18 between the first and second portions 12, 14. The pre-tensioning step involves tightening the nut 55 to a predef1ned tension which causes the nut 55 to bear against the cylindrical seat 61. This, in tum, causes a downwards force to be applied to the elongated collar 100 which, in turn, causesa downwards force to be applied to the elongated support member 50 by virtue of thesubstantial friction at the yielding section 70. These forces urge the first and secondportions 12, 14 to engage one another at the junction 57. The resilient collar 42 is drawninto the lumen 19 simultaneously urging the outer portion 17 outwardly and developing the point anchor 18 at the junction 57. id="p-57"

[0057] The collar 42 comprises a tapered nose 45 and tail 48 and, as most clearlyshown in Figure 3, additionally comprises a gripping section 15 having a series ofindentations or protuberances applied to its surface by knurling or a similarmanufacturing process. The gripping section 15 provides additional friction torquebetween the collar 42 and the inner surface of the lumen 19 at a junction 57 between thecollar 42 and the elongated body 20. This additional friction torque impedes rotation ofthe collar 42 when a nut 55 is tightened when the bolt apparatus 10 is pre-tensioned during the installation process described above. id="p-58"

[0058] After the apparatus 10 has been pre-tensioned, locking means (not shown)may, optionally, be added to the threaded section 110 of the elongated collar 100 that isprotruding from rock face in order to lock the nut 55 in place and to stop it fromloosening or coming free. In one preferred embodiment of the present invention, thelocking means comprises a spring (now shown) having one or more coils that arecomplementary to the threaded section 110. In use, the spring is fed onto the lowerrnostend of the elongated collar 100 and is forcefully pushed up the threaded section 110 untilthe spring abuts the nut 55. The coils of the spring occupy the space defined by the rootsof the threaded section 110 which signif1cantly impedes the ability of the nut 55 to revolve around the threaded section 110, thus locking the nut 55 in place. [005 9] Once installed, mesh and spray concrete or similar means may also be used as known in the art.[0060] It is to be understood that the friction means of the first portion 12 substantially restrains the apparatus 10 within the borehole and anchors the second portion 14 collar 42 in position. Upon a rock body failure, creep or similar geological event whereby the rock face loses support and can move, a weight of the rock face is 11 transferred to the thrust plate 62 and, by extension, to the cylindrical seat 61, nut 55 andelongated collar 100. id="p-61"

[0061] As shown in Figure 7, the friction between the elongated collar 100 and theelongated support member 50 at the yielding section 70 allows the elongated collar 100 to slide in a controlled manner along the elongate length of the elongated support member 50 by a distance proportional to the rock face weight that has been transferred tothe thrust plate 62. In the Figure, a rock body is shown wherein the rock face has brokenoff from the main rock body and moved by a distance D following a seismic or otherdynamic rock event. The movement of the elongated collar 100 relative to the elongatedsupport member 50 allows the apparatus 10 to yield thereby extending its ability tocontinue to support the rock face and provide a safe environment for persons present in the area. id="p-62"

[0062] Further, as the elongated collar 100 slides along the elongate length of thesupport member 50 during the yielding process, as shown in Figure 7 this, in tum, causesthe bottom end 52 of the elongated support member 50 to move inside the lumen 115 ofthe elongated collar 100 at the bottom of the apparatus 10. In effect, the relativemovement of the elongated support member 50 inside the lumen 115 of the elongatedcollar 100 indicates that the apparatus' yielding means have been engaged. Miningoperators may, therefore, easily determine when a rock body failure or movement event has taken place by inspecting the base end of rock bolts installed in the rock area. id="p-63"

[0063] Further, known prior art rock bolts that feature yielding mechanisms compriseyielding means that are disposed substantially towards the top of the bolt. Such bolts are,therefore, not able to withstand and support rock bodies that have experienced shearfractures near to the rock face. Shearing near to the rock face causes these bolts to fail astheir yielding means are not able to govem a relative movement between the rock face and the bolt's localised anchor means effectively. The shearing causes such bolts to twist, substantially reducing their load bearing strength, and in extreme cases snap. Incontrast, in the present invention the yielding section 70 is disposed substantially towards the lower end of the apparatus 10. The yielding mechanism is, therefore, capable of operating when significant forces are placed on the lower end of the apparatus 10 by 12 the shearing action, thus enabling the apparatus 10 to Withstand and accon1n1odate these types of rock failures. id="p-64"

[0064] Modifications and Variations as Would be apparent to a skilled addressee are deemed to be Within the scope of the present invention.

Claims (12)

1. A ground support apparatus (10) for use in supporting a rock body, the groundsupport apparatus (10) comprising: an elongated support member (50); and an elongated collar (100),characterised in that the elongated collar (100) comprising a lumen (115) that slidablyreceives the elongated support member (50) and a flange assembly that, at least in part, iscapable of substantially abutting a rock face of the rock body,the ground support apparatus (10) further comprising: an elongated body (20), Wherein the elongated body (20) has a first end (22), a secondend (24) and a contoured outer portion (17) def1ning, at least in part, a lumen (19), Whereinthe elongated support member (50) and the elongated collar (100) each extend, at least inpart, through the lumen (19) of the elongated body (20); and a localised anchor means adapted to substantially restrain the ground supportapparatus (10) Within a borehole formed Within the rock body, the localised anchor meanscomprising a resilient collar (42) that is non-releasably attached to the elongated supportmember (50) and is capable of travelling, at least in part, into the lumen (19) of the elongatedbody (20),Whereby, during installation of the ground support apparatus (10) into the borehole, amovement of the elongated support member (5 0) causes the resilient collar (42) to travel intothe lumen (19) of the elongated body (20) and outWardly displace the contoured outer portion(17) to anchor the ground support apparatus (10) in the borehole, andin use, a movement of the rock body causes the elongated collar (100) to travel slidably, atleast in part, along the elongated support member (5 0) thereby perrnitting the ground support apparatus (10) to yield and govem the rock body movement.

2. The ground support apparatus (10) according to claim 1, Wherein the lumen (115) ofthe elongated collar (100) comprises a yielding section (70) Where a diameter of the lumen(115) is less than a diameter of at least one other section of the lumen (115) for increasingfrictional communication between the lumen (115) and the elongated support member (5 0) at the yielding section (70). 14

3. The ground support apparatus (10) according to claini 1 or 2, wherein the flangeassembly con1prises a:nut (55) that threadedly engages with a coniplenientary threaded portion (110)disposed on an exterior surface of the elongated collar (l00); andthrust plate (62) disposed between the nut (55) and the rock face which substantially abuts the rock face.

4. The ground support apparatus (10) according to clain1 3, wherein the nut (55) is a locking nut.

5. The ground support apparatus (10) according to claini 3, wherein the ground supportApparatus (10) further con1prises a coiled spring that is fastened to the threaded portion (110)on the elongated collar (100) such that an elongate length of the spring occupies a channeldefined by roots of the threaded portion (110), whereby the spring in1pedes an ability of thenut (55) to revolve about the threaded portion (110) thereby locking the nut (55).

6. The ground support apparatus (10) according to any of clain1s 3 or 5, wherein theflange assembly additionally con1prises a substantially cylindrical seat (61) disposed between the nut (55) and the thrust plate (62).

7. The ground support apparatus (10) according to any preceding clain1, wherein thecontoured outer portion (17) con1prises a substantially arcuate wall (26) forrned about the lunien (19) of the elongated body (20).

8. The ground support apparatus (10) according to claini 7, wherein the arcuate wall (26)con1prises a gap (28) that is: forrned between opposed edges (30, 32) of the arcuate wall (26); and disposed substantially along a longitudinal axis of the elongated body (20).

9. The ground support apparatus (10) according to claini 7 or 8, wherein the outerportion (17) is adapted such that it undergoes radial con1pression and frictionally engages aninner surface of the borehole when the ground support apparatus (10) is inserted into the borehole during installation.

10. The ground support apparatus (10) according to any preceding c1aim, Wherein the resi1ient co11ar (42) is Welded to the e1ongated support member (50).

11. The ground support apparatus (10) according to any of c1aims 1 to 9, Wherein theresi1ient co11ar (42) comprises a 1umen (44) having an intema11y threaded section thatthreaded1y engages With a complimentary threaded section disposed on an extemal surface of the e1ongated support member (50).

12. The ground support apparatus (10) according to any preceding c1aim, Wherein theresi1ient co11ar (42) comprises a nose portion and tai1 portion, the nose portion comprising asection that is substantia11y knurled for increasing frictiona1 communication between thenose portion and the 1umen (19) of the e1ongated body (20) during insta11ation of the ground support apparatus (10).