AU2017201806A1 - Rock bolt - Google Patents

Abstract

A rock bolt for supporting a rock body comprising an elongate support cable, an elongate rod connected to the support cable, a collar having a lumen, wherein the lumen is configured to receive slidably the rod, a stop means connected to the rod for limiting travel of the rod through the collar's lumen, a flange means connectable to the support cable, the flange means being configured to abut a rock face of the rock body when the rock bolt is installed into a borehole formed in the rock body, and an elongate hollow protective tube. The protective tube defines an internal volume containing, at least in part, the rod and the stop means. The protective tube is configured to prevent liquid cementitious or resinous grout mixture from entering into the internal volume during installation of the rock bolt into the borehole and allows the rod and stop means to travel through the internal volume in use. When a movement of the rock face of the rock body occurs in use, the rod is caused to slide through the collar's lumen thereby permitting the rock bolt to yield and govern the movement. 404-20 -g12 - 28 --- 42 Fig. 3

Description

TITLE “ROCK BOLT”

FIELD OF INVENTION

[0001] The present invention relates to rock bolts for supporting rock bodies and, in particular, to cable rock bolts,

BACKGROUND

[0002] It is known to use a rock bolt for reinforcing a rock body in an underground, mining or civil engineering operation and for improving the safety of nearby personnel .

[0003] Rock bolts are typically fitted into a borehole that has been pre-driiled into a rock body with one end of the bolt protruding from a rock face of the rock body. A thrust plate can then be mounted to the protruding end. The thrust plate is often used in combination with a support mesh and/or spray concrete that forms 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.

[0004] A rock bolt must be anchored deep within the rock body so that it can support the rock effectively and limit movements of the rock face. Often a rock bolt is secured within the borehole using a liquid cementitious or resinous grout mixture that solidifies to lock the rock bolt rigidly in position within the rock body.

[0005] One form of known rock bolt that is anchored in this manner is a cable rock, bolt which comprises an elongate metallic support cable, [0006] It is known to use a multi-strand cable rock bolt comprising a plurality of individual metal strands woven or wound together to form an elongate support cable. It is also known, to use one or m ore flared bulbous portions along the length of the support cable thereby varying a cross sectional dimension of the rock bolt which allows grout mixture to infiltrate easily into the rock bolt before setting. This improves the anchoring and increases the magnitude of a pull-out force that is required to dislodge the rock bolt in use.

[0007] Problems arise with known cable rock bolts in dynamic rock conditions. Seismic and other earth movements, which may frequently take place during underground tunnelling and mining operations, may cause the rock face of a tunnel or excavated region to move and become less stable, thus placing significant load on rock bolts installed in the rock face. Rock failures may cause installed cable rock bolts to undergo substantial tension, bend or twist, reducing their load bearing strength, and in extreme cases snap.

[0008] The present invention attempts to overcome, at least in part, the aforementioned disadvantages of previous cable rock bolts.

SUMMARY OF TEE INVENTION

[0009] In accordance with one aspect of the present invention, there is provided a rock bolt for supporting a rock body, comprising: an elongate support cable; an elongate rod connected to the support cable; a collar having a lumen, wherein the lumen is configured to receive slidably the rod; a stop means connected to the rod for limiting travel of the rod through the collar's lumen; a flange means connectable to the support cable, the flange means being configured to abut a rock face of the rock body when the rock bolt is installed into a borehole formed in the rock body; and an elongate hollow protective tube that defines an internal volume containing, at. least in part, the rod and the stop means, wherein the protective tube is configured to prevent liquid cementitious or resinous grout mixture from entering into the internal volume during installation of the rock bolt into the borehole and allows the rod and stop means to travel through the interna! volume in use, whereby, when a mo vement of the rock face of the rock body occurs in use, the rod is caused to slide through the collar's lumen thereby permitting the rock bolt to yield and govern the movement.

[0010] A circumference of an. internal surface of the collar's lumen may be configured to increase a frictional communication between the internal surface and the rod.

[0011] The rod may he, at least in part., hollow and comprise a lumen configured to receive, at least in part, the support cable for connecting the support cable to the rod by interference fit.

[0012] The rock bolt may further comprise a bushing means disposed between an external surface of the support cable and an interior surface of the rod's lumen for increasing frictional communication between the support cable and the rod's lumen.

[0013] The bushing means may comprise a plurality of complimentary bush members.

[0014] Each bush member may be a semi-cylindrical member having a knurled outer surface and striated inner surface.

[0015] The bushing means may comprise a channel formed about a circumference of the bushing means, tire channel being configured to receive a biaser or fastening means for clamping the bush members to the support cable during assembly of the rock bolt.

[0016] The support cable may be a multi-strand cable comprising a plurality of individual strand members wound or woven together along an elongate axis, [0017] The support cable may comprise at least one portion wherein the individual strand members forming the support cable flare outwardly.

[0018] The flange means may comprise a thrust plate.

BRIEF DESCRIPTION OF DRAWINGS

[001.9] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: [0020] Fig. 1(a) is a first partial elevation view of a preferred embodiment of a rock bolt according to the present invention; [0021 ] Fig. 1 (b) is a second partial elevation view of the preferred embodiment; [0022] Fig. 1(c) is a third partial elevation view of the preferred embodiment; [0023] Fig, 2(a) is a perspective view of a bushing means that may be used with the rock bolt according to the present invention; [0024] Fig. 2(b) is a perspective view of three bushing members that may be comprised in the bushing means; [0025] Fig. 2(c) is a partial enlarged perspective view of an end of the rod of the rock bolt of Figs. 1(a) to 1(c); [0026] Fig, 3 is a cross-sectional schematic view of the rock bolt of Figs. 1(a) to 1(c), wherein the rock bolt has been installed into a borehole formed in a rock body; and [0027] Fig. 4 is a further cross-sectional schematic view of the rock bolt of Figs. 1(a) to 1(c), wherein the rock bolt has been installed into a borehole formed in a rock body that has undergone a rock failure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0028] Referring to Fig 1 (a), there is shown a rock bolt 10 for supporting a rock body, comprising an elongate support cable 12, an elongate rod 14 connected to the support cable 12, a collar 16 having a lumen 18, wherein the lumen 18 is configured to receive slidably the rod 14, a stop means 20 connected to the rod 14 for limiting travel of the rod 14 through the collar’s lumen 1.8, a flange means 22 connectable to the support cable 12, the flange means 22 being configured to abut a rock face of the rock body when tire rock bolt 10 is installed into a borehole formed in the rock body. As shown in schematic form in Fig. 1(b) and in opaque form in Fig. 1(c), the rock bolt 10 further comprises an elongate hollow protective tube 24. The protective tube 24 defines an internal volume 26 containing, at least in part, the rod 14 and the stop means 20. The protective tube 24 is configured to prevent liquid cementitious or resinous grout mixture from entering into the internal volume 26 during installation of the rock bolt 10 into the borehole and allows the rod 14 and stop means 20 to travel through the internal volume 26 in use. The rock bolt 10 is configured such, that when a movement of the rock face of the rock body occurs in use, the rod 14 is caused to slide through the collar’s lumen 18 thereby permitting the rock bolt 10 to yield and govern the movement, [0029] More particularly, the support cable 12 is a multi-strand cable comprising a plurality of individual strand members wound or woven together along an elongate axis. The individual wire strand members are wound in a twisted or helical configuration.

[0030] Each wire strand member is made of a metallic material having a high degree of tensile strength such as, for example, a steel material, [0031] The support cable 12 comprises at least one bulbous portion 28 wherein the individual strand members of the support cable 12 are flared outwardly. The bulbous portion 28 permits cementitious or resinous grout mixture that is applied during installation of the rock bolt 10 into a borehole to infiltrate the internal space formed by the flared strand members.

[0032] Whilst a single bulbous portion 28 is used in the embodiment shown in the Figures, it will be appreciated that a plurality of bulbous portions may be used in the rock bolt 10, the portions being disposed at intervals along the elongate length of the support cable 12.

[0033] The rod 14 is, at least in part, hollow and comprises a lumen (not shown) configured to receive, at least in part, the support cable 12 for connecting the support cable 12 to the rod 14 by interference fit. Preferably, the part of the support cable 12 that is received by the lumen of the rod 14 substantially occupies the entire elongated length of the lumen of the rod 14.

[0034] Frictional communication between the support cable 12 and the lumen of the rod 14 serves to attach the support cable 12 to the rod 14 by strong interference fit. To increase the strength of this attachment, a bushing means is, preferably, also disposed inside the lumen of the rod 14 sandwiched between an external surface of the support cable 12 and an internal surface of the lumen of the rod 14.

[0035] Referring to Fig, 2(a), there is shown a preferred embodiment of the bushing means used in the rock bolt 10, referred to generally by reference numeral 30. The bushing means 30 comprises a plurality of substantially symmetrical complementary inserts 32 arranged in a circular configuration about a common central axis, [0036] As shown in Fig. 2(b), each individual insert 32 comprises a semi-cylindrical swaged member made from a metallic material, Each insert 32 has a knurled outer surface 34 and a profiled inner striated surface 36, [0037] During manufacture of the rock bolt 10, the inserts 32 are placed around and clamped to an end of the support cable 12 before the end is placed into the lumen of the rod 14, To assist with this process, each swaged insert 32, preferably, has a circumferential channel 38 that is adapted to receive a biaser or fastening means, such as a rubber O-ring or circlip, for example, to clamp each swaged insert 32 to the end of the elongate support cable 12 during the assembly process.

[0038] The knurled outer surface 34 and profiled inner striated surface 36 of each swaged insert 32 each provide additional friction so that they securely grip, respectively, the internal surface of the lumen of die rod 14 and the support cable 12 when the support cable 12 is inserted into the lumen of the rod 14 during assembly of the rock bolt 10, [0039] The rock bolt 10 comprises a yielding mechanism that enables the rock bolt 10 to )-4 eld and govern a movement of the rock face of the rock body in which the rock bolt 10 is installed In use. The yielding mechanism principally comprises the rod 14, collar 16, stop means 20 and protective housing 24.

[0040] The protective housing 24 preferably abuts, and more preferably is attached to, the collar 16. Referring to Fig. 1(b), the protective housing 24 is shown schematically and comprises an elongated hollow tubular member having a lumen passing along its longitudinal length that defines an internal volume 26.

[0041] The internal volume 26 contains the rod 14 and the stop means 20 and serves to protect these elements of the yielding mechanism from grout material that is applied into the borehole during installation of the rock bolt 10.

[0042] The lumen 18 of the collar 16 slidably receives the rod 14 and provides that the rod 14 may travel through and along the lumen 18 until the stop means 20 abuts the collar 16 thus limiting any further travel of the rod 14 through the lumen 18, [0043] The collar 16 is, preferably, crimped such that a circumference of the collar 16 and its lumen 18 is reduced. During manufacture of the rock bolt 10, the crimping is achieved using, for example, a radial press machine, or equivalent cold pressing method, to exert a plurality of large inward forces radially about a circumference of the collar 16, This causes the collar 16 and the lumen to undergo a substantial deformation causing their cross-sectional area to reduce forming a stricture. The stricture substantially increases a frictional communication between an internal surface of the lumen 18 and the rod 14, The friction provides that the rod 14 will only travel through the lumen 18 of the collar 16 when a substantial pulling force is applied to the rod 14, [0044] The stop means 20 comprises a flange 40 which, in use, abuts the collar 16 when the rod 14 has travelled through the lumen 18 of the collar 16 to the maximum permitted extent.

[0045] Referring to Fig. 3, there is shown the rock bolt 10 installed in a borehole 42 that has been pre~driiled into a rock body 44 that needs to be supported.

[0046] To install the rock bolt 10, the rock bolt 10 is firstly inserted into the borehole 42 using a mechanical apparatus as known in the art such as, for example, using a jumbo rig. Once inserted, a liquid cementitious or resinous grout mixture 46 is applied to the borehole to anchor the rock bolt 10 therein.

[0047] The grout mixture 46 infiltrates the space that is formed between the rock bolt 10 and the borehole 42 and, in particular, the spaces created by, and internal to, each flared bulbous portion 28 of the support cable 12. The protective housing 24 ensures that the grout mixture does not flow into its internal volume 26. The grout mixture, therefore. does not come into contact with, the rod 14 or stop means 20 which enables the yielding mechanism to operate notwithstanding the addition of the grout mixture 46, [0048] The grout mixture 46 is then left to cure which anchors the rock bolt 10 inside the borehole 42 including, in a particular, the collar 16 and protective housing 24, [0049] After the grout mixture 46 has cured sufficiently, a thrust plate 22 is then attached to a lowermost end of the support cable 12 which forms a flange for pressing against and supporting a rock face 50 of the rock body. Mesh and spray concrete or similar means may also then be applied, as known in the art, to reinforce the support afforded by the rock bolt 10.

[0050] Upon a rock body failure, creep or similar geological event whereby the rock face 50 loses support and can move, a weight of the rock face is transferred to the thrust plate 22 and, by extension, to the elongated support cable 12 and rod 14.

[0051] Friction between the rod 14 and the lumen 18 of the collar 16 advantageously allows the rod 14 to slide in a controlled manner through the lumen 18 of the collar 16 according to the rock face weight transferred to the thrust plate 22, This enables the rock bolt 10 to yield and govern the rock body movement.

[0052] The rod 14 may continue to slide and govern, the rock body movement until the stop means 20 abuts the collar 16, as is illustrated in Figure 4, [0053] The yielding process advantageously permits the rock bolt 10 to continue to support the rock face 50 and provide a safe environment for persons present in the area following dynamic rock activity.

[0054] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

[0055] In the preceding description of the invention and the following claims, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” are used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims (9)

1. A rock bolt for supporting a rock body, comprising; an elongate support cable; an elongate rod connected to the support cable; a collar having a lumen, wherein the lumen, is configured to receive slidably the rod; a stop means connected to the rod for limiting travel of the rod through the collars lumen; a flange means connectable to the support cable, the flange means being configured to abut a rock face of the rock body when the rock bolt is installed into a borehole formed in the rock body; and an. elongate hollow protective tube that defines an internal volume containing, at least in part, the rod and the stop means, wherein tire protective tube is configured to prevent liquid cementitious or resinous grout mixture from entering into the internal volume during installation of the rock bolt into the borehole and allows the rod and stop means to travel through the internal volume in use, whereby, when a movement of the rock face of the rock body occurs in use, the rod is caused to slide through, the collar’s lumen thereby permitting the rock bolt to yield and govern the movement.

2. The rock bolt according to claim 1, wherein a circumference of an internal surface of the collar’s lumen is configured to increase a frictional communication between the internal surface and the rod.

3. The rock bolt according to claim I or 2, wherein the rod is, at least in part, hollow and comprises a lumen configured to receive, at least in pari, the support cable for connecting the support cable to the rod by interference fit.

4. The rock bolt according to claim 3, wherein the rock bolt further comprises a bushing means disposed between an external s urface of the support cable and an interior surface of the rod’s lumen for increasing frictional communication between the support cable and the rod’s lumen.

5. The rock bolt according to claim 4, ’wherein the bushing means comprises a plurality of complimentary bush members.

6. The rock bolt according to claim 5, wherein each bush member is a semi-cylindrical member having a knurled outer surface and striated inner surface,

7. The rock bolt according to claim 5 or 6, wherein the bushing means comprises a channel formed about a circumference of the bushing means, the channel being configured to receive a biaser or fastening means for clamping the bush members to the support cable during assembly of the rock bolt. 8. 'The rock bolt according to any one of the preceding claims, wherein the support cable is a multi-strand cable comprising a plurality of individual strand, members wound or woven together along an elongate axis,

9. The rock bolt according to claim 8, wherein the support cable comprises at least one portion wherein the individual strand members forming the support cable flare outwardly,

10. The rock bolt according to any one of the preceding claims, wherein the flange means comprises a thrust plate.