AU2010348888B2

AU2010348888B2 - A yielding spiral bolt appendage for a rock bolt

Info

Publication number: AU2010348888B2
Application number: AU2010348888A
Authority: AU
Inventors: Amir Gharbani; Roland Walker
Original assignee: Dywidag Systems International Canada Ltd
Current assignee: Dywidag Systems International Canada Ltd
Priority date: 2010-03-19
Filing date: 2010-03-19
Publication date: 2014-01-09
Anticipated expiration: 2030-03-19
Also published as: EP2547867A1; MX2012002391A; WO2011113131A1; CA2767209C; CA2767209A1; AU2010348888A1; AU2010348888A8; US20130004245A1

Abstract

A yielding spiral bolt appendage for attachment to a rock bolt has a cylindrical shank portion for attachment to the insertion end of the rock and a helical flute portion having a tip for rupturing a resin cartridge and achieving mixing when rotated. The shank has a first tapered portion and a second tapered portion for resisting movement of the appendage once the resin has set.

Description

1 A YIELDING SPIRAL BOLT APPENDAGE FOR A ROCK BOLT Technical Field [0001] This invention relates in general to the field of mining and construction and particularly to ground support equipment and specifically to a yielding spiral bolt appendage for a rock bolt. Background [0002] Rock bolting is well known in civil engineering and mining operations. Bolting is done to secure loose rock to stable formations behind. This prevents rock falls and rock bursts which are known to be a major cause of death and injury in the construction and mining industries. [0003] The rock surrounding an excavation subjected to stress, fractures into slabs sub-parallel to the tunnel outline. The fractures extend into the surrounding rock to varying depths, depending on such factors as the magnitude and orientation of the stress and the strength of the rock. Dilation occurs during the fracturing process and more significantly, as a result of subsequent stress increases brought about by subsequent mining in the vicinity. The rock bolt is a yielding tendon capable of providing effective support in areas prone to seismic events or high stress changes. [0004] A resin is used to adhere the yielding tendon to the rock. Often the resin is a binary type of adhesive contained in cartridges comprising a bonding agent and a hardening catalyst. Once the capsules are pierced the bonding agent and catalyst mix and the resin begins to set. In operation the resin cartridge(s) is inserted into a predrilled hole that passes through an unstable rock formation into a stable rock formation. A rock bolt is inserted into the drilled hole. The exposed end of the rock bolt that extends outside of the drilled hole is typically equipped with a nut for connection to a rotating device. The insertion end is often tipped with an apparatus to pierce the resin cartridges and mix the resin as the rock bolt is being rotated. It is important to the strength of the bond between the rock bolt, the resin and the rock body that the mixing be thorough. Less than adequate mixing will result in a weakened rock bolt installation.

2 [0005] A number of resin mixing apparatus have been proposed. One such device is shown in US Patent #4,704,053 VERSATILE ROOF BOLT ASSEMBLY issued to Hipkins et al on November 3, 1987. Hipkins discloses an anchor bolt assembly including a helical coil external of and connected to a bolt shaft that is coupled to the end of the rock bolt. The tip of the bolt shaft has a frustoconical plug that is used to pierce the resin cartridges as the bolt is rotated to mix the resin. The disadvantage associated with the Hipkins apparatus is that it is a relatively complicated apparatus and hence expensive to manufacture and use in the quantities necessary for rock bolting a major excavation. The Hipkins device comprises a coupler to couple the apparatus to the rock bolt, the helical coil welded to the outside of the apparatus and the frustoconical plus at the head of the apparatus. The coupler itself may present a possible yield point when the assembly is under tension during rock displacement. [0006] Therefore, there is a need for a mixing apparatus that is easy to manufacture and cost effective for use in large quantities while providing the necessary mixing results to establish a strong bond between the rock bolt and the rock formation. Object of the Invention [0007] It is an object of the present invention to substantially achieve at least the above need, or to at least provide a useful alternative. Summary of the Invention [0008] There is disclosed herein a yielding spiral bolt appendage for threaded attachment to an externally threaded rock bolt insertion end for placement into a predrilled hole containing a resin system, said spiral bolt appendage comprising a body having a hollow internally threaded shank portion for attachment to said threaded rock bolt insertion end and a helical fluted portion for acting on said resin system, wherein the resin system comprises at least one resin cartridge, wherein the hollow internally threaded shank portion is tubular and comprises an outside surface, an outside surface top end, an outside surface bottom end, an inside surface top end, an inside surface bottom end, an inside threaded surface, and an apex disposed on said outside surface between said outside surface top end and said outside surface bottom end, and 3 wherein the shank portion further comprises a first taper from said apex to said outside surface top end and a second taper from the apex to said outside surface bottom end. [0009] There is also disclosed herein a yielding spiral bolt appendage for use in combination with a rock bolt assembly, said rock bolt assembly comprising a tension member comprising an externally threaded insertion end for insertion into a predrilled hole into a face of a rock formation and a threaded opposite end exposed out of said predrilled hole, wherein said predrilled hole contains a resin system comprising at least one resin cartridge and wherein said threaded opposite end has a threaded nut attached thereto and a bearing plate forward of said threaded nut, said threaded nut attachable to a rotating machine for rotation towards said face so that said bearing plate is in contact with the face for tensioning the tension member and wherein said yielding spiral bolt appendage comprises a body having a hollow internally threaded shank portion for attachment to said threaded rock bolt insertion end and a helical fluted portion for acting on said at least one resin cartridge, wherein the hollow internally threaded shank portion is tubular and comprises an outside surface, an outside surface top end, an outside surface bottom end, an inside surface top end, an inside surface bottom end, an inside threaded surface, and an apex disposed on said outside surface between said outside surface top end and said outside surface bottom end, and wherein the shank portion further comprises a first taper from said apex to said outside surface top end and a second taper from the apex to said outside surface bottom end. [0010] In a preferred embodiment, there is a spiral bolt appendage for a rock bolt comprising a body having a shank portion for attachment to the rock bolt integral with a helical fluted portion for acting on a resin system placed within a drill hole. In one embodiment of the invention the appendage is threaded onto the end of a rock bolt. In another embodiment the appendage is welded to the end of a rock bolt. In one embodiment of the invention the body is cast from a suitable metal alloy such as hardened steel. In another embodiment of the invention the body is forged. In another embodiment of the invention the helical fluted portion may be welded to the shank portion. In one embodiment of the invention the helical fluted portion comprises a one half pitch helix. However, in other embodiments of the invention the helical fluted portion may be longer than one-half pitch to suit the installation requirements. The shank portion comprises a bore having a closed end and an open end for receiving an end of the rock bolt. The bore includes a threaded portion for threaded attachment with the end of the rock bolt. The shank portion comprises a cylinder having a first tapered portion and a second tapered portion and an 4 apex between the two tapers. In another embodiment of the invention there is provided a rock bolt comprising a tension member comprising a first end for insertion into a predrilled hole in a rock formation and a second end disposed outside of the predrilled hole having a nut for attachment to a rotating machine. The first end of the rock bolt is threaded to a spiral bolt appendage. In yet another embodiment of the invention there is provided a rock bolting system comprising at least one resin cartridge for placement into a predrilled hole in a rock formation, a rock bolt comprising a tension member having an insertion end having a spiral bolt attached thereto for insertion into the predrilled hole and for piercing the resin cartridge thereby releasing and mixing the resin so that it sets adjacent to the spiral bolt. The tension member exposed end is disposed outside of the predrilled hole for attachment to a rotating machine for rotating the tension member and thereby mixing the resin. [0011] It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. Brief Description of the Drawings [0012] A preferred embodiment of the invention will be described hereinafter, by way of an example only, with reference to the accompanying drawings, wherein: [0013] Figure 1 is a diagram of one preferred embodiment of the invention attached to a rock bolt and installed in a drilled hole. [0014] Figure 2 comprises a side view of the embodiment of the invention 'A', a top view of the embodiment of the invention 'B' and a bottom view of the embodiment of the invention 'C'. [0015] Figure 3 is a cross-sectional view of the embodiment of the invention along its axis. [0016] Figure 4 is a perspective view of the embodiment of the invention.

5 Detailed Description [0017] Referring to Figure 1, there is shown one embodiment of the invention, a spiral bolt appendage 10 for a rock bolt 5, installed in a drilled hole 2 in order to fix an unstable rock formation 3 to a stable sub-parallel rock formation 4. The invention is attached to the end of a rock bolt 5 and embedded in a resin 6 to fix the rock bolt to the rock formation. The appendage may be threaded to the end of the rock bolt as described herein or it may be welded to the end of the thread bolt in alternate embodiments. The portion of the rock bolt that extends outside of the drilled hole 2 includes a nut 7 and a bearing plate 8. The nut is tightened against the bearing plate by a rotating device (not shown) to tension the rod. During a yielding event wherein the unstable formation is displaced from the stable formation, tension is placed on the rock bolt until the spiral bolt appendage begins to pull out of the hardened resin. In this manner, yielding forces are absorbed by the resin and transmitted to the stable rock formation thereby slowing the yielding event. [0018] Referring now to Figure 2, there is shown one embodiment of the invention in three views. View 'A' is a side view of the invention. View 'B' is a top view of the invention and view 'C' is a bottom view of the invention. The invention has a length 12, a width 20 and an axis 18 about which it is rotated. The invention comprises a body that is cast from a suitable metal capable of withstanding the focus applied to the body. In one embodiment the metal is a hardened steel alloy. Other alloys are possible. In other embodiments the body can be forged. In a preferred embodiment the body is cast per ASTM 536 grade 120-90-02. The body is comprised of a fluted section 14 and a cylindrical shank portion 16. The fluted section 14 has a top surface 22 having a width 24 that is adequate to pierce resin cartridges placed in a drilled hole. In other embodiments of the invention the fluted section 14 can be welded to the shank portion 16. In the cast or forged embodiment of the body, the bottom 30 of the fluted section 14 is integral to the top surface 28 of the shank portion 16. The bottom 32 of the shank portion 16 comprises a bored hole 30 in which the bottom end of the rock bolt is inserted in a threaded arrangement. In another embodiment of the invention, the body is welded to the bottom of the rock bolt. [0019] Still referring to Figure 2, there is a first taper that is represented by angle 17 that extends from the apex line 38 to the top 28 of the shank portion 16. There is also a second taper that is represented by angle 19 that extends from apex line 38 to the bottom 32 of the shank portion 16.

6 In static testing, the tapers have been found to further improve the yielding characteristics of the rock bolt and resin. Referring back to Figure 1, the tapers are embedded in the resin 6. Taper 17 and taper 19 will resist tensioning forces attempting to push the rock bolt further into the drilled hole or pull the rock bolt out of the drilled hole. The tapers transfer more of the yielding forces to the resin and thereby slow the yielding of the rock bolt. [0020] In a preferred embodiment of the invention the first taper 17 angle is 0.7 degrees and the second taper 19 angle is 1.5 degrees. Other angles can also be used. The length 12 of the body is preferably 3.25 inches with the shank portion 16 being preferably 2.25 inches long and the fluted portion 14 being one inch long. The width of the shank portion 16 at end 32 is preferably 0.78 inches and at apex 38 the width of the shank portion is preferably 0.82 inches. The width 24 of tip 22 is preferably 0.25 inches and the width of the fluted portion at its maximum is 0.78 inches. The fluted section 14 comprises a one-half pitch helix and in a preferred embodiment the pitch of the helix is 2 inches. Other dimensions are possible to suit a particular rock bolt installation. [0021] Referring now to Figure 2 and Figure 3, there is shown (in Figure 3) a cross-section along axis 18 one preferred embodiment of the invention comprising the shank portion 16 and the fluted portion 14. The first taper 17 extends along length 39 from apex 38 to the top 28 of the shank portion 16. The second taper 19 extends along length 36 from apex 38 to the end 32 of the shank portion 16. Bore 30 is illustrated as extending from end 32 of the shank portion 16 substantially to the top of the shank portion 16. The inside surface of the bore 30 is threaded to accept the threaded end of the rock bolt. [0022] Referring now to Figure 4, there is shown a perspective view of the body comprising the fluted section 14 and the shank portion 16. The first taper extends from apex 38 along length 39 to the top of the shank portion and the second taper extends from apex 38 along length 36 to the bottom 32 of the shank portion. Within bore 30 the inside surface 40 is threaded to mesh with the end of the rock bolt to which the body is attached. In one embodiment of the invention the thread is 3/4-10 UNC 2B LH. [0023] It has been found in static testing of the invention that the body of the invention permits effective mixing of the resin within the drill hole so that there is a consistent yield strength of the rock bolt across a sample tested.

7 [0024] It will be appreciated by those skilled in the art that other variations of the embodiments described herein may also be practiced without departing from the scope of the invention. Other modifications are therefore possible.

Claims

1. A yielding spiral bolt appendage for threaded attachment to an externally threaded rock bolt insertion end for placement into a predrilled hole containing a resin system, said spiral bolt appendage comprising a body having a hollow internally threaded shank portion for attachment to said threaded rock bolt insertion end and a helical fluted portion for acting on said resin system, wherein the resin system comprises at least one resin cartridge, wherein the hollow internally threaded shank portion is tubular and comprises an outside surface, an outside surface top end, an outside surface bottom end, an inside surface top end, an inside surface bottom end, an inside threaded surface, and an apex disposed on said outside surface between said outside surface top end and said outside surface bottom end, and wherein the shank portion further comprises a first taper from said apex to said outside surface top end and a second taper from the apex to said outside surface bottom end.

2. The appendage of claim 1, wherein said body is cast so that said shank portion is integral with said helical fluted portion.

3. The appendage of claim 1, wherein said body is forged.

4. The appendage of claim 1, wherein the helical fluted portion is welded to the shank portion.

5. The appendage of claim 1, wherein the helical fluted portion comprises an one-half pitch helix and a tip for piercing the at least one resin cartridge and wherein the helical fluted portion is rotated to achieve mixing of the resin within said predrilled hole resulting in set resin around the body.

6. The appendage of claim 1, wherein said first taper acts on said set resin to resist inward movement of the rock bolt and wherein said second taper acts on the set resin to resist outward movement of the rock bolt.

7. A yielding spiral bolt appendage for use in combination with a rock bolt assembly, said rock bolt assembly comprising a tension member comprising an externally threaded insertion end for insertion into a predrilled hole into a face of a rock formation and a threaded opposite 9 end exposed out of said predrilled hole, wherein said predrilled hole contains a resin system comprising at least one resin cartridge and wherein said threaded opposite end has a threaded nut attached thereto and a bearing plate forward of said threaded nut, said threaded nut attachable to a rotating machine for rotation towards said face so that said bearing plate is in contact with the face for tensioning the tension member and wherein said yielding spiral bolt appendage comprises a body having a hollow internally threaded shank portion for attachment to said threaded rock bolt insertion end and a helical fluted portion for acting on said at least one resin cartridge, wherein the hollow internally threaded shank portion is tubular and comprises an outside surface, an outside surface top end, an outside surface bottom end, an inside surface top end, an inside surface bottom end, an inside threaded surface, and an apex disposed on said outside surface between said outside surface top end and said outside surface bottom end, and wherein the shank portion further comprises a first taper from said apex to said outside surface top end and a second taper from the apex to said outside surface bottom end.

8. The appendage of claim 7, wherein the helical fluted portion comprises a helix comprising at least one-half pitch and a tip for piercing the at least one resin cartridge and wherein the helical fluted portion is rotated to achieve mixing of the resin within said predrilled hole resulting in set resin around the body.

9. The appendage of claim 7, wherein the first taper acts on said set resin to resist inward movement of the rock bolt and wherein said second taper acts on the set resin to resist outward movement of the rock bolt.

10. The appendage of claim 9, wherein said first taper declines about 0.7 degrees from a horizontal and said second taper declines about 1.5 degrees from said horizontal.

11. A yielding spiral bolt appendage substantially as hereinbefore described with reference to the accompanying drawings. DYWIDAG-Systems International Canada Ltd. Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON