AU2004203853B2 - Friction Bolt - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE

SPECIFICATION

FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor: Address for Service: Invention Title: Details of Basic Application(s): INDUSTRIAL ROLL FORMERS PTY

LIMITED

JEFFREY ROBERT FERGUSSON FRASER OLD SOHN Patent Attorneys Level 6, 118 Alfred Street MILSONS POINT NSW 2061 FRICTION BOLT Australian Patent Application No. 2003 904 320 Filed 14 August 2003 The following statement is a full description of this invention, including the best method of performing it known to us: 2945BY-AU Field of the Invention The present invention relates to rock bolts and, in particular, to friction rock bolts.

Background Art Friction rock bolts are used in underground mining and civil engineering to secure the surface of rock in an opening or tunnel to reduce the risk of rock fall. The bolts are forcibly inserted into an undersized blind hole drilled in the rock.

One type of friction rock bolt takes the form of a tubular body, normally cylindrical in shape which has a slit extending between the leading end and trailing end of the bolt. The leading end is normally tapered and the trailing has a collar which enables the trailing end to engage a load distributing washer or bearing plate.

In order to install the friction bolt, first a blind hole is drilled in the rock which is substantially circular in cross section. The diameter of the drilled hole is slightly smaller than the outside diameter of the cylindrical body. The tapered leading end is then fitted into the hole and the friction bolt is then forced into the hole by using repeated percussive force to an extent sufficient to press the bearing plate firmly into position. The bearing plate which fits around the trailing end of the bolt distributes the axial load of the friction bolt over a large area of the rock surface and thereby contains surface spalling.

Forcing the friction rock bolt into the hole compresses the tubular body thereby narrowing the width of the slit. The resilience provided by the slit allows the tubular body to be compressed along its length, rather than crushed, as it is forced into the hole. As a consequence of this resiliency, the tubular body is urged to expand by virtue of its hoop strength and exert radial forces against the wall of the hole as the friction bolt attempts to expand back to its original shape. In the event that a tensile load is applied to the bolt, a high frictional force arises between the bolt and the hole as a result of this elastic compression of the bolt. As the frictional load increases, the bolt begins to slip and commence withdrawal from the hole. This frictional resistance is overcome at a force which is approximately equal to 30%-60% of the ultimate tensile strength of the bolt itself.

2945BY-AU 21 Aug 2008 10:53 FRASER OLD AND SOHN 21 ug200 1:53 FRSEROL AN SHM0299552700 p.

4 00 A disadvantage of friction rock bolts is that the load bearing capacity reduces 00 progressively towards the leading end of the bolt.

To overcome this problem, it is known to fill the friction bolt with cement grout from leading end to the trailing end after installation of the bolt. However, this suffers from the disadvantage that it makes the bolt very stiff, in many respects like a reinforcing bar in a V')h concrete structure. This has the consequence that the bolt can fracture as a result of small 00 Mn amounts of transverse movement of the rock, In contrast, ungrouted, the friction bolt would 0 deform elastically or plastically.

cto o Object of the Invention The aim of the present invention is to provide a friction rock bolt, and assciated equipment, which has a good ability to withstand high tensile loads without slipping, but which will also tolerate small amounts of transverse movement in the rock so that the bolt plastically de-forms, or yields, without breaking, Smmary of the Invention In accordance with the first aspect of the present invention there is disclosed a friction bolt assembly comprising a friction bolt known per se and having a tapered tip and a longitudinally extending slit, and at least one grout capsule carried within said bolt by a retention means which is engaged with said bolt without protruding into said slit.

In accordance with the second aspect of the present invention there is disclosed a grout capsule and carrier for a friction bolt assembly as above, said capsule comprising a pliant sheet formed into a tube, the interior of said tube being filled with a cementitious hardenable material, and said capsule being held within a carrier having retention means which are engaged said bolt without protruding into said slit.

In accordance with the third aspect of the present invention there is disclosed an installed friction bolt assembly as above inserted into a blind hole drilled in a rock body, wherein said friction bolt is bonded to said rock body by grouting at a specific location constituting some part only of the length of said bolt.

In accordance with a fourth aspect of the present invention there is disclosed a method of grouting a friction bolt at part only of the length of the bolt, said bolt having a 3 COMS ID No: ARCS-202950 Received by IP Australia: Time 11:05 Date 2008-08-21 SZ-LO-9OOZ (P-nY-A) 0le(ZZ:t 0W!j. :eileJlsnv dl Aq pGAIaO0jI. L666L-SOJV :ON QI SflOO 00 0 0 Z2945BY-AU 00 longitudinally extending slit, said method comprising the steps of: inserting said friction bolt into a blind hole to thereby frictionally engage said bolt and hole, en (ii) engaging at least one grout capsule with the leading end of said friction bolt by a 00 5 retention means engaged with said bolt and not protruding into said slit, and o (iii) permitting setting of, or actuating setting of, the grout material contained in said capsule(s).

C",1 Brief Description of the Drawings Embodiments of the present invention will now be described with reference to the drawings in which: Fig. I is an exploded perspective view of a conventional friction bolt to which is added the grout capsule and carrier of the first embodiment, Fig. 2 is a similar perspective view showing the grout carrier and capsule assembled with the friction bolt, Fig. 3 is a side elevation of the assembled bolt of Fig. 2, Fig. 4 is a cross sectional view taken along the line 4-4 of Fig. 3, Fig. 5 is an end elevation of the leading end of the bolt of Figs. 2-4, Fig. 6 is a cross sectional view taken along the line 6-6 of Fig. 3, Fig. 7 is a view similar to Fig. I but illustrating an alternative embodiment of three cascade connected grout capsules and carriers, Fig. 8 is a perspective view illustrating the hydrating of an installed grout capsule, Figs. 9-11 are each schematic side illustrations showing the steps involved in the installation of the assembled rock bolt of Fig. 2, Fig. 12 is a view similar to Figs. 9-11 but illustrating the performance of the rock bolt as a result of tensile loads being applied, and Fig. 13 is a view similar to Fig. 12 but illustrating the performance of the rock bolt when transverse loads are applied.

Detailed Description As seen in Figs. 1-6, a conventional friction bolt I has a cylindrical side wall 2 which has a longitudinally extending slit 3. The leading end of the bolt I is tapered at 4 whilst the trailing end 5 is provided with a welded ring flange or collar 6.

4

-C

OOLSSGG620 WHOS amU (170 N3SUdJ II:bT soa Inc ea As indicated in Fig. 1, a grout assembly 10 is able to be inserted into the trailing end 5 of the rock bolt 1. The grout assembly 10 is formed from a grout capsule 11 which is essentially a sausage fabricated from pliant water permeable material and is preferably substantially non-rupturable eg textile fabric material. This contrasts with the paper capsules utilised in some prior art devices which are highly liable to rupturing, especially if.mishandled or roughly handled prior to installation.

At the trailing end of the grout assembly is a plastic cylindrical cap 12 which has two small holes in its base through which the wire 13 of a carrier 14 passes. The carrier 14 has two arms 15 joined by a bight 16 which engages the base of the cap 12 (Fig. 4).

In addition, the arms 15 have inverted free ends 17 which, after insertion as illustrated in Fig. 2, engage the tapered leading end 4. As best seen in Fig. 6 the interior of the grout capsule 11 is preferably filled with a cementitious hardenable material 19 such as Portland cement.

Fig. 7 illustrates an alternative embodiment with three cascade connected grout assemblies 10. The leading grout assembly 10 is as before, however, the two trailing grout assemblies have their inverted free ends 17 engaged with the bight 16 of the preceding grout assembly. In Fig. 7 the friction bolt 100 is substantially the same as the friction bolt 1, except that it is longer. In Fig. 8, the friction bolt 1, 100 is shown having its leading end immersed in a trough 25 of water in order to hydrate the grout within the grout capsules 11.

As illustrated in Figs. 9-11, with the grout so hydrated, the bolt 1 is passed through a bearing plate 28 and the leading end 4 of the bolt 1 is inserted into a blind hole 29 drilled into three rock strata 30, 31 and 32. As illustrated in exaggerated scale in Fig. 10, insertion of the bolt 1 into the hole 29 compresses the slit 3 as the bolt 1 is driven home by a percussive hammer 33.

As the bolt 1 is being forced into the hole 29, the grout 19 is being compressed against the cap 12 by the percussive action. This tampering force causes excess water and grout fines to be compacted out of the grout retained within the grout capsule 11.

In addition, the carrier 14 prevents the grout assembly 10 from moving away from the leading end 4 of the bolt 1. Thus the situation illustrated in Fig. 11 is reached where 2945BY-AU I r 6 the bolt 1 is fully inserted, the grout within the grout capsule 11 has been compacted to accommodate the smaller internal diameter of the bolt 1, and some of the grout and grout fines has escaped through the permeable wall of the grout capsule 11 so as to fill the area of the hole 29 adjacent the leading end 4.

Once the grout 19 has set, the grout forms a good bond between the forward portion of the bolt I and the stratum 30. As a consequence, as seen in Fig. 12, if the strata 31 and 32 move downwardly as seen in Fig. 12 as indicated by the arrows in Fig. 12, the bolt 1 is able to elongate initially elastically, and if necessary, plastically without breaking. However, the leading end 4 remains permanently fixed within the stratum 30. So long as the ultimate tensile strength of the bolt I is not exceeded, the strata 31 and 32 remain supported.

By adjusting the length of the grout capsule 11, or the number of grout assemblies 10, the degree of strength of the point anchor caused to form by the bonding between the grout and the hole 29 can be adjusted. If desired, the point anchors can be sufficiently strong to ensure that the bolt resists movement up to its ultimate tensile strength. Alternatively, the strength of the point anchor can be reduced so that the bolt 1 commences to slip at, say, 90% of the ultimate tensile strength of the bolt. In either event, the movement of the rock strata 31-32 is substantially controlled. Typically, if the grout column was approximately 50mm in length then the grout would offer only minimal resistance to applied forces. However, if the grout column was about 300mm long, the bolt 1 would pull through the hole 29 at loads approximating to the yield strength of the bolt material. Similarly, if the grout column was approximately 600mm in length, then the grout would fully anchor the leading end of the bolt to the hole 29.

In an alternative embodiment (not illustrated) the leading end 4 of the bolt I can be plugged, for example with a plug of cotton wadding or similar material. This plugging can take place either before or after installation. If the wadding is inserted after installation the wadding is inserted through the trailing end 5 and pushed against the tapered leading end 4 by means of a wooden rod, for example. The one or more grout capsules 11 are hydrated and passed into the trailing end 5 after the bolt 1 has been inserted. Again the wooden rod is used to insert the hydrated cement capsule 2945BY-AU into position and tamp same into place thereby causing moisture and grout fines to be expelled from the capsule 11 without rupturing the capsule 11. The leading end of such a tampering rod preferably has a soft bulbous portion which acts as a piston which therefore ensures that the tamping of the grout capsule 11 does not result in grout being extruded passed the tampering rod towards the trailing end 5 of the bolt 1.

As seen in Fig. 13, if the rock strata 31 and 32 should move sideways relative to the rock stratum 30 where the tip of the bolt 1 is anchored, then the cylindrical side wall 2 of the bolt 1 is free to elastically or plastically deform and again the strata 31 and 32 are supported. Had the entire interior of the bolt 1 been filled with grout as in the prior art, under these circumstances the bolt 1 would almost certainly have snapped at a location intermediate its opposite ends.

The foregoing describes only some embodiments of the present invention and modifications, obvious to those skilled in the art, can be made thereto without departing from the scope of the present invention.

For example, arrangements other than the wire carrier 14 can be used to hold the grout assembly in place during installation. One such arrangement is a pivoted toggle carried at the leading end of the capsule 11. The toggle is passed through the leading end of the bolt 1 and then pivoted so that engagement between the toggle and leading end prevents the capsule 11 moving rearwardly towards the collar 6. Other forms of such arrangements will be apparent to those skilled in the mining and construction arts.

The term "comprising" (and its grammatical variations) as used herein is used in the inclusive sense of "having" or "including" and not in the exclusive sense of "consisting only of'.

2945BY-AU

Claims (18)

1. A friction bolt assembly comprising a friction bolt known per se and having a tapered tip and a longitudinally extending slit, and at least one grout capsule carried within said bolt by a retention means which is engaged with said bolt without protruding into said slit. kn

2. The assembly as claimed in claim I where said retention means comprises a 00 en carrier engaged with said tip.

03. The bolt assembly as claimed in claim I or 2 and having a plurality of grout o capsules.

4. The bolt assembly as claimed in claim 3 wherein each of said capsules has a corresponding carrier and said carriers are cascade connected.

A friction bolt assembly substantially as descr ibed herein with reference to the drawings.

6. A grout capsule and carrier for a friction bolt assembly as claimed in claim 1, said capsule comprising a pliant sheet formed into a tube, the interior of said tube being filled with a cemnentitious hardenable material, and said capsule being held within a carrier by a retention means which is engaged said bolt without protruding into said slit.

7. The capsule and carrier as claimed in claim 6 wherein said catrer comprises a trailing plug and a U-shaped hanger having a pair of arms and a bight located there between, said bight and plug being inter-engaged and the free ends of said arms being bent over the free end of said bolt to form said engagement means.

8. A plurality of cascade connected capsules and carriers as claimed in claim 7 wherein the firee ends of the arms of the or each trailing capsule and carrier are linked with the bight of the or each preceding capsule and carrier.

9. A grout capsule and carrier substantially as herein described with reference to the drawings.

An installed friction bolt assembly as claimed in claim I and inserted into a blind hole drilled in a rock body, wherein said friction bolt is bonded to said rock body by groutin g at a specific location constituting some part only of the length of the said bolt, COMS ID No: ARCS-202950 Received by IP Australia: Time 11:05 Date 2008-08-21 9E-LO-90O Oe CLZ:,L W!j :e!leJsnV dl Aq PAOAOal LL666L-S0lV :ON I SWoc 00 0 0 Cl ~2945HY-AU 00 Clq

11. The installed friction bolt assembly as claimed in claim 10 wherein said grouting is located only adjacent the leading end of said friction bolt. en

12. An installed friction bolt assembly substantially as herein described with 00 reference to the drawings.

13. A method of grouting a friction bolt at part only of the length of the bolt, said bolt having a longitudinally extending slit, said method comprising the steps of; O inserting said friction bolt into a blind hole to thereby frictionally engage Clq said bolt and hole, (ii) engaging at least one grout capsule with the leading end of said friction bolt by a retention means engaged with said bolt and not protruding into said slit, and (iii) permitting setting of, or actuating setting of, the grout material contained in said capsule(s).

14. The method as claimed in claim 13 wherein step (ii) is carried out prior to step

15. The method as claimed in claim 14 wherein said grout capsule(s) is/are carried with said friction bolt during insertion into said hole.

16. The method as claimed in any one of claims 13-15 wherein step (iii) comprises the hydrating of a cementitious grout via a water permeable grout capsule.

17. The method as claimed in any one of claims 13-16 wherein step (iii) includes applying a percussive force to said grout capsule(s).

18. A method of grouting a friction bolt at part only of its length, said method being substantially as herein described with reference to the drawings. Dated this 2 8 h day of July 2008 INDUSTRIAL ROLL FORMERS PTY LIMITED By: FRASER OLD SOHN Patent Attorneys for the Applicant 9 a8-C OOL2ssGG2O IHOS fFJU 010 ?3SUNJ sT: iT 8002 In 82