AU717527B2 - A support assembly - Google Patents

Description

4i,

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT a Applicant(s): BHP ENGINEERING PTY LTD Invention Title: A SUPPORT ASSEMBLY The following statement is a full description of this invention, including the best method of performing it known to me/us: -la- A SUPPORT ASSEMBLY The present invention relates to a support assembly that is adapted to be anchored in rock and is suitable for use in a range of applications in underground mines and elsewhere.

In general terms, the support assembly of the present invention is suitable for use in any application in an underground mine or elsewhere in which it is *c necessary to anchor a member, such as a roof support member or a mine conveyor, to a rock formation.

The present invention relates particularly to the use of the support assembly as part of a support system for supporting a rock formation.

The present invention also relates to the support system per se.

For the purpose of clarity, the following discussion of the support assembly of the present invention is in the context of a support system for supporting the roof of an underground mine.

It will be appreciated that the support system of the present invention is applicable equally to support rock in the walls of an underground mine and to other applications in underground mines, tunnels, or other rock excavations, such as rock cuttings, and elsewhere.

H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -2 The support of rock in underground mining is a fundamental part of efficient mining operations.

Various methods and products are used to support rock in the roof of a mine including rock bolts, cable bolts, steel straps, mesh, bearing plates, steel beams, pit props, and timber crib blocks. All these support methods and products are designed to support the roof and to prevent roof movement. However, once significant roof movement has taken place, it is often necessary to restrain the rock from ultimate collapse. Known roof support members for this purpose include steel cable trusses, steel bar trusses, or cable slings.

15 A truss for roof support is a steel reinforcing member which is installed horizontally against the roof and is firmly anchored at each end. As roof movement occurs, the truss is deformed and a tensile force is generated in the truss. Since the tensile stiffness and strength of the truss is high, further roof movement is restricted once the truss is deformed into a flat catenary shape. In this way, the truss system offers roof support after significant roof movement has already occurred.

Currently, there are two main truss systems available.

The first system uses either a solid steel bar or a cable which is placed against the roof and ias secured by an anchor block attached to a rock bolt at each end of the truss. Such a system is disclosed in Australian patent application AU-A-32901/95 by Jennmar H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -3 Corporation entitled "Method and Apparatus for Supporting a Mine Roof". The anchored block is therefore subjected to a horizontal force once the truss, begins to function, and this horizontal force is transferred directly onto the end of the rock bolt supporting the anchor block. This horizontal force creates a shear force in the end of the rock bolt, often where the thread has been cold rolled into the end of the rock bolt. Rock bolts are not designed to withstand this shear force and, consequently, the end of the rock bolt can fail in shear causing the whole truss system to fail. This is the major disadvantage of this truss system.

9*oo 15 The second type of truss system currently available uses two steel cables. One end of each cable is grouted into the roof and acts like a standard cable S- bolt. The other end of each cable is locked together in the middle of the truss system by barrel and wedge 20 assemblies on either side of a twin-holed block of steel. The truss is tensioned by a standard cable pretensioning jack. This system is simpler, but it has two major disadvantages. Firstly, the grout must be allowed to cure before the truss can be tensioned (usually seven days). Secondly, when load is applied to the truss, the cable cuts into the rock where the cable is anchored in the roof and creates a "cheese cutter" effect. This means that the cable truss is not anchored firmly at each end and, consequently, the cable truss will not effectively resist deformation of the roof.

As is evident from the above discussion, each type of truss system currently available has H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 4- -4 considerable problems.

An object of the present invention is to provide a support system for the roof of an underground mine that alleviates the problems of the known truss support systems described above.

Another object of the present invention is to provide a support assembly for anchoring members, such as a roof support member, in rock.

According to the present invention there is provided a support system to resist deformation of rock, which support system comprises: S. a support member (as herein defined); (ii) a pair of spaced-apart support assemblies for supporting a span of the support member, with each support assembly comprising a post anchored, wedged, or otherwise retained in a hole in the rock, and the post having an opening which receives the support member; and (iii) a means to couple the support member to each support assembly so that the support assemblies support the span of the support member.

The term "support member" is understood herein to mean any suitable elongate member, such as a cable, bar or rod.

H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 It is preferred that the post be a hollow post.

In the case of a hollow section post, it is preferred that the opening which receives the support member comprises aligned openings in opposed sections of the wall of the post.

With such an arrangement, it is-preferred that each support assembly further comprises a rock bolt assembly which anchors the hollow section post in the hole in the rock.

It is preferred that the rock bolt assembly 15 comprises a rock bolt having: a threaded end; (ii) grout or resin or other suitable means y "20 which retain the rock bolt in a rock bolt hole in the rock with the threaded end extending from the rock bolt hole into the space enclosed by the tubular post, and (iii) a nut located on the threaded end of the rock bolt.

With this arrangement, it is preferred that the hollow section post comprises a plate or other means that closes one end of the post and that the plate or other means comprises an opening through which extends the rock bolt with the nut of the rock bolt assembly H:\Maria\Keep\BHP PN967t A SUPPORT ASSEMBLY.doc 5/5/97 -6 threaded against the plate or other means to hold the post in the hole.

It is preferred that the hollow section post be positioned in the hole with the plate or other means adjacent the distal end of the hole. With this arrangement, the threaded end of the rock bolt and the nut of the rock bolt assembly can be confined within the post and not extend from the hole in the rock. This is an important feature in the context of a roof of an underground mine where it is preferable to avoid rock o*00: bolts protruding downwardly from the roof in order to o maximise roof clearance and to minimise damage caused by contact of vehicles or other equipment with rock bolts.

a.

Further to the preceding paragraph it is preferred that the lengths of the hollow section post and the hole be selected to that the post extends a short distance only from the hole.

The post may be of any suitable cross section and formed from any suitable material.

It is preferred that the hollow section post be tubular.

It is preferred that the maximum width of the post be relatively large compared to that of the support member.

The term "width" in this context is understood to refer to a dimension that is transverse to the longitudinal axis of the post.

H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 f I -7 It is preferred that the maximum width of the post be at least 5 times that of the support member.

It is preferred more particularly that the maximum width of the post be at least 10 times that of the support member.

It is preferred that the support member be a cable.

S* It is preferred that the coupling means be barrel and wedge assemblies which lock onto the cable S. and contact sides of the hollow section posts that are 15 remote from the span of the support member that is supported by the hollow section posts.

According to the present invention there is also provided a support assembly that is adapted to be anchored in rock, which support assembly comprises a post having a hollow section wall and at least one pair of aligned openings in the wall for receiving therethrough a member to be supported by the support assembly.

The support assembly may be used as part of the support system of the present invention. However, the support assembly of the present invention is not limited to this application and may be used generally in underground mines or elsewhere where it is necessary to anchor a member, such as a mine conveyor, to a rock formation.

H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -8 As is described above in relation to the support system of the present invention, in use, the post may be anchored, wedged, or otherwise retained in the hole of the rock.

It is preferred that the hollow section wall be tubular.

It is preferred that the support assembly comprises a rock bolt assembly for anchoring the hollow section post in the hole in the rock. As is described •above in relation to the support system of the present "invention, the combination of the hollow section post o and the rock bolt assembly is an important feature of e* 15 the support assembly because it makes it possible for the rock bolt assembly to be confined within the post.

It is preferred that the support assembly further comprises a plate or other means that closes one 20 end of the post and that the plate has an opening for 4** receiving therethrough a rock bolt of a rock bolt assembly for retaining the post in the rock.

The present invention is described further by way of example with reference to the accompanying drawings of which: Figure 1 is a schematic vertical cross section of a roadway in an underground mine which illustrates a preferred embodiment of the support system of the, present invention supporting rock in a section of the roof of the roadway and which includes a preferred H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -9 embodiment of a support assembly of the present invention; Figure 2 is an enlarged view of the circled section of Figure 1.

Figure 3 is a perspective view of a tubular post of the support assembly shown in Figure 2; Figure 4 is an axial cross section of the tubular post; S: Figure 5 is an end view of the tubular post in the direction of the arrow A in Figure 4; 86 Figure 6 is a section along the line 6-6 of Figure 4.

Figure 7 is a schematic plan view of a section 20 of a roadway in an underground mine which illustrates a preferred array of the support system of the present invention; Figure 8 is a perspective view of an alternative embodiment of the tubular post shown in Figure 3; Figure 9 is an axial cross-section of the tubular post of Figure 8; Figure 10 is an end view of the tubular post in the direction of the arrow A in Figure 9; and H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 Figure 11 is a section along the line 11-11 in Figure 9.

With reference to Figure 1, the preferred embodiment of the support system of the present invention is positioned to resist deformation of rock in a section of the roof 3 of a roadway 5 in an underground mine.

As is described in more detail below, the support system shown in the drawings includes a preferred embodiment of a support assembly of the present invention.

15 More particularly, the support system comprises: a support member in the form of a "cable truss" 7; 20 (ii) two spaced apart support assemblies, generally identified by the numeral 9, that are anchored or otherwise retained in the rock and support a span of the cable truss 7; and (iii) a means, generally identified by the numeral 19 in Figure 2, that couples the cable truss 7 to the support assemblies 9.

With reference to Figure 2 (which is an enlarged view of the circled section of Figure each support assembly 9 comprises a tubular post which has an upper H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -11 section that is anchored in a hole 12 drilled in the roof 3 and a lower section that extends a short distance from the hole 12 into the roadway With reference to Figures 2 to 7, the post has a cylindrical wall 11, an end wall 13 having a central opening 15, and a plurality of aligned pairs of openings 17 in the cylindrical wall 11 in the lower section of the post that extends into the- roadway 5. As can best be seen in Figure 2, one pair of the aligned openings 17 receives one end section of the cable truss 7.

The other pairs of openings 17 are provided to receive end sections of several other truss cables.

15 This may be required in situations, such as shown in Figure 7, where the support system shown in Figure 1 forms part of an array. Figure 7 illustrates schematically an arrangement of: 20 4 posts which form the corners of a rectangular array with 2 posts adjacent each side 37 of the roadway; and (ii) 4 cable trusses 7 positioned so that each post supports 2 of the cable trusses 7.

In order to minimise interference, it is preferred that the hole pairs be offset axially. In addition, the hole pairs are located around the circumference of the cylindrical wall 11 at positions which correspond to the preferred orientation of cable trusses 7 in the mine.

H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -12 The support assembly 9 further comprises a rock bolt assembly which retains the post in the hole 12.

Specifically, the rock bolt assembly comprises a rock bolt 21 that is retained in a rock bolt hole 25 by grout or other suitable means. The rock bolt 21 further comprises a threaded end 23 that extends into the space enclosed by the post. The rock bolt assembly further comprises a "cup and saucer" bearing plate assembly or other suitable bearing plate assembly, generally identified by the numeral 29, and a nut 31 threaded on the threaded end 23 which react against the plate 13 of the post and thereby retain the post in the hole 12.

i With reference to Figure 2, the coupling means 19 comprises a barrel and wedge assembly associated with each post. Specifically, each barrel and wedge assembly 19 locks onto an end section of the cable truss 7 and contacts the side of the associated post that is remote from the span of the cable truss 7 that is supported by 20 the posts. This arrangement prevents the cable truss 7 sliding through the openings 17 in the post in response to an applied load resulting from deformation of rock.

It is noted that the dimensions of the posts are preferably selected so that the diameter of the cylindrical walls 11 is relatively large compared with that of the cable truss 7.

Furthermore, it is noted that the diameter of the holes 12 is selected so that there is a relatively small clearance between the sides of the holes 12 and the cylindrical walls 11 of the posts.

H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -13 It is also noted that the length of the posts can be varied to suit specific mine conditions. For example, in very weak rock conditions it may be preferable to have a slightly longer embedment length of the posts in the rock.

It is also noted that the lower end of the posts may be strengthened to prevent collapse under extreme load. By way of example, each post may be strengthened by welding reinforcing gussets onto the cylindrical wall 11. Alternatively, as is shown in Figures 8 to 11, each post may be strengthened by positioning an outer sleeve 41 on the cylindrical wall 11 and providing an end plate 43 to close the open end. The outer sleeve 41 may be welded to the cylindrical wall 11. The end plate 43 may be threaded to mate with an internal thread on the cylindrical wall 11. Alternatively, the end plate 43 could comprise a bayonet fitting (not shown).

The above-described support system operates in a fundamentally different way to existing truss support systems. Specifically, when load is applied to the span of the cable truss 7 supported by the support assemblies 9, the load is transferred to the ends of the posts.

Since the posts are located with minimal clearance in the holes 12 and are securely retained in the holes by means of the rock bolt assemblies, movement of the posts in response to the load is significantly limited. In addition, since the posts are a relatively large diameter relative to that of the cable truss 7, the posts will not cut into the rock as load is applied to the cable truss 7. In addition, since a relatively long length of the posts are located in the rock and are H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -14 anchored securely by the rock bolt assemblies, the posts can resist the force generated by the cable truss 7 since this force is transferred directly into the rock.

A particular feature of the above-described support assembly 9 is that the lower end (ie the threaded end 23) of the rock bolt 21, the nut 31, and the bearing plate assembly 29 are recessed into the roof 3. This provides the following advantages.

1. The lower end of the rock bolt 21 does not protrude into the roadway 5 and therefore assists with roof clearance in thin seam mining operations.

15 2. The bearing plate assembly 29 is located up in the roof strata away from the immediate exposed roof. The immediate exposed roof will be more broken and cracked than rocks higher up in the roof depending on the geology and stress conditions existing in the roof. Therefore, the bearing plate 29 will be in contact with more competent rocks and will offer greater end restraint.

3. The rock bolt 21 will be located slightly higher up into the roof strata and will therefore have a greater effective length than a conventionally installed rock bolt.

4. The recessed bolting offers protection to the lower end of the rock bolt 21. In particular, for underground coal mining operations, the longwall method of mining requires that the hydraulic chocks be moved for each new longwall block of coal approximately every H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 12 months. When these chocks are moved they are often "walked" down roadways which have previously been bolted. In this case the chocks can either break off the end of protruding rock bolts or can actually push rock bolts up into the roof causing a shear failure of the resin anchor.

Many modifications may be made to the preferred embodiment described above without departing from the spirit and scope of the present invention.

By way of example, whilst in the preferred embodiment of the support assembly the post comprises a cylindrical wall, it can readily be appreciated that the 15 present invention is not limited to this arrangement and the wall may be of any suitable configuration.

Furthermore, whilst the preferred embodiment of the support system is shown in Figure 1 with the cable i 20 truss 7 substantially spanning the width of the roadway 5 and the support assemblies 9 located adjacent the sides of the roadway 5, it can readily be appreciated that the present invention is not limited to this arrangement. By way of example, in another arrangement support assemblies 9 may be positioned in the centre and at the sides of the roadway with the central support assembly 9 protruding a greater distance into the roadway 5 than the support assemblies 9 at the sides.

In this situation a cable truss 7 passes through the central support assembly 9 at a greater distance from the roof 3 than at the sides and therefore forms a pseudo-catenary shape and, consequently, offers greater restraint to roof movement than if the cable truss 7 was H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -16flush against the roof 3.

Furthermore, whilst the preferred embodiment of the support system comprises a barrel and wedge assembly 19 which connects the cable truss 7 to the posts, it can readily be appreciated that the present invention is not limited to this arrangement and it extends to any suitable means for this purpose. For example, the support system may comprise a nut which can be threaded onto a cable truss in the form of a solid bar with threaded ends.

Furthermore, whilst in the preferred embodiment of the support system, the barrel and wedge assembly 19 15 is located externally of the hollow section post, it can readily be appreciated that the present invention is not so limited to this arrangement and it extends to arrangements in which the coupling means is located within the hollow section post.

a H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97

Claims (18)

1. A support system to resist deformation of rock, which support system comprises: a support member (as herein defined); (ii) a pair of spaced-apart support assemblies supporting a span of the support member, with each support assembly comprising a post anchored, wedged, or otherwise retained in a hole in the rock, and the post having an opening which receives the 15 support member; and (iii) a means coupling the support member to each support assembly so that the support assemblies support the span of the 20 support member.

2. The system defined in claim 1 wherein the post is a hollow post.

3. The system defined in claim 2 wherein the opening which receives the support member comprises aligned openings in opposed sections of the wall of the hollow post.

4. The system defined in claim 2 or claim 3 wherein each support assembly further comprises a rock bolt assembly which anchors the hollow section post in the le in the rock.

G:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 1/28/00 v* -18- The system defined in claim 4 wherein the rock bolt assembly comprises a rock bolt having: a threaded end; (ii) grout or resin or other suitable means which retain the rock bolt in a rock bolt hole in the rock with the threaded end extending from the rock bolt hole into the space enclosed by the tubular post, and (iii) a nut located on the threaded end of the 15 rock bolt.

6. The system defined in claim 5 wherein the hollow section post comprises a plate or other means that closes one end of the post and the plate or other means 20 comprises an opening through which extends the rock bolt with the nut of the rock bolt assembly threaded against the plate or other means to hold the post in the hole.

7. The system defined in claim 6 wherein the hollow section post is positioned in the hole with the plate or other means adjacent the distal end of the hole so that the threaded end of the rock bolt and the nut of the rock bolt assembly are confined within the post and do not extend from the hole.

8. The system defined in any one of claims 2 to 7 wherein the hollow section post is tubular. H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 -19-

9. The system defined in any one of the preceding claims wherein the maximum width of the post is relatively large compared to that of the support member.

10. The system defined in claim 9 wherein the maximum width of the post is at least 5 times that of the support member.

11. The system defined in claim 10 wherein the maximum width of the post is at least 10 times that of the support member.

12. The system defined in any one of the preceding claims wherein the support member is a cable.

13. The system defined in claim 12 wherein the coupling means comprises barrel and wedge assemblies which lock onto the cable and contact sides of the hollow section posts that are remote from the span of 20 the support member that is supported by the hollow section posts.

14. A support assembly that is adapted to be anchored in rock, which support assembly comprises a post having a hollow section wall and at least one pair of aligned openings in the wall for receiving therethrough a member to be supported by the support assembly.

15. The support assembly defined in claim 14 further comprises a rock bolt assembly for anchoring the hollow section post in the hole in the rock. H:\Maria\Keep\BHP PN9671 A SUPPORT ASSEMBLY.doc 5/5/97 HL\' 1-1

16. The support assembly defined in claim 15 further comprises a plate or other means that closes one end of the post and the plate has an opening for receiving therethrough a rock bolt of a rock bolt assembly for retaining the post in the rock.

17. A truss system substantially as hereinbefore described with reference to the accompanying drawings.

18. A support assembly substantially as hereinbefore described with reference to the accompanying drawings. Dated this 5 th day of May 1997 1. BHP ENGINEERING PTY LTD By Its Patent Attorneys GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia. G s *0 So. H\Maria\Kep\BH PN9671 A SUPPORT ASSEMlLY.doc 5/5/97