AU2014100864A4 - Ground support mesh - Google Patents

Abstract

A ground support wire mesh comprising a first layer of elongate wire members and a second layer of elongate wire members transverse to the first layer. The wire mesh has at least one deformable section that comprises at least one wire member from at least one layer spanning the deformable section. The part of each wire member spanning the deformable section has a set of one or more bends extending along the part. Forces acting on the wire mesh due to rock movements cause the wire members spanning the deformable section to undergo tension that causes the bends in the wire member to unravel permitting the deformable section and mesh to yield. Fig 18 1g, iB

Description

AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR AN INNOVATION PATENT (Original) APPLICATION NO: LODGED: COMPLETE SPECIFICATION LODGED: ACCEPTED: PUBLISHED: RELATED ART: NAME OF APPLICANT: Australian Steel and Wire Pty Ltd ACTUAL INVENTOR: Richard Edgar Sobey ADDRESS FOR SERVICE: LORD AND COMPANY, Patent and Trade Mark Attorneys, of PO Box 530, West Perth, Western Australia, 6872, AUSTRALIA. INVENTION TITLE: "GROUND SUPPORT MESH" The following Statement is a full description of this invention including the best method of performing it known to me/us: TITLE GROUND SUPPORT MESH FIELD OF THE INVENTION [0001] The present invention relates to a ground support mesh. More particularly, though not exclusively, the invention relates to a ground support mesh suitable for use in rock strata, mine roof and other ground support systems. BACKGROUND OF THE INVENTION [0002] In underground tunnelling and mining operations, rock bolts are commonly used to reinforce the roof or exposed surface of an excavated area and stabilise the rock face. Rock bolts are installed in holes that are drilled into the rock face and come in a variety of designs. Rock bolts typically comprise an elongate rod or tube, which may be secured in the drill hole by physical anchoring means and/or cement or chemical resin grout. Once the bolt is secured, a bearing or thrust plate is then added to the end of the bolt that bears against the rock face and is secured in place by attaching and tightening a tensioning nut. [0003] Ground support systems often also make use of wire support meshes. An array of support meshes are secured to the roof or rock surface to further reinforce the rock and to protect personnel working in the area from falling debris. Each support mesh is typically placed on the rock face and then clamped between the rock bolts that have been installed and the bearing/thrust plates to secure them. [0004] Prior art support meshes typically comprise two layers of individual wire members that are arranged longitudinally and laterally to form a grid. The wire members in the two layers are commonly joined together where they intersect, for example by welding, which provides the mesh with a degree of rigidity and stiffness and improves its load bearing strength. 2 [0005] Seismic and other earth movements may frequently take place during underground tunnelling and mining operations causing the rock face of a tunnel or excavated region to move and become less stable. Rock movements can place significant load on support meshes that are secured on the rock face causing their wire members to undergo strain. This will often cause the affected meshes to break at the wire member intersections, thus compromising their tensile strength and ability to withstand and support an unstable rock face. [0006] Prior art support mesh designs have attempted to accommodate and mitigate the adverse effects caused by rock movements typically by focussing on improving the strength of the wire member intersections. For example, some designs have made used of peripheral connecting means that are arranged and secured around each intersection, as an alternative to welding them. Despite these attempts, mesh designs that have their wire members joined at the intersections, and which rely on these joins as a means for providing the mesh's overall structural rigidity and load bearing strength, remain vulnerable to rock movements. [0007] The present invention attempts to overcome at least in part the aforementioned disadvantages. [0008] References to prior art are intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the present application. SUMMARY OF THE INVENTION [0009] Whilst maintaining a high tensile strength is an important attribute for an effective support mesh, the applicant has found that if the support mesh is also capable of exhibiting a degree of yield behaviour under load, then this significantly improves its dynamic energy absorption capacity. This yielding enables the mesh to continue to 3 withstand, support and provide a protective barrier to personnel located under a rock face that has become unstable and dynamic. [0010] According to one aspect of the present invention, there is provided a wire ground support mesh comprising a first layer of elongate wire members and a second layer of elongate wire members transverse to the first layer. The support mesh has at least one deformable section that comprises at least one wire member from at least one layer spanning the section. The part of each wire member that spans the section has a set of one or more bends extending along the part. Forces acting on the wire mesh due to rock movements cause the wire members spanning the deformable section to undergo tension. This causes the bends in the wire member to unravel permitting the deformable section and mesh to yield. [0011] Once all bends in the wire members under load have unravelled to their maximum extent, the support mesh's ability to yield is reduced dramatically. The mesh thereafter continues to operate and behave like a conventional support mesh whereby the individual wire members comprising the mesh each provide a high degree of tensile strength and resistance to the rock face. The initial yielding behaviour allows the support mesh to accommodate and adaptively resist rock face movements that would otherwise compromise the strength and effectiveness of the support mesh. The longevity and effectiveness of the mesh is thereby improved, providing significant cost and safety benefits. [0012] In a further embodiment, the wire members that comprise at least one of the deformable sections of the support mesh comprise wire members in both the first and second layers, and the set of bends in each wire member spanning the deformable section is preferably an alternating sequence of troughs and apexes. Further, each trough in each wire member in the first layer is preferably positioned substantially opposite to an apex in the second layer, and each apex in each wire member in the first layer is preferably positioned substantially opposite to a trough in the second layer. This arrangement of 4 interleaving troughs and apexes enables the support mesh to yield, when placed under load, in a uniform and consistent manner. [0013] In a further embodiment, the ground support wire mesh may additionally comprise a bolting section which enables the mesh to be secured to the rock surface more effectively. The bolting section will preferably be defined by two or more groups of wire members in the mesh, each group being positioned around the outer perimeter of the mesh and defining one side of the bolting section. Each group will preferably comprise two or more substantially parallel wire members, and each wire member in each group will intersect wire members in at least one other group. The wire members that intersect will preferably be joined together at the intersections, for example by welding. The wire members that comprise the bolting section will preferably be larger in diameter than the wire members that are not in the bolting section. [0014] The bolting section provides an area of increased rigidity and resistance on the surface of the support mesh. The thrust/bearing plates and tensioning nuts are clamped to the bolting section when the mesh sheet is secured to the rock face strata. DESCRIPTION OF THE DRAWINGS [0015] The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 A shows a perspective view of a ground support wire mesh in accordance with the present invention; Figure lB shows an enlarged view of a section of the ground support wire mesh shown in Figure IA; Figure 2A shows a side view of a ground support wire mesh in accordance with the present invention; and 5 Figure 2B shows an enlarged view of a section of the ground support wire mesh shown in Figure 2A. DESCRIPTION OF AN EMBODIMENT OF THE INVENTION [0016] Referring to Figures IA and 2A, there is shown a ground support mesh (10) in accordance with a preferred embodiment of the present invention. The ground support mesh (10) comprises a first layer of elongate wire members (20) and a second layer of elongate wire members (30) that are transverse to the first layer (20). The ground support mesh (10) has a deformable section (40) which is delineated by points A, B, C to D marked on the mesh in Figure 1A. The deformable section (40) is defined by a plurality of wire members that span the deformable section (40) each having a plurality of bends extending along the length of the wire member spanning the deformable section (40). As illustrated in Figure 1A, this arrangement provides that the wire members in the first and second layers spanning the deformable section (40) do not come into contact with each other at the points at which they cross. [00171 Figure 1B shows an enlarged view of the area marked 45 on the ground support mesh (10) in Figure IA. Referring to this figure, the plurality of bends shown in the embodiment consists of an alternating sequence of troughs (50 and 60) and apexes (70 and 80) that extend along the elongate length of each wire member that spans the deformable section (40). Each trough (50) in each wire member in the first layer (20) is preferably positioned substantially opposite to an apex (70) in the second layer (30) and each apex (80) in each wire member in the first layer (20) is positioned substantially opposite a trough (60) in the second layer (30). [0018] In the event of movements of the supported rock face due to seismic activity or rock failure, forces acting on the wire members that define the deformable section cause them to undergo significant tension. These tensile forces cause the bends that span the deformable section to unravel thereby extending the length of the wire members and permitting the deformable section and mesh to yield. The yielding significantly improves 6 the dynamic energy absorption capacity of the mesh and enables it to continue to withstand, support and provide a protective barrier across the rock face in dynamic rock conditions. [0019] Further, the ground support mesh (10) may also comprise a bolting section 100. The bolting section is defined by two or more groups of wire members (110) that are preferably positioned around the outer perimeter of the wire mesh. Each group (110) preferably comprises two or more substantially parallel wire members (120). The wire members comprising each group (110) are joined, preferably by welding them, to the wire members that they intersect in the other groups. The bolting section provides an area of increased rigidity and resistance on the surface of the support mesh. The thrust/bearing plates and tensioning nuts are clamped to the bolting section when the mesh sheet is secured to the rock face strata. [0020] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. 7

Claims (5)

1. A ground support wire mesh comprising: a first layer of elongate wire members and a second layer of elongate wire members transverse to the first layer, and at least one deformable section of the wire mesh comprising: at least one wire member from at least one layer spanning the deformable section, wherein the part of each wire member spanning the section has a set of one or more bends extending along the part, wherein forces acting on the wire mesh due to rock movements cause the wire member(s) spanning the deformable section to undergo tension, and wherein the tension causes the bends in the wire member(s) to unravel thereby permitting the deformable section and mesh to yield.

2. A ground support wire mesh as defined in claim 1, wherein the wire members that comprise at least one of the deformable sections comprise wire members in both the first and second layers, and: the set of bends in each wire member spanning the deformable section is an alternating sequence of troughs and apexes, each trough in each wire member in the first layer is positioned substantially opposite an apex in the second layer, and each apex in each wire member in the first layer is positioned substantially opposite a trough in the second layer.

3. A ground support wire mesh as defined in any preceding claim, that includes wire members that define a bolting section of the mesh, wherein: the bolting section is defined by two or more groups of wire members, each group is positioned around the outer perimeter of the wire mesh and defines one side of the bolting section, each group comprises two or more substantially parallel wire members, 8 each wire member in each group intersects wire members in at least one other group, and the wire members that intersect are welded together at the intersections.

4. A ground support wire mesh as defined in claim 4, wherein the wire members comprising the bolting section are larger in diameter than the wire members not comprising the bolting section.

5. A ground support wire mesh as defined in any preceding claim having only one deformable section, wherein the deformable section covers a majority of the surface area of the wire mesh. 9