AU785307B2

AU785307B2 - A mine roof support mesh

Info

Publication number: AU785307B2
Application number: AU48925/02A
Authority: AU
Inventors: Graeme Mcgregor
Original assignee: OneSteel Reinforcing Pty Ltd
Current assignee: Infrabuild Construction Solutions Pty Ltd
Priority date: 2001-06-26
Filing date: 2002-06-25
Publication date: 2007-01-11
Anticipated expiration: 2022-06-25
Also published as: AU785307C; AU4892502A; NZ519777A; AUPR592701A0

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): ONESTEEL REINFORCING PTY LTD Invention Title: A MINE ROOF SUPPORT MESH The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 A MINE ROOF SUPPORT MESH The present invention relates to a mine roof support mesh for stabilizing roof strata of underground mines.

It is known to stabilise roof strata of underground mines with rock bolt assemblies that comprise rock bolts anchored, typically by means of cement or chemical resin grout, in holes drilled in roof strata and tensioned by nuts threaded onto the rock bolts.

Typically, bearing plates are positioned between the nuts and roof strata.

The purpose of rock bolt assemblies is to apply a clamping or confining action to a section of roof strata to control deformation of the section and to enhance the strength of the section. More specifically, the purpose of rock bolt assemblies is to allow load to be transferred from a section to rock bolts to sustain the load. The spacing of rock bolt assemblies is a function directly of the characteristics of roof strata.

It is also known to stabilise roof strata by using W-straps with rock bolt assemblies. The purpose of W-straps is to resist downward sagging of roof strata. Wstraps are formed from pressed or roll-formed metal.

In use, W-straps are positioned against roof strata and rock bolts of rock bolt assemblies are positioned to extend through spaced-apart pre-punched holes in the W-straps and into holes drilled in the roof strata. Tensioning nuts and bearing plates of rock bolt assemblies hold the W-straps in position and, more particularly, clamp the W-straps at a series of spaced positions to roof strata.

3 Conventional W-straps are relatively narrow and do not cover the whole roof strata. In addition, W-straps cover very little of the strata and hence if are to be effective in some cases need to be placed side by side, thus becoming expensive because of the numbers of W-straps and rock bolt assemblies required and the amount of drilling required. In addition, W-straps also have only a very limited number of preset bolt positions.

In order to retain loose rock that otherwise could fall into a mine drive from sections of roof strata not covered by W-straps, it is known to use modified Wstraps which comprise mesh tied or welded to W-straps to cover the spaces between adjacent W-straps. These modified W-straps are expensive and difficult to handle and to transport.

It is also known to stabilize roof strata by using roof support mesh with rock bolt assemblies. The mesh is formed from a first layer of parallel wires that are welded to a second layer of parallel wires that are transverse to the wires of the first layer.

As with W-straps, in use, sheets of roof support mesh are positioned against roof strata and rock bolts of rock bolt assemblies are positioned to extend through openings in a "bolting" section of the mesh and into holes drilled in the roof strata. Thereafter, tensioning nuts and bearing plates of rock bolt assemblies are positioned on the rock bolts and clamp the mesh sheets to roof strata.

An object of the present invention is to provide an improved roof support mesh.

According to the present invention there is provided a mine roof support mesh for supporting an area 4 of a roof of a mine, which mesh includes three layers of wires with the wires of the first and the second layers being connected together and the wires of the second and the third layers being connected together, whereby the wires of the second layer are sandwiched between the wires of the first and the third layers, the wires of the first and the third layers are parallel to each other, and the wires of the second layer are parallel to each other and are transverse to the wires of the first and the third layers.

The above-described mesh defines a rigid beamtype structure that has a higher stiffness compared to mine roof support mesh known to the applicant.

Specifically, the above-described mesh has a stiffness that is at least 4 times that of unbent mine roof support mesh known to the applicant.

It is preferred that the wires of the first layer be offset with respect to the wires of the third layer to facilitate stable stacking of a plurality of sheets of the mesh disposed horizontally and stacked one on top of the other in a vertical stack.

In this connection, offsetting the wires makes it possible to form stable stacks of sheets of the mesh with the stacks having vertical sides as a result of successive sheets being positioned directly on top of underlying sheets and with the wires being disposed horizontally, ie without the wires of the first layer of one sheet interfering with the wires of the third layer of a successive or an underlying sheet and causing uneven stacking of the sheets.

Being able to form stable, vertical stacks of sheets of mesh as described in the preceding paragraph makes it possible to store larger numbers of sheets of 5 mesh safely in a given area at a factory and at a mine site and to transport larger numbers of sheets of mesh safely from a factory to a mine site and from a top of a mine site to underground.

This is a significant improvement over known mesh, particularly known mesh that has upturned and/or downturned end sections this mesh is difficult to stack in stable stacks. In particular, known mesh that has upturned and/or downturned end sections becomes increasingly unstable in stacks as the wire diameter increases and as the bend angle of the upturned and/or downturned end sections increases.

It is preferred that the mesh include a bolting section that is distinguished visually from the remainder of the mesh.

It is preferred that the mesh include a bolting section that is defined by wires in the mesh that visually distinguish the bolting section from the remainder of the mesh.

The term "bolting" section is understood herein to mean a preferred section of the mesh to be contacted by rock bolt assemblies for clamping the mesh to a roof strata.

The remainder of the mesh is hereinafter referred to as the "loose rock retention" section of the mesh.

It is preferred that the bolting section has a larger cross-sectional area of wire per unit area of mesh than the loose rock retention section so as to increase the force capacity and the resistance to shearing the mesh in the bolting section of the mesh.

6 By way of example, the bolting section may be defined by a pair of wires in the first layer, each wire of the pair defining one side of the bolting section, and each wire of the pair having a larger cross-sectional area than the other wires in the mesh.

By way of further example, the bolting section may be defined by two groups of wires, each group defining one side of the bolting section, and each group including one or more wires in the first layer and one or more wires in the third layer that are offset with respect to each other so that the wires in both layers appear to be in contact or to be more closely spaced than the other wires in the mesh when viewed from above or below the mesh. The wires in the bolting section may be the same or different cross-sectional area than the wires in the remainder of the mesh. There are a numer of possible combinations in this category. By way of example, there may be two wires in each group in the first layer and one wire in each group in the third layer. In addition, by way of example, there may be one wire in each group in the first layer and two wires in each group in the third layer. In addition, by way of example, there may be one wire in each group in the first layer and one wire in each group in the third layer.

By way of further example, the bolting section may be defined by two groups of wires in the first layer, each group defining one side of the bolting section, and each group including two or more wires that are in contact or are more closely spaced than the other wires in the mesh. The wires in the bolting section may be the same or different cross-sectional area than the wires in the remainder of the mesh.

Preferably the spacing between pairs of wires in the bolting section or between groups of wires in the 7 bolting section is less than the spacing between wires in the remainder of the mesh.

It is preferred that the other wires in the mesh be single wires rather than groups of wires.

It is preferred that the mesh be curved to increase the stiffness of the mesh.

It is preferred that the curved mesh be formed so that the mesh bends under the weight of the mesh and forms a flat product when the mesh is held at the ends and lifted clear of an underlying support.

In situations where the mesh is curved and the curved mesh includes a bolting section that is defined by larger cross-sectional area wires or by groups of two or more wires, it is preferred that the first layer be the layer that has a smaller radius than the other layers. It is noted that the present invention is not limited to this arrangement and also extends to the reverse arrangement in which the first layer has a larger radius than the other layers of the mesh.

It is preferred that the wires be formed from steel.

The wires may be any cross-sectional shape.

By way of example, the wires may be circular in cross-section.

It is preferred that the wires be circular in cross-section.

It is preferred that the wires be at least 4mm in diameter.

8 By way of further example, rather than being circular, the wires may be non-circular with flat sections that provide greater surface area of contact between contacting wires in the mesh than can be achieved with wires having non-circular cross-sections.

The non-circular cross-section wires may be formed by any suitable means.

For example, the wires may be formed by in-line rolling wires of circular cross-section into wires of noncircular cross-section.

For example, the rolled wires may be figure 8 or other non-circular cross-section shape which is substantially flat.

With the above discussion in mind, it can be appreciated that there are a number of options for achieving a given wire cross-sectional area in a given section of the mesh.

By way of example, a single wire of circular cross-section of 10mm diameter has approximately the same cross-sectional area as 2 wires of circular cross-section of 7mm diameter positioned side by side, 3 wires of circular cross-section of 5.7mm diameter positioned side by side and a single wire of circular cross-section of 10mm diameter that is roll-formed to a figure 8 form.

The wires may be connected together by any suitable means.

Preferably the wires are welded together.

The present invention is described further by way 9 of example with reference to the accompanying drawings, of which: Figure 1 is a side elevation of one preferred embodiment of a mine roof support mesh formed in accordance with the present invention; Figure 2 is a side elevation of the mesh shown in Figure 1 viewed in the direction of the arrow A in Figure 1; Figure 3 is a side elevation of a plurality of sheets of the mine roof support mesh shown in Figure 1 positioned in a vertical stack; Figure 4 is a side elevation of the mine roof support mesh shown in Figures 1 and 2 positioned in use against an area of a mine roof; and Figure 5 is a side elevation of another preferred embodiment of the mine roof support mesh in accordance with the present invention.

The mine roof support mesh 3 shown in Figures 1 and 2 is constructed from steel wires 5, 7, 9 of the same diameter that are positioned and welded together to form three layers of wires.

The wires identified by the numeral 5 form the first layer, the wires identified by the numeral 7 form the second layer, and the wires identified by the numeral 9 form the third layer.

The wires 5, 9 of the first and the third layers are parallel to each other and the wires 7 of the second layer, ie the layer that is sandwiched between the first and the third layers, are parallel to each other and are 10 transverse to the wires 5, 9 of the first and the third layers.

When viewed in top plan, the mesh is generally rectangular, flat sheet.

The mesh 3 defines a rigid beam-type structure that has higher stiffness than other mesh products that are known to the applicant.

The length and width dimensions of the mesh 3 may be selected as required.

The first layer of the mesh 3 shown in Figures 1 and 2 includes two adjacent pairs of wires 5 with the wires of each pair being in contact with each other. The pairs of wires 5 distinguish this section of the mesh from the remainder of the mesh and define two sides of a bolting section of the mesh.

In addition to marking the location of the bolting section of the mesh, the pairs of wires concentrate metal in the bolting section and thereby improve the resistance of the mesh to shear failure at the bolting section.

The wires 5, 9 of the first and the third layers are positioned so that the wires 9 of the third layer are offset with respect to the wires 5 of the first layer.

With this arrangement, a plurality of sheets of mesh disposed horizontally can be stacked in a stack with vertical sides (as shown in Figure 3) without any interference between the wires of the first and third layers in successive/underlying sheets of mesh. As a consequence, it is possible to form a stable, vertical stack of sheets of mesh with all of the wires being horizontally disposed.

11 Figure 4 illustrates how the mesh 3 may be used to support an area of a roof strata. With reference to the figure, a sheet of the mesh 3 is retained against the roof strata by means of a plurality of rock bolt assemblies (only one of which is shown in the figure) acting against the bolting section of the mesh. Each rock bolt assembly includes a rock bolt 19, a bearing plate 21, a washer 23, and a tensioning nut 25 that clamps the mesh sheet to the roof strata 17.

Figure 4 illustrates the preferred orientation of the mesh sheet with the wires 5 in the first layer of the mesh being positioned as the lower layer of the mesh.

It is also evident from Figure 4 that, whilst the wires 9 in the third layer of the mesh that are in the vicinity of the bolting section of the mesh are positioned outwardly of the wires 5 in the first layer that define the sides of the bolting section, these wires 9 nevertheless are sufficiently close to the bolting section, ie in a critical section of the mesh, to contribute to the stiffness and strength of the mesh in the bolting section of the mesh.

The spacing and diameter of the wires in the mesh 3 may be selected as required to achieve target mechanical properties of the mesh.

One option for improving the stiffness of the mesh 3 shown in Figures 1 to 4 is to form the mesh as a curved sheet which bends under its own weight when held at the ends and lifted clear of a support (such as a stack of mesh sheets) and forms a flat sheet. The amount of curvature in the sheet may be selected depending on the target mechanical properties of the mesh.

12 It is preferable that the curved mesh be formed with the wires 5 of the first layer being the lower layer of the mesh as viewed with the curved mesh on the ground and the mesh in a convex orientation. In this arrangement, the lower layer of the mesh has a smaller radius than the other layers of the mesh.

The mesh 3 shown in Figure 5 is identical to that shown in Figures 1 to 4 save that the wires 5 and 9 of the first and third layers are not offset.

As a consequence, in order to form a stable stack of mesh sheets, it is necessary to laterally displace successive sheets in the stack so that the wires 5, 9 of the first or third layers of one sheet in the stack do not interfere with the wires 5, 9 of the first or third layers of a successive or underlying sheet in the stack.

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

By way of example, whilst the preferred embodiments described above are made from steel wires of the same diameter, the present invention is not so limited and extends to mesh made from wires of different diameters.

Furthermore, whilst the preferred embodiments described above include a bolting section in the form of two pairs of wires 5 in the first layer with the wires of each pair being the same diameter, the present invention is not so limited and extends to any suitable construction that visually distinguishes the bolting section from other sections of the mesh. By way of example, the bolting section may be defined by larger diameter wires or by 13 groups of 3 or more smaller diameter wires. By way of further example, each pair of wires may comprise one wire from the first layer and one wire from the third layer that is offset with respect to the first layer wire so that the wires appear to be in contact or to e closely spaced when the mesh is viewed from above or below.

Furthermore, whilst the wires 5, 7, 9 in the preferred embodiments described above are generally equally spaced apart, the present invention is not so limited and the spacing between the wires in different sections of the mesh may be varied according to the end use requirements of the mesh. Typically, the spacing of the wires in the bolting section would be equal to or less than that in the remainder of the mesh.

Claims

1. A mine roof support mesh for supporting an area of a roof of a mine, which mesh includes three layers of wires with the wires of the first and the second layers being connected together and the wires of the second and the third layers being connected together, whereby the wires of the second layer are sandwiched between the wires of the first and the third layers, the wires of the first and the third layers are parallel to each other, and the wires of the second layer are parallel to each other and are transverse to the wires of the first and the third layers.

2. The mesh defined in claim 1 wherein the wires of the first layer are offset with respect to the wires of the third layer to facilitate stable stacking of a plurality of sheets of the mesh disposed horizontally and stacked one on top of the other in a vertical stack.

3. The mesh defined in claim 1 or claim 2 includes a bolting section that is defined by wires that visually distinguish the bolting section from the remainder of the mesh.

4. The mesh defined in claim 3 wherein the bolting section has a larger cross-sectional area of wires per unit area of mesh than the remainder of the mesh so as to increase the force capacity and the resistance to shearing the mesh in the bolting section of the mesh.

The mesh defined in claim 3 or claim 4 wherein the bolting section is defined by a pair of wires in the first layer, with each wire of the pair defining one side of the bolting section, and each wire of the pair having a larger cross-sectional area than the other wires in the mesh. 15

6. The mesh defined in claim 3 or claim 4 wherein the bolting section is defined by two groups of wires, each group defining one side of the bolting section, and each group including one or more wires in the first layer and one or more wires in the third layer that are offset with respect to each other so that the wires in both layers appear to be in contact or to be more closely spaced than the other wires in the mesh when viewed from above or below the mesh.

7. The mesh defined in claim 3 or claim 4 wherein the bolting section is defined by two groups of wires in the first layer, with each group defining one side of the bolting section, and each group including two or more wires that are in contact or are more closely spaced than the other wires in the mesh.

8. The mesh defined in claim 6 or claim 7 wherein the other wires in the mesh are single wires rather than groups of wires.

9. The mesh defined in any one of claims 6 to 8 wherein the two or more wires of each group have a smaller cross-sectional area than the other wires in the mesh.

The mesh defined in any one of the preceding claims wherein the mesh is a curved rather than a flat sheet to increase the stiffness of the mesh.

11. The mesh defined in claim 10 wherein the curved mesh sheet is formed so that the mesh bends under the weight of the mesh and forms a flat sheet when the mesh is held at the ends and lifted clear of an underlying support.

12. The mesh defined in claim 10 or claim 11 wherein, 16 in situations where the mesh includes a bolting section that is defined by larger cross-sectional area wires or by groups of two or more wires, the first layer is the layer that has a smaller radius than the other layers.

13. A mine roof support mesh substantially as hereinbefore described with reference to the accompanying drawings.