AU2007202992A1 - Mine mesh - Google Patents

Description

-2 C A MINE ROOF SUPPORT MESH

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The present invention relates to a mine roof support mesh for stabilising roof strata of underground mines.

The present invention relates particularly, C although by no means exclusively, to a mine roof support C mesh for stabilising roof strata of underground metalliferous mines.

It is known to stabilise roof strata of underground metalliferous mines with rock bolt assemblies that comprise rock bolts that are anchored, typically by means of friction, in holes that are drilled in roof strata. The holes are smaller diameter than the bolts and, in use, the bolts are forced into the holes and are retained therein by a friction fit. Typically, the rock bolt assemblies include bearing plates that are positioned between rings welded to the lower ends of the bolts and the roof strata.

The purpose of rock bolt assemblies for metalliferous mines is to apply a clamping or confining action to a section of roof strata of underground mines 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 failing section to the rock bolts to sustain the load. The spacing of rock bolt assemblies is a function directly of the characteristics of roof strata.

It is known to prevent rock fragments falling downwardly from roof strata, particularly roof strata of roadways of underground metalliferous mines, by using roof support mesh with rock bolt assemblies. Typically, roof support mesh is positioned to extend across roof strata H;\GRM\Keep\Speci\OneSteel\metalliferous Mesh Pinal.doc 27/06/07 3 and retain rock fragments that would otherwise fall downwardly.

Typically, roof support mesh for metalliferous mines is quadrilateral and is formed from a first layer of parallel elongate members (generally referred to as "line wires") and a second layer of parallel elongate members (generally referred to as "cross wires") that are transverse to the line wires and are welded together at the intersections of the wires so that there are square openings of the same size along the length and across the width of the mesh. Each line wire and cross wire may be a single wire or multiple wires, such as double wires, positioned side by side in contact with each other.

Typically, roof support mesh for metalliferous mines in Australia is made from 4.0 mm, 5.0 mm, and 5.6 mm diameter wires and has square openings of 100 mm defined by the intersecting line wires and cross wires along the length and across the width of the mesh, sheet widths of 1.7, 1.8, and 2.4 m, and sheet lengths of 3.0, 4.0, 4.2, 4.6, and 6.0 m.

Roof support mesh having 100 mm openings and a width of 2.4 m is the most widely used mesh in metalliferous mines in Australia. The length of the mesh varies to suit mine conditions and the length ranges from 6.0 m in 100 mm increments.

The present invention focuses on roof support mesh for metalliferous mines that has a width of at least 2.4 m.

In use of roof support mesh to support a roof stratum of an underground metalliferous mine roadway drive, typically groups of three or four sheets of mesh are positioned against the roof stratum across the drive H:\GRM\Keep\Speci\OneSteel\Metalliferous Mesh Finaldoc 27/06/07 -4 C (ie with the length dimension of the mesh transverse to Sthe length dimension of the drive) and successively along the drive.

The sheets across the drive and successively along the drive are positioned in overlapping relationship.

C The sheets are retained in position by way of rows of rock bolt assemblies across the drive and at Sspaced intervals along the drive length. The rows of rock bolt assemblies across the drive are generally referred to as "rings".

Specifically, the rock bolts of rock bolt assemblies for metalliferous mines are positioned to extend through openings in overlapping sections of the mesh sheets and into holes drilled in the roof strata. In addition, the bearing plates of the rock bolt assemblies retain mesh sheets in position against the roof strata.

A standard practice in the mining industry in Australia is to have at least one complete opening, i.e.

at least two line wires, between the rock bolt assemblies and the side of a mesh sheet used in metalliferous mines.

Thus, the rock bolt assemblies are positioned in the second openings inboard of the sides of a mesh sheet. In a situation in which the line wires are spaced 100 mm apart, this means that the rock bolt assemblies are at least 150 mm from the sides of the sheet because they are designed to be placed centrally between the wires.

Sheets of mesh greater than approximately 2.0 m in width typically have three rows of rock bolts. The sheets include two outer rows of rock bolts that are along each edge of the sheet and an inner row of rock bolts at the nominal centre of the sheet. The rows or "rings" of H:\G1\Keep\Speci\OieSteel\Metalliferou Mesh Finaldoc 27/06/07

I

5 bolts are transverse to the direction of the drive.

The distance between the two outer rows of rock bolts at the sheet edges is referred to as the "sheet ring spacing".

The outer row of rock bolts that is toward the working face of the mine is referred to as the "inbye' ring of rock bolts and the other row of rock bolts that is away from the working face of the mine is referred to as the "outbye" ring of rock bolts.

The distance between the central row of rock bolts and the outer row of rock bolts that is toward the working face of the mine is referred to as the "inbye intermediate ring spacing" and the distance between that central row of rock bolts and the other row of rock bolts that is away from the working face of the mine is referred to as the "outbye intermediate ring spacing".

One consequence of the above-described arrangement of line wires and cross wires in roof support mesh for metalliferous mines is that there is a sheet ring spacing of 2100 mm between one outer row of rock bolt assemblies along one side of a 2.4 m mesh sheet and the other outer row of rock bolt assemblies along the other side of that mesh sheet. In the context of roof support mesh that is bolted to a roof, the distance between the inbye and the outbye ring is 2100 mm. This total sheet ring spacing is effectively the mesh coverage of a sheet along the length of the drive of a metalliferous mine.

Operators installing rock bolt assemblies in metalliferous mines work in cramped and difficult underground conditions with poor visibility and are under considerable pressure to install rock bolt assemblies quickly in order to maximize production in the mines.

H:\GR\Keep\Speci\OneStee2\Metalli erous Mesh Finaldoc 27/06/107 6 Accordingly, maximizing sheet ring spacing is important as the bolt consumption is reduced for a given length of drive. A consequence of maximizing the sheet ring spacing is an increase in the speed of installation and an overall reduction in the cost of roadway development.

Because the rock bolts are normally placed in the second openings inboard of the sides of a mesh sheet as described above, the cost of roadway development can be reduced by reducing the opening along each edge of the sheet to 25, 50 or 75 mm for example. For a reduction of mm of the width of the openings, the overall width of the sheet is reduced by 100 mm and hence the mass of the most commonly used 2.4 x 3 m sheet is reduced by approximately 0.6 kg or This might reduce the cost of the mesh by approximately for example.

The applicant has realised that it is possible to increase the sheet ring spacing and therefore the mesh coverage for a given width of mesh to be used in an metalliferous mine by reducing the 100 mm spacing of the pairs of line wires on opposite sides of the mesh, whilst retaining the original sheet width.

For example, reducing the spacing of both pairs of line wires from 100 mm to 50 mm, whilst retaining the original sheet width, increases the sheet ring spacing and therefore the mesh coverage by 100 mm. For a 2.4 m wide sheet, the sheet ring spacing and therefore the mesh coverage is increased from 2100 mm to 2200 mm, an increase of approximately 4.75%. For this example the inbye intermediate ring spacing and the outbye intermediate ring spacing are equal at a nominal spacing of 1100 mm.

Reducing the 100 mm spacing of the pairs of line wires on opposite sides of the mesh, as described in the preceding paragraph, while maintaining a given sheet width H:\GRM\Keep\Spei \OneSteel \Metal liferous Mesh Final.doc 27/06/07 7 and by maintaining 100 mm wide openings across the remainder of the mesh, can only be achieved by adding a line wire to the mesh. The addition of a line wire involves an additional cost. The additional mass for the a 3 m long sheet for example is approximately 0.6 kg which may increase the cost by approximately The increase in cost however is insignificant when compared to the savings generated by the increase in the sheet ring spacing by 100 mm approximately 4.75%. Roadway development costs are comparatively substantial and hence an increase in the sheet ring spacing and therefore the mesh coverage of approximately 4.75% represents a significant saving per sheet width placed along a drive.

Alternatively the line wire spacings could be increased to approximately 104.5 mm to overcome the need for an additional line wire.

Accordingly, whilst there may be a trade-off between the savings achieved by increasing the sheet bolt spacing and the cost of additional line wires, in overall terms the cost of the additional line wire is insignificant when compared to the savings generated by increasing the ring spacing.

The same sheet ring spacing can be achieved with a 2.5 m wide sheet with standard 100 mm openings across the sheet. However, the sheet mass is increased by a further approximately 0.6 kg and would offer no benefit over the 2.4 m wide sheet with the wires rearranged as described.

There are productivity benefits for manufacturers of mesh sheets for metalliferous mines that can be achieved by manufacturing 2.5 m wide sheets. 2.5 m is generally the maximum width mesh that can be manufactured.

m is also the maximum width mesh that can be transported safely without the need for special H:\GRM\Keep\Speci\OneSteel\Metalliferous Mesh Final.doc 27/06/07 8 provisions. As far as the applicant is aware, there are no commercially available 2.5 m wide sheets of roof support mesh used in metalliferous mines in Australia.

Reducing the two outer openings of a 2.5 m wide sheet to 50 mm and introducing an extra line wire or redistributing the line wires, as described above for a 2.4 m wide sheet, increases the sheet ring spacing and therefore the mesh coverage by a further 100 mm or approximately 4.5 and generates proportionally the same savings in the cost of roadway development. For this example the inbye and the outbye intermediate ring spacings are again unequal and are 1100 and 1200 mm.

For a conventional sheet of mesh, i.e. a mesh sheet with 100 mm wide openings, for metalliferous mines the same inbye and the outbye intermediate ring spacings can only be achieved by increasing the width of the mesh to 2.6 m. This width sheet is generally beyond the capacity of most mesh machines. The mass of the sheet would increase by a further approximately 0.6 kg and offer no benefit over the 2.5 m wide sheet with the wires rearranged as described.

The same principle of wire distribution can be applied to sheets that are wider than 2500 mm to achieve further increases in sheet ring spacings.

Some metalliferous mines are restricted in the width of the sheet that can be readily transported from the surface to underground and along the roadways already developed in the mine. Therefore, to be able to generate an increase in sheet ring spacing and therefore mesh coverage with no or little increase in the width of the sheet provides a major advantage to the mine.

The applicant has realised that increasing the H:\CR\Keep\Speci\OneStee1\Metaliferous8 Mesh Finaldoc 27/06/07 9 sheet ring spacing and therefore the mesh coverage by reducing the 100 mm spacing of the pairs of line wires on opposite sides of the mesh while maintaining a given width of sheet is an opportunity that provides maximum benefits for wider sheets, more particularly for sheets having widths of 2.4 m and 2.5 m. These benefits include manufacturing and transportation benefits, as well as the above-described benefit of increasing the sheet ring spacing for a given width of mesh.

With the above in mind, according to the present invention there is provided a 2.4 m or a 2.5 m wide or wider quadrilateral sheet of roof support mesh for metalliferous mines that includes opposed ends and opposed sides and parallel line wires and parallel cross-wires that are welded together at intersections of the wires and is characterized in that the spacing between the line wires on the sides of the mesh and the immediately adjacent inboard line wires is less than the spacing between the other line wires in the mesh.

As a consequence, as described above, for a given width of mesh and with rock bolt assemblies positioned in corresponding lines of openings, the total sheet ring spacing and therefore the total mesh coverage of the mesh is greater than that for a sheet of conventional mesh which has square openings of the same size along the length and across the width of the mesh.

Thus, the arrangement of line wires and cross wires in the roof support mesh for metalliferous mines invented by the applicant makes it possible for a given length and width of mesh to have a greater sheet ring spacing and therefore a better mesh coverage than the conventional mesh of the applicant. This is a considerable advantage because it reduces the number of mesh sheets required and the number of rock bolt H:\GRM\Keep\Speci\OneSteel\Metalliferous Mesh Final.doc 27/06/07 10 assemblies required for a given length of drive. This is a considerable advantage in terms of mesh cost, bolting time, and rock bolt assembly cost.

The line wires on the sides of the mesh and the immediately adjacent inboard line wires form outer side sections of the mesh, with each outer side section including a side line wire on one side of the mesh and the immediately adjacent inboard line wire on that side of the mesh.

Each outer side section of the mesh may include an additional line wire (or wires) that is inboard of the side line wire and the inboard line wire described in the preceding paragraph.

The line wires that are inboard of the outer side sections of the mesh form an inner section of the mesh.

The spacing between the inboard line wire of each outer side section and the additional line wire that is adjacent the inboard line wire may be less than or greater than or equal to the spacing between the side line wire and the inboard line wire of the outer section of the mesh.

The spacing between the additional line wire and the inboard line wire may be less than or greater than the spacing between adjacent line wires in the inner section of the mesh.

In a situation in which the spacing between adjacent line wires in the inner section of the mesh is 100 mm, in one embodiment, preferably the spacing between adjacent line wires in each outer side section of the mesh is between 20 and 80 mm, more preferably 50 mm.

H\GR\Keep\Speci\OneSte( l\Metaliferous Meah Final.doc 27/06/07 11 In another, but not the only other possible embodiment, preferably the spacing between the side line wire and the inboard line wire in each outer side section of the mesh is between 20 and 80 mm, more preferably 50 mm, and the spacing between the additional line wire and the inboard line wire in each outer side section of the mesh is between 130 and 170 mm, more preferably 150 mm.

Preferably the spacing between adjacent line wires in the inner section of the mesh is substantially uniform.

Equally, there may be situations in which the spacing is not uniform.

Preferably the spacing between adjacent line wires in the inner section of the mesh is between 90 and 110 mm.

Typically, the spacing between adjacent line wires in the inner section of the mesh is 100 mm.

Preferably the spacing between adjacent cross wires in the inner section of the mesh is between 90 and 110 mm.

Typically, the spacing between adjacent cross wires in the inner section of the mesh is 100 mm.

Preferably the line wires and the cross wires are formed from steel.

The steel wires may be coated or uncoated.

The line wires and the cross wires may be any cross-sectional shape. Thus, where the line wires and the HK\GRM\Keep\Spec\OneStel\Metalliferous Mesh Final doc 27/,06/07 12 cross wires are non-circular, the reference to diameter is understood herein to mean the equivalent of the wires.

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

Preferably the wires are circular in crosssection.

Preferably the wires are at least 4 mm in diameter.

According to the present invention there is provided an underground roadway of a metalliferous mine that includes a plurality of sheets of mine roof support mesh as described above bolted to a roof stratum and positioned in side by side overlapping relationship across and along the length of the roadway.

The present invention is described further by way of example with reference to the accompanying drawings, of which: Figure 1 is a top plan view of a sheet of a roof support mesh for an underground metalliferous mine in accordance with one embodiment of the present invention; and Figure 2 is a top plan view of a sheet of a roof support mesh for an underground metalliferous mine in accordance with another embodiment of the present invention.

The mine roof support mesh 3 for use in underground metalliferous mines shown in Figure 1 is a quadrilateral sheet that is 2.4 m wide and 3.0 m long and includes 26 parallel line wires 5 and 31 parallel cross H:\GRM\Keep\Speci\OneStee1\Metalliferous Mesh Final.doc 27/06/07 13 wires 7 that are perpendicular to the line wires SThe line wires 5 and the cross wires 7 are welded together at the intersections of the wires.

C The wires are steel wires, typically 5.6 mm in Sdiameter.

Ci The line wires 5 are all at 100 mm spacing, save for the two outer wires along each side that are at a mm spacing. These pairs of line wires on the sides of the mesh form outer side sections of the mesh. The mesh between these pairs of line wires forms an inner section of the mesh.

The cross wires 7 are all at 100 mm spacing.

The above-described arrangement of line wires and cross wires 7 means that the mesh includes a central line of openihgs 9, i.e. a line of openings that is equidistant from both sides of the mesh, with a centre-line of the mesh running through the central line of openings 9 mid-way between the line wires 5a, 5b that define the central line.

In use, a plurality of sheets of the mesh can be positioned in an overlapping relationship to support the roof strata of underground metalliferous mines and be retained in position by rock bolt assemblies.

Figure 1 includes a series of 9 letters The letters identify the locations of rock bolt assemblies (not shown) that, in use, retain the mesh against a roof stratum in an underground metalliferous mine.

It is evident from Figure 1 that the rock bolt assemblies are arranged in a pattern of three rows of rock H:\GRM\Keep\Speci\oneSteel\Metalliterous Mesh Final.doc 27/06/07 14 bolt assemblies that extend along the length of the mesh, Swith two outer rows of rock bolt assemblies being positioned in the lines of openings that are the second line of openings in from the sides of the mesh, and with a third row of rock bolt assemblies being positioned in the central line of openings 9.

CI The sheet ring spacing of the two outer rows of C rock bolt assemblies for the mesh shown in Figure 1 is 2200 mm.

The sheet ring spacing of 2200 mm, which is the total mesh coverage, is 100 mm larger than the sheet bolt spacing of 2100 mm of a conventional 2.4 m wide sheet of mesh that has 25 line wires spaced apart at 100 mm intervals across the width of the sheet mesh. This is a considerable advantage in terms of cost roadway development, as is described above.

Figure 2 shows another embodiment of a sheet of mine roof support mesh for metalliferous mines in accordance with the present invention.

The sheet shown in Figure 2 is identical to the sheet shown in Figure 1 save that the sheet is 2.5 m rather than 2.4 m wide and, therefore, has 27 rather than 26 line wires 3.

The sheet ring spacing of the sheet is 2300 mm.

This sheet ring spacing and therefore mesh coverage is 200 mm larger than the sheet ring spacing of 2100 mm of a conventional 2.4 m wide sheet of mesh that has 25 line wires spaced apart at 100 mm intervals across the width of the sheet mesh. This is a considerable advantage in terms of cost roadway development, as is described above.

Many modifications may be made to the preferred H:\GRn\Keep\Speci\OneSteel\metalliferous Mesh FinaA.doc 27/06/07 15 g embodiments of the present invention described above Swithout departing from the spirit and scope of the present invention.

By way of example, whilst the outer side sections of each sheet of mesh 3 shown in the Figures comprise the Stwo outer line wires 5 on each side of the mesh 3, the CA present invention is not so limited and extends to C- arrangements in which the outer side sections comprise one or more than one additional line wire inboard of these line wires H\GRM\Keep\Speci\OneSteel\Metalliferous Mesh Final.doc 27/06/07

Claims (14)

1. A 2.4 m or a 2.5 m wide or wider quadrilateral sheet of roof support mesh for metalliferous mines that includes opposed ends and opposed sides and parallel line wires and parallel cross-wires that are welded together at intersections of the wires and is characterized in that the spacing between the line wires on the sides of the mesh and the immediately adjacent inboard line wires is less than the spacing between the other line wires in the mesh.

2. The mesh defined in claim 1 wherein the line wires on the sides of the mesh and the immediately adjacent inboard line wires form outer side sections of the mesh, with each outer side section including a side line wire on one side of the mesh and the immediately adjacent inboard line wire on that side of the mesh.

3. The mesh defined in claim 2 wherein each outer side section of the mesh includes one or more than one additional line wire that is inboard of the side line wire and the inboard line wire.

4. The mesh defined in claim 3 wherein the line wires that are inboard of the outer side sections of the mesh form an inner section of the mesh.

The mesh defined in claim 3 or claim 4 wherein the spacing between the inboard line wire of each outer side section and the additional line wire that is adjacent the inboard line wire is less than or greater than or equal to the spacing between the side line wire the inboard line wire of the outer section of the mesh.

6. The mesh defined in claim 5 wherein the spacing between the additional line wire and the inboard line wire Hi \GRM\Keep\Spec\OneSlee1\metal iferous Mesh Final.dc 27/06/07 17 is less than or greater than the spacing between adjacent line wires in the inner section of the mesh.

7. The mesh defined in claim 5 or claim 6 wherein, in a situation in which the spacing between adjacent line wires in the inner section of the mesh is 100 mm, the spacing between adjacent line wires in each outer side section of the mesh is between 20 and 80 mm, more preferably 50 mm.

8. The mesh defined in claim 5 or claim 6 wherein, in a situation in which the spacing between adjacent line wires in the inner section of the mesh is 100 mm, the spacing between the side line wire and the inboard line wire in each outer side section of the mesh is between and 80 mm, more preferably 50 mm, and the spacing between the additional line wire and the inboard line wire in each outer side section of the mesh is between 130 and 170 mm, more preferably 150 mm.

9. The mesh defined in any one of claims 4 to 8 wherein the spacing between adjacent line wires in the inner section of the mesh is substantially uniform.

10. The mesh defined in claim 9 wherein the spacing between adjacent line wires in the inner section of the mesh is between 90 and 110 mm.

11. The mesh defined in any one of claims 4 to wherein the spacing between adjacent cross wires in the inner section of the mesh is between 90 and 110 mm.

12. The mesh defined in any one of the preceding claims wherein the line wires and the cross wires are formed from steel.

13. The mesh defined in any one of the preceding H \GR\Keep\Speci\OneSteel\Metal iferous Mesh Final doe 27/06/07 18 claims wherein the wires are at least 4 mm in diameter.

14. An underground roadway of a metalliferous mine that includes a plurality of sheets of mine roof support mesh defined in any one of the preceding claims bolted to a roof stratum and positioned in side by side overlapping relationship across and along the length of the roadway. l;\GR\Keep\Speci\OneStee1\Metalliferous Mesh Finaldoc 27/06/07