AU2006100305B9

AU2006100305B9 - A mine roof support mesh

Info

Publication number: AU2006100305B9
Application number: AU2006100305A
Authority: AU
Inventors: Kim N Henley; Graeme Stuart Mcgregor
Original assignee: OneSteel Reinforcing Pty Ltd
Current assignee: OneSteel Reinforcing Pty Ltd
Priority date: 2002-09-25
Filing date: 2006-04-20
Publication date: 2007-01-04
Anticipated expiration: 2011-09-25
Also published as: AU2007200078A1; AU2007200078B2; AU2006100305B4; AU2006100305A4; AU2007200078C1

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION INNOVATION PATENT Applicant: 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 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 that are anchored, typically by means of cement or chemical resin grout, in holes that are 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 failing 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 known to stabilise roof strata, particularly roof strata of roadways of underground mines, by using roof support mesh with rock bolt assemblies.

Typically, roof support mesh is rectangular 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.

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, the mesh is long and 700-1700mm wide.

H:\angelal\keep\GRM Speci\OnesteedUncreased Bolt Spacingdoc 20/04/06 3 In use of the roof support mesh to support a roof strata, such as a roof strata of an underground mine roadway, sheets of mesh are positioned against the roof strata and rock bolts of rock bolt assemblies are positioned to extend through openings in "bolting" sections of the mesh sheets 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 the roof strata.

The standard practice in the Australian mining industry is to bolt a sheet of roof support mesh to a new section of roof strata immediately after the section has been excavated so that there is maximum possible mesh coverage as a roadway is being formed.

Consequently, in the case of excavating a new roadway, the standard practice in the Australian mining industry includes the following sequence of steps repeated along the length of the roadway: SExcavate a section of the roadway, typically 1-2m long depending on the roof strata and the width of the roof support mesh being used in that roadway.

Stop excavating when the section has been excavated.

Position a sheet of roof support mesh against the roof, with the line wires transverse to the direction of the roadway, and in overlapping relationship with a previously positioned roof support mesh, drill bolt holes and bolt a required number of bolt assemblies (typically 5) at the overlap regions of the sheets across the width of the roadway.

The above-described sequence of steps results in H:\angelal\keep\GRM Speci\Onesteclncreased Bolt Spacing.doc 20/04/06 4 periodic interruption to excavating a roadway. More particularly, the time required to carry out the abovedescribed bolting step for each section of a roadway has a direct impact on the road way development rate of an underground mine and is a significant component of the mining cost.

There has been significant research and development into bolting equipment and bolting assemblies with a view to improving bolting productivity and performance and therefore improving the rate of road way development.

The present invention is concerned with further improving the rate of road way development by focussing on the roof support mesh.

As is indicated above, rock bolts are positioned in the overlap regions of adjacent mesh sheets.

Consequently, the width of a roof support mesh that can be used in any given section of a roadway is related to the required bolt spacing along that section of the roadway.

The required bolt spacing is determined by mine operators having regard to the roof strata conditions. Thus, in any given section of a roadway, the road way development rate is limited by the required bolt spacing. Thus, road way development rate can not be arbitrarily increased by deciding to increase the bolt spacing and therefore use wider mesh sheets. In addition, whilst wider sheets reduce the number of bolting interruptions and rock bolt assemblies that are required to cover a given length of roadway and are an advantage in this respect in terms of road way development rate and cost, wider sheets require heavier cross wires that increase the cost of the mesh and are more difficult to handle. The latter point is a particularly important issue in the confined conditions in underground mines.

H:'angelal\keep\GRM Speci\Onesteel\ncreased Bolt Spacing.doc 20/04/06 5 The present invention is based on the realisation that a significant improvement in road way development rate can be realised by moving the position of the bolting section of roof support mesh from the position that has been the accepted position in the Australian mining industry for the last 7 years. This achieves a significant increase in maximum bolt spacing for a given mesh size without increasing mesh cost, weight and handling characteristics of the mesh.

The most widely used roof support mesh in the Australian mining industry over the last 7 years is a mesh that is described in Australian standard patent application 720908 and Australian petty patent 735219 in the name of the applicant. The roof support mesh is generally rectangular and formed from parallel line wires and parallel cross wires welded together at the intersections of the wires. One side of the mesh is upturned and the other side is down-turned to improve the rigidity of an otherwise flat sheet. The mesh is characterised by a bolting section that is defined by a pair of double line wires adjacent one side of the mesh.

The pair of double line wires visually distinguish the bolting section from the other section of the mesh and concentrate reinforcement in the bolting section.

Typically, the line wires in the section of the mesh other than the bolting section are spaced apart at 100mm centres and the cross wires in the mesh are spaced apart at 100mm centres and the wire diameters are at least 4mm. The roof support mesh has dominated the Australian market for mesh for underground coal mining since it was introduced into the market 7 years ago.

When the roof support mesh was invented a decision was made to position the pair of double line wires at least 100mm from the closest side of the mesh.

H:\angelal\keep\GRM Speci\Onstel\ncreascd Bolt Spacing.doc 20/04/06 6 Typically, this meant that there were 2 line wires between the pair of double line wires and the side of the mesh.

One factor in the decision was an attempt to provide a "strap" section extending between the ends of the mesh and incorporating the bolting section that had a width that was close to that of standard W-straps that were the main mine roof support in use in Australia at that time.

Another factor in the decision was a concern to provide a conservative product specification delivering a product having sufficient rigidity and sufficient mesh between the strap section and the side of the mesh to minimize adverse consequences in the event of a failure of the double line wires on that side of the bolting section.

The decision to position the pair of double line wires at least 100mm from the closest side of the mesh had a direct impact on the amount of overlap required to position the bolting section of an overlying sheet of the mesh to cover mesh of an underlying sheet. In practice, the decision meant that at least 225mm of the width of the overlying sheet at the side of the sheet that includes the bolting section is required to provide adequate overlap with the underlying sheet. The overlap width directly impacts on the maximum possible bolt spacing of a mesh sheet of a given width. For example, a sheet of mesh having a width of 1150mm has a maximum bolt spacing of 925mm. By way of further example, a sheet of mesh having a width of 1650mm has a maximum bolt spacing of 1425mm.

The selection of the position of the pair of double line wires at least 100mm from the closest side of the mesh was accepted without question in the mining industry in Australia. By way of example, the selection was followed by Smorgon Steel and subsidiaries in a double wire-type mesh released by Smorgon. Furthermore, the selection was part of mesh specifications required by mines.

H:\angelal\kep\GRM Speci\Onesteel\Increased Bolt Spacingdoc 20/04/06 28/11 2006 12:20 FAX 61 3 92438333 GRIFFITH HACK a oo6 the pair o to a side requires a impacting finding ha developmen possible t and 1650mm least 5%) 7he applicant has now found that the position of double cross wires can be considerably closer )f a mine roof support mesh and therefore considerably smaller overlap width without tdversely on the performance of the mesh. This 3 a significant impact on the road way rate and cost. Specifically, it makes it use a given width mesh sheet, such as 1150mm wide sheets, for a larger bolt spacing (at ;han was thought possible previously.

According to the present invention there is provided a mine roof support mesh for supporting an area of a roof 4f a mine, which mesh includes: a first layer of parallel line wires and a second layer of parallel cross wires that are transverse to the line wires and are welded together at the intersections of the wires, the wires being made from steel and having a circular cross-section of at leas 4mm in diameter, the line wires including wires that define a bolting section of the mesh (as described erein) on one side only of the mesh, the bolting section being defined by two groups of line wires, each group each group with each c wires in ti bolting sec centre of t less than I defining one side of the bolting section, and including two or more wires that are in contact ther or are more closely spaced than the other a mesh and thereby visually distinguish the tion from the remainder of the mesh, and the lie bolting section (as described herein) being 25mm from one side of the mesh.

ie term "bolting" section is understood herein referred section of the mesh to be contacted by semnblies for clamping the mesh to a roof to mean a rock bolt strata.

e term "centre of the bolting section" is H:-aa2ml\ke pa\RM HON p en c;i\Ono e\;nczeaefle d bo1t Spaming Am ccdmn ov 26 /11/0 COMS ID No: SBMI-05492202 Received by IP Australia: Time (H:m)12:21 Date 2006-11-28 14/06 2006 10:04 FAX 61 3 9243333GRFIHHC GRIFFITH HACK [a 006/0 14 0 -8understood herein to mean the position that would be ;Z occupied in use of the mesh by a properly positioned rook bolt.

S Preferably the centre of the bolting section is V) 7 0-120m from the said one side of the mesh.

o More preferably the centre of the bolting sect-ion is 70-100mm from the said one side of the aesh.

INO o The bolting section may be defined by larger cross-sectional area of wires per unit area of mesh than the remainder of the mesh so as to increase the resistance to shearing the mnesh in the bolting section of the mesh.

Preferably the wires in each group of line wire.

are more closely spaced than the other line wires in the mesh.

Typically the other wires in the mesh are single wires rather than group. of wires.

The two or more wires of each group may have a smaler cross-sectional area than the other wires in the mesh.

It is preferred that the mesh include sections that are out of a flat plane in order to increase the stiffness of the mesh.

By way of example, the mesh may include upturned and down-turned sections at the sides of the mesh.

The wires may be any cross-sectional shape.

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

H \~~s~ckeeDSpuc\Onfte*%1ncuan Bolkt upsclng.4og 14/06/045 COMS ID No: SBMI-03867i22 Received by IP Australia: Time 10:07 Date 2006-06-14 14/06 2008 10:05 FAX 61 3 92438333 GRIFFITH HACK l007/014 9 It is preferred that the wires be circular in cross-section.

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 meah than can be achieved with wires having non-circular cross-sections.

The non-circular cross-section wires may be Hi \jolik\klep\SBnl\OneBeol\IncrBaed Bolt SpacingM-da li/olis COMS ID No: SBMI-03867122 Received by IP Australia: Time 10:07 Date 2006-06-14 10 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 diameter that is roll-formed to a figure 8 form.

The present invention is described further by way of example with reference to the accompanying drawings, of which: Figure 1 is a perspective view of a sheet of a preferred embodiment of a roof support mesh in accordance with the present invention; Figure 2 is a vertical section of a roadway in an underground mine which illustrates installation of a plurality of sheets of the mesh shown in Figure 1 to a roof of a mine; and Figure 3 is end views of the mesh shown in Figure H:\angelal\keep\GRM Speci\OnesteeKIncreased Bolt Spacingdoc 20/04/06 11 1, a modified form of the Figure 1 mesh, and a commercially available roof support mesh.

The mine roof support mesh 3 shown in Figure 1 includes a first layer of parallel line wires 5 and a second layer of parallel cross wires 7 that are transverse to the line wires 5. The wires 5, 7 are welded together at the intersections of the wires. The wires are steel wires.

When viewed in top plan, the mesh is generally rectangular, flat sheet with one upturned side and one down-turned side. The upturned and down-turned sides are provided to improve the rigidity of the sheet.

The line wires 5 include a pair of double wires proximate to the down-turned side of the mesh. Each wire of the double wires 5a is a larger cross-sectional area wire than the other line wires 5 and the cross wires 7 in the mesh.

The pair of double wires 5a define a bolting section 13 of the mesh. Specifically, the pair of double wires 5a distinguish this section of the mesh from the remainder of the mesh and concentrate steel in the vicinity of bolts that in use secure the mesh to a mine roof and thereby improve the resistance of the mesh to shear failure at the bolting section 13.

In accordance with the present invention the centre of the bolting section 13 is less than 125mm from the side of the mesh and the overlap width of the mesh is less than 225mm. Specifically, in the embodiment shown in the drawings, the centre of the bolting section 13 is from the side of the mesh and the overlap width is 160mm.

The significance of this position of the bolting section 13 is discussed further below in relation to Figure 3.

H:\angelal\kcep\GRM Speci\Onestellncreased Bolt Spacing.doc 20/04/06 12 With reference to Figure 2, in use, a plurality of sheets of the mesh shown in Figure 1 are installed on a roof 17 of an underground mine roadway as the roadway as part of the procedure for excavating the roadway. The procedure includes placing a first sheet 3a against the roof 17, with the line wires 5 extending transverse to the direction of excavation, and holding the sheet in position by means of a predetermined number of rock bolt assemblies located with the rock bolts 19 extending through apertures in the bolting section 13 and the bearing plate 23 and nuts 25 acting against the reinforced section 13. After the next section of the roadway has been excavated, a second sheet 3b is then placed against the roof strata in overlapping relationship in the first module 3a and then bolted through the reinforced section 13. This procedure is continued with successive sheets 3c, 3d as the roadway is excavated in the direction of the arrow in the figure.

In this embodiment, the preferred sheet widths are 700- 1700mm and the lengths are As is indicated above, the present invention is based on the realisation that a significant improvement in road way development rate can be achieved by moving the position of the bolting section of roof support mesh from the position that has been the accepted position in the Australian mining industry for the last 7 years. This is illustrated in Figure 3.

Figure 3 shows two sheets of mesh in end elevation and the right hand side of a third sheet of mesh in end elevation, with the line wires 5 and the cross wires 7 of the sheets shown in diagrammatic form.

Specifically, the top figure (Figure 3a) in Figure 3 is a commercially available mine roof support mesh of the applicant that is in accordance with H:\angelal\kecp\GRM Speci\OnesteeRlncreased Bolt Spacing.doc 20/04/06 13 Australian standard patent application 720908 and Australian petty patent 735219. The figure shows that the pair of double wires 5a that form the bolting section 13 at the left hand side of the sheet are 125mm inboard of the left side of the mesh based on the bolting centre of the pair of double wires. This was thought to be the minimum possible spacing of the bolting section from the side of the mesh at the time the mesh was invented and up to the time of making the subject invention. The mesh requires at least 225mm overlap for adjacent sheets of the mesh. This means that a 1150mm wide sheet of the mesh provides a maximum bolt spacing of 925mm as shown in the figure. The basis for the minimum overlap spacing of 225mm can be seen from the right hand side of Figure 3a which illustrates the left hand side of an overlapping (ie bottom) sheet positioned on the underlying (ie top) sheet.

Specifically, the overlap region comprises the spacing between the side of the mesh and the 1 St inboard line wire 5, the 50mm spacing between the ist and 2 nd inboard line wires 5, the 25mm spacing between the 2 nd inboard line wire 5 and the centre of the bolting section (indicated by the arrow), and the additional spacing of 100mm between the centre of the bolting section and the end of the overlap. These spacings total 225mm.

The bottom left hand figure (Figure 3b) in Figure 3 is the mesh shown in Figure 1. The figure shows that the pair of double wires 5a that form the bolting section 13 are only 75mm inboard of the left side of the mesh based on the bolting centre of the pair of double wires.

This outboard position of the bolting section 13 relative to the standard position of the bolting section 13 shown in Figure 3a means that the overlap region of adjacent sheets of the mesh can be less and the maximum bolt spacing between adjacent sheets can be greater than for the standard mesh sheet having the same width shown in Figure 3a. Specifically, the maximum bolt spacing for the H:\angelal\keep\GRM Speci\Onesteel\ncreased Bolt Spacing.doc 20/04/06 14 mesh is 975mm, ie 50mm greater than the mesh shown in Figure 3a. This increase in the bolting spacing has a significant impact on road way development rate, which is a significant issue, with no increase in mesh cost and handling characteristics.

The bottom right hand figure (Figure 3c) in Figure 3 is a modified form of the right hand side of the mesh shown in Figure 3b. The consequence of this modification is to further increase the maximum bolt spacing of the mesh. Specifically, the right hand side of the mesh includes a pair of double wires 5a at the side and a ist inboard line wire 100mm from the double line wires 5a. The centre of the bolting section (illustrated by the arrow) is mid-way between the wires 5, 5a, ie only from the side of the mesh. In the Figure 2 mesh there is a spacing of 100mm between the centre of the bolting section and the right side of the mesh. Thus, the Figure 3 mesh effectively increases the maximum possible bolt spacing for the same width mesh by 50mm to 1025mm.

In overall terms, the Figure 3 mesh has a maximum bolt spacing that is 100mm greater than the conventional Figure 1 mesh, ie an increase of approximately 10%. Such an increase has a significant impact on drive construction rate.

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 have been described in the context of mesh having 2 layers of intersecting line and cross wires, the present invention is not so limited and extends to arrangements that include 3 or more layers of wires.

H:\angelal\keep\GRM Speci\Onestcl\ncrcased Bolt Spacing.doc 20/04/06

Claims

2. The mesh defined in claim 1 wherein the centre of the bolting section is 70-120mm from the said one side of the mesh.
3. The mesh defined in claim 2 wherein the centre of the bolting section is 70-100mm from the said one side of the mesh.
4. The mesh defined in any one of the preceding claims wherein the position of the bolting section is selected so that less than 225mm of the mesh at that side of the mesh is required to overlap a sheet of the mesh with a successive mesh sheet in order to secure the mesh sheets to a roof strata using more rock bolt assemblies N.WIbum.CmetawI~4QOQ~4PP9d~uAu;~5ni~..7flAV,2 SwrfbmllI33d COMS ID No: SBMI-05515534 Received by IP Australia: Time 10:24 Date 2006-11-30 30/11 2006 10:18 FAX 61 3 92438333 GRIFFITH HACK Z006/009 16 passing through the bolting. A mine roof support mesh subatantially as hereinbefore described with reference to the accompanying drawings. N:WelbWno.\rCleasPImulWnvldW4759,AUrsp..ia .Auz peutoincia t2w- l-JO dac COMS ID No: SBMI-05515534 Received by IP Australia: Time 10:24 Date 2006-11-30