Field

The invention relates a mine bearing element for holding a mesh sheet in place against a rock formation .

The rock formation may be any rock formation . The rock formation may be underground or above-ground . For example , the rock formation may be in an underground mine , a rail tunnel , or a road tunnel . By way of further example , the rock formation may be in an above-ground mine or part of civil engineering works adjacent railways or roads or elsewhere .

Suitably, although by no means exclusively, the rock formation defines a wall or a roof in an underground mine , such as a wall or a roof in a drive in an underground mine .

The invention also relates to a method of securing overlapping mesh sheets to a rock formation using a mine bearing element .

The invention also relates to a method of manufacturing a mine bearing element .

Background

The following description focuses on rock formations in mines . It is noted that the invention is not limited to this application .

Mine sites often have rock formations that are unstable with the potential to cause damage to equipment and/or injury to personnel . The instability may lead to a collapse of a rock formation that causes substantial damage or loose rocks being dislodged from a rock formation and causing isolated damage .

It is known to use mesh to cover exposed surfaces of rock formations to confine loose rocks and prevent them falling into an open area and causing damage . The mesh may be sheets or in rolls .

It is also known to use rock bolts grouted in drilled holes in rock formations and nut assemblies , including mine bearing plates , to tension the rock bolts and apply compressive forces to rock formations to provide overall stability to rock formations .

The rock bolts are also used as anchors for holding mesh against exposed surfaces of rock formations .

Specifically, to hold mesh against a rock formation , rock bolts are inserted into drilled holes in the rock formation and grouted in position ; the mesh is then positioned against the rock formation with rock bolts extending through openings in mesh , a bearing plate is then coupled to each rock bolt extending through mesh openings and tensioned against the mesh to secure it against the rock formation . Each bearing plate is tensioned by threading a nut and washer onto the end of the rock bolt and tensioning it against the bearing plate .

As can be appreciated, a significant amount of force is applied to the bearing plate when tensioning the nut against it . The force applied can be enough to deform the bearing plate against the mesh rendering it incapable of securing the mesh to the rock formation .

The mesh is often in the form of mesh sheets or rolls of mesh that are positioned against a rock formation in an overlapping arrangement .

There are a number of problems associated with securing mesh sheets or rolls of mesh in this arrangement . For example , securing a 1 ^st sheet and then separately securing an overlapped 2 ^nd sheet requires multiple fastening steps involving more labour and more rock bolts and bearing plates .

It is desirable to ameliorate at least one of the above disadvantages or to at least provide a useful alternative .

Summary

In broad terms , the invention provides a mine bearing element for holding a mesh sheet in place against a rock formation , the mine bearing element comprising : a body having (a) a rock bolt engagement portion , (b) a mesh engagement portion , and (c) a transition that connects together the mesh engagement portion and the rock bolt engagement portion in the as -manufactured form of the bearing element , with the transition including a stiffening rib .

In use , in one embodiment , the mine bearing element is positioned on a preinstalled rock bolt secured to the rock formation , with the mesh sheet positioned between the rock formation and the mine bearing element , and the rock bolt engagement portion is threaded onto the preinstalled rock bolt to force the mine bearing element towards the rock formation and to hold the mesh sheet against the rock formation .

The term "mesh sheet" is understood herein to be a broad term that includes , for example , flexible mesh in rolls that can be unwound from the rolls and rigid sheets of mesh , typically 6 m x 2 .4 m, with parallel line wires and parallel cross wires welded to the line wires , typically at 100 mm spacings , to define apertures .

The stiffening rib increases the rigidity of the mine bearing element when compared with a conventional at least substantially flat mine bearing plate . The increased rigidity makes it possible for the mine bearing element to carry larger loads that are applied to rock bolts when nuts are tightened onto rock bolts than would otherwise be the case without the rib , i . e . , to resist collapse as a consequence of axial loading . This increased rigidity is because the geometry of the transition has a greater moment of inertia than a substantially flat plate having the same thickness . Without being bound by theory, this is due to more material being distributed further from the bending axis than would otherwise be the case when compared with the flat plate .

The transition and the mesh engagement portion may define a cavity that typically is configured to enclose a nut on a preinstalled rock bolt . This feature means that the mine bearing element is capable of securing an overlapped portion of two successive mesh sheets against a wall or a roof using the preinstalled rock bolt . This reduces the number of fastening steps as an additional rock bolt and bearing plate is not required to secure the overlapped portion of the two mesh sheets . The nut may be tensioned against a bearing plate before being enclosed by the mine bearing element .

More particularly to the description in the preceding paragraph , in use , in one embodiment , where there is already in position a pre-existing assembly of :

(a) a preinstalled rock bolt secured to the rock formation ,

(b) a 1 ^st mesh sheet held against the rock formation , and

(c) a mine bearing element (a " 1 ^st mine bearing element" , such as a standard mine bearing element) holding the mesh sheet in position with the rock bolt engagement portion , such as a nut and washer , of the 1 ^st mine bearing element threaded onto the preinstalled rock bolt , a 2 ^nd mesh sheet is positioned on the preinstalled rock bolt (by positioning the 2 ^nd mesh sheet so that the rock bolt extends through an aperture in the mesh sheet) and a 2 ^nd mine bearing element (as described in the preceding paragraph) is positioned on the preinstalled rock bolt against the 2 ^nd mesh sheet , with the cavity defined by the transition and the mesh engagement portion enclosing the rock bolt engagement portion of the 1 ^st mine bearing element , and the rock bolt engagement portion of the 2 ^nd mine bearing element is threaded onto the rock bolt to screw the 2 ^nd mine bearing element towards the rock formation to force and hold the 2 ^nd mesh sheet against the rock formation . The rock bolt engagement portion may comprise a threaded nut that is configured to threadably engage with the preinstalled rock bolt .

The rock bolt engagement portion may comprise a washer that engages with the transition .

In use , the nut may force the washer into engagement with the transition .

The nut and washer may be separate components or integrated into a single component .

The washer may comprise a curved engagement surface that enables the angle of engagement with the transition to be adjustable .

The rock bolt engagement portion may extend from the transition .

The rock bolt engagement portion and the transition may be separate components that are connected together when assembling the mine bearing element . Forming these components as separate components makes it possible to optimize the mechanical properties for each component for an end-use application . This may mean different materials selection and/or thicknesses of the components .

The connection may be selected so that the rock bolt engagement portion and the transition separate if the mine bearing element can no longer freely rotate with the rock bolt engagement portion as it is being threaded onto the preinstalled rock bolt to hold the mesh sheet in position . The stiffening rib may extend axially in use in relation to an installed rock bolt .

The stiffening rib may extend axially in relation to an installed rock bolt and radially outwardly in relation to the rock bolt engagement portion .

The transition may be in the form of a plate , as described herein .

The term "plate" is understood herein to include flat plates and shaped plates .

The plate may be a shaped plate that includes a flat section and the stiffening rib extending outwardly from the flat section .

The transition may be any suitable length .

The stiffening rib may be a protrusion or ridge that extends from the flat section .

The transition may comprise a plurality of stiffening ribs .

The stiffening ribs may be any suitable stiffening ribs .

The plurality of stiffening ribs may be disposed radially outwardly in relation to the rock bolt engagement portion .

The stiffening ribs may be positioned in areas of the transition which experience high stresses when load is applied during tensioning of the mine bearing element to secure the mesh against the rock formation .

In some embodiments , some of the high stresses are experienced in a region of the transition that surrounds the rock bolt engagement portion .

The stiffening ribs may be equally spaced from each other . By equally spacing the stiffening ribs , the rigidity of the mine bearing element is better suited to loads that are evenly distributed about the body . However , it can be appreciated that the stiffening ribs may be unevenly spaced for situations in which the loads are unevenly distributed about the body .

The stiffening ribs may be arranged in a star pattern .

The stiffening ribs may be integrally formed with the transition . Integrally forming the ribs with the transition avoids the use of separate fastenings steps and separate fasteners that would otherwise be required to secure the stiffening ribs to the transition .

The mesh engagement portion may be any suitable length .

The mesh engagement portion may include a tubular element .

The tubular element may include a cylindrical side wall having an edge which in use contacts the mesh sheet .

The tubular element may be a sleeve .

The tubular element may be a ring . The tubular element may be a cylindrical shape , i . e . , with a circular cross-sectional area .

However , it is also envisaged that the tubular element may have a cross-sectional area that is non-circular , for example polygonal , i . e . , rectangular , triangular , pentagonal , or hexagonal .

The tubular element may have a cylindrical side wall having an edge which defines the mesh engagement portion .

The body may be made from steel . The steel may be any suitable grade . However , it is also envisaged that the body may be made from any other suitable material . Suitable materials may include metals or metal alloys comprising one or more of iron , aluminium, stainless steel , and titanium. Suitable materials may be plastics materials and composites such as carbon fiber reinforced polymers or glass fiber reinforced polymers .

The invention also provides a mine bearing element for holding a mesh sheet in place against a rock formation comprising : a body having a rock bolt engagement portion and a mesh engagement portion , the body comprising a stiffening rib disposed between the rock bolt engagement portion and the mesh engagement portion .

The invention also provides a method of securing overlapping mesh sheets to a rock formation that includes the use of the above-described mine bearing element . The above-described mine bearing element may be manufactured by any suitable options .

The invention also provides a method of manufacturing the above-described mine bearing element , the method comprising : forming the rock bolt engagement portion ; forming the mesh engagement portion ; forming the transition having a stiffening rib ; securing together the transition and the mesh engagement portion ; and securing together the transition and the rock bolt engagement portion .

An advantage to forming the mesh engagement portion and transition separately is that the wall thicknesses of each component can be carefully controlled and/or adjusted for specific applications . By contrast , if the components were integrally formed, for example in a machine press , the maximum wall thickness would be a limiting factor .

This is because the amount of force that the machine press needs to apply to form the body increases with wall thickness .

The step of forming the rock bolt engagement portion may comprise forming a threaded nut that is configured to threadably engage with the preinstalled rock bolt .

The step of forming the rock bolt engagement portion may comprise forming a washer that , in use , engages with the transition . In use , the nut may force the washer into engagement with the transition .

The step of forming the washer may comprise forming a curved engagement surface on the washer that enables the angle of engagement with the transition to be adjustable .

The step of forming the tubular element may involve rolling a sheet of steel such that the ends meet and then securing the ends together .

The ends may be secured together by welding .

The step of forming the transition may involve deforming a steel plate to form the stiffening rib .

The step of forming the transition may involve pouring molten metal into a mold that includes a stiffening rib and allowing the molten metal to solidify .

The step of forming the transition may involve pressing a flat sheet of metal to deform the sheet so as to provide the stiffening rib .

The rock bolt engagement portion may be secured to the transition by welding .

The rock bolt engagement portion may be temporarily secured to the transition , for example by tack welding .

When the rock bolt engagement portion is tensioned above a toque limit , i . e . , a breakaway torque , the temporary connection between the rock bolt engagement portion and the transition is sheared . This allows the rock bolt engagement portion to rotate about the rock bolt without imparting movement to the transition . It is advantageous to avoid rotating the transition as doing so may damage the mesh .

Brief Description of the Drawings

The invention is described further by way of example with reference to the accompanying drawings of which :

Figure 1 is a top perspective view of a mine bearing element according to an embodiment of the present invention .

Figure 2 is a bottom perspective view of the mine bearing element shown in Figure 1 .

Figure 3 is a side view of the mine bearing element shown in Figure 1 .

Figures 4A-4D show schematic illustrations of a method of using a mine bearing element according to the embodiment of Figure 1 to secure overlapping mesh sheets to a rock formation according to another embodiment of the present invention , including :

Figure 4A showing a plan view of a 1 ^st mesh sheet against a rock formation with a pair of rock bolts in the rock formation , and with a left-hand-side of Figure 4A showing a mine bearing plate secured to the mesh using a nut threaded onto an end of one of the rock bolts ;

Figure 4B showing a cross-sectional view of the arrangement shown on the left-hand-side of Figure 4A;

Figure 4C showing a plan view of a 2 ^nd mesh sheet positioned in an overlapping relationship with the 1 ^st mesh sheet , with a right-hand-side of Figure 4C showing a mine bearing element according to the embodiment of Figure 1 used to secure the 1 ^st and 2 ^nd mesh sheets in an overlapping relationship ; and

Figure 4D shows a cross-sectional view of the arrangement shown on the right-hand-side of Figure 4C .

Figure 5 shows a method of manufacturing a mine bearing element according to another embodiment of the present invention .

Detailed Description of Specific Embodiments

Figures 1-3 show a mine bearing element 10 according to an embodiment of the present invention .

The mine bearing element 10 is used for holding a mesh sheet in place against a rock formation that defines a wall or a roof in an underground mine .

It is noted that the use of the mine bearing element 10 is not confined to rock formations in underground mines and can be used elsewhere , such as in relation to rock formations in above-ground mines , rail tunnels , road tunnels , and civil engineering works adjacent railways or roads or elsewhere .

The mine bearing element 10 comprises a body 12 defined by :

(a) rock bolt engagement portion in the form of a nut 14 with an integrally formed washer 15 ,

(b) a mesh engagement portion in the form of a tubular element , more particularly in the form of a ring 16 , and

(c) a transition in the form of a shaped plate 18 (as described herein including by way of example in the next paragraph) that connects together the ring 16 and the nut 14/washer 15 .

In the embodiment shown in Figures 1-3 , the transition is a plate 18 that includes a flat section and a plurality of stiffening ribs 20 that extend outwardly from the flat section and are radially disposed around the nut 14 in a star pattern (or any other suitable pattern) . The stiffening ribs 20 are included in the transition to increase the rigidity of the plate 18 over that of a flat plate with an equivalent thickness . The stiffening ribs 20 are located in a region of the transition (and the body 12 generally) that experiences high stresses when tensioned against the mesh sheet .

A distal end of the ring 16 forms a contact surface that , in use , abuts the mesh sheet .

The plate 18 and the ring 16 define a cavity 22 .

In the embodiment shown in the Figures (particularly Figure 2 ) , the cavity 22 is configured to receive a nut of a preinstalled rock bolt in the rock formation . As a consequence , the mine bearing element 10 can be applied onto a preinstalled rock bolt/bearing plate/nut assembly that already secures a mesh sheet to the rock formation . This makes it possible to secure two mesh sheets in an overlapping relationship .

The plate 18 extends from the ring 16 so as to provide an outer lip . The ring 16 is secured to the plate 18 via a weld 24 on the outer lip .

The nut 14 has a hexagonal profile body having an end with a washer 15 integrally formed thereon . The washer 15 has a curved engagement surface that abuts the plate 18 when the nut 14 is tensioned on an end of a rock bolt . The curved engagement surface enables the angle of engagement with the plate 18 to be adjustable , for example to adjust for an uneven surface of the rock formation .

The nut 14/washer 15 is secured to the plate 18 via a temporary connection in the form of a tack weld 26.

When the nut 14 is tensioned above a toque limit , i . e . , a breakaway torque , the tack weld 26 is sheared . This allows the nut 14/washer 15 to rotate about the rock bolt without imparting movement to the rest of the body 12 , i . e . , the plate 18 and the ring 16. It is advantageous to avoid rotating the body 12 as doing so may damage the mesh sheet .

The mine bearing element 10 is formed from steel , although it is noted that it may be formed from any other suitable material . The steel may be any suitable steel grade , such as steel grades currently used for known mine bearing plates .

However , it is also envisaged that the body may be made from any other suitable material . Suitable materials may include metals or metal alloys comprising one or more of iron , aluminium, stainless steel , and titanium. Suitable materials may be plastics materials and composites such as carbon fiber reinforced polymers or glass fiber reinforced polymers .

The three components of the mine bearing element 10 , namely the nut 14/washer 15 , ring 16 , and the plate 18 , are manufactured as separate components and are assembled together . As noted above , forming these components as separate components makes it possible to optimize the mechanical properties for each component for an end-use application . This may mean different materials selection and/or thicknesses of the components . It is noted that the invention is not confined to this arrangement . The invention extends to embodiments where any two or more of the components are integrally formed .

The mine bearing element 10 is capable of carrying high loads .

The capacity of the mine bearing element 10 to carry high loads is dependent on a number of factors . Factors relating to the mine bearing element 10 itself include the structure of each of the components , the combination of the three components , the materials selection (s) for the components , and the dimensions of the components . Another factor is the selection of the rock bolt , including the diameter . Another factor is the standard practice for rock bolts to be designed to fail under load before mine bearing plates fail (to obtain the full capacity of the rock bolt) . Another factor is the standard practice for the lengths of nuts to be sufficiently long so that the nuts do not strip the threads on rock bolts . A skilled person would realize that the list of factors is not exhaustive and other factors may be relevant .

In one embodiment , where the mine bearing element 10 is designed to be used with 20 mm diameter rock bolts capable of carrying loads up to 20 tonnes :

- the plate 10 is formed from 5 mm thick steel of the same grade as steel used for standard mine bearing plates ,

- the length of the nut 14 is at least 45 mm (to avoid thread stripping) ,

- the ring 16 is made from the same grade steel and can be a smaller thickness . One embodiment of a method of using the mine bearing element 10 in accordance with the invention is now described with reference to Figures 4A-4D .

Figures 4A and 4B show a rock formation 30 , a pair of rock bolts 32 installed in holes in the rock formation 30 and grouted therein , and a 1 ^st mesh sheet 34a held against said rock formation 30 .

On the left-hand-side of Figure 4A a mine bearing element , in the form of a bearing plate 36 , is tensioned against the 1 ^st mesh sheet 34a by threading a nut 38 onto an end of the rock bolt 32 and driving it against the bearing plate 36. At this stage of the method, the 1 ^st mesh sheet 34a is secured against the rock formation 30 on the left-hand- side of the rock formation 30 .

The bearing plate 36 and the nut 38 are standard, known products .

Figures 4C and 4D show a 2 ^nd mesh sheet 34b positioned over the bearing plate 36 such that it overlaps the 1 ^st mesh sheet 34a in a region designated A.

On the right-hand-side of Figure 4C , the mine bearing element 10 shown in Figures 1-3 is secured to the rock bolt 32 by threading the nut 14 of the mine bearing element 10 onto the end of the rock bolt 32 and driving it against the overlapped portion A of the 1 ^st and 2 ^nd mesh sheet 34a , 34b .

As can be seen from Figure 4D , the mine bearing element 10 sits over the nut 38 of the pre-installed rock bolt 30 .

As previously described, the plate 18 and the ring 16 of the bearing element 10 define a cavity 22 that is configured to receive the nut 38 of the preinstalled rock bolt 30 . This feature allows the mine bearing element 10 to be applied on the preinstalled rock bolt 30 and the bearing plate 36 and the nut 38 to secure two mesh sheets 34a, 34b in an overlapping relationship.

In the above-described method, the mine bearing element 10 is used to secure two mesh sheets 34a, 34b in an overlapping relationship and is configured to envelop an existing, preinstalled bearing plate 36 and nut 38. However, it can be appreciated that the same mine bearing element 10 shown in Figures 1-3 can also be used to secure a single mesh sheet against a rock formation. As such, the mine bearing element 10 may be used in place of the standard bearing plate 36.

A method 100 of manufacturing the mine bearing element 10 will now be described with reference to Figure 5.

The method 100 comprises the following steps: 120: forming the rock bolt engagement portion, i.e. , the nut 14/washer 15;

140: forming the tubular element, i.e. , ring 16;

160: forming the transition, i.e. , the plate 18, having a stiffening rib 20;

180: securing the transition, i.e. , the plate 18, to the tubular element, i.e. , the ring 16; and

200: securing the transition, i.e. , the plate 18, to the rock bolt engagement portion, i.e. , the nut 14/washer 15.

An advantage to forming the ring 16 and the plate 18 separately is that the wall thicknesses of each component can be carefully controlled and/or adjusted for specific applications. By contrast, if the components were integrally formed, for example in a machine press, the maximum wall thickness may be a limiting factor. This is because the amount of force that the machine press needs to apply to form the body 12 increases with wall thickness .

The step of forming the ring 16 involves rolling a sheet of steel such that the ends meet and then securing , i . e . , welding , the ends together .

The step of forming the plate 18 involves pressing a flat sheet of metal to deform the sheet so as to provide a stiffening rib 20 .

The nut 14 is secured to the plate 18 by tack welding to form a temporary connection 26.

When the nut 14 is tensioned above a toque limit , i . e . , a breakaway torque , the temporary connection 26 between the nut 14 and the plate is sheared . This allows the nut 14 to rotate about the rock bolt without imparting movement to the rest of the body 12 , i . e . , the plate 18 and the ring 16. It is advantageous to avoid rotating the body 12 as doing so may damage the mesh sheet .

Whilst the preferred embodiment of the mine bearing element 10 has been described as having a tubular element , the present invention extends to embodiments in which the mine bearing element 10 does not include a tubular element .

In the foregoing description of preferred embodiments , specific terminology has been resorted to for the sake of clarity . However , the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose .

In the claims which follow and in the preceding description of the invention , except where the context requires otherwise due to express language or necessary implication , the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense , i . e . , to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention .

Also , the various embodiments described above may be implemented in conjunction with other embodiments , for example , aspects of one embodiment may be combined with aspects of another embodiment to realize yet other embodiments . Further , each independent feature or component of any given assembly may constitute an additional embodiment .

Further patent applications may be filed in Australia or overseas based on , or claiming priority from, the present application . It is to be understood that the following provisional claims are provided by use of example only and are not intended to limit the scope of what may be claimed in any such future applications . Features may be added to or omitted from the provisional claims at a later date so is to further define or re-define the invention or inventions .