A Mine Bearing Element

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.

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 1sheet and then separately securing an overlapped 2sheet 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.

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×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:

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.