WO2004042195A1

WO2004042195A1 - Mine support component

Info

Publication number: WO2004042195A1
Application number: PCT/ZA2003/000165
Authority: WO
Inventors: Nico Erasmus; Joseph Cornelius Visagie
Original assignee: GRINAKER-LTA Ltd; Grinaker Lta Ltd
Current assignee: GRINAKER-LTA Ltd; Grinaker Lta Ltd
Priority date: 2002-11-08
Filing date: 2003-11-06
Publication date: 2004-05-21
Anticipated expiration: 2005-05-08
Also published as: AU2003291210A1; ZA200405098B

Abstract

A lightweight cement block for use in a mine support which is precast with embedded mesh reinforcing and which is formed on an underside with channel formations which receive forks of a forklifter to facilitate transport of the block and which define zones of weakness to promote controlled yielding of the block.

Description

MINE SUPPORT COMPONENT

BACKGROUND OF THE INVENTION

[0001] This invention relates to a mine support component which can be used in an underground excavation to provide support between a footwall and an opposed hanging wall.

[0002] Various types of mine supports have been designed for use in diverse applications. Generally it can be said that supports which are suitable for use in South African gold mines are not necessarily suited for use in coal mines. In coal mines relatively large seams of coal are excavated, usually by a mechanical means such as a continuous miner, and the closure rate, in the resulting excavation, between a footwall and an opposed hanging wall, may be quite different from what is encountered in a deep level gold mine.

[0003] The underground excavation in a relatively low level coal mine may be substantial in height. This means that it is possible to make use of machines for manipulating underground supports, a possibility which does not often present itself in deep level mines where stoping widths are normally narrow.

SUMMARY OF INVENTION

[0004] The invention provides a mine support component which includes a cementitious block formed with at least one recessed formation which defines a zone of weakness which promotes yielding of the block when it is axially loaded in excess of a predetermined value. [0005] Preferably the block includes a plurality of the formations.

[0006] Each formation preferably exhibits a dual function in that, apart from defining the aforementioned zone of weakness, it provides a means whereby transport or manipulation of the block by a transport mechanism is facilitated.

[0007] Preferably each formation is adapted to engage with a corresponding formation on a transport mechanism such as fork lifter. A respective fork of a fork lifter is preferably engageable with the formation. This allows the block to be made to a large size and mass for, using suitable mechanical means it is possible to transport blocks to an installation site underground and then erect the blocks to form an appropriate support.

[0008] In a preferred embodiment of the invention the block is formed with at least two spaced and substantially parallel recessed formations each of which defines a respective elongate channel extending in, what in use, is an underside of the block.

[0009] The block is preferably formed from lightweight cementitious material appropriate support eg. aerated or foamed concrete.

[0010] The block may have a density in the range of 500 to 800 kg/m³. The block may be reinforced in any appropriate way for example by the inclusion of reinforcing material which is embedded in the cementitious mixture. The reinforcing material may take on any appropriate form and preferably includes mesh of steel wire or an equivalent material which has adequate strength properties. The mesh may extend at least in two directions through the block and preferably is positioned and shaped so that a plurality of mesh reinforcing layers are formed inside the block. [0011] It is desirable to form the block from cementitious material and reinforcing material, which can be cut with relative ease by a mechanical miner.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention is further described by way of example with reference to the accompanying drawings in which:

Figure 1 illustrates a mine support which is erected, in an underground excavation, using a plurality of mine support components according to the invention,

Figure 2 shows one of the mine support components in outline, with internal reinforcing,

Figure 3 is a side view of the mine support component showing the arrangement of

the reinforcing; and

Figure 4 illustrates a curve of load versus displacement for a support of the kind shown in Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENT

[0013] Figure 1 of the accompanying drawings illustrates a mine support 10 which

is constructed in an underground excavation 12 between a footwall 14 and an opposed hanging wall 16.

[0014] The support 10, in this example, is formed from three support components 20A, 20B and 20C which, for all practical purposes, are identical to one another.

[0015] Each support component 20 is in parallelepiped form and, depending on requirement, may be substantially cubic. The component comprises a cementitious block 22 of substantial dimensions, for example with each side having the length of 600mm or greater. Typically the block is of the order of 1 m x 1 m x 1 m, and is formed at a suitable site on surface or underground by casting cementitious material in a suitable mould. The cementitious material is preferably aerated, using techniques which are known in the art, and has a density in the range of 500 to 800 kg/m³. In its under surface 24 the block is formed with two substantially parallel and elongate recessed formations which define channels 26 and 28 respectively.

[0016] Each channel performs two functions. Firstly it provides a zone of weakness in the underside of the block and secondly it is dimensioned and positioned so that a fork of a fork lifter, not shown, can engage with ease with the channel.

[0017] The number of channels may be increased and, more particularly, a first pair of channels may extend in one direction in the underside 24 and a second pair of channels 26A and 28A, indicated in Figure 2, may extend in a transverse direction in the underside 24.

[0018] The block 22 is reinforced by means of embedded mesh material 34. The mesh may vary according to requirement but typically is made from 4mm steel wire with mesh apertures from 50mm to 200mm. A first mesh panel 36 is bent into a U- shape, and a number of sheets 38 of mesh, each sheet being folded into a substantially closed-shape, are then positioned between opposing sides 40 and 42 of the U-shape mesh 36 (see Figure 3).

[0019] The mine support components 20 are intended particularly for use in an underground excavation in a mine where a height 50 of the excavation between the footwall and the hanging wall (see Figure 1 ) is substantial, between 3m and 4m (say) or higher. Due to the dimensions of the excavation 12 it is possible for vehicles such as fork lifters to move with ease in the excavation.

[0020] The blocks 20 are transported to an intended location of use underground and can be manipulated, on site, using a fork lifter. The forks of the fork lifter are readily engaged with the channels 26 and 28, or 26A and 28A on the underside 24 of each block and the blocks can therefore be lifted, manipulated, and placed in a desired position, with relative ease.

[0021] The blocks are assembled, one on top of the other, to form the support column 10. If a gap exists between the upper surface 54 of the top block 20C and the hanging wall 16 then the gap can be filled with a prestressing bag or device (not shown) of a kind which is known in the art. When the device is actuated the support 10 is axially loaded and therefore is capable of almost immediately displaying its designed load versus yield characteristic.

[0022] The channel formations 26 and 28 in each block defines zones of weakness. Consequently when the support 10 is stressed in the axial direction, as closure of the hanging and footwalls take place, each block is capable of yielding in a relatively controlled manner as the channels 26 and 28 promote crumbling of the block material in the regions adjacent the channels.

[0023] The number of formations which define zones of weakness can, if necessary, be increased to provide a greater distance over which the support 10 can yield in a controlled manner. In this respect it should be noted that, generally, only small amount of controlled yielding capability is required if a support used in a coal mine for the degree of closure is relatively limited.

[0024] The reinforcing 34 prevents the blocks from yielding catastrophically. The type and the degree of reinforcement can be adjusted, as necessary, to provide a support 10 with a desired degree of stiffness.

[0025] Each block is made from material, ie. aerated concrete and steel wire reinforcing, which can be cut by a continuous coal miner or a long wall shearer. In other words although the support 10 provides a substantial load bearing capability it can, when necessary, for example if it interferes with a mining operation, be cut by the same machine which is used to extract coal from a coal face.

[0026] The relatively large and massive blocks which are used in a support according to the invention make it possible for cementitious supports with predictable characteristics to be provided economically and effectively in underground locations. The situation should be contrasted, by way of example, with the circumstances which surround the use of relatively small cementitious blocks which are of a size and mass to enable them to be manipulated by hand. In this instance the material and labour cost is high and dictates against the use of these blocks to provide cost-effective support. The massive and big blocks proposed by the invention for use in conditions in which the blocks can be manipulated by mechanised means allows for a cost-effective cementitious support structure, with controlled yielding capability, to be erected.

[0027] Figure 4 illustrates a curve of load versus displacement for a support 10 of the kind shown in Figure 1 formed from three stacked cubic, cementitious blocks each of 1 m x 1 m x 1 m with a density of about 750kg/m³, and reinforced in the manner shown in Figures 2 and 3.

[0028] The support has an initial yield point of about 1200kN and over a zone "Z" this increases to about 1600kN with a corresponding displacement, or yield, of about 110mm.

Claims

1. A mine support component which includes a cementitious block formed with at least one recessed formation which defines a zone of weakness which promotes yielding of the block when it is axially loaded in excess of a predetermined value.

2. A component according to claim 1 wherein the block includes a plurality of the informations.

3. A component according to claim 1 or 2 wherein each formation provides a means whereby transport or manipulation of the block by a transport mechanism is facilitated.

4. A component according to any one of claims 1 to 3 wherein each formation is adapted to engage with a corresponding formation on a transport mechanism.

5. A component according to claim 4 wherein each formation is adapted to engage with a respective fork of a fork lifter.

6. A component according to any one of claims 1 to 5 wherein the block is formed with at least two spaced and substantially parallel recessed formations each of which defines a respective elongate channel extending in, what in use, is an underside of the block.

7. A component according to any one of claims 1 to 6 wherein the block is formed from lightweight cementitious material.

8. A component according to claim 7 wherein the block has a density in the range of 500 to 800kg/ιm³.

9. A component according to claim 7 or 8 wherein the block is reinforced by the inclusion of reinforcing material which is embedded in the cementitious material.

10. A component according to claim 9 wherein the reinforcing material includes mesh or steel wire.

11. A component according to claim 10 wherein the mesh extends at least in two directions through the block.

12. A component according to claim 11 wherein the mesh is positioned and shaped so that a plurality of mesh reinforcing layers are formed inside the block.

13. A support made from a plurality of components each component being according to any one of claims 1 to 12, stacked on above the other.