GB2302889A

GB2302889A - A pre-stressing device for a mine prop

Info

Publication number: GB2302889A
Application number: GB9613126A
Authority: GB
Inventors: Neil Gordon Berry
Original assignee: BMS MINE SUPPORTS
Current assignee: BMS MINE SUPPORTS
Priority date: 1995-06-30
Filing date: 1996-06-21
Publication date: 1997-02-05
Anticipated expiration: 2016-06-21
Also published as: GB2302889B; PL315016A1; GB9613126D0

Abstract

A pre-stressing device for a load carrying apparatus such as a mine prop 132 comprises a pair of load bearing members 112.2,142 locatable at positions spaced from each other between one end of the load carrying apparatus and a rigid support; a wedge member having a wedge surface 118.2,118.3 locatable at an angle relative to the direction in which the load, in use, exercises a force; a bar member 120.1,120.2 locatable against the wedge surface of the wedge member; and means, e.g. a threaded shaft member 122 engaging a complementary internally threaded hole in the bar member, for displacing the bar member in a lateral direction in relation to the direction of the force, causing the wedge member to push against the load bearing members and to cause the load bearing members to exercise a reaction opposing the force.

Description

TITL: Mine Support FIELD OF THE INVENTION This invention relates to the supporting of heavy loads. More particularly, the invention relates to a device suitable for use in locating and/or pre-stressing a mine prop, to a longitudinally adjustable mine prop and to a support for a heavy load.

BACKGROUND TO THE INVENTION Roof supports of a variety of designs are widely used in underground mining operations to support hanging walls. They are generally required to support loads in excess of 15 tonnes, usually in the range of approximately 20 tonnes.

They are also required to yield under conditions of pressure hursts, but to continue after such pressure bursts to support the hanging wall and to present a resistance to the hanging wall which does not increase or decrease significantly with the passage of time.

Because of the difficultics and dangers involved with the recovery of mine roof supports after a period of time when the hanging wall has moved closer to the foot wall, conventional roof supports are often left in place instcad of being recovered for re-use. Also, because of blasting operations and underground transport and handling of ore, roof supports are frequently damaged and accordingly have a limited life span, which in turn contributes to high costs.

There accordingly exists a need to provide inexpensive mine supports.

However, there also exists a need for a mine support to be easily locatable between the foot wall and the hanging wall.

Some conventional hydraulic and mechanical props are however, longitudinally extendible, in order to address this need.

In South African Patent No. 93/7660, we describe an adjustable roof support which includes adjusting means comprising a pair of shanks lying on a common longitudinal axis and having opposite-handed thread formations co-operating with socket elements having complementary female thread formations, the shanks and complementary elements being so arranged as to allow optional displacement thereof towards or away from each other by way of a screwing action about the longitudinal axis of the shanks. The length of the entire prop is thus adjustable and it accordingly obviates the need for an additional locating and pre-stressing device.

The aforementioned prop is recoverable and can be used repeatedly. Such conventional supports are usually relatively expensive. Cheaper props frequently make use of timber, which is cheaper, but such props are not easily adjustable or extendible in a longitudinal direction, so as to be easily locatable between the hanging wall and the toot wall.

One such conventional prop which utilises timber is described in South African Patent No. 88/3()27. The prop according to this patent comprises an elongate timber load supporting element having at an end region thereof a series of transversely extending slot-like recesses in the timber surface located to he spaced apart axially and circumferentially at least part way along the length in the end region, the recesses being adapted to allow,when the element is axially compressed, timber fibre expansion into the recesses to cause a controlled yielding of the prop. Although it is very effective as a mine support and although it is comparatively cheap, this support is not easily extendible in a vertical direction.

South African Patent No. 87/7086 describes a jack adapted for shoring the foundations of buildings, which includes a shaft member and at least one headpiece or footpiece screwingly interengageable with the shaft member to be longitudinally displaceable with respect to the shaft member by screw action, and engaging means on the shaft member or on the headpiece or footpiece by means of which the shaft member and the headpiece or footpiece can be screwed relative to each other. This jack functions by a longitudinal displacement of the headpiece or footpiece relative to the shaft member. It is of heavy construction, expensive to manufacture and is not suitable for use in underground mines.

South African Patent No. 90/8961 describes an adjustment device for a mine prop which is telescopically extendible in the longitudinal direction, wherein the adjustment device comprises an adjustment member rotatably mountable to a telescope member of the mine prop, wherein the guide member is mountable to another telescope member, and wherein the adjustment member is also capable of lateral movement relative to the telescope members when the adjustment member is rotated, whereby such lateral movement causes the guide member and its associated telescope member to move longitudinally relative to the adjustment member and its associated telescope member. This device comprises a pair of nuts on a shaft, each of the nuts having an inclined surface located against a complementary inclined surface on a ring, both surfaces being flat.In use, one of the nuts is screwed towards the other, causing their inclined surfaces to move towards one another, and the ring to be displaced in an upward direction.

South African Patent No. 92/7149 describes a pit prop of the kind comprising an elongated stick, a head plate, a base plate and a loading device lor pre-loading the pit prop when it is in position, said loading device being located between the stick and one of the plates. The loading device comprises a pair of movable nuts carried by a threaded member respectively on the threads, so that.

on rotation of the threaded member, the nuts move towards or away from one another on the threaded member, the nuts having flat engagement surfaces which slide respectively over flat, inclined surfaces on a pressure member, causing relative movement between the two pressure members in the direction of the axis of the stick. Again, the engagement surfaces and the inclined surfaces are all flat.

There accordingly exists a need for a pre-stressing device which is cheap so that it can be left in position after it has bcen used to pre-stress a conventional prop of which the length is not easily variable, such as the prop described in South African Patent No. t18/3027.

There also exists a need for a device suitable for use in locating a mine prop between a hanging wall and a foot wall, which is inexpensive and which is adapted to take up small differences between the length of the prop, on the one hand, and the distance between the hanging wall and the foot wall, on the other.

SUMMARY OF THE INVENTION According to one aspect of the invention, there is provided a pre-stressing device for a load carrying apparatus adapted to carry a load exercising a force in a first direction, the pre-stressing device comprising: - a pair of load bearing members locatable at positions spaced from each other between one end of the apparatus and a rigid support such that the load bearing members will, in use, oppose the load: - a wedge member locatable between the pair of load bearing members, the wedge member having a wedge surface locatable at an angle relative to the first direction and being restricted. in use.

from movement in a lateral direction, but being free to move in the first direction and in a direction opposite thereto; - a substantially cylindrical bar member locatable against the wedge surface of the wedge member; and - means for displacing the bar member in a lateral direction in relation to the first direction, causing the wedge member to push against one of the load bearing members and, as a consequence, to cause the load bearing member to exercise a reaction opposing the force.

The load carrying device may be a mine prop.

The surface of the wedge member may be flat or, alternatively, it may, in cross-section comprise an arc of a circle or an ellipse.

The angles of the wedge surfaces of the wedge members may be the same.

Each of the wedge members may convenicntly have a pair of wedge surfaces, each wedge surface being locatable at an angle relative to the first direction.

The angles may be complementary.

In one embodiment of the invention, the angles are complementary and the pre-stressing device comprises a pair of bar members, one of the p;iir of bar members being locatable against one of the wedge surfaces on either side of the longitudinal axis.

Each of the wedge members may be connected to one of the load bearing members.

In another embodiment of the invention, the pre-stressing device comprises two pairs of substantially triangularly shaped wedge members, each of the wedge members having a pair of complementary sides, and a base. The base of each wedge member may be connectable to a load bearing member. The arrangement is preferably such that two wedge members are arranged on either side of the longitudinal axis with their bases directed in opposite directions.

The pair of bar members may be locatable against the inclined surfaces of the opposing wedge members such that, when they are displaced towards each other, they cause opposing wedge members to be forced away from each other.

and, when the bar members are displaced away from each other, the opposing wedge members are allowed to move towards each other under the influence of gravity.

In still another embodiment of the invention, the surface of the wedge member is dome-shaped. This shape offers the advantage that it could facilitate use of the pre-stressing device where misalignment of the pre-stressing device with the load carrying device is not critical, resulting in a rapid location of the pre-stressing device between the load carrying apparatus or mine prop, on the one hand, and the hanging or foot wall of the mine on the other hand.

In yet another embodiment of the invention, the surface of the wedge member is provided by a cylinder cut lengthwise, and arranged with its axis located in a lateral direction, in use. The pre-stressing device in accordance with this embodiment of the invention may comprise a pair of cylindrical bar members, one on either side of a central region of the wedge member, with the axes of the bar members locatable in substantially parallel relationship relative to the axis of the wedge member. One of the pair of bar members may be locatable against the wedge surface on either side of the longitudinal axis of the load carrying apparatus. such that. when the bar members are moved towards each other. thcv are pushed in the longitudinal direction by the wedge surface.

According to another aspect of the invention, there is provided a device suitable for use in pre-stressing a mine prop, the device being locatable between either a top or bottom end of the mine prop and, respectively, the foot wall or hanging wall of an underground mine, tunnel or the like, wherein the device comprises: - a pair of load bearing members; - a pair of wedge members, each wedge member having a pair of wedge surfaces located at an angle relative to each other, the pair of wedge members being locatable in laterally spaced relationship from each other, one on either side of an extended centre line of the prop; - a pair of substantially cylindrical bar members, one of which is locatable adjacent corresponding wedge surfaces of the wedge members and the other of which is locatable adjacent the opposite wedge surfaces of the wedge members; and - a shaft member co-operating with the bar members, and adapted to cause the bar members, upon rotation of the shaft member, to be displaced towards or away from each other, whereby the wedge members may be displaced away from or towards each other.

According to another aspect of the present invention, there is provided a device suitable for use in locating and/or pre-stressing a mine prop comprising: - a first load bearing member locatable between one end of the mine prop and either the foot wall or the hanging wall of an underground mine, tunnel or the like; - a second load bearing member located between the first load bearing member and the foot wall or the hanging wall, as the case may be;; - a pair of wedge members, locatable between the first and second load bearing members, each wedge member in turn having a pair of wedge surfaces located at an angle relative to each other and to the longitudinal direction, each wedge surface sloping away from a central region towards a distal end of the wedge member, the pair of wedge members being locatable in laterally spaced relationship from each other between the first and second load bearing members, the wedge surfaces of each wedge member being directable in the same direction of from one load bearing member towards the other; - a pair of substantially cylindrical bar members, one of which is locatable adjacent corresponding wedge surfaces of the wedge members on one side of an extended centre line of the prop and the other of which is locatable adjacent the opposite wedge surfaces of the wedge members; and - a shaft member having a first externally threaded portion at one end thereof adapted to engage with a complementary internally threaded hole through one of the pair of bar members intermediate its ends, and a second externally threaded portion of opposite hand located intermediate the first threaded portion and the opposite end of the shaft member and adapted to engage with a complementary internally threaded hole through the other of the pair of bar members, intermediate it ends, whereby the bar members may be screwingly displaced away from or towards each other, causing the bar members, upon displacement thereof towards each other, to slide against the wedge surfaces towards the apexes of the wedge members, which in turn causes the load bearing members to be displaced away from each other and, upon displacement of the bar members away from each other, to slide against the wedge surfaces away from the apexes of the wedge members, causing the load bearing surfaces of the load bearing members to be displaced towards each other.

The shaft member may be provided at one end thereof with a head which may be suitably shaped so as to facilitate rotation of the shaft, causing the load bearing members to be displaced away from or towards each other.

The device may comprise two pairs of wedge members, the apexes of one pair of wedge members being directed in one direction from one of the load bearing surfaces in the direction of the other, and the apexes of the other pair or wedge members being directed in the opposite direction, and being locatable in close proximity thereto, the bar members being locatable between the pairs of wedge members.

The device may be locatable inside a housing adapted to hold the parts of the device together. The housing may be in the form of a tube of substantially circular cross-section, the device being locatable in one end of the tube and the other end being connectable to a conventional mine prop such as a length of timber as in RSA Patent No. 88/3027.

One of the load bearing members may be integrally formed with a pair of wedge members. In the event that the device comprises two pairs of wedge members, each of the load bearing members may be formed integrally with one of the pairs of wedge members.

According to a further aspect of the present invention, there is provided a longitudinally adjustable mine prop comprising a device as hercinbeforc disclosed.

According to still another aspect of the invention, there is provided a support for a heavy load, comprising: - a first load bearing member locatable on a base; - a second load bearing member for supporting the load; - a pair of wedge members locatable between the load bearing members, each wedge member having an inclined surface; - a substantially cylindrical bar member locatable adjacent corresponding wedge surfaces of the wedge members; and - means for displacing the bar member relative to the inclined surfaces of the wedge members causing the wedge members to be displaced away from or towards each other.

We have found that the substantially cylindrically shaped bars of the pre-stressing device in accordance with the invention contribute significantly to the reduction of friction between the outer surfaces of the bars, on the one hand, and the wedge surfaces of the wedge members on the other hand. This friction can be reduced even lower by the application of a suitable lubricant. Thus.

instead of having a surface-to-surface contact as is the case with prior art devices, the device in accordance with the invention provides line contact between the bars and the wedge surfaces. In addition, the combination ()f a cylindrical surface and a flat or domed surface considerably cnhanccs the introduction of lubricant to the line of contact.

A further advantage of those embodiments of a pre-stressing device in accordance with the invention in which a pair of wedge members having flat surfaces are used, is that ii,rces on either side of the extended lngitudinal axis of the prop can remain balanced, which enhances the stability of the pre-stressing device. In those embodiments of the invention in which wedge members having dome-shaped surfaces are used, the pre-stressing device can be located more easily and is misalignment of the pre-stressing device with the prop not necessarily unacceptable.

Where the surface of the wedge member comprises an arc of a circle such as in the case of a dome-shaped wedge member or in those embodiments in which the wedge surface is formed by a cylinder cut lengthwise, longitudinal displacement of the bar member(s) is initially greater and thereafter smaller, when the bar member(s) is(are) moved towards each other. This feature makes fine adjustment simpler and facilitates pre-stressing to a higher load than is possible with a flat surplice.

A further advantage of a pre-slressing device in accordance with the invention is that it lends itself to the use of relatively inexpensive materials and methods of manufacture, so that the need for recovery of the pre-stressing device is considerably reduced. In most cases, the risk associated with the recovcry of the pre-stressing device in accordance with the invention will by far outway the possible benefits, so that it can be abandoned and written off.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawings, in which: - Figure 1 is a plan view of one embodiment of a support in accordance with the invention for supporting a heavy load: Figure 2 is a side elevational view of the support of Figure 1: and - Figure 3 is a side elevational view of a device or a support in accordance with the invention, suitable for use in locating and/or pre-stressing a mine prop.

- Figure 4 is a part sectional, side elevational view of another device or a support in accordance with the invention, suitable for locating and for pre-stressing a mine prop.

DETAILED DESCRIPTIOh' OF THE DRAWINGS In Figures 1 and 2, reference numeral 10 generally indicates a support in accordance with the invention, for supporting a heavy load.

The support 10 comprises two pairs of substantially triangular elements 12.1, 12.2 and 12.3, 12.4. Each of the elements 12.1, 12.2 comprises a first rectangular load bearing member 14 locatable on a base, whilst each of the elements 12.3, 12.4 comprises a second load bearing member 16 for carrying the load or to support a mine prop.

Each of the elements 12.1 ... to 12.4 further comprises a pair of elongated substantially V-shaped wedge members in the form of a bar 18 hent al an angle so as to form an apex 18.1 and two wedge members 18.2, 18.3. The ends of the bars 18 are welded to the ends of the respective load bearing members 14.

16. Each pair of wedge members 12.1, 12.2 and 12.3, 12.4 are locatable in spaced relationship from each other between the first and second load bearing members, the apex of each wedge member being directable in the same direction of from one load bearing member towards the other.

As can be seen in Figure 2, the apex 18.1 of the one pair of wedge members is directed in one direction from one of the load bearing surfaces in the direction of the other, whilst the apexes of the other pair of wedge members are directed in the opposite direction and are locatable in close proximity to the apexes of the first mentioned pair of wedge members.

The support further comprises a pair of cylindrical bar members 20.1, 20.2.

The bar member 20.2 is located adjacent corresponding wedge surfaces of the wedge members 18.3, whilst the bar member 20.1 is located adjacent corresponding wedge surfaces 18.2 of the wedge members 18.

A shaft member 22 which has a first externally threaded portion 22.1 at one end thereof engages with a complementary internally threaded hole 20.21 through the bar 20.2. The hole 20.21 is intermediate the ends of the bar member 20.2.

The shaft member also has a second externally threaded portion 22.2 of opposite hand which is located intermediate the first threaded portion 22.1 and the opposite end of the shaft member 22. The second externally threaded portion 22.2 is adapted to engage with a complementary internally threaded hole 20.11 through the bar member 20.1, intermediate its ends.

In use, the first load bearing members 14 are placed on a suitable support surface, whilst a load, which may be a mine prop, is placed on the second load bearing surface 16. By screwing the shaft member 22 in one direction, the bar members 20.1, 20.2 can be displaced towards each other, causing the bar members 20.1, 20.2 to slide against the wedge surfaces 18.2, 18.3 of the wedge members 18, towards the apexes 18.1 of the wedge members 18. This displacement causes the load bearing members 14, 16 to be displaced away from each other in a vertical direction. Conversely, when the shaft member 22 is screwed in the opposite direction, the bar members 20.1, 2().2 are displaced away from each other, sliding against the wedge surfaces 18.2, 18.3 of the wedge members 18 in a direction away from their apexes 18.1.This causes the load bearing surfaces 14, 16 to move towards each other, with the result that the load can be lowered.

Referring to Figure 3, there is shown a device 110 suitable for locating a mine prop 130 in accordance with RSA Patent No. 88/3027. The mine prop 13() comprises a length of timber which has a series of transversely extending, slot-like recesses 134 provided at one end thereof. The support 130 further comprises a cylindrical tube 136 nailed to the length of timer 132 by means of nails 138.

The device 110 is accommodated inside the tube 136, which serves as a housing. The component parts of the device 110 are held together by knocking a top portion of the tube 136 inwardly as shown at 140 in Figure 3.

The device 110 shown in Figure 3 is the same as the support of Figures 1 and 2, save that, instead of two pairs of triangular elements it only has one pair of triangular elements 112.3, 112.4. In the place of the other pair of triangular elements, it is provided with a circular wear plate 142.

The shaft member 22, 122 may be provided at one end thereof with a head 22.3, 122.3 which may be suitably shaped so as to facilitate rotation of the shaft 22, 122. Conveniently, in order to set the load taken up by the device 110, a torque wrench may be provided whereby a predetermined torque could be applied to the head 122.3 in pre-stressing the device 110, which is consistent with a load of say 15, 20, 25, etc., tonnes.

Referring to Figure 4, there is shown a pre-stressing device 210 in accordance with another embodiment of the invention. The device 210 comprises a dome-shaped wedge member 212 located between a pair of flat load bearing members 214, 216. In cross-section, the surface of the wedge member 212 thus incorporates an arc of a circle. Cylindrical bar members 218, 220 are located against opposite sides of the wedge member 212. As in Figures 1 to 3. a shaft member 222, which is provided with two lengths of opposite-handed thread.

extends through complementarily threaded holes through the bar members 2l S.

220. The shaft member 222 is provided with a head 222. 1 for turning it.

As will be appreciated, when the shaft member 222 is rotated in one direction.

the bar members 218, 220 are displaced towards each other whilst they are displaced away from each other when the shaft member 22 is rotated in the opposite direction. In this way, a mine prop can be pre-stressed if the device 210 has been placed below the prop.

As will also be appreciated, when the bar members are displaced towards each other, they initially rise relatively fast. However, as they approach the top of the domed surface their vertical displacement reduces. This has the advantage that considerably higher stresses can be achieved than with conventional devices where flat surfaces are used.

Claims

1. A pre-stressing device for a load carrying apparatus adapted to carry a load exercising a force in a first direction, the pre-stressing device comprising: - a pair of load bearing members locatable at positions spaced from each other between one end of the apparatus and a rigid support such that the load bearing members will, in use, oppose the load: - a wedge member locatable between the pair of load hearing members, the wedge member having a wedge surface locatable at an angle relative to the first direction and being restricted in use from movement in a lateral direction but being free to move in the first direction and in a direction opposite thereto: - a substantially cylindrical bar member locatable against the wedge surface of the wedge member; and - means for displacing the bar member in a lateral direction in relation to the first direction, causing the wedge member to push against one of the load bearing members and to cause the load bearing member to exercise a reaction opposing the force.

2. A pre-stressing device as claimed in claim 1, comprising a pair of wedge members locatable between the pair of load bearing members, on either side of an extended longitudinal axis of the apparatus, each wedge member having a wedge surface locatable at an angle relative to the first direction.

3. A pre-stressing device as claimed in claim 1, wherein the angles of the wedge surfaces of the wedge members are the same.

4. A pre-stressing device as claimed in claim 2, wherein each of the wedge members has a pair of wedge surfaces, each wedge surface being locatable at an angle relative to the first direction.

5. A pre-stressing device as claimed in claim 4, wherein the angles are complementary.

6. A pre-stressing device as claimed in claim 5, comprising a pair of substantially cylindrical bar members, one of the pair of bar members being locatable against one of the wedge surfaces on either side of the longitudinal axis of the load carrying apparatus.

7. A pre-stressing device as claimed in claim 2. wherein each of the wedge members is connected to one of the load bearing members.

8. A pre-stressing device as claimed in claim 1, comprising two pairs of substantially triangularly shaped wedge members, each of the wedge members having a pair of complementary sides and a base, the base of each wedge member being connectable to a load hearing member, the arrangement being such that two wedge members are arranged on either side of the extended longitudinal axis of the load bearing apparatus, with their bases directed in opposite directions, the pair of bar members being locatable against the inclined surfaces of the opposing wedge members such that, when the bar members are displaced towards each other, they cause opposing wedge members to be forced away from each other and, when the bar members are displaced away from each other, the opposing wedge members are allowed to move towards each other under the influence of gravity.

9. A pre-stressing device as claimed in claim 1, wherein the wedge member has a surface which, in cross-section, comprises an arc of a circle or an ellipsc.

10. A pre-stressing device as claimed in claim 9, wherein the wedge member has a substantially dome-shaped surface.

11. A pre-stressing device as claimed in claim 9, wherein the surface of the wedge member is provided by a portion of a cylinder cut lengthwise.

12. A pre-stressing device as claimed in claim 9, comprising a pair of substantially cylindrical bar members, one of the pair of bar members being locatable against the wedge surface on either side of the longitudinal axis of the load carrying apparatus, such that. when the bar members are moved towards each other, they are pushed in a longitudinal direction by the wedge surface.

13. A pre-stressing device as claimed in claim 9, wherein the wedge member is connected to one of the load bearing members.

14. A device suitable for use in pre-stressing a mine prop, the device being locatable between either a top or a bottom end of the mine prop and, respectively, the foot wall or hanging wall of an underground mine, tunnel or the like, wherein the device comprises: - a pair of load bearing members; - a pair of wedge members, each wedge member having a pair of wedge surfaces located at an angle relative to each other, the pair of wedge members being locatable in laterally spaced relationship from each other, one on either side of an extended centre line of the prop; - a pair of substantially cylindrical bar members, one of which is locatable adjacent corresponding wedge surfaces of the wedge members and the other of which is locatable adjacent the opposite wedge surfaces of the wedge members; and a shaft member co-operating with the bar members, and adapted to cause the bar members, upon rotation of the shaft member, to be displaced towards or away from each other, whereby the wedge members may be displaced away from or towards each other.

15. A device suitable for use in locating and/or pre-stressing a mine prop comprising: a first load bearing member locatable between one end of the mine prop and either the foot wall or the hanging wall of an underground mine, tunnel or the like; a second load bearing member located between the first load bearing member and the foot wall or the hanging wall, as the case may bc;; a pair of wedge members, locatable between the first and second load bearing members, each wedge member in turn having a pair of wedge surfaces located at an angle relative to each other and to the longitudinal direction, each wedge surface sloping away from a central region towards a distal end of the wedge member, the pair of wedge members being locatable in laterally spaced relationship from each other between the first and second load bearing members, the wedge surfaces of each wedge member being directable in the same direction of from one load bearing member towards the other;; - a pair of substantially cylindrical bar members, one of which is locatable adjacent corresponding wedge surfaces of the wedge members on one side of an extended centre line of the prop and the other of which is locatable adjacent the opposite wedge surfaces of the wedge members; and - a shaft member having a first externally threaded portion at one end thereof adapted to engage with a complementary internally threaded hole through one of the pair of bar members intermediate its ends, and a second externally threaded portion of opposite hand located intermediate the first threaded portion and the opposite end of the shaft member and adapted to engage with a complementary internally threaded hole through the other of the pair of bar members, intermediate it ends, whereby the bar members may be screwingly displaced away from or towards each other. causing the bar members. upon displacement thereon towards each other, to slide against the wedge surfaces towards the apexes of the wedge members, which in turn causes the load bearing members to be displaced away from each other and, upon displacement of the bar members away from each other, to slide against the wedge surfaces away from the apexes of the wedge members, causing the load bearing surfaces of the load bearing members to be displaced towards each other.

16. A device as claimed in claim 15, wherein the shaft member is provided at one end thereof with a head which is suitably shaped so as to facilitate rotation of the shaft, causing the load bearing members to be displaced away from or towards each other.

17. A device as claimed in claim 15, comprising two pairs of wedge members, the apexes of one pair of wedge members being directed in one direction from one of the load bearing surfaces in the direction of the other, and the apexes of the other pair of wedge members being directed in the opposite direction, and being locatable in close proximity thereto, the bar members being locatable between the pairs of wedge members.

18. A device as claimed in claim 15, wherein the device is locatable inside a housing adapted to hold the parts of the device together.

19. A device as claimed in claim 18, wherein the housing is in the form of a tube of substantially circular cross-section, the device being locatable in one end of the tube and the other end being connectable to a conventional mine prop.

20. A device as claimed in claim 15, wherein one of the load bearing members is integrally formed with a pair of wedge members.

21. A device as claimed in claim 15, wherein each of the bid bearing members is integrally formed with one of the pairs of wedge members.

22. A longitudinally adjustable mine prop comprising a device as hereinbefore disclosed.

23. A support for a heavy load comprising: - a first load bearing member locatable on a base; - a second load bearing member for supporting the load; - a wedge member locatable between the load bearing members.

the wedge member having an inclined surface; - a substantially cylindrical bar member locatable against the inclined surface of the wedge member; and - means for displacing the bar member in a lateral direction over the inclined surface of the wedge member causing the wedge member to he displaced in a longitudinal direction.