WO2000011318A1

WO2000011318A1 - Apparatus for prestressing a support in underground mining

Info

Publication number: WO2000011318A1
Application number: PCT/ZA1999/000070
Authority: WO
Inventors: Pierre Marc FOUCHÉ; Johann Smit; Michael Reinhardt Grobbler
Original assignee: Grinaker Construction Limited
Priority date: 1998-08-24
Filing date: 1999-08-24
Publication date: 2000-03-02
Also published as: AU5929699A

Abstract

Apparatus (16) for prestressing a support (60) which includes a flexible container (20), a settable composition (22) in the container, and valve means (24) fixed to the container (20) through which fluid under pressure may be introduced into the interior of the container (20).

Description

APPARATUS FOR PRESTRESSING A SUPPORT IN UNDERGROUND MINING

BACKGROUND OF THE INVENTION

This invention relates to the prestressing of supports of the kind used, for example, in underground mining operations.

Underground mining supports are made from various materials e.g. timber or cementitious blocks which are assembled in appropriate arrays, stacked one above the other, to provide support between a hanging and a foot wall. It is desirable for reasons which are known in the art and which are hence not elaborated herein to ensure that a pack is prestressed to an acceptable degree shortly after installation i.e. without waiting for closure between the hanging and foot wall to take place.

SUMMARY OF THE INVENTION

The invention provides apparatus for prestressing a support which includes a flexible container, a settable composition in the container, and valve means fixed to the container through which fluid under pressure may be introduced into the interior of the container.

The settable composition may be a cementitious grout powder or paste or any other suitable binding or settable material.

The container may be of any appropriate form and may for example include an internal liner, which is fluid impervious, and one or more external layers which reinforce the liner.

The liner may be made from polyethylene or any appropriate material and the outer layers may be from woven polypropylene or any other appropriate material. These materials are given merely by way of example and are non-limiting.

The container may be in the form of a flexible bag of appropriate dimensions. Suitable dimensions are approximately 650 x 350 x 33mm, without fluid inside the container. The container, once filled with fluid, changes in shape and dimension to a parallelepiped body of approximately 600 x 300 x 100mm.

The container may be bound within a rigid or semi-rigid housing which permits movement of the container in at least one direction at least until the settable composition has set.

The valve means may be positioned to ensure that fluid which passes through the valve means into the container interior is effectively mixed with the settable composition. The quantity of settable composition inside the container and the maximum internal volume of the container are chosen so that adequate mixing takes place, and the container is suitably filled and pressurised, when the appropriate quantity of fluid is introduced into the container for mixing with the settable composition.

In order to enhance the mixing of the fluid and the settable composition the invention may, according to a variation, provide for the fluid to be introduced into the settable composition at each of a plurality of locations. This may be achieved in any appropriate way. A particularly advantageous method makes use of a manifold structure, which may be inside the container, through which the fluid is introduced. The manifold structure is formed with a plurality of outlets through which fluid is discharged, in a plurality of jets, into the settable composition.

With the last mentioned form of the invention the container may have an internal partition which includes a plurality of apertures and the valve means is connected to the container to introduce fluid into the container on one side of the partition with the settable composition being located inside the container on an opposing side of the partition.

The fluid may be gaseous but, normally, is liquid eg. water. The fluid may be a gas/liquid mixture, eg. a mixture of air and water, and may include one or more additives eg. for pressurising, or accelerating the setting of, the composition, or for any other purpose.

The invention also provides a method of prestressing a support which includes the steps of pressurising a container which acts on the support by means of a fluid which is introduced into the container from an external source, allowing the fluid to act on a settable composition contained in the container, and allowing the composition to set while the interior of the container is held in a pressurised condition.

The pressurised condition may be established by the external source, or may be established by the mixing of the fluid and the composition, or both techniques may be employed.

The fluid may be gaseous or liquid eg. water or a gas/liquid mixture eg. an air/water mixture.

The fluid may include one or more additives which influence the setting of the composition eg. which react at least with the composition to pressurise, or accelerate the setting of, the said resulting mixture, or for any other desired purpose.

Preferably the external source is an external source of water at an appropriate pressure.

Preferably the composition in the container is grout which may be in the form of a cementitious powder.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of examples with reference to the accompanying drawings in which: Figure 1 is a side view of a support pack which is prestressed with apparatus according to a first form of the invention,

Figure 2 is a view similar to that shown in Figure 1 illustrating apparatus according to a variation of the invention,

Figure 3 is a somewhat schematic perspective view of the apparatus which is included in the arrangement shown in Figure 2, and

Figure 4 illustrates a different form of the invention. DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 of the accompanying drawings illustrates a support pack 10 of any appropriate construction, for which no novelty is claimed, in an underground location. The support pack 10 rests on a foot wall 12 and opposes a hanging wall 14.

Support apparatus 16 according to the invention is located on an upper side of the pack 10 immediately below the hanging wall 14.

In this example of the invention the apparatus 16 includes a multi-layer polyethylene liner 18 which is in the form of a closed bag and a surrounding woven polypropylene bag 20. The liner 18 is water impervious but is relatively weak. On the other hand the polypropylene bag 20 is strong and possesses considerable bursting strength but, as it is woven, it is not water tight.

The liner bag 18 contains a predetermined quantity of grout powder 22. As far as is practically possible air is excluded from the bag 18.

A one-way valve 24, of any appropriate construction, is connected to the liner and extends through the woven polypropylene outer bag 20.

The grout 22 is a high yield grout and, compared to grouts which are not so classified, takes up a comparatively large quantity of water.

Once the apparatus 16 has been located on a pack 10, in the manner described, water from a suitable supply source, not illustrated, is connected to the valve 24. The water flows into the interior of the container formed by the compound assembly of bags 18 and 20 and expands the bags to their maximum volumes under the circumstances. The water source preferably has a relatively high pressure so that the force which is ultimately exerted by the expanded bags is substantial. The pack 10 is thereby stressed in its loading direction.

The water, as it comes into contact with the grout, wets, or mixes with, the grout, and is absorbed by the grout. When the water source is disconnected from the valve 24, the valve shuts automatically and the interior of the bag is maintained pressurised by the water and grout contents thereof.

As has been stated the water interacts and mixes with the grout powder 22 which then sets, while the bags are internally pressurised. As the grout sets under pressure the force which is initially exerted by the water inside the bags is, at least to a substantial extent, maintained once the cementitious mixture has set.

It has been found that under certain conditions the mere introduction of water, through the single inlet formed by the valve 24, does not lead to adequate mixing of the water and the grout powder. The arrangement shown in Figure 2 is intended to enhance the mixing between the water and the grout powder by varying the way in which the water is introduced into the powder.

Figure 2 illustrates a modified apparatus 16A positioned on top of a pack 10. Where applicable reference numerals which are the same as those employed in Figure 1 are used in Figure 2 to indicate components which are similar to or the same as those illustrated in Figure 1.

The polyethylene liner 18 has an internal partition 26 which effectively divides the liner into two sub-bags 28 and 30 respectively. The valve 24 is positioned to admit water into the sub-bag 28. The grout powder 22 is located inside the sub-bag 30. In the illustrated example the sub-bag 30, and hence the grout powder, are above the partition 26 and hence above the sub-bag 28.

The partition 26 includes a plurality of relatively small holes or apertures 32 at regularly spaced intervals over a surface of the partition.

Water which flows through the valve 24 enters the sub-bag 28 and fills the sub-bag. As the sub-bag is pressurised by the inwardly flowing water it expands to its maximum volume under the circumstances. Water is able to escape from the sub-bag 28 through the various apertures 32 in a corresponding plurality of relatively small water jets. These water jets are aimed directly into the grout powder 22 at a corresponding number of spaced locations. Thus the sub-bag 28 acts as a manifold for it causes the water to flow into the grout powder at a substantial number of points and a more efficient mixing action of the water with the grout powder is thereby achieved.

The water which flows into the upper sub-bag 30, and the resulting fluent grout mixture, leads to the upper sub-bag 30 being pressurised. The quantity of water which remains in the lower sub-bag is relatively small and, at least to a substantial extent, the water is, in any event, absorbed by the grout powder. By maintaining the volume of the sub-bag 28 relatively small compared to the volume of the upper sub-bag essentially the entire interiors of the two bags 18 and 20 are fully pressurised by the grout mixture which, as before, sets while the internal pressure thereof, which is initially achieved by the pressurised water passed through the valve 24, is maintained.

Figure 3 is a somewhat schematic perspective illustration of the apparatus 16A. The compound bag assembly, once expanded in the manner described, has approximate dimensions as follows: length 40 - 600mm; width 42 - 300mm; height 44 - 100mm. To achieve these dimensions the bag assembly, in an uninflated condition, has a length of about 650mm, a width of about 350mm and a height, inclusive of the grout powder contents, of about 33mm.

In the aforegoing examples the liner or bag 18 contains a cementitious grout powder which is caused to set by the addition of water, which wets, or mixes with, the powder. Although this is a preferred arrangement it is merely illustrative for any other suitable composition could be used in place of the powder. Also, more generally, the water could be replaced by a suitable liquid which acts on, eg. wets or mixes with, the composition thereby placing it in a state in which it sets. The liquid which is used may include a gas and for example may be in the form of an air/water mixture. Another variation is to include in the liquid, eg. the water, one or more additives which affect the setting or nature of the composition. For example gas may be entrained in the water for aerating and pressurising a cementitious grout powder. Another possibility is to make use of an additive which aerates the grout, or accelerates the setting thereof. The invention is not limited in this regard.

Two embodiments of the invention have been described. The invention is however not limited to the precise details shown in the accompanying drawings or described hereinbefore. An important aspect of the invention resides in the fact that the mixing, or wetting of, the grout powder with the water is achieved inside the container which houses the grout powder. Another important aspect is that the cementitious composition is allowed to set whilst the interior of the bag is held in a pressurised condition which is achieved by using water from a pressurised source.

The preceding examples describe the prestressing of support packs. Figure 4 on the other hand illustrates the prestressing of an elongate support 60 which bears on a yielding assembly of lightweight concrete blocks 62 erected on a footwall 64. A cup-shaped housing 66, made for example of sheet metal or a plastic material, contains prestressing apparatus 68 which is a smaller version of, though similar in all essential respects to, the apparatus 16 which has been described hereinbefore. The housing 66 is between an upper end of the support and an opposing surface of the hanging wall 70. When the apparatus 68 is pressurised eg. by the introduction of water, the apparatus 68 is expanded and the contents thereof are allowed to set, under pressure, so that the support is pre- stressed. As the apparatus 68 expands its outwards movement is confined by the housing which nonetheless allows free movement of the apparatus in a direction which is parallel to the longitudinal direction of the support.

It will be appreciated that the grout powder may be substituted by a cementitious paste or any other suitable binding or settable composition depending on the particular application, without limiting the scope of the invention.

Claims

1. Apparatus for prestressing a support which includes a flexible container, a settable composition in the container, and valve means fixed to the container through which fluid under pressure may be introduced into the interior of the container.

2. Apparatus according to claim 1 wherein the container includes an internal liner which is fluid impervious, and one or more external layers which reinforce the liner.

3. Apparatus according to claim 1 or 2 wherein the valve means is positioned to ensure that fluid which passes through the valve means into the container interior is effectively mixed with the settable composition.

4. Apparatus according to any one of claims 1 to 3 wherein the fluid is introducible into the settable composition at each of a plurality of locations.

5. Apparatus according to claim 4 which includes a manifold structure which is formed with a plurality of outlets through which fluid is discharged, in a plurality of jets, into the settable composition.

6. Apparatus according to claim 5 wherein the container has an internal partition which includes a plurality of apertures and the valve means is connected to the container to introduce fluid into the container on one side of the partition with the settable composition being located inside the container on an opposing side of the partition.

7. Apparatus according to any one of claims 1 to 6 which includes a housing which permits movement of the container in at least one direction at least until the settable composition has set.

8. A method of pressurising a support which includes the steps of pressurising a container which acts on the support by means of a fluid which is introduced into the container from an external source, allowing the fluid to act on a settable composition contained in the container, and allowing the composition to set whilst the interior of the container is held in a pressurised condition.

9. A method according to claim 8 wherein the pressurised condition is established by at least one of the following:

(a) the external source, and

(b) mixing or wetting the composition with the fluid.

10. A method according to claim 8 or 9 wherein the fluid includes an additive which influences the setting of the composition.