WO2002033221A2

WO2002033221A2 - Explosion proof walls

Info

Publication number: WO2002033221A2
Application number: PCT/ZA2001/000119
Authority: WO
Inventors: Sean Philip Brennan; Duncan Peter Campbell
Original assignee: Sean Philip Brennan; Duncan Peter Campbell
Priority date: 2000-08-15
Filing date: 2001-08-15
Publication date: 2002-04-25
Also published as: WO2002033221A8; WO2002033221A3; AU2002231376A1

Abstract

A fire wall, blast wall or containment wall for underground stopes and other areas is built by bringing underground empty bags which are filled with broken rock, stones and sand, laying them in one or two rows stretcher bond in the form of an arch whose ends are buttressed against the sides of the stope, etc. A steel mesh is on the concave side or between the two rows if there are two rows and wires are used to bind the bags using loops provided on the bags to the mesh. A ballast of broken rock and dust is piled up on the concave side of the wall, contained between the bag wall and a back wall.

Description

FIELD OF THE INVENTION

This invention lies primarily in the field of mining and in particular underground mining

5

BACKGROUND

Explosions in underground mines are an appalling phenomenon, the flame front and shock wave advance along working faces, stopes and shafts at ιo speeds which make escape impossible Very little chance of survival exists for miners Coal and other "fiery" mines have been well recognised as particularly prone to this danger, due to suspended coal dust, pockets of methane and other flammable gases However, some or other of these are encountered in other mining operations, including gold mining operations,

15 with similar dangers Very sophisticated and costly appliances exist, derived from military technology, for detecting and quenching an advancing flame front The inventor is aware of an existing stratagem of suspending bags of stone dust in mine stopes, which has on occasion quenched advancing flame fronts, but is not a sufficiently secure protection to receive

20 mine regulatory approval

These measures, however, have not sufficiently dealt with the problem and mining regulations require unused stopes, passages and other areas where explosive conditions may develop to be walled off with explosion 2 proof walls

Up to now, reinforced concrete walls and brick and mortar walls have been built underground as fire walls, blast walls or containment walls, but the disadvantages of this approach are the cost, high building standards and ) massive construction required in the difficult conditions underground and remote locations from the shafts, which are encountered The walls built in this way are not reusable but must be broken down and the rubble dealt with where a passage is to be opened up again.

A considerable problem thus exists in underground mining .

THE INVENTION

A solution of this problem according to the present invention is an arch structure with ends of the arch buttressed into side walls of a stope or passage or other area to be walled off, with the concave surface of the structure facing a locality to be protected. The invention covers a wall in the form of a segment of an arch, suitably buttressed. A primary application of the invention is to provide protection against explosions as described above, but the application of the invention can be extended to other types of loadings/forces.

According to the invention, the arch structure may be a one-dimensional, or simple, arch (i.e. arched in the horizontal plane, only) or a two- dimensional, or complex, arch (i.e. arched in both the horizontal and vertical planes). The simple arch may be preferred for arches made in accordance with the preferred embodiment of the invention, with sand bags. However, with more advanced training of labourers, the complex arch can also be built with sand bags. Use of sand bags has advantages, as are described below.

A parabolic arch structure provides the advantage of only compressive forces generated by a pressure differential across the structure, the higher pressure being on the convex side. This enhances strength greatly, compared to a planar structure, as has been used in the art, to wall off areas. In accordance with a preferred embodiment of the invention, the structure is made of sand bags packed or laid, to build up the structure.

Construction, in conditions prevailing underground, of the arch of the invention with sand bags has certain advantages, as will be described below. Alternatively, the arch construction can be accomplished by casting a monolithic structure, or, the arch structure can in certain conditions e formed partially as a monolithic casting and partially with packed sand bags.

The expression sand bag is used herein as a convenient graphic description but must be interpreted herein to extend to any flexible or collapsible containers, e.g. bags of any sand, crushed rock, sand and crushed rock, cement, cement-like material or other suitable filling. Crushed rock has a flame quenching property.

Bags specially adapted for use in this invention are also provided, as will be described below.

The term arch refers to a suitable structural arch appropriate to the conditions of the base against hich the arch is buttressed and to the bags used, in particular the compressive strength of the arch formed with the bags. The arch may be constructed to a selected radius of curvature, which approximates to a parabolic shape, according to structural principles. As an example applicable in fairly typical conditions the radius may be selected between fifty per centum (50%) and seventy per centum (70%) of the width of the stope, passage or other area to be walled off, between the buttress positions, more preferably approximately sixty per centum (60%) thereof. The bags may be grouted between each other to complete an arched wall and its structural integrity and imperviousness. The bags may be laid in any number of rows (whether attached or not), but commonly in two rows and may be laid in stretcher bond or as required.

5

The arched wall is preferably supplemented by a ballast located at the concave side of the wall against the arch, for example, conveniently in the form of crushed rock and stone dust, to establish a substantial tonnage of rock ballast against the concave side and a means of flame front it) quenching. This ballast is useful as an assurance of flame quenching and as a support to assist in maintaining the integrity of the arched wall, especially against the effects of a reverse or negative shock wave as arises as a part of a passing shock wave cycle or otherwise.

15 In accordance with the invention a back wall is provided on the concave side of the arched sand bag wall spaced at a suitable distance from the arch to allow a desired tonnage of the ballast to be filled into the space between the arch and the back wall. The back wall may be constructed, for example, by means of poles and corrugated steel sheets. Even a further

20 wall can be erected.

There may be a further back wall to serve as a gas barrier which is temporary or may be left there for other purposes.

25 Preferably the arched wall includes a steel mesh against which are located the bags on the convex side of the mesh or the mesh may be interleaved between rows of sand bags. The mesh may be tied to layers of steel reinforcing and/or the bags. This mesh assists in resisting a reverse or negative shock wave that arises as part of a passing Shockwave cycle, or

3t) otherwise. The arched wall and the ballast and back wall are preferably penetrated by pipes fitted with valves for water drainage and for gas sampling purposes.

Thus the present invention provides an advantageous method of construction of an explosion proof wall, which is characterised in the first place by the shape of an arch and as a subsidiary feature, by the use of sand bags to construct a bagged wall. Other common names for the wall would be a fire wall, blast wall or containment wall.

The method may also be carried out, subject to certain constraints, by relatively unskilled labour. Thus preferably the method is carried out by first erecting a steel mesh segment of an arch and then packing sand bags against the mesh on the concave side thereof. Mesh or other reinforcing may be interleaved between the bags and/or tied to the mesh segment of an arch.

The bags may be packed in a number of rows, e.g. two, and stretcher bond lay may be used as well as grouting between the bags.

The sand bags may be taken below ground empty in the shaft skip and along the stopes to the required area (which may be several kilometres underground) and loaded with sand, sand-cement mixture, crushed rock, crushed rock-cement mixture and the like underground. The method may include filling of the bags on site using local material, e.g. crushed rock, etc, It will be appreciated that a filled bag of the kind envisaged by this invention may weigh between fifty and eighty kilograms (10-80 kg). However, other bag sizes may be adopted, depending on various considerations,

The method is preferably preceded by appropriate preparation of secure buttressing on the sides of the stope or other area against which the ends of the arch segment will bear. Similarly foundation trenches may be prepared into which the initial layers of bags are laid. The bags maybe built up to the hanging wall and accommodated with grouting to an irregular surface and/or set into recesses, for good sealing. The bag constructed wall can use crushed rock which has quenching properties, but of greater significance, the bags can squash or otherwise take up movement, more readily than a monolithic arch, if there should occur a closure between hanging wall and foot wall or between side walls, or if there occurs other movement of the buttressing rock. This can be an important advantage over integrally cost arch structures, in certain mines which, due to their extreme depth or geological conditions, are subject to movement.

Where conditions make it appropriate, however, an area may be walled off by producing an arched structure according to the invention by casting into form-work or brattice work. It may be advantageous to construct the arch with a monolithically cast footing or low arch, completing the closure of the arch with the use of sand bags,

The method may be carried out behind a gas wall which is erected as an initial step of the method, as a measure of security against poisonous gases that would affect operations in the stope. This can be light poles wired together and supporting a protective sheeting.

A back wall may be constructed as a later step of the method and a space between the back wall and the arched bag wall filled with crushed rock and stone dust as a ballast as has been referred to above.

The invention further provides a bag adapted for use in the arched wall and method of the invention. The bag is preferably of woven or other textile construction, e.g. of suitable polymer. According to the invention the bag has ties attached to it or has sheaths or loops or other guides to assist locating ties, for example wire ties, for binding bags to each other and/or to the arched steel mesh.

5 THE DRAWINGS

The invention will be more fully described by way of an example of a fully bag constructed arch, with reference to the drawings, in which : -

10 figures 1 , 1A and 1 B are plan views of various examples of arched sand bag walls,

figures 2, 2A and 2B are elevations (on a reduced scale in the case of figure 2) of the walls shown in figures 1 , 1A and 1 B respectively, ι-> and

figure 3 is a plan view of a bag used in constructing the wall while still unfilled. 0

THE PREFERRED EMBODIMENTS

As shown in figures 1 and 2, the sand bag arch construction 1 comprises a plurality of bags 2 built up in two rows to provide a double wall with ends of 25 the arch buttressed into side walls 3 of an underground mine stope 4, The sides of the stope are cut away to provide secure buttressing, as shown at 6 and 7. The sand bag wall is set into trench 22 so as to found the wall on a solid base. Similarly the top of the wall is set into the hanging wall at 23 into a roof cut-out as required,

30 The sand bags are filled with a mixture of sand and cement which is packed into the bags prior to use in the wall at a convenient location where sand has been delivered from the surface or is available from mine tailings or otherwise. The mixture in the bags may be wetted by water to ensure good curing but the mixture may adequately set merely due to the very humid conditions prevalent in underground mines in many cases. The arch has a design radius of curvature 5 of three comma five metres (3,5m) in a stope of a standard width in many mining operations of six metres (6m), A typical stope height is two metres (2m). These sizes vary in various conditions.

The bags are grouted between each other as indicated at 27.

The arched wall is supplemented by a stone dust ballast 8 packed into the space left between the arched wall and a back wall 9. The ballast is broken and crushed rock taken from underground and the stone dust fire retardant, The ballast may comprise stone dust in bags, which are split by a knife once laid. The back wall is constructed of poles 10 erected crosswise ("props") and poles 11 erected upright ("soldiers"), which are wired together. About 85 tons of ballast may be provided against the arch wall in this way. The sides of the back wall are sealed with Aerocell Ventseal (trademark) foam or equivalent.

A steel mesh 12 is initially erected in an arch form across the stope and provides a form to guide the erection of the arched bag wall. A number of mesh sheets 13 are tied to the arched mesh and to the back wall and become sandwiched or interleaved between the layers of bags and the stone dust bags.

Application of the invention may require insertion of the following pipes ;- Pipe 14 at a low level provides a drain for ground water from the closed off area 15 with a valve 16. This would be kept normally closed, to avoid risk of methane gas etc. passing through the barrier, or opened to allow testing for water when desired or kept open as a permanent or a periodic water drain, as required.

Pipe 17 at a high level provides a gas test pipe with a valve 18, which is normally kept closed but may be opened to allow testing for methane, etc.

Prior to constructing the arched wall, a gas wall (brattice or barrier) 19 is erected to close off the stope for the sake of safety of the workers against gas poisoning. The gas wall is made of a frame of light poles 20 and a plastic sheet 21. The plastic is Gundle Green (trademark) or equivalent plastic sheet glued to polypropylene brattice sheet fixed to the frame. The sides are sealed to the walls of the stope by use of Aerocell Ventseal (trademark) foam or equivalent.

The invention as described will be carried out by providing the arch in a horizontal plane (i.e. the arch is seen in plan view) with the sand bag wall vertical (i.e. as seen in elevation) but the scope of the invention will not exclude a double curvature, (i.e. arched both as seen in plan view and a. seen in elevation).

Figures 1 A and 2A show a variant in the construction in which two single layer bag walls are erected with a space between them filled with broken and powdered rock. The same reference numerals have been used to show the same components or analogous components,

Figures 1 B and 2B show another variant, on the same basis. Figure 3 shows a preferred bag 26 to be used in the invention which comprises a woven polypropylene bag 26 open at one end 24 for filling and having pockets, bands or sheaths 25 sewn or bonded onto the outside of the bag on at least one side These serve to guide and retain in position wires or other ties which are passed through and used to tie the bags to each other and/or to the steel mesh arch

It will be apparent to those skilled in the art that other embodiment within the scope of this invention, in regard to the arch construction, the method and the bag design are possible

Reference numerals :

1 arched bag wall

2 bags

3 side walls of stope

4 underground mine stope

5 radius of curvature of arch

6 cut away for buttressing wall

7 cut away for buttressing wall

8 stone dust ballast

9 back wall

10 crosswise poles for back wall

1 1 upright poles for back wall (soldiers)

12 steel mesh

13 mesh sheets

14 pipe for ground water

15 area closed off

16 valve

17 gas test pipe

18 valve

19 gas wall (brattice)

20 frame of light poles

21 plastic sheet

22 trench for bag wall

23 hanging wall

24 open end of bag

25 bands or sheaths on bag

26 bag

27 grouting between bags

Claims

CLAIMS:

1. An arch structure with ends of the arch structure buttressed at buttress positions in side walls of a stope or passage or other area to be walled off, with the concave surface of the structure facing an area to be protected, having an arch curvature selected from at least one of a horizontal and/or a vertical curvature, constructed of at least one of a monolithic cast structure and/or a packed sand bag structure, of flexible or collapsible containers or bags containing sand, crushed rock, sand and crushed rock, cement, cementitious material or other suitable filling.

2. An arch structure as claimed in claim 1 , which is constructed to a selected radius of curvature according to structural principles with a radius selected between fifty per centum (50%) and seventy per centum (70%) of the width of the stope, passage or other area to be walled off, between the buttress positions

3. An arch structure as claimed in either one of claims 1 or 2, in which the bags are grouted between each other to complete the arched wall and its structural integrity and imperviousness.

4. An arch structure as claimed in any one of claims 1 to 3, in which the bags are laid in two rows and are laid in stretcher bond.

5. An arch structure as claimed in any one of claims 1 to 4, in which the arched wall is supplemented by a ballast located at the concave side of the wall against the arch, in the form of crushed rock and stone dust.

6. An arch structure as claimed in claim 5, in which a back wall is provided on the concave side of the arched sand bag wall spaced at a suitable distance from the arch to allow a desired tonnage of the ballast to be filled into the space between the arch and the back wall.

7. An arch structure as claimed in any one of claims 1 to 6, in which the arched wall includes a steel mesh against which are located the bags on the convex side of the mesh or the mesh is interleaved between rows of sand bags.

8. An arch structure as claimed in claim 7, in which the mesh is tied to layers of steel reinforcing and/or the bags.

9. An arch structure as claimed in any one of claims 1 to 8, in which the arched wall and the ballast and back wall are penetrated by pipes fitted with valves for water drainage and for gas sampling purposes.

10, An arch structure for closing off an underground stope or other area, as herein generally described.

11. An arch structure for closing off an underground stope or other area, as herein specifically described with reference to the drawings and as illustrated.

12. A method of closing off a stope or other area by means of an arch structure as claimed in any one of claims 1 to 1 1 , which comprises the steps of packing bags or other containers with broken rock, sand or other suitable material, then erecting one or more rows of the bags in the form of an arch from one edge of the stope or other area to another edge, the edges serving as buttresses for the arch, optionally casting a part of the arch or a footing as a monolithic arch structure.

13. A method of closing off a stope or other area as claimed in claim 12, in which the steps are preceded by erecting an arch of steel mesh and building the row(s) of bags against the concave side of the mesh.

14. A method of closing off a stope or other area as claimed in claim 13, which is followed by tying the bags and/or wire reinforcing to the steel mesh.

15. A method of closing off a stope or other area as claimed in any one of claims 12 to 14, which includes the steps of erecting a back wall and piling up between the back wall and the arch wall stones, broken rock, sand and/or other suitable material,

16. A method of closing off a stope or other area as claimed in any one of claims 12 to 15, which includes applying grouting between the bags and/or preparing buttress areas and trenches and/or laying of pipes which will communicate from one side to the other of the wall and ballast of present.

17. A method of closing off a stope or other area as herein described.

18 A bag or other flexible or collapsible container for use in a wall as claimed in any one of claims 1 to 11 or in a method as claimed in any one of claims 12 to 17, which comprises bands or sheaths sewn or bonded onto the outside of the bags on at least one side thereof.

9. A bag or other flexible or collapsible container for use in a wall as claimed in any one of claims 1 to 11 or in a method as claimed in any one of claims 12 to 17, as herein specifically described with reference to the drawings and as illustrated.