Support Pillar Mining Method

Abstract

A support pillar mining method, and more particularly, a support pillar mining method allows for the selective mining of an identified segment in a support pillar. The method includes the steps of (i) cutting, in the support pillar, a removable segment with a saw; (ii) retaining, in the support pillar, a support portion extending from a foot wall to a hanging wall; and (iii) removing, from the support pillar, the cut removable segment wherein the support portion extending from the foot wall to the hanging wall supports the hanging wall after the cut removable segment has been removed from the support pillar.

Description

FIELD OF THE INVENTION

[0001] The invention relates to a support pillar mining method, and more particularly, to a support pillar mining method which allows for the selective mining of an identified segment in a support pillar.

BACKGROUND TO THE INVENTION

[0002] Many underground mining operations utilise the so-called bord and pillar or room and pillar mining methods. The bord and pillar mining method involves mining a panel and leaving a plurality of rows of spaced apart virgin material in place to support the panel whilst it is still being mined. When the panel has been fully mined, i.e. the reef has been mined to its end, a large room is left consisting of a roof (also known as the hanging wall) supported above a floor (also known as a foot wall) by the pillars (also known as support pillars) of virgin material.

[0003] These support pillars contain the same ore that was mined during the mining of the panel and represent significant economic value. Accordingly, various attempts have been made over the years to extract (or mine) the ore from these support pillars.

[0004] Owing to safety concerns and as a matter of convenience, these support pillars are often mined in a retreating manner, in which the direction of mining is turned around. Here, the support pillars closest to the panel back are mined first with the support pillars closest to the room's entrance being mined last.

[0005] In most cases it is accepted that the hanging wall surrounding a support pillar will collapse after the support pillar has either been removed completely or partially mined.

[0006] One such method is described in U.S. Pat. No. 4,312,540 entitled "Continuous mining apparatus and method". This published US patent application describes a secondary mining method whereby coal is removed from pillars in such a manner that the pillar is either totally or partially destroyed. The method involves the steps of (a) providing a continuous miner having a cutter assembly, conveyor assembly and base assembly; (b) stationing the base assembly of the continuous miner at a point adjacent the pillar to be removed; (c) extending the cutter assembly away from the fixed base assembly a distance sufficient to permit the cutter assembly to extend completely through the pillar to be removed in order to make a single continuous cut through the entire pillar; and (d) repositioning the continuous miner in order to make additional cuts through the pillar thereby to remove a portion or all of the pillar. It is notable that, as stated in the patent application, the pillar would be totally or partially destroyed after it has been minded. Therefore, the pillar would no longer support a hanging roof after it has been mined. Accordingly, the secondary mining method described in this patent application remains unsafe to workers and the continuous miner itself. It is also noted, as shown in FIG. 20 of the patent application and described in its specification that the continuous miner can only make cuts of a certain shape and dimension. That is, the continuous miner cannot make custom cuts in a pillar so as to minimize the risk of the particular pillar collapsing whilst it is being mined.

[0007] Attempts have been made to develop alternative mining strategies and to move away from the conventional bord and pillar mining method. On such method is described in published international patent application number PCT/IB2007/052134 entitled "A mining method and system for use therein". The invention described in this patent application provides a method of mining that includes the steps of (a) providing a continuous mining machine; (b) cutting at least one linear primary passage into an ore body; and (c) cutting a plurality of secondary passages into the ore body, the secondary passages being disposed at oblique angles relative to the primary passage, whereby a roof zone of the ore body is supported by walls of material that separates the secondary passages. The mining method described in this patent application does not, however, have any application in an already developed mine which has been developed according to the conventional bord and pillar mining method. That is, the mining method described in this patent application can only be used when developing a new underground mine as the safety of workers and the continuous miner itself can only be guarded if the extensive passageways described in the patent application are cut in the described, sequential manner.

[0008] Various efforts have been made to have the hanging wall collapse in a controlled manner, but owing to the unpredictable nature of geological features, these methods often fail and result in a significant loss in human lives. One such method is described in published international patent application number PCT/IB2014/065357 entitled "Pillar extraction mining method". This patent application describes a method of mining or extracting a support pillar from an underground room and pillar mining operation which includes forming at least one removable segment in a pillar and moving the segment substantially intact from its original location to a mining position distal from its original location, operatively from where the segment may be mined. The patent application also discloses a sequence of pillar removal to control caving during pillar recovery. The safety of workers and mining equipment remain a concern, however, as a collapsing hanging wall is inherent to the mining method described in this patent application.

[0009] Current continuous mining machines which are utilised in the mining of support pillars suffer from the disadvantage that precise and custom cuts cannot be made to mine (i.e. extract) an identified segment in the support pillar (in an instance where the support pillar will only be mined partially) and, as a result thereof, the hanging wall often collapses in an uncontrolled manner owing to the fact that the support pillar can no longer support the weight of the surrounding hanging wall.

[0010] One such method is described in U.S. Pat. No. 4,458,947 entitled "Mining method". This patent application describes a method of mining wherein ore in the pillars are recovered by drilling a series of holes in the pillars. This method, however, suffer from the disadvantage that only holes of constant shape and size can be drilled into the pillars to recover ore therefrom. The patent application continues to provide that the holes in the pillars are preferably drilled before the pillars themselves are formed. This speaks directly to the lack of flexibility which is inherent in the method described in this patent application.

SUMMARY OF THE INVENTION

[0011] It is accordingly an object of the present invention to provide a support pillar mining method which overcomes, at least partially, the abovementioned problems and/or which will be a useful alternative to existing support pillar mining methods.

[0012] According to a first aspect of the present invention, there is provided a support pillar mining method which includes the steps of:

[0013] cutting, in the support pillar, a removable segment with a saw;

[0014] retaining, in the support pillar, a support portion extending from a foot wall to a hanging wall; and

[0015] removing, from the support pillar, the cut removable segment

[0016] wherein the support portion extending from the foot wall to the hanging wall supports the hanging wall after the cut removable segment has been removed from the support pillar.

[0017] The cut removable segment may be shaped and dimensioned so as not to adversely affect the security or safety factor of the pillars beyond an acceptable range, after the cut removable segment has been removed from the support pillar. An acceptable range depends on the specific load bearing capacity which a particular pillar has to have.

[0018] There is provided for the support pillar mining method according to the first aspect of the present invention to include, prior to the cutting step, the additional steps of:

[0019] drilling, in the support pillar, a hole from a first face of the support pillar to a second face of the support pillar; and

[0020] threading, through the drilled hole, the wire saw which is to cut the removable segment.

[0021] It is envisaged that the cut removable segment may extend from the first face of the support pillar to the second face of the support pillar. The first and second faces of the support pillar may be opposing faces. There is provided for an end profile of the cut removable segment to take the form of any one of a circle, an oval, a square, a rectangular, a triangle, a rhombus, a trapezoid, an arch and a hyperbole.

[0022] The removable segment may be cut in the support pillar by:

[0023] making a first horizontal cut in the support pillar to form a bottom face of the removable section;

[0024] making a second horizontal cut in the support pillar to form a top face of the removable section; and

[0025] making a vertical cut in the support pillar to form a side face of the removable section.

[0026] There is provided for the method to include, prior to making a second horizontal cut in the support pillar, the additional step of introducing a spacer in a space left by the first horizontal cut, whereby the spacer may serve as a load bearing member once the cut removable segment weighs down on the spacer.

[0027] The method may, further, include the additional step of introducing a friction reducing means in a space left by the first horizontal cut, whereby the friction reducing means may facilitate the eventual removal of the cut removable segment from the support pillar.

[0028] The retained support portion may straddle the space left in the support pillar after the cut removable segment has been moved out of the support pillar. There is also provided for the support portion to extend across a side region of the space left in the support pillar after the cut removable segment has been removed.

[0029] There is provided for the removal of the cut removable segment from the support pillar to include the steps of:

[0030] urging the cut removable section out of the support pillar;

[0031] sequentially cutting the cut removable segment into distinct sections as said cut removable segment is being urged out of the support pillar;

[0032] transporting the cut sections away from the support pillar.

[0033] Still further, there is provided for the removal of the cut removable segment from the support pillar to include the steps of:

[0034] urging the cut removable section out of the support pillar in a first direction;

[0035] sequentially cutting the cut removable segment into distinct sections from a first end region of the cut removable segment, as said cut removable segment is being urged out of the support pillar in the first direction;

[0036] urging the cut removable section out of the support pillar in a second direction;

[0037] sequentially cutting the cut removable segment into distinct sections from a second end region of the cut removable segment, as said cut removable segment is being urged out of the support pillar in the second direction;

[0038] leaving, in the support pillar, a section of the cut removable segment for supporting the support pillar and hanging wall.

[0039] There is further provided for a filler material to be introduced in a space left behind the cut removable segment as said cut removable segment is being urged out of the support pillar. It is envisaged that the filler material may reinforce the structural integrity of the support pillar.

[0040] There is provided for the cut removable segment to take a wedge-like form, the wedge-like form of the cut removable segment serving to ease the process of urging the cut removable segment out of the support pillar.

[0041] According to a second aspect of the present invention, there is provided for the use of the mining method according to the first aspect of the present invention in a newly developed underground mine, the underground mine including a room having a hanging wall which is supported by elongate support pillars.

[0042] According to a third aspect of the present invention, there is provided for the use of the mining method according to the first aspect of the present invention and as substantially described and defined herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will now further be described, by way of example only, with reference to the accompanying drawings wherein:

[0044] FIG. 1 is a plan view of a typical bord and pillar underground mine;

[0045] FIG. 2 is perspective view showing the mining method according to a first aspect of the present invention, wherein a first horizontal cut is being made in the support pillar;

[0046] FIG. 3 is a perspective view showing the mining method shown FIG. 2, wherein a first horizontal cut has been made and a second horizontal cut is being made in the support pillar;

[0047] FIG. 4 is a perspective view showing the mining method shown FIG. 3, wherein a first vertical cut is being made in the support pillar;

[0048] FIG. 5 is a perspective view of the mining method shown in FIG. 4, wherein a second vertical cut is being made in the support pillar;

[0049] FIG. 6 is a perspective view of the mining method shown in FIG. 5, wherein the cut removal segment has been cut into smaller segments;

[0050] FIG. 7 is a side view of the mining method of the invention, wherein a cut removable segment is pushed out of the support pillar in a first direction;

[0051] FIG. 8 is a side view of the mining method shown in FIG. 7, wherein the cut removable segment is being cut into sections as said cut removable segment is pushed out of the support pillar in a first direction;

[0052] FIG. 9 is a side view of the mining method shown in FIG. 8, wherein the cut removable segment has been pushed out of the support pillar and cut into sections;

[0053] FIG. 10 is a side view of the mining method shown in FIG. 8, wherein the cut removable segment is pushed out of the support pillar in a second direction opposite the first direction;

[0054] FIG. 11 is a side view of the mining method shown in FIG. 10, wherein the cut removable segment is being cut into sections as said cut removable segment is pushed out of the support pillar in the second direction;

[0055] FIG. 12 is a side view of the mining method shown in FIG. 11, wherein a section of the cut removable segment is left in the support pillar;

[0056] FIG. 13 is a side view of the mining method shown in FIG. 12, wherein the section left in the support pillar is pushed towards the centre of the support pillar;

[0057] FIG. 14 is a side view of the mining method shown in FIGS. 2 to 5, wherein the cut removable segment is pulled out of the support pillar;

[0058] FIG. 15 is a perspective view showing the cut removable section taking a wedge-like form;

[0059] FIG. 16 is a front view of different end profiles which the cut removable segment may take; and

[0060] FIG. 17 is a plan view of a newly developed bord and pillar underground mine, the outlay of the pillars having been planned to utilise the mining method shown in FIGS. 2 to 16.

DETAILED DESCRIPTION OF THE INVENTION

[0061] With reference to the drawings, in which like numerals refer to like features, FIG. 1 shows a plan view of a typical bord and pillar underground mine where a panel (10) of an ore bearing reef has been mined in a direction indicated by arrow A. The panel (10) has now reached the end (12) of the minable reef and support pillars (14) containing the same ore that was mined during the mining of the panel (10) are left in place to support the hanging wall (not shown).

[0062] FIGS. 2 to 8 shows a support pillar mining method according to a first aspect of the present invention.

[0063] As shown in FIG. 2, holes (16) and (18) are drilled in the support pillar (14) from a first face (20) of the support pillar (14) to a second face (22) of the support pillar (14). A wire (24) of a diamond wire saw (26) is threaded through the holes (16) and (18).

[0064] FIG. 3 shows a first horizontal cut (28) having been cut between the holes (16) and (18) into the support pillar (14), thereby forming a bottom face (30) of a cut removable segment (not shown in FIG. 3, as the cut removable segment is still being formed).

[0065] Most advantageously, spacers (not shown) and/or a friction reducing means (not shown) can be introduced into the space left by the first horizontal cut (28) (the space between the bottom face (30) of the cut removable segment (not shown in FIG. 3) and the support pillar (14)). The spacers (not shown) will serve as load bearing members after a second horizontal cut (not shown in FIG. 3) has been made in the support pillar (14); the weight of the cut removable segment (not shown in FIG. 3) will bear down on the spacers (not shown). The friction reducing means (not shown) may take the form of a lubricant and/or spheres and/or rods. The spheres (not shown) and/or rods (not shown) may be manufactured from a metal, a metal alloy, a composite material or ceramics. The spheres (not shown) and/or rods (not shown) may serve as both the spacers (not shown) and friction reducing means (not shown).

[0066] As shown in FIG. 3, new holes (32) and (34) are drilled in the support pillar (14) from the first face (20) of the support pillar (14) to a second face (22) of the support pillar (14). The wire (24) of the diamond wire saw (26) is threaded through the holes (32) and (34) to make a second horizontal cut (not shown in FIG. 3).

[0067] It will be appreciated that all four holes (16), (18), (32) and (34) could be drilled through the support pillar (14), prior to threading the wire (24) of the diamond wire saw (26) through any one of these holes (16), (18), (32) and (34).

[0068] FIG. 4 shows a second horizontal cut (36) having been cut between the holes (32) (34) into the support pillar (14), thereby forming a top face (38) of a cut removable segment (not shown in FIG. 4, as the cut removable segment is still being formed).

[0069] FIG. 5 shows the wire (24) of the diamond wire saw (26) having been threaded through holes (16) and (32) to cut a first vertical cut between said holes (16) and (32) to form a first side face (40) of the cut removable segment (not shown in FIG. 5, as the cut removable segment is still being formed). A second side face of the cut removable segment will be formed by threading the wire (24) of the diamond wire saw (26) through holes (34) and (18) and cutting a vertical cut between holes (34) and (18). Furthermore, as shown in FIG. 5, the wire (24) of the diamond wire saw (26) can be moved to a position adjacent to the first vertical cut between holes (16) and (32), so as to cut a second vertical cut (33) between the bottom face (30) and top face (38) of the cut removable segment (not shown in FIG. 5).

[0070] FIG. 6 shows the cut removable segment (42) having been cut into the support pillar (14), with the cut removable segment (42) having been further cut, in a longitudinal direction, into smaller segments (42a) (42b) (42c) (42d) and (42e). It will be appreciated that the cut removable segment (42) may be cut into any number of smaller segments. As shown in FIG. 6, a support portion (44) is left in the support pillar (14) with the support portion (44) straddling the cut removable segment (42).

[0071] FIG. 7 shows the cut removable section (42) being urged out of the support pillar (14) in a direction indicated by arrow C. In this instance, the cut removable segment (42) is pushed out of the support pillar (14) by means of a push mechanism (46). The push mechanism (46) may take the form of a hydraulic ram.

[0072] It will be appreciated that the push mechanism (46) may be mounted on any one of:

[0073] the support pillar (14) which is being minded;

[0074] a support pillar (14) adjacent to the support pillar (14) which is being mined; and

[0075] a ground surface adjacent to the support pillar (14) which is being mined.

[0076] FIG. 8 shows the cut removable segment (42) being cut into distinct sections (48) as said cut removable section (42) is being pushed out of the support pillar in a direction indicated by arrow C. These distinct sections (48) can then be transported away from the support pillar (14). For example, the distinct sections (48) can then be transported to the surface of the underground mine. It will be appreciated that the cut removable segment (42) may be pushed completely out of the support pillar (14) and sequentially cut into sections (48), leaving a space (50) in the support pillar (14); as shown in FIG. 9. A filler material (not shown) may be introduced in the space (50) to reinforce the structural integrity of the support pillar (14) after the cut removable segment (42) has been urged out of the support pillar (14).

[0077] FIGS. 10 to 13 shows an embodiment of the method, whereby the cut removable segment (42) is partially urged out of the support pillar (14) in a first direction indicated by arrow C, sequentially cut into sections (48) on a first side of the support pillar (14), then, partially urged out of the support pillar (14) in a second direction indicated by arrow D, sequentially cut into sections (48) on a second side of the support pillar (14) and where a section (42a) is left in a space (50) which formed in the support pillar (14) due to the cut removable segment (42) having been partially urged out of the support pillar (14), the section (42a) serving to support the support pillar (14) and hanging wall (not shown). As shown in FIGS. 12 and 13, the section (42a) may be urged towards the centre of the support pillar (14) so that the section (42a) may support the support pillar (14) and hanging wall (not shown).

[0078] As shown in FIG. 14, the cut removable segment (42) may be pulled out of the support pillar (14) by a pull mechanism (52), as opposed to pushed out of the support pillar (14). The pull mechanism (52) may take the form of a winch system.

[0079] It will be appreciated that the pull mechanism (52) may be mounted on any one of:

[0080] the support pillar (14) which is being minded;

[0081] a support pillar (14) adjacent to the support pillar (14) which is being mined; and

[0082] a ground surface adjacent to the support pillar (14) which is being mined.

[0083] FIG. 15 shows the cut removable segment (42) taking a wedge-like form. Here, the holes (16), (18), (32) and (34) were drilled in a sloping manner, from one face of the support pillar (14) to an opposing face of the support pillar (14). The wedge-like form will ease the process of urging the cut removable segment (42) out of the support pillar (14) in a direction indicated by arrow C.

[0084] As shown in FIG. 16, an end profile (54) of the cut removable segment (42) may take various forms, including a triangle, a pentagon, a rectangle, and a combination of these.

[0085] FIG. 17 shows a top view of the layout of a newly developed bord and pillar underground mine, wherein the layout is made possible by the use of the mining method according to the first aspect of the present invention. As shown in FIG. 17, elongate pillars (56) may be left in place, as opposed to the traditional smaller pillars (14), to support the hanging wall (not shown). The mining method according to the first aspect of the present invention may be utilised to selectively remove a segment (not shown) of the elongate support pillars (56), whilst retaining, in the elongate support pillar (56), a support portion extending from the foot wall (not shown) to the hanging wall (not shown). The aforementioned layout and accompanying mining method will result in reduced development costs as less material has to be removed during the development of the panel (10).

[0086] It will be appreciated that the cuts between the holes (16) and (18), (32) and (34), (16) and (32) and (18) and (34) will be made as the wire (24) of the diamond wire saw (26) is driven longitudinally and pushed or pulled against the mining face (i.e. that portion of the support pillar (14) which will form a face of the cut removable segment (42)). A cut between the different holes can be made by driving the wire (24) of the diamond wire saw (26) along a longitudinally path defined by a series of pulleys, and wherein the position of one of the pulleys is changed, as the wire (24) is being driven, in a manner to cause the wire (24) to form the cut in the support pillar (14).

[0087] By employing the above-described support pillar mining method, precise and custom cuts can be made in a support pillar to form an identified removable segment which contain ore. The identified removable segment may then be removed from the support pillar whilst material surrounding the removable segment is left in place, in the support pillar, to continue to support the support pillar and hanging wall.

[0088] It will be appreciated by those skilled in the art that the above support pillar mining method will produce much less waste material (which needs to be processed in a metallurgical process together with the ore) than a support pillar mining method where the entire support pillar is minded or where segments of fixed shape and dimension are extracted from support pillars. The support pillar mining method described herein allows a user thereof to modify the shape and dimension of a removable segment to ensure that the maximum amount of ore containing material is cut out off or extracted from the support pillar, whilst leaving the maximum amount of waste material in the support pillar to support the hanging wall.

[0089] Importantly, by employing the above-described support pillar mining method, security or safety factor of the pillars (the ratio of pillar strength/pillar load) will remain virtually unchanged, or, within an acceptable range, after the cut removable segment has been removed from the support pillar. It will be appreciated that the safety factor of a mine is often set by legislation, regulations or safety rules.

[0090] As an example, the cut removable segment may be shaped and dimensioned to ensure that the safety factor is not less than 1.6. Here, the safety factor is calculated as follows:

Safety factor = strenght load ##EQU00001## Strenght = 7176 W 0.46 h 0.66 ##EQU00001.2## Load = 24.88 H .times. ( W + B ) 2 W ##EQU00001.3## H = depth to the floor of the coal seam from surface ##EQU00001.4## B = room width ##EQU00001.5## W = pillar width ##EQU00001.6## h = height of the workings ##EQU00001.7##

[0091] It will be appreciated by those skilled in the art that this invention is not limited to the precise details as described herein and that many variations are possible without departing from the scope of the invention.

[0092] It will further be appreciated that the foregoing examples have been provided merely for the purposes of explanation and is in no way to be construed as limiting of the present invention. While the present invention has been described with reference to exemplary embodiments only, it is understood that the words which have been used herein are words of description and illustration, rather than words of limitation. The present invention is also not intended to be limited to the particulars disclosed herein. Rather, the present invention extends to all functionally equivalent methods and uses, such as are within the scope of the invention.

Claims

1. A support pillar mining method, the method including the steps of: cutting, in the support pillar, a removable segment with a saw; retaining, in the support pillar, a support portion extending from a foot wall to a hanging wall; and removing, from the support pillar, the cut removable segment wherein the support portion extending from the foot wall to the hanging wall supports the hanging wall after the cut removable segment has been removed from the support pillar.

2. The method of claim 1, wherein the saw is a diamond wire saw.

3. The method of claim 2, wherein the method, prior to the cutting step, includes the additional steps of: drilling, in the support pillar, a hole from a first face of the support pillar to a second face of the support pillar; and threading, through the drilled hole, the wire saw which is to cut the removable segment.

4. The method of claim 1, wherein the cut removable segment extends from a first face of the support pillar to a second face of the support pillar.

5. The method of claim 4, wherein the first and second faces of the support pillar are opposing faces.

6. The method of claim 1, wherein an end profile of the cut removable segment takes the form of any one of a circle, an oval, a square, a rectangular, a triangle, a rhombus, a trapezoid, an arch and a hyperbole.

7. The method of claim 1, wherein the removable segment is cut in the support pillar by: making a first horizontal cut in the support pillar to form a bottom face of the removable section; making a second horizontal cut in the support pillar to form a top face of the removable section; and making a vertical cut in the support pillar to form a side face of the removable section.

8. The method of claim 7, wherein the method, prior to making a second horizontal cut in the support pillar, includes the additional step of introducing a spacer in a space left by the first horizontal cut, the spacer being introduced into said space to serve as a load bearing member once the cut removable segment weighs down on the spacer.

9. The method of claim 7, wherein the method includes the additional step of introducing a friction reducing means in a space left by the first horizontal cut, the friction reducing means being introduced into said space to facilitate the eventual removal of the cut removable segment from the support pillar.

10. The method of claim 1, wherein the retained support portion straddles a space left in the support pillar after the cut removable segment has been moved out of the support pillar.

11. The method of claim 1, wherein the retained support portion extends across a side region of a space left in the support pillar after the cut removable segment has been removed.

12. The method of claim 1, wherein the removal of the cut removable segment from the support pillar includes the steps of: urging the cut removable section out of the support pillar; sequentially cutting the cut removable segment into distinct sections as said cut removable segment is being urged out of the support pillar; and transporting the cut sections away from the support pillar.

13. The method of claim 1, wherein the removal of the cut removable segment from the support pillar includes the steps of: urging the cut removable section out of the support pillar in a first direction; sequentially cutting the cut removable segment into distinct sections from a first end region of the cut removable segment, as said cut removable segment is being urged out of the support pillar in the first direction; urging the cut removable section out of the support pillar in a second direction; sequentially cutting the cut removable segment into distinct sections from a second end region of the cut removable segment, as said cut removable segment is being urged out of the support pillar in the second direction; leaving, in the support pillar, a section of the cut removable segment for supporting the support pillar and hanging wall.

14. The method of claim 1, wherein a filler material is introduced in a space left behind the cut removable segment as said cut removable segment is being urged out of the support pillar.

15. The method of claim 14, wherein the introduced filler material reinforces the structural integrity of the support pillar.

16. The method of claim 1, wherein the cut removable segment takes a wedge-like form, the wedge-like form of the cut removable segment serving to ease the process of urging the cut removable segment out of the support pillar.

17. Use of the method of claim 1 in a newly developed underground mine, the underground mine including a room having a hanging wall which is supported by elongate support pillars.