WO2015056201A1

WO2015056201A1 - Pillar extraction mining method

Info

Publication number: WO2015056201A1
Application number: PCT/IB2014/065357
Authority: WO
Inventors: Pieter Du Toit
Original assignee: Individual
Current assignee: Individual
Priority date: 2013-10-17
Filing date: 2014-10-16
Publication date: 2015-04-23
Anticipated expiration: 2016-04-17

Abstract

Disclosed is a method of mining or extracting a support pillar from an underground room and pillar mining operation which includes forming (by eg forming top and bottom wedge shaped cuts) at least one removable segment in a pillar (7) and moving (eg pulling) the segment substantially intact from its original location (10A) to a mining position (10C) distal from its original location, operatively from where the segment may be mined. Also disclosed and claimed are sequences of pillar removal to control caving during pillar recovery.

Description

PILLAR EXTRACTION MINING METHOD

FIELD OF THE INVENTION

This invention relates to a method of mining and more particularly a pillar extraction mining method for underground mines that utilise bord and pillar or room and pillar mining methods.

BACKGROUND TO THE INVENTION

Many underground mining operations utilise so-called bord and pillar or room and pillar mining methods. These involve developing, i.e. mining, a panel and leaving a plurality of rows of spaced apart virgin material in place to support the panel while it is still developed. When the panel has been fully developed, i.e. the reef has been mined to its end, a huge room is left consisting of a roof (hanging wall) supported above a floor (foot wall) by the pillars of virgin material.

These pillars contain the same reef that was mined originally and thus represent value. Since the panel has been developed fully, all the necessary services such as water, electricity, and ore removal services are already in place. These pillars are therefore often mined in a retreating manner, in which the direction of mining is turned around. The pillars are now recovered from the end of the panel back to the start. In most cases it is accepted that the roof will collapse when the pillar supports are mined.

In some older type workings there may not be services and in these, dangerous conditions may have developed due to water build up and, especially in coal mines, underground fires because of the presence of oxygen and oxidation of coal pillars. Still, even in these workings the ore remaining in the pillars represent value and there is an incentive to recover as much value as possible from it. The prevailing conditions in these older workings increase the risk to property loss or damage and injury or death to mine workers with recovery of pillar supports significantly, yet the economic benefits are still often deemed to outweigh these increased risks.

Typically these pillars are mined by having a continuous miner ("CM") machine cut through them. There have been numerous instances of burial of CM machines, loss of life, injuries and damage to other equipment. The methods deployed up to 1996 at the Highveld B Colliery in South Africa resulted in unpredictable roof behaviour with an average of one CM machine buried for every three panels mined. In 1996 twelve CM machines were buried at Highveld B Colliery and its neighbouring colliery (refer "An integrated risk management approach for underground coal pillar extraction in South Africa"; LIND, G., The Journal of The South African Institute of Mining and Metallurgy, February 2005, pages 137 to 147). Generally, when a CM machine is buried there is accompanying loss of life or injury to mine workers.

Improved methods were developed which included the so-called NEVID extraction method. This involved the cutting of slices from a pillar instead of mining the entire pillar or as much thereof until it collapses. The introduction of the NEVID method reduced the risks, but since its introduction there have still been occurrences of CM machines being buried, occurrences of the goaf (that part of a mine from which the mineral has been partially or wholly removed, and in which pillars are removed to be replaced by support props) overrunning the working area and occurrences of local roof falls.

There are several other known methods of mining for mining such pillars. These methods all comprise extracting ore from the pillars with the pillars located in their original positions.

As mentioned above for the NEVID method, high safety risks are associated with these conventional methods. Pillar extraction mining statistically contributes to a significant proportion of safety incidents, but is only responsible for a small proportion of mining product produced. The relative risk of conventional pillar mining methods is thus greater than with other types of mining.

As with the steps taken at the Highveld B Colliery the high safety risks have resulted in measures being taken to mitigate the risks. These measures include limiting pillar extraction to at most partial pillar extraction, creating what is known as a checker bord pattern, that is, taking approximately 80 % of every second pillar, and employing methods known to persons skilled in the art, including Split and Lift, Split and Quarter, and Duncan method, and also the mentioned NEVID method.

The result of the above measures is that even with the safest conventional pillar extraction methods yield rates are low, and risks remain high. This has led industry to develop alternative techniques which focus on installing additional supports adjacent the pillars to take the load from the roof once the pillar has been mined out, and to attempt to control the closure that results from mining the pillar from its location. These methods introduce their complications, such as having to provide slurry and cement for pumping into fluid tillable percolating type supports. These supports are not conventional for this type of mining, especially in coal mines, and using such supports are also not without complications.

There is a need for a pillar extraction method that does not require the installation of additional supports using slurry and cement, which decreases the inherent risk in pillar extraction and increases the yield rates thereof.

OBJECT OF THE INVENTION

It is an objective of the invention to provide a method of pillar extraction mining which at least partly overcomes the abovementioned problems.

SUMMARY OF THE INVENTION

In accordance with this invention there is provided a method of mining a support pillar from an underground mining operation which includes forming at least one removable segment in such 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.

There is further provided for the pillar to comprise a first pillar and for the segment to be moved to a mining position adjacent a second pillar proximate the first pillar, and preferably for the mining position to be in a first road between a first pillar row within which the first pillar is located and a second pillar row adjacent and preferably substantially parallel with the first pillar row, and still further preferably for the method to include repeating the steps of forming and moving a segment for mining thereof for each pillar in the first pillar row, after which the steps of forming and moving a segment for mining thereof for each pillar in the second pillar row is performed, starting with either the first or the last pillar in the second pillar row, and thereafter successively for each further pillar row in the underground mining operation that is to be mined.

There is still further provided for the mining position to be located between a second pillar in the first pillar row and a first pillar in the second pillar row, and further preferably for the mining position to be located in the intersection of the first road and a road transverse to the first road extending between the first and second pillars of the first pillar row and the and the first and second pillars of the second pillar row. According to a further feature of the invention there is provided for the first pillar segment to be moved towards a mining position at least partly between the first and second pillars in the second pillar row, and repeating this for each subsequent pillar segment in the row which contains the pillar from which each such segment is removed, apart from the last pillar segment which is moved into the mining position that the second to last pillar segment was moved into.

There is still further provided for the method to include forming a removable segment in the second pillar of the first pillar row after the first pillar segment is formed but before the first pillar segment is moved to its mining position.

According to a further feature of the invention the method includes removing a section from a cut pillar to provide space for a segment to be moved from a segmented pillar from which a removable segment is to be formed, the segmented pillar and cut pillar being located in adjoining pillar rows and having matching positions in their respective pillar rows, and moving the removable segment from the segmented pillar into the space between the cut pillar and a pillar adjacent it in the cut pillar row, with the section that is removed from the cut pillar being shaped and sized to ensure the gap between the cut pillar and its adjacent pillar is large enough for the removable segment to be moved into.

There is also provided for the method to include the step of installing an optional temporary support during the process of forming the removable segment in a pillar, preferably by means of a remote controlled machine.

The invention provides for the process of forming a segment in a pillar to include making two cuts across a substantially vertical axis of the pillar, and for the cuts to be angled to form a wedge shaped segment with the foot of the wedge facing the intended mining position of the segment.

There is further provided for the segment preferably to be formed by means of a cutting process performed by a cutting machine using any one of a diamond wire sling, a saw or a band; alternatively any one of high pressure water cutting, laser or plasma technology cutting machine to be used to form the segment; further alternatively any suitable cutting means for the type and structure of the pillar. There is further provided for the segment to be moved by pulling a sling or a band extended around the segment or through an aperture formed in the segment, alternatively by locating a clamp at least partly around the segment and pulling it to its mining position.

There is still further provided for a segment, being larger than its mining position, to be repositioned after its formation in the pillar.

There is also provided for the method to include sizing of the segment or mining the segment by means of a continuous mining machine, from or in its mining position, and to load the segment or material mined from it for further transport.

The invention also provides for the method to include the step of removing loose material from a pillar before a segment is formed; and the step of drilling extraction anchor holes in the pillar from which the segment is formed and in an adjacent pillar, complimentary to the intended direction of movement of the segment to its mining position.

There is still further provided for the method to include drilling an extraction hole diagonally through a second pillar of a second pillar row for moving a first pillar in a first pillar row to its mining position, and further to include extending through the extraction hole a sling or a band for pulling the first pillar segment , operatively enabling the moving of the first pillar segment to be performed with the second pillar of the second pillar row between pulling means used to move the segment and the first pillar segment.

These and other features of the invention are described in more detail below. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the invention is described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a plan view of a bord and pillar road section showing the movement of a pillar segment from its original, uncut position, to its mining position;

Figure 2 is a side view of a pillar cut into a wedge shape segment and movement of the segment into its mining area adjacent a second pillar; Figure 3 is a plan view of extraction of the panel of Figure 1 , with the first to third pillars already cut and moved, and the fourth pillar being moved; and

Figure 4 is a schematic diagram of one cycle of one embodiment of the pillar extraction mining method.

DETAILED DESCRIPTION OF THE INVENTION

A preferred embodiment of the invention relates to the mining of a pillar from a bord and pillar coal mine.

Figure 1 shows a plan view of a panel (1 ) of a coal seam that has already been mined according to the bord and pillar method. This panel (1 ) has now reached the end (2) of the minable seam. The panel is evaluated to determine the sequence and direction of extraction using the method according to the invention. Various factors are relevant to this determination, including considerations of roof conditions, geology, ventilation, adjacent caved areas, and principle stress directions.

As shown in Figure 1 the goaf has already collapsed (3) onto the first two rows of pillar supports (4, 5). The effective first row that can now be mined using the method according to the invention is the third row ("A") from the end (2) of the seam. If these first two rows (4, 5) had not collapsed, the extraction would commence with the first row (4) before the end (2) of the seam.

In the present description, the third row ("A") from end (2) of the seam becomes the first pillar row for extraction, and so forth.

Loose material is barred from the pillars (6). Thereafter the remaining pillar slabbings are cleaned and any material on the floor is removed, typically with a load haul dumper.

Extraction anchor holes are drilled in the first pillar (7) in the first pillar row ("A"). Holes are also drilled in the second pillar (8) of the second pillar row ("B") in line with the direction (9) of the intended movement of a segment from the first pillar (7).

With the optimal pillar extraction sequence and direction having been determined, the first pillar (7) in the panel is cut, forming a pillar segment (10). The pillar (7) is cut twice (1 1 , 12). The first cut (1 1 ) is proximate the top (13) of the pillar (7) and the second cut (12) is proximate the bottom (14) of the pillar (7).

Each cut (1 1 , 12) is made through a substantially vertical axis of the pillar (7) and at an angle offset from the horizontal to form a wedge shaped segment (10). The wedge is shaped to have its foot (15), i.e. its broadest part, facing the extraction direction and its apex (16) away from it.

A person skilled in the art will appreciate that numerous methods may be used to form the pillar into the segment. Cutting methods include but are not limited to using a machine (23) that utilises a diamond wire sling, saws or bands, as shown in Figure 3. Alternatively high pressure water cutting, laser or plasma cutting technology can also be used depending on the ore type.

As shown in Figure 3, in certain circumstances, roof conditions may necessitate temporary roof support during cutting. Movable breaker lines (not shown) provided by remote controlled machines have the capacity to provide support and assist with controlling caving.

Once the wedge shaped segment (10) of the first pillar (7) is cut, the same process is repeated on the pillar earmarked as second (17) in the planned sequence for extraction. The second pillar (17) will be held in position with a support mechanism.

Thereafter the first pillar wedge shaped segment (10) is dislodged. The segment (10) will slide out when force (9) is applied to it. The force required will be relatively low as the load (18) on the wedge created by the overlying strata (19) will assist in this action.

The segment (10) will be moved into an intersection area (21 ) adjacent the remains of the first pillar (7). The segment (10) is thus moved, as shown in Figures 1 and 2, from its initial position (10A) where it still forms part of the first pillar (7), through a position (10B) where it is almost clear of the remains of the first pillar (7), to a position (10C) where it is located in the intersection (21 ).

The intersection area (21 ) is surrounded by the remains of the first pillar (7) and three other pillars (8, 17, and 22), namely the second pillar (17) in the first pillar row ("A") and the first (22) and second (8) pillars in the second pillar row ("B"). Put otherwise, it is positioned equidistant in relation to the four pillar points (7, 8, 17, and 22). This area (21 ) is known as a safe area. This is because this intersection (21 ) was most likely supported during the bord and pillar operation and may not need any additional support to mine the moved pillar (7).

Notwithstanding the above, attention will be given to any slips, joints or discontinuities that may exist in the roof (19). If any of these conditions are present, an assessment will be conducted to determine whether additional support, such as roof bolts, should be installed alternatively special measures will be taken to ensure the operation is safe.

Two rows of breaker line support may be required where roof conditions are such there is a risk of the caving that may overrun the still safe areas.

Movement of the segment (10) can be effected with numerous methods. One option is movement using the sling or band method. Here the sling or band is wrapped around the first pillar (7) then pulled through an opposite pillar (8) or around it (8), in the direction of the pull (9). It is also possible to extend the sling or band through an aperture formed through the pillar segment to move it.

Alternatively a specially designed grab and pull machine will clamp around the corners of the segment (10) and pull that towards the mining position (21 ).

A skilled person will appreciated that the invention is not limited to any particular method of movement exemplified above.

In some instances where the pillar is larger than the intersection (21 ) dimensions, the segment (10) may have to be repositioned after the first cuts to remain in the safe area of the intersection (21 ). It is also possible that the segment (10) may be split and quartered before moving it in instances where the pillar (7) or the pillar segment (10) is too large for the intersection (21 ).

A continuous mining machine such as a standard narrow drum continuous miner or rock breaker will then be used to size or mine the wedge and load it for further conveyance. It will mine a drum width on either side of the pillar and if material remains, it will be pulled closer again and cut until completed.

In some instances the pillar segment that is moved may be larger than the gap between adjoining pillars. Instead of, or in addition to reducing the size and shape of the pillar segment to complement the gap size, a pillar adjacent the gap may be cut before the move commences. The pillar right behind the pillar that is to be moved may be cut in this way. It then increases the gap size to accept the pillar segment from the pillar that is being moved. This also has the advantage that when it becomes the cut pillar's turn to be moved it has already been sized, and if the sizing has been planned and executed correctly it will then fit the gap behind it in the next row. The pillar behind it, i.e. the pillar in row three, may then not have to be cut to make place for it (the pillar from row two). The next pillar, i.e. the pillar in row three, may then again be oversized for the gap in pillar row and the pillar behind it in row four may have to be cut again.

Another advantage of first cutting a pillar behind the pillar that is intended for movement in a specific moving cycle is that if the goaf falls that pillar is cut already, and there will then not be problems in pulling the pillars from the second row. This also applies to pillars in subsequent rows.

Alternatively, for each pillar that is being moved the pillar behind it may be cut to a predetermined extent, which will ensure that each pillar that is being moved has a gap diagonally behind it in the next pillar row to be moved into.

Figure 4 shows a schematic representation of a basic embodiment of the invention. It commences with cleaning, then pillar 1 (P1 ) is drilled and cut, then pillar 2 (P2) is drilled and cut, then pillar 1 is moved, and finally pillar 1 is mined.

By making use of the method of the invention it is possible to mine support pillars from an underground mine by moving a substantial segment thereof to a safe location. The wedge shape of the segment and the graphitic nature of coal ensure that with pulling the cut segment is pushed out by the roof above it. This allows the roof to close in a controlled manner, with the equipment and personnel safely behind another support pillar. The segment is drawn into a still supported area from where it can safely be mined.

The recovery from the segment is expected to be relatively high, with losses only from barring of the pillar, the cut lines into it, and some breakage during movement of the segment.

Use of the invention holds other benefits in addition to those already mentioned, including improved safety by moving the pillar into a safe place, economic benefits by increasing the reserve base, and low mining costs. It also holds environmental advantages by safely collapsing the roof, removing maximum coal to reduce acid forming water and burning of underground coal. The requirement to barricade surface areas because of unsafe surface conditions which may lead to an unexpected collapse of the surface similar is also reduced.

It will be appreciated that the invention may apply to mining of a single pillar and need not require a sequence of pillars. It will be appreciated that the method may also be applied to mines other than coal mines, for example gold, chrome, and platinum mines, to name but some. The cutting equipment will be modified to achieve reliable cutting for such mines, and the prevailing conditions in each mine will be assessed before the extraction commences to determine the optimum cutting conditions, and the relevant forces required to move the pillar segment to its mining position.

Claims

1 . A method of mining a support pillar from an underground mining operation which includes forming at least one removable segment in such 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.

2. A method as claimed in claim 1 in which the pillar comprises a first pillar and the segment is moved to a mining position adjacent a second pillar proximate the first pillar.

3. A method as claimed in claim 2 in which the mining position is located in a first road between a first pillar row within which the first pillar is located and a second pillar row adjacent and substantially parallel with the first pillar row.

4. A method as claimed in any one of claims 1 to 3 which includes repeating the steps of forming and moving a segment for mining thereof for each pillar in the first pillar row, after which the steps of forming and moving a segment for mining thereof for each pillar in the second pillar row is performed, starting with either the first or the last pillar in the second pillar row, and thereafter successively for each further pillar row in the underground mining operation that is to be mined.

5. A method as claimed in claim 1 in which the mining position is located between a second pillar in the first pillar row and a first pillar in the second pillar row.

6. A method as claimed in claim 5 in which the mining position is located in the intersection of the first road and a road transverse to the first road extending between the first and second pillars of the first pillar row and the first and second pillars of the second pillar row.

7. A method as claimed in claim 1 in which the pillar comprises a first pillar in a first pillar row and the segment comprises a first pillar segment which is moved to a mining position at least partly between first and second pillars in a second pillar row adjacent and substantially parallel with the first pillar row, and repeating this for each subsequent pillar segment in the row which contains the pillar from which each such segment is removed, apart from the last pillar segment which is moved into the mining position that the second to last pillar segment was moved into.

8. A method as claimed in any one of claims 1 to 6 or 7 which includes the step of forming a removable segment in the second pillar of the first pillar row after the first pillar segment is formed but before the first pillar segment is moved to its mining position.

9. A method as claimed in any one of claims 1 to 8 which includes removing a section from a cut pillar to provide space for a segment to be moved from a segmented pillar from which a removable segment is to be formed, the segmented pillar and cut pillar being located in adjoining pillar rows and having matching positions in their respective pillar rows, and moving the removable segment from the segmented pillar into the space between the cut pillar and a pillar adjacent it in the cut pillar row, with the section that is removed from the cut pillar being shaped and sized to ensure the gap between the cut pillar and its adjacent pillar is large enough for the removable segment to be moved into..

10. A method as claimed in any one of claims 1 to 9 which includes the step of installing an optional temporary support during the process of forming the removable segment in a pillar, preferably by means of a remote controlled machine.

1 1 . A method as claimed in claim 10 in which the step of forming a segment in a pillar includes making two cuts across a substantially vertical axis of the pillar, with the cuts being angled to form a wedge shaped segment with the foot of the wedge facing the intended mining position of the segment.

12. A method as claimed in claim 1 1 in which the segment is formed by means of a cutting process performed by a cutting machine using any one of a diamond wire sling, a saw or a band; alternatively any one of a high pressure water cutting, laser or plasma technology cutting machine, further alternatively any suitable cutting means for the type and structure of the pillar.

13. A method as claimed in claim 12 in which the segment is moved by pulling a sling or a band extended around the segment or through an aperture formed in the segment, alternatively by locating a clamp at least partly around the segment and pulling it to its mining position.

14. A method as claimed in any one of claims 1 to 13 which includes a segment, being larger than its mining position, to be repositioned after its formation thereof in the pillar.

15. A method as claimed in any one of claims 1 to 14 which includes the step of sizing of the segment or mining the segment by means of a continuous mining machine, from or in its mining position, and to load the segment or material mined from it for further transport.

16. A method as claimed in any one of claims 1 to 15 which includes the step of removing loose material from a pillar before a segment is formed; and the step of drilling anchor holes for extraction in the pillar from which the segment is formed and in an adjacent pillar, complimentary to the intended direction of movement of the segment to its mining position.

17. A method as claimed in claim 3 which includes drilling an extraction hole diagonally through a second pillar of a second pillar row for moving a first pillar in a first pillar row to its mining position.

18. A method as claimed in claim 17 which includes extending through the extraction hole a sling or a band for pulling the first pillar segment, operatively enabling the moving of the first pillar segment to be performed with the second pillar of the second pillar row between pulling means used to move the segment and the first pillar segment.