AU2004202735B2 - An airflow barrier - Google Patents

Description

AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): MINOVA AUSTRALIA PTY LTD Invention Title: AN AIRFLOW BARRIER The following statement is a full description of this invention, including the best method of performing it known to me/us: - 2 AN AIRFLOW BARRIER Field of the Invention The present invention broadly relates to an air flow 5 barrier suitable for directing airflow in an underground mine or tunnel and to methods of forming such airflow barriers. Background of the Invention 10 Mine ventilation barriers commonly known as "stoppings" are erected to direct air within an underground mine to provide fresh air for a safe working environment and to direct contaminated air (noxious gases, dust and moisture) and heat away from personnel and 15 machinery. Such stoppings have to be able to withstand differences in air pressure caused by separating airflow paths within the mine with minimal and preferably no leakage. Because of the presence of gases in underground 20 coal mines and coal dust generated by coal winning, it is necessary for stoppings to be fire resistant and often to be explosion resistant. Stoppings typically are made from a range of materials such as brick, steel, wood, plaster, brattice 25 cloth, hessian and many commonly available building construction materials. Because of the nature of the strata and disturbance of the stresses within the rock mass, mine roadways are often subject to movement over a period of time. Despite ground support systems that are 30 usually in place, stoppings are often subjected to convergence during their life. Most stoppings are composed of a relatively rigid material such as brick or cement-based products. Once 53387 - 3 excessive ground movement takes place, the stopping may be damaged and may leak. Repairs of such damaged stoppings are often difficult. To overcome this problem, stoppings have recently 5 been made from cloth materials or other suitable materials attached to a suitable backing frame. The requirement for cloth materials in underground coal mines is that they must be fire resistant and anti-static according to a standard test procedure. In general, however, known 10 stoppings that have cloth sheet have a limitation due to the system of fixing in the roadway to withstand the pressure of explosions. Such cloth is usually fitted to the mine roadway using bolt anchors that pass through holes in the cloth and are glued into a previously drilled 15 hole using a suitable resin or cement-based grout. Large strains tend to concentrate in the cloth in the vicinity of each breach of the cloth where the bolts pass through. This may result in tearing of the cloth as the pressure on the stopping is increased and limits the ability of the 20 stopping to withstand higher pressures. Summary of the Invention In a first aspect, the present invention provides an 25 airflow barrier suitable for directing contaminated air in an underground mine or tunnel away from personnel or fresh air to the personnel, the airflow barrier comprising a sheet of flexible material and a support structure including a frame for supporting at least a portion of the 30 sheet, the frame incorporating a frame section having an elongated channel and retaining means for securing at least a portion of the perimeter edge margin of the sheet within the channel so that at least some of possible tear forces and/or sheet strain forces are distributed along 53387 -4 that portion. In contrast to prior art airflow barriers, possible tear and/or strain forces are counteracted by distributing those forces along at least a portion of the edge margin 5 of the sheet. Therefore, the likelihood that the sheet will tear is reduced and the airflow barrier may withstand larger overpressures and may be given an explosion rating. The retaining means and the channel may be arranged for securing more than half of the length of the perimeter 10 edge portion of the sheet. The frame may also extend around and support the entire edge margin of the sheet. In one embodiment, the frame is arranged to support the sheet at a plurality of portions of the perimeter edge of the sheet. For example, the portions may be portions in 15 which the flexible sheet is in use subjected to higher stress. The mine or tunnel usually comprises a floor and ceiling and opposing side walls, and in one form, the frame is used only along the ceiling and the floor, and 20 the remaining part of the support structure uses a more conventional fixing technique using anchor bolts along the side walls. The span length of the ceiling and floor is usually significantly longer than the side walls and as such there is a tendency to have high stress 25 concentrations on the sheet adjacent the ceiling and floor. In one form, the retaining means is in the form of an elongate member that locates within the channel of the frame. Preferably, in this arrangement, the channel is 30 shaped to incorporate a restricted opening that allows the elongate retaining member to be captured within the channel. In this arrangement, the portion of the edge margin is secured to the retaining member. This may be by 53387 - 5 directly bonding the portion of edge margin of the sheet to the elongate member or by folding over the edge margin to form a sleeve in which the elongate retaining member is positioned. 5 In one arrangement, the retaining means is in the form of a rigid elongate member and is secured to the edge portion of the flexible sheet prior to location within the channel of the framed portion. In the arrangement where the frame section is formed separate from the mine or 10 tunnel wall, the elongate member may be inserted from one end of the channel section prior to it being fixed to the mine wall so that the sheet projects through the open slit. In use, preferably the interior dimensions of the 15 channel and the exterior dimensions of the elongate member are chosen so that the elongate member fits loosely within the interior of the channel but is unable to be pulled through the channel opening. This has the particular advantage that the airflow barrier, when fitted across a 20 mine roadway, may allow for relatively large amounts of roadway convergence without the barrier losing strength or separating from the roadway barrier. In an alternative embodiment, the retaining means comprises a range of elements or a particulate material 25 such as sand that is positioned in the sleeves of the sheet and located within the channel section. In another form, the retaining means is in the form of fastening elements which are able to be inserted into the channel opening. In this arrangement, preferably the 30 edge portions of the flexible sheet are located within the channel and are secured in place by inserting the fastening elements in the channel which effectively wedges 53387 - 6 the edge margin of the sheet between the fastening elements and one side of the elongate channel. The fastening elements may be in the form of plugs, wedges or other suitably shaped elements. In one form, 5 the elements are disposed at spaced intervals along the channel. In another form, the fastening elements is in the form of an elongate strip which extends along a major portion, if not all, of the channel. An advantage of this later arrangement of the frame, 10 is that the channel may include parallel side walls as the arrangement does not require a constricted opening. Also, the portion of the edge margin can easily be inserted when the section of the frame incorporating the channel is in place. However, the strength of the connection is 15 somewhat less than the other form of frame, as the edge margins are more susceptible to being pulled out from the channel. In another alternative embodiment, the retaining means may not be positioned in sleeves of the sheet, but 20 may be arranged to clamp edge portions of the sheet so that possible tear forces and/or sheet strain forces are distributed along the portion of the retaining means. In one form, the section of the frame is formed from a hollow section, typically made from steel, but may be 25 manufactured from any metal material or functional equivalent material that is approved for use in an underground coal mine or underground metalliferous mine. The section may be extruded, cast, folded or otherwise formed. The sections are fixed to the mine or tunnel wall 30 typically by a mechanical fasteners or anchors. In one form, the frame section is formed from an elongate pipe that have a central passage that defines the 53387 channel and an open slit along its length that defines the opening of the channel. In another form, the frame sections are formed insitu in portions of the mine or tunnel. In this arrangement, 5 the frame section is formed by cutting the channel either directly into the mine or tunnel wall or alternatively, by applying a settable material to the wall (such as a cementitious material) and then cutting the necessary channel into the cast material. The advantage of this 10 latter arrangement is that it can provide a more regular surface in which to incorporate the channel. Also, it can simplify the cutting process in situations where the rock strata is particularly hard as it obviates the need to cut directly into the rock. 15 In this latter arrangement, preferably the retaining means is in the form of the fastening element as this allows the use of a simple channel section as it does not require a restricted opening of the channel to be formed. In one form, a frame is used around the entire 20 periphery of the flexible sheet. In one form, the top and bottom frames are formed from channel metal sections and rigid elongate retaining members and the side frames have the channel sections formed insitu and fastening elements are used as the retaining means. 25 It is to be appreciated that the airflow barrier need not be rectangular or square, but may have any other shape. Further, dependent on the shape of the sheet and dependent on the requirements, it will be appreciated that the support structure of the airflow barrier may comprise 30 any number of frames of different configurations and/or may incorporate other arrangements of fixing along sections of the sheet perimeter. The sheet may be composed of any suitable material 53387 -8 including geofabrics/ felt materials, woven synthetic fibres and other woven and non-woven fabric materials. Preferably, the sheet is not held taut within the support structure. This allows the flexible sheet to bow 5 under differential air pressure and during an explosion. The advantage of this arrangement is that it allows the sheets to contact an edge of the channel which distributes the loading along the sheet contacting the edge. Moreover, it ensures that on applying tension to the sheet, the 10 force is not directly in line with the channel, but at an angle, thereby reducing likelihood of the edge margins of the sheet being pulled out from the support structure. In a further aspect, the present invention relates to a method of forming an airflow barrier in an underground 15 mine or tunnel. The airflow barrier is suitable for directing contaminated air in an underground mine or tunnel away from personnel or fresh air to the personnel. The method comprises the steps of providing a support structure arranged to support the perimeter edge margins 20 of a flexible sheet, the support structure including a frame incorporating a section having an elongate channel, and retaining means that are engagable with the section; mounting a flexible sheet to the support structure, the mounting including locating at least a portion of the edge 25 margin of the sheet in the elongate channel and securing the edge margin portion thereto by the retaining means, wherein the barrier is mounted to the support structure such that possible tear forces and/or sheet strain forces induced at the edge margin portions are distributed along 30 that portion disposed within the elongate channel. In a preferred form, the method of this aspect of the invention incorporates the elements of the airflow barrier in any form described above. 53387 - 9 In one form, the method further comprises the step of applying a settable material around the perimeter of the flexible sheet so as to improve the seal between the sheet and the tunnel or mine. 5 The application of the airflow barrier described in any form above is not limited to roadways of mines and the airflow barrier may be used for any other purpose that requires the direction of airflow to be controlled. In another aspect the present invention provides an 10 air flow barrier formed by the above-described method. The invention will be more fully understood from the following description of preferred embodiments of the invention. The description is provided with reference to the accompanying drawings. 15 Brief Description of the Drawings Figure 1 shows a side-view of an airflow barrier according to a preferred embodiment of the present invention, 20 Figure 2 shows a cross-sectional representation of portion of the airflow barrier, Figure 3 shows a load and canvas displacement versus time plot for test arrangement as described in Example 1, Figure 4 is a schematic cross section of a mine 25 roadway, and Figure 5 is a cross sectional plain view of an alternative securing arrangement of the airflow barrier. Detailed Description of a Preferred Embodiment 30 Referring to Figures 1 and 2, the airflow barrier 10 comprises a frame 12 and a flexible sheet 14. The frame 12 is bolted into the roof and floor of mine roadway 16. The frame comprises a retaining means which in this embodiment 53387 - 10 comprises a member that is a tube 20. The edge portions of the sheet 14 are folded around the tube 20 and sewn with a heavy industrial synthetic thread so that each tube 20 is surrounded by the sheet 14. In this embodiment, the sheet 5 is substantially square and the frame has two tubes 20 that are associated with the two opposing edges of the sheet. Each tube 20 is positioned in a slotted steel tube 22. The slotted steel tube 22 is attached to the mine roadway 16 via evenly spaced welded steel roof bolt 10 plates. The two opposing free ends of the sheet 14 are bolted to the sides of the opening using suitable steel roof bolts and resin anchored bolt attachment system. In this example, the sheet 14 is woven from P.E.T. polymer fibres and coated with PVC liquid. In this 15 embodiment the sheet 14 has a thickness of approximately 2mm and the tested strength of the sheet is 200 x 200kN/m. The sheet is woven and coated so that it is substantially airtight. Sewing in additional strengthening material can further reinforce the sheet material. 20 Figures 4 and 5 illustrate a variation to the airflow barrier 10 wherein the opposing free ends 30 of the sheet 14 are mounted in slots 28 formed in opposite side walls 32, 34 of the mine roadway 16. As best seen in Figure 4, the mine roadway 16 25 includes opposite side walls 32, 34, ceiling 36 and floor 38. In the illustrated form, the mine roadway 16 incorporates ribs 40 which are formed from a cemenitious material such as shotcrete. The shotcrete ribs 40 are incorporated into the mine opening 16 so as to facilitate 30 the cutting of the slots 28 which are operative to receive the flexible sheet 14. In another arrangement, the slots can be applied directly into the rocks strata. 53387 - 11 In the illustrated form, the roof and floor profiles (36, 38) were also made smooth by the application of shotcrete. The slots formed in the rib 40 extend from roof to 5 floor and are approximately 20mm wide and 200mm in depth. As in the earlier embodiment, the slotted steel tubes 22 are secured along the roof and floor profile 36 and 38, whereas the free end 30 of the sheet 14 are inserted into the slots 28 on the opposite side walls 32 and 34. The 10 free ends 30 of the sheet are then secured in place by fastening element 42 which are in the form of soft wooden wedges which are driven into the slots 28. In a 2.25 metre high roadway, 8 wedges are used in each rib 40 although it is to be appreciated that the number of wedges 15 used could vary. Once the flexible sheet 14 is wedged in the slots, the slots and the periphery of the sheet are spray sealed typically by a thin sprayable liner such as that sold under the trade mark TEKFLEX. This sealant is often used 20 for controlling grounds spoiling in underground mines and is normally spray applied approximately 5mm in thickness. It is to be appreciated that other thin spray-on liners (flexible membrane products) could be used for this application. Also, other renders such as cement based 25 mortars, gypsum based plasters could be used to seal the edges of the slot although this is not a preferred option. The slots 28 are spray sealed from the same side as the cloth had been wedged. In addition, the flexible sheet 14 is designed not to be taut so as to bow slightly 30 away from the wedges 42 as best illustrated in Figure 5. This causes the sheet 14 to bear against an edge 44 of the slot 28 thereby allowing any force on the sheet 14 to be 53387 - 12 distributed along the sections of the sheet which are in contact with the edge 44 of the slot 28. An embodiment of the airflow barrier 10 was tested as follows: 5 Example 1 For this example, a airflow -barrier comprising a flexible sheet as described in the previous section was used. The sheet was composed of a cloth woven from P.E.T. polymer fibres and coated with PVC. In this example the 10 sheet has a thickness of approximately 2mm and was of a rectangular shape sized so that it could be fitted to a frame structure having a size of 4.0 x 2.7m. The sheet was mounted on a rectangular steel frame that consisted of a combination of bolted universal columns. A flat laying 15 steel frame was securely bolted to vertical columns of the load application frame at a height of 1100 mm from the laboratory floor. Two large concrete blocks centrally placed under the longer sides of the frame provided additional support while the shorter sides were supported 20 on steel props. The frame assembly clearance from the laboratory floor level was approximately 1 m, a sufficient height to accommodate canvas sagging during loading. Sheet loading was carried out with a 70 tonne capacity hydraulic jack mounted at the centre of the load 25 application frame. The ram was powered by a pressure pack Rexroth 630 ATO. The hydraulic jack piston displacement during loading was monitored by an inbuilt internal displacement facility. The sheets vertical deflection (sagging) during loading was monitored with a displacement 30 wire potentiometer (Pot) fixed on the loading frame. A load cell Interface Model 24/HL mounted to the lower end of the jack monitored the applied load in kN. 53387 - 13 The edges of the longer sides of the sheet were secured inside slotted pipes (G 350 -grade steel, outer diameter 60.5mm, wall thickness 5.4 mm) mounted along the longer side of the rectangular test frame. Two types of 5 anchoring materials were used. Edges of the sheet were folded into loops and sewn together. Steel tube of 20mm diameter were positioned in respective loops and in respective slotted pipes so that the steel tubes anchor the sheet within the slotted pipes. Following the sheet 10 mounting, each 3950 mm long slotted pipe was fixed on to the test frame by bolting it through five evenly spaced, 150 mm square domed Plates welded to the pipe. The short sides of the sheet were directly fixed on the short sides of the steel frame by piercing the canvas 15 and bolting it with 150mm steel domed plates. Previous testing has shown that sheet failure occurred parallel to and within the longer sections of the flexible membrane. The failure of the sheet within the longer span was attributed to the applied load being concentrated within 20 the shorter span of the fabric membrane. Thus the slotted pipe frames were considered to attract most of the load applied to the sheet. A layer of sand of total weight 1027 kg was uniformly placed on the mounted sheet. The purpose of the sand layer 25 was to cushion and minimise the possible impact of differential loading of the sheet surface. The sand layer was sprayed over four layers of 7.5 mm thick conveyor belt sections. A 2.5m x 1.45 m x 25 mm marine steel plate was then placed over the sand layer in the middle of the 30 fabric stopping. Placed over the steel plate were three layers of steel beams, which acting as a spacer, thus reducing excessive jack piston travel during dynamic loading stage. The total static weight placed initially on 53387 - 14 the sheet prior to jack loading in the second and final phase of loading was in the order of 2222 kg. During the first phase of the test, a total of 4 plates were welded across the pipe/frame structure 5 surfaces. The welded plates began to snap when 111 kN jacking force was applied by the ram. Also noticed was slight inward buckling and twisting of the test frame's longer sides. The loads were quickly eased off from the sheet and four additional plates were welded on each 10 longitudinal side of the test frame. The main frame was further reinforced to stop it from bending and twisting. Timber posts placed between the horizontally lying frame structure and the loading channel beam carrying the ramming system assisted in minimising frame bending and 15 twist. The test was resumed and a total load of 180 kN force was applied until the plates were once again snapped. Figure 3 shows a load and canvas displacement versus time plots, 30 and 32 respectively, for this test 20 arrangement. Points A and B in the Figure show the points at which the loads were being eased off from the sheet to enable further structure reinforcement. The test was terminated when the welded plates began to fail at the total applied load of 223 kN (218.76 t) and 25 without any sign of sheet failure. The sheet was not damaged The load of 223 kN was equivalent to a pressure of 2.685 psi, and was 0.034 MPa (0.685 psi) greater than the specified amount of (0.0138MPa) 2 psi. The placement of the sand layer over the sheet was found to contribute 30 to even distribution of the applied load on the fabric surface as well as the anchorage lines, particularly along the slotted pipe length. 53387 - 15 The total load applied on sheet was 20.371 tonnes (2.226 + 18.145 t). This was equivalent to a pressure of 0.0185 MPa. (2.71 psi). This pressure was generated on a sheet area of 2.7 x 4.0 M 2 . 5 Advantages of the airflow barrier 10 include the following: " For the construction of most airflow barriers, all the components are transported underground and the barrier is assembled from its individual components. For many 10 barriers the volume of materials required to be transported underground to the site where construction of the barriers is required may be prohibitive and not timely in the mining cycle. This task is time consuming and in the case of brick or concrete blocks requires 15 considerable skill and effort. In contrast the airflow barrier 10 is pre-assembled on the surface may be simply attached to the underground opening with resin anchored steel bolts or some other suitable bolt system. In addition a sealant can be applied where the barrier 20 contacts the roadway periphery to ensure effective sealing. " A further problem of most barrier systems is that they cannot be removed from their location and reassembled at a new location. The airflow barrier 10 can simply be 25 unbolted and assembled at a new site. The barrier can also be unbolted and secured to the roof to allow the passage of men and materials whereas other engineering rated barrier methods require fixing into the roadway. * A further problem is that despite roadway support 30 systems, changing forces within the mine roadways due to mining cause roadways to change shape. Most barrier systems are constructed from rigid materials that become permanently damaged by roadway movement and cannot 53387 - 16 easily be repaired. The flexible barrier 10 is able to deform from its original configuration as the roadway changes shape without affecting its ability to provide a pressure rating. 5 * Many barrier systems are constructed by spraying a powder product onto a pre-erected formwork using the dry shotcrete process. This tends to generate dust that requires strict ventilation controls and in some locations limits the use of the product where personnel 10 are affected by the dust-laden air. The erection of the membrane stopping virtually eliminates this potential hazard. It is to be understood that, if any prior art publication is referred to herein, such reference does not 15 constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or in any other country. In the claims which follow and in the preceding description of the invention, except where the context 20 requires otherwise due to express language or necessary implication, the word "comprising" is used in an inclusive sense, i.e. the features specified may be associated with further features in various embodiments of the invention. Variations and/or modifications may be made to the 25 parts previously described without departing from the spirit or ambient of the present invention. 30 53387

Claims (22)

1. An airflow barrier suitable for directing contaminated air in an underground mine or tunnel away 5 from personnel or fresh air to the personnel, the airflow barrier comprising a sheet of flexible material and a support structure including a frame for supporting at least a portion of the sheet, the frame incorporating a frame section having an elongated channel and retaining 10 means for securing at least a portion of the perimeter edge margin of the sheet within the channel so that at least some of possible tear forces and/or sheet strain forces are distributed along that portion. 15

2. An airflow barrier according to claim 1, wherein the retaining means and the channel are arranged for securing more than half of the length of the perimeter edge portion of the sheet. 20

3. An airflow barrier according to claim 1 or 2, wherein the frame extends around and supports the entire edge margin of the sheet.

4. An airflow barrier according to claim 1 or 2, 25 wherein the frame is arranged to support the sheet at a plurality of portions of the perimeter edge of the sheet.

5. An airflow barrier according to claim 4, wherein the portions are portions in which the flexible sheet is in 30 use subjected to higher stress.

6. An airflow barrier according to any preceding claim, wherein the channel is shaped to incorporate a restricted 53387 - 18 opening and wherein the retaining means is in the form of an elongate member that locates and is captured within the channel. 5

7. An airflow barrier according to claim 6, wherein the portion of the edge margin of the sheet is secured to the elongated member.

8. An airflow barrier according to either claim 6 or 7, 10 wherein the portion of the edge margin of the sheet is folded to form a sleeve in which the retaining member is located.

9. An airflow barrier according to any one of claims 6 15 to 8, wherein the elongate member is rigid.

10. An airflow barrier according to claim 8, wherein the elongate member is formed from particulate material that is positioned within the sleeve of the sheet. 20

11. An airflow barrier according to any one of claims 6 to 10, wherein the exterior dimensions of the elongate members are chosen so that the elongate member fits loosely within the interior of the channel. 25

12. An airflow barrier according to any one of claims 1 to 5, wherein the retaining means is in the form of fastening elements which are able to be inserted into the channel opening so that portions of the edge margins of 30 the sheet located within the channel are secured in place by inserting the fastening elements in the channel so as to wedge the edge margins between the fastening elements and one side of the elongate channel. 53387 - 19

13. An airflow barrier according to claim 12, wherein the channel includes parallel side walls. 5

14. An airflow barrier according to any preceding claim, wherein the frame section is formed from a hollow section, typically made from steel.

15. An airflow barrier according to claim 14, wherein the 10 frame section is formed from an elongate pipe having a central passage that defines the channel and an open slit along its length that defines the opening of the channel.

16. An airflow barrier according to any one of claims 1 15 to 14, wherein the frame section is formed in situ in a wall of the mine or tunnel.

17. An airflow barrier according to claim 16, wherein the channel of the frame section is formed in a settable 20 material applied to a wall surface of the mine or tunnel.

18. An airflow barrier according to any preceding claim, wherein the support structure includes a plurality of frames. 25

19. A method of forming an airflow barrier in an underground mine or tunnel, the airflow barrier being suitable for directing contaminated air in an underground mine or tunnel away from personnel or fresh air to the 30 personnel, the method comprising the steps of: - providing a support structure arranged to support the perimeter edge margins of a flexible sheet, the support structure including a frame incorporating a section having 53387 - 20 an elongate channel, and retaining means that are engagable with the section; mounting a flexible sheet to the support structure, the mounting including locating at least a portion of the 5 edge margin of the sheet in the elongate channel and securing the edge margin portion thereto by the retaining means, wherein the barrier is mounted to the support structure such that possible tear forces and/or sheet strain forces induced at the edge margin portions disposed io within the elongate channel are distributed along that portion.

20. A method according to claim 17, further comprising the step of applying a settable material around the 15 perimeter of the flexible sheet so as to improve the seal between the sheet and the tunnel or mine.

21. An air flow barrier formed by the method as claimed in claim 19 or 20. 20

22. An airflow barrier or a method substantially as herein described with reference to the drawings. 1624067_1 (GHMatters) 10/08/09