H:\tw\Interwoven\NRPortbl\DCC\TW\60424191. docx- 12/03/2013 GAS MIGRATION CONTROL METHOD Background of the Invention [0001] The present invention relates to a method of controlling gas migration through a surface in an underground coal mine. Description of the Prior Art [0002] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates. [0003] Currently underground coal mines utilise bolt and meshing techniques for supporting tunnel side walls and roofs, for example as part of heading or roadway developments. The installation process for such bolt and mesh arrangements typically involves mining the tunnel and installing preliminary bolts, followed by a second stage in which additional bolts and the retaining mesh are installed. [0004] A significant challenge in the operations of underground coal mines is the control of hazardous gas levels. Underground mining environments include substantially enclosed volumes that are isolated from typical atmospheric conditions above ground, which can allow concentrations of gases to accumulate that may present, for example, risks of explosion and/or harmful effects to personnel such as poisoning or suffocation. [0005] Underground coal mines in particular are prone to accumulations of gases which migrate through surfaces of the coal mine such as tunnel walls, particularly where these are formed in the vicinity of coal strata. Conventional gas control techniques in underground coal mines typically involve the use of extensive ventilation and gas monitoring systems to ensure safe gas levels. However, these techniques fail to address the problem of gas migrating into the underground coal mine environment in the first place H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 -2 [0006] An example of this process will now be described with reference to Figures 1A and 1B. [0007] In this example, during a first pass, a continuous miner 100 or other similar mining machine, mines a heading to create a tunnel 110, and uses a bolting rig 101 to install retaining bolts 111 and a mesh 112 in the tunnel walls and roof. The bolts 111 are typically nylon bolts, which act to provide primary support, whilst the mesh 112, acts to provide support for the strata between the bolts 111. The bolts and mesh are installed in accordance with requirements defined by a geotechnical engineer, as will be appreciated by persons skilled in the art. [0008] Following installation of the primary support, the heading is inspected by the mine site geotechnical engineer and a secondary support is defined and installed. To achieve this, as shown in Figure 1B, a cable bolting machine 120 having cable pusher and grout pump is used to insert and grout cable bolts 113 into place. The cable bolts can extend long distances into the strata and often require grouting to ensure the cable bolts are secured within the strata. [0009] There is significant cost involved with the installation of bolts into the strata as a form of primary and secondary support. Additionally, headings and roadways developed in this manner also require stone dusting to reduce the explosive environment created with the presence of large amounts of airborne coal dust. Accordingly an alternative technique for providing tunnel support is required. [0010] Whilst application of fibre reinforced concrete (fibrecrete) via shotcrete rigs is known, there has been limited use of this process in coal mining due to the fact that shotcrete rigs cannot be used within Explosive Risk Zone (ERZ) Areas of coal mines. Summary of the Present Invention [0011] In one broad form the present invention seeks to provide a method of controlling gas migration through a surface in an underground coal mine, the method including dispensing fibre reinforced concrete onto the surface to form a sealing layer over the surface. [0012] Typically the surface includes at least a portion of a tunnel surface.
H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 -3 [0013] Typically the fibre reinforced concrete includes a concrete mixture and polymer fibres. [0014] Typically the fibre reinforced concrete further includes at least one of fly ash and silica fume. [0015] Typically the method includes dispensing the material so that the sealing layer at least partially penetrates the surface. [0016] Typically the method includes forming the sealing layer over a coal strata surface. [0017] Typically the method includes: a) identifying a coal strata surface; and, b) forming the sealing layer to cover at least the coal strata surface. [0018] Typically the method includes forming the sealing layer responsive to a gas level in the underground coal mine. [0019] Typically the method includes: a) monitoring gas levels for different sections of the underground coal mine; b) determining a section of the underground coal mine having a gas level that exceeds a predetermined threshold; and, c) forming the sealing layer over a surface of the determined section. [0020] Typically the gas levels are monitored by monitoring gas exhausted from the underground coal mine. [0021] Typically the method includes dispensing the material so that the sealing layer has a thickness based on properties of the surface. [0022] Typically the method includes: a) determining properties of the surface; b) determining a required thickness for sealing the surface based on the properties; and, c) dispensing the material to form the sealing layer with the required thickness.
H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 -4 [0023] Typically the method includes selecting a composition of the fibre reinforced concrete based on properties of the surface. [0024] Typically the method includes dispensing the fibre reinforced concreter from a spray nozzle of a vehicle. [0025] Typically the vehicle has a flameproof engine. [0026] Typically the method is performed using a vehicle having: a) a chassis; b) a plurality of wheels or tracks c) a flameproof engine for driving the wheels or tracks via a drive train; d) a material dispensing system including: i) a hopper that contains the material in use; ii) a movable boom; iii) at least one spray nozzle supported by the boom; iv) one or more pipes for coupling the spray nozzle to the hopper; and, v) a pumping system for pumping material from the hopper to the spray nozzles, thereby dispensing material from the spray nozzles onto a surface of the tunnel. [0027] Typically the method includes dispensing the fibre reinforced concrete onto a tunnel surface to form the sealing layer and to provide a lining layer to thereby support the tunnel. [0028] Typically the method includes forming the sealing layer over a coal surface of a mine ventilation seal. [0029] In another broad form the present invention seeks to provide a method of controlling gas migration through a surface in an underground coal mine, the method including dispensing fibre reinforced concrete from a spray nozzle of a vehicle onto the surface to form a sealing layer over the surface, wherein the vehicle has a flameproof engine. [0030] In another broad form the present invention seeks to provide a method of providing a tunnel support in an underground coal mine, the method including dispensing material from a spray nozzle of a vehicle onto a surface of the tunnel to thereby support the tunnel.
H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 -5 [0031] Typically the method includes providing bolts in at least one of the tunnel walls and roof before dispensing the material. [0032] Typically the material is at least one of: a) a concrete product; and, b) fibrecrete. [0033] Typically the method includes dispensing material to form a material layer over at least part of the tunnel surface. [0034] Typically the method includes dispensing material so that the layer has a respective thickness on different parts of the tunnel surface. [0035] Typically the method is performed using a vehicle having: a) a chassis; b) a plurality of wheels or tracks c) a flameproof engine for driving the wheels or tracks via a drive train; d) a material dispensing system including: i) a hopper that contains the material in use; ii) a movable boom; iii) at least one spray nozzle supported by the boom; iv) one or more pipes for coupling the spray nozzle to the hopper; and, v) a pumping system for pumping material from the hopper to the spray nozzles, thereby dispensing material from the spray nozzles onto a surface of the tunnel. [0036] In another broad form the present invention seeks to provide a method of lining a tunnel in an underground coal mine, the method including dispensing material from a spray nozzle of a vehicle onto a surface of the tunnel. [0037] In another broad form the present invention seeks to provide an apparatus for lining a tunnel, the apparatus including a vehicle having: a) a chassis; b) a plurality of wheels or tracks H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 -6 c) a flameproof engine for driving the wheels or tracks via a drive train; d) a material dispensing system including: i) a hopper that contains the material in use; ii) a movable boom; iii) at least one spray nozzle supported by the boom; iv) one or more pipes for coupling the spray nozzle to the hopper; and, v) a pumping system for pumping material from the hopper to the spray nozzles, thereby dispensing material from the spray nozzles onto a surface of the tunnel. [0038] Typically the vehicle includes: a) a sensor; and, b) a controller coupled to the sensor, the controller being adapted to receive signals from the sensor and selectively deactivate the engine depending on the received signals. [0039] Typically the sensor is at least one of: a) a gas sensor that senses gas levels, the controller selectively deactivating the engine in the event that gas levels exceed a predefined gas level; and, b) a temperature sensor that senses a temperature, the controller selectively deactivating the engine in the event that temperature exceed a predefined temperature. [0040] Typically the engine provides power to the pumping system for pumping the material. [0041] Typically the vehicle includes an electrical system suitable for use in an underground coal mine ERZ area. [0042] Typically the vehicle is at least one of: a) usable in or certified for use in an explosive risk zone; and, b) usable in or certified for use in an underground coal mine.
H:\tw\Interwoven\NRPortbl\DCC\TW\60424191. docx- 12/03/2013 -7 Brief Description of the Drawings [0043] An example of the present invention will now be described with reference to the accompanying drawings, in which: [0044] Figure 1A and 1B are schematic end views of a prior art tunnel supporting process; [0045] Figure 2 is a schematic diagram of an example of an apparatus for use in lining a tunnel; [0046] Figure 3A and 3B are schematic end views of a tunnel supporting process; [0047] Figures 4A to 4D are photographs of a specific example of an apparatus for lining a tunnel; and, [0048] Figure 5 is a schematic end view of a gas migration control process. Detailed Description of the Preferred Embodiments [0049] An example apparatus for dispensing material to provide a tunnel lining will now be described with reference to Figure 2. [0050] In this example, the apparatus is in the form of a vehicle 200 having a chassis 210, a number of wheels 211 (although tracks could alternatively be used) and a flameproof engine 220 for driving the wheels 211 via a drive train. A material dispensing system is also provided, the dispensing system including a hopper 231 that contains the material in use, a movable boom 232, at least one spray nozzle 233 supported by the boom 232. One or more pipes and/or hoses 234 are provided for coupling the spray nozzle 233 to the hopper 231, with a pumping system 235 operating to pump material from the hopper 231 to the spray nozzles 233, thereby dispensing material from the spray nozzles. [0051] The vehicle will also typically include other features, including a frame 212, body work, an engine cover, cab or the like, as well as operational controls, such as steering joysticks, an accelerator / brake or the like. [0052] In one example, the vehicle 200 is used to dispense a concrete product, such as fibrecrete, onto a surface of a tunnel in an underground coal mine to thereby form a lining that acts as a tunnel support. In this regard, the vehicle is provided with a flameproof engine, allowing the vehicle to be used in ERZs, in turn allowing the vehicle to enter and dispense H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 the fibrecrete or other similar materials within coal mines, which has not previously been possible in this mobile form. [0053] An example process for supporting a tunnel by lining a tunnel surface using the apparatus of Figure 2 will now be described with reference to Figures 3A and 3B. [0054] In this example, during a first pass, a continuous miner 300 or other similar mining machine, mines a heading to create a tunnel 310, and uses a bolting rig 301 to install retaining bolts 311 in the tunnel walls and roof. The bolts 311 are typically nylon bolts, which act to provide primary support. It will be noted however that unlike traditional techniques described above with respect to Figures 1A and 1B, a mesh is not necessarily required. [0055] Following installation of the primary support, the heading is inspected by the mine site geotechnical engineer before the vehicle 200 applies a layer of concrete material 312 to the tunnel walls and roof, to thereby form a lining (having a nominated thickness) over at least the tunnels walls and roof. [0056] The concrete material is applied at high velocity so that the concrete material adheres to the tunnel surface, and infiltrates fissures in the tunnel surface, thereby mechanically coupling the concrete lining layer to the tunnel surface and enhancing the support provided. As part of this process, the layer can also be provided with a respective thickness on different parts of the tunnel surface, thereby varying the degree of support provided. [0057] During this process, secondary bolts 313 may also be inserted into the walls and roof, although this is not essential and may depend on a condition of the tunnel, the types of stratathrough which the tunnel passes, or the like. However, it will be noted that the secondary bolts 313 are shorter than the primary bolts 311 and the cable bolts 113 used in the prior art techniques, making them easier to install, as will be appreciated by persons skilled in the art. [0058] Accordingly, the above described vehicle 200 can be used in order to apply concrete materials to surfaces in tunnels of underground coal mines, to thereby establish a tunnel lining, which in turn acts as part of a tunnel support.
H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 -9 [0059] The use of fibrecrete, or other similar materials, to provide a tunnel support in an underground coal mine can provide a number of benefits over typical tunnel support techniques. [0060] For example, the fibrecrete layer seals the tunnel surface, and hence the coal strata. This reduces air borne coal dust and gas migration as well as preventing the coal and strata from fretting, as well as reducing the need for stone dusting. The concrete materials typically provide a smooth surface, which allows for enhanced ventilation performance as the fibrecrete produces a smoother envelope with less drag. [0061] The fibrecrete can provide structural support, which reduces or eliminates the need for meshing as the fibrecrete layer (in combination with bolts) provides the required strata support. This reduces the time required to install support by avoiding the need for mesh and also reducing bolting requirements. [0062] The use of the above method and apparatus can allow for enhanced safety by reducing manual handling of mesh. Furthermore, the apparatus can be provided as an autonomous vehicle allowing for automated application of the tunnel lining, thereby reducing worker exposure to hazards. [0063] Installation of the fibrecrete via a purpose built flame proof shotcrete rig allows high impact placement of the fibrecrete onto the strata which ensures adhesion and infiltration of the fibrecrete into the coal strata to form a secure bond between the shotcrete layer tunnel arch structure and the roof/wall coal strata being supported. [0064] Accordingly, the above described method and apparatus provide a number of benefits over the art. [0065] A number of further features will now be described. [0066] In one example, the vehicle 200 includes a controller for controlling one or more aspects of operation of the vehicle. For example, the controller can be coupled to one or more sensors, the controller being adapted to receive signals from the sensor and selectively deactivate the engine depending on the received signals. The sensors can be for sensing gas and/or heat, allowing the controller to selectively deactivate the engine in the event that H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 10 measured gas or heat levels exceed a predefined gas or heat levels, respectively. Additionally and/or alternatively, other action can be taken such as generating alarms to alert workers. [0067] The controller can be of any suitable form and typically includes an electronic processing device for receiving signals from the sensors, processing these and generating control signals. In one example, the electronic processing device is a microprocessor, microchip processor, logic gate configuration, firmware optionally associated with implementing logic such as an FPGA (Field Programmable Gate Array), or any other electronic device, system or arrangement capable of interacting with the sensors. [0068] The controller may also form part of a vehicle control system, such as a control system for operating the vehicle autonomously, as will be understood by persons skilled in the art. [0069] In one example, the engine provides power to the pumping system for pumping the material. This allows all power to be deactivated centrally in the event that the need arises, whilst also reducing the need for multiple power systems, which would complicate use of the vehicle in underground mines. [0070] The vehicle typically also includes an electrical system, which allows the vehicle to operate safely in underground coal mines and within ERZ areas. [0071] It will be appreciated that the above vehicle can therefore be usable in or certified for use in an explosive risk zone such as an underground coal mine. [0072] A specific example of an apparatus for applying fibrecrete, in the form of a shotcrete rig, will now be described with reference to Figures 4A to 4D. [0073] In this example, the shotcrete rig 400 includes a shotcrete rig chassis having four wheels 411 and supporting a modified frame 412 that contains the flameproof engine (not shown). The material dispensing system is supported by the frame and includes a hopper 431 that contains the material in use, a movable boom 432, at least one spray nozzle 433 supported by the boom 432. Delivery hoses 434 are provided for coupling the spray nozzle 433 to the hopper 431, with a pumping system operating to pump material from the hopper 431 to the spray nozzles 433, thereby dispensing material from the spray nozzles. A feeder H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 11 pipe 436 may also be optionally mounted to the hopper 431, whilst a scrubber tank indicator 437 can be mounted on a roof of the vehicle. The frame further supports hydraulic jacks 414 for additional vehicle stability and an operator cabin 415, as well as approved lighting 416. [0074] The flame proof engine is mounted in an engine compartment 413, and provides the power for travel and operation of the rig and concrete pumping components. The flameproof engine is specifically designed to be able to provide power for the rig in ERZ areas within a coal mine and has shutdown capabilities in case of excessive heat generation [0075] A radiator and/or scrubber system 417 is mounted to a rear of the frame to allow heat dispersal away from the engine, thereby reducing operator risk, as well as providing the radiator near available airflow to maximize cooling. [0076] The electrical system incorporates approved wiring, lighting and gas detection and shutdown systems, mounted in a control boxes 441, which provides shutdown of the machine in the event that excessive gas levels are detected within the work area. An electrical shut out 442 and engine shut out 443 are provided to allow for manual shut-down. Typically such features are mandatory for operation of vehicles in UG coal mining environments. [0077] In use, the vehicle can apply a fibrecrete layer by way of spraying fibrecrete at high velocities onto the coal/strata which provides a fibrecrete layer to the perimeter of the heading tunnel envelope. The fibrecrete is shot with such force that when it impacts onto the coal / strata, high adhesion is ensured as the fibrecrete infiltrates into the fissures of the coal strata. [0078] The thickness of the fibrecrete layer depends on the load resistance required and is defined by the mine site geotechnical engineer. Generally thickenings of the fibrecrete layer are provided at the intersection between the walls and roof and also at the toe of the walls. This provides extra load carrying capacity in terms of the stress points which exist at these points when load distribution occurs throughout the strata due to nearby mining activities and ground loadings. [0079] The thickness of the fibrecrete layer and the size and number of bolts required for secondary support is defined by the mine site geotechnical engineer and is designed to H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 12 provide the most cost effective support model combination required for safe ongoing use of the heading/roadway for coal mining purposes. [0080] As mentioned above, the fibrecrete layer may also beneficially seal surfaces to which it is applied, to thereby reduce gas migration. Thus, the techniques discussed above for providing a tunnel lining to support the tunnel may also be adapted to control gas migration through surfaces in the underground coal mine. [0081] Accordingly, in one example, a method of controlling gas migration through a surface in an underground coal mine may include dispensing fibre reinforced concrete onto the surface to form a sealing layer over the surface. It will be appreciated that whilst this sealing layer may be providing over a tunnel surface as discussed above, the surface may be any surface within the underground coal mine, and not exclusively a tunnel surface. [0082] Furthermore, the method may involve dispensing the fibre reinforced concrete onto a tunnel surface to form the sealing layer and to simultaneously provide a lining layer to thereby support the tunnel. However, whilst the sealing layer may be provided to also function as a lining layer for supporting the tunnel, it should be understood that this is not essential, and the sealing layer may be formed solely for the purpose of sealing a surface without necessarily providing a tunnel supporting function. [0083] In any event, by forming a sealing layer over the surface the potential for gas migration through the surface can be substantially reduced, or even eliminated, depending on relevant properties of the surface and the sealing layer. In particular, the sealing layer can be formed on coal strata surfaces to directly seal the coal strata surfaces and thus minimise the gas migration from the coal strata into underground roadways or the like, which can help to reduce gas concentration in the underground environment. It will be understood that the sealing layer may also reduce gas migration in the opposite direction, namely from open volumes of the underground coal mine into the coal strata. [0084] The sealing layer can be formed using the shotcreting process as discussed above including dispensing the fibre reinforced concrete from a spray nozzle of a vehicle having a flame proof engine. The example shotcreting rig 400 discussed above may thus also be used in providing sealing layers for gas migration control. In view of the discussion above, the H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 13 shotcreting process beneficially causes the fibre reinforced concrete to infiltrate into the fissures of the coal strata and thus penetrate the surface to provide an effective sealing layer. [0085] The shotcreting process may thus be used to seal off areas of the underground coal mine having coal strata which are emitting high levels of gas which in turn creates a volatile and unsafe atmosphere in the underground coal mine and causes significant delays to the mining operations. Trials of these techniques have demonstrated that as sealing layers of fibre reinforced concrete are applied to these areas of high gas emissions the gas levels in the area are subsequently reduced and the atmospheric conditions improve significantly. This has been evidenced and monitored using existing underground coal mine gas monitoring systems. [0086] Further optional features of the method of controlling gas migration will now be outlined. [0087] The fibre reinforced concrete will typically include a concrete mixture interspersed with fibres. The concrete mixture will generally include cement, aggregate and sand mixed with water, with quantities typically determined as per the standard supplier mixture design. In one example, a 10 mm aggregate is used, although the type of aggregate, and sand, will often be dependent on the local supplier quarries in practice, and thus the composition of the mixture may need to be adjusted to suit the particular materials that are locally available. [0088] Preferably polymer fibres will be used although other types of fibres may be used such as metal fibres. In any event, the quantity of fibres added to the mixture may be selected depending on the required properties, such as toughness, of the fibre reinforced concrete. [0089] Further ingredients may be added to the fibre reinforced concrete mixture, such as fly ash and/or silica fume. In one example, the fibre reinforced concrete mixture may include a quantity of fly ash making up a total of about 25% by weight of the total cementitious material content of the mix. Other admixtures may also be included to adjust particular properties of the sealing layer, as required. [0090] In any event, the composition of the fibre reinforced concrete may be selected based on properties of the surface, such as to ensure desirable sealing properties, although it should be appreciated that, in practice, the composition may be selected to provide sub-optimal H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 14 sealing performance in view of other competing requirements such as cost effectiveness or compatibility with the shotcreting process. [0091] As mentioned, the sealing layer will be particularly beneficial for preventing gas migration from the coal strata. Accordingly, it may be desirable to form the sealing layer over coal strata surfaces within the underground coal mine to thereby seal from gas migration from the adjacent coal strata. Whilst in some examples, entire tunnel surfaces may have sealing layers of fibre reinforced concrete applied to completely seal the tunnel, in some circumstances it may be desirable to take a more selective approach to preferentially sealing coal strata surfaces. Thus, in one example, a process of controlling gas migration may involve identifying a coal strata surface and forming the sealing layer to cover at least the coal strata surface. It will be appreciated that this may allow for significant cost savings if the entire surface does not need to be sealed. [0092] An example of controlling gas migration through a coal strata surface is shown in Figure 5. Figure 5 depicts an underground coal mine section 500 having a wall surface 501 and a roof surface 502, which may be part of a tunnel or other open volume of the mine. Retaining bolts 511 have been provided in the surfaces 501, 502 for primary support as discussed above and a roadway 512 is provided to allow vehicle access. [0093] In this example, the wall surface 501 is adjacent to a coal strata 503 to thereby define a coal strata surface which may be particularly prone to gas migration from the coal strata. Accordingly, a sealing layer 521 has been formed over the coal strata surface as shown to thereby reduce the gas migration. As indicated by arrows 531, 532, the sealing layer 521 will help to reduce gas migration from the coal strata 503 into the underground coal mine section 500. Furthermore, as indicated by arrows 533, 534, the sealing layer 521 can also reduce gas migration from the underground coal mine section 500 into the coal strata 503. [0094] In other examples, the sealing layer may be formed responsive to a gas level in the underground coal mine. Thus, gas levels may be monitored throughout the underground coal mine and sealing applied only in regions where the amount of gas migration needs to be reduced. In one implementation, a process of controlling gas migration may therefore include monitoring gas levels for different sections of the underground coal mine, determining a H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 15 section of the underground coal mine having a gas level that exceeds a predetermined threshold and forming the sealing layer over a surface of the determined section. It will be appreciated that the gas levels may be monitored by monitoring gas exhausted from the underground coal mine. This may take advantage of existing gas monitoring systems which will usually be provided in underground coal mines conjunction with ventilation systems. [0095] The dispensing of the fibre reinforced concrete using the shotcreting process may be controlled so that thickness of the sealing layer is based on properties of the surface. For instance, the thickness may be determined in accordance with surface properties such as the surface porosity or the material composition of the surface, or whether the surface is a rock surface or a coal strata surface. Accordingly, in one example, the method may include determining properties of the surface, determining a required thickness for sealing the surface based on the properties, and dispensing the material to form the sealing layer with the required thickness. [0096] In one example, the thickness of a sealing layer of fibre reinforced concrete that is selectively applied to a coal strata surface may be in the range of 50 mm to 150 mm, although the specific thickness may be dependent on the properties of the coal strata. [0097] It should be understood that in the event the sealing layer is also intended to function as a tunnel lining for supporting the tunnel, the required thickness for sealing the surface may be different to the thickness necessary to provide adequate support for the tunnel. As such, the thickness may be selected bearing both requirements in mind. [0098] It will be appreciated that the above method of forming a sealing layer is applicable to a range of different surfaces in underground coal mines, and is not limited to use in forming a sealing layer over a coal strata surface as exemplified above. For example, a sealing layer may be applied to a surface of an existing mine ventilation seal, or a surface of a wall adjacent to or forming a part of a mine ventilation seal. [0099] In this regard, it is noted that mine ventilation seals are traditionally keyed into tunnel walls with the resulting joint being sealed with gunite. However this is often inadequate for preventing gas migration across the seal because fissures in the interfacing tunnel walls will H:\tw\Interwoven\NRPortbl\DCC\TW\6042419_1.docx-12/03/2013 - 16 not be sealed and the gunite is brittle and prone to cracking, further reducing the seal effectiveness. [0100] Such issues associated with existing mine ventilation seals can be mitigated by dispensing fibre reinforced concrete onto surfaces of the mine ventilation seals and the surrounding strata face to form sealing layers in accordance with the above discussed methods. [0101] Throughout this specification and claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers or steps but not the exclusion of any other integer or group of integers. [0102] Persons skilled in the art will appreciate that numerous variations and modifications will become apparent. All such variations and modifications which become apparent to persons skilled in the art, should be considered to fall within the spirit and scope that the invention broadly appearing before described.