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• W5113445 abstract "Both safety and productivity in underground gassy coal mines can be improved substantially if an appropriate gas management system is introduced. A strong direct relationship exists between the gas emission rate, roof and floor strata relaxation zones characteristic, mining activities and gas drainage practices. Detailed knowledge of geological factors, gas and coal-rock properties, as well as mining systems are necessary for the methodology used in predicting overall underground gassiness, and planning gas capture and ventilation systems. Early gas emission calculations for various mining activities, particularly for the longwall mining system are essential. A reasonably accurate prediction of gas make as well as the design of ventilation, gas recovery (drainage holes) techniques can be made using 'Floorgas' and 'Roofgas' computer simulations, provided sufficient geological, mining, and gas data are made available. STATE OF THE ART Several techniques for predicting gassiness during longwall coal production have been developed. Many are only relevant to regional mining, gassy and geological conditions. Most methods adopt the same basic parameters: the stratigraphy above and below the seam, insitu gas contents of the working and adjacent seams, the strata relaxation coefficient, and the degree of gas liberation. The accuracy of the final results, however, depends substantially on individual coefficients, which are developed specifically for the above techniques, and therefore cannot be reused in other mines or regions (countries). Comparative test results, using various coefficients, have shown that large errors are possible in these methods, within the range of -50% to +120% (Dunmore, 1979). The advent of computer modelling methods, and particularly finite element techniques, enables predictions based on the nature and extent of the relaxation zone surrounding the longwall to be made when using local geomechanical, geological and mining input data. Such a model has been developed and evaluated at Lunagas Pty Limited, Newcastle, Australia, under the name of 'Floorgas and Roofgas Geomechanical and Gas Release Models', and has been cornmercialised to operate on a Windows based platform. Outputs from both programs (Figs. 1, 2 and 3) are used to design gas capture technologies, including cross measure or directional holes drilled from underground, and gas wells drilled from the surface. They are also used for precise gas make predictions and assessment of gas conditions necessary for planning gas management strategies. Gassiness predictions based on the 'Floorgas' and 'Roofgas' models were compared with underground gas measurements from high production longwalls in Australia and other countries between 1992 and 1997. The results are sound, indicating accurate predictions of 90 to 95% efficiency, if the appropriate input data are available. 'FLOORGAS' AND 'ROOFGAS' The programs can be used as engineering tools in the underground mining areas for: prediction of gas emissions to the underground workings, 1 2. design of gas drainage holes and gas capture strategies, Principal Consultant and Managing Director, Lunagas Pty Ltd. 587 COAL98 Conference WoUongong 18 -20 February 1998 3. ventilation planning in underground coal mines, 4. planning for strata control, 5. definition of shearing zones and vertical loads, and 6. planning for coalbed methane utilisation and environmental control. (Lunarzewski, 1992; Lunarzewski et.al., 1995). When using the Floorgas' and 'Roofgas' programs, the following benefits are achievable: Identification of gas discharge and shear zone positions in the floor, strata relaxation angles and various gas discharge zones position in the roof, which are both relevant to local geological and mining conditions. 2. Calculation and definition of prediction coefficients such as specific gas emission and the relationships between gas beration, longwall width, and coal production levels. 3. Optimisation of cross-measure drainage hole length, location, number, and angles of deviation and inclination. 4. Optimisation of in seam drainage hole locations, the number and direction. 5. Assessment of active gas resources and their contribution in the pollution emission process. The programs generate graphical outputs typified in Figs. I, 2 and 3, depicting vertical cross-sections of longwall strata at various selected distances ahead of and behind the longwall face. 'F1oorgas' output displays extend down to lOOm below the working seam, while a 'Roofgas' output can show strata relaxation up to 2OOm above the working seam. The 'Floorgas' program generates a vertical load distribution function along the chain-pillar and adjacent longwall panelslgoaf areas. On the basis of the generated load, the program calculates vertical and shear stresses for each cubic metre of rock element being modelled. The program is a product of long-tenn detailed analyses and it uses results gained from various coal mines world-wide, with particular reference to mining and geological conditions in coal mines with daily productions greater than 5000 tonnes per longwall. 'Roofgas' calculates the position and shape of five gas release zones, with various degassing intensities, using the Lunagas empirical model (Lunarzewski, 1992). Then boundaries are quantitatively defined both in terms of discontinuous deformation of rocks and gas release percentages. INPUT DATA Input Data is assembled from three (3) defined sources. Geomechanical in which Mechanical properties of the roof strata are expressed as uniaxial compressive strength (UCS) values and Strata stresses expressed as horizontal and vertical stress magnitudes, horizontal to vertical stress ratio, and horizontal stress direction related to longwall axis position. COAL98 Conference Wollongong 18 .20 February 1998 588 1." @default.
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• W5113445 date "1998-01-01" @default.
• W5113445 modified "2023-09-27" @default.
• W5113445 title "A new approach in planning gas drainage practices" @default.
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