1、翻译部分英文原文3D numerical modeling of longwall mining with top-coal cavingN.E. Yasitli, B. UnverDepartment of Mining Engineering, Hacettepe University, Beytepe 06532, Ankara, TurkeyAccepted 8 August 2004Available online 23 December 2004AbstractThere is a considerable amount of lignite reserve in the form
2、 of thick seams in Turkey. It is rather complicated to predict the characteristics of strata response to mining operation in thick seams. However, a comprehensive evaluation of ground behavior is a prerequisite for maintaining efficient production, especially when the top-coal-caving method behind t
3、he face is applied. Top-coal caving is the key factor affecting the efficiency of production at thick-coal seams. During production of top coal by caving behind the face not only a significant amount of coal is lost in the goaf but the coal drawn by means of caving is diluted considerably with surro
4、unding rock. Therefore, it is not possible to carry out an efficient production operation unless caving of top coal behind the face is optimized. In this paper,results of 3D modeling of the top-coal-caving mechnism by using the finited difference code FLAC3D at the M3 longwall panel of the Omerler U
5、nderground Mine located at Tuncbilek (Turkey) are presented. According to the modeling results, maximum vertical abutment stresses were formed at a distance of 7m in front of the face. An analysis of the conditions of top coal has revealed that a 1.5m thick layer of coal just above the shield suppor
6、ts is well fractured. However, a 3.5m thick layer of coal above the fractured part is either not fractured or is fractured in the form of large blocks leading to obstruction of windows of shields during coal drawing. It is concluded that, in order to decrease dilution and increase extraction ratio a
7、nd efficiency of operation, top coal should be as uniformly fractured as possible.Hence, an efficiencient and continuous coal flowing behind the face can be maintained. A special pre-fracture blasting strategy just sufficient enough to form cracks in the top coal is suggested by means of comparing w
8、ith the results of numerical modeling.1 IntroductionCoal seams may be classified as thick, moderate and thin. Thick-coal seam categorization differs among countries, but a thickness of 4.8m is accepted as the lower limit . Thick seams comprise half of the worlds coal reserve and 7080% of thick-coal
9、seams are produced by means of underground mining methods . Production methods at the former Yugoslavia, Hungary, Poland, France, India and Chian are generally similar; however, differences arise due to local condi-tions.Thick-coal-seam mining is different from conven-tional single-slice coal mining
10、 in many aspects. Although there are operating longwall faces up to a height of 6m in some parts of the world, in practice it is difficult to extract a slice of more than 4m. Depending on the local characteristics of a coal seam, such as seam, inclination, continuity, surrounding rock and coal seam
11、mechanical properties and susceptibility of coal to spontaneous combustion, a face height of 22.5m is preferred.Production of thick seams having variable slope and thickness may prevent the application of slicing, hence, a face is located at the floor of the seam and the coal above the face is won b
12、y means of caving behind the face. Production of thick seams by using top-coal caving is much simpler in comparison to slice mining and requires less development; consequently, the efficiency of production is significantly higher. The top-coal-caving method was first applied in the 1940s in Russia a
13、nd then subsequently used in France, former Yugoslavia, Hungary, Romania, former Czechoslovakia and Turkey. The method has been in use in China and India since the 1980s. At present the method is used extensively in China and India. There are a couple of mines using the method in former Yugoslavia a
14、nd Turkey, whereas in other countries due to depletion of reserves, geological constraints, technological and economical reasons the method is not used at present. Although this method is not currently used extensively in France and former Yugoslavia, these countries had conducted pioneering work fo
15、r other countries for the development of the production method.Despite being an attractive method due to higher production efficiency and lower development requirements, longwall mining with the top-coal-caving method imposed significant difficulties in terms of flowing characteristics of coal, timi
16、ng and rate of coal drawing, loss of coal in the goaf and dilution. The primary purpose of this research was to investigate the above-stated shortcomings and find ways to overcome difficulties related mainly to top-coal caving.There have been numerous efforts to improve the efficiency of thick-coal-seam mining. Jha and Karmakar investigated the factors affecting production. Strata behavior during caving and dilution of caved top coal was investigated at in situ
