【正文】 ed. (3) The seam needs remined. Mining under water bodies began in 195frs in China. At the beginning the thick coal seams and multiseams were tried to be extracted under waterbearing alluvium. In 197039。 and a theckness of 0～ 14m, the unstable coal seams, the seams suffered by magmatic intrusion, and the seams methane or dust content. Some other techniques were also explored, such as the hydromechanical mining under the shield of metal mesh, the topcoal drawing with the hell to pressured water ettluxion m case ot mclmect SllCln39。s. The 20 MPa highpressure hidromechanical mining technique was carried out in 1970’s. Now the cutting pressure practically used is generall,above 10MPa, only in few weak coal seams cutting pressure of less than 10MPa wa employed. Shortwall unsupported hyderomechanicalrnining is the main from of nowadays hydromechanical mining technology, this method was used for extracting the coal seams ovarifi0us conditions, such as the seams with an inclination of 8。s in China. the cutting pressure increased fron 5~39。s pillarless mining developed quickly, the technique of driving en tries or retaining entries along gob edges got much development. Especially, the sidewall ill. ling technique for the entries retained along gob edges achieved success, which opened a broad prospects for pillarless mining and created more favourable conditions for enlarging the appli. cation scope of advancing mining. In addition, the success of mining over raises or crosscuts improved the maintenance of entries and reduced coal losses, which further pleted the longwall mining method. Combined sectional layouts will be employed in a long period because multiseamdepos. iting formations are encountered in most cases in China. However, it needs developing to the direction of simplification, centralization and pillarless mining. Cheaper sidewall filling mate rials and sidewall filling technologies also need to be further studied. Under suitable conditions, centralized layout in each seam, retaining entries along gob edges and advancing mining are adopted. Sets of continuous miners were imported form , and room amp。 ) medium thick and thick coal seams mined by means of multislicing, fullyseam mining (with a thickness of ～ )etc. Then some particular conditions would be considered, such as the fullYSeam mining (with a 遼寧工程技術(shù)大學(xué)畢業(yè)設(shè)計(jì) 5 thickness of ～ and an inclination angle of less than 15186。 It is considered that the fully mechanized mining technique used in simple gently inclined medium thick coal seams or the thick coal seams mined by slicing has been ripe. Generally speaking, this technique has been reached or approached to the internation level of early 80’s, and has achieved significant technicoeconomic results. The fully mechanized mining technique used in gently inclined thin coal seams (the hardness being of less than mediam grade, the thickness of more than m), inclined medium thick coal seams, gently inclined thick coal seams (～ ) and steeply inclined thick coal seams (mined by means of the mining method with topcoal 39。 (here the number 3 means the roof, the coal seam and the floor), big inclination angle。focusing efforts on developing the fully mechanized mining equipment used for difficult conditions, such as the weak339。 increasing the monthly face production and economic profit。 In thick coal seams, highface stoping caving method was changed into the downward inclined slicing with topcoal retained or under the protection of false timber roof, the downward horizontally slicing caving method with false topcoal or timber roof, and a few changed into ascending hydraulic filling method. Meanwhile, roof grading was carried out according to the experiences at hme and abroad in order to benefit selecting different roof control methods for different roof conditions. During this period, great achievement was obtained in the reform of old mining methods. Up to 1957, the output produced by means of longwall mining in the state operated coal mines accounted for %, the coal recovery rate of mining sections raised to about 70%, and the working environment and conditions of safe production were apparently improved. The roof control in longwall face eliminates the situation of no supports as in old mining methods, the support types changed gradually from timber props and framed timbers to metal frictional props plus hinged bars. in gently inclined and inclined thick or extrathick coal seams, the topslicing caving mining under the protection ofartificial false roof was tested and improved. The oringinal false timber roof was changed into bamboo curfain, waaved twigs of the chaste tree, and mainly into metalmesh false roof. Moreover, clay grouting was used for forming regenerated roof. In gently inclined extrathick coal seams, ascending inclined slicing longwall mining on the strike associated With hydraulic filling was also practised. For steeply inclined thin and medium thick coal seams, inverted bench mining by means of pressed air hammer was tested at the beginning, then tongwall mini ng was adopted. In steeply inclined thick coal seams, the horizontally slicing and slant slicing were practised firstly, and the method of mining under the protection of flexible shields was latter tested successfully and spreaded. Besides, the strip shrinkage stoping to the rise, the oblique longwalltype shrinkage stoping on the strike and the sublevel blasting mining method were also practised. The bined mining method with the help of metal shield mesh was tested too in extrathick steeply inclined coal seams. Many experiences have been accumulated in the process of adopting longwall mining. For example, the clay grouting used in inclined slicing longwall caving mining on the strike for extracting th