| This dissertation has carried out a systematic theoretical and applied technical study on the key technology of the top-coal caving mining for the very thick seam——to increase the top-coal recovery rate. By means of observation statistical and classified analysis, the distribution laws of cracks and pores in eleven main mining seams in China is quantitatively or qualitatively studied , which include the crack-system , the crack-network , the fractal laws of crack scale distribution , the porosity distribution , the variation laws of pore diameters and their relativities with coal metamorphic. They provide the classification parameters and bases for estimating quantitatively the top-coal caving characteristic and the engineering effect from the top-coal water-infusion in advance. By means of the testing in situ,simulating experimentation using similar material models and the finite element calculation , the ground pressure behavior , the top-coal deformation, movement, fragmenting and caving out in the top-coal caving workface are studied about the hard , medium-hard and soft coal. Using the simulation experimentation of similar material, the caving structure on hard,medium-hard and soft coal are quantitatively or qualitatively studied. And by theory analysis and the finite element orthogonal numerical simulate, the influence on the top-coal caving characteristics from the seams and the mining technological conditions and their relativities are quantitatively or qualitatively studied.Using the fuzzy mathematics method, the top-caving characteristics are classified into five kinds according to the coal conditions . The methods for controlling and treating the five kind top-coals are put forward. The classification method and its used parameters have been provided to be reasonable by the application for 29 coal seams in our country. Base on the difference between the water flow in the cracks and the water diffuse in the pores, the principles that the water infusion holes should be set in the upper part of top-coal and water infusion time are put forward. By means of the mechanics analysis, the synthetic expression that water infusion makes the coal shear strength decrease by ?τis get. The permeability coefficients and their variation laws with tri-stresses from the 18 coal seams all over the county are tested in the laboratory. The seams are classified into five kinds according to their permeability using the fuzzy mathematics method. Based the classified results, the water infusion methods and their parameters are put forward. The classified method and selected classified parameters are proved to be reasonable by applied to the 18 seams. Based on the fractured zoning theory of the abutment pressure in front of the coal wall, the reasonable positions are defined for water pre-infusion in front of the workface for mining the hard, medium-hard and soft coal seams. On the base of the theoretical study on the water pre-infusion to soften top-coal , the method for defining the parameters of the top-coal water pre-infusion, such as the borehole interval,water quantity, pressure, sustained time etc.,have been given out . The study results applied to the fully mechanized workface in Wangzhuang mine has achieved remarkable technical ,economical and social beneficial results.
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