The Study Of Soften Property Of Hydraulic Fracturing Hard Top-coal

Steep coal seam of our country is rich, and a lot of mines. The production in steep coal mines is about 5% but the amount of mines is about 20% in the country. The steeps coal mines are mainly located in Wulumuqi, Yaojie, Huainan, Kailuan, Xuzhou, Changguang, Nantong, Zixing, Datong, Huating etc... The sublevel caving mining of steep coal seam as an economic, safe, efficient mining method are widely used in steep thick coal seam mining. At the caving process, the top coal is broken and collapse forming loose irregular stack under the combined effect of the stress of the mining, the coal self weight, the weight of residual coal and waste rock at upper-paragraph and repeatedly support by the supporter. But sometimes, the seam coal strength is greater than 1, and less mining stress is not sufficient to enable the above-mentioned role to fracture top coal to meet the requirements to release, moreover, with the height of sublevel increases, the recovery rate will be lower, so we need to fracture top-coal in advance. In this paper, the author analyses the mechanism of hydraulic fracturing of coal and the role of hydraulic softening of coal, analyses the hydraulic property of the B1 & B2 coal in the Xiaohonggou mine by the experimental research and theoretical analysis, analyses the main factors of hydraulic fracturing and evaluates these factors using the fuzzy clustering analysis, and analyses the infusion parameters by the method of numerical simulation. The main job done and the results are as follows:(1) Analyses the change of coal failure strength under pore water from the mechanical point and the rupture strength of fractured coal under pressure water, revealed the mechanism of softening of hydraulic fracturing.(2) Through testing, analyses the coal mine hydraulic property and the change in mechanical properties under the action of water, as well as the different failure state under the different moisture content of coal. (3) Analyses the main factors of hydraulic fracturing of sublevel caving mining of steep coal seam and evaluates these factors using the fuzzy clustering analysis, and evaluates the softening character of B1 & B2 seam in the Xiaohonggou mine.(4) Calculates the rock displacement and stress conditions use the numerical methods, on this base, analyses the infusion parameters by the method of numerical simulation.