Study Of Pre-cracking Hard Coal By Water Infusion In Sub-level Caving Mining

With the development the sub-level caving, it's scope of being used has increasingly expanded, and has succeeded in using in hard coal seam by artificial assist methods such as water infusion in coal seam, pre-blasting in coal seam. Besides pre-cracking coal, water infusion in coal seam has comprehensive effect on preventing coal dust and fire ,however ,the key of the water infusion is to determine water pressure. Based on the analysis, the paper deeply study the problem of pre-cracking hard top-coal by water infusion, the main conclusions are drawn as follows:(1) In sub-level caving mining, statistics distribution of weibull is adopted to analyzed top-coal failure, damage parameter is defined, the paper use damage mechanics to analyze and point out the relationship between falling ability of top-coal and the coal seam depth, strength of coal, primary facture and horizontal stress.(2) Based on the theory of fluid-solid interaction mechanics , coupling seepage-stress of coal by water infusion is analyzed ,and control equation is established by using the finite element method.(3) Based on existing rock fracture mechanics and meso-damage mechanics, the model of damage localization at the crack tip was quoted, and the strata stress ,water pressure and damage localization stress were considered, the damage localization at crack tip of coal and the criterion of crack development are analyzed and discussed under-water pressure.(4) The paper mainly apply fracture the theory of fracture mechanics to deduce the formula of the minimum water pressure, analyze the influcential factor which have influence upon water pressure in the hard steep coal seam, and reveal the relationship between water infusion pressure and coal seam depth and pitch.