Study on seepage features of coal-bed cracks under controlling stress

To counter the problems existing in water fracturing method of top hard coal under controlling of strata stress field, the relationship between seepage of open type of crack in coal mass under controlling of stress and capillary force, open degree of crack,stress value and water pressure gradient is studied detailed using hydraulic pressure test. The seepage nature law of crack in stress field is founded, and the influence relationship from pressure and waterpower gradient on the open degree of crack and state of crack stream is inquired. The site investigation results show that at different drain opening in coal mass relief area, the water leakage of open degree of crack is different, the volume below 7% at 3 5 m away from the injection point; below 8% at 2 5 m; below 19% at 1 5 m. The model in this article has practical value to select parameters of controlling hydraulic pressure in water fracturing of coal mass and to improve the rate of top coal recovery.