Prediction And Study On Water-inrush From Floor In Three-Soft Coal Seam With High Intrusion In Liu Jialiang Coal Mine

In North China area, the floor aquiclude of coal mines are faced with water inrush due to Ordovician high pressure water with the depth of mining increasing. The hidden fracture in floor aquiclude shorten the effective thickness of aquiclude Under the conditions of mining with pressure, and the nature water intrusion fracture developed to be the water inrush channel affected by the combination of water pressure and mine ground pressure during coal mining. The degree of progressive intrusion hight differs due to the lithology combination of floor aquiclude, so it is meaningful to study the extension of hidden fracture in "three soft" coal for water-inrush prevention.In this paper, the author use material simulation experiment to observe the characteristics of stress deformation and failure of floor during coal mining when hidden fractures exist in the floor aquiclude, and study the mechanism of progressive intrusion water-inrush. Then combine the initial stress condition and principle of rock damage, study the stress deformation and failure of floor and calculate the floor damage depth under mining and the progressive intrusion hight of pressure water by taking the model of progressive intrusion water-inrush for an example. Finally, the author evaluate the water-resistting performance of floor aquiclude and predict water inrush through numerical simulation according to the geological conditions of working face5124in Liu Jialiang coalmine uner pressure mining by detecting the initial intrusion hight,the original rock stress test, the floor damage depth under mining. Following conclusions are drawn in the study:(1) It is indicated that fractures of different occurrence are effected in different degree in the material simulation experiment. The fracture present to be state of tension when the tendency of the fault is consistent with the advancing direction of working face, in this condition, it contributes to water-inrush, and the fracture is effected in the deep area containing water at first, while the fracture in shallow area is effected latter, otherwise, the water-inrush possibility is low.(2) Stress-strain test is used to detect the floor damage depth during mining as a new way, by coupling filling the strain sensors with concrete in the drill holes, make sure that the elasticity modulus of concrete is consistent with rock in measuring, and take the ultimate strain of concrete when it is broken as the standard to evaluate the floor damage depth, good results have been achieved.(3) Use elastic mechanics to analysis the stress distribution, and take the floor aquiclude in goaf as rectangular plate. Calculate the component of stress according to the boundary conditions, it is indicated that shear stress τxy is the main force to cause interformational sliding in floor aquiclude, while horizontal stress σx,σy is the main force to cause vertical cracks, heaving floor and the rapture. The maximum main stress of floor is proportional to the square side length of goaf area and confined water pressure, while it is inversely proportional to the thickness of floor aquiclude.(4) Use FLAC3D software to simulate the process of coal mining according to the geological conditions of wokingface5124in Liu Jialiang coalmine. Take Mohr-Coulomb theory as the principle to judge the destruction of rock, the residual strength after the rock is broken is shown by stress-strain softening model. Calculate the influence of coal mining according to the given boundary conditions and groundwater pressure, it shows that soft rock has the ability to resist deformation, espically, the rock mass made up with soft and hard lithology has a stronger water-resisting ability. The progressive intrusion fracture could not run through the whole floor, and the effective thickness can resist water pressure from confined water, in the end, the working face advanced safely, which proved the prediction is right.