The Mechanism and the Control Techniques of Water and Sand Inrush in Working Face of Shallow Coal Seam
When a shallow coal seam is mined, water/sand-conductive channels will penetrate the overlying bedrock and link up water-bearing sand layer. If the control measures are inappropriate, water/sand disaster is easy to occur. Firstly, on the basis of analysis of four necessary conditions during formation of water inrush disaster in working face, that is "water-filling source, water-filling channel, water-filling intensity and protection capacity", the thesis pointed out that the reason of water
... reason of water inrush is that the actual water inflow goes beyond the protection capacity in a working face, while what prediction method of water inflow in working face is adopted decides the magnitude of protection capacity, hereby, according to mining sequence and as regard to the difference of water recharge boundary at different mining position such as first mining face, secondary mining face and cross-valley mining face, the matched prediction methods of water inflow were put forward for different mining face by using "the combined method of dynamic and static water ", providing the technical support for determination of the drainage system in mining face, ensuring that no water inrush accident will occur in mining face. Secondly, based on the four necessary conditions during sand inrush disaster, that is" water/sand source, channel, power source and flowing space", it put forward that the critical hydraulic slope initiated by sand particle was taken as discriminate condition, the complete well flow theory of unsteady flow was used to solve the actual hydraulic slope, from the correlation of the actual hydraulic slope of sand inrush and the critical hydraulic slope, the calculation formula for the actual hydraulic slope in water-bursting channel was determined, the corresponding calculation methods were given for their related parameters such as influence radius and width of water/sand-conductive channel, and on the basis of determination of the calculation methods of the critical hydraulic slope, the discrimination Vol. 21 , Bund. 24 7756 formula for the height of water head during water/sand inrush was deduced, providing the theoretic basis for the drop of water head in overlying water-containing sand layer above the mining face threatened by sand inrush disaster .One more, according to the formation mechanism and the occurrence conditions of water/sand inrush disaster, four steps of disaster prevention and control, i.e. "exploration of conditions, determination of the basic factors, prevention and control of water inrush, prevention and control of sand inrush" were put forward, proving technical guidance for prevention and control of water/sand inrush disaster in working face. Finally, aiming at the problem of water/sand inrush in working face 22406 in Halagou Mine, "the combined method of dynamic and static water" was adopted to predict the water inflow at different mining sections of working face, providing the basis for determination of the protection capacity of working face so as to avoid water inrush. Moreover, from the four necessary conditions of sand inrush, through analysis and calculation, it arrives at that the mining face is threatened by sand inrush, on the basis of this, the height of safe water head in overlying water-containing sand layer was determined, technical and engineering measures on surface and in underground mines for prevention of water/sand inrush were proposed, ensuring the safe extraction of working face in section of thin bedrock.