Abstract：Surface subsidence induced by underground coal mining can have severe damage to civil-engineered structures and residential property on the ground surface. The technique of grouting into the separated strata to control the surface subsidence is a novel technique widely applied in some coalfields in China. It has been proved to be an economic and effective method to control the movement of the strata and the formation of the subsidence. Though great process has been achieved，the mechanism of controlling the subsidence remains unclear since the movement and bed separation characteristics of overburden strata above mine voids induced by underground mining are very complicated problems influenced by many factors. One of the important tasks in the technique of grouting into the mining induced separated strata to slow down the surface subsidence is to determine the location of the separated strata and the magnitude of bed separation. Despite many years of considerable descriptive research，an accurate quantitative method for bed separation does not appear. In the paper，the location and the magnitude of separated strata during coal mining operations was analyzed and the rationality of the boundary conditions was validated on the basis of the elastic shell theory and the correspondingly calculating equations of bed separation was formulated in the end. It will be helpful for a better understanding of the bed separation characteristics induced by mining extractions and a wide application of the technique of grouting into the separated strata to control the surface subsidence.
