1.College of Geosciences and Surveying Engineering,China University of Mining and Technology (Beijing),Beijing ,China;2.State Key Laboratory of Coal and CBM Co-mining,Shanxi Jincheng Anthracite Mining Group Co.,Ltd.,Jincheng ,China

Fault frictional strength is limited condition of in-situ stress,how to evaluate it is a question worth considering in coal and CBM mining process，through the analysis of fault frictional strength and its control on the in-situ stress,the relationship between the ratio of maximum to minimum principal stress and fault frictional strength was established,then the in-situ stress calculation model was set up.Research results show that the ratio of maximum to minimum principal stress is constrained by fault frictional strength in coal seam,which comes to the ultimate of fault friction strength in critical direction,fault slip will occur.Based on the fault classification of Anderson,in-situ stress is divided into three stress states,in-situ stress calculation model of normal fault,parallel displacement fault and reverse fault considering frictional strength are established.The characteristics of in-situ stress for coal reservoirs in the Southern Qinshui Basin are analyzed.There are two different stress mechanisms in different depth of coal reservoir in the Southern Qinshui Basin,when the buried depth is less than 650 m,the original stress is in the normal fault stress mechanism;when the buried depth is more than 650 m,the original stress may be in the stress mechanism of parallel displacement fault.