Critical failure time of roof and standing pillars in China western mining area

Stress and displacement field of roof and standing pillars ( RSP) are always in a state of flux,its stability should be studied before recovering the standing pillars. The creep process of coal pillars is analyzed by Flac3D . The process could be divided into three stages:rapid deformation,slow deformation and accelerating failure. Also,the laws of plastic zone and inner stress distribution pattern of coal pillars at different stages are obtained. Based on the theoreti- cal analysis,one thin plate on elastic found model is established to analyze the relationship between the roof deforma- tion,the force on the pillars and the ranges of plastic zones of coal pillars,and the proposed model allows to reveal the dynamic evolution of the decreasing-failure process of RSP. Furthermore,a criterion for evaluating the critical failure time of RSP is then given in this study,which is illustrated through an engineering case.