Analysis on instability deformation and burst liability of composite weak structures

In order to control the stress concentration and energy accumulation in impact coal-rock mass,the concept of composite weak structure is proposed. Based on the strength ratio and volume of the soft-hard strata,the composite degree KC,which can pinpoint the stress concentration and energy dissipation degree of composite weak structure,is introduced. On this basis,the RFPA numerical simulation method is used to compare and analyze the instability characteristics and stress-strain curve changes in various composite weak structures. Weakening the impact tendency by composite weak structure from the point of view of burst liability is studied. The results show that strength ratio and volume size are the main factors for composite weak structure to control impact energy,the weakening stage in the process of failure and instability of composite weak structure is the unique stage of dissipating impact energy,and the dissipation degree is closely related to the KC. The KC not only change the fracture development degree,failure form and stress-strain curve of the whole structure,but KC is also inversely proportional to the maximum concentration stress,stress peak location and energy dissipation degree; the dissipative effect by the composite weak structure is verified by the elastic energy index WET and the impact energy index KE. Composite weak structure can reduce the elastic energy stored in coal-rock mass and increase the loss of dissipative energy,which can weaken the burst liability of coal-rock,reduce impact energy release and risk level,and achieve the purpose to prevent and control the rockburst.