Mechanism of thrust fault rupture causing by unloading effect

Rock burst caused by thrust fault instability,as one of the most common disasters,threatens the safety of coal mines. But it is still unclear on the effect of thrust fault slipping to rock burst,making the prevention of rock burst very difficult. To explore the mechanism of thrust fault rock burst under unloading condition,the features of bursting were analyzed on the basis of engineering and geological conditions of Yima mine. Combining the similar simulation experiment and numerical simulation test, the unloading effect caused by mining disturbance and the fault rupture process were studied. Then the spatiotemporal evolution of displacement field when fault slipped was revealed on the basis of laboratory experiment,afterwards the mechanical model presenting the fault slides was proposed with the stick- slip process. The research results are as follows: ① with the decrease of the distance between the mining area and F16 fault,the risk and released energy of rock burst increase rapidly. ② Mining can cause unloading effect,which is mining disturbance inducing new cracks and partly abscission in the fault,stress concentration and reduction appearance alter- nately in the fault zone,upper part slides counterclockwise and lower part slides counterclockwise. There are four pha- ses,which are linear(I),nonlinear(II),sub-instability(III) and instability (IV) when fault ruptures. ③ The transient normal and shear strain of fault dislocation mainly presents a trend which is sudden drop-sudden increasing-decrea- sing-stability,while the upper part is more unstable than the lower part when the fault slips. Fault rupture is a chain re- action which includes the failures of hypocenter element,surrounding rock bar element,adjacent rock bar element and adjacent fault zone element and so on. New understanding such as the patterns of fault slip under unloading,rupture process and energy transporting etc. ,were described in this paper.