By the finite difference software package fast lagrangian analysis of continua(FLAC)

a time-relied analysis is carried out to study failure process of heterogeneous serial and parallel rock pillars under cyclic dynamic loading. The theory of loading-unloading response ratio(LURR) is introduced to analyze dynamic stability of pillar. A LURR model of pillar is established by studying the laws of loading-unloading response ratio of pillar under dynamic loading. Through analyzing on the failure process of pillar

the loading-unloading parameter is determined as the periodical variation of dynamic loading. The displacement of pillar key point and elastic strain energy evolution regularities of failure elements are selected as loading-unloading response parameters respectively. Thereafter

the LURR time series of pillar is determined during the period of dynamic loading. It is found that the parameter Y of LURR can measure unstable degree of pillar. It can be applied to evaluate the stable state or predict the peak strength of pillar effectively. The results show that the loading-unloading response ratio theory is a very effective nonlinear dynamic analysis method in the dynamic stability prediction of underground pillar.