The object of this study is to investigate the unloading failure mechanism of hard rocks in the unloading process. A commercial finite element program LS-DYNA was employed to simulate the rock unloading process. The implicit and explicit methods were performed in sequence to simulate the static initialization-dynamic unloading process of rocks. The numerical results indicated that the rock failure can be induced by releasing of the initial stress, and the previous result of the equivalent initial stress release rate (EISRR) theory based on the 1D stress state is not suitable for 3D stress state. In 3D stress state, a new definition of equivalent strain energy release rate (ESERR) was introduced. The further study indicated that the ESERR can characterize the effect of different confining stresses and different unloading path on rock unloading. A significant finding is that the ESERR can quantitatively describe the characteristics of the unloading process under 3D stress state. This finding indicated that in practical underground excavation engineering, dynamically controlling the ESERR can be used to increase excavation potential of rocks and minimize the needed external excavation energy by using the initial energy.'

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