Experimental study on excitation effect for unstable rock

The unstable rock has a sudden falling feature, which is a dynamic process to release energy speedily, and will put an evident excitation effect on the rocks around it. The excitation effect can be expressed by the excitation acceleration, peak velocity and excitation displacement. Focusing on the falling unstable rock, an experimental model of excitation effect is proposed. More than 130 thousands acceleration test data are obtained. The test results show that the duration of excitation effect of unstable rock can last about 30 ms; and the values of the excitation acceleration, peak velocity and excitation displacement in vertical direction are about double times larger than the ones horizontal direction; and the excitation acceleration in vertical direction can reach 48.7979 m/s²; the peak velocity is 27.2 mm/s; and the excitation displacement can reach 0.0560 mm. Based on those experimental phenomena, two important issues which must be highlighted for the damage mechanism of unstable rock are analyzed. The first issue is that the stress on the end of dominant fissure in the damage process will evolve from pure tension state to weak shear-strong tension state to strong shear-weak tension state and pure shear state, and the other issue is to describe the mechanical evolution processes for various states, to consider the excitation effect on the damage process of unstable rock, and to analyze the stability of the rock around the damaging moment of the unstable rock. The results may provide a scientific basis for further studies on the collapse mechanism and disaster effect of unstable rock.