RESEARCH ON TRANSIENT CHARACTERISTICS OF EXCAVATION UNLOADING

On the basis of the analysis of process of excavation unloading and the calculation of its releasing duration,it is shown that the excavation unloading during rock blasting is a transient process under middle to high in-situ stress conditions.It is proposed that the transient characteristics of the excavation unloading and correspondingly induced dynamic responses of surrounding rock should be considered under middle to high in-situ stress conditions.Problems such as the determination of divisional excavation unloading corresponding to millisecond delay initiation,the path of transient releasing of excavation unloading,releasing of excavation unloading-induced vibration and the mechanism of dynamic loosening of jointed rock mass induced by the transient unloading of in-situ stress,etc.are also discussed.Finally,two historical cases of excavation unloading-induced vibration and dynamic failure of jointed rock mass in Pubugou and Ertan Hydropower stations are presented as verifications.