Factors influencing vibration effects induced by in-situ stress transient unloading of deep rock mass

The blasting vibration control is one of the most significant factors during deep tunnel excavation. In this study, the characteristics and influencing factors of vibration induced by ground stress transient unloading were investigated by an integrated approach of field monitoring and numerical simulation of the diversion tunnel No. 2 of Pubugou hydropower station. It is shown that the induced vibration by in-situ stress transient unloading of excavation surface plays an important role in the whole blasting excavation vibration under the medium and high in-situ stress conditions. When the wave impedance of rock is fixed, the induced vibration is controlled by the in-situ stress level, initial stress of excavation surface, excavation surface area and vibration attenuation index. The intensity of induced vibration is the highest at the station when the comprehensive effect of excavation surface in-situ stress and excavation surface area reaches the greatest. The blasting vibration intensity of deep tunnel is governed by the combined effect of explosion and in-situ stress transient unloading. The induced vibration can be effectively reduced by decreasing the row spacing of blast-holes and excavation footage, and adopting small holes diameter and partial excavation methods during deep tunnel excavation.