Precutting of tunnel perimeter for reducing blasting-induced vibration and damaged zone - numerical analysis

Abstract

Cost-effective tunnel excavation can be achieved with the blasting method. Unfortunately, blasting technique brings with it blastinginduced vibration and noise, which can cause critical social problems such as public complaints. Thus, the development of a novel tunnel excavation method, one that can reduce the blasting-induced vibration, is strongly demanded for the effective management of urban spaces. Thus, this study introduces an innovative vibration-reduced excavation method that combines the conventional blasting technique with the precutting process and carries out a feasibility study of the proposed tunnel excavation method using three-dimensional finite element analyses. The micro-scale study focuses on the stopping holes and contour holes while the macro-scale study deals with the case of a real scale tunnel. From the micro-scale analyses, it can be deduced that the proposed method is effective for the reduction of blasting-induced vibration compared to the conventional line-drilling method. From the macro-scale simulation, it is found that the reduction of blasting-induced vibration is independent of the thickness of the precutting free surface but dependent on the depth of the precutting free surface. As the depth of the precutting free surface increases, blasting-induced vibrations as well as the depth of the excavation-damaged zone can be significantly reduced. Vibration energy induced by blasting does not transmit through the free surface and is trapped inside the target tunnel face. Guided blasting waves cause stress concentration at the target face and maximize the blasting efficiency. It is expected that the construction cost will decrease due to a decrease in the number of drilling holes, the weight of the explosive charges, the overbreak space, and the excavation-damaged zone. In particular, the reductions of the overbreak space and excavation-damaged zone enhance the safety of tunnel construction.