| Summary: | 碩士 === 國立中興大學 === 土木工程學系所 === 103 === In order to avoid the impacts of open cut excavation, the No-Dig methods were developed and adopted. The most common No-Dig methods could be pipejacking and shield tunneling in Taiwan area. Certain procedures have been developed to prevent the surface subsidence induced by overcut; however, study of the impacts of vibration on the adjacent surface building is still very limited. When the alignment of a pipejacking or shield tunneling is close to IC factories, low frequency vibrations could be critical to the production of the factories. In this study, numerical method was adopted to simulate the vibration induced by No-Dig tunneling and its impact to the adjacent surface area. Different soil properties and vibration data (waves) were adopted as variables in the simulations. The numerical simulations were used to understand the impacts of vibration at designated locations for a set duration.
There are two primary source of vibration for a shield tunneling, i.e., vibration between disc cutters and mining face, and vibration from the engine and other parts of the shield machine. This study only focuses on the first vibration source. A close relationship exists between the composition of surrounding soil mass and the transmissibility of vibration. Soil possesses a damping property that weakens the vibrations. The 3D finite element analysis software ABAQUS was used in this study. Geometric and material damping effect theories were used to calibrate the analysis results of a small scale model. Then the parameter sensitivity analyses and vibration isolation design analysis of a large scale model was performed.
Single directional vibration in the horizontal direction, i.e., vertical to the excavation mining face, was used in the simulations. The results show that as the horizontal distance from the wave source (vertical) increases the amplitude of the wave also decreases. For the wave with a higher frequency, the energy decays significantly when the wave travels over a distance, as the wave amplitude decreases to an extremely low degree. However, the wave with a lower frequency still retains its waveform. The analysis of the influence on amplitude indicates that the ratio of attenuation is constant for the same material and it is not related to the wave amplitude. Furthermore, analysis of damping ratio effects shows that the wave attenuation increases as the damping factor of material increases. Under the adopted parameters, the analyses showed that vibrations at 20 Hz frequency are difficult to attenuate.
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