| Based on the Artificial Island of Hong Kong-Zhuhai-Macau Bridge Project, firstly the impact of free field boundary condition on the field seismic response is analyzed aimed at free field model. And using the artificial island model that Yan-Jing-Ru established, the article analyzes the impact of free field boundary condition on the artificial island site. Then acceleration responses of artificial island-foundation system and the peak displacement of the island surface were studied subjected to unidirectional, bidirectional and multidirectional earthquake loading of different spectral characteristic composition. The main work and conclusions are as follows:1. The impact of free field boundary condition on the dynamic response of the site with island and the free site are analyzed and compared, the results indicate that, the acceleration along the ground survey line of the free site and the artificial island site is larger than that without taking free field boundary condition into consideration. And the peak acceleration along the depth is gradually increasing when considering the free field boundary condition. While the acceleration firstly increases and then decreases along the depth when neglecting the free field boundary condition, which is not in accord with the practical. After the artificial island was constructed, the peak acceleration of the artificial island surface is smaller than the corresponding free site, and so is the Fourier spectrum. So constructing the artificial island make the vibration energy decreases. At the same time, the results indicate that soft site will filter the most high frequency components and remain the low frequency components.2. The impact of free field boundary condition on the peak displacement and settlement of the site with island are analyzed and compared in different cases, the results indicate that, the impact of free field boundary condition on the peak displacement of X along the ground surface is not remarkable, while on the peak displacement of Z is remarkable, and the result is larger than that without considering the free boundary condition. The impact of free field boundary condition on the settlement of the ground surface is remarkable. And the settlement is larger when taking the free field boundary condition into consideration.3. The largest stress position of the piling wall is consistent no matter if considering the impact of the free field boundary condition. And the largest stress appears in the position of the piling wall that the curvature great. When considering the impact of free filed boundary condition, the stress is larger especially when the model is subjected with bidirectional earthquake loading. The impact of free field boundary condition on the X displacement of the pilling wall is larger, in particular that the X displacement along the depth of the pilling wall varies smaller when considering the impact of free field boundary condition. At the same time, the displacement of the pilling wall along the short axis is greater, which means that the pilling wall is instable along the short axis. So it is necessary to strengthen the artificial island slope protection. |
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