Abstract:

As the land resources become more and more valuable, the excavation of superdeep foundation pits and the construction of superhighrise buildings above existing tunnels have become a trend of the development of downtown area. However, ensuring the safe operation of the existing tunnels is a prerequisite for the development of the new projects. With Yuzhong Midtown Project and the existing highway tunnel running below the project as the research background, the authors establish the threedimensional model to simulate the whole process of tunnel construction, deep foundation pit excavation and building group loading by using Midas/GTS finite element software. In the process of analysis, the authors analyze the quality defects of the tunnel, such as the cracks and the lack of lining thickness at local positions, considering the features of the tunnel construction, the inspection results of the status of the tunnel, as well as the surrounding rock loosening ring and the material degradation. The authors also analyze the degree of the impact of the project construction on the tunnel in aspects of displacement field, stress field, plastic zone distribution and lining internal force changes. Conclusions drawn are as follows: 1) In the process of the construction of the project, the change of the vertical displacement of the crown is more obvious than that of the horizontal displacement of the arch side; 2) The influence of the excavation of the foundation pit on the displacement of the tunnel is severer than that of the loading of the buildings; 3) The change of the internal force of the tunnel lining is not obvious, the safety factor of the tunnel lining can meet the requirements of relevant codes and the safe operation of the tunnel can be ensured.

Key words: highrise building, ultradeep foundation pit, existing tunnel, finite element analysis