Deformation behaviors and control indexes of metro-station deep excavations based on case histories

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As a part of metro system, the deformation behaviors of metro-station deep excavations are affected by regional geological conditions, supporting structure forms, construction workmanships, etc. Currently, the systemic study based on case histories focusing on a whole city or a whole metro line is relatively limited. Taking Changzhou Metro Line 1 in China as the engineering background, and the field monitoring data of 26 metro-station deep excavations along the whole line are collected. Based on the statistics of collected data, the deformation behaviors of both retaining structure and ground settlement outside the excavation are analyzed, and some empirical relationships are obtained and compared with the statistical results in the other cities. Then, a finite element numerical simulation is supplemented to further study the deformation behaviors of deep excavation and verify the reliability of empirical relationships obtained from field monitoring. Finally, according to the risk levels of deep excavation itself, surrounding environment and geological conditions, different monitoring levels of deep excavations are classified, and the deformation control indexes of metro-station deep excavations under different monitoring levels are given. The research indicates, the maximum lateral displacement of retaining wall is 0.07% ∼ 0.46% of excavation depth with an average of 0.20%; the influence scope of deep excavation is about 3 times the excavation depth behind the wall, and the maximum ground settlement is 0.05% ∼ 0.48% of excavation depth with an average of 0.13%; according to the classification standards of monitoring level, 8 deep excavations are classified into level I and 18 deep excavations are classified into level II in the whole line; the deformation control indexes of deep excavation under level I and II are: 0.17% and 0.27% of excavation depth for the lateral displacement of retaining wall, 0.07% and 0.08% of excavation depth for the lateral displacement of the top of retaining wall, 0.11% and 0.18% of excavation depth for the ground settlement. It is expected the obtained results can provide some references for the construction of Changzhou metro system.