As a result of China’s urbanization, it has been a common phenomenon that adjacent deep excavations were constructed near underground structures, which can have a series of detrimental effects on existing tunnels. Thus, it is crucial to assess the tunnel response induced by the overlying excavation, with the aim of maintaining the safety and serviceability of operating tunnels. The shield tunnel is idealized as an infinite beam lying upon a three parameter Kerr-model and the vertical force equilibrium equation of the tunnel element is established. Then, a theoretical solution is derived for capturing the soil–tunnel interaction. To prove the accuracy of the proposed method, the calculation results are compared with field measurements, along with the data of finite element studies. Thereafter, a parametric analysis will be conducted to assess some characteristic factors for tunnel responses caused by overlying excavations, such as tunnel-excavation horizontal distance, tunnel bending stiffness, and the buried depth of the tunnel. The results indicate that the increase in the bending stiffness and the buried depth of tunnel, as well as the tunnel-excavation horizontal distance, will significantly alleviate the tunnel deformation. However, the inner force will be increased when increasing the tunnel bending stiffness.
3 July 2024 in International Journal for Numerical and Analytical Methods in Geomechanics
Metro foundation pits are important components of urban infrastructure projects. Dewatering and excavation are essential stages in foundation pit construction; however, this process can significantly induce groundwater drawdown, as well as diaphragm wall deformation and surface settlement. Based on a subway station foundation pit project, in this study, we employ three-dimensional numerical software to simulate the process of dewatering and excavation. A refined model is used to investigate groundwater seepage, the deformation of the retaining structure, and surface settlement under spatial effects. The finite element model accounts for stratified excavation and applied prestress conditions for the support system within the foundation pit. Its accuracy is validated through a comparison and analysis with measured data from the actual foundation pit. The results indicate that foundation pit excavation leads to significant groundwater drawdown around the pit and the formation of a characteristic “funnel-shaped” drawdown curve. Moreover, extending the diaphragm wall length contributes to maintaining a higher external groundwater level surrounding the foundation pit. The horizontal displacement of the diaphragm wall increases progressively during dewatering and excavation, and the bending moment of the diaphragm wall exhibits a trend consistent with its horizontal displacement. Surface settlement decreases as the length of the diaphragm wall increases.