Comparative study of construction methods for deep excavations above shield tunnels

Although an appropriate construction method contributes to minimizing the excavation-induced impact on existing facilities, few studies have focused on the comparison and optimization of the construction methods for engineering projects in practice. In this paper, Three-dimensional (3D) numerical simulations are carried out to compare the construction methods for an excavation above shield tunnels through a case history, which has been constructed by a novel excavation method, referred to as divided alternate excavation method (DAEM). A 3D numerical model is developed in the finite element (FE) software, ABAQUS 6.10, to simulate the practical construction process of the DAEM, and the numerical results are analyzed in combination with the field data. Comparative studies are performed by simulating the hypothetical construction schemes of two conventional excavation methods that were proposed for the investigated case. Numerical results confirm the effectiveness of the DAEM on controlling the excavation-induced underlying tunnel deformation. Extensive parametric studies of the DAEM are performed for further investigation. Through the comparative studies and parametric studies, suggestions are proposed for optimization of construction methods for deep excavations above shield tunnels.