Abstract
Loess geological tunnels are characterized by weak geological structure and poor self-stability of surrounding rock, so effectively controlling the excavation face distances of different caverns is of great significance for guiding the safe construction of large-section tunnels. Based on the excavation of large-section loess tunnel from Xi’an Metro Line 4, the optimal excavation face distance is determined based on Midas numerical model. Then, the surface settlement and horizontal deformation are analyzed based on monitoring data, and, finally, the rationality of excavation face distance is verified. The results show that the influence of excavation face distance on surface settlement, vault settlement, and horizontal deformation is consistent. The surface settlement mainly occurs in the range of −20∼20 m from the tunnel centerline and the settlement trough formed has asymmetric characteristics. The vault settlement and horizontal deformation undergo first a rapid settlement and then a slow settlement. The connection between initial support and middle partition is mainly tensile stress and the middle and bottom parts of the supporting structure are mainly compressive stress. Numerical results suggest that the optimal excavation faces distance of L1, L2, and L3 which can be 4, 9, and 9 m, respectively. Construction monitoring data show that the double-sides heading method has a significant effect on surface settlement, vault settlement, and horizontal deformation. The surface settlement occurs within the range of −17∼6 m from the tunnel centerline. The maximum vault settlement and horizontal deformation are 73.00% and 65.50% of the maximum allowable. It can be seen that the actual excavation parameters optimized by Midas numerical model have high reliability.
Highlights
With the rapid development of urban traffic engineering, subway construction project has become an important symbol of urban construction and development speed [1, 2]
Based on the geological data, this paper first simulates the excavation process of different caverns under different excavation face distances based on the Midas/NX 3D numerical model and analyzes the surface settlement, vault settlement, horizontal deformation law, and the deformation characteristics of supporting structure. en, the optimal excavation face distances are determined based on the numerical simulation results
To accurately determine the influence of excavation face distance of each cavern on the settlement characteristics of ground surface and vault, only one excavation face distance change is considered in each calculation, and the optimal excavation face distance between each cavern is calculated in turn according to the construction and excavation sequence. en, based on the excavation scheme as shown in Figure 1(c) and the numerical model as shown in Figure 2, e influence of excavation face distances L1 (0.5D, 1D, 2D, 3D), L2 (0D, 1D, 2D, 3D, 5D), and L3 (1D, 2D, 3D, 5D) on the surface settlement and vault settlement and horizontal convergence characteristics and distribution characteristics of principal stress of supporting structure are studied
Summary
With the rapid development of urban traffic engineering, subway construction project has become an important symbol of urban construction and development speed [1, 2]. Based on the geological data, this paper first simulates the excavation process of different caverns under different excavation face distances based on the Midas/NX 3D numerical model and analyzes the surface settlement, vault settlement, horizontal deformation law, and the deformation characteristics of supporting structure. Characteristics of surface settlement, vault settlement, and horizontal deformation of tunnel are analyzed based on the actual monitoring data in the construction process using double-sides heading method, the rationality of actual excavation parameters optimized is verified, and the research results have a reference significance for the prediction of settlement and deformation of tunnel surrounding rock
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