Influence of Soft Soil Area River Excavation on Underlying Metro Tunnel Deformation and Control Measures

Abstract

Objective The unloading-induced upheaval deformation resulting from river excavation above metro shield tunnels may affect metro tunnel normal operation. Therefore, it is necessary to study the deformation effects of soft soil area river excavation on underlying metro tunnels and formulate control measures for metro tunnel deformation. Method The general overview of a case project is presented, and finite element method is conducted on its field-measured data analysis to validate the reasonability of the soil constitutive model and parameters. Based on the characteristic soft soil profile and soil parameters of Ningbo region stratum, a simplified soil mass model is established. The impact of changes in river excavation width, depth and the burial depth of soft soil layers on the deformation of underlying metro tunnels is analyzed sequentially. Two deformation control measures of gantry-type soil reinforcement and gantry-type beam-slab reinforcement, are introduced. A comparative analysis is performed between the finite element calculation results considering the control deformation measures and the baseline model. Result & Conclusion During soil reinforcement and river excavation stages, the deformation of underlying metro tunnel manifested as settlement and upheaval, respectively. When maintaining the same cross-sectional area for river excavation, reducing the river excavation depth and increasing the river excavation width are conducive to minimizing underlying metro tunnel deformation. Vertical displacement of the metro tunnel is primarily influenced by the rebound deformation of the soil below it. The gantry-type beam-slab reinforcement measure exhibits a noticeable control effect on metro tunnel upheaval deformation.

Keywords

• metro shield tunnel
• soft soil area
• river excavation
• tunnel deformation
• numerical simulation
• deformation control