Integrated Assessment for the Deformation of Ground Surface and Tunnel Invert Induced Deep Excavation

The surface deformation behind deep excavation support in sand soil was validated. Furthermore, the displacement of ground surface and invert of buried circular tunnel (diameter D = 6 m) induced by deep excavation in layered soft soil was evaluated. The validation was performed for the results of centrifuge models of sand soil by applying Mohr-Coulomb model (MC) in 2D finite element analysis. In addition, the evaluation was conducted for the MC model by applying Hardening Soil with Small Strain Stiffness (HSS) on a model in soft soils. Beginning an excavation in soft soils causes drawdown stresses that causing an abrupt increase in tunnel movement (strain dependent stiffness). MC model cannot adopt the effect of excavation increase on the surface of soft soil and on the invert of tunnel (under-predicted deformation). HSS adopts a steep drawdown for soft soil surface above the tunnel and indicates a marked decrease in the heave of tunnel invert (over-predicted deformation). According to the deformation of sand surface behind diaphragm wall of excavation, an accepted convergence was observed between the centrifuge sand tests and 2D numerical analysis.