Numerical Simulation of Deep Excavation Considering Strain-Dependent Behavior of Soil: A Case Study of Tangluo Street Station of Nanjing Metro

A case study of Tangluo Street of the Nanjing Metro is considered to understand the modulus evolution with strain to serve the deep excavation design in the city center for sensitive environment control. Laboratory tests were conducted on soft clay sample from the Yangtze river floodplain to determine the parameters of the hardening soil model with small-strain stiffness (HSS model), and back analyzed using the finite element method. The key parameters of HSS model were determined: the reference tangent modulus, reference secant modulus, reference loading, and unloading modulus and reference initial modulus were 3.4, 1.8, 47.7, and 54.2 MPa, respectively. The simulation suggests that the displacement distribution by the HSS model agrees well with the field measurements. On back-analyzing using the Mohr–Coulomb model with a modulus four to five times the oedometer modulus, the calculated deformation was close to that obtained from simulation using the hardening soil model with small-strain stiffness (HSS model), and in situ observed displacement. This degree of amplification also reflects the deformation-controlling requirement of retaining structures and should be mobilized with changes in the requirement.