Three-Dimensional Analysis of Complex Deep Excavation Groups Based on Small Strain Constitutive Model

In the process of rapid development of underground space, the scale of excavation group becomes larger and larger. The design and construction of deep and large excavation group in soft soil face greater challenges. It is important to grasp the stress and deformation characteristics of the excavation group and the influence on the environment to ensure the safety of the excavation groups and the rationality of design. Based on the excavation group of Zhapu Road and Tiantong Road in Shanghai soft soil area, three dimensional finite element analyses were carried out by using the Plaxis 3D software package. The soils were modeled by using the HS-Small model, which can consider the properties of soils under small strain. The displacements of the diaphragm wall and the deformation of adjacent subway tunnels were investigated and compared with the monitored data. The study reveals that the soil shear strain is in the small-strain range of less than 1% in the excavation works of foundation pit groups in soft soil areas, which illustrates the necessity of adopting the small-strain soil constitutive model for the finite element analysis of foundation pit groups. Three dimensional finite element analyses can give fairly reasonable predictions of excavation deformation and this method is suitable for deformation analysis of complex deep excavation group.