Three-Phase FE-Model Including Finite Deformation

The increasing need for fast, convenient and economical transport of people and goods requires an increasing number of subsurface traffic routes. Thus, the construction of shallow tunnels is encountered frequently. In urban areas, ground settlements caused by tunneling may be crucial to existing buildings and infrastructure. If the tunnel has to be driven below the groundwater table, the groundwater has to be displaced from the working area at the tunnel face. In this case, deformations of the ground and surface settlements result from both the dewatering of the soil and the advance of the tunnel face. The research project aims in the extension of a coupled three-phase formulation for tunneling below the groundwater level, using compressed air for dewatering of the soil, to include large deformation theory and an improved constitutive model for unsaturated soils. The coupled three-phase model for the soil, consisting of a deformable soil skeleton and pores filled with water and air, is characterized by treating the flow of the fluids water and air in the soil and the deformations of the soil simultaneously, allowing to take into account intrinsic interactions between the flow and the deformation problem in a physically consistent manner. An extension of the three-phase model to the finite deformation theory is inevitable for assessing the deformation response in soft soils and for considering localization phenomena, marking the initiation of failure. Furthermore, a model taking into account large deformations allows for investigating the limits of commonly employed small deformation formulations. An improved model for unsaturated soils including a suction term yields a more realistic description of the behavior of soils exhibiting pronounced swelling, such as silts or clays.