Effects of non-coaxiality and soil anisotropy on tunneling-induced subsurface settlements

Nowadays, constitutive models for soils used for numerical modelling of tunnelling are normally restricted to the assumption of soil strength isotropy and coaxiality. A plane strain, elastic-perfectly plastic non-coaxial soil model with an anisotropic yield criterion is proposed. The non-coaxial soil model developed is then implemented into the commercial finite element software ABAQUS via the user-defined material subroutine (UMAT). Numerical simulations are performed on two-dimensional city shallow earth tunnel excavations using the newly proposed non-coaxial soil model. A case study is performed to compare the numerical results with the centrifuge test ones. The results show that the representative soil elements around tunnel experience severe principal stress orientations. The prediction of normalized subsurface settlement trough can be improved by considering the initial soil strength anisotropy. A larger value of the non-coaxial coefficient results in a larger magnitude of the maximum vertical displacement. It is concluded that no consideration of soil anisotropy and non-coaxiality may result in unsafe design in tunnelling.