Finite element modelling of seismic liquefaction in soils

Abstract

Numerical aspects of seismic liquefaction in soils as implemented in the finite element code, PLAXIS, is described in this paper. After description of finite element equations of dynamic problems, three practical dynamic boundary con ditions, namely viscous boundary tractions, tied degrees of freedom and free field elements are reviewed. Possibilities and limitation of each type of boundary condition is highlighted. The formulation of a constitutive model, called as UBC3D-PLM, which describes the mechanical behaviour of soils under cyclic loading is also presented. The model is an extension of the two dimensional UBCSAND model developed at University of British Colombia which utilises isotropic and kinematic hardening rules for primary and secondary yield surfaces to properly take into account accumulation of excess pore water pressure and effect of soil densification during cyclic loading. By means of a simp lified Rowe’s stress-dilatancy theory, the model is capable of modelling liquefaction for different stress paths. It will be presented in this paper how most of the model parameters can be found from the corrected SPT blow count which makes the model easy to use for practical applications. Finally, the model is used for modelling a real boundary value problem and the results are compared with field measurements.