A simple dynamic approach for the numerical modelling of soil as a two-phase material

In many geotechnical problems, the presence of water and air in the voids of a soil skeleton has an influence on the behaviour of the soil. Effects such as time-dependent deformations, temporary reduction in the shear strength of the soil or even liquefaction of loosely layered sands can occur. To account for these effects in a geotechnical analysis, the soil has to be considered as a multiphase material with interaction between the single phases. A simple dynamic approach for the numerical modelling of a fully saturated soil with the finite element method using an explicit time integration rule is presented here. The governing equations describing the soil as a two-phase material are implemented within the framework of a user subroutine working as a constitutive model in the analysis. Simple problems considering different boundary conditions, static and dynamic loading conditions and non-linear material behaviour are investigated to verify the implemented approach. The results are compared with analytical solutions and with solutions obtained by the finite element method using an implicit equation solver. Compared with implicit integration methods, the approach presented has the advantage that - for dynamic analyses especially. An explicit integration method is often computationally more efficient for the analysis of large models with relatively short dynamic response times and for the analysis of extremely discontinuous processes such as dynamic pile driving.