A Continuum Model for Soil Large Deformation and A Study on Numerical Aspects of Strong Discontinuities

A three-invariant continuum cap plasticity model is developed for modeling large deformation of soil. This model is capable of simulating multiple failure mechanisms including loss of strength under tension and combined shear and compaction yielding. It features a nonlinear pressure-dependent shear yield surface as well as a cap surface governing inelastic compaction hardening which is formulated as an explicit expression of porosity. A set of numerical examples are carried out, including triaxial compression and compression-shear test, in order to examine the model under confined loading conditions, and observe performance of the model when spectral directions are changing. Also, a comparative study is performed that investigates numerical features of different schedules, end-of-step vs. within iterations, for updating fracture path by employing the local and global tracking strategies. Embedded strong discontinuities within an enhanced finite element framework are used to model propagating discontinuities and fracture behavior of quasi-brittle materials. It is shown that end-of-step updating, which is a standard, can cause inaccuracies in peak strength and fracture energy for large time steps. Updating within iterations rectifies the accuracy issues, but at the expense of an increased computational cost. Both schedules yield comparable performance as the step size is refined.