Computational Framework For Multilayer Plasticity Based On Critical State Soil Mechanics

In this work a computational plasticity model for soils under cyclic loading is presented. The model is based on the Critical State Soil Mechanics Theory. Multiple nested surfaces are employed in order to properly predict the soil behaviour under a large variety of loading types. The first, innermost surface of the model acts always as yield surface, whereas the last, outermost surface of the model acts as consolidation surface, a sort of bounding surface. The remaining surfaces are used only as a tool to compute the effective hardening modulus inside the consolidation surface. In contrast with the classical Cam-Clay plasticity, the model permits the dissipation of some energy for cycles inside the consolidation surface, while preserving all the features of the classical Cam-Clay models under monotonic, consolidating loading. The cycles inside the consolidation surface preserve the Masing extended behaviour at any stress level. The model uses a stored energy function for the elastic strains, so elastic strains do not dissipate energy. This is an important feature in a model for cyclic plasticity, as for example in earthquake engineering. The model is amenable of being implemented via a totally implicit algorithm. Two distinct algorithms are present during the integration procedure. One is for the case of loading/unloading inside the consolidation surface. This algorithm is presented in this work. The other algorithm is for the case of loading on the consolidation surface. In this case, a typical Cam-Clay model may be employed without remarkable changes. This work presents a useful framework for the simulation of cyclic loading of soils using nested surfaces plasticity in the light of Critical State Soil Mechanics.