Generalized intergranular strain concept and its application to hypoplastic models

This work presents a generalized approach for the consideration of small-strain effects in constitutive models for soils. These are thereby particularly important for the simulation of cyclic deformations of soil subjected to small strain amplitudes. The novel generalized intergranular strain (GIS) approach represents an overlay concept for constitutive models and is based on the well-known intergranular strain (IS) concept after Niemunis and Herle (1997), resp. its improvement (ISI) after Duque et al. (2020). However, the novel GIS concept can easily be transferred to different constitutive models (e.g. hypoplastic or elasto-plastic formulations). Based on an extended generalized hypoplastic formulation, the GIS concept is combined with the base hypoplastic constitutive model for sand after von Wolffersdorff (1996) (HP) incorporating the extracted asymptotic state boundary surface (ASBS). The latter is derived and visualized. Different element test simulations with the coupled HP+GIS model and the well-known HP+IS formulation are presented and compared using a parameter set of Zbraslav sand. Thereby, the intrinsic feature of the GIS concept, which prevents overshooting of the ASBS, becomes apparent. Based on the ISI formulation, nonlinear accumulation effects can be reproduced in the GIS concept using a further scalar historiotropic state variable.