Neohypoplasticity for Sand Coupled With the Generalized Intergranular Strain Concept

This work presents the coupling of the recently revisited advanced hypoplastic constitutive sand model called neohypoplasticity (NHP) with the more recently introduced concept of the generalized intergranular strain (GIS) to account for soil behavior due to small strains. The latter is essential for the simulation of cyclic deformations. In addition to the effective Cauchy-stress $\sigma$ and the void ratio $e$, the resulting NHP+GIS formulation includes a fabric tensor $z$ (to account for the anisotropic soil structure), the intergranular strain $h$, and a cyclic preloading variable $\Omega$ as state variables. The parameter calibration of the 11 NHP and 10 GIS parameters is discussed in detail and significantly simplified compared to previous NHP versions. Element test simulations of monotonic and cyclic tests and their comparison with experimental data from Karlsruhe fine sand (KFS) and Zbraslav sand (ZS) reveal the satisfying performance of the novel model. The NHP+GIS model captures soil anisotropy effects and static liquefaction in loose sand. Cyclic mobility can be modeled irrespective of soil density. Finally, the NHP+GIS model is applied to a bifurcation problem under plane strain conditions, demonstrating its applicability in initial boundary value problems.