No abstract

It is shown that the use of visco-plastic shear or volumetric strain as the stress history-independent hardening parameter in an elasto-viscoplastic model for sand may result in inaccurate numerical simulations of geotechnical boundary value problems. A new elasto-viscoplastic constitutive model for sand is proposed, formulated based on a stress path-independent irreversible (or visco-plastic) strain energy-based hardening function. The function was derived based on results from drained plane strain compression (PSC) tests on saturated dense Toyoura sand along a wide variety of stress path. The model is coupled with an existing isotropically work-hardening and-softening, non-associated, elasto-plastic model for sand. The constitutive model takes into account the eŠects of loading rate due to viscous properties on the stress-strain behaviour as well as those of pressure level, inherent anisotropy and void ratio and work softening associated with strain localization into a shear band. It is shown that the proposed model can much better simulate the eŠects of stress history on the deformation characteristics of sand than many previous models. The FEM code incorporating the model is validated by simulating physical PSC tests and bearing capacity model tests of a strip footing on sand performed by previous studies.

Differences in the strength and deformation characteristics in plane strain compression between different batches of two sand types were critically evaluated. Two types of plane strain apparatuses were used. Large differences were observed between different batches of each type of sand, yet virtually no differences were found in particle physical properties including gradation, specific gravity, minimum and maximum void ratios, particle shape, and crushability. For each type of sand, differences in the measured peak strength between two types of plane strain tests were very small when effects of several possible influencing factors were accounted for. The prepeak dilatancy characteristics were noticeably different between the two types of plane strain tests, but the reason(s) could not be identified. The trend of inherent strength anisotropy was found to be very similar for the two plane strain apparatuses, but did depend on the sand type.