Abstract
The paper presents a new single-surface elasto-plastic model for unsaturated cemented soils, formulated within the critical state soil mechanics framework, which should be considered as an extension to unsaturated conditions of a recently proposed constitutive law for saturated structured soils. The model has been developed with the main purpose of inspecting the mechanical instabilities induced in natural soils by bond degradation resulting from the accumulation of plastic strains and/or the changes in pore saturation. At this scope, the constitutive equations are used to simulate typical geotechnical testing conditions, whose results are then analysed in light of the controllability theory. The results of triaxial tests on an ideal fully saturated cemented soil and on the corresponding unsaturated uncemented one are first discussed, aiming at detecting the evidence of potentially unstable conditions throughout the numerical simulations. This is followed by similar analyses considering the combined effects of both the above features. For each analysed case, a simple analytical stability criterion is proposed and validated against the numerical results, generalizing the results, and highlighting the crucial role of state variables and model parameters on the possible occurrence of failure conditions.
Highlights
Natural soils can be structured, according to Burland [10] or Leroueil and Vaughan [37], and partially saturated
The model has been developed with the main purpose of inspecting the mechanical instabilities induced in natural soils by bond degradation resulting from the accumulation of plastic strains and/or the changes in pore saturation
The model aims at reproducing the main features of the hydro-mechanical response of unsaturated cemented soils under monotonic loading conditions, adopting a single-surface isotropic hardening elasto-plastic formulation based on a single stress variable to account for partial saturation effects
Summary
Natural soils can be structured, according to Burland [10] or Leroueil and Vaughan [37], and partially saturated. Despite the rather different origins, structure and partial saturation share some similar mechanical effects as both induce higher initial stiffness and strength which, at the microstructural scale, should be qualitatively related to the enhanced interparticle bonding due to cementation or capillary menisci, respectively. The model aims at reproducing the main features of the hydro-mechanical response of unsaturated cemented soils under monotonic loading conditions, adopting a single-surface isotropic hardening elasto-plastic formulation based on a single stress variable to account for partial saturation effects. The effects of structure degradation and partial saturation on the response of idealized natural soils are numerically investigated adopting the proposed model, separating first and combining these two key features. Some conclusions are addressed, together with possible future developments of the research
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