Hydro‐mechanical response of collapsible soils under different infiltration events

The behavior of a partially saturated soil during surface‐water infiltration is analyzed by means of an elasto‐plastic constitutive model formulated in terms of effective stress and extended to unsaturated conditions. The model is calibrated considering laboratory‐scale experimental results under suction‐controlled conditions. The wetting process in two collapsing soils, initially loaded at in situ stresses, is simulated by imposing two different boundary conditions: surface ponding and water flow. The stress paths resulting from the imbibition process are analyzed at different points inside the layer. Copyright © 2015 John Wiley & Sons, Ltd.     

Consequences on water retention properties of double-porosity features in a compacted silt

The paper deals with an experimental investigation aimed at studying microstructural features and their consequences on water retention properties of statically compacted unsaturated silt. The evolution of the microstructure of the aggregate fabric induced by compaction is investigated by studying the pore size distribution changes under different initial conditions (void ratio and water content). The material used is low plasticity silt from Jossigny near Paris, France. A series of mercury intrusion porosimetry tests (MIP) were performed at different void ratios and water contents to provide microstructural information. The arrangement of aggregation/particles and pore network was also investigated with environmental scanning electron microscopy (ESEM). The MIP data were used to determine the water retention curve on drying for the specific pore network configuration induced on compaction. The MIP data were used to formulate and calibrate a multimodal water retention model for a specific pore network configuration, which is obtained by linear superposition of subcurves of a modified van Genuchten type. The study is then complemented with controlled suction oedometer tests on compacted samples to obtain the water retention properties of the material at two different void ratios. Finally, we compare the water retention properties obtained by the simulated progression of the different pore network configurations induced on the hydraulic path with the water retention properties under suction-controlled conditions. Good agreement between the two methods for the drying path is reached.     

Numerical analysis of wetting-induced instabilities in partially saturated soils under plane strain conditions

This paper concerns the hydromechanical stability of partially saturated soils during wetting. The response of a loose silty sand is numerically/theoretically investigated with the main aim of identifying both triggering mechanisms and predisposing factors to instability. This latter is testified by both a rapid increase in the pore water pressure and an unexpected loss of numerical convergence. The study has been conducted at different scales from laboratory tests to boundary value problems, and in both cases, the controllability theory has been employed to both interpret and justify the numerical results.     

Unsaturated structured soils: constitutive modelling and stability analyses

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.