Unsaturated structured soils: constitutive modelling and stability analyses

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.

Wetting-induced instabilities: triggering mechanism and predisposing factors

“…The hydro-mechanical soil behaviour was described by combining the WR2-Unsat model [9] and the Van Genuchten relationship for the definition of the Water Retention Curve (WRC).…”

“…The ideal wetting tests were performed on elementary soil volumes under the usual geotechnical testing conditions by controlling water content and total stresses. The soil behaviour was described using the WR2-Unsat model [9], consisting of an extension to unsaturated conditions of a recently proposed constitutive law for saturated structured soils [10]. The retention behaviour was described by employing the well-known Van Genuchten model, establishing a oneto-one relationship between suction and saturation degree.…”

Elliptical cylindrical equivalent model for consolidation of unsaturated soil improved by PVD

“…[21][22][23][24][25][26] In the past decades, many scholars have been aware of the importance of unsaturated soil, and have paid more and more attention to the unsaturated soil mechanics. [27][28][29][30][31][32] With the great progress made, many well-developed consolidation theories for unsaturated soils have been available. Barden 31 pioneered the analysis of 1D consolidation of compacted unsaturated clay.…”

“…Unsaturated soil is a three‐phase system composed of a soil skeleton, water, and air, which leads to more complex compressibility and seepage situations than those of saturated soil 21–26 . In the past decades, many scholars have been aware of the importance of unsaturated soil, and have paid more and more attention to the unsaturated soil mechanics 27–32 . With the great progress made, many well‐developed consolidation theories for unsaturated soils have been available.…”

Evolution of anisotropy with saturation and its implications for the elastoplastic responses of clay rocks

“…Many hydromechanical models in the unsaturated range have been developed to model porous media subjected to drying and wetting process. [46][47][48][49][50][51][52][53][54][55][56] Some of these models [57][58][59] extend the modified Cam-Clay (MCC) model 60,61 or the Barcelona Basic Model (BBM) 62 to account for the mechanical behavior of partially saturated materials. Various authors have further extended these plasticity models to account for the effects of evolving anisotropy.…”