The focus of the project COUPLED was to have a better understanding of the distinct directional dependent response of problematic clayey soils, which results from a preferential arrangement of their soil particles in a given direction (anisotropic fabric). To achieve this goal, the formulation and subsequent validation of a coupled anisotropic constitutive model for soils was developed.
Due to the one-dimensional loading conditions applied to the soil during the compaction process, it is typical in compacted soils to exhibit an anisotropic fabric. Furthermore, the compaction process is carried out under unsaturated conditions, which means that compacted soils are typically unsaturated. Very often, civil engineers use compacted soils for the construction of embankments for rails, roads and flood defences. When the soil of such embankments is subjected to rainfall, it progressively saturates, eventually becoming fully saturated. Subsequently, when the embankment is subjected to dryer conditions, evaporation of the pore water may occur, which restores the initial partially saturated condition of the soil.
A good understanding of how these alternations between saturated and unsaturated conditions of the soil occur as a consequence of seasonal variations is key to the safety of the geotechnical design. This is because both the mechanics and the hydraulics of the embankment are controlled by how water is stored within the pores of the embankment. Such understanding of the processes of saturation and desaturation of the in-situ soil is even more relevant today as climate change is manifesting itself year after year in the form of extreme weather events.
Surprisingly, even though compaction is a broadly used method in civil engineering to improve the mechanical properties of the in-situ soil, very few models for unsaturated soils (if any) account for fabric anisotropy. Therefore, the development of a constitutive model able to handle anisotropic behaviour under partially and fully saturated conditions becomes very relevant for a proper safety assessment of any geotechnical design involving anisotropic soils. Modelling realistically soil behaviour by means of advanced constitutive models is important not only for gaining engineering knowledge on soil’s response, but also because it provides a numerical tool from where soil responses under various loading or environmental conditions can be quantified in a consistent manner. In addition, application of such engineering knowledge to geotechnical design reduces the very large uncertainties commonly faced by geotechnical engineers, contributing to the overall safety of the infrastructure.
The overall objective of COUPLED was to give insight, by means of a novel anisotropic constitutive model, on the mechanical behaviour of soils exhibiting an anisotropic fabric (including fully and partially saturated conditions). The core of the new model is the Glasgow Coupled Model (GCM), an existing fully coupled elasto-plastic constitutive model for saturated and unsaturated soils. To account for anisotropic responses, the GCM is combined with the S-CLAY1, an existing critical state elasto-plastic model for saturated anisotropic soils. The newly proposed model has been named the Anisotropic Glasgow Coupled Model (A-GCM) and its abilities to handle anisotropic behaviour under partially and fully saturated conditions is demonstrated in COUPLED by comparing model simulations against high quality experimental data.
