Experimental and numerical analysis of the unsaturated soil shrinkage and swelling behaviour under different compaction conditions

(English) The thesis presents part of an ongoing nvestigation on the Thermo-Hydro-Mechanical (THM) behaviour and cracking of deformable unsaturated soils undergoing cycles of drying and wetting. An experimental approach was first adopted to understand the principal mechanisms of the THM behaviour. A main principal variable is the negative porewater pressure (suction). Suction is an essential component for the constitutive relations. Direct measurements at high suction range is only possible to this date using High Capacity Tensiometers (HCTs). As such, the novel Northumbria HCT (N-HCT), with an extended suction measuring range (3.5 MPa), was sought after. The N-HCT was employed, in conjunction with other established and proposed direct and indirect suction measurement techniques, to provide the full suction measurement range (saturation to dry conditions). Additionally, a unifying volumetric measurement technique is proposed, based on defining a mathematical model that describes a unique relationship between void ratio and water content, referred to as the Soil Shrinkage and Swelling Curves (SSCs). Having a well-defined SSC, along with the full suction range, allows obtaining complete Soil Water Retention Curves (SWRCs), in drying and wetting paths. SWRCs are a main characterising component of constitutive models for describing the porewater retaining capacity and flow. Obtaining the SWRCs and SSCs provides the relationship between the evolution of the three main variables of the unsaturated soil behaviour: porewater, suction, and void ratio. Additionally, the desaturation and saturation rates were computed. A novel approach is proposed to divide the soil drying into five stages, and the wetting to another four stages. Different yielding points are suggested to mark the transition between the proposed stages, with each holding a coupled hydromechanical significance. While some of the transitional points are conventional, the role of the inflexion point of the SWRC is yet to be established. A strong correlation between the latter and the shrinkage limit is determined and verified for various soils from the literature encompassing different soil types, fabrics, and textures. Finally, the implication on the mechanical constitutive relations and the geotechnical designs is studied. The principal aim of this thesis was to construct a full numerical model that can replicate, to high accuracy, the THM behaviour of soils exposed to free atmospheric conditions. Hav