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...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2023 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/690023 |
| Acceso en línea: | http://hdl.handle.net/10803/690023 https://dx.doi.org/10.5821/dissertation-2117-402165 |
| Access Level: | acceso abierto |
| Palabra clave: | Àrees temàtiques de la UPC::Enginyeria civil 624 |
| Sumario: | (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. Having such a fully capable model would significantly reduce the uncertainties during the design process of any infrastructure and earthworks project using soils as engineered material (embankments, slopes, landfills). The constitutive equations and their corresponding parameters must be well-defined. The experimental campaign helped caliberate the mechanical component, the SWRCs, and the hydraulic, relative, and thermal conductivities for the soils being simulated. The applied atmospheric conditions on the soil surface are translated into imposed numerical boundary conditions. This entails all relevant atmospheric factors: wind (to transfer coefficients), temperature (heat flux), relative humidity (vapour concentration), rainfall (infiltration rate), and solar radiation (heat flow rate). The developed model successfully captures the THM behaviour and the cracking intensity of the soil exposed to different atmospheric conditions. The simulations were carried out on seven different laboratory specimens in an environmental chamber with controlled atmospheric conditions and one larger-scale field experiment exposed to free atmosphere. Having a developed model capable of simulating soils prepared at a wide variety of different initial conditions and exposed to varying imposed atmospheric conditions can prove to be a valuable feature to predict cracking and shrinkage behaviour for advanced designs of infrastructures using soils as engineering materials. |
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