Experimental and constitutive modelling of microstructural-hydro-mechanical coupled behaviour of saturated and unsaturated soils

Wu, Tianchi 2024. Experimental and constitutive modelling of microstructural-hydro-mechanical coupled behaviour of saturated and unsaturated soils. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

Microstructure plays a foundational role in the hydro-mechanical behaviour of soils, including volume change, strength, water retention ability and permeability. It is important to study the interaction between microstructure and the hydro-mechanical behaviour of soils, which can provide a better understanding of the behaviour of soil from the perspective of microstructure. This study presents both experimental and modelling work on microstructural-hydro-mechanical coupled behaviour of fine-grained soils. For the experimental investigation, pore size distribution (PSD) is adopted as the indicator of microstructure, the coupled behaviour is thus the interaction between evolution of PSD and mechanical loading or volume change. Compacted samples of a soil (low-plastic silt) were tested under various loading conditions, including compaction, saturation, consolidation, saturated isotropic loading and saturated and unsaturated shearing. Further, the PSDs of the samples under specific loading conditions were determined by Mercury Intrusion Porosimetry (MIP) tests. The soil-water characteristic curves were also obtained by chilled-mirror dew point tests to study the water retention behaviour of the soil. For the modelling investigation, a constitutive model based on the evolution of microstructure is established building on the approach of an existing mechanistic model. In this model, the evolution of microstructure is represented via changes in the pore size distribution (PSD) and assumed to be related solely to the change of void ratio induced by loading and unloading. A PSD-dependent Bishop’s effective stress coefficient χ, which represents the coupled impact of PSD evolution on hydro-mechanical behaviour of soils, was used to calculate the effective stress. The model can reproduce and predict the hydro-mechanical behaviour and evolution of microstructure and their interaction within a unified framework. It also has a potential in studying soil-water characteristic curve and multi-field-coupling of soils. Model response and sensitivity analysis are reported based on idealized parameters to give a primary evaluation on the performance of the model and feasibility of using PSDs from MIP. Model validation was conducted by comparing the modelling results and the experimental results of the low-plastic soil. According to both experimental and modelling results, it can be concluded that the compression of volume mostly evolves from the decrease of the volume of larger pores while small pores are less affected but sensitive to change in degree of saturation. The interaction between PSDs and hydro-mechanical behaviour can be satisfactorily reproduced and predicted by the PSD-dependent model. This demonstrates the potential of considering the effects of microstructure when studying the hydro-mechanical behaviour of other soils and applying the microstructural-hydro-mechanical coupled behaviour in engineering applications.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Engineering
Uncontrolled Keywords:	Soil microstructure; Constitutive model; Hydro-mechanical behaviour; Triaxial tests; Mercury intrusion porosimetry; Soil-water characteristic curve
Date of First Compliant Deposit:	9 May 2025
Last Modified:	09 May 2025 15:52
URI:	https://orca.cardiff.ac.uk/id/eprint/178182

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