Perrotta, Laura (2025) Multiscale investigations on Lightweight Cemented Soils (LWCS) through experimental, semi-analytical and computational methods. [Tesi di dottorato]

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Abstract

The doctoral research work is focused on the mechanical behaviour and failure mechanisms of Lightweight Cemented Soils, i.e., heterogeneous geomaterials characterised by a double porosity microstructure consisting of foam-induced large voids immersed in a cemented small-porous soil matrix. The aim of the research is to develop a constitutive model of the material that directly takes into account its complex microstructure. X-ray microtomography scans of LWCS samples at different curing times were performed, allowing to investigate the evolution of the spatial distribution of foam-induced large pores over curing time. Moreover, in-situ triaxial tests (i.e., x-ray scanning performed during triaxial loading) were executed to provide direct three-dimensional observations of LWCS foam-induced porosity changes under loading paths, and the subsequent failure mechanisms. Then, x-ray microtomography scans were coupled with image analysis techniques to obtain the displacement and strain fields of the tested samples. x-ray images were also segmented for defining porosity changes at increasing strain levels. Semi-analytical Mean-Field Eshelby-based Homogenisation approaches were used to determine the elastic relevant mechanical parameters of LWCS, coupled with x-ray microtomography observations. A computational homogenisation procedure was then employed. An insight into the identification of an appropriate Representative Volume Element (RVE) size for random heterogeneous materials, as LWCS, was carried out. The influence of RVE size on the homogenised elastic stiffness of LWCS was evaluated through a numerical model based on 3D scans of the samples. RVE size selection was then validated comparing LWCS elastic stiffness derived from computational homogenisation with available experimental results and with results from Mean Field homogenisation methods. The identified morphologies coming from the x-ray scans were given as an input to a FE model with enhanced discontinuities, so that a direct quantitative comparison between experimental and numerical observations was made. Finally, a new constitutive formulation for LWCS mechanical behaviour was developed within the framework of Thermodynamics with Internal Variables (TIV), through a proper choice of a relevant internal variable. The process developed in the current work to analyse LWCS can be adapted to investigate a wide range of complex and heterogeneous geomaterials.

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