Search

The importance of physico-chemical processes at the particle scale for the engineering scale behaviour of fine-grained geomaterials is undisputed. Yet, despite great advances in the discipline, experimental evidence that fully resolves the clay micromechanics i.e. linking the evolving microstructure and interparticle actions under loading, is lacking. This paper will discuss the challenges ahead in quantifying the evolving kinematics and interparticle interactions of fine-grained geomaterials. As such, the current limitations, and the potential opportunities of experimental methodologies for manipulating, monitoring and (post-mortem) analysing fine-grained materials at the particle scale will be discussed. In addition to the need of integrating multiple experimental techniques that span several length scales and modalities, the critical role of advanced data reduction and analysis is highlighted, as required for a measurement as opposed to qualitative observation. Throughout the paper, the link between experimental clay micromechanics and modelling will be discussed.

The aim of this paper is to propose a new approach permitting the investigation of the 3D pore variation of kaolin K13 in relation with mechanical loading. A mechanical loading consisting of one-dimensional compression and oedometric loading is applied to a sample of centimeter scale. A postmortem protocol using scanning electron microscopy (SEM) coupled with Focused Ion Beam (FIB) was carried out to observe and then obtain a large number of slices of an extracted sub-volume from the small sample. Image analysis using a new processing method enabled the reconstruction of the observed and extracted sub-volume in the form of a rebuilt sub-volume. The segmentation of pores and particles was carried out using an approach based on machine learning and the pore space properties can be quantified. Pore morphology was identified based on two parameters namely the flatness and the elongation. Spatial orientation can also be locally determined. The proposed treatment enabled the distribution of pore size (termed Im_PSD) to be deduced and these were then compared with the results of Mercury intrusion porosimetry technique. [ABSTRACT FROM AUTHOR]

In this paper, the desiccation shrinkage and cracking of soils are studied in the framework of the extended finite element method (XFEM). The XFEM is introduced first, then, the results of existing desiccation experiments of soils are introduced and analysed, the parameters of the extended finite element model are determined from the results of the desiccation experiments. The finite element scheme used to describe the desiccation shrinkage of soils which obtained from the hydro-mechanical formulation of the continuous medium is proposed. Then, a 3D hydro-mechanical model for the desiccation experiments is established with ABAQUS via the subroutine of UMAT and the XFEM tools in ABAQUS. The proposed numerical approach is validated by reproducing the desiccation experiments. It was shown that the numerical simulations fit well the experimental measurements. The numerical results, on the other hand, provide some useful information about both desiccation shrinkage and cracking of soils. The proposed approach simple and highly efficient and constitutes a promising approach in studying the crack initiation and propagation in soils induced by the desiccation shrinkage. [ABSTRACT FROM AUTHOR]

Desiccation cracking in clayey soils is a complex phenomenon investigated by researchers over many decades. Understanding and mitigating this issue will have a significant influence on the performance of raw earth construction materials and geotechnical engineering. In the current study, the digital image correlation technique was used to provide a thorough insight about the shrinkage anisotropy and the cracking mechanisms during drying. A series of free shrinkage tests were performed on an initially saturated slurries in order to assess the effects of the intrinsic characteristics of the material, the surface tension, the sample thickness and the geometric boundary conditions on the crack initiation and propagation in clays. The results show that increasing sample thickness prevents cracks formation in a non-swelling clay and delays it in a swelling clay. A vertical uplift was observed in the swelling clay due to a concave bending of the material during the desiccation shrinkage. An important anisotropy in the vertical shrinkage was observed compared to the horizontal shrinkage. The geometric boundary conditions indirectly influence the internal drying stress that becomes anisotropic. The intrinsic characteristics have a greater effect on the shrinkage behavior of the material than the hygrothermal and geometric boundary conditions. [ABSTRACT FROM AUTHOR]

This study presents a series of triaxial tests to highlight the effect of saturation degree ranging from 79.8% to 100% on the behavior of sand subjected to cyclic loading, the development of pore water pressure increment, the volumetric strain at liquefaction state, and the behavior of sand subjected to monotonic loading after liquefaction. The tested sand was Hostun RF sand, fine clear sand that has been widely used in laboratory testing in France. The results show that there is a difference between the behavior of samples having saturation degrees higher and lower than 95%. Besides, the development of pore water pressure increment is affected significantly by the value of cyclic stress ratio (CSR) and saturation degree. The Saturation degree also affects the appearance of criteria of liquefaction as Excess Pore-water Pressure (EPP) and Double Amplitude of axial strain (DA). The analysis of the effect of saturation degree on sample volumetric strain exhibits nonlinear liquefaction criteria for a given maximum value of CSR. The monotonic loading tests after liquefaction showed a small difference between the monotonic compressed behavior of the samples before and after liquefaction. [ABSTRACT FROM AUTHOR]

During the drying process, an initially saturated clay deforms mainly due to the loss of water. It causes clay shrinkage that represents one of the fundamental reasons of cracking by desiccation. It is of great interest to understand the desiccation process in such complex soils. However, the main point is that many properties of the material, such as water content distribution, displacement, strain and stress fields, remain difficult to reach by experimental approach only. Numerical simulations may help estimate these variables, and reinforce in a significant way the experimental measurements. The proposed method of analysis allows to understand more deeply the process of drying in clays including shrinkage, crack initiation and finally, crack network development. This research, combining numerical simulations and laboratory tests allows to go further in investigating the drying phenomenon in remolded and initially saturated kaolinitic clay. [ABSTRACT FROM AUTHOR]

The goal in this work is to understand how the microfabric of a kaolinitic matrix evolves when it is submilted to an axisymmetric triaxial loading path. The approach consists in doing a triaxial lest on slightly overcon soli dated saturated specimens, then to follow the microsiructure changes (orientation of the clay particles and porosity) during the test using scanning electron microscope observations. In the initial state, the clay is consolidated under oedometric conditions and the observations show an anisotropy of the microfabric with a preferential orientation of the particles according to the horizontal plane perpendicular to the direction of the loading. On an isotropic path, the analysis shows a progressive reorientation of the particles towards a more isotropic fabric. This evolution continues at the beginning of the triaxial loading, whereas the particles tend to become preferentially oriented along an inclined plane at the end of the loading. The evolution of the porosity is derived from mercury intrusion porosimetry tests, confirmed by SEM photograph observations. The results suggest the existence of a double porosity in the initial state of the specimen. This double porosity seems to be maintained during the isotropic loading, then evolve lowards a unimodal porosity, with a slight decrease in the pore size, during the triaxial loading. Key words: kaolinite, triaxial tests, evolution of the microfabric, scanning electron microscope, mercury intrusion porosimetry L'objectif de cette recherche est de comprendre comment evolue la microtexture d'une matrice kaolinitique lorsque celle-ci est soumise a un chemin triaxial de revolution. L'approche consiste a realiser un essai triaxial sur des eprouvettes du materiau sature faiblement surconsolide, puis a suivre l'evolution de la microstructure (orientation des particules et porosite) le long du chemin de chargement par des observations au microscope electronique a balayage. A l'etat initial, le materiau est consolide de facon uniaxiale, et les observations montrent une anisotropic microstructurale avec orientation privilegiee des particules suivant le plan horizontal perpendiculaire a la direction du chargement. Sur chemin isotrope, l'analyse montre une reorientation progressive des particules vers une isotropie structurale. Cette evolution se poursuit en debut de chargement triaxial pour tendre ensuite vers une orientation privilegiee des particules selon un plan incline en fin de chargement. L'evolution de la porosite est examinee a partir de mesures par porosimetrie au mercure, illustrees par des images seuillees de photos MEB. Celles-ci suggerent l'existence d'une double porosite a l'etat initial, qui semble se maintenir lors du chargement isotrope, puis evoluer vers une porosite unimodale, avec une legere diminution de la taille des pores, sur le chemin triaxial. Mots-cles : kaolinite, essais triaxiaux, evolution microstructurale, microscopie a balayage, porosimetrie au mercure, Introduction Lorsqu'un chargement est applique a une eprouvette d'argile saturee remaniee, en suivant un chemin donne dans le plan des contraintes, il induit des mecanismes de deformation complexes dependant de [...]