Influence of the Initial Clay Fabric on the Progressive Destructuring Process under One-Dimensional Compression

This study aims to show how the interactions between clay particles and their environment can influence the fabric structuring of clayey soils, as well as to highlight the consequences on their mechanical behavior. For this purpose, samples of kaolinite clay sedimented within solutions at different pHs, which may induce either flocculated or dispersed clay fabric, were prepared and analyzed. The approach consists of using sedimentation tests to form different microstructures at the slurry state of the clay; then, oedometric tests and the scanning electron microscopy (SEM) technique were used to analyze both mechanical behavior and clay microfabric features at different loading levels. It was found that during the sedimentation, low pH values produced flocculated clay particles forming aggregates with edge-to-face (EF) associations, resulting in a clay fabric with large voids. In contrast, at high-pH conditions, kaolinite particles were dispersed with face-to-face (FF) associations, resulting in denser fabric and reduced poral spaces. By increasing the one-dimensional compression load, the initially flocculated-structured clay showed a higher compression capacity than the initially dispersed-structured clay, due to the reduction of both interaggregate and intra-aggregate pores, leading to the progressive convergence of the stress–strain curves. Consequently, at high stress levels, the fabric of the initially flocculated clay progressively converges toward the dispersed clay fabric. High-resolution SEM photographs showed at the microscale a progressive transition under loading from a flocculated clay fabric, a card-house-like structure, to aligned particle stacks that are quite similar to the microfabric observed in the case of initially dispersed-structured clay. Quantitative analysis of the pore size distribution (PSD), based on SEM observations and image processing, highlights the distinct initial fabrics and their evolution under mechanical loading.