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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.

Bio-cemented soils can exhibit various types of microstructure depending on the relative position of the carbonate crystals with respect to the host granular skeleton. Different microstructures can have different effects on the mechanical and hydraulic responses of the material, hence it is important to develop the capacity to model these microstructures. The discrete element method (DEM) is a powerful numerical method for studying the mechanical behaviour of granular materials considering grain-scale features. This paper presents a toolbox that can be used to generate 3D DEM samples of bio-cemented soils with specific microstructures. It provides the flexibility of modelling bio-cemented soils with precipitates in the form of contact cementing, grain bridging and coating, and combinations of these distribution patterns. The algorithm is described in detail in this paper, and the impact of the precipitated carbonates on the soil microstructure is evaluated. The results indicate that carbonates precipitated in different distribution patterns affect the soil microstructure differently, suggesting the importance of modelling the microstructure of bio-cemented soils. [ABSTRACT FROM AUTHOR]

Water retention in compacted clays is dominated by multi-modal pore size distribution which evolves during hydro-mechanical paths depending on water content and stress history. A description of the evolutionary fabric has been recently introduced in models for water retention, but mostly on a heuristic base. Here, a possible systematic approach to account for evolving pore size distribution is presented, and its implications in models for water retention are discussed. The approach relies on quantitative information derived from mercury intrusion porosimetry data. The information is exploited to introduce physically based evolution laws for the parameters of water retention models. These laws allow tracking simultaneously the evolution of the aggregated fabric and the consequent hydraulic state of compacted clays. The influence of clay microstructure, mechanical constraints and water content changes on the water retention properties is highlighted and quantified from experimental data on different compacted soils with different activity of the clayey fraction. The framework is discussed with reference to a widespread water retention model and validated against experimental data on a Sicilian scaly clay compacted to different dry densities and subjected to a number of hydro-mechanical paths. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]