Micromechanical properties characterization of reconstituted cohesive soils: A structure-retaining sampling and statistical assessment approach

Understanding the microscale mechanical characteristics of soil is critical for advancing multiscale soil mechanics. To assess the microscale mechanical properties and behaviors of grains/particles in cohesive soils interface, a structure-retaining sampling method, combined with atomic force microscopy (AFM), nanoindentation (NI), and microhardness (MH) testing were developed. Key parameters, including indentation modulus (E) and hardness (H), Vickers hardness (HV), creep modulus (Ec), and viscosity (η) were assessed. Results demonstrate that soil structure and interface stability give rise to three typical forms of soil force-depth responses, which we classify as soil force-depth characteristic curves (SFDCCs), and indicate that 3000 nN is an appropriate load for nanoindentation tests to ensure minimal variability in SFDCC behavior. A quadratic relation between E and H was observed, highlighting their interdependence. Additionally, an increase in clay mineral content and a decrease in maximum dry density were found to reduce E, H, and HV values, suggesting the role of microstructural factors. Creep behavior was effectively modelled using a Kelvin-based framework, revealing a linear correlation between Ec and η. These findings provide new insights into soil micromechanics and serve as a comprehensive validation of the proposed methodology, establishing it as an effective tool for future multiscale soil mechanics research.