Microstructure of compacted low-plasticity soils: the initial fabric and its evolution on stress and suction paths

Soils used in earthworks undergo different hydro-mechanical paths due to the compaction and construction process, the change in climatic conditions or the groundwater level oscillations. Their hydromechanical behaviour is greatly affected by their initial microstructure set on compaction that evolves differently in compliance with the stress paths. The current study investigates the differences in the initial microstructure in a low-plasticity clayey silt compacted at the dry and wet of the optimum. Themicrostructure was characterized by mercury intrusion porosimetry. The definition of a microstructural void ratio (em) inside the soil aggregates and its ratio to the total void ratio (em /e) allowed plotting contours of equal em and em /e in the Proctor compaction plane for the as-compacted states. Additionally, the evolution of the initial microstructure along different stress and suction paths was evaluated. The microstructural voidratio reached after the hydro-mechanical paths did not reproduce the contours of the as-compacted states in the compaction plane. In fact, the microstructural void ratio inside saturated soil aggregates follows Terzaghi’s effective stress through a microstructural compressibility parameter, which provides a straightforward approach for predicting the evolution of the microstructure of compacted low-plasticity soils subjected to different stress-suction paths.