Strength–Stiffness–Suction Relations of Compacted Silt

This study aimed to develop the strength–stiffness–suction relations of compacted red mudstone fill (RMF) material through a comprehensive experimental program that included water retention, uniaxial compression, and bender element tests. Three stages, namely, the initial increase stage, primary increase stage, and secondary increase stage, were identified for the evolution of strength and stiffness with the initial suction. A unified normalization framework was developed to capture the S-shaped evolution curve, in which the effect of the void ratio was incorporated. The proposed model was validated as applicable to a wide range of clays and silts, regardless of whether the soil is in a compacted state or following a hydraulic path. Microstructural analyses were performed using a combination of mercury intrusion porosimetry (MIP) and scanning electron microscopy analyses. The consequences of the three-stage behavior of the strength and stiffness were mainly manifested in the soil fabric. The specimen at a high initial suction showed a monomodal pore structure, where a dense aggregate structure was observed. Increasing the saturation degree resulted in a transition from the monomodal to bimodal structure. In particular, the pore size distribution of the saturated specimen returned to monomodal, where an aggregate structure was absent and the clay matrix was flocculated. The structural modification corresponded to the development of strength and stiffness, which were well characterized by the conceptual framework in terms of changes in the microstructural void ratio with the water ratio.