Normalised constitutive equations of sand–silt mixture with respect to matric suction and silt content

Due to the abundance of sands containing fine particles in nature, it is often necessary to adapt existing constitutive models to accurately predict the behaviour of sand-fine mixtures. Therefore, normalising the essential mechanical behaviour aspects of the sand–silt mixture with respect to the matric suction and silt content was investigated in this article. For this purpose, a series of physical and mechanical laboratory tests were performed on samples composed of sand and silt in saturated and unsaturated states. The experimental data were used to normalise critical state lines and soil–water retention curves (SWRCs) based on specifically developed mathematical formulations. The results show that a unique SWRC can be deduced for fc ≤ fth and fc > fth by considering the SWRC of the sand–silt mixture at the threshold value (fth) as the reference curve. Additionally, by utilising equivalent mean effective stress and a new relationship for the equivalent void ratio, the critical state line was normalised, becoming independent of matric suction and fine content. This approach provides a streamlined and applicable analysis of sand–silt mixtures. Furthermore, an existing bounding surface plasticity model for sand was developed, successfully simulating key soil behaviours such as contractive and dilative responses, peak shear strength and the critical state.