Triaxial Compression of Sand-Fines Mixtures at Low Confining Pressures

Abstract A series of triaxial compression tests was performed on a natural sand-fines mixture under both drained and undrained conditions at initial confining pressures ranging from 20 to 300 kPa. The tests aimed to better understand the mechanical behaviour of the soil at low stress levels. Additionally, images of the soil fabric were taken using a µ CT device, revealing that the fabric was characterised by the sand grains being fully embedded within the fine-grained matrix and that only few direct contacts between the sand grains existed. The results of the triaxial tests showed that the fabric of the sand-fines mixture significantly influenced the macroscopic properties of the specimens when compared to clean sands. In the drained triaxial tests, the dilatancy and friction angles showed minimal dependence on the confining pressure, even at pressures below 60 kPa. The undrained triaxial tests showed different response patterns in the development of excess pore water pressure. Tests starting from lower confining pressures resulted in a greater build-up of pore water pressure after reaching the phase transition line, whereas at higher confining pressures the soil exhibited lower excess pore water pressures.