Compressibility and small strain stiffness of kaolin clay mixed with varying amounts of sand

This experimental investigation quantifies the compressibility and small strain stiffness of kaolin clay mixed with varying amounts of sand particles. The theoretical background of binary mixtures, including critical and limiting fines contents, porosity of binary mixed soils, and the concept of interfine void ratio, were reviewed. In addition, modified oedometer tests were conducted to measure both the compression index (C_c) and maximum shear modulus (G_max) of sand-clay mixed soils. The results of this study demonstrate that the critical fines content (FC*) of tested mixed soils is less than 40% and the limiting fines content (FC_L) is around 80%; therefore, the C_c and G_max of tested mixed soils with fines content (FC) = 80% and 90% are entirely determined by the small particles, reflecting the applicability of the concept of interfine void ratio for mixed soils with FC > FCL. In contrast, the C_c and G_max of tested sand-clay mixed soils with FC = 40% and 60% can be captured by the concept of equivalent interfine void ratio with fitting parameter m = 0. Therefore, the mechanical behaviors of tested sand-clay mixed soils with FC* < FC < FC_L are determined by both large and small particles.