Sand fraction effect on hydro-mechanical behavior of sand-clay mixture

Abstract The sand-clay mixture was prepared to simulate special soils with discontinuous gradations, e . g . the residual soils, clinosols or hydraulic filling soils. Incremental loading oedometer tests were conducted to investigate their hydro-mechanical behaviors. The results were first analyzed based on the plots in the semi-logarithmic planes ( i . e . normalized void ratio by that at liquid limit versus vertical effective stress, and ver sus hydraulic conductivity). It appears that the normalized void ratio by that at liquid limit allows valuable and reliable normalization of the compressibility and permeability curves. To investigate the influence of sand fraction, a four-phase model of sand-clay mixture was introduced, enabling the void ratios of clay and sand to be determined. Further analysis showed that the sand void ratio and the normalized clay void ratio by that at liquid limit are also suitable parameters to describe the sand skeleton formation. Moreover, the normalized clay void ratio by that at liquid limit is an appropriate parameter to describe the hydraulic behavior of soils with or without sand fraction. When the sand skeleton was partly formed, the vertical stress was partly supported by the skeleton resulting in a different compression behavior from that of common clays. The partial formation of skeleton was found to depend on the relative dimension of coarse to fine grains as well as the stress state. This implies that during compression the interaction between sand and clay evolves, from non-, partial- to complete sand skeleton, reaching at the end of the maximum void ratio of sand.