Influence of plastic fines on the critical state mobility of calcareous sands

Calcareous ooze, often classified as a type of clay, is ubiquitously found in marine environments, and its incorporation within sandy substrates can markedly influence the engineering properties of sands. Despite its significance, the impact of calcareous ooze on the behavior of calcareous sand remains underexplored. This study conducts a series of undrained triaxial tests to evaluate the shear behavior and fluid characteristics of mixtures of calcareous sand and ooze under both monotonic and cyclic loading. The experimental findings reveal that the presence of plastic fines substantially alters the shear behavior of the soil. Specifically, both shear strength and liquefaction resistance of the mixtures demonstrate a decline with increasing fines content under monotonic and cyclic loading conditions, respectively. Additionally, the angularity and roughness of ooze particles mechanically interlock adjacent sands, thereby increasing the critical friction angle from ${37.70}^{°}$ to ${39.26}^{°}$ as fines content rises from 0 to 30 %. Flow failure was observed during cyclic testing, with strain accumulation occurring rapidly during the final cycles. Furthermore, a novel parameter normalized viscosity ratio is introduced for quantifying the soil viscosity, exhibiting a linear relationship with the normalized effective stress ratio. The present study suggests that both of viscosity under monotonic or cyclic loading should be classified as critical state viscosity and fluid characteristics of the soil at critical state with non-zero effective stress should be considered.