The viscosity of fine-grained sediments: A comparison of low- to medium-activity and high-activity clays

Viscosity is generally recognized as an indicator of landslide mobilization. Viscous behavior at relatively low (high) shear rates is an important predictor of the motion of slow- (fast)-moving landslides. The viscosity in a modified Bingham model at low and high shear rates was examined. The viscous characteristics are primarily dependent on the physico-chemical properties of the materials in question (e.g., grain size, mineralogy, salinity). In this context, the viscous characteristics of low- to medium-activity and high-activity clays (bentonite with different salinities) were compared. Empirical relationships exist between the liquidity index and the plastic viscosity regardless of the mineralogical composition. This study also demonstrated a positive relationship between the liquidity index and the viscosity in a modified Bingham model with n = 1. The results showed that low- to medium-activity and high-activity clays fall into a similar range for fine-grained sediments mixed with salt water (30 g/L). However, an effect of salinity was evident when using high-activity clays mixed with fresh water. Modified Bingham model is a useful and powerful tool for describing pre- and post-yield viscosity in engineering practice. By correlating the geotechnical and rheological properties of fine-grained sediments, index properties can help to estimate the appropriate values for the rheological parameters of these soils.