A Critical Assessment of the Effect of Initial Fabric on Key Small-Strain Design Parameters of Slurry-Deposited Silts and Sands

Abstract

Whereas moist-tamped specimens of silts and sands are most used in engineering practice to characterize tailings, offshore sediments, and fluvial/alluvial deposits, design parameters derived from moist-tamping data sets can be significantly different from those obtained from slurry or underwater deposition. This study shows that moist-tamped silty and sandy specimens may exhibit phase transformation at stress ratios that are 25% to 50% lower than those observed for slurry-deposited specimens. Conversely, the small-strain stiffness of the moist-tamped specimens tested can be 50% higher than those from slurry deposition. With tailings dams’ performance receiving increased worldwide attention due to recent dam failures in several parts of the world, this study provides new, specific, and concerning insights about the crucial impact that the selection of moist tamping can have on design parameters. More realistic and rigorous laboratory testing procedures involving tailings remain a key requirement for engineering assessments of tailings behavior. A novel slurry-deposition setup is presented that allows underwater reconstitution of silts, sands, and their mixtures, yielding high-quality uniform specimens. Systematic uniformity checks, which are mandatory to avoid segregation of silty materials, are described. A detailed analysis of typical errors affecting initial void ratio evaluation is also presented to ensure that comparisons between different methods are done with the highest degree of confidence possible.