Behavioral Thresholds in Mixtures of Sand and Kaolinite Clay

Nearly all soils are comprised of mixtures of coarse and fine particles. Behavior under mechanical and thermal loading of soil is strongly influenced, and in some cases governed, by the ratio of coarse to fine particles. A better understanding of the fundamental behavior of soil mixtures will provide insight to design decisions for new and emerging geotechnologies. In this work, behavioral threshold fines fractions were identified by experimental methods, where the threshold was defined as the point where changes in the coarse/tine mixture ratio result in abrupt behavior changes. Binary mixtures of sand and kaolinite clay ranging from 0 to 100% fines content were subjected to consistency and undrained shear strength testing with the fall-cone apparatus, compressibility tests using an oedometric cell, thermal conductivity tests with a thermal needle probe, and stress-strain-strength testing in undrained triaxial shear. Results indicate that behavioral thresholds exist at a critical fines content where a minimum void ratio occurs and at a percolation threshold where continuous force chains are present. The behavior changes are explained using theories of effective properties and percolation. Interpretations of these results lead to a clearer understanding of soil behavior. (C) 2015 American Society of Civil Engineers.