Laboratory Assessment of the Mechanical Properties of an Unsaturated Mid-Atlantic Silty Sand

Natural soil formation processes involve variable particle size distributions that vary spatially within a deposit, giving rise to an array of soils that transition from one general soil type to another within essentially similar deposits. Characterization of such transition soils in the active zone is something past research has largely overlooked. An evaluation of the unsaturated strength behavior of a transition soil was carried out on a native mid-Atlantic silty sand. A suite of unsaturated consolidated drained axisymmetric triaxial shear tests was performed, and the stress-strain and volume change characteristics of the transition silty sand under different values of matric suction, confining pressure, strain rate, and fines content were investigated. It is found that the triaxial shear strength increases with increasing matric suction, confining pressure, strain rate, and fines content. The volumetric strain increases with increase in matric suction and confining pressure, and it decreases as fines content and strain rate are increased. The experimental results are used to further validate a state-dependent constitutive model for unsaturated soils that was recently proposed based on the theory of bounding surface plasticity and the framework of hyperelasticity. It is shown that the model simulations are in good agreement with the experimental data.