Hydraulic Behavior of Collapsible Compacted Gneiss Soil

The hydraulic behavior of a residual gneiss soil compacted at conditions that produce collapsible characteristics was studied using a triaxial permeameter system that allows independent control of net stresses and matric suction. Wetting paths under differing but constant loads were utilized to reflect field conditions associated with a collapsing soil earth fill dam. The experimental results showed that different stress paths produce different amounts of volumetric collapse and distinct variations in the coefficient of permeability, which at relatively high matric suctions was mainly affected by the increase in degree of saturation. However, as the soil approached saturation, the coefficient of permeability became dependent on void ratio and net mean stress, with the saturated coefficient of permeability being reduced at larger amounts of collapse. The results also suggested that entrapped air in the soil voids may produce a significant reduction in the coefficient of permeability. A constitutive relationship for the coefficient of permeability that takes net mean stress changes into account was proposed based on best-fit analyses.