Infiltration of water in unsaturated soils has long been an interest of study in geotechnical engineering. A wide range in permeability coefficient has been proven to be a major obstacle in analyzing seepage problems. Soil-water characteristic curve (SWCC) is a fundamental constitutive relation for the explanation of the engineering behaviour of unsaturated soil. The effect of anisotropy on SWCC and unsaturated coefficients of permeability and diffusion has been studied in this paper, by taking sets of duplicate disturbed and undisturbed specimens prepared in the vertical, 45º inclined and horizontal directions. The results showed that there is a noticeably anisotropic in the basic characteristics of SWCC and the unsaturated coefficients of permeability and diffusion specially at the low values of suction. The variations of the hydraulic conductivity and vapor diffusivity versus suction gradient were opposite. Furthermore there is a noticeable difference between the disturbed and undisturbed specimens in the SWCC and coefficients of diffusion and permeability.
Key words: Anisotropy; directional variation; hydraulic conductivity; soil-water characteristic curve; unsaturated soil.