This research will investigate the influence of the physico- chemistry and microstructure of clays on their mechanical properties. Previous work indicates that the impact of depositional environment and post depositional environmental conditions and stresses may have significant influence on engineering properties and mechanical behavior of clay systems. Among the parameters and properties that will be investigated are index properties, stiffness, compressibility, shear strength and permeability. Scanning electron microscopy and X-ray diffraction techniques will be utilized to assess the effect of mineralogy, and microstructure on such parameters and behavior. Artificially prepared samples of clay premixed or permeated with various contaminating compounds will be subjected to a number of laboratory tests, microstructure and mineralogy analyses as indicated above. The samples will be prepared both by consolidating from slurry and sedimenting in a large scale sedimentation tank. The outcome of the research is anticipated to further the understanding of the complex interrelationships between micro and macro properties of clay systems and help researchers and practitioners to better predict long-term behavior of such systems under threat of rapidly changing environmental conditions.