Abstract: To study the permeability and anisotropy of upper Shanghai clays, oedometer tests were carried out under different pressures in both horizontal and vertical directions. Permeability was determined by the square root of time method and log time method, and the relationships between coefficient of permeability and void ratio and the flow direction were discussed. The reason of the difference in the horizontal and vertical permeability coefficients is analyzed on the microscopic level by using scanning electron microscope. Results reveal that the coefficient of permeability of upper Shanghai clays increases with the increase of void ratio. For a single test, the relationship between coefficient of permeability and void ratio is linear in e-lgk coordinate system and the permeability change index is roughly Ck=0.5e0. For all tests, the relationship between coefficient of permeability and void ratio is curved in e-lgk coordinate system. Anisotropy of upper Shanghai clays under different pressure conditions is not obvious, which is related to the formed flocculent structure in the process of soil particle deposition. In other words, the difference of the pore content in the horizontal and vertical directions leads to the anisotropy in the coefficient of permeability.

Key words: Shanghai clay, coefficient of permeability, void ratio, anisotropy, micro structure