DETERMINATION OF THE PERMEABILITY OF PART IALLY SATURATED LOW-POROSITY CLAYS

The presence of impermeable natural or artificial clayey layers plays a fundamental role in protecting ground water from pollution. In the c ase of low porosity and partially saturated clays, the experimental de termination of transfer coefficient is particularly difficult because of a considerable reduction in hydraulic head and of water-particle in teractions that reduce the interstitial water mobility. Experimental w ork was carried out to obtain, in a simple way, the hydrodynamic chara cteristics of two clayey formations: Boom and Bassin Parisien. The hyd raulic profiles were determined by soaking tests on 300 mm high clayey columns and the sorption-desorption isotherms were evaluated by the s aline solution technique on several samples of both clays. The spatio- temporal analysis of the hydraulic profiles reveals the variations in isothermal diffusion coefficient according to the water content. In ac cordance with the hypothesis of local equilibrium, the sorption-desorp tion isotherms give the characteristic curve of each formation in a po tential versus water content relationship. The total diffusivity combi ned with retention curves allows to calculate the permeability as a fu nction of the saturation.