Compressibility and strength of active clays: influence of pore fluid dielectric constant

This paper reports experimental results relative to the influence of pore fluid composition on liquid limit, intrinsic compressibility, permeability and residual shear strength of some smectitic soils. The soils were reconstituted with distilled water, aqueous ionic solutions at various concentrations and organic fluids with different dielectric constants. The reconstitution procedure of the materials that underwent compression tests was such as to make comparable the results relative to so different fluids. All the results were analysed with reference to the static dielectric constant D of the pore fluid. As D increases from 2 (cyclohexane) to 80 (water), liquid limit and compression index increase, whereas permeability and residual shear strength decrease. Formamide (D=110) has effects similar to those of water in the case of fluid adsorption properties, volume change behaviour and permeability, whereas it causes a noticeable increase in residual shear strength. The maximum of liquid limit and compression index, and the minimum of permeability fall in the range 80<D<110 (mixture water-formamide).