Compressibility and residual shear strength of smectitic clays: influence of pore aqueous solutions and organic solvents

This paper reports experimental results relative to the influence of pore fluid composition on liquid limit, compressibility and residual shear strength of three clayey soils: the Ponza bentonite, a commercial bentonite, the Bisaccia clay. Compressibility was evaluated by means of oedometer tests and the residual shear strength was determined by means of direct shear and ring shear tests. The soils were powdered and tested dry and reconstituted with distilled water, salt solutions at various concentrations and organic fluids with different dielectric constants, both lower and higher than that of water. In order to evaluate the influence of pH, some tests were carried out by using HCl solutions. The results show that the effects of so different fluids can be compared directly with reference to their static dielectric constant D. As D increases from 1 to 80, liquid limit and compression index increase and the residual shear strength decreases. The liquid limit of the materials prepared with formamide (D = 110) assumes values very close to those obtained with distilled water, whereas the compression index is slightly lower and the residual shear strength much higher than in water