A New Osmotic Oedometer with Electrical Resistivity Technique for Monitoring Water Exchanges

Abstract

This article presents a new osmotic oedometer that is able to measure changes in the degree of saturation (Sr) during suction-controlled drying-wetting and oedometric tests. A circular four-electrode cell made of polyvinyl chloride was developed. The geometric factor of the cell was determined by numerical simulation and validated by calibration tests. A total of 29 samples was statically compacted in the oedometric cell at different moisture contents and dry densities. Based on these measurements, the normalized electrical resistivity was defined and correlated with the Sr. After that, three suction-controlled drying-wetting and oedometric tests were performed on the samples statically compacted at the water content of 21 % and dry density of 1.62 g/cm3, which corresponds to the standard Proctor optimum conditions. The results show (i) the potential of the new oedometer for the study of the hydromechanical behavior of unsaturated soils, (ii) the ability of the electrical resistivity technique to estimate the variation of the Sr in unsaturated oedometric tests, with a relative error smaller than 5 %, and (iii) the coupled effect of vertical stress and suction on the change in void ratio (e) and Sr shown in the (e - suction pressure [s] - vertical total stress [σv]) and (Sr - s - σv) state surfaces.