Pore Water Extraction—Comparison of Saturation Extract and High-Pressure Squeezing

A study of the influence of the chemical environment on the engineering behavior of clayey soils warrants an understanding of the chemistry of the pore water present in the soil, together with the physico-chemical properties of the soil minerals. There are several techniques available for the extraction of the pore water from soil samples. Following a review of these techniques, two methods were considered suitable for the extraction of pore water from overconsolidated clay deposits. Pore water was extracted from several clay shales and bentonitic clays from western Canada using the high-pressure mechanical squeezing technique and the saturation extract technique during this study.

Based on the results of a previous study, it was expected that the pore water concentration determined using the saturation extract method would yield higher salt concentrations since the relationship between the concentration and the inverse of the water content is nonlinear. This phenomenon was confirmed in the present study. A comparison of the composition of the pore water extracted using the two techniques indicated that the saturation extract technique always yielded pore water with higher salt concentration. Based on this observation, it is concluded that the extrapolation of the pore water concentration at low moisture contents from known salt concentrations at higher (diluted) moisture contents should be viewed with caution.