Effect of Initial Osmotic Suction on the Volume Change Behavior of Saturated Soil
Siamak Yoosefi, Mohammadreza Jebeli, William J. Baker, Christopher L. Meehan
Abstract
Global warming and subsequent sea level rise will cause the intrusion of saltwater into freshwater aquifers, affecting the pore fluid composition of both saturated and unsaturated soils. The change in hydration force caused by the dissolution of a charged solute (e.g., natural seawater salt) in pore water can reduce the water potential and produce osmotic suction in a soil. Previous studies have indicated that the volume change properties of reconstituted clay soils are dependent on both clay mineralogy and the pore fluid chemistry. In this study, the effects of salt content on the volume change behavior of two types of clay, that is, a natural lean clay collected from a coastal site in Delaware and a commercially available kaolinite, were investigated. The goal of this study was to investigate the effects of salt content on the compressibility behavior of the two aforementioned clays by performing one-dimensional consolidation tests. In this study, the initial osmotic suction of the saturated soil samples was changed by mixing the soils with varying amounts of sodium chloride (NaCl), in order to yield different salt contents. Compressibility test results showed that the compression ratio decreased as the osmotic suction increased from 0 to 3 MPa at an electrical conductivity (EC) = 49,000 (μS/cm). Additionally, increasing the level of salinity of the pore fluid from EC = 49,000 (μS/cm) to the saturated NaCl solution salinity, that is, EC > 100,000 (μS/cm), increased the compression ratio. This observed behavior is discussed in accordance with the effect of pore fluid salinity on the clay soils’ physiochemical factors, in particular the van der Waals attractive forces that occur at the clay particle scale.