Influence of saturation on hydromechanical properties of glacial tills

A partially saturated condition resulting in a multi-phase pore fluid (air-water mixture) shapes the mechanical and hydraulic behavior of fine-grained soils. The purpose of this experimental investigation is to assess how the properties of glacial tills, utilized for a shallow geothermal project in central Illinois, change with the degree of saturation. The saturation process is a function of time and water pressure that results in the compression of the air bubbles while forcing them to dissolve into the surrounding pore fluid as the applied pressure increases. Measurements of the Skempton's B coefficient under the undrained condition at fixed value of the effective mean stress provide the assessment of the degree of saturation. B-values are increasing with the decrease of pore fluid compressibility and eventually become constant (and ≈1 for soils) when full saturation is achieved. The implications of a partially saturated condition were evaluated by conducting undrained compression tests and permeability measurements at B = 0.05 (94% water saturation), B = 0.44 (97% water saturation), and B = 0.95 (fully saturated). The results corroborated increased compressibility and decreased permeability at partial saturation, emphasizing the importance of assessing the saturation conditions at which material properties are reported.