Effects of Salinity on the Geotechnical Characterization of Fine-Grained Soils and Mine Tailings

The objectives of this study were to evaluate the effects of soluble salts (i.e., salinity) on the geotechnical characterization of fine-grained soils and mine tailings and to identify applicable test methods to characterize high-saline soils. Three fine-grained soils were used in this study: soda ash mine tailings, kaolin clay, and bentonite clay. The soda ash (sodium carbonate) mine tailings contained high-saline pore fluid and, predominantly, sodium on the exchange complex, whereas kaolin and bentonite clay were used for comparison with the soda ash tailings. Soluble salts were removed from the tailings using dialysis to create specimens with different pore fluid salinity, whereas sodium chloride (NaCl) was added to kaolin and bentonite. The 1: 5 electrical conductivity (EC1:5) of the as-collected soda ash tailings was 19.3 dS/m (deciSiemens per meter), and five additional specimens were prepared with EC1:5 ranging between 1.12 and 17.3 dS/m. The EC1:5 of kaolin specimens ranged from 0.14 to 27.4 dS/m and bentonite specimens ranged from 3.78 to 116 dS/m. The effects of pore fluid salinity were evaluated on Atterberg limits, specific gravity, and particle-size distribution via hydrometer tests. Liquid limit (LL), plastic limit, and clay content decreased for all three materials with increasing pore fluid salinity. Temporal evaluations of soil plasticity suggest that hydration times of at least 2 days are required to solubilize salts and capture salinity effects on LL. Additionally, experimental methods were developed for correcting errors in hydrometer and specific gravity tests that may originate from the presence of soluble salts.