Effect of varying pore water salinity on frost susceptibility behaviour of soils

•The presence of NaCl in pore water restricted the frost penetration depth as well as the total frost heave in clayey silt of low plasticity.•An improvement of 70% in the value of post-thaw CBR was observed due to 5% NaCl concentration in pore water.•Hydraulic conductivity of soil was affected because the water migration reduced with increasing pore water salinity.•Micro-structural changes in the soil sample, observed through SEM, revealed lesser slackening of saline soil due to freeze–thaw cycles compared to non-saline soil. The susceptibility of soil to frost action is a major distress for engineering infrastructure constructed over it in regions that experience seasonal freezing and thawing. The soil deposits which are not otherwise problematic for use as a subgrade/foundation material can become very problematic under seasonal freeze-thaw. Since presence of dissolved salts in pore water depresses the freezing-point and increases the unfrozen water content, it can be ascertained that pore water salinity can affect soil frost susceptibility due to seasonal temperature variations by reducing the total ice content during freezing. An experimental investigation was carried out to assess the effect of pore water solute content on the behaviour of a frost susceptible soil subjected to freeze-thaw cycles in a laboratory test setup as per ASTM D5918-13. The presence of solute primarily depressed the freezing point of the soil. The heave rate, maximum heave and the frost penetration depth was found to decrease with increasing solute concentration in pore water. The effect on the thaw-CBR value, variation in water migration pattern and micro-structural changes along the depth of the sample was also examined. It was found that the presence of solutes negates the undesirable effects during freezing by controlling ice segregation, frost penetration and heaving of the soil which in turn limit the adverse weakening during thawing. The destruction to soil at micro-structural level was also restricted in the samples containing solute in their pore water.