Evaluation of the effect of freeze-thaw cycles on the compressibility of powdered shale-clay in the presence of lead and zinc heavy metals

With the population growth, technological advancement, and the increase in heavy metal pollutants, besides the location of a quarter of the earth's surface in cold regions, it is necessary to study the effect of freeze-thaw cycles on clay and predict its behavior over time. The effect of freeze-thaw cycles on the behavior of clay contaminated with heavy metals has been less studied. In addition, low plasticity clay and shale sedimentary rock are frequent in Iran. As an innovation in this article, the effect of the freeze-thaw cycles on the compressibility behavior of shale-clay soil in the presence of lead and zinc heavy metal pollutants is investigated. The combination of low plasticity clay with 40 and 60% crushed shale was investigated. For this purpose, 60 one-dimensional and Atterberg limit tests were conducted on the samples in the presence of 0, 5 and 25 cmol/kgsoil of lead nitrate and zinc nitrate pollutants. According to the obtained results, the most changes in liquid limit are related to the samples contaminated with 25 cmol of lead nitrate after 12 cycles of freeze-thaw cycles with a 43% reduction. And the lowest changes in liquid limit are related to the combination of 40% kaolinite with 25 cmol of zinc nitrate pollutant. Also, the results obtained from the consolidation test indicate that the compressibility of the samples was affected by the concentration of lead and zinc heavy metal pollutants and the freeze-thaw cycles. The increase of heavy metal pollutants led to a decrease in the initial void ratio and compressibility index of the samples compared to freeze-thaw cycle, which led to an increase in these ratios. The maximum changes were made in the first four cycles of the freeze-thaw cycle, and the changes were insignificant until the 12th cycle.