Experimental study on the effect of acid and alkaline rains on geotechnical properties of fine-grained soil

In the current study, the effects of acid and alkaline rains on the physical properties of a particular type of clay with low plasticity is evaluated. In order to reproduce the process of interaction between artificial rain and soil, an infiltration setup was fabricated. Solutions of diluted sulfuric acid (H2SO4) and dissolved sodium hydroxide (NaOH) were used to create acidic or alkaline rains, respectively. Distilled water was also used as a reference pH value. Subsequently, the reconstituted samples in a mold are infiltrated by acid or alkaline rains in different pH levels and different fluxes of rainfall. Atterberg limits, Coefficient of permeability, California bearing ratio (CBR) test, and unconfined compressive strength (UCS) of the soil samples were evaluated, to investigate the changes of the mechanical properties of the soil after being exposed to acid or alkaline rain. The obtained results indicated that acidic contamination had a strong influence on the strength characteristics of soils, and the mineralogy of the clay fraction as well as the concentration of acid in the pore fluid could significantly influence the stress-strain behavior of studied soil. However, further decrease in pH (pH=3) and increase in rain fluxes (20 years) caused a significant reduction of the strength. Furthermore, the results indicate that the values of the LL, PI and the soil permeability has increased and the unconfined compressive strength and the CBR has decreased as the artificial rain become more acidic or alkaline, and precipitation years increased from one-year to twenty-years.