Effect of acidic and alkaline pore fluid on the mechanical properties of fine-grained soil

Acidic and alkaline contaminants are among the most important contaminants that enter the soil through various ways such as factory effluents, residential areas, and acidic rain. In addition to environmental impacts, the geotechnical effects of these contaminants must be considered. In this study, the effect of pore fluid pH from acidic to alkaline range on the mechanical and structural behavior of fine-grained soil is investigated. For this purpose, soil is contaminated using sulfuric acid and sodium hydroxide contaminants, and a series of unconfined compression strength (UCS), unconsolidated undrained (UU) triaxial tests, Atterberg’s limits, and other micro-/macrostructural analysis tests at pH of 1, 3, 5, 9, 11, and 13 as well as distilled water (pH = 6.8) were done on Tehran fine-grained soil. The results show that with increasing pH value, unconfined compression strength, elastic modulus, maximum deviator stress, cohesion, and internal friction angle increase. Also, Atterberg’s limits including liquid and plastic limits are minimum at pH value of 6.8. In acidic-contaminated samples, unconfined compression strength shows a descending trend by increasing the curing time from 1 to 28 days, and in alkaline-contaminated samples, the strength increases with increasing curing time.