Effect of pH value on contaminated clay soil

Clay soil is one of the most unusual and widely used soil types in geotechnical engineering and construction due to its various physical and chemical properties that make it a key material in many engineering applications. This research focuses on studying the effect of changes in pH resulting from acidic contaminants, an important indicator of chemical reactions inside the soil, and their effect on the geotechnical characteristics of clayey soil. These contaminants simultaneously alter pH values, making the study of these changes essential for understanding the extent of deterioration in soil mechanical and chemical properties and assessing the damage caused by contamination. The study covered fundamental geotechnical checks, such as the Atterberg limits, Proctor check, unconfined compression check, SEM, and pH check. Clayey soil samples were artificially contaminated using four different contaminant ratios (10%, 20%, 30%, and 50%) relative to the weight of water used for soaking for 24 hours. The results showed that the variations in chemical and physical characteristics were slight, as pH values gradually increased and stabilized after three weeks. From a mechanical perspective, resistance showed a significant increase, recording a ratio of 10,921% increase at 20% concentration after four weeks, followed by a further ratio of 2,851% increase at 50% concentration compared to uncontaminated soil. However, after 56 days, this significant increase began to decline, with resistance decreasing to a ratio of 51% at 20% concentration and a ratio of 5.15% at 50% concentration, compared to values recorded four weeks after the test. Scanning electron microscope (SEM) images also showed an increase in the ratio of voids with increasing contaminant concentration, indicating a negative impact of contamination on the soil microstructure.