Physical–mechanical properties and microstructure degradation of acid–alkali contaminated granite residual soil

Abstract

Acid—alkali pollution can lead to problems related to surrounding conditions, the health of the earth, and changes in soil physical–mechanical properties and microstructure. However, the response characteristics of acid–alkali pollutants to soil physical–mechanical properties and micro mechanisms under flowing conditions are still unclear. To address this gap, we used a self-developed circulating seepage device to investigate the water–soil chemical interaction of granite residual soil (GRS) under flowing conditions with different pH levels (3, 5, 7, 9, 11, 13) and soaking times (7, 14, 21, 28 days). The results indicate that changes in mineralogy, chemistry, and microstructure are responsible for the changes in physical–mechanical properties of GRS under acid–alkali pollution. We observed that the limit moisture content, shear strength, and internal friction angle of GRS had obvious stages before and after soaking for 7 days. Zeta potential test revealed that EDL in soil has timeliness, which corresponds to physical–mechanical properties. It can be seen that the water–soil chemical interaction of GRS polluted by acid–alkali solutions mainly include the erosion effect and electric double layer (EDL) effect. We found that the thickness of EDL can be characterized by the change in the plasticity index. The plasticity index of GRS under acid erosion is positively correlated with the internal friction angle (IFA), which deviates from the general soil law.