The physical–mechanical properties degradation mechanism and microstructure response of acid–alkali-contaminated Xiashu loess

Water pollution has changed the physical and mechanical properties of Xiashu loess, which has become an important factor in the frequent occurrence of Xiashu loess landslides. In order to understand the mechanism of Xiashu loess landslide in acid or alkali environment, a large number of Xiashu loess samples were collected in Nanjing City, Jiangsu Province. X-ray diffraction, energy-dispersive analysis of X-ray, compression test, direct shear test, and scanning electron microscope test (SEM) were used to analyze physical properties, mechanical properties, and microstructure of acid–alkali-contaminated Xiashu loess. The results show that the newly formed insoluble (slightly soluble) substances in the alkalization Xiashu loess increase its density and decrease the void ratio and water content. In sulfuric acid solution, the minerals in Xiashu loess mainly suffer dissolution reactions, which leads to decrease in soil density and increase in void ratio and water content. In the SEM image, the surface of acidified Xiashu loess soil particles is rough and uneven, while the surface of alkalized Xiashu loess soil particles is smooth and flat. This is an important reason that the internal friction angle of acidified Xiashu loess is significantly higher than that of alkalized Xiashu loess.