The expansion deformation characteristics of expansive soil under acid pollution

Soil pollution incidents occur frequently in China. After contamination by acid, the expansion performance of expansive soil is further intensified, posing a significant threat to infrastructure. Using sulfuric acid as the contaminant source, expansion deformation tests of expansive soil under sulfuric acid immersion were conducted, followed by scanning electron microscopy and X-ray diffraction analyses to investigate the evolution of the microstructure and mineral composition of the samples under acidic conditions. The results demonstrated that the acidic environment increased the expansion rate of the samples, with higher sulfuric acid concentrations correlating to greater expansion rates. Under acidic conditions, cementing materials (e.g., free oxides) in expansive soil underwent varying degrees of dissolution and leaching, thereby weakening the connections between overlapping structures. This process resulted in a more dispersed arrangement of the surface-overlapping structures, accompanied by a continuous increase in both the volume and number of micropores. The post-acid-rain expansion deformation of expansive soil can be quantified using the e-pe fractal relationship. Furthermore, the e-pe fitting analysis of the experimental data revealed that the enhancement of expansion performance by acid rain primarily stems from the reduction in cementing content, leading to an increase in the expansion coefficient (κ).