Influences of Wetting–Drying Cycles on Expansion and Shrinkage, Crack, and Leaching Behaviors of Lime Solidified Pb(II) Contaminated Expansive Soil

Abstract

The stabilization/solidification method can improve the engineering properties and reduce the environmental risks of heavy metal-contaminated expansive soil. However, the solidification effects deteriorate for soils experiencing wetting–drying (W–D) cycles. For this objective, the expansion/shrinkage, cracking, and leaching behaviors, as well as the corresponding internal relations, of lime-solidified lead-contaminated expansive soil were investigated. The results showed that during the W–D process, the volumetric strain increased, particularly along the radial direction. The cracks gradually developed and increased in length, width, and surface-crack ratio. Contaminant leaching and mobility increased, increasing environmental risk. In addition, a higher Pb(II) concentration in the solidified soil exhibited a more notable expansion potential release, crack development, and leaching capacity. X-ray diffraction and scanning electron microscopy results revealed the redistribution of soil particles and pores rather than chemical changes in mineral components during the deterioration process, and increasing the lead concentration accelerated the deterioration of W–D cycles. Finally, based on the grey correlation analysis, deterioration effects in leaching behaviors were controlled by expansion/shrinkage exponential release for solidified soil experiencing lower W–D cycles and higher Pb(II) concentrations, whereas leaching behaviors were controlled by crack behavior for solidified soil experiencing higher W–D cycles and lower Pb(II) concentrations.