Spatiotemporal evolution of the physical and mechanical properties of domestic-source-contaminated soil during the acidification stage.

Domestic-source-contaminated soil (DSCS) contains high organic matter, and its properties and structure dynamically change with contaminant degradation and seepage depth. Investigating its evolution patterns is beneficial for the stability assessments and remediation of contaminated soil foundations. The acidification stage is a critical phase in the degradation process of DSCS, during which organic acids strongly influence soil structure and engineering properties. This study focuses on the acidification stage of DSCS and investigates the effects of degradation time and vertical seepage depth through laboratory seepage tests and theoretical analysis. The results indicate that the spatiotemporal evolution of DSCS exhibits distinct stagewise characteristics. With degradation, the soil strength initially deteriorates and subsequently recovers, and the compressibility first increases but then decreases, while the plasticity gradually increases. In the early acidification stage, acetic acid dominates and induces chemical dissolution. This leads to the disintegration of soil aggregates and an increase in pore volume, resulting in significant increases in the plasticity index and compression coefficient, while the characteristic bearing capacity continuously decreases. During the middle and late acidification stages, fulvic acid gradually becomes the dominant pollutant. Its organic cementation and flocculation effects continuously increase, resulting in the formation of new stable aggregates. Consequently, the soil strength transitions from a state of deterioration to recovery and enhancement. Spatially, the plasticity index and characteristic bearing capacity generally exhibit gradually decreasing distribution patterns along the vertical seepage depth. These findings provide insights into contaminated soil evolution mechanisms and offer a basis for assessment and remediation of DSCS foundations.