The deformation characteristics of soil after thermal desorption are crucial for the evaluation of engineering properties, but the evolution mechanism is currently unclear. This study focuses on the thermal desorption of contaminated soil, conducting Geo-dynamic Systems consolidation-rebound tests to reveal the evolution mechanism of consolidation–rebound deformation and pore pressure characteristics, and exploring the evolution mechanism through pore structure, particle size distribution, and Cation Exchange Capacity tests. Results show that the consolidation characteristics of uncontaminated soil increase and then decrease with heating temperature, with 400 °C as a turning point. In contrast, the consolidation deformation of contaminated soil continues to decrease. The vertical deformation of the soil in the pre/early consolidation stage is greater before 400 °C, while after 400 °C, the deformation continues to increase with consolidation pressure, and higher heating temperatures enhance the soil’s rebound deformation ability. Pore water pressure changes in two stages, with temperature ranges of 100–300 °C and 300–600 °C, and with increasing heating temperature, the characteristics of pore pressure change from clay to sand. Mechanism tests reveal that inter-aggregate pores affect initial deformation, while intra-aggregate pores affect later deformation, both showing a positive correlation. Aggregate decomposition increases initial deformation capacity at 100–400 °C while melting body fragmentation increases later deformation capacity at 500–600 °C. CEC decreases with increasing heating temperature, reducing inter-particle resistance and increasing soil deformation capacity. Particle size distribution and Cation Exchange Capacity impact consolidation–rebound pore pressure.

The structural stability of barrier layers is critical for the long-term effectiveness of landfill remediation projects, although leachate pumping and organic contamination can cause structural degradation, reduce remediation performance, and increase the risk of pollutant release. The objectives of this study were to determine the consolidation–rebound mechanisms of sand–bentonite mixtures through standardized tests and to analyze deformation under diesel contamination using multi-scale approaches, including pore-structure characterization, particle-size distribution, cation exchange capacity, and oil-blocking effects. The results revealed that uncontaminated soil (0.0 wt.% diesel) exhibited non-linear compression behavior, with an initial decrease and a subsequent increase with increasing sand content; when the consolidation pressure exceeded 400 kPa, the compression rate decreased markedly. The compression deformation of the contaminated soil increased and was positively correlated with the sand and diesel contents, with accelerated deformation at >4.0 wt.% diesel. The rebound capacity decreased under combined sand–diesel effects. Microstructural analysis indicated that initial compression was controlled by inter-aggregate pores, whereas mid- to late-stage compression was influenced by intra-aggregate pore evolution and particle breakage. Increased diesel content shifted aggregate breakage from single/secondary to tertiary patterns, altering later compression behavior. Coupled hydration reduction and enhanced oil-blocking suppressed rebound significantly, worsening with increasing diesel content. Technical–economic analysis revealed that pure bentonite (0% sand) was optimal under uncontaminated conditions and that a 10% sand mixture was best under contaminated conditions. The sand–bentonite barrier exhibited amplified consolidation–rebound deformation and reduced stability with increasing sand and diesel contents, providing a theoretical basis for long-term landfill remediation assessment.