This study investigates the pore structure characteristics of a marine soft soil of the Beibu Gulf, Guangxi Province, China and its variation with clay content. Pore-size distribution was measured by Mercury intrusion porosimetry (MIP) and analyzed based on fractal theory. The analysis of the results relies on the distinction of several types of pores: micropores, small pores, mesopores and macropores, separated by the critical pore diameters of 0.02 μm, 0.18 μm and 0.78 μm, respectively. Mesopores and small pores were dominant, accounting for more than 75% of the total pore volume. Small pore volume increases with clay content at the expense of the mesopore volume. Between 22.31% and 32.31% clay, the connectivity of pores improves with clay content, while the tortuosity of pores increases from 22.31% to 32.31% of clay and then decreases between 32.31% and 37.31% clay. Marine soft soil in the Beibu Gulf is characterized by multiple fractal dimensions. Macropores had a large (close to 3) fractal dimension, independent of clay content. Mesopores and small pores had a smaller fractal dimension comprised between 2.1 and 2.4, while the fractal dimension of micropores did not exceed 1.5. The fractal dimension of mesopores and micropores are influenced significantly by the clay content. The study of the porosity of the marine soft soil of the Beibu Gulf could serve as a useful basis for the prediction of its hydraulic properties.

To determine the high-temperature effect on the soil particle composition (SPC) and its mechanism in Nanning, China, a laboratory experiment was designed based on the high-temperature environment caused by forest fires and considering thermal desorption. The effect mechanism was examined based on the soil organic matter and soil minerals (kaolinite). The experimental results indicated that the SPC was not changed before 200°C. With increasing heating temperature, the content of silt and clay decreased, while the content of sand greatly increased after 200°C. The analysis believes that the reduction of the content of organic matter has promoted the reduction of the content of silt and clay to a certain extent. The decrease in the silt and clay content inevitably increased the sand content, but this was also related to the soil minerals (kaolinite), and a reaction occurred producing a cementing substance that absorbed both silt and clay to form new sand. The temperature effect on the SPC was divided into three parts. The first part was observed from 100 to 200°C, while the soil composition was unchanged. The second part was from 200 ~ 400°C. This part is related to the reduction of organic matter content. The third part was determined to be between 400 and 800°C, which was mainly related to clay minerals. The fusion of silt and clay during the formation of new sand resulted in a decrease in its content beyond 400°C.

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.