Microstructure change rule during the consolidation process of peat soil from Yunnan province

Peat soil is a loose, moisture-rich organic matter accumulation formed by the deposition of plants in swamps and lakes after their death. It is characterized by high moisture content, large void ratio, high compressibility, and strong rheological properties. These characteristics result in a complex consolidation process. A systematic understanding of the consolidation mechanism of peat soil is essential for elucidating its consolidation behavior. Previous studies have failed to provide consistent information on the microscopic morphology of peat soil. Moreover, quantitative studies on pore structure changes during peat soil consolidation remain lacking. To resolve these research gaps, the microscopic morphology and pore types of peat, highly organic peaty soil, and medium organic peaty soil from certain regions of Yunnan province, China, were observed and analyzed using scanning electron microscopy. Additionally, quantitative research on pore structure changes during peat soil consolidation was conducted. The results show that the humic acid in peat soil of Yunnan province has no pores, and there is no pore between humic acid and clay minerals. There are three typical pore structures, and the three typical pores were quantitatively analyzed. During consolidation, the consolidation deformation of peat soil is primarily caused by the internal pore compression of plant residues and pores between plant residues. At the same time, the revelation of the differentiated influence mechanism of load levels on the compression of inter/intra-plant residue pores. The decrease in the proportion of pores between plant residues first increased and then decreased with an increase in load, reaching a peak between 100–200 kPa. The decrease in pores inside the plant residues increased with an increasing load. Additionally, pore compression between the plant residues under different load levels primarily caused the compression deformation of Dali peat during the primary consolidation stage. By contrast, the pore compression inside the plant residues primarily caused the compression deformation during the secondary consolidation stage.