## 3 Results and Discussion  
### Qualitative Analysis of Soil Microstructure  
At 8000 times magnification, microscopic images of representative sections of each SEM sample were captured. Particle morphology, connection mode and pore shape and  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Group** & **A** & **B** & **C** & **D** & **E** & **F** \\ \hline Consolidation pressure/MPa & 0 & 0.2 & 0.2 & 0.2 & 0.2 & 0.2 \\ Consolidation time/min & 0 & 30 & 60 & 240 & 720 & 1440 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Consolidation compression experiment.  
size were used to evaluate changes in the microstructure of soil samples under different experimental conditions. Figure 3 shows SEM images of the samples under different compression consolidation times.  
Figure 3a shows that the sample had a flocculation structure before consolidation, and individual particles were spread as debris, aggregates and irregular flake-like aggregates. There was cementation between the particles, but no directionality. Numerous huge pores were discontinuous and isolated (shown as rectangles in Figure 3a). Particle gaps were  
Figure 3: Microstructure of soil samples under different consolidation times: (**a**) 0 min; (**b**) 30 min; (**c**) 60 min; (**d**) 240 min; (**e**) 720 min; (**f**) 1440 min.  
widely distributed, and the integrity was poor. Figure 3b reveals that, after 30 min of consolidation, there were more flaky joints, fewer large pores and a significant increase in small pores, showing the dispersion of debris and feather flocs (shown as circles in Figure 3b), although the direction was not evident. This is because soil skeleton particles were crushed and broken during the consolidation process, and the large pores were crushed first, resulting in one pore being crushed into two or more. As a result, the medium pores were crushed as well, resulting in fewer medium and large holes and an increase in the number of small pores. As the consolidation time increased, soil samples formed bigger aggregates composed of edge-edge and edge-surface between flake-like structures. Such a trend was in conformity with the study on the evolution of the microstructure of soft clay under consolidation loading conducted by [PERSON] et al. [41]. As the degree of soil compaction rose, the connection strength also increased, and the arrangement became more ordered (marked as arrows in Figure 3c,d). Over a long period of consolidation, neighboring soil particles approached, aggregated and compacted, and then the microstructure transformed from a skeleton-type overlapping structure to a closed-type flake structure, resulting in an obvious agglomeration event. The connection mode between structural units, which was previously based mostly on edge-edge and edge-surface, shifted to one dominated by surface-surface, and the structure became more stable. Therefore, the compaction effect of the soil was significant at the microscopic scale.  
When the six images below are compared, it is clear that the long-term consolidation process involved the breaking of large holes, increases in small and medium pores and the gradual compression of the soil. The above findings reflect the qualitative change in soil after consolidation and compression under different test conditions. Macroscopically, the axial strain of the soil sample increased after long-term consolidation and compression. The experimental findings show that the change in the mesostructure can explain the macroscopic properties of soft soil after lateral consolidation and compression to a certain extent.