# Pores Evolution of Soft Clay under Loading/Unloading Process
## 3 Experimental Results
### FESEM Images and Pore Size Distribution
The percentage of large pores decreased to the minimum value of 4.082% at 100 kPa, and increased to 9.542% as the pressure increased to 1600 kPa under the loading process. However, the pore evolution analyzed by pore-size distribution contradicted the previous study [33], which showed that the percentage of large pores sharply decreased when the microstructure of soft clay rearranged. The distribution of pore-size did not reflect well the change of large pores. For example, when the even large pores is broken into several pores including pores bigger than 0.6 \(\upmu\)m, the number of large pores increase, but the area might decrease. In this situation, the area percentages of pores would be used to calculate the distribution of large pores, as shown in Figure 9. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{\(\boldsymbol{P}\) (kPa)} & \multicolumn{3}{c}{**Loading**} & \multicolumn{3}{c}{**Unloading**} \\ \cline{2-7}  & \multicolumn{2}{c}{**Percentage**} & \multirow{2}{*}{\(k\)} & \multirow{2}{*}{\(R^{2}\)} & \multicolumn{2}{c}{**Percentage**} & \multirow{2}{*}{\(k\)} & \multirow{2}{*}{\(R^{2}\)} \\  & **(\%)** & & & & & \\ \hline
50 & 67.013 & 4.737 & 0.955 & 67.829 & 4.853 & 0.978 \\
100 & 70.469 & 4.859 & 0.962 & 68.726 & 4.860 & 0.975 \\
200 & 70.915 & 4.731 & 0.965 & 69.231 & 4.751 & 0.990 \\
400 & 68.046 & 4.639 & 0.958 & 65.625 & 4.854 & 0.963 \\
800 & 69.799 & 4.846 & 0.950 & 68.601 & 4.941 & 0.987 \\
1600 & 69.466 & 4.943 & 0.956 & 69.198 & 4.834 & 0.959 \\ \hline \end{tabular}
\end{table} 
Table 3: Pore-size distribution and slope of the fitting line (\(<\)0.2 \(\upmu\)m). Figure 8: Pore-size distribution (\(>\)0.2 \(\upmu\)m). Figure 9: Area percentage of large pores (0.6 \(\upmu\)m) under the loading/unloading process. The area percentage of large pores underwent significant changes with pressure. Below 100 kPa, the microstructure was converted into the natural state, and the area percentage of large pores was high. As the pressure increased, the area percentage of large pores decreased to 91.087% under loading, while it decreased by 1.562% and 3.192% at 50 kPa and 100 kPa under unloading, respectively. From 100 kPa to 400 kPa, the area percentage of large pores sharply reduced to 84.771% under loading process, while it increased by 4.689 and 3.728 at 200 and 400 kPa under the unloading process, respectively. Above 400 kPa, the increase of area percentage of large pores slowed down. Under the loading process, the area percentage of large pores increased to 87.829%, while it increased slightly under the unloading process. The distribution of small pores was basically unchanged, while that of large pores changed nonlinearly with pressure under the loading/unloading process. The pore-size distribution under loading/unloading was better analyzed by area percentage of large pores. The area percentage of large pores decreased to 84.771% until 400 kPa, and then increased under the loading process, while it decreased below 100 kPa, and then increased under each unloading process. However, further explanation is needed in combination with the following analysis.