## 5 Results and Discussions  
### Measured Settlements  
Figure 3 and Table 3 show the ground settlements (\(S_{gs}\)) and the stratified settlements (\(S_{ss}\)) in the vacuum and surcharge preloading regions. As shown in Figure 3 and Table 3, on the 83 rd day, the central \(S_{gs}\) and \(S_{83}\) in the vacuum preloading region are 0.7 to 0.93 times that in the surcharge preloading region. These ratios belong in the range from 0.8 to 1.0 provided by [PERSON] [28]. Figure 3 also shows that \(S_{ss}\) reduce along depth and have a good fitness by negative exponential function with correlation coefficients of 0.93 and 0.87, respectively. The consolidation degree, \(U_{st}\), is calculated by the ratio of \(S_{t}\) to the final average settlements of ground and strata (\(S_{1,\infty}\)), predicted by the hyperbolic method with the formulas \(S_{t}=S_{0}+\frac{I}{\alpha_{1}+\beta_{1}t}\) and \(S_{1,\infty}=S_{0}+\frac{1}{\beta_{1}}(t\rightarrow\infty)\). \(S_{0}\) is the measured ground and stratified settlement (mm) on the 20 th day and 30 th day for vacuum and surcharge preloading with 80 kPa, respectively; \(\alpha_{1}\) and \(\beta_{1}\) are constants. \(S_{1,\infty}\) and \(U_{st}\) are tabulated in Table 3. Table 3 shows that \(U_{st}\) of foundation depth from 0 m to 15 m by the vacuum preloading is 1% greater than the one of surcharge preloading, while the \(U_{st}\) of vacuum at a depth of 15-21 m is 3% to 5% smaller than the one of surcharge. \begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Depth/m**} & \multicolumn{3}{c}{**Vacuum Preloading**} & \multicolumn{3}{c}{**Surcharge Preloading**} \\  & \(S_{\textbf{83}}\)**/mm** & \(S_{\infty}\)**/mm** & \(S_{\textbf{83}}\)**/\(S_{\infty}\)** & \(S_{\textbf{83}}\)**/mm** & \(S_{\infty}\)**/mm** & \(S_{\textbf{83}}\)**/\(S_{\infty}\)** \\ \hline
0 & 1098 & 1204 & 91\% & 1185 & 1317 & 90\% \\
3 & 820 & 898 & 91\% & 999 & 1105 & 90\% \\
9 & 660 & 734 & 90\% & 815 & 911 & 89\% \\
15 & 350 & 413 & 85\% & 500 & 565 & 88\% \\
21 & 75 & 83 & 90\% & 88 & 93 & 95\% \\ \hline \end{tabular}
\end{table} 
Table 3: Consolidation degrees using ground and stratified settlements of vacuum preloading and surcharge preloading. Figure 3c shows the curves of the stratified settlements. In contrast to surcharge preloading, vacuum preloading reinforcement of soft foundations exhibits an accelerated increase in soil strength during the initial stages, followed by a deceleration in the later stages of reinforcement. Conversely, surcharge preloading demonstrates a more gradual increase in soil strength throughout the reinforcement process [29]. This distinction is attributed to the disparate reinforcement mechanisms inherent to each preloading method. Vacuum preloading employs an impermeable plastic film and geotextile sealing to strengthen soft ground foundations. By generating negative pressure within the soil, vacuum pumps facilitate the gradual extraction of soil pore water and air, leading to a continuous decrease in pore water pressure and an increase in the foundation's effective stress. The vacuum pressure's direct action on the fluid within the soil pores and indirect action on the soil skeleton via the pore fluid approximates an isotropic isobaric situation, enabling  
Figure 3: Curves of ground settlements and stratified settlements: (**a**) historical curve of ground settlements in the vacuum preloading; (**b**) historical curve of ground settlements in the surcharge preloading; (**c**) historical curve of stratified settlements; (**d**) fitting function of stratified settlements. immediate application of the set load value. Consequently, a larger initial settlement is attained, and ground settlement remains relatively uniform [22; 30]. In contrast, surcharge preloading applies the external load directly to the soil skeleton or particles, necessitating a stepwise loading process that precludes a one-time application of the set load value.