## 5 Results and Discussions
### Relationship between Excess Pore Water Pressures and Primary Consolidation Settlement  
Figure 6 plots the average excess pore water pressures (\(u_{t}\)). As shown in Figure 6, the \(u_{t}\) monotonously increases up to the maximums on the 63 rd day, then basically remains stable in vacuum preloading. On the 63 rd day, the \(u_{t}\) of vacuum preloading decays linearly from \(-70\) kPa to \(-10\) kPa along the depth of the ground, with an attenuation coefficient of 3.1 kPa/m. The reason for this is the PVDs's block, bending, and brakee induced by stratified settlement [6; 9; 17; 31; 32; 33; 34]. The \(u_{t}\) of surcharge preloading reaches maximum on the 30 th day, then dissipates up to the minimums on the 53 rd day. The \(u_{t}\) of surcharge preloading on the 30 th day is piecewise linear along depth, i.e., it increases from 15 kPa to 30 kPa with depth in the range of 3-15 m, and slightly reduces to 27 kPa with depth in the range of 15-21 m. The \(u_{t}\) monotonously increases up to the maximum on the 63 rd day, then basically remains stable in vacuum preloading. This shows existents in soil structure compression and stress redistribution during the consolidation process [5].  
Figure 6: \(u_{t}\) of vacuum preloading and surcharge preloading: (**a**) distribution of \(u_{t}\) along the depth of vacuum preloading; (**b**) distribution of \(u_{t}\) along the depth of surcharge preloading; (**c**) historical curve of vacuum preloading; (**d**) historical curve of surcharge preloading.  
The consolidation degrees (\(U_{wt}\)) are plotted in Figure 6 and tabulated in Table 5. \(U_{wt}\) is calculated using \(u_{t}\) by the hyperbolic method with the formula \(u_{t}=u_{0}+t/(\alpha_{2}+\beta_{2}t)\), \(u_{\infty}=u_{0}+\frac{1}{\beta_{2}}(t\rightarrow\infty)\), \(U_{wt}=\frac{\Delta u_{t}}{u_{\infty}}\), where \(u_{0}\) refers to the measured average excess pore water pressure (kPa) at any depth on the 20 th day and 30 th day in vacuum and surcharge preloading, respectively. \(\Delta u_{t}\) is the difference between \(u_{t}\) and its maximum (kPa). \(u_{\infty}\) is the final excess pore water pressure. \(\alpha_{2}\) and \(\beta_{2}\) are the constants. As shown in Table 5, the \(U_{wt}\) decreases with the depth from 3 m to 15 m, then increases from 15 to 21 m on the 83 rd day.  
Figure 7 plots the primary consolidation settlement (\(S_{pt}\)) vs. \(u_{t}\). The secondary consolidation settlement (\(S_{st}\)) during preloading retains a low level, and the effect of \(u_{t}\) on \(S_{st}\) can be ignored. Figure 7a shows that during the vacuum preloading, the \(S_{pt}\) obviously increases by 540 mm, equal to 90% primary consolidation settlement, with \(u_{t}\) ranging from 0 kPa to \(-\)40 kPa, while it gently increases by approximately 60 mm with \(u_{t}\) over \(-\)40 kPa. Therefore, it can be deduced that \(u_{t}\) with \(-\)40 kPa is an important value during the monitoring of \(u_{t}\), \(S_{t}\) in the vacuum preloading. As shown in Figure 7b, during the surcharge preloading, \(S_{pt}\) slowly increases with \(u_{t}\) beneath 20 kPa and increases significantly with \(u_{t}\) between 20 kPa and 25 kPa.