## 3 Test Results and Analysis  
### Pile Top Load-Settlement Relationship  
The ultimate bearing capacity of each pile and the corresponding pile top settlement are listed in Tables 3-5. Figure 9 presents the pile top load-settlement relationship of model piles with different grouting volumes. In terms of the trend of curves, the load-settlement relationship of each pile is approximately linear at low loads, while the curve gradually becomes nonlinear until it reaches the ultimate bearing capacity. In each grouting group, the length of the linear segment is significantly longer than that of the non-grouted pile (N00), indicating the enhancement of bearing stiffness with grouting. The final settlement of almost all piles was found to be considerable due to the limited support provided by cohesive soils compared to sandy soil formations. The test results revealed that several piles experienced sudden collapse upon surpassing their ultimate bearing capacity, emphasizing the need to consider potential failure modes in the design and construction of pile foundations in cohesive soils. The ultimate bearing capacity of N00 is 0.8 kN, while post-grouting significantly increases the ultimate bearing capacity. Furthermore, from Tables 3-5, it can be observed that, as the grouting volume increases, the improvement in the ultimate bearing capacity of the pile becomes more pronounced. As the grouting volume increased from 1 L to 3 L, the bearing capacity of the pile tip, pile side, and combined grouting group increased from 1.6 kN, 4.4 kN, and 4.4 kN to 5.7 kN, 7.3 kN, and 7.9 kN, respectively. In terms of pile top settlement, the ultimate settlement of N00 is 3.86 mm. Except for pile T16, all \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Group Number** & **Grouting Form** & **Pile Number** & \
\begin{tabular}{c} **Grouting** \\ **Volume/L** \\ \end{tabular} &
\begin{tabular}{c} **Grouting** \\ **Pressure/MPa** \\ \end{tabular} \\ \hline
1 & Non-grouting & N00 & 0 & 0 \\
2 & Pile tip grouting & T16 & 1 & 0.6 \\  & & T26 & 2 & 0.6 \\  & & T36 & 3 & 0.6 \\  & & T25 & 2 & 0.5 \\  & & T27 & 2 & 0.7 \\
3 & Pile side grouting & S16 & 1 & 0.6 \\  & & S26 & 2 & 0.6 \\  & & S36 & 3 & 0.6 \\  & & S25 & 2 & 0.5 \\  & & S27 & 2 & 0.7 \\
4 & Combined grouting & TS16 & 1 & 0.6 \\  & & TS26 & 2 & 0.6 \\  & & TS36 & 3 & 0.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Test groups. grouting piles have borne more than 3 kN load when reaching this settlement. Therefore, post-grouting can reduce the pile-top settlement remarkably. As shown in Figure 9, when the grouting volume is 1 L, the ultimate bearing curve decreases from N00 for all grouting forms. This indicates that the reinforcement effect of grouting on the soil-pile system is not strong enough when the grouting volume is relatively small, resulting in significant pile displacement under large ultimate loads. The ultimate bearing capacity curve shows a significant upward trend after the grouting volume reaches 2 L, indicating that an adequate grouting volume is more favorable for controlling the pile settlement. Figures 10 and 11 present the variation curves of ultimate bearing capacity and settlement concerning the grouting form and grouting pressure. As shown in Figure 10, under the condition of the same volume of grout, the ultimate bearing capacity curve of the grouting pile shows an upward trend from pile tip grouting to pile side grouting and then to combined grouting. The reason for this can be attributed to the relatively small lateral friction and tip-bearing resistance of the pile in cohesive soils with shallow depths. Therefore, single grouting at either the pile tip or pile side is unable to effectively reinforce the contact surface between the pile and soil on both sides. In contrast, combined grouting, although with a reduced grout volume from individual grout ports, has a wider reinforcement coverage around the pile. Moreover, the reinforcing effect on the soil around the pile is more pronounced on the pile side than on the pile base.