## 4 Analysis of Test Results
### Distribution of Pile Side Resistance  
The combined post-grouting technique represents a significant advancement over traditional pile end grouting as it integrates both pile end and pile side post-grouting technologies. This combination results in substantial improvements in both pile tip-and-side resistance. The bearing capacity of piles is primarily derived from these two components. During the combined post-grouting process, the pile side grout strengthens the surrounding soil and alleviates issues related to the mud skin formed during pile installation. Figure 4 illustrates the variation in pile side resistance (\(q_{\text{si}}\)) along depth (\(H\)) for each soil layer of test piles at different stages under ultimate load. The figures reveal that, although the distribution patterns of pile side resistance before and after grouting remain largely unchanged, the pile side resistance at the same depth is significantly enhanced due to the injected grout. It is important to note that when a single pile is loaded, the pile side resistance gradually increases from the top to the bottom until it reaches its ultimate value. Under smaller loads, the deep pile side resistance may not be fully exerted. However, as shown in Figure 4, under ultimate load, the pile side resistance at all depths has reached its ultimate value. Table 4 provides statistics on the ultimate pile side resistance at each depth. The data indicate that the pile side resistance within the entire pile length of test piles TP1 and TP2 is increased after grouting compared to before. Due to the similar nature of the soil layer, there is no significant difference in the shallow pile side resistance, and the increase in side resistance is consistent. Notably, the increase in pile side resistance is particularly pronounced at approximately 1 m from the pile end. Specifically, the side resistance of test piles TP1 and TP2 at this depth increased by 78.72% and 80.21%, respectively. This enhancement is attributed to the pre-pressurization effect of the cement grout injected into the pile end, which extends to a certain range of the surrounding soil, thereby increasing the stress in the pile side soil within this range. The results demonstrate that combined post-grouting not only reinforces the soil on the pile side and improves the mud skin through pile side grouting but also further densifies the soil within a specific range of the pile end through the upward return of the grout at the pile end. This comprehensive approach significantly enhances the bearing performance of the pile foundation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Pile No.**} & \multicolumn{2}{c}{**Before Grouting**} & \multicolumn{2}{c}{**After Grouting**} \\ \cline{2-5}  & **Ultimate Bearing Capacity** & **Displacement of Pile Top** & **Ultimate Bearing Capacity** & **Displacement of Pile Top** \\  & **(kN)** & **(mm)** & **(kN)** & **(mm)** \\ \hline TP1 & 27,644 & 30.33 & 36,765 & 33.53 \\ TP2 & 26,560 & 33.23 & 36,765 & 30.56 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Ultimate bearing capacity and corresponding pile top settlement of test piles.