## 4 Experimental Results  
### Effect of Grouting Pressure on the Grouting Diffusion Range  
Figure 5a-c present the horizontal and vertical grout diffusion distance-grouting pressure curves for the grout volume at 200 mL, 300 mL, and 400 mL, respectively, with different normal load conditions. For the sake of simplicity, the legend is expressed as initial normal stress \(\sigma_{c}\)-applied normal stress \(\sigma_{s}\). For example, the legend showing 100-25 means the soil is consolidated at the initial normal stress of 100 kPa and is grouted at the applied normal stress of 25 kPa. Figure 5 shows that the returned height of the grouting cement along the pile body increases non-linear with the increase of the grouting pressure under different loading and unloading conditions when the grout volume is 200 mL. When the grout volume is 400 mL, the returned height reaches the maximum value when the grouting pressure is 600 kPa. When the grout volume is 300 mL, the variation laws of the returned height of the grouting cement with grouting pressure under different loading and unloading conditions are between the grout volume at 200 mL and 400 mL.  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Grouting** & **Grout Volume (mL)** & & **Normal Stress (kPa)** & \\
**Pressure (kPa)** & & 200 & 25 & 50 & 75 & 100 \\
500 & 300 & 25 & 50 & 75 & 100 \\  & 400 & 25 & 50 & 75 & 100 \\ \hline  & 200 & \(\times\) & \(\times\) & \(\times\) & 100 \\
600 & 300 & \(\times\) & \(\times\) & \(\times\) & 100 \\  & 400 & \(\times\) & \(\times\) & \(\times\) & 100 \\ \hline  & 200 & \(\times\) & \(\times\) & \(\times\) & 100 \\
700 & 300 & \(\times\) & \(\times\) & \(\times\) & 100 \\  & 400 & \(\times\) & \(\times\) & \(\times\) & 100 \\ \hline \end{tabular}
\end{table}
Table 3: Test program not considering unloading condition.  
Figure 5: Horizontal and vertical growth diffusion distance-grouting pressure curves: (**a**) 200 mL; (**b**) 300 mL; (**c**) 400 mL.  
The vertical grout diffusion distance-grouting pressure curves in Figure 5 present that the changes of the radial expansion distance of the grouting cement returned along the pile body with increasing grouting pressure are not monotonic under different load conditions and grout volumes. When the grouting pressure is 600 kPa, the corresponding radial expansion distance reaches the maximum at the grout volume of 200 mL and 300 mL. The returned height of the grouting cement is greater than the radial expansion distance under the same work conditions. The reason for this phenomenon is explained later in the Section 5.  
Table 4 shows the distance difference between the returned height and the radial expansion distance between the maximum and minimum grouting pressures. Table 4 presents that with the increase in grout volume, the contribution of the grouting pressure on the returned height increased and gradually weakened. When there exists an unloading condition in the soil, with the increase of grout volume, the increase of grouting pressure has an obstructive effect on the returned height increase. When there were no unloading conditions in the soil, with the increase of grout volume, the increase of grouting pressure would gradually strengthen the contribution on the radial expansion distance increased.