## 4 Experimental Results
### Effect of Grout Volume on the Grouting Diffusion Range  
Figure 6a-c present the horizontal and vertical grout diffusion distance-grout volume curves for the grouting pressure at 500 kPa, 600 kPa, and 700 kPa, respectively, with different normal load conditions. Figure 6 shows that the returned height increases with the grout volume increased for the grouting pressure at 500 kPa and 600 kPa. When the grouting pressure is 700 kPa, the relationship between the returned height and grout volume is affected by the degree of unloading. Defined the unloading degree as the ratio of the difference of initial normal stress and applied normal stress to the initial normal stress [21]. As the unloading degree decreases, the variation laws between the returned height and grout volume transferred from a positive correlation to a negative correlation. When the unloading degree is 0, the returned height remains unchanged with the increase of the grout volume. The radial expansion distance is maintained within the range of 5-8 cm with different grout volume and load conditions for the grouting pressure at 500 kPa and 600 kPa. The radial expansion distance fluctuates little with the grout volume under the same load conditions. When the grouting pressure is 700 kPa, the radial expansion distance fluctuates little when the grout volume is less than 300 mL, whereas its value increases significantly with the increase of grout volume when the grout volume is greater than 300 mL. Table 5 shows the distance difference between the returned height and the radial expansion distance between the maximum and minimum grout volume. Table 5 presents that with the increase of grouting pressure, the increase of grout volume gradually weakens the contribution on the returned height increased, and may even have an obstructive effect, whereas its contribution on the radial expansion distance is weakened first and then gradually strengthened. This may be due to the transfer of the grouting mode caused by the changes in grouting pressure and grout volume. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{
\begin{tabular}{c} **Grout** \\ **Volume (mL)** \\ \end{tabular} } & \multicolumn{4}{c}{**Difference of the Returned Height (cm)**} & \multicolumn{4}{c}{**Difference of the Radial Expansion Distance (cm)**} \\ \cline{2-9}  & \multicolumn{4}{c}{**Load Conditions (kPa)**} & \multicolumn{4}{c}{**Load Conditions (kPa)**} \\ \cline{2-9}  & **100-25** & **100-50** & **100-75** & **100-100** & **100-25** & **100-50** & **100-75** & **100-100** \\ \hline
200 & 4 & 2.4 & 4 & 1.2 & \(-1.5\) & \(0.8\) & \(0\) & \(0\) \\
300 & 2.5 & 1 & 1.4 & 0.8 & \(-3\) & \(-0.8\) & \(-1\) & \(0.5\) \\
400 & 1 & \(-3\) & 0 & 0 & \(-1\) & \(-0.3\) & \(1.3\) & \(2.4\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Difference in the grout diffusion range between the maximum and minimum grouting pressures. Figure 6: Horizontal and vertical growth diffusion distance-grout volume curves: (**a**) 500 kPa; (**b**) 600 kPa; (**c**) 700 kPa. Figure 7a,b show the comparison of grout diffusion distance-grout volume between loading and unloading conditions for the grouting pressure at 500 kPa. As the grout volume increased, the returned height increased non-linearly for the soil stress history with loading conditions but increased linearly for the soil stress history with unloading conditions. Moreover, the parallel nature of the lines shows a similar rate of increase in the returned height with grout volume for different soil stresses history with loading conditions. The increased rate of the returned height with increasing grout volume under the unloading condition is lower than that under the loading condition for the same applied normal stress condition. Figure 7: Grout diffusion distance-grout volume curves under loading and unloading conditions: (a) horizontal grout diffusion; (b) vertical grout diffusion.