# Effect of Micropiles on Clean Sand Liquefaction Risk Based on CPT and SPT
## 4 Concluding Remarks  
The effect of jet grouting using micropiles to mitigate the risk of liquefaction on soil mainly containing clean sand was investigated. The resulting factor of safety values based on CPT and SPT simplified liquefaction analyses showed soil improvement against liquefaction after soil remediation. In addition, the R-squared values showed a comparable correlation between the \((N_{1})_{60\text{cs}}\) values in the coarse-grained soil (\(R^{2}=0.847\)) and the fine-grained soil layers (\(R^{2}=0.796\)). The correlations between q\({}_{\text{CINCS}}\) indices in fine-grained soil \(R^{2}=0.786\) were stronger than the q\({}_{\text{CINCS}}\) values among the clean sands \(R^{2}=0.497\). These R-squared values based on the SPT and CPT methods highlight the considerable effect of using jet-grouted micropiles on improvement of the existing soils. According to three CPT-based liquefaction analyses, the [PERSON] method predicts the most effective soil improvement by micropiles in that the factor of safety in 34.4% of clean sand layers was improved considerably (\(FS>2\)). Boulanger and Idriss and Eurocode methods showed comparable and more conservative evaluations with 12.5% improvement in this range of factor of safety. Results of the SPT-based analyses showed the most stringent improvement of the factor of safety after jet grouting (\(FS>2\)), in 35.5% of the SP soil, following both Boulanger and Idriss and NCEER approaches. The average trend lines of the factor of safety are quite comparable for all three SPT-based liquefaction assessment methods. The highest improvement range against the liquefaction (\(FS=5\)), which was achieved in various depths of clean sand layers, highlights the effectiveness of jet grouting by micropiles based on both CPT-based and SPT-based approaches. The trend lines show consistent values of factor of safety in SPT analysis compared to abrupt changes of these values in the CPT-based \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline  & \multicolumn{3}{c}{**Boulanger and Idriss**} & \multicolumn{3}{c}{**Eurocode**} & \multicolumn{3}{c}{**NCEER**} \\ \cline{2-11}  & \multicolumn{2}{c}{**Clean Sand**} & \multicolumn{2}{c}{**SP-SC, SP-SM,**} & \multicolumn{2}{c}{**Clean Sand**} & \multicolumn{2}{c}{**SP-SC, SP-SM,**} & \multicolumn{2}{c}{**Clean Sand**} & \multicolumn{2}{c}{**SP-SC, SP-SM,**} \\  & \multicolumn{2}{c}{**(SP)**} & \multicolumn{2}{c}{**SC, SM**} & \multicolumn{2}{c}{**(SP)**} & \multicolumn{2}{c}{**SC, SM**} & \multicolumn{2}{c}{**(SP)**} & \multicolumn{2}{c}{**SC, SM**} \\ \hline Criterion & Number of & Case & Number & Case & Number & Case & Number & Case & Number & Case & Number & Case \\ C-1 & & 5 & 2.0 & 11 & 57.9 & 23 & 74.2 & 15 & 78.9 & 16 & 51.6 & 12 & 63.2 \\ C-2 & 11 & 35.5 & 1 & 5.3 & 2 & 6.5 & 2 & 10.5 & 4 & 12.9 & 0 & 0.0 \\ C-3 & 0 & 0.0 & 0 & 0.0 & 0 & 0.0 & 0 & 0 & 0 & 0.0 & 0 & 0.0 \\ C-4 & 11 & 35.5 & 7 & 36.8 & 6 & 19.4 & 2 & 10.5 & 11 & 35.5 & 7 & 36.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparative evaluation of factor of safety improvements for SPT-based liquefaction triggering assessment following Boulanger and Idriss, Eurocode, and NCEER methods and specifications after jet grouting by micropiles.