## 4 Test Results
### Creep Test and Plastic Characteristics  
The creep tests were implemented under \(P=1300\) kN at loading phase and displacements (\(\Delta\delta\)) were recorded (Figure 6). It has been shown that when the displacement is below 1 mm for 10 minutes under 1.3 \(TL\), the micropile is stable against a creep [14]. As shown in Figure 6, all creep displacements were less than 1 mm, so the micropiles installed were acceptable; however, the variation in creep was shown to be different according to the installation methods. For \(Gr\), the slopes of the creep displacement gradually decreased as time passed. On the other hand, \(Ge\) and \(Ru\) were shown to be roughly consistent after approximately 3-5 min creep testing, which implies faster stabilization on creep than \(Gr\).  
The magnitudes of the creep displacements (\(\delta_{\text{creep}}\)) are summarized in Table 4 in addition to the magnitudes of the plastic displacement after completing the unloading cycle (i.e., plastic displacement, \(\delta_{\text{p}}=\delta_{\text{t}}-\delta_{\text{e}}\)). The \(\delta_{\text{creep}}\) for \(Gr\) is 2.2 and 4 times higher than those for \(Ge\) and \(Ru\), respectively. Besides, the standard deviations of \(\delta_{\text{creep}}\) showed the fluctuation of the displacement as \(\sigma_{\text{creep(Gr)}}=0.10\) mm, \(\sigma_{\text{creep(Ge)}}=0.03\) mm, and \(\sigma_{\text{creep(Ru)}}=0.01\) mm. The magnitudes of the creep displacements and corresponding standard deviations indicated more stable bonding between the micropile and soil in an order of \(Ru\), \(Ge\), and \(Gr\). The trend of \(\delta_{\text{p}}\) and \(\sigma_{\text{plastic}}\) showed a similar trend with \(\delta_{\text{creep}}\) and \(\sigma_{\text{creep}}\), but they were slightly different. The average \(\delta_{\text{p(Gr)}}\) and \(\delta_{\text{p(Ge)}}\) was shown to be similar at 2.8 mm and 2.3 mm respectively, while \(\delta_{\text{p(Ru)}}\) was 1.1 mm. The \(\sigma_{\text{plastic}}\) of \(Gr\) was 1.10 mm, while \(Ge\) and \(Ru\) were shown to be similar at 0.36 mm and 0.27 mm, respectively.  
The variations in creep and plastic displacements would include the spatial variability of the ground; however, there seem to be clear trends according to the different installation methods. The pressure-gruted micropiles using the geotextile and rubber packers showed superior plastic characteristics than the one using gravitational grouting. Even the rubber packer may eliminate the uncertainties resulting from the geological and installation-related issues.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type** & \(Gr\) & \(Ge\) & \(Ru\) \\ \hline \(\delta_{\text{creep}}\) (average) [mm] & 0.1, 0.22, 0.24, 0.24 & 0.07, 0.12, 0.13 (0.11) & 0.04, 0.06, 0.06, 0.08, 0.08 \\ \(\delta_{\text{p}}\) (average) [mm] & 1.1, 2.0, 3.4, 3.6, 4.0 (2.8) & 1.9, 2.1, 2.8 (2.3) & 0.8, 0.8, 1.3, 1.3, 1.4 (1.1) \\ \(\sigma_{\text{creep}}\) [mm] & 0.10 & 0.03 & 0.01 \\ \(\sigma_{\text{p}}\) [mm] & 1.10 & 0.36 & 0.27 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Creep and plastic displacements.  
Figure 6: Results of creep tests. (**a**) Micropiles installed using only gravitational grouting (\(Gr\)), (**b**) geotextile packer (\(Ge\)), and (**c**) rubber packer (\(Ru\)).