## 3 Material and Test Program  
### Testing Material Properties and Installation of Micropiles  
The dimensions and properties of the borehole, grout, and reinforcing bar used in the installation of the micropiles are summarized in Table 2. Auxiliary components were used such as a casing (_SS400_, _fy_: 400 MPa, KS D 3503), a plate (_SM490_, _fy_: 490 MPa, KS 2014), and a coupler and nut (Steel grade _500/550_, _fy_: 500 MPa, _fu_: 550 MPa). Assuming a target load (_TL_) = 1000 kN equivalent to a rock anchor [24], all design parameters satisfy the geotechnical and structural requirements provided by [PERSON] et al. [14]. Three micropiles were installed using different grouting methods: (1) gravitational grouting; (2) pressurized grouting with a geotextile packer; and (3) pressurized grouting with a rubber packer. For the micropile with the gravitational grouting, a reinforcing bar was inserted into a borehole and the grouting was injected via gravity. For the pressure-grouted micropile with a geotextile packer, a geotextile packer was attached to a target position of the reinforcing bar and manually fixed with wires (Figure 3a). The reinforcing bar with the flat packer was inserted into a borehole, and the packer was filled with pressure grouting through the preinstalled small pipe and fitted at the borehole (Figure 3b). At this stage, the induced slime (i.e., the mixture of water, soil, and grout) moved to the upper part of the borehole when the grout was injected (Figure 3b). It was unavoidable  
Figure 2: Profiles of the construction site. (**a**) Stratification of the site and (**b**) examples of fractures surveyed by BIPS (Note, \(N_{\text{measured}}\): measured \(N\) value by SPT, \(k\): hydraulic conductivity of soils, RQD: rock quality designation, TCR: total core recovery, _SM_: sandy silt, _CL_: clay with low plasticity, and _SP_: poorly graded sand). that the slime remained at the upper part of the borehole. The impurity of the grouting by the slime impaired the interfacial stress of the grouting [25; 26]. The micropile using a rubber packer was installed as follows. A reinforcing bar with the rubber packer was inserted into the borehole. The rubber packer was expanded via air and grouting was induced with pressure. The rubber packer consisted of a rubber tube between two steel disks. The rubber tube was inflatable by air through a nozzle attached. The rubber packer had threads so that the rubber packer could be screwed onto the reinforcing bar (Figure 3c). Another nozzle attached to the rubber packer was to \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Property** & **Value** & **Note** \\ \hline \multirow{2}{*}{Borehole} & Depth (or pile length) [m] & 10.5 & \(L_{\text{b}}\) \\  & Diameter [mm] & 177 & \(D_{\text{hole}}\) \\ \hline \multirow{4}{*}{Grout} & Type of cement & Portland cement & \\  & Area [mm\({}^{2}\)] & 20,187.9 & \multirow{2}{*}{Borehole area—Micropile area; \(A_{\text{g}}\)} \\  & Water/cement [\%] & 45 & No admixture used \\  & Elastic modulus [GPa] & 29.9 & \(E_{\text{g}}\) \\  & Compressive strength [MPa] & 40 & \(f_{\text{ck}}\) \\ \hline \multirow{4}{*}{Reinforcing bar} & Length [m] & 12 & \multirow{2}{*}{Pile head of 1.5 m exposed above the ground surface; \(L\)} \\  & Diameter [m] & 0.075 & \(D_{\text{nebar}}\) \\  & Area [mm\({}^{2}\)] & 4417.9 & \(A_{\text{s}}\) \\  & Elastic modulus [GPa] & 210 & \(E_{\text{s}}\) \\  & Ultimate strength [MPa] & \(>\)550 & \(f_{\text{u}}\) \\  & Yield strength [MPa] & \(>\)500 & \(f_{\text{y}}\) \\ \hline \multirow{2}{*}{Micropile} & Area [mm\({}^{2}\)] & 24,605.7 & \multirow{2}{*}{Area of borehole, \(A_{\text{p}}\)} \\  & Elastic modulus [GPa] & 62 & \((A_{\text{g}}E_{\text{g}}+A_{\text{s}}E_{\text{s}})/(A_{\text{g}}+A_{\text{s}})\), \(E_{\text{predicted}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Material properties of micropiles. Figure 3: Construction processes of pressure-ground micropiles using (**a,b**) geoetxtile and (**c,d**) rubber packers.