## 4 Analyses of Test Results  
### Load-Settlement  
The load-settling curve of the repetitive loading test is shown in Figure 11. The calculated values of the maximum settlement, residual settlement, and moduli of the subgrade reactions are summarized in Table 6. When comparing the first and second tests, the results of the first cycle exhibited a difference of approximately 2%. Because the test results contained a significant amount of plastic settlement on the surface, there was little difference between the results of the two tests using the same backfill material. In  
Figure 10: Location of the sensors. the second cycle, the maximum settlement increased by 25%, and the residual settlement increased by 221% in the second test compared with the first test; the ground reaction force coefficient accordingly decreased by 20%. This difference may be owing to the large increase in the stiffness of the reinforced soil as more geogrids in the first test were placed in the impact range of the load. The effect of increasing the stiffness of the subgrade via the reduction of the geogrid vertical spacing was similar to that of previous studies, in which the load was applied inside the reinforced area. The test results show that the reduction in the settlement, owing to the installation of the reinforcement, can be obtained even for a load outside the reinforcement area, and the settlement is reduced as the vertical spacing between the reinforcements is narrowed. The load-settling curves of the first and second static loading tests are shown in Figure 12; at loads of 500 kPa or less, the slopes of the two curves are similar, and at pressures above 500 kPa, the slopes of the two curves change. The reason for this may be \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Case**} & **Max. Settlement** & **Residual Settlement** & **Modulus of Subgrade** \\  & **(mm)** & **(mm)** & **Reaction, K\({}_{\bullet}\) (kPa/m)** \\ \hline \multirow{2}{*}{1 st test} & 1 st cycle & 15.87 & 9.46 & 30.876 \\ \cline{2-5}  & 2 nd cycle & 7.60 & 0.73 & 64,474 \\ \hline \multirow{2}{*}{2 nd test} & 1 st cycle & 16.17 & 9.26 & 30,303 \\ \cline{2-5}  & 2 nd cycle & 9.48 & 2.34 & 51,688 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Test result of repetitive loading test. Figure 11: Load-settlement curve of repetitive loading test. because the yield occurred in the soil under the load plate at the inflection point of the curves (at a load of 500 kPa) and plastic behavior began. At loads of 500 kPa or more, the increase in the stiffness of the reinforced area by the reinforcement has a more significant effect on the settlement reduction; therefore, a difference in the slope between the two curves may have occurred. Even at the maximum load of 1000 kPa, the settlement was 20.75 mm and 24.76 mm in the first and second tests, respectively, which did not reach the allowed maximum settlement (25.4 mm) proposed by [PERSON] et al. [21]. Similar to previous studies that applied long reinforcements [22], the effect of increasing the bearing capacity using short reinforcements was confirmed. The allowable bearing capacity of both sections were calculated, as shown in Table 7, using the P-S curve method (Figure 13) and [PERSON]'s equation considering a safety factor of 2. The allowable bearing capacity (\(q_{a}\)) and modulus of the subgrade reaction (\(K_{\text{s}}\)) of the soil were calculated according to Equations (1) and (2), as described by [PERSON] [23]:  
\[q_{a}=\frac{K_{\text{s}}}{40\ \text{F.S}}, \tag{1}\]  
where \(q_{a}\) is the allowable bearing capacity (kPa), \(F\)S is the safety factor taken as 2, and \(K\)s is the initial tangent modulus of the subgrade reaction (kPa/m);  
\[K_{\text{s}}=\frac{\Delta_{\sigma}}{\Delta_{Settlement}}, \tag{2}\]  
where \(\Delta\sigma\) is the difference between two successive vertical stresses (kPa), and \(\Delta_{settlement}\) is the difference between two successive vertical displacements (m).