## 3 Results
### Cyclic/Post-Cyclic Loading Conditions  
The cyclic/post-cyclic pullout behavior of the geogrid was evaluated through tests conducted under 25 kPa and 100 kPa confining pressures. Figure 11 shows the variation of \(\mathrm{P_{R}}\) as a function of the geogrid frontal displacement based on the monotonic and cyclic/post-cyclic tests. As expected, at the commencement of cyclic loads, large frontal displacement occurs, leading to the mobilization of a significant portion of friction and bearing resistance; therefore, for high normal stress, during the post-cyclic loading stage, the pullout resistance is lower than that achieved under monotonic loading. This degradation of pullout capacity after cyclic loading is consistent with the findings of previously related research [28, 29, 31, 35]. The cumulative frontal displacement of the geogrid during cyclic loading was similar for both types of equipment (Figure 11). Higher cumulative cyclic displacement was measured for the lower normal stress of \(\mathrm{\sigma_{n}}\) = 25 kPa (Figure 11a). Under higher normal stress (Figure 11b), a premature failure of the geogrid in tension (tensile failure) occurred in the small-scale test in the post-cyclic stage. Conversely, when the large-scale equipment was used, the failure was attributed to sliding along the interface. It can also be observed that the displacement of the geogrid at maximum pullout force generally increased in the post-cyclic test, in comparison to that measured under monotonic loading conditions. This trend held true except for when the geogrid underwent tensile failure in the test under \(\mathrm{\sigma_{n}}\) = 100 kPa (Figure 10b). Table 4 indicates the values of maximum pullout resistance (\(\mathrm{P_{R}}\)), the ratio of the maximum post-cyclic shear stress to the maximum shear stress attained in the comparable monotonic pullout test (\(\mathrm{\tau_{cyc}}/\mathrm{\tau_{mon}}\)), and the peak pullout interface apparent coefficient of friction (\(\mathrm{\mu_{s/GSY}}\)) for the post-cyclic tests. It can be observed that, under the lower normal stress, no degradation of pullout resistance upon cyclic loading (reflected by the \(\mathrm{\tau_{cyc}}/\mathrm{\tau_{mon}}\) ratio) was observed; rather, the mobilized shear stress increased slightly. Conversely, under  
Figure 10: Confined tensile stiffness as a function of geogrid strain: (**a**) \(\mathrm{\sigma_{n}}\) = 25 kPa; (**b**) \(\mathrm{\sigma_{n}}\) = 50 kPa; and (**c**) \(\mathrm{\sigma_{n}}\) = 100 kPa. the higher normal stress, lower values of pullout resistance and mobilized shear stress were obtained under post-cyclic conditions. Figure 12 shows the variation in \(\upmu_{\text{s/GSY}}\) as a function of the applied normal stress. The results refer to the two pieces of equipment used, and the different loading conditions adopted (monotonic or cyclic/post-cyclic). For all the test conditions examined, it can be observed that the \(\upmu_{\text{s/GSY}}\) decreases as the applied normal stress increases. This behavior can be explained due to the soil dilatancy effects at the interface [14]. Moreover, for \(\upsigma_{\text{n}}=25\) kPa, the \(\upmu_{\text{s/GSY}}\) values obtained from the small pullout box exceeded those from the large box, regardless of the loading conditions. However, for higher normal stresses (\(\upsigma_{\text{n}}=50\) and \(100\) kPa), the differences between the \(\upmu_{\text{s/GSY}}\) values associated with distinct equipment types were less significant. Except for the small box test under \(\upsigma_{\text{n}}=25\) kPa, the \(\upmu_{\text{s/GSY}}\) values attained under monotonic loading conditions exceeded those reached under post-cyclic loading.