## 4 Discussion  
As previously mentioned, the evolution of displacements recorded by tell-tales T1 to T3 in the small box equipment for \(\sigma_{\text{n}}=50\) kPa was rather similar, as shown in Figure 6a. This indicates that only the front geogrid section underwent significant elongation during the load transfer phase of the pullout test and sliding occurred without significant deformation over the back half of the reinforcement. As shown in Figure 7b, for the large box, the instrumentation data revealed a non-linear distribution of shear stress over the whole geogrid length, where displacement values decreased with the distance from the loaded edge. These findings are in agreement with the studies of [PERSON] et al. [16] and [PERSON] et al. [25], in which the geosynthetic deformation in the confined region was found to be more significant in the frontal zone and less significant towards the rear end. However, as mentioned, significant deformation occurred over the whole geogrid length in the large-scale test prior to the pullout phase, as opposed to the small-scale test. This occurrence may be associated with the fact that the specimen width was considerably lower than the pullout box width in the case of the large-scale tests. Previous studies have shown that when the reinforcement specimens are narrower than the pullout box, the non-dilating zone in the soil surrounding the specimen behaves as a restrain against soil dilation in the dilating zone (i.e., above and below the reinforcement), which generates shear stresses at the border between the two zones leading to an increase in the effective normal stress at the soil-reinforcement interface [14]. In turn, higher normal stresses induce a progressive mobilization of the interaction mechanisms at the interface, resulting in a more significant non-linear displacement distribution along the reinforcement length [16], as well as higher pullout resistance values (Figure 8). As reported before, for lower applied normal stresses, when comparing the confined tensile stiffness at low strain values (less than 2%) for different types of equipment, a significant variability was identified (Figure 10a,b). This may be due to the different reinforcement mobilization (i.e., active length) in the distinct testing boxes. Despite this variability under lower strains, the confined stiffness values at 2% strain (or higher) showed reasonable agreement. Conversely, under a higher normal stress of 100 kPa, the confined stiffness values were similar for both types of equipment over the whole range of available strain values. This is likely associated with the fact that, under the higher normal stress, the deformation of the geogrid specimen tested in the small box extends to sections located further away from the clamp, resulting in similar deformations on the central section of the reinforcement (between tell-tales T2 and T3) in both tests, and hence similar confined stiffness values. Table 5 presents the ratios between the results obtained from small and large equipment (SB/LB), expressed in terms of the maximum pullout resistance (P\({}_{\text{R}}\)), maximum shear stress (\(\tau_{\text{i}}\)) and pullout interface apparent coefficient of friction (\(\mu_{\text{s/GSY}}\)) for both monotonic and cyclic/post-cyclic loading conditions. In Table 5, it can be concluded that for lower applied normal stress (\(\sigma_{\text{n}}=25\) kPa) and regardless of the loading conditions, the apparatus scale influences the measured pullout resistance, which is in accordance with the results reported by [PERSON] and [PERSON] [9].