## 3 Results
### Monotonic Loading Conditions  
In this study, the geogrid pullout resistance (P\({}_{\text{R}}\)) was evaluated considering the effective area of the geogrid and the average force values, as recommended by [PERSON] et al. [12]. The influence of the pullout test apparatus scale was verified through monotonic tests at three applied normal stresses (\(\sigma_{\text{n}}\)). Table 3 presents a summary of these test results, displaying the maximum pullout resistance (P\({}_{\text{R}}\)), the corresponding frontal geogrid displacement (\(\upmu_{\text{PR}}\)), the confined stiffness at 2% strain (J\({}_{\text{C2\%}}\)), the maximum shear stress (\(\tau_{\text{i}}\)) and the pullout interface apparent coefficient of friction (\(\mu_{\text{s/GSY}}\)). Figure 7 presents the comparison between the pullout force versus geogrid displacement from the small box (Figure 7a) and large box (Figure 7b) at 50 kPa applied normal stress. From Figure 7a, it is observed that the displacement values from tell-tales T1 to T3 were similar for the small-scale equipment, even though they were installed at different locations along the geogrid length. Conversely, the displacements recorded in the large-scale tests varied considerably throughout the whole reinforcement length. The longer the distance from the rear edge, the higher the displacement values, as shown in Figure 7b. Although different instruments (tell-tales and LVDTs) were used in the large-scale equipment, the results of pairs L1-T1 and L2-T5 were quite consistent. Figure 7: Displacement instrumentation response: (**a**) small box (\(\sigma_{\text{n}}\) = 50 kPa); (**b**) large box (\(\sigma_{\text{n}}\) = 50 kPa). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Test** & **P\({}_{\text{R}}\) (kN/m)** & **\(\upmu_{\text{PR}}\) (mm)** & **J\({}_{\text{C2\%}}\) (kN/m)** & \(\tau_{\text{i}}\) (kPa)** & \(\mu_{\text{s/GSY}}\) & \(\sigma_{\text{n}}\) (kPa)** & **Equipment** \\ \hline
1 & 15.68 & 27.16 & 725 & 36.47 & 1.46 & 25 & SB \\
2 & 22.19 & 25.55 & 779 & 51.61 & 1.03 & 50 & SB \\
3 & 27.57 & 15.82 & 838 & 64.12 & 0.64 & 100 & SB \\
4 & 20.90  
Figure 8 illustrates the influence of equipment scale on the pullout resistance of the geogrid for different applied normal stresses. When comparing the measured pullout resistance at lower applied normal stresses (25 and 50 kPa), it becomes apparent that the use of the large box led to significant increases in the maximum pullout resistance of 33.29% and 20.32%, respectively. However, for the tests performed under 100 kPa, the pullout resistance obtained from the large box exceeded that from the small box by only 4.9%. These results suggest that increasing the applied normal stress leads to a convergence of the values of pullout resistance estimated from both types of equipment. In pullout tests involving extensible geosynthetic reinforcements, the shear stress mobilized along the interface is non-uniform. It is dependent upon the reinforcement confined stiffness (extensibility) and the mobilized shear stresses over the active length of the reinforcement [14; 16; 48]. The active length corresponds to the confined geosynthetic length over which the mobilization of interaction mechanisms takes place, which can be determined based on the displacements recorded in discrete locations over the specimen length during the test. The experimental interpretation can be simplified by using Equation (4), as proposed by [PERSON] et al. [16]. This equation replaces the actual shear stress mobilized along the interface by an equivalent uniform average shear stress distribution (\(\tau_{AL}\)) that can be expressed as the ratio between the applied pullout force (\(P_{R}\)) and the double active length of the geosynthetic (\(L_{A}\)):  
\[\tau_{AL}=\frac{P_{R}}{2L_{A}} \tag{4}\]  
Figure 9 illustrates the maximum shear stress mobilized in the pullout tests (i.e., at the moment of achieving maximum pullout resistance), as determined by Equation (4), plotted against the applied normal stress, as well as the respective linear best-fit lines.