## 2 Materials and Methods
### Pullout Test Devices  
According to the ASTM pullout test standard [40], the large-scale pullout test box should have minimum dimensions of 610 mm in length, 460 mm in width and 305 mm in height. Additionally, the width of the box should be determined as the greater of 20 times the D\({}_{85}\) of the soil or 6 times its maximum particle diameter, while ensuring the length is greater than 5 times the maximum aperture size of the geosynthetic. The box must provide a minimum depth of 150 mm above and below the geosynthetic, whereby the soil depth above and below the geosynthetic is at least 6 times the D\({}_{85}\) of the soil and 3 times its maximum particle diameter. Finally, the box should allow for a minimum embedment length of 610 mm beyond the sleeve, as well as a geosynthetic length-to-width ratio not lower than 2.0. The large pullout box (LB) utilized herein (Figure 2) consists of a rigid steel box, reinforced with U-shaped steel beams, which was first developed by [PERSON] [45]. Its dimensions are 1500 mm long, 700 mm wide and 480 mm high. As can be observed, the box exceeds the dimensions prescribed by ASTM D6706 [40]. The system can apply a tensile force of up to 60 kN to the reinforcement. For normal load application, an airbag is used, providing a uniform surcharge that replicates field conditions [45]. The boundary effects generated by the inner walls of the box can affect the measured pullout resistance value. As mentioned by [PERSON] and [PERSON] [9], one of the options to reduce such effects consists of leaving a minimum distance of 150 mm between the geosynthetic and each pullout box wall. Additionally, [PERSON] and [PERSON] [9] recommended using a metallic sleeve at the level of the reinforcement to mitigate the frictional effects at the front wall, as its implementation causes the point of application of the pullout force to be transferred inside the soil mass, as illustrated in Figure 2.  
The small pullout box (SB) consists of a rigid steel box with inner dimensions of 245 mm in length, 300 mm in width and 145 mm in height, as shown in Figure 3. These \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **Unit** & **Value** \\ \hline Polymer & - & PP \\ Thickness & mm & 1.05 \\ Mean grid size & mm & 45 \(\times\) 45 \\ Short-term tensile strength & kN/m & 43.24 \\ Elongation at maximum load & \% & 5.75 \\ Secant stiffness at 5\% strain & kN/m & 523 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Geogrid properties. Figure 2: Large-scale pullout test apparatus: (**a**) overall view; (**b**) inextensible wires fixed along the GGR. dimensions closely resemble those of a large-scale direct shear test apparatus and are approximately half of the minimum dimensions indicated by ASTM D6706 [40]. The upper surface of the box features a reaction cap attached to a pressure-controlled air bag used for applying the normal load. Positioned in the rear region is a support for the attachment of four tell-tales, which are linked to the geosynthetic by inextensible wires. The small box was originally developed by [PERSON] et al. [15] to investigate the individual geogrid ribs. However, a comparison between the results from both devices considering the monotonic and cyclic pullout response of geosynthetic reinforcements to evaluate the associated scale effects had not yet been performed. In the case of the small-scale equipment, keeping a significant distance between the sidewalls of the box and the reinforcement or the inclusion of a metallic sleeve is not possible due to the limited dimensions of the box. Therefore, to reduce the sidewall friction, a different solution proposed by [PERSON] and [PERSON] [9] was adopted, which consisted of installing two geomembranes on each wall, lubricated with graphite calcium grease, as shown in Figure 3. In order to use the same load application system in both pieces of equipment and to be able to establish the respective comparisons, an adaptation support for the small equipment in the large box was designed.