## 1 Introduction
The pullout resistance of geosynthetic reinforcements in granular soils can be evaluated by a theoretical relationship proposed by [36] and represented by Equation (1), where \((P_{R})\) is the geosynthetic pullout resistance per unit width, \((L_{R})\) is the geosynthetic length in the anchorage zone, \((\sigma_{n})\) is the effective normal stress at the reinforcement level, \((f_{b})\) is the soil-reinforcement pullout interaction coefficient and \((\phi)\) is the soil friction angle. \[P_{R}=2L_{R}\sigma_{n}f_{b}\tan\phi \tag{1}\]  
In the absence of information concerning the soil friction angle to be considered in Equation (1), the pullout resistance of geosynthetics can be expressed in terms of the pullout interface's apparent coefficient of friction, \(\mu_{S/GSY}\) (Equation (2)) [14]:  
\[P_{R}=2L_{R}\sigma_{n}\mu_{S/GSY} \tag{2}\]  
To account for the non-linearity of the pullout force along the length of extensible reinforcements, a scale effect correction factor \((\alpha)\) was introduced by [PERSON] et al. [2] (Equation (3)):  
\[P_{R}=2L_{R}\sigma_{n}F^{*}\alpha \tag{3}\]  
where \(F^{*}\) is the pullout resistance factor. In fact, the interface shear strength is not uniformly mobilized over the length of extensible geosynthetic reinforcements. The scale effect correction factor \((\alpha)\) accounts for the non-linear stress decrease throughout the reinforcement length and the development of progressive failure and depends mainly on the strain-softening of the soil and the reinforcement extensibility and length [2]. In the experimental data, which are lacking, the recommended values are 1.0 for metallic reinforcements, 0.8 for geogrids and 0.6 for geotextiles. The pullout resistance factor (\(F^{*}\)) may be determined through laboratory or field pullout tests using the backfill material intended for the project. However, if such data are unavailable, a conservative estimate of \(F^{*}\) for geosynthetic materials can be obtained considering \(F^{*}=2/3\) tan \(\phi\)[2]. Pullout tests have been extensively used to assess the interface mechanism and analyze the reinforced soil structure parameters. However, several factors can influence the results of pullout tests. The experimental and numerical data on the apparatus scale effect suggest that the apparatus size is susceptible to influencing the results of pullout tests [9; 10; 11]. [PERSON] and [PERSON] [9] and [PERSON] [6] verified that pullout test results are influenced by boundary conditions and friction coefficients between soil and geogrid can be overestimated in small-scale tests. This effect can be minimized by the lubrication of the internal face of the box frontal wall. [PERSON] and [PERSON] [11] observed that pullout apparatus with lower height resulted in stiffer interface response and higher maximum pullout load. Moreover, they noted a minimal impact of box height for heights exceeding the geosynthetic length. The authors recommended that the soil sample height should exceed 0.6 m.  
A small pullout box was developed by [PERSON] et al. [15] to evaluate the strength of individual geogrid ribs (i.e., longitudinal and transverse ribs). Moreover, the same equipment was used to evaluate the unsaturated soil conditions by [PERSON] et al. [37] and [PERSON] [38]. [PERSON] [39] compared the results from monotonic tests using small- and large-scale equipment and concluded that the shear stress and interaction coefficient values were practically concomitant. [PERSON] [39] and [PERSON] et al. [13] evaluated the effect of the size of the geogrid and the internal width of the equipment and concluded that as the specimen width approaches the internal dimensions of the box, the pullout force tends to a constant value. Therefore, for the analyzed geogrids, the authors recommended using twelve longitudinal elements. The test method described in the ASTM D6706 [40] standard considers using large-scale equipment and is intended to be a performance test simulating design or as-built conditions [40].