# Behaviour of the Steel Welded Grid during a Simplified Pullout Test in Fine Sand
## 4 Results and Discussion
As the authors of this study only have the value of this displacement at two points, assuming its rectilinear slope, the anchorage length (for the maximum pullout forces applied in the tests) for the fine sand tested is approximately 2.3 to 3.0 m. These lengths are certainly underestimated, as the displacement value does not decrease in a linear way. Unfortunately, due to the lack of a third measurement point along the length of the reinforcement, the exact course of the curve describing this phenomenon cannot be determined. It is worth noting that, on the basis of the research carried out, it is possible to easily determine the value of the apparent friction coefficient \(\mu_{k}\) using Relationship (1):  
\[\mu_{k}\ =\ T_{max}/(2\cdot S\cdot\sigma_{\mathrm{z}}), \tag{1}\]  
where:  
\(T_{max}\)--a maximum pulling force [kN] (according to Table 2),  
\(S\)--a mesh area [m\({}^{2}\)] (0.34 m\({}^{2}\) for ZnAl, 4.50 mm and 0.75 m\({}^{2}\) for others),  
\(\sigma_{v}\)--a vertical stress at the level of the reinforcing steel mesh [kPa] (60 kPa in test). The summary of the friction coefficients between the reinforcement and the soil \(\mu_{k}\) calculated according to the above formula is presented in Table 4. The obtained values of the friction coefficient 0.39-1.47 are similar to those given by [PERSON] et al. [45], who reported values of the coefficient \(\mu_{k}\) equal to 0.31-0.72. It is worth noting that in this study, for a steel mesh with a wire diameter of 4.5 mm, the friction coefficient (\(\mu_{k}\) = 1.47) is much greater than that of [PERSON] et al. [45] for a steel grid with a wire diameter of 12 mm (\(\mu_{k}\) = 0.72). This can be explained by the fact that the friction coefficient is determined not only by the diameter of the mesh wire (the larger it is, the greater the coefficient of friction is), but also the mesh opening (the smaller it is, the greater the friction coefficient is, because more wires are located on the same surface across the force action). In this study, we used 76.2 \(\times\) 76.2 mm mesh opening, while [PERSON] et al. [45] examined grids with the mesh opening from 125 \(\times\) 140 mm to 125 \(\times\) 505 mm. On the other hand, [PERSON] et al. [46] showed coefficients of friction equal to \(\mu_{k}\) = 1.04-1.78 for welded meshes with a wire diameter of 6.3-12.7 mm and a mesh opening from 152 \(\times\) 152 mm to 152 \(\times\) 225 mm. At the same time, it was confirmed that the coating type of the mesh wire affects the friction coefficient. The zinc-coated wires of the same diameter (or similar) to the polyvinyl chloride (PVC)-coated ones are characterized by a higher coefficient of friction, which is consistent with the results of the hexagonal wire mesh studies realised by [PERSON] et al. [48]. By comparison, [PERSON] and [PERSON] [47] demonstrated for woven meshes (with a similar geometry as in [PERSON] et al. [45] and [PERSON] et al. [40]) a coefficient of friction equal to \(\mu_{k}\) = 0.2-0.30. This clearly shows that the welded meshes are more suitable for soil reinforcement than the commonly used woven meshes.