# Behaviour of the Steel Welded Grid during a Simplified Pullout Test in Fine Sand
## 5 Conclusions  
This study deals with the interaction of welded steel mesh, used for the production of gabions, with the soil depending on (1) the soil type (in this case fine sand FSa) and \begin{table}
\begin{tabular}{c c} \hline  & **Friction Coefficients between** \\
**Mesh Type** & **the Reinforcement and the Soil** \\  & \(\mu_{k}\) **[-]** \\ \hline Zn + PVC 4.30 mm & 0.61 \\ Zn + PVC 3.20 mm & 0.39 \\ ZnAl 4.50 mm & 1.47 \\ ZnAl 3.00 mm & 0.39 \\ \hline \end{tabular}
\end{table} 
Table 4: Coefficient of friction between reinforcement and soil \(\mu_{k}\) based on the presented tests. (2) the mesh parameters. The tested meshes (four types) were differentiated with respect to the diameter of the steel wire (2.7-4.5 mm) as well as the type of anticorrosion coating (Zn + PVC or ZnAl). Each of them had the same opening size: 76.2 \(\times\) 76.2 mm. For the analysis, a proprietary stand was constructed (based on the geogrid test stand) to carry out a simplified pullout test. Undoubtedly, it can be concluded that it is possible to make a retaining structure using soil reinforcement technology using steel welded meshes with a much smaller diameter (3.0, 3.8 and 4.5 mm) than 6-12 mm, used for the production of gabion baskets. This is the basic premise for the application of sustainable geotechnical principles in practice. To confirm the above statement, a trial design replacement of the retaining structure with an extension of the abutment was performed using the parameters obtained during the tests described in this study. Originally, the retaining wall was designed using soil reinforced with flat steel bars with a facing of precast concrete elements. The wall has a height of 9.50 m from the top of the foundation to the highest point of the backfill. The replacement design of this retaining wall assumes that it will be made of gabions of a welded mesh made of Zn + PVC 4.30 mm wire. The facing made of gabion baskets is vertical. Facing basket reinforcement 1.0 m thick and 9.0 m long were adopted at a spacing of 0.75 m between the three lowest reinforcement layers and 1.0 m between the higher layers of soil reinforcement. A detailed description of the design process, the solutions adopted, and the geometry of the structure is presented in [29; 49]. It is hereby shown that gabion retaining structures with welded meshes made using reinforced soil technology are possible for use in infrastructure construction applications. Furthermore, on the basis of the conducted tests and the analysis of the obtained results, it can stated that the low deformability (hence greater stiffness) of the tensile welded meshes embedded in soil allows them to be used for soil reinforcement in all types of reinforced soil structures, including the abutments of engineering facilities (the maximum deformation in the elastic work phase was only equal to 0.35%). In the case of woven meshes, this type of use is not so obvious. Another valuable observation is the dependence whereby the mesh with higher stiffness (e.g., made of a thicker wire, with smaller opening or stiff welded node), during the pullout test, obtained higher resistance to pulling from the soil compared to a less stiff mesh. This is a favourable phenomenon from the point of view of the use of retaining structures. The reinforcement effect can be explained by the favourable phenomenon of mesh wedging between soil grains. Taking into account that fine sand was considered in this study, it may be assumed that the effect will be greater in soils with a larger grain size. The authors plan to continue the initiated series of studies using other soils. In addition, the obtained results are a good basis for further model tests both in the laboratory and in situ on welded meshes in function of reinforcing soil. The main objective is to propose all coefficients necessary for the design of the engineering structures mentioned above in the future. In this study, the first of such parameters was determined--the apparent friction coefficient \(\mu_{K}\).