# Behaviour of the Steel Welded Grid during a Simplified Pullout Test in Fine Sand
###### Abstract  
This study considered the possibility of using steel gabion baskets made of welded mesh for a soil-strengthening function. Examples of such applications are known for meshes made of wires with diameters from 6.3 to 12.7 mm and mesh openings from 125 to 225 mm. In the case of a welded grid, the pulling resistance of fine-grained soil consists of two factors: frictional resistance and bearing resistance. Therefore, for the purposes of this issue, a simplified laboratory pullout test was carried out with four types of welded steel grid (common in Europe) embedded in the fine sand. The geometry of the grid (opening size: 76.2 \(\times\) 76.2 mm), the type of steel (low carbon steel, tensile strength from 500 to 700 MPa), the diameter of the wire (2.7-4.5 mm) and its cover (ZN + PVC or ZnAl) were taken into account during the analysis. It was unequivocally stated that as the stiffness of the steel grid itself increases, its strength increases during the pullout test, which is not so obvious in the case of popular steel woven meshes. In addition, it has been shown that steel welded meshes with wire diameters less than 6 mm are suitable for soil reinforcement in structures with gabion facing, and the determined apparent friction coefficient (\(\mu_{k}\) = 0.39-1.47) takes values similar to the friction coefficient given in references for welded meshes of larger diameters. This is a positive premise for starting further research on the use of wires of smaller diameters for welded mesh production used as soil reinforcement. p 20 China around 1000 B.C. along the Yellow River [4]. It is believed that the first modern wire mesh gabions were made in the Bologna area of Italy around 1879 [5]. The use of gabions filled with stones is environmentally friendly (Figure 1d) [6]. The main reason for the limited impact on the environment is the reduction in the materials used compared to traditional reinforced concrete structures, especially steel and concrete, the manufacture of which requires the use of cement, which is a highly energy-consuming raw material to produce. It is true that the steel of the gabion baskets is also an energetically expensive material, both in terms of production and the recycling process. However, it has the feature of being able to be totally recycled an unlimited number of times. Even the zinc used for steel galvanization is fully recyclable [1]. Both natural and recycled materials or alternative materials--e.g., clothing and plastic--can be used as ballast material for gabion baskets [7,8]. The development of anticorrosion protection techniques has made steel wire structures durable. Their durability is estimated at over 100 years [9, 10, 11]. The fact that about 30-40% of the volume of gabions are air voids has a positive influence on the durability of the gabion structures, thanks to which they are characterized by excellent water permeability (hydraulic conductivity \(k>2.5\times 10^{-3}\) m/s), which facili  
Figure 1: Examples of the use of gabion baskets in Poland (own pictures): (**a**) gravity retaining wall made of gabion baskets; (**b**) the slope of a motorway embankment reinforced with gabions; (**c**) gravity retaining wall supporting a motorway embankment; (**d**) an example of a gabion wall erected in harmony with the environment. tates the drainage of water from behind the retaining structure and prevents its level from rising [10; 11; 12; 13; 14; 15; 16]. Phenomena related to the influence of water on retaining structures are often neglected or treated with insufficient care when analysing the surroundings of bridge structures, which leads to numerous minor failures that are difficult to eliminate due to the scale of earthworks. The importance of proper drainage system implementation is often underestimated, both at the design and execution stages [17]. A geotechnical engineer should always be consulted for design solutions in such situations, and it should be noted that gabion retaining structures, apart from their structural function, also drain water from the soil medium.