# Triaxial Test of Coarse-Grained Soils Reinforced with One Layer of Geogrid
## 1 Introduction  
Geosynthetics are widely employed in diverse infrastructure projects. While their initial applications were focused on soil reinforcement, separation, filtration, and drainage [1, 2], geosynthetics have since found expanded utility. They are now employed in preventing asphalt cracks [3, 4], addressing significant settlement concerns beneath pile-supported embankments [5], fabricating stone columns [6], constructing shallow strip foundations [7, 8], protecting pipelines [9], and reducing CO\({}_{2}\)[10], among other uses. In road infrastructure, geogrids are a common choice, specifically designed for enhancing load-bearing capacity and reducing soil settlement [11, 12, 13]. Although both functions involve mechanical improvements, the properties required to fulfill them are distinctively different [14]. Much research has been done to study the behavior of soil reinforced with geogrids using numerical simulation, analytical methods, laboratory experiments, and in situ experiments. While it has been acknowledged that different laboratory experiments can effectively replicate the behavior of soil and geogrids in specific components of embankments [15], a significant portion of these tests has been carried out using the direct shear apparatus [16]. These experiments encompass diverse aspects, such as different soil types, particle sizes, soil densities, and moisture contents [17, 18, 19, 20, 21], as well as variations in the type of geogrids, aperture sizes, and shapes [22, 23, 24, 25]. An important parameter found to increase the reinforcement effect is the number of geogrid-reinforcement layers [26]. These studies have a shared objective: to obtain a precise understanding of how soil and geogrids interact, thus optimizing the effective use of geogrids [27]. In addition, the angle of internalfriction and cohesion obtained during direct shear tests are used in modeling with software packages. The precision of the results is influenced by the reproduction of the stress applied to the sample [28], so tests with a triaxial pressure apparatus, during which it is possible to set the lateral pressure, have the advantage [29; 30]. The change in the angle of internal friction, the change in cohesion, and the effect of geogrid reinforcement are the main properties obtained by the triaxial pressure apparatus tests for samples without geogrids and with geogrids [31]. The results obtained showed that the geogrid creates apparent cohesion and a small change in the angle of internal friction [32]. The effect of the geogrid is better reflected through the reinforcement effect, which is expressed as the ratio of the maximum deviatoric stress with the geogrid to the maximum deviatoric stress without the geogrid [33]. Obtained results depend on the type of soil, the type of geogrid, and the confining pressure at which the tests were carried out [34]. The type of soil significantly influences triaxial pressure tests, with the geogrid's effectiveness tied to soil properties [35]. While most tests focus on coarse-grained soils for laboratory convenience, the influence of cohesive soils is also considered [36]. The following parameters affecting deviatoric strength are attributed to soil type: soil compaction, average particle size, and density [34]. Recent research has highlighted the influence of the uniformity coefficient on soil shear strength [37]. Geogrid selection is a critical factor in soil reinforcement. Even when geogrids share the same tensile strength, the mesh size influences the strength of the specimen [38]. Notably, whether biaxial or triaxial, geogrid variations do not impact the results of triaxial tests [39]. In laboratory testing, a specimen with a diameter of 100 mm and a height of 200 mm exhibited maximum strength parameters when the geogrid was positioned at 80% of the specimen's height [40]. Experimental data reveal that geogrid-reinforcement coefficients increase with the number of geogrid layers.