## 1 Introduction
[22] reinforced loess soil with poor mechanical properties with basalt fiber additives in three different fiber lengths (6 mm, 12 mm, and 18 mm) and four different fiber contents (0.3%, 0.6%, 0.8%, and 1.0%). The maximum increase in strength was observed in the experimental group with a fiber content of 0.6% with a length of 12 mm, and it was determined that the shear strength of leucine of basalt fiber was improved. In their study, [PERSON] and [PERSON] [23] showed that the addition of basalt fiber to the local soil sample located in the Srinagar region increases the strength of the soil by decreasing the liquid limit and plastic limit, and improves the properties of the soil by decreasing the plasticity index by 62.64%. [PERSON] et al. [24] concluded that the use of glass fiber and basalt fiber would be effective as reinforcement for higher bearing capacity and fewer cracks in granite residual soil. In their studies, fiber contents were chosen as 3%, 4%, and 5%, respectively, and fiber lengths were used as 6 mm, 9 mm, and 12 mm, respectively. While most of the studies on soil cover fine-grained soil groups, studies on cohesion-free sand soils are insufficient. Therefore, it is particularly important to study basalt fiber-reinforced cohesionless sand soil. Macromesh fiber is a polypropylene (99%)-based macro synthetic fiber reinforcement in copolymer structure. It is variously named macro polypropylene fiber, spun polypropylene fiber, high-performance polypropylene fiber, macro synthetic fiber, and macro synthetic twisted bundle fiber [25]. They are environmentally friendly and new-generation reinforcements produced from high-performance polypropylene raw materials and have a longer life than traditional reinforcements [26; 27]. In recent years, its effect on fiber-reinforced strengthening studies has begun to be investigated. [PERSON] et al. [28] strengthened the soil-cement composites made with cohesionless soil with the addition of single fibrillated-tapespolpropylene fibers (SFPF) and bundles of coiled fibrillated-tapes polypropylene fibers (BCPPF) and showed that the polypropylene fiber reinforcements used had a significant effect on the bending behavior. [PERSON] et al. [29], twisted, barchip, and fibrillated, three different macro polypropylene fibers were added to the concrete in three different volume ratios 0.2%, 0.4%, and 0.6%, and the reinforcement of macro PP fibers affected the ductility behavior and ductility of the concrete. investigated the effect on mechanical properties. According to the results, the twisted, and barchip fiber-reinforced concrete has higher compressive strength than the fibrillated fiber. It has been studied mostly on concrete and polymer composites but the studies on their effects on soil are few [30; 31]. A single fiber type chosen as an additive in fiber additives can often significantly improve one or more of the material's properties. However, each type of fiber often has some weak points. For example, filament fiber can improve tensile strength but has the problem of poor dispersion. Therefore, recently researchers have mixed different fiber types to take full advantage of the reinforcing effect of each fiber especially in the field of concrete. Studies have been carried out in different combinations such as polymer-polymer hybrid fiber and polymer-natural hybrid fiber, steel-steel hybrid fiber, and steel-polymer hybrid fiber [32; 33]. As a result of the studies, it has been seen that hybrid fibers can improve the toughness, ductility, energy dissipation capacity, and durability performance of concrete [30; 34]. When the existing studies on improvement with fiber additives are evaluated, the effects on the soil are examined as a result of the addition of one or more fibers to the soil separately under various varying conditions [35; 36; 37]. However, studies on the effect of using two or more fibers together in a hybrid form on soil are very insufficient. This study is aimed to contribute to the deficiencies in the literature mentioned above.