## 1 Introduction
Synthetic fibers as geotextiles dominate the market, but using natural fibers should not be disregarded, since it offers environmental and economic benefits. Geotextiles made from natural fibers have attracted the interest of several researchers to enhance their strength performance, bringing it in line with that of synthetic fibers [13; 14; 15; 16]. Natural geotextiles are made from a variety of plant fibers. Some examples of plant fibers used to make geotextiles are coconut, jute, water hyacinth, palm, pineapple, and abaca. The main components of natural fibers that determine their physical properties are cellulose, hemicellulose, and lignin [14]. Among these fiber compositions, lignin and cellulose are the two components that determine the service life and durability of the fibers [13]. Coconut fiber contains 7.56% hemicellulose, 42.90% cellulose, and 41.28% lignin [17]. The high polysaccharide content (hemicellulose and cellulose) of natural fibers such as coir makes them highly hydrophilic. The hydrophilicity of fibers negatively affects their adhesion to hydrophobic materials, which can weaken and degrade the resulting composite [18]. Fibers also change their size due to moisture content, which can be avoided by removing moisture from fibers before applying them to any composite product [19]. Previous studies have focused on the application of natural fibers in the creation of natural fiber geotextiles for various purposes. [PERSON] [20] studied the application of pineapple leaf fibers as the main material for geotextiles. The study showed that the utilization of pineapple leaf fibers is viable, since the tests showed that its properties are comparable to those of commercially available abaca geotextile. Furthermore, it was identified in the study that even though pineapple geotextile is thinner than abaca geotextile, the former can sustain higher tensile stresses than the latter. [PERSON] [21] focused on the utilization of corn stalk geotextile nets for erosion mitigation. The experiments yielded positive results. The corn stalk geotextile nets that were developed were most effective in soil mitigation at 30\({}^{\circ}\) and 60\({}^{\circ}\) slopes. [PERSON] et al. [22] focused on measuring the sediment yield in coconut fiber geotextile (coco mat)-reinforced slopes. The experimentation involved the use of three different coco mat designs. The first was a stitched fiber coco mat, while the other two were woven geotextiles with different mesh sizes. The results of the study showed that coco mats were effective in containing soil erosion, especially when the nonwoven type was used. The nonwoven coco-mat-reinforced slope yielded the least amount of sediment due to runoff. The advantages and disadvantages of a natural geotextile vary depending on how long it is utilized. A natural geotextile's biodegradation can be seen as an advantage for short-term reinforcements because it helps vegetation, but it can also be seen as a disadvantage in the long run because its life span is only about 2 to 5 years, whereas a synthetic geotextile's life span is over 10 years but can cause environmental harm. This knowledge enables researchers to pinpoint the sources of biodegradability and devise strategies to improve those necessary properties. Although weaknesses are present in natural fibers, they can be alleviated or improved by utilizing different fiber modification techniques through treatments. In this study, we utilized a nonwoven natural geotextile from coconut fibers called coir geotextile as soil reinforcement for slopes. Coir geotextiles can be either woven or nonwoven. The difference between nonwoven and woven geotextiles is the manner of fabrication of the coir [23]. In a nonwoven geotextile, the fibers are mechanically intertwined by pressing the coconut fibers. On the other hand, in woven geotextiles, the fibers are intertwined with a weaving process. These two types of geotextiles offer different benefits depending on the properties being evaluated.