# Experimental Study on Pullout Behavior of Coir Geotextiles Based on Transparent Soil
## 1 Introduction
The results of the tests showed that the coir geotextile improved the load-bearing capacity of the foundations to a great extent, but the reinforcement parameters needed to be optimized for the design of the reinforcement. [PERSON] et al. (2020) found, through monotonic loading tests, that the addition of coir geotextiles at the interface of the subsoil and the subbase significantly reduced the settlement of highly plastic soils, and the settlement of two types of coir-geotextile-reinforced soils was reduced by 18% and 8%, respectively. [PERSON] et al. (2020) conducted a study on coir geotextiles and non-woven coir fibers where these were subjected to tensile tests and the results showed that the coir geotextiles were suitable as a reinforcing material for road base reinforcement, while non-woven coir fibers were not. [PERSON] et al. (2020) found, through field tests, that when the unit mass of the two coir geotextiles was 740 g/m\({}^{2}\) and 365 g/m\({}^{2}\), respectively, the elastic modulus of the reinforced roadbed of two kinds of coir geotextiles was 1.41 times and 1.25 times higher than the elastic modulus of the unreinforced soil body, respectively. [PERSON] et al. (2020) used the Roccscience Slide2 version 9.017 software to carry out a numerical analysis, and the results showed that the strength performance of coir geotextiles in strengthening slopes was almost equivalent to that of synthetic geotextiles. Based on the California Bearing Ratio (CBR) test, [PERSON] and [PERSON] (2020) found that, when the content of coir geotextiles increased, the stiffness and CBR value of the black cotton soil subgrade also increased. In the context of the global push for low-carbon and environmentally sustainable practices, the use of renewable, biodegradable, and natural materials has received a great deal of attention. Coconut fiber, extracted from coconut shells, is one such material that offers a sustainable alternative to traditional non-renewable resources. Its development and utilization are of great significance for reducing environmental pressure and reducing dependence on synthetic materials. However, the interaction mechanism between coir geotextiles and the subsoil is still poorly understood, especially in terms of interface pullout behavior that affects its performance in soil reinforcement applications. In this paper, the transparent soil technique is used to clarify the interface pullout mechanism between coir geotextiles and the soil. Transparent soil technology refers to the preparation of artificial soil by mixing solid particles with pore liquids with the same refractive index. The solid particles constituting the transparent soil can be fused quartz sand, etc., and the pore liquid constituting the transparent soil can be mineral oil, etc. Typically, researchers can use the PIV (Particle Image Velocimetry) software or the DIC (Digital Image Correlation) software to analyze the deformation displacement of transparent soil. Although the preparation cost of transparent soil is higher than that of natural soil, it has the advantages of non-invasiveness, integrity, whole process, and fine measurement. Based on the transparent soil technology, the mechanism of coir geotextile pullout behavior is analyzed, and the reinforcement effect of coir geotextiles is evaluated by using the interfacial friction coefficient. The results of this study are helpful to broaden the understanding of natural fiber reinforcement materials, provide certain guidance for the design and implementation of a soil system reinforced with coir geotextiles, and promote the application of natural fiber materials.