# Experimental Study on Pullout Behavior of Coir Geotextiles Based on Transparent Soil
## 3 Results and Discussion
### Influence of Normal Stress
The interfacial friction coefficient between the geogrid and the transparent soil was always in the range of 0.6 to 0.7, while the interfacial friction coefficient between the coir geotextile and the transparent soil showed a decreasing trend. Because under the action of high normal stress the coir geotextile was more prone to deformation and destruction than the geogrid, then the reinforcement effect was weakened. [PERSON] et al. [36] conducted a pullout test on gabion mesh standard sand with a tensile strength of 28.1 kN/m. At 20 kPa, the interfacial friction coefficient in the present study was slightly lower than that obtained by [PERSON] et al. [36]. At 40 kPa, the interfacial friction coefficient in the present study basically coincided with the results obtained by [PERSON] et al. [36]. As the normal stress increased to 40 kPa, the gabion mesh studied by [PERSON] et al. [36] and the coir geotextile in the present study experienced a high degree of deformation and failure under high normal stress, and the interfacial friction coefficient of both materials dropped to a low level. In order to further study the interfacial interaction between the coir geotextile and the subsoil, the displacement contour of the interfacial reinforcement and the soil was analyzed by using an image analysis technique. For the division processing of the displacement contour, this paper referred to the studies of [PERSON] et al. [30] and [PERSON] et al. [37]. In the present study, the position around the reinforced soil interface was studied, and the place where the horizontal displacement of the particles was about 0 on the reinforced soil interface was selected as the upper and lower boundaries. For example, in Figure 10, the red dotted line is the upper and lower boundary of the shear band, and the red solid line in the middle represents the position of the coir geotextile. The thickness of the upper interface of the shear band was defined as the thickness between the coir geotextile and the upper boundary, and so on for the lower interface thickness of the shear band. There was a common control group, that is, the anchorage length was 500 mm, the normal stress was 20 kPa, and the pullout rate was 1 mm/min. In addition, Figures 10, 12, and 14 illustrate all the displacement contours that had formed an obviously stable contact area on the interface. Figure 10 shows the particle displacement contour under different normal stresses. It can be seen from Figure 10 that, when the normal stress increased from 10 kPa to 10 kPa, the displacement contour of the interfacial friction coefficient is not well understood. Figure 9: The relationship between the interfacial friction coefficient of the reinforced soil and normal stress [35; 36]. to 20 kPa successively, the corresponding thickness of the interfacial shear band increased from 13 mm to 16 mm successively. Moreover, when the normal stress further increased to 40 kPa, the thickness of the interfacial shear band also increased to 20 mm. In other words, the thickness of the interfacial shear band increased with the increase in normal stress, indicating that normal stress had a certain influence on the meso-motion behavior of the interfacial reinforced soil. When the normal stress increased, the reinforcement and the soil became closer, the driving effect of the coir geotextile on the surrounding soil particles was stronger, and the thickness of the shear band at the interface of the reinforcement and the soil was thicker.