# Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material
## 3 Results and Discussion
The results showed the lowest pullout force  
Figure 6: The pullout curves for materials A, B, and C tested at normal stresses of 50 and 150 kPa. Figure 7: Damage of the straps in backfill material A.  
for the lowest normal stress of 50 kPa and the highest for a normal stress of 150 kPa for all backfill material samples (Figure 8). The highest pullout forces were obtained for the well-graded backfill material C, which also has the highest uniformity coefficient C\({}_{u}\), while the lowest pullout force was obtained for material A, which has the lowest uniformity coefficient. During the pullout test, the density of the backfill was measured using the sand replacement method. The results show that, as the density of the material increases, the pullout force also increases. The average measured values of the backfill density are shown for materials A, B, and C in Figure 8. This difference in pullout force is significant at both lower and higher normal stresses. For the backfill material C, the pullout force at 50 kPa was 3.2 times higher than that of backfill material A. At a stress of 150 kPa, this difference is somewhat smaller but still significant, and the force was 2.9 times higher for backfill material C compared to material A. Normal stresses have a great influence on the pullout force, but the influence of grain size distribution is somewhat bigger. For backfill material A, the pullout force at a normal stress of 150 kPa is lower than the pullout force for material B and C at a normal stress of 50 kPa. The results of the tests carried out show that, when selecting the material for the construction of an MSEW, it is better to choose a well-graded material since higher pullout forces can be achieved for the same strap length. For most projects, especially MSEWs on slopes where the length of reinforcement is limited, where the MSEW is high, or where greater deformations are expected due to weak subgrade, a shorter strap length will ultimately result in a more cost-effective construction of the structure because less material will be used for construction. The shear stresses (\(\tau\)) at the contact of the backfill material and the geosynthetic strap during pullout tests determined by Expression (1) show an increase in shear stresses with an increase in normal stresses and an increase in shear stresses with an increase in the uniformity coefficient of the backfill material. The shear stresses for all three materials and under different normal stresses are shown in Figure 9. Based on these values, the strength parameters of the contact zone between the geosynthetic strap and the backfill material are determined. Since the samples of the backfill material are coarse grained, the strength parameters were analyzed assuming zero cohesion. Friction angles were determined as secant values. The secant friction angles for each backfill material (A, B, and C) and for each individual normal stress are shown in Figure 10. The secant friction angles from pullout tests and the secant friction angles obtained in the direct shear tests show that the shear strength parameters of tested materials behave inversely in pullout tests and in  
Figure 8: Pullout force for materials A, B, and C.  
direct shear tests. In the direct shear test, the largest secant friction angles were obtained for backfill material A, followed by B, and finally, the smallest secant friction angles were obtained for material C. In the pullout tests, the largest secant friction angles were obtained for backfill material C, and the smallest were obtained for material A (Figure 10). In addition, the largest dilatancy angles for backfill material A were also determined. So, it can be concluded that for uniformly graded, coarse-grained backfill materials that do not contain fine particles, the secant friction angle of the backfill material obtained from direct shear should be used with caution in MSEW design since a larger secant friction angle of the backfill does not mean that it will achieve greater pullout resistance.