# Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material
## 4 Conclusions  
This paper presents the influence of grain size distribution with different coefficients of non-uniformity on the mechanism of interaction between geosynthetic straps and crushed stone backfill. The main conclusions that can be drawn from this work are the following:  
When crushed stone with larger grain diameters is used in reinforced soil structures, it is necessary to meet the AASHTO [38] requirement for uniformity coefficient C\({}_{\rm u}\) > 4. If the backfill material used had a uniformity coefficient of less than 4, the friction interaction coefficient was found to be much lower than the values used in practice. Crushed stone, especially with larger grain diameters, has very high values for the internal friction angle. The use of the expression to determine the friction interaction coefficient for depths greater than 6 m, which corresponds to 2/3 of the tangents of the internal friction angle of the backfill material, should be used with caution. For the crushed stone aggregate with Cu < 4, it is justified to take a maximum friction angle not greater than 36 degrees. For the well-compacted crushed stone aggregate with Cu > 4, the friction interaction coefficient calculated by Expression 3 underestimates the friction interaction coefficient for polyester strap and crushed stone. The secant friction angles from the pullout tests and the secant friction angles from the direct shear tests have shown that the shear strength parameters of the tested backfill materials behave inversely so that a larger secant friction angle of the backfill does not mean that it achieves a larger pullout resistance. The tests showed that the highest interaction coefficient was obtained with the backfill material that had the highest uniformity coefficient and highest backfill density. This shows that the grain size distribution and the density of the backfill material has a significant influence on the behavior of the strap and that it is important that the strap is in contact with as many grains as possible. To mobilize the entire strap, the largest deformations are required for a well-graded crushed stone. The grain size distribution has the greatest influence on the stress-deformation behavior of the straps. For the strap length of 1.25 m with well-graded material C, pullout tests under a normal stress of 50 kPa mobilize a 50% smaller length of the strap compared to material A. At a normal stress of 150 kPa, this difference is even greater. The value of normal stress affects the stress-deformation behavior of the strap only for well-graded backfill material. For uniformly graded crushed stone, the entire length of the strap is mobilized at similar horizontal deformations, which are smaller than for well-graded backfill material. The phenomenon of lateral friction acting on the sides of the strap was demonstrated. In this study, the contribution of the lateral friction force in the pullout force was 16.1%. For the two closely spaced strap, the pullout forces per strap are 6.8% lower than the pullout forces for one strap. This result is important for the design of MSEWs since the lower pullout resistance must be taken into account for parts in construction where two straps are laid side by side. Tests have shown that, if the backfill material is uniformly graded, damage to the strap occurs during installation and testing, while if the backfill material is well graded, such damage is not noticed. During the pullout tests of the geosynthetic straps, the grain size distribution of backfill material was shown to have a significant effect on the resistance of the strap to pulling out, as well as on the deformation of the strap itself during testing. For future testing, it would be beneficial to carry out tests with two separate strips at different strip spacings and to determine the zone of the backfill material that is mobilized during the pullout. The influence of roundness would also need to be investigated for coarse-grained materials.