# Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material
## 3 Results and Discussion  
The results and their analysis are presented in this chapter. In the first part, the influence of the grain size distribution of the backfill material and the normal stress on the pullout mechanism were analyzed. Additionally, the damage of the polyester straps during the pullout tests in regard to the grain size distribution of the backfill material was discussed. In the second part, the stress-strain behavior of the straps was analyzed. The third part deals with the determination of the lateral friction at the edges of the straps and the fourth part discusses the obtained values of the friction interaction coefficient and compares them with values from previous studies. The Influence of the Grain Size Distribution of the Backfill Material and the Normal Stress on the Pullout Force of Geosynthetic Strap  
The first backfill material, labeled A, had a grain size of 30 to 60 mm. This uniformly graded, narrow grain size range was chosen to study the effects of the lower density of the backfill on pullout resistance. As can be seen in Table 2, the mentioned material has the largest range of void ratio and, accordingly, the lowest density. The second and third backfill materials (labeled B and C) had wider grain size ranges. Backfill material B was also uniformly graded. Backfill material C was well graded with the smallest void ratio range and, accordingly, the highest density. With a wider grain size range, the density of the material is higher as the smaller grains fill the pores. The influence of grain size distribution on the pullout force of the geosynthetic strap can be seen from the curves of pullout forces and measured displacements along the strap (Figure 6). In the case of backfill material A, which is uniformly graded, the curves are not smooth. The flattest curves can be seen for the well-graded material C. It can be concluded that the strap is trapped less in the backfill material in the case when it is pulled out of a well-graded material with a wider grain size. As the strap is pulled out, some grains rotate and move around the strap, and the angular parts of the grain break through the surface of the strap. Once this resistance is overcome, the force decreases until the angular parts of the grain are driven back into the strap. In support of this theory about angular grains being pressed into the strap is the damage to the strap that was noted after the strap was taken out from the box. Significant damage to the strap was noted only in the uniformly graded backfill material A (Figure 7), while there was no such damage in backfill materials B and C. For material B, these jumps are observed at the maximum force reached and are larger at lower stresses. For material C, these jumps are minimal and are also more pronounced at lower stresses. Since these jumps in force are more pronounced at lower stresses for all materials and are the greatest for the material with the largest angle of dilatancy, it can be concluded that these jumps are related to the angle of dilatancy of the material. On the other hand, the lowest force was obtained with the material with the largest dilatancy angle. So, in the selection of the backfill material, it is important that the strap has a larger contact surface with the backfill material, i.e., to achieve the largest possible number of grains in contact with the strap. Most of the previous studies on geosynthetic straps and backfill material interaction used lower overburden stresses [21; 22; 23]. Namely, it was assumed that at the higher normal stresses, for which values correspond to a wall higher than 6 m, the friction interaction coefficient is constant. In this study, the pullout tests were performed under two normal stresses of 50 kPa and 150 kPa for backfill material A and B and under three normal stresses of 50, 100, and 150 kPa for backfill material C. These stresses correspond to wall heights of approximately 2.5 and 7.5 m. The higher normal stresses were of interest because of the great height of the walls built in Croatia.