# Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material
## 3 Results and Discussion
### The Stress-Strain Behavior of the Strap during the Pullout Tests  
The pullout tests revealed that the mobilization of the straps varied greatly depending on the grain size distribution of the backfill material and the applied normal stresses. The pullout force was measured on the piston, while displacements were monitored on the piston and at four points distributed along the length of the strap using extensometers. The first point (E1) at which displacements were measured was located at the position where the strap enters the box. This point was chosen to ensure that the fastening system that attaches the strap to the piston does not loosen. Therefore, the readings of the deformation in this segment do not represent only the deformation of the strap but rather a possible loosening of the fastening system. The second point (E2) was located inside the box, 200 mm from the sleeve. The third point (E3) was in the center part of the box, while the fourth point (E4) was 200 mm from the back end of the box. Figure 11 shows the readings of the displacements for backfill material C pulled out at the normal stress of 100 kPa. The curves represent readings recorded at every 10 mm of the piston displacement. Based on the above, the strap and the deformations of the strap can be divided into four zones and two subzones. Zone 1 represents a free part of the strap (between the piston and the E1). Subzone 2A also represents a free part of the strap (inside the sleeve, between E1 and the strap entrance at the front of the box). Subzone 2B represents part of the strap emplaced in fine sand (between the strap entrance at the front of the box and E2). The fine sand was used in this subzone between the strap and the backfill material to prevent grain pinching at the sleeve. Zone 3 represents the emplaced part of the strap in backfill material between E2 and E3. Zone 4 also represents the emplaced part of the strap in backfill material between E3 and E4. At the beginning of the pullout test, the deformation of the strap in Zone 1 is zero. All deformations of the strap occur in Zone 2. This can be attributed that the part of the strap in contact with the surrounding material in subzone 2B takes over all the pullout force applied by the piston. As the development of the test progresses, the deformations of the strap in Zone 1 gradually increase, the deformation of the strap start in Zone 2 and  
Figure 10: Secant friction angles for materials A, B, and C from direct shear test (DS) and secant friction angles at the strap–backfill contact from pullout tests (PU). finally start in Zone 3. The start of the deformation in Zone 2 and Zone 3 represents the mobilization of the strap under the applied pullout force in Zone 2 and Zone 3, respectively. E4 is placed close to the rear end of the pullout box, so the start of displacement readings on this extensometer (E4) can be considered as the point where the strap starts to displace with the entire length in the pullout box (this point is represented as a red line in Figure 11). In this case, for the backfill material C tested under the normal stress of 100 kPa, this point occurs at the displacement of the piston of 120 mm. Figure 12 shows the readings of the displacements at extensometers placed inside the box (E2, E3, and E4) for backfill material A, B, and C pulled out at the normal stresses of 50 and 150 kPa. The readings are also recorded at every 10 mm of piston displacement. The grain size distribution significantly affects the stress-deformation behavior of the straps in these cases. For a normal stress of 150 kPa, the entire length of the strap is mobilized at a piston displacement of 30 mm for material A, 50 mm for material B, and 140 mm for material C. The value of the normal stress influences the stress-deformation behavior of the strap only for backfill material C. In that case, at 50 kPa, 100 kPa, and 150 kPa, the entire strap is mobilized at a displacement of 70, 120, and 140 mm, respectively.