# Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material
###### Abstract
Since polyester straps are used to construct increasingly higher walls [29; 30; 31], it is necessary to verify the behavior of the strap at higher stresses. [PERSON] [21] studied the pullout resistance of polyester straps at low overburden stresses (20 kPa \(\frac{3}{4}\) 100 kPa) for three different types of backfill material and showed that the friction interaction coefficient at low overburden stresses can be higher than the internal friction angle of the backfill material. The author explained this by the effect of constrained dilatancy and textured surface of the strap. The effect of dilatancy was also studied by the authors of [16; 23]. They pointed out that when the strap is pulled out of the backfill material, the backfill material tends to dilate. Dilation occurs at the contact between the strap and the backfill material and at the zone in the backfill material adjacent to the strap. However, dilatancy can be prevented by the action of the surrounding backfill material, resulting in an increase in normal stress at the contact between the strap and the backfill material. [PERSON] et al. [32] showed a higher value of the friction interaction coefficient in coarser backfill material. This difference is related to a higher backfill density and a higher backfill uniformity coefficient \(\mathrm{C_{u}}\), which results in a larger dilatancy angle and internal friction angle of the backfill material. The tests revealed that using two straps during testing resulted in a higher friction interaction coefficient. The authors stated that the possible causes of higher friction interaction coefficient when testing two parallel straps is the effect of the arching or dilatancy of the backfill material between the straps. [PERSON] et al. [33] also conducted pullout tests with two parallel polyester straps, where they investigated how the loop at the free end of the strap affects the interaction. They performed tests in poorly graded dry sand under normal stresses below 80 kPa using two parallel straps and one strap placed in a U shape. The results show that a U-shaped strap significantly increases the pullout resistance force and the friction interaction coefficient parameter. [PERSON] et al. [23] studied the pullout resistance of polymer straps embedded in marginal tropical soils. They concluded that an increase in the typical characteristics of cohesive soil (e.g., fines content and plasticity index) leads to a decrease in pullout resistance, while an increase in the frictional properties of granular soil (e.g., friction angle) has the opposite effect. They also measured the vertical stress on the reinforcement during a pullout test. The tests showed that the stress during pullout regarding the initial state of stress increases significantly for clean sand and mixtures with lateritic weathering content below 25%. The obtained results also showed that the relationship between the actual and initial stresses is linear, which allows the prediction of the interaction friction coefficient. [PERSON] et al. [24] conducted pullout tests with a polymeric strap using construction and demolition waste as backfill material. The results show that such a type of backfill material is suitable for the construction of MSEW structures. [PERSON] et al. [28] used the same backfill material to perform pullout tests with geosynthetics. They showed that the proper compaction of the backfill material is an essential requirement for all types of mechanically stabilized earth (MSE) structures. [PERSON] and [PERSON] [34] showed that the width of the strap has a greater effect on the pullout force and tensile strength than the horizontal spacing of the reinforcement. They also proposed the effective area method based on the prediction of the strap-selected length as a more economically feasible design method. In Croatia, several MSEWs with geosynthetic straps have been built in recent years, with two very high MSEWs standing out because of their dimensions. The first is the Strikici wall built in 2006, which is 26.8 m high and 500 m long.