# Pullout Behavior of a Polymeric Strap in Compacted Dry Granular Material
###### Abstract  
Strap reinforcement is very commonly used as reinforcement material in mechanically stabilized earth walls (MSEW). Metal straps are mostly used as reinforcement material. However, in humid climates, where the risk of damage to metal straps due to corrosion is high, the use of geosynthetic straps is quite justified. In the Croatian coastal region, geosynthetic straps were used as reinforcement for two very high MSEWs. In both cases, the backfill material crushed stone aggregate from the neighboring site was used. According to the relevant standards, it is recommended that the backfill material should have a uniformity coefficient of Cu \(\geq\) 4.0. To meet these requirements, it is usually necessary to sieve and crush the backfill material. To evaluate the influence of the uniformity coefficient on the friction interaction coefficient between a geosynthetic straps and a crushed stone aggregate, a series of pullout tests with different confining stresses and aggregate grain size distributions were conducted. The pullout tests were performed for three different uniformity coefficients of the crushed stone aggregate. The results confirmed the justification to use backfill material with a uniformity coefficient higher than 4.0. The pullout tests were performed with one sharp, two closely spaced straps, and two separated straps. The results showed that lateral friction contributes to the pullout force in the amount of 16.1% of the total force. p 2023 2023 2023 2023  
be considered during MSEW construction. According to [3], backfill material cost accounts for 33% of the total cost of an MSEW. [PERSON] and [PERSON] [4] compared the price of an MSEW with different straps and geogrids. In their study, the costs of the backfill material account for more than 50% of the total cost of the MSEW. According to a performed cost analysis, using geogrids in combination with local soil as a backfill is considered the cheapest option. In contrast, [5] showed that the backfill of the MSEW accounted for 13% of the total cost. According to [6], the recommended criteria for backfill material in MESWs include having less than 15% material passing sieve No. 200 and a plasticity index not exceeding 6.0. According to [7], for using default values of friction interaction coefficient for metallic straps, the backfill material must have a uniformity coefficient of \(\mathrm{C_{u}}\geq 4\). For the backfill material that falls outside of these limits, pullout tests must be performed to determine the friction interaction coefficient. [PERSON] et al. [8] note that these requirements have disqualified a large number of produced aggregates or made their use in the construction of MSEWs more difficult and/or expensive. The authors also conducted an experimental study to investigate the effect of aggregate uniformity on the pullout resistance of ribbed steel straps when the aggregate uniformity coefficient ranged from 1.4 to 14.0. They concluded that the recommended friction interaction coefficient values are too conservative. The study showed that an aggregate backfill material with a uniformity coefficient as low as 1.4 can be used to design an MSEW with ribbed steel straps. Most previous research focused on the interaction mechanism when the reinforcement was a metal strap or geogrid [9; 10; 11; 12; 13; 14] or a geotextile/geogrid [15; 16; 17; 18; 19; 20]. In the last 30 years, a small number of pullout tests have been performed with polyester straps to determine the friction interaction coefficient between the strap and the backfill material [21; 22; 23; 24], the effect of normal stress and backfill material density on the strap-backfill material interaction [25], the effect of constrained dilatancy [25], and the deformation of the extensible reinforcement in the backfill material [26; 27]. Most pullout tests were performed for tests under 100 kPa, which corresponds to a wall height of about 6 m [21; 22; 23; 24; 28].