Knowledge of the mechanism of interaction between the soil and the reinforcement element is crucial for the design of reinforced soil structures. It depends on the type of the reinforcing element and the soil that is used. The majority of previous research studied the mechanism of interaction either between the metal strip or nets, or else geosynthetic nets or geotextile and soil, while a small number of tests were conducted to determine the mechanism of interaction between geosynthetic strips and soil. In studies that were conducted to determine the mechanism of interaction between geosynthetic strip and soil, tests were conducted in cases when the fill material used was sand or, less frequently, gravel, while there are no available data in the literature for tests performed with crushed stone as fill material. Since in Croatia broken rock and geosynthetic reinforcement strip were used in the construction of two high reinforced earth walls (Strikic and Sveta Trojica), there was a need to study the mechanism of interaction between the crushed stone and geosynthetic reinforcement. Previous studies have shown that coefficients of interaction in the gravel are higher than those in the sand. Therefore, it is to be expected that the coefficients of interaction in crushed stone are to be higher than those for the gravel. In order to clarify the mechanism of interaction between the elements of reinforcement and soil, the laboratory direct shear tests and pull-out tests on reinforcement elements and soil were performed. Direct shear test with reinforcement is similar to usual direct shear test, for which the reinforcement is incorporated in the device and shear, and the test registers shear force and displacement. For pull-out test, reinforcement is incorporated between two layers of the soil, and after emplacement the reinforcement is pulled out from the soil. During the test, withdrawal forces and displacements are registered at particular points on the reinforcement. The goal of testing is to determine the force required to pull out the reinforcement or the force at which the reinforcement broke. The resulting pull-out force is divided with the surface of the reinforcement material and the obtained value is the draw resistance (coefficient of interaction) which is used in the design of reinforced soil structures. The mechanism of interaction between soil and reinforcement depends on the type of soil used and on the type of reinforcement elements. This thesis is attempting to determine the mechanisms of interaction between extensible geosynthetic strips and crushed stone. In order to better clarify the mechanism of interaction between soil and geosynthetic strips, soil strength parameters are necessary (for which direct shear test is performed), as well as parameters of the interaction between the elements of the soil (for which pull-out tests are performed). In this study, the effect of particle size distribution of the material on the coefficient of interaction between geosynthetic strips and soil was observed. Tests were performed on uniformly graded crushed stone fraction with a range of 30 to 60 mm and a well graded crushed stone fraction with a range of 4-60 mm, and from 0 to 60 mm. Strength parameters of the crushed stone are determined in a large direct shear device developed at the Faculty of Mining, Geology and Petroleum Engineering. Device dimensions are 300x300x300 mm and the maximum diameter of the grain that was investigated is 31,5 mm. The results of these tests showed that the friction angle and dilatancy are highest in uniformly graded material, while the smallest friction angles are specific to well graded material. Coefficients of interaction between geosynthetic stripe and crushed stone were determined in a large pull-out test device, GFOS model. These tests were also carried out for three different granulometric compositions: uniformly graded material with fraction range of 30 to 60 mm and a well-graded material with fraction range of 4-60 mm and from 0 to 60 mm. Tests were performed in the case of extraction of one strip and for two separated and two connected geosynthetic strips. One-strip extraction was conducted in order to determine the influence of particle size distribution and density of material on the interaction coefficient. For the extraction of the two strips, the effect of side friction on interaction coefficient was observed. The results of the study show that well graded materials (0-60 mm) show the greatest angles of friction between soil and strip, which is contrary to the results of direct shear test, where the uniformly graded material had greatest friction angles. Tests with two separate strips and two connected strips showed that side friction contributes to the coefficient of the interaction. In addition to laboratory tests for determining coefficients of interaction and parameters that affect the coefficient of interaction, feedback analyses have been conducted for strip pull-out in Plaxis 2D. In feedback analyses, parameters for materials were determined with direct shear and interaction coefficients were determined by pull-out test.