Various methods of soil stabilization are used to have a qualitative and economical design of road subgrades. Lack of compressibility, low bearing capacity, high permeability are amongst particular features of some soil types which makes them unsuitable for pavement construction usages. This study aimed to evaluate the effect of adding amine based resin and randomly distributed polypropylene fibers on dune sand improvement. The amount of resin and PP fibers from 0.5 to 2.5% and 0.025 to 0.1% by weight of dry soil grains were used, respectively. The unconfined compressive strength test was done to assess the effect of resins and fibers which are added to the soil separately and in combination. All samples were tested after a constant time of 24 hours. The results show that the samples uniaxial strength steadily increased with the increasing resin. The addition of 1.5% resin increases the uniaxial strength and failure strain 5.5 and 2 times, respectively. The amount of 0.05% of PP fibers was determined as the optimum amount which increases the strength up to 2.8 times. Among the various combination of resin and fibers, the maximum amount of strength is attained by the combination of 0.025% PP and 1.5% resin which yielded the strength of 713.7 kPa, i.e. 9 times more than the untreated soil. The evaluation of the soil behavior stabilized with resin using direct shear tests showed that addition of resin up to 2% increases the internal angle of friction about 10° and it becomes 53.3°. Moreover, a noticeable cohesion increase up to 141 kPa is obtained. Resilient modulus test results in different conditions show the dependence of this main parameters of the soil on the applied stress conditions. Hence, type of loading is selected in accordance with the traffic loading mentioned in AASHTO T307 standard. According to obtained results of resilient modulus and modulus of elasticity which differ in almost all combinations of soil and additives, a comparison between the results in both static and dynamic tests shows the importance of testing under cyclic loading condition. Keywords Soil improvement, Dune Sand, Polypropylene Fibers, Amine Based Resin, Unconfined Compressive strength test, Direct Shear test, Resilient Modulus Test
