Investigating Geo-scrap aperture size effect on ballast shear resistance behavior using large-scale direct shear test

Reinforcement of ballast with the help of Geogrids is one of the methods that have been studied by various researchers in the technical literature to increase the load capacity as well as reduce the deterioration of the ballast through the reduction of crushing and settlement. In this article, by introducing a new type of geogrids made with the help of waste rubber belts called Geo-scrape, their effect on the shear behavior of ballast in a large-scale shear test has been investigated. In this direction and in order to investigate the effect of the dimensions of the geo-scrap on the ballast shear behavior and by placing the geo-scrap with the dimensions of 5x5, 10x10 and 25x25 cm square in the upper layer, various tests were carried out under vertical loads of 50, 100 and 150 Kilopascal has been done and the results are presented in the form of shear stress-horizontal displacement curve, maximum shear strength, internal friction angle and dilatancy angle. The summary of the results shows that the mesh of 5x5 cm2 has provided the most favorable conditions for the ballast in terms of increasing the shear strength, increasing the internal friction angle and decreasing the dilatancy angle. So that by placing the geo-scrape with the dimensions the mesh of 5x5 cm2, the shear strength, internal friction angle and dilatancy angle are increased by 20%, 7% and 30% respectively compared to the unreinforced state.