چكيده به لاتين
Most of the ballasted tracks in the eastern and southeastern regions of Iran are built on sandy areas, which causes major problems such as sand penetration into the ballast pores, track fouling and decrease of shear strength. Therefore, polyurethane materials are used to improve the behavior of the ballasted tracks and increase its shear strength. In this thesis, by injecting polyurethane air filter (produced by Kaboudan Shimi Zarrin Company) into the ballast of Shahriar mine and performing the direct shear test in large scale by shear box machine available in the Railway Faculty of Iran University of Science and Technology, We extracted shear parameters of polyurethane-reinforced ballast and investigated them. It should be noted that in order to make the desired polyurethane and achieve the optimum ratio of polyol and isocyanate, pressure tests on cubic polymer samples and cylindrical polyurethane-reinforced ballast samples with different ratios were defined and finally, based on the results, the ratio of 2 polyol units to 1 isocyanate unit was confirmed, and this ratio was used to make polyurethane for injection into the shear box test specimens. The shear box tests were performed using 3 different loads of 50, 100 and 150 kPa. For an instance, it was concluded that after injection of polyurethane to the ballast, the maximum shear stress at the load of 150 kPa has increased from 205.9 to 324.7 kPa(57.73%), indicating better performance of ballast in the presence of polyurethane. It can also be concluded that the shear strength and lateral strength increase which the increasing in the lateral strength can prevent lateral track deflection and also increase track safety.
Based on the mohr coulomb failure envelope ,the internal friction angle has increased from 41.97 to 45.97 degree(9.5%) compared to the non-polyurethane specimens, and the adhesion coefficient for the polyurethane-reinforced ballast has increase from 66.67 to 168.37 kPa (160.35%), indicating a signifcant improvement in ballast shear parameters.
