چكيده به لاتين
Stiffness changes of ballasted tracks in different areas of the railway tracks, especially in the transmission zones such as the entrance and exit of bridges due to the high dynamic forces wich are applied to the track and the vehicle is always considered as an important subject. Therefore, today, in order to increase the stifffness, the use of polyurethane materials in ballast tracks has become very popular. In addition, in the eastern and southeastern regions of Iran, ballast tracks pass through sandy areas. By studying the technical literature, we find out that the sand penetration into the ballast pores causes fouling and stiffness changes of tracks. Therefore, the use of polyurethane materials in ballast tracks can be a solution to prevent the penetration of sand into the ballast. In this thesis, by using the ballast box which is available in the railway faculty of Iran University of Science and Technology and by injecting polyurethane air filter, which is produced by Kaboudan Shimi Zarrin Company, into the ballast of Shahriar mine, we have studied the amount of changes in its settling, stiffness and damping compared to the non-polyurethane ballast. Since polyurethane is composed of two components of polyol and isocyanate, first to obtain the optimal ratio of these two components, pressure tests were performed on cubic polymer samples and cylindrical samples of polyurethane-reinforced ballast with different ratios, and finally the ratio of 2 units of polyol was concluded for 1 unit of isocyanate. In the last step, the polyurethane-reinforced ballast sample with obtained ratio, was loaded below 100,000 cycles to evaluate its settling, stiffness and damping. For example, after injection, settelment of polyurethane-reinforced ballast compared to non-polyurethane ballast decreased from 10 to 9.5 mm (5%), and also plastic settlement of polyurethane-reinforced ballast was 0.92 mm, indicating The good performance of polyurethane in preventing the permanent settlement and increasing the maintenance period of the tracks. Also, based on the drawn hysteresis rings, the stiffness of polyurethane-reinforced ballast compared to the samples without polyurethane increased from 45103 to 62016 N/mm (37.5%) and damping ratio decreased from 0.1 to 0.05 (51.9%).
