چكيده به لاتين
A large part of Iran's railways consists of ballasted tracks. When contaminants enter the ballasted tracks, they weaken their performance and impair their safety. Ballast shear strength plays a vital role in maintaining track stability. Contamination can be caused by various factors, including fine-grained infiltration from the bed, high crushing, or the entry of materials such as sand, clay, or coal dust. Since a significant part of Iran's ballasted tracks are located in desert areas, they are exposed to desert sand contamination. The presence of moisture and then drying of the contaminated ballast and the type of ballast used can also cause changes in shear strength. For this purpose, in the leading thesis, the shear strength of wet sand-contaminated ballast after drying was investigated using a large-scale direct shear test on two types of ballasts of Coohin and Shahriyar mines. Samples with three contamination levels of 14%, 25%, and 34%, with two humidity levels of 9% and 15%, were tested. The results showed that the highest shear strength and internal friction angle are related to clean ballast (Shahriar: 207.8 kpa and 51.39 ° Coohin: 238.9 kpa and 56.09 °), and fouling percentage and dried moisture lead to a decrease in these values. At low contamination rates and low humidity at which the sample is dried, the sample behaves similarly to the dry state. However, in high fouling percentage (25 and 34%) and high humidity (15%), with increasing of fouling, the shear strength and friction angle increase relative to other contaminated states, but it does not reach a clean state. Therefore, the highest shear strength among the fouling samples related to the sample with 34% contamination in the dried moisture of 15% (Shahriar: 202.5 kpa and 51.09 ° Coohin: 235.8 kpa and 55.81 °) which is close to clean ballast. Comparing the results of two types of ballasts, it can be concluded that Coohin ballast with a 126.35 MPa mother rock strength (UCS) higher (44%) than Shahriar ballast, increase in shear strength between 7-14% and friction angle between 8-12% in a clean and dirty condition. Also, comparing the difference in shear strength between the two types of contaminated ballasts compared to the clean state showed that the ballast with more UCS resistance is 1.5% less different than the ballast with less UCS resistance.
