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Study of Stability of Unsaturated Railway Embankment Founded on Saline and Desalinated Loess

Kolahdooz, Ali | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52728 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Ahmadi, Mohammad Mehdi
  7. Abstract:
  8. Loess with a dispersion potential is one of the problematic soils of Iran. This study aims to investigate the impact of dispersion potential on the water flow in a three-phase medium and determine the effect of salinity on the stability of an unsaturated railway embankment by employing the soil-water retention curves of the materials. To satisfy this objective, the natural dispersive loess of the Chabahar region is desalinated in this study and the hydraulic properties of both saline and desalinated soils are comprehensively investigated. First, the soil-water retention curves of the materials are measured through the filter paper test method. Afterward, the saturated hydraulic conductivity of the materials is measured with the falling head test. Finally, with the measured soil-water retention curves and the saturated hydraulic conductivities, the unsaturated hydraulic conductivity functions of the materials are estimated based on an appropriate relation.In the next step and with the determined hydraulic properties of the materials, an unsaturated railway embankment is numerically simulated and subjected to various rainfall patterns in order to determine its stability during the rainfall infiltration. The experimental results show that by removing the natural salinity of the soil, the retention capability of the soil drops significantly; thus, the unsaturated hydraulic conductivity of the materials tremendously decreases. As a result, the results of the numerical study show that rainfall cannot infiltrate in the desalinated embankment due to the low rate of unsaturated hydraulic conductivity; however, it infiltrates in the saline embankment and makes the soil suction decrease. Therefore, the safety factor of the desalinated embankment does not considerably change, but the safety factor of the saline embankment dramatically declines. In conclusion, the results show that by increasing the natural salinity of the soil, the instability of an unsaturated railway embankment subjected to rainfall decreases significantly
  9. Keywords:
  10. Salinity ; Loess Soil ; Slope Stability ; Unsaturated Soil ; Soil Mechanics ; Soil-Water Retention Curve

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