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Laboratory Investigation of the Effects of Sodium Chloride Concentration on Soil Water Retention Curve and Volumetric behavior Using an Unsaturated Automatic Oedometer

Nasiri, Hamed | 2020

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54112 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sadeghi, Hamed
  7. Abstract:
  8. Laboratory studies to investigate the effects of different saline concentrations (such as sodium chloride or calcium chloride) on the soil water retention behavior of clayey soils and their volumetric changes have received much attention recently. However, many previous studies have investigated these effects in only one path of the SWRC (wetting or drying path) and the effects of saline concentration on hydraulic hysteresis have not been considered. In addition, researchers have frequently studied these effects on SWRC on clay samples, and little research has been done on collapsible soils. Therefore, the most important purpose of this study is to investigate the effects of increasing sodium chloride concentration on SWRC and volumetric changes of a collapsible soil in two cycles of wetting and drying.Chemical analysis shows that the collapsible soil located in Chabahar, contains significant amounts of sodium chloride in its structure. In order to investigate the effects of concentration of the NaCl as an independent parameter, an artificial soil was produced that was similar to the Chabahar collapsible soil in terms of grain size distribution, Atterberg limits and collapse index. In addition, in this study, the development of an automatic unsaturated oedometer device was performed. Simultaneously with this development, a water deaerator was built to make sure that the dissolved air of the distilled water or saline solution is completely eliminated. After the development of the device, three series of experiments were performed for determination of SWRC of the artificial collapsible soil in two cycles. The accuracy of the three main experiments was confirmed by two reproducibility tests. The experiments were all performed by keeping the osmotic suction constant and having only one variable which is matric suction. Scanning electron microscopy images were also taken from the samples to investigate the reasons of the macroscopic observations.The results of this study show that with increasing the concentration of the sodium chloride, the artificial soil with a constant matric suction has a lower degree of saturation in both cycles. As the concentration of sodium chloride in the soil increases, the air entry value in the first cycle decreases and the desorption and the adsorption rates increase.Hydraulic hysteresis in both cycles increases with the increasing of the saline concentration and of course the total degree of hysteresis increases linearly with increasing molar concentration of saline solution in both cycles. The maximum of the hysteresis curve occurs in the vicinity of the air entry value of each sample. The volumetric changes of the samples decreases in both saturated and unsaturated states with increasing the concentration of the saline solution
  9. Keywords:
  10. Hydraulic Hystersis ; Soil-Water Retention Curve ; Automatic Unsaturated Oedometer ; Osmotic Suction ; Wetting-Drying Cycles ; NaCl Molar Concentration

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