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Development of a New Analytical Model based on Soil-water Retention Curve Microstructure Considering the Effects of Osmotic Potential

Golaghaei Darzi, Ali | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54258 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sadeghi, Hamed
  7. Abstract:
  8. The soil-water retention curves (SWRC) is an unsaturated soil mechanics hydro chemical state surface, which expresses the relationship between the soil suction and water content. The soil-water retention curve could describe the water adsorption and desorption process that happened in soils. The difference between the desorption or drying retention curve and the adsorption or wetting retention curves in a specific soil specimen indicates the hydraulic hysteresis phenomenon. Generally, the amount of water remaining in the drying process is greater than the amount of water adsorbed in the wetting process at a certain amount of suction. Suction due to the combined effects of capillary and adsorption mechanism, usually defined in terms of matric suction. The matric parameter evokes the concept of structure and is used to express the components of suction that occur due to the interaction between pore water and the relative displacement of soil particles (soil microstructure). On the other hand, suction due to soluble substances in the pore water forms another component of total suction called osmotic suctio. In other words, total suction is the product of the algebraic sum of the matric and osmotic suction components. Direct measurement of soil-water retention curves is a process with high expertise costly. Due to the complexity of the measurement and the considerable cost of sampling, there is not usually so much measurement data. Therefore, alternative methods for direct measurements are always needed. One of the methods used to obtain the soil-water retention curve is analytical modeling. According to the analytical relationships in the technical literature, these models can be classified into nine categories. After a comprehensive review of existing models, it has been found that the weakness of nearly all the proposed models is in ignoring the effects of salts on soil microstructure and water retention capacity evolution. Therefore, this study aims to investigate the effects of osmotic potential on soil microstructure and presents a new analytical model that has the authority to simulate the effects of different salts with different concentrations on the soil-water retention curve. Generally, the models proposed in this study can be categorized into three groups: the first group is the models related to the low to the medium suction range, which explicitly emphasizes the capillary retention mechanism. The second one is the models related to the entire suction ranges, which deal with both adsorption and capillary retention mechanisms, and the third is the model that investigates the hydraulic hysteresis phenomenon. The equations presented in this study are based on the well-known van Genuchten (1980) model, which by using new concepts such as pore fluid salinity index (PSI) and fractal dimension (Ds), the ability to investigate the effects of osmotic potential and subsequent soil microstructure evolution have been considered. In addition to validating the proposed models, at the end of this study, using the suction stress concept in interaction with the proposed models, a new relationship is presented to investigate the volume change behavior in a specific type of collapsed soil
  9. Keywords:
  10. Soil-Water Retention Curve ; Analytical Modeling ; Hydraulic Hystersis ; Osmotic Potential ; Soil Microstructure

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