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Effects of Microstructure and Salinity Concentration on Hydraulic Conductivity of Silty Clay Soils

Khodadadi, Saeed | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 54652 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sadeghi, Hamed
  7. Abstract:
  8. Various contaminants and their leachate, when they penetrate into the soil, cause changes in soil microstructure, this change in microstructure leads to changes in soil permeability and volume. In this study, first, the effects of soil microstructure change on the hydraulic conductivity of saturated soil were investigated using the change in initial saturation degree during compaction for compacted samples and the change in sample construction in reconstituted samples. Also, the simultaneous effect of changing the initial microstructure and salt solution on the hydraulic conductivity of saturated silty clay soils using a three-axial permeability device with the ability to measure volume change and permeability by constant height method was investigated. In this study, the microstructural method of scanning electron microscopy (SEM) and the new method of three-dimensional imaging (CT scan) have been used to interpret the results. The 3D imaging method has the ability to extract information such as the three-dimensional shape of soil pores and soil structure, soil porosity, and the pore size distribution curve in the large pore range. The results show that at low porosity ratio (less than 0.616) the compacted samples in the wet part of the compression curve have less permeability than the compacted samples in the dry part of the compression curve and in the high porosity ratio (more than 0.616) the opposite is true. Also, for deposited samples, the permeability is lower in each porosity ratio than the compacted sample. The reason is the dispersed microstructure in the reconstituted samples and the compacted samples in the low porosity ratio in the wet part of the compression curve. In another part of the results, it is shown that the effect of salt on increasing soil permeability in samples with dispersed microstructure such as compacted samples in the wet part of the density curve in the ratio of low porosity and reconstituted samples is more than other samples. The reason for this phenomenon is the reduction of the thickness of the double layer and the irregularity of the dispersed microstructure and its tendency to coagulate (flocculate) the microstructure due to the increase of salt solution. Also, three-dimensional and one-dimensional consolidation diagrams show that salt leads to a decrease in compaction index and an increase in soil yield stress, which these changes have a greater effect on dispersed structural samples
  9. Keywords:
  10. Microstructure ; Salts ; Saturated Permeability ; Three Dimensional Imaging ; Triaxial Permeameter Device ; Hydraulic Conductivity ; Silty Sand

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