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Evaluation of Anisotropic Hydraulic Conductivity of as Compacted and Vegetated Soils with a Cube Triaxial Permeameter

Gholami, Mostafa | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 56446 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sadeghi, Hamed
  7. Abstract:
  8. Vegetation can be used as a research solution at the cutting edge of knowledge, cost-effective, aesthetic, pleasing, and environmentally friendly in natural hazards. Understanding the hydraulic properties, including the permeability of vegetated soils, is very important for various environmental applications. Different and sometimes conflicting behaviors have been observed in literature. There has been no general consensus in the literature regarding permeability due to the influence of several factors. In addition, there are many uncertainties about the effect of plant cultivation and root system effects on anisotropic soil permeability. It is essential to address this issue because of the dominance of two-dimensional subsurface flows and the direct influence of the anisotropy ratio in relation to hydraulic conductivity on the redistribution of pore water pressure during rainfall and, consequently the instability of natural and artificial slopes such as road and railway embankments. The primary objective of this study is to evaluate the anisotropic permeability characteristics of soils with and without vegetation using a laboratory approach. First, in order to solve the known sources of error in the conventional methods of permeability measurement as well as the problems caused by sampling in sensitive soils, a cube triaxial permeameter device was modified to investigate the anisotropic permeability. In the next step, the anisotropic hydraulic conductivity of artificial bentonite-based materials was first studied, and new insights were provided on the complex evolution of anisotropic hydraulic conductivity with bentonite content, compaction energy, loading, and unloading. Then, by cultivating the plant in a controlled laboratory environment and preparing it at different ages, as-compacted, bare, and rooted soils were studied. The results revealed an enhancement of as-compacted anisotropy ratio from 1 to almost 7 with bentonite contents. However, the anisotropy ratio was suppressed with isotropic loading for 40% and 70% bentonite, while it was enhanced for 10% bentonite content. The as-compacted specimens were revealed isotropic because of the loosely-packed preparation procedure resulted in a dominant flocculent structure. In addition, wetting-drying cycles led to an increase in the anisotropy ratio from 1 to 5 in bare soil. Also, root growth and the rise in biomass led to a decrease in permeability in both orthogonal directions. In vegetated soils, the anisotropy ratio increased from 0.5 to 5 with increasing effective stress. In addition, the root system led to the elastic behavior of the soil under confining pressure. The observed behaviour was explained according to postulated interactions between Vetiver root system and soil pore structure
  9. Keywords:
  10. Hydraulic Conductivity ; Permeability Anisotropy ; Cube Triaxial Permeameter Device ; Vegetated Soil ; Soil-Plant Interaction ; Compacted Soil

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