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Physical Modeling of a Fully Instrumented Bare and Vegetated Slope Model Under Different Hydraulic and Geometric Conditions

Yazdani Bone Kohal, Farshad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57460 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Sadeghi, Hamed
  7. Abstract:
  8. Rainfall is a primary trigger for initiating landslides. It primarily increases soil moisture and reduces matric suction, leading to a decrease in soil shear strength and consequently causing landslides. In light of global warming and the growing emphasis on environmentally friendly methods, the use of vegetation to fulfill engineering and environmental requirements in slope engineering has recently garnered attention. Vegetation reinforces slopes through both hydraulic and mechanical means. To survive, vegetation perform photosynthesis, absorbing water from the soil surface and carbon dioxide from the atmosphere. This water absorption increases matric suction, thereby enhancing soil shear strength. Mechanically, the presence of roots enables the soil to withstand tensile stress, which manifests as increased cohesion.This study utilizes a combination of physical modeling and numerical modeling approaches. Initially, a physical model was designed and developed to analyze the hydraulic behavior of slopes during rainfall. This physical model's capabilities include precise instrumentation across most slope areas, allowing for a comprehensive and detailed examination of water flow under two-phase conditions. Additionally, the study includes numerical analysis of slopes with and without vegetation to assess slope stability and evaluate environmental and economic aspects. The study revealed that due to two-dimensional flow in slopes, the lower parts of the slope are wetter. As the slope angle increases, the wetting front infiltrates less into the soil because surface runoff becomes more dominant than soil infiltration. Additionally, wet-dry cycles in slopes increase the air entry value in the soil-water retention curve. Also, younger vegetation demonstrated more effective maintenance and recovery of matric suction up to 25 kPa compared to older vegetation. Furthermore, vegetation significantly increases the factor of safety by up to 0.3 compared to slopes without vegetation. The mechanical contribution to the factor of safety, due to increased cohesion from root growth, rises from one-third to two-thirds. Moreover, when stability is ensured by vegetated slopes, up to 249 kg of carbon dioxide can be absorbed, and slope stabilization costs can be reduced by up to 2.5%
  9. Keywords:
  10. Shallow Landslide ; Vegetation ; Slope Stability ; Life Cycle Assessment ; Soil Erosion ; Bioengineered Slope

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