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Experimental Study on the Effects of Initial Suction and Particle Shape on Consolidation and Shear Behavior of Unsaturated Sandy Soils

Mousavi Avindin, Zahra Alsadat | 2023

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57289 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Jafarzadeh, Fardin
  7. Abstract:
  8. Particle morphology refers to the dimensions, shape, surface texture, roundness, and form of the particles. Morphology has a direct impact on the interaction between soil particles. Friction, particle rearrangement, dilation, and interlocking are influenced by the shape and size of the particles. The extensive impact of morphology on soil properties and behavior necessitates a comprehensive examination by geotechnical engineers to predict the behavior of granular materials accurately. Morphology significantly affects soil behavior under shear, volumetric changes, dilative behavior, shear strength, and soil behavior during consolidation testing, as well as changes in void ratio and compression index. Recently, extensive studies have focused on the effect of morphology on soil behavior under saturated conditions, and the combined effects of morphology and soil suction still require further investigation. Considering these factors, this research investigates the effects of initial suction and particle morphology of unsaturated sandy soil under consolidation and shear tests. Accurate assessment of particle shape effects necessitates quantification; thus, this study uses indices of sphericity, roundness, and regularity (ρ) to differentiate particle shapes. The sands used in this research include Firoozkooh (the most angular), Babolsar, Mesr, and Glass beads (the roundest). To examine the effect of initial suction, water retention curves were prepared for Mesr and Glass beads sands using the filter paper method, while for Firoozkooh and Babolsar sands, data from existing articles were used. The results indicated that with increased angularity, the air entry value and water retention capacity of the soil increase. Consolidation tests were conducted under two cycles of loading and unloading. The results of these tests showed that changes in the void ratio due to increased stress were nearly identical for dry samples in the first loading path and distinguished in the second loading path. It was also observed that under high suction values, void ratio changes for angular particles were greater, a trend reversed for lower initial suctions. Volumetric strain changes under consolidation tests were similar to void ratio changes. Direct shear tests conducted under two normal stresses of 50 and 100 kPa showed that a decrease in the ρ index leads to an increase in peak shear stress and shear strength of the sample, a result that increases with normal stress. Additionally, the results indicated that an increase in the ρ index reduces the dilative volume increase of the samples and decreases the peak dilation angle and peak and critical friction angle
  9. Keywords:
  10. Granular Materials ; Unsaturated Soil ; Direct Shear ; Consolidation Test ; Friction ; Dilatancy ; Particle Morphology

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