Date

2022-6

Author

Ekici, Anıl

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Different proportions of gravel, sand, nonplastic silt, kaolin, and bentonite were mixed to obtain ten coarse-fine mixtures (CFM) having 0%, 12%, 20%, 30%, 40% fines content (FC) and 5% and 15% plasticity indices (PI). Mixtures were evaluated to identify behavioral thresholds and address backfill restrictions in commonly used guidelines to design reinforced earth walls. All CFM specimens were initially compacted to 95% of standard Proctor dry density at optimum moisture content. Index, hydraulic properties, and specific surface areas were investigated. FC=15% for PI=5% and FC=12% for PI=15% represented the transition between fine and coarse-grain domination according to particle packing. Unconfined compressive strength, CU triaxial, and large-scale compression tests were conducted. FC=20% was the transitional boundary for CFM with PI=5%, reflected in shifting of the dilation tendency to contraction, while samples having PI=15% mainly had relatively high initial contraction followed by dilation. Consolidation data in triaxial tests indicated that FC of 30% to 40% for PI=15% was the transition at which normally-consolidated clay-like behavior began. Strength of CFM and interaction with geogrids (with and without drainage property) were investigated through large direct shear tests (300x300 mm) under 55, 105, and 155 kPa normal stresses. Interface shear strength coefficients ranged between 0.65- 1.05. Bond efficiencies increased with normal stress and decreased with PI. Geogrid’s drainage component did not affect the interface strength for unsaturated specimens. In saturated mixtures, drainage was more critical for FC=40% than FC=20%, as strength reductions due to excess pore pressures were significant, especially for FC=40% and PI=15%.

Subject Keywords

Fines content, Plasticity index, Coarse-fine mixtures, Reinforced earth fill criteria, Geogrid interaction

URI

https://hdl.handle.net/11511/98202

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Graduate School of Natural and Applied Sciences, Thesis