2 Soil Structure

2 Soil Structure - Soil Structure Das Chapter 2...

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1 Soil Structur Soil Structure Das Chapter 2 Geotechnical Engineering Soil Wate Rock Water
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2 Key Soil Engineering Properties Compressibility Settlement Strength Ability to carry load Permeability (hydraulic conductivity) Flow of water through soils Settlement Failure
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3 Palace of Fine Arts, Mexico A strange case of Palace of Fine Arts in the Alameda area of Mexico City. Built sometime between 1900 and 1934, it was a magnificent and strongly built structure It was built was a magnificent and strongly built structure. It was built on grade, level with the square and other buildings nearby. But because of loose sand permeated with water in the subsurface, the massive structure sunk 6 ft into the ground! (Luckily, it settled evenly minimizing structural damage.) Believe it or not, in the 1960's the building moved again. This time it moved 12 ft up! The weight of skyscrapers being built around the Palace had pushed the subsurface water and soil around sufficiently to raise the building. (Source: Why Buildings Fall Down , M. Levy and M. Salvadori, WW Norton & Company, 1992) Shear Failure
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4 Soil Shear Failure Permeability
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5 Soil Structure Assemblage of individual particles Bulky particles Plate particles (Includes flaky or needle particles) Card house structure Cohesionless and Cohesive soils Silt, sand and gravel are cohesionless soils Individual particles flow when dropped or Individual particles flow when dropped or shaken Silt and clay are cohesive soils Particles bound together and do not flow when dropped. . Breaks up into chunks
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6 Bulky Particles Spherical particles Boulders cobbles gravel sand and sil Boulders, cobbles, gravel, sand, and silt Coarse, granular or cohesionless soils Small surface area large mass Gravity forces dominate behaviour F g = m * g m= particle mass g is earth’s gravitation constant (9.81m/s 2 ) Particle Shape and Classification Engineering response impacted by: Particle shape Particle shape ( Angular, round, etc) Range of particle sizes (distribution) Percent gravel, sand, and silt particle shape description usually made based on visual classification Rounded sub-rounded angular sub angula Rounded, sub-rounded, angular, sub-angular
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7 Bulky Particles Shape depends on deposition environment and particle composition Quartz, gold, feldspar, etc Shape good indication of how soil formed Particle size classification Many different systems (USCS, ASTM, AASHTO, MIT, British, etc) Soil Classification Systems
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8 UNIFIED Soil Classification System (USCS) Particle diameter (mm) Boulder > 300 Cobble 76.2 - 300 Gravel 4.75 – 76.2 Sand 0.075 – 4.75 Si 005 007 Bulky Particles Cohesionless Silt .005 – 0.075 Clay 0.002 - .005 Colloid < 0.002
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2 Soil Structure - Soil Structure Das Chapter 2...

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