ECIV 330 Soil Mechanics Chapter2 Basic Characteristics of Soils

ECIV 330 Soil Mechanics Chapter2 Basic Characteristics of Soils

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Unformatted text preview: ECIV 330 Soil Mechanics Prof. Bill X. Yu Spring, 2008 Chapter II Basic Characteristics of Soils Requirements A preliminary knowledge on the origins and composition of soils, common types of clay minerals Understand the principle of sieve analysis and hydrometer test Be familiar with obtaining information from particles size distribution curve (Cc, Cu etc) Physical interpretation of Atterberg limits Know how to use classify soils using USCS and AASHTO systems Proficient in phase relationship Understand soil compaction behaviors 2.1 Rock Cycle and Origin of Soils Soils are formed by weathering of rocks Weathering includes (Chemical and Physical). Variation in particle size and shape depends on: Weathering Process Transportation Process Variation in soil structure depends on: Soil Minerals Deposition Process Weathering Process Mechanical weathering Thermo (water), glacier ice, wind, running water, ocean waves Minerals were kept Chemical weathering Soluble salt, organic or inorganic acids Original minerals transformed to other types by chemical reactions Residual soils vs. transported soils Residual soils Formed by weathered products at their place of origin Gradation of particle sizes, grain sizes increase with depth Transported soils Water ---- Alluvial Soil (Fluvial, Estuarine, Lacustrine, Coastal, Marine) Ice -------- Glacial Soils Wind -------- Aeolian Soils (Sand Dunes, Loess) Gravity ----- Colluvial Soil Ref. Tawfig, 2000 Question to think? What type of soils are usually produced by the different weathering & transportation process Boulders Gravel Cohesionless Sand Physical Silt Cohesive Clay Chemical 2.2 Clay Minerals Complex aluminum silicates composed of two basic units Silica tetrahedron, and alumina octahedron Three most common types of clay minerals kaolin, illite (clay mica), montmorillonite Clay Minerals (cont.) Structures of clay minerals Clay Minerals (cont.) Electrical double layer Due to negative charge on the surface of clay Bound water versus free water Regular oven-drying does not remove adsorbed water adjacent to clay surface. This water is tightly bound to the soil and has a higher viscosity and density than water in the outer layer or free water in the soil . Determine clay behaviors Clay Minerals (cont.) Electrical double layer (examples) 2.3 Specific gravity, particle size distribution, and particle shape Specific gravity of soil (G s ) Ratio of the unit weight of a given material to the unit weight of water (It has no unit) Most soils Gs fall within 2.6 to 2.9 Sand around 2.65 Clay around 2.6 to 2.9 Particle size distribution Size range of particles present in a soil expressed as a percentage of the total dry weight Sieve analysis (for particle sizes larger than 0.075mm in diameter) Hydrometer analysis (for particle sizes smaller than 0.075mm in diameter) Particle size distribution (cont.) Shematic of sieve analysis Ref. Tawfiq, 2000 Particle size distribution (cont.)Particle size distribution (cont....
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ECIV 330 Soil Mechanics Chapter2 Basic Characteristics of Soils

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