structure - Period #5: Soil Consistency and Structure A....

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Unformatted text preview: Period #5: Soil Consistency and Structure A. Motivation: In geotechnical engineering, we need to determine the range of potential behaviors of a given soil type based on only a few simple tests . Typical concerns are the following: i) soils might shrink or expand excessively in an uncontrolled manner after they’ve been placed in geotechnical structures (roadway subgrades, dams, levees, foundation materials, etc). ii) soils might lose their shear strength , and ability to carry loads safely. Tests used to detect potential problems for coarse-grained soils (gravels & sands) are different than those used to detect potential problems for fine-grained soils (silts & clays). Coarse-Grained Soils: water content is generally not a major factor major factor leading to shrinkage is the structure of the soil skeleton. Fine-Grained Soils: water content is a major factor , especially when the soil contains so-called active clays . soils shrink soils expand gain strength lose strength water content 1 53:030 Class Notes; C.C. Swan, The University of Iowa 2 B. Structure of Cohesionless, Granular, Coarse-Grained Soils When speaking of cohesionless, granular soils, there are many possibilities: Soils with angular grains: Loose, angular soil Dense, angular soil Soils with uniform, rounded grains: Honey-combed soil Square-packed grains Hexagonally packed grains very loose (e > 0.90) loose (e = 0.90) dense (e = 0.35) 53:030 Class Notes; C.C. Swan, The University of Iowa 3 • Soils in loose or honeycombed states are avoided, or compacted before being being built upon, since they are prone to densification when subjected to vibratory or shock loading (as from earthquakes or...
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This note was uploaded on 11/10/2010 for the course CIVIL 53:30 taught by Professor Swan during the Fall '09 term at University of Iowa.

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structure - Period #5: Soil Consistency and Structure A....

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