Soil classification, Atterberg limits, compaction, effective stress, consolidation, shear strength, bearing capacity and slope stability.
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- Define the Unified Soil Classification System (USCS)
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A system that classifies soils based on grain size distribution, Atterberg limits, and organic content into groups like gravel (G), sand (S), silt (M), clay (C), and organic (O)- What is the dividing sieve number between coarse and fine-grained soils in USCS?
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No. 200 sieve (0.075 mm opening); coarse-grained has more than 50% retained on it- Distinguish coarse gravel from coarse sand in USCS classification
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Gravel is retained on No. 4 sieve (4.75 mm); sand passes No. 4 but is retained on No. 200- What does AASHTO soil classification primarily use that USCS does not?
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AASHTO places more emphasis on group index and suitability for highways; USCS focuses on engineering behavior- Define clay in soil classification
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Mineral particles smaller than 0.002 mm (2 microns), with cohesion and plasticity when wet- What is silt and how does it differ from clay?
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Silt is particles between 0.002 and 0.075 mm; less plastic and has lower cohesion than clay- Define liquid limit (LL)
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Water content at which soil transitions from plastic to liquid state; determined by flow cup test at 25 blows- Define plastic limit (PL)
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Water content at which soil transitions from semi-solid to plastic state; determined by rolling thread test- Define shrinkage limit (SL)
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Water content below which further moisture loss does not reduce soil volume- What is the plasticity index and how is it calculated?
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PI = LL - PL; indicates the range of water content over which soil exhibits plastic behavior- Define liquidity index (LI)
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LI = (w - PL) / (LL - PL), where w is natural water content; indicates how close soil is to liquid state- What is the Standard Proctor test?
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Compaction test with a 5.5 lb hammer, 12 inch drop, 3 layers of 25 blows each; determines maximum dry density and optimum moisture- How does Modified Proctor differ from Standard Proctor?
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Modified uses a 10 lb hammer, 18 inch drop, 5 layers of 25 blows; produces higher maximum dry density- What is optimum moisture content (OMC)?
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Water content at which soil achieves maximum dry density during compaction- Define maximum dry density
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Highest dry unit weight achieved during compaction at optimum moisture content
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