Informational GATE Meeting Topic: Identification (LAUSD Policy) Thursday, October 3, 2013.
Textural Identification Properties of Soil Topic D.
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Transcript of Textural Identification Properties of Soil Topic D.
Visual Classification System
• Based on visual identification of soils• Soils divided into three categories:
1. Granular2. Non-granular (Clays and Silts)3. Organic Soils
Topic D
Granular Soils
• Proportion • Gradation• Shape of gravel and course sand grains
noted.–Rounded, subrounded, subangular,
angular
Topic D
Non Granular Soils• Material passing No. 200 sieve.• Degree of plasticity –controlling factor–Clays (plastic)–Silts (non plastic)
• Occurs in combination with granular.• For granular size soils with clay sizes combine granular and
cohesive systems.
Topic D
Clays vs. SiltsIdentification Tests
• Differentiate between non-plastic cohesionless silt and plastic clay soils.
Topic D
1. Dilatancy Test
• Shake, squeeze and release wet soil.–Silt material when squeezed •Dry dull surface
–When released and shaken•Glassy wet surface
• Decreases with increasing clay content.
Topic D
2. Dry Strength Test• Portion of soil is dried completely.• Press material between fingers.• Clays– High Strength– Doesn’t break easily– Predominantly clay materials
• Silts– Very low strength– Breaks apart easily
Topic D
4. Soil Thread Test• Estimates degree of plasticity. • Differentiates between organic and inorganic
materials.• Take sample and add water.• Roll out threads 1/8” in diameter.• Fold and repeat until thread crumbles.• Similar to Plastic Limit test
Topic D
5. Thread Diameter Test
• Adjust water content: –For ball to form & flatten when dropped 2
feet.• Roll smallest non-crumbled thread• The thinner the thread the more plastic
Topic D
6. Dispersion Test
• Determine the settling rate–Shake sample in a water filled test tube.–Allow particles to settle:
a) Sand and Gravel settle out in seconds to minutesb) Pure silts settle out in less than 1 hourc) Clays remain suspended for hours to days
Topic D
How Soil Feels Matters
• Tough–highly plastic, inorganic fat clay
• Weak–Leaner sandy, or silty clays.
• Spongy or elastic–Organic and inorganic
Topic D
Organic Soils
• Contain organic matter• Affect the engineering properties of soil.• Examples-Topsoil, peat, and organic silt.
Topic D
Clay Soils
• Any color• More plastic means
more effort to pull apart.
• High plasticity – Smear looks shiny
and waxy.
Organic Soils
• Dark gray, black, and brown
• Have a Hydrogen sulfide smell (stink).
• Smear looks dull and silty.
• Low shear strength• Respond to dilatancy
test.Topic D
Describing Soil
–Color–Predominant Soil Type–Grain Size–Depositional Features–Degree of Saturation/Relative Moisture–Density (granular soils) or consistency
(cohesive soils)Topic D
Describing Soil
• Major Constituent is upper Case• Second (20-50%) constituent is adjective
modifying major.–Example (70% gravel, 30 % sand)=
sandy GRAVEL
Topic D
Constituents 10-20%
• Come after the main constituent with a hyphen.–Example (55% gravel, 30% sand, 15%
silt)= sandy GRAVEL-trace to some silt.
Topic D
Constituents 10% or less
• Indicated by “trace” and come after grain size.–Example (50% Gravel, 30% sand, 12%
silt, & 8% clay)= sandy GRAVEL, trace to some silt, trace clay.
Topic D
Two Components=20-35%
• Exist as secondary components• “Some” is used for one–Example (52% sand, 27% clay, and 21%
silt)= clayey SAND-some silt
Topic D
Descriptive TermsSoil Color
• Confined to a few basic terms.• Terms can be combined to give pairs.• Useful descriptive terms are helpful.–Example-Rusty or reddish brown.
Topic D
Descriptive TermsDensity – Granular Soils
• Based on Standard Penetration Test (SPT) results performed in test borings.–N-Value - Number of blows of a falling
weight required to drive a sample spoon a given distance into soil.
Topic D
Descriptive TermsConsistency – Non Granular
• Based on Unconfined Compression Test–Axially loading a soil sample under a
constant strain rate until failure is obtained. (Also can be related to pocket penetrometer testing.)
Topic D
Other Descriptive Terms
• Topsoil: Organic soil at surface • Peat: Soft organic soils –Lots of decaying vegetable matter.
• Varved: Alternating thin layers of silt and clay.
• Glacial Till: Dense with a variety of grain sizes.
Topic D
Other Descriptive Terms
• Interbedded: Hard to differentiate between various soil types.
• Loess: Wind blown deposits of silt. – immediately under the topsoil.
• Fill: Artificially placed material.
Topic D