151.227.153.155: Clarification

2025-04-07T06:09:29Z

Clarification

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{{Short description|System describing soil texture and grain size}}
The '''Unified Soil Classification System''' ('''USCS''') is a [[soil classification]] system used in [[engineering]] and [[geology]] to describe the [[Soil texture|texture]] and [[Particle size|grain size]] of a [[soil]]. The classification system can be applied to most [[unconsolidated]] materials, and is represented by a two-letter symbol. Each letter is described below:


{|
! First and/or second letters
! Second letter
|-align="center" valign="top"
|
{|class="wikitable"
|-
! Letter
! Definition
|-
! G
| [[gravel]]
|-
! S
| [[sand]]
|-
! M
| [[silt]]
|-
! C
| [[clay]]
|-
! O
| [[organic material|organic]]
|-
! PT
| [[peat]]
|}
|
{|class="wikitable"
|-
! Letter
! Definition
|-
! P
| poorly graded (many particle of about the same size<ref name=":0">{{Cite book|last=Day, Robert W.|url=https://www.worldcat.org/oclc/837179787|title=Geotechnical engineer's portable handbook : with the 2012 international building code|date=2013|publisher=McGraw-Hill|isbn=978-0-07-178971-4|edition=2nd|location=New York|oclc=837179787}}</ref>)
|-
! W
| well-graded (many different particle sizes<ref name=":0" />)
|-
! H
| high liquid limit<ref name=":1">{{cite tech report|year=2006|title=D 2487 – 06: Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)|publisher=[[ASTM International]]|url=https://lauwtjunnji.weebly.com/uploads/1/0/1/7/10171621/astm_d-2487_classification_of_soils_for_engineering_purposes_unified_soil_classification_system.pdf}}</ref>
|-
! L
| low liquid limit<ref name=":1" />
|}
|}

If the soil has 5–12% by weight of fines passing a #200 sieve (5% < P#200 < 12%), both grain size distribution and plasticity have a significant effect on the engineering properties of the soil, and dual notation may be used for the group symbol. For example, GW-GM corresponds to "well-graded gravel ''with silt''."

If the soil has more than 15% by weight retained on a #4 sieve (R#4 > 15%), there is a significant amount of gravel, and the suffix "with gravel" may be added to the group name, but the group symbol does not change. For example, SP-SM could refer to "poorly graded SAND with silt" or "poorly graded SAND with silt and gravel."

== Symbol chart ==
{| class="wikitable"
|-
! colspan="3" | Major divisions
! Group symbol
! Group name
|-
| rowspan="8" | Coarse grained soils more than 50% retained on or above No.200 (0.075 mm) [[sieve]]
| rowspan="4" | [[gravel]] > 50% of coarse fraction retained on No.4 (4.75 mm) sieve
| rowspan="2" | clean gravel <5% smaller than No.200 Sieve
! GW
| well-graded gravel, fine to coarse gravel
|-
! GP
| poorly graded gravel
|-
| rowspan="2" | gravel with >12% fines
! GM
| silty gravel
|-
! GC
| clayey gravel
|-
| rowspan="4" | [[sand]] ≥ 50% of coarse fraction passes No.4 (4.75 mm) sieve
| rowspan="2" | clean sand
! SW
| well-graded sand, fine to coarse sand
|-
! SP
| poorly graded sand
|-
| rowspan="2" | sand with >12% fines
! SM
| silty sand
|-
! SC
| clayey sand
|-
| rowspan="6" | Fine grained soils 50% or more passing the No.200 (0.075 mm) sieve
| rowspan="3" | [[silt]] and [[clay]] [[liquid limit]] < 50
| rowspan="2" | [[inorganic]]
! ML
| silt
|-
! CL
| lean clay
|-
| [[organic material|organic]]
! OL
| organic silt, [[organic clay]]
|-
| rowspan="3" | silt and clay liquid limit ≥ 50
| rowspan="2" | inorganic
! MH
| [[Elasticity (physics)|elastic]] silt
|-
! CH
| fat clay
|-
| organic
! OH
| organic clay, organic silt
|-
| colspan="3" | Highly organic soils
! PT
| [[peat]]
|}

=== ASTM D-2487 ===

{| class="wikitable" style="text-align:center"
! rowspan="2" colspan="4" | Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests
! colspan="2" | Soil Classification
|-
| Group Symbol
| Group Name
|-
| rowspan="8" | COARSE-GRAINED SOILS 
More than 50% retained on No.200 Sieve
| rowspan="4" | Gravels 
More than 50% of coarse fraction on No. 4 Sieve
| rowspan="2" | Clean Gravels 
Less than 5% fines
| {{abbr|Cu|Coefficient of uniformity}} ≥ 4 and 1 ≤ {{abbr|Cc|Coefficient of curvature}} ≤ 3
| GW
| Well-graded gravel
|-
| Cu < 4 and/or Cc < 1 or Cc > 3
| GP
| Poorly graded gravel
|-
| rowspan="2" | Gravels with Fines 
More than 12% fines
| Fines classify as ML or MH
| GM
| Silty Gravel
|-
| Fines classify as CL or CH
| GC
| Clayey gravel
|-
| rowspan="4" | Sands 
50% or more of coarse fraction passes No.4 sieve
| rowspan="2" | Clean Sands 
Less than 5% fines
| Cu ≥ 6 and 1 ≤ Cc ≤ 3
| SW
| Well-graded sand
|-
| Cu < 6 and/or Cc < 1 or Cc > 3
| SP
| Poorly graded sand
|-
| rowspan="2" | Sands with Fines 
More than 12% fines
| Fines classify as ML or MH
| SM
| Silty sand
|-
| Fines classify as CL or CH
| SC
| Clayey sand
|-
| rowspan="8" | FINE-GRAINED SOILS 
50% or more passes the no. 200 Sieve
| rowspan="4" | Silts and Clays 
Liquid limit less than 50
| rowspan="2" | Inorganic
| [[Plasticity index|PI]] > 7 and plots on or above "A" line
| CL
| Lean clay
|-
| PI < 4 and plots below "A" line
| ML
| Silt
|-
| rowspan="2" | Organic
| Liquid limit—oven dried < 0.75
| OL
| Organic clay
|-
| Liquid limit—not dried
| OL
| Organic silt
|-
| rowspan="4" | Silts and Clays 
Liquid limit 50 or more
| rowspan="2" | Inorganic
| PI plots on or above "A" line
| CH
| Fat clay
|-
| PI plots below "A" line
| MH
| Elastic silt
|-
| rowspan="2" | Organic
| Liquid limit—oven dried < 0.75
| OH
| Organic clay
|-
| Liquid limit - not dried
| OH
| Organic silt
|-
| colspan="4" | HIGHLY ORGANIC SOILS
| PT
| Peat
|}<ref name=":1" /><ref>ASTM Standard D2487, 2000, "Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)," ASTM International, West Conshohocken, PA, 2000, DOI: 10.1520/D2487-00, www.astm.org.</ref>

== See also ==

* [[AASHTO Soil Classification System]]
* [[AASHTO]]
* [[ASTM International]]
* [[USDA soil taxonomy|USDA Soil Taxonomy]] (Soil classification for agricultural purposes)

== References ==
*{{Citation|publisher=American Society for Testing and Materials |year=1985 |series=D 2487-83 |title=Classification of Soils for Engineering Purposes: Annual Book of ASTM Standards |volume=04 |issue=8 |pages=395–408 |url=http://www.astm.org/Standards/D2487.htm}}
*{{Citation|author=Evett, Jack and Cheng Liu |publisher=Prentice Hall |year=2007 |title=Soils and Foundations |edition=7 |pages= 9–29 |isbn=978-0132221382}}

;Specific
<references />

{{soil science topics}}

[[Category:Soil classification]]

Unified Soil Classification System - Revision history

151.227.153.155: Clarification