World Library  
Flag as Inappropriate
Email this Article

Unified Soil Classification System

Article Id: WHEBN0003681488
Reproduction Date:

Title: Unified Soil Classification System  
Author: World Heritage Encyclopedia
Language: English
Subject: Soil mechanics, Donald Burmister, Lateral earth pressure, Grain size, Soil classification
Collection: Encodings, Geotechnical Engineering, Sedimentology, Soil
Publisher: World Heritage Encyclopedia

Unified Soil Classification System

The Unified Soil Classification System (USCS) is a soil classification system used in engineering and geology to describe the texture and 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 (with the exception of Pt):
First and/or second letters Second letter
Letter Definition
G gravel
S sand
M silt
C clay
O organic
Letter Definition
P poorly graded (uniform particle sizes)
W well-graded (diversified particle sizes)
H high plasticity
L low plasticity

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

Major divisions Group symbol Group name
Coarse grained soils
more than 50% retained on or above No.200 (0.075 mm) sieve
> 50% of coarse fraction retained on No. 4 (4.75 mm) sieve
clean gravel <5% smaller than #200 Sieve GW well-graded gravel, fine to coarse gravel
GP poorly graded gravel
gravel with >12% fines GM silty gravel
GC clayey gravel
≥ 50% of coarse fraction passes No.4 sieve
clean sand SW well-graded sand, fine to coarse sand
SP poorly graded sand
sand with >12% fines SM silty sand
SC clayey sand
Fine grained soils
50% or more passing the No.200 sieve
silt and clay
liquid limit < 50
inorganic ML silt
CL clay of low plasticity, lean clay
organic OL organic silt, organic clay
silt and clay
liquid limit ≥ 50
inorganic MH silt of high plasticity, elastic silt
CH clay of high plasticity, fat clay
organic OH organic clay, organic silt
Highly organic soils Pt peat

See also


This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.