Unified Soil Classification System

This test determines the liquid limit, plastic limit, and the plasticity index of soils. These test results are used to classify fine-grained soils and the fine-grained fraction of coarse-grained soils according to the Unified Soil Classification System (USCS). The test for plastic limit uses the one-point method (Method B).

Liquid Limit

Wet Soil and Tare Mass:		Units:
Dry Soil and Tare Mass:
Tare Mass:
Blow Count:
Water Content (%):
Liquid Limit:

Plastic Limit

Wet Soil and Tare Mass:
Dry Soil and Tare Mass:
Tare Mass:
Plastic Limit:

Classification

Plasticity Index:
Classification:

Criteria			Group Symbol	Group Name
Gravels > 50% retained on No. 4 Sieve	Clean Gravels < 5% fines	Cu ≥ 4 & 1 ≤ Cc ≤ 3	GW	Well-graded gravel
	Clean Gravels < 5% fines	Cu < 4 and/or Cc < 1 or Cc > 3	GP	Poorly graded gravel
	Gravels with Fines > 12% fines	Fines ML or MH	GM	Silty gravel
	Gravels with Fines > 12% fines	Fines CL or CH	GC	Clayey gravel
Sands > 50% of coarse fraction passed No. 4 Sieve	Clean Sands < 5% fines	Cu ≥ 6 and 1 ≤ Cc ≤ 3	SW	Well-graded sand
	Clean Sands < 5% fines	Cu < 6 and/or Cc < 1 or Cc > 3	SP	Poorly graded sand
	Sands with Fines > 12% fines	Fines ML or MH	SM	Silty sand
	Sands with Fines > 12% fines	Fines CL or CH	SC	Clayey sand
Silts and Clays LL < 50	Inorganic	PI > 7 and plots on or above "A" line	CL	Lean clay
	Inorganic	PI < 4 or plots below "A" line	ML	Silt
	Organic	PI ≥ 4 and plots on or above "A" line	OL	Organic clay
	Organic	PI < 4 or plots below "A" line	OL	Organic silt
Silts and Clays LL ≥ 50	Inorganic	PI plots on or above "A" line	CH	Fat clay
	Inorganic	PI plots below "A" line	MH	Elastic silt
	Organic	Plots on or above "A" line	OH	Organic clay
	Organic	Plots below "A" line	OH	Organic silt
Highly Organic Soils			PT	Peat

For more information on this test and many other geotechnical tests please see our GDMS software.

Reference

ASTM D2487-06 Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System)

Unified Soil Classification System

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