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
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
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
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
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
PI < 4 or plots below "A" line ML Silt
Organic PI ≥ 4 and plots on or above "A" line OL Organic clay
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
PI plots below "A" line MH Elastic silt
Organic Plots on or above "A" line OH Organic clay
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)

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