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Soil Classification SystemsTopic E
Topic E
Soil Classification Systems
Topic E
Classification systems are a way to identify soils in a consistent unbiased manner based on physically measured properties.
Soil Classification Systems
• AASHTO • Unified Soil• USDA• FAA• Burmister
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Soil Classification SystemPage E-2
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AASHTO Classification System
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AASHTO Classification System
• AASHTO – American Association of State Highway Transportation Officials
• Based on suitability of soil as a subgrade material.
• Ranking of soils as a quality subgrade material.
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AASHTO Grain Size Definitions
Coarse Gravel Passing 3 inch sieve and retained on 1 inch sieve
Medium Gravel Passing 1 inch sieve and retained on 3/8 inch sieve
Fine Gravel Passing 3/8 inch sieve and retained on No. 10 sieve
Coarse Sand Passing No. 10 sieve and retained on No. 40 sieve
Fine Sand Passing No. 40 sieve and retained on No. 200 sieve
Silt/Clay Passing No. 200 sieve
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AASHTO Classification
General Classification Granular Materials(35% or less passing No. 200 sieve)
Silty-Clay Materials(More than 35% passing No. 200 sieve)
Group Classification A-1 A-3 A-2 A-4 A-5 A-6 A-7
A-1-a A-1-b A-2-4 A-2-5 A-2-6 A-2-7A-7-5
A-7-6
Sieve AnalysisPercent Passing
No. 10 50 max
No. 40 30 max 50 max 51 min
No. 200 15 max 10 max 10 max 35 max 35 max 35 max 35 max 36 min 36 min 36 min 36 min
Characteristics of P40 material
Liquid Limit 40 max 41 min 40 max 41 min 40 max 41 min 40 max 41 min
Plastic Index 6 max NP 10 max 10 max 11 min 11 min 10 max 10 max 11 min 11 min
Group Index 0 0 0 4 max 8 max 12 max 16 max 20 max
A-7-5, PI ≤ LL - 30
A-7-5, PI > LL – 30
When classifying start with category furthest on the left and move right till it fits category. (Page E-8)
AASHTO• Grouped on load-carrying capacity.• 7 basic groups
–A-1 (best) to A-7 (poorest)–Similar broad characteristics
• Subgroups–0 (best) to 20 (poorest)
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Granular Materials
Less than 35% passing No.200 sieve.
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Granular Materials
• A-1 Soils–Coarse to fine non-plastic soils.
• A-1-a–Contain stone fragments or gravel.
• A-1-b–Contain Coarse sand.
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Granular Materials• A-2 Soils
–Poorer then A-1• A-2-4 & A-2-5
–Granular materials of A-4 & 5 groups.• A-2-6 & A-2-7
–Granular materials of the A-6 & 7 groups.
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Granular Materials
• A-3 soils–Fine sand, little fines–Sands deficient in coarse material.–Lack stability.–Good subgrades.
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Silt-Clay Materials
• Greater than 35% passing No. 200 sieve
• Silts – PI ≤ 10• Clays – PI > 10
• PI = Plasticity Index
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Silt-Clay Materials• A-4 soils
–Silt with small amounts of coarse material.–Subject to frost.–Varying textural composition.
• A-5 Soils–Poorly graded soils–Not suitable for subgrades
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Silt-Clay Materials
• A-6 Soils–Clay–Good for fills and subgrades
• At low moisture content
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Silt-Clay Materials
• A-7 soils–Elastic–Problematic subgrades
• A-7-5–Volume change
• A-7-6–High volume change
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Group Index Rating
• Based on gradation, L.L., and P.I. of the soil.
• Group Index=0.2a + 0.005ac + 0.01bd• See page E-11 in manual.
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Group Index & Subgrades• Excellent- A-1-a(0) Soils• Good- 0 to 1 group indexes• Fair- 2 to 4 group indexes• Poor- 5 to 9 group indexes• Very poor- 10 to 20 group indexes• Tends not to correlate well with Silty materials.
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ExamplesAASHTO Classification System
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Example - 1AASHTO Classification System
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Gradation
Project ID 1411-03-00Highway STH 33Project Limits USH 41 to CTH ZComments
Test Boring No. 7 Depth 3 - 5Sample No. 2
Test Date
October 5, 2010
Tester Jonathan Joslin
Dry mass before wash 267.0g Dry mass after wash 228.5g Sieve Size Accum % %
SI, mm U.S. Mass Retn'd Passing
19 3/4" 22.5 8.4 91.57%
4.75 #4 108.5 40.6 59.36%2.000 #10 141.0 52.8 47.19%0.425 #40 179.5 67.2 32.77%0.150 #100 213.5 80.0 20.04%0.075 #200 228.5 85.6 14.42%
PAN
LL = NP
PI = NP
AASHTO Classification
A-1-b
Example - 2AASHTO Classification System
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Example - 2AASHTO Classification System
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Sieve Analysis – Percent PassingNo. 10 = 37%No. 40 = 25 %No. 200 = 13%LL, PI = Non plastic
AASHTO Classification
A-1-a
Example - 3AASHTO Classification System
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Percent Passing No. 200 Sieve = 63%
Liquid Limit (LL) = 32Plasticity Index (PI) = 15
AASHTO Classification
A-6
Unified Soil Classification SystemUSCS
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Grain Size IdentificationUSCS – (ASTM)
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Page E-1
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Page (E-9)
Unified Soil Classification System (Table 4 (E-9) in manual)
• Textural and plasticity qualities.• Grouped by performance.• Properties:
–% of gravel, sand, and fines.–Shape of grain-size distribution curve.–Plasticity & compressibility characteristics.
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Coarse-grained Soils
• 50% or less material passing #200 sieve• Subdivided
–Gravels-Greater percentage of coarse fraction.
–Sands-Greater portion passing #4 sieve.
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ExampleUSCS Classification System – Coarse Grained Soils
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1 – Greater than 50% passing No. 200 sieve? No
Coarse Grained Soil
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2 – Determine Sand vs. GravelGravel - P 3-inch to R No. 4 = 59%
Sand - P No. 4 to R No. 200 = 30%
Gravel
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3 – Determine D60, D30 and D10
D60 =
D30 =
D10 =
10 mm
2 mm
0.07 mm
Example USCS Classification System – Coarse Grained Soils
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4. Determine Cu and Cc
Cu = D60 /D10 = 10/0.07 =
D60 = 10 mm
D30 = 2 mm
D10 = 0.07 mm
143
Cc = (D30 ^ 2)/(D60 x D10) = 5.7
Example USCS Classification System – Coarse Grained Soils
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Cu = D60 /D10 = 10/0.07 = 143
Cc = (D30 ^ 2)/(D60 x D10) = 5.7
If Cu is greater than 4 and Cc is between 1 to 3 than GW
For P200 < 5%
If both sets of criteria are not met for GW than GP
LL, PI = Non plastic
For P 200 between 5 and 12%
If Cu is greater than 4 and Cc is between 1 to 3 than GW-GM or GW-GC
If both sets of criteria are not met for GW than GP-GM or GP-GC
USCS Classification = GP-GM
AASHTO Classification? A-1-aP200 = 11%
Fine-grained Soils
• More than 50% smaller then #200 sieve• Subdivided (based on LL and PI):
–Silts–Clays
• Secondary divisions–Based on low or high liquid limit.
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Example USCS Classification System – Fine Grained Soils
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Example USCS Classification System – Fine Grained Soils
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LL = 37PL = 20PI = 17
P 200 > 50%Not Organic
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Page E-9
Example USCS Classification System – Fine Grained Soils
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LL = 37PL = 20PI = 17
USCS Classification:
AASHTO Classification?
A-6
CL
Organic Soils
• Compressible• Undesirable for construction• Symboled “pt.”• Peat, humus, and swamp soils
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AASHTOSoil Type
Comparable USCS Soil Type
Most Probable Possible Unlikely
A-1-a GW, GP SW, SP GM, SM
A-1-b SW, SP, GM, SM GP --
A-3 SP -- SW, GP
A-2-4 GM, SM GC, SC GW, GP, SW, SP
A-2-5 GM, SM -- GW, GP, SW, SP
A-2-6 GC, SC GM, SM GW, GP, SW, SP
A-2-7 GM, GC, SM, SC -- GW, GP, SW, SP
A-4 ML, OL CL, SM, SC GM, GC
A-5 OH, MH, ML, OL -- SM, GM
A-6 CL ML, OL, SC GC, GM, SM
A-7-5 OH, MH ML, OL, CH GM, SM, GC, SC
A-7-6 CH, CL ML, OL, SC OH, MH, GC, GM, SM
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USCSSoil
Type
Comparable AASHTO Soil Type
Most Probable Possible Unlikely
GW A-1-a -- A-2-4, A-2-5, A-2-6, A-2-7
GP A-1-a A-1-b A-3, A-2-4, A-2-5, A-2-6, A-2-7
GM A-1-b, A-2-4, A-2-5, A-2-7 A-2-6 A-4, A-5, A-6, A-7-5, A-7-6, A-1-a
GC A-2-6, A-2-7 A-2-4 A-4, A-6, A-7-6, A-7-5
SW A-1-b A-1-a A-3, A-2-4, A-2-5, A-2-6, A-2-7
SP A-3, A-1-b A-1-a A-2-4, A-2-5, A-2-6, A-2-7
SM A-1-b, A-2-4, A-2-5, A-2-7 A-2-6, A-4 A-5, A-6, A-7-5, A-7-6, A-1-a
SC A-2-6, A-2-7 A-2-4, A-6, A-4, A-7-6 A-7-5
ML A-4, A-5 A-6, A-7-5, A-7-6 --
CL A-6, A-7-6 A-4 --
OL A-4, A-5 A-6, A-7-5, A-7-6 --
MH A-7-5, A-5 -- A-7-6
CH A-7-6 A-7-5 --
OH A-7-5, A-5 -- A-7-6
USDA Classification System
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FAA Classification System
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Table 5: FAA Classification
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Table 6: Textural Classification
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