Soil Classification Systems Topic E. Soil Classification Systems Topic E Classification systems are...

Soil Classification SystemsTopic E

Topic E

Soil Classification Systems

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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


A-1-b


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Sieve Analysis – Percent PassingNo. 10 = 37%No. 40 = 25 %No. 200 = 13%LL, PI = Non plastic


A-1-a


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Percent Passing No. 200 Sieve = 63%

Liquid Limit (LL) = 32Plasticity Index (PI) = 15


A-6

Unified Soil Classification SystemUSCS

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Grain Size IdentificationUSCS – (ASTM)

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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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LL = 37PL = 20PI = 17

P 200 > 50%Not Organic

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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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