1. Soil Classification Systems
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2. Soil Classification Systems
Classification systems are a way to identify soils in a consistent unbiased manner based on physically measured properties.
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3. Soil Classification Systems
AASHTO
Unified Soil
USDA
FAA
Burmister
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4. Soil Classification System Page E-2
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5. AASHTO Classification System
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6. 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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7. 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
Page E-1
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8. 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-2-7
A-7-5
A-7-6
Sieve Analysis
Percent Passing
No. 10
50 max
No. 40
30 max
51 min
No. 200
15 max
10 max
35 max
36 min
Characteristics of P40 material
Liquid Limit
40 max
41 min
Plastic Index
6 max NP
11 min
Group Index
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)
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9. AASHTO Subgroups 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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10. Granular Materials
Less than 35% passing No.200 sieve.
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11. Granular Materials A-1-b 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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12. 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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13. Granular Materials A-3 soils Fine sand, little fines
Sands deficient in coarse material.
Lack stability.
Good subgrades.
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14. Silt-Clay Materials Greater than 35% passing No. 200 sieve
Silts – PI ≤ 10
Clays – PI > 10
PI = Plasticity Index
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15. 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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16. Silt-Clay Materials A-6 Soils Clay Good for fills and subgrades
At low moisture content
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17. Silt-Clay Materials A-7 soils Elastic Problematic subgrades A-7-5
Volume change
A-7-6
High volume change
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18. Group Index Rating Based on gradation, L.L., and P.I. of the soil.
Group Index=0.2a ac bd
See page E-11 in manual.
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19. 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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20. Examples AASHTO Classification System
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21. Example - 1 AASHTO Classification System
Gradation
Project ID
Highway
STH 33
Project Limits
USH 41 to CTH Z
Comments
Test Boring No. 7
Depth
3 - 5
Sample No. 2
Test Date
October 5, 2010
Tester
Jonathan Joslin
Dry mass before wash
267.0 g
Dry mass after wash
228.5
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
85.6
14.42%
PAN
LL = NP
PI = NP
AASHTO Classification
A-1-b
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22. Example - 2 AASHTO Classification System
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23. Example - 2 AASHTO Classification System
Sieve Analysis – Percent Passing
No. 10 = 37%
No. 40 = 25 %
No. 200 = 13%
LL, PI = Non plastic
AASHTO Classification
A-1-a
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24. Example - 3 AASHTO Classification System
Percent Passing No. 200 Sieve = 63%
Liquid Limit (LL) = 32
Plasticity Index (PI) = 15
AASHTO Classification
A-6
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25. Unified Soil Classification System USCS
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26. Grain Size Identification USCS – (ASTM)
Page E-1
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27. Page (E-9)
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28. 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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29. 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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30. Example USCS Classification System – Coarse Grained Soils
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31. 1 – Greater than 50% passing No. 200 sieve? No
Coarse Grained Soil
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32. 2 – Determine Sand vs. Gravel Sand - P No. 4 to R No. 200 = 30%
Gravel - P 3-inch to R No. 4 =
59%
2 – Determine Sand vs. Gravel
Sand - P No. 4 to R No. 200 =
30%
Gravel
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33. Topic E

34. D60 = 10 mm 3 – Determine D60, D30 and D10 D30 = 2 mm D10 = 0.07 mm
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35. Example USCS Classification System – Coarse Grained Soils
4. Determine Cu and Cc
D60 = 10 mm
D30 = 2 mm
D10 = 0.07 mm
Cu = D60 /D10 = 10/0.07 =
143
Cc = (D30 ^ 2)/(D60 x D10) =
5.7
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36. Example USCS Classification System – Coarse Grained Soils
Cu = D60 /D10 = 10/0.07 = 143
USCS Classification = GP-GM
Cc = (D30 ^ 2)/(D60 x D10) = 5.7
LL, PI = Non plastic
AASHTO Classification?
A-1-a
P200 = 11%
For P200 < 5%
If Cu is greater than 4 and Cc is between 1 to 3 than GW
If both sets of criteria are not met for GW than GP
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
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37. 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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38. Example USCS Classification System – Fine Grained Soils
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39. Example USCS Classification System – Fine Grained Soils
Not Organic
LL = 37
PL = 20
PI = 17
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40. Page E-9
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41. Example USCS Classification System – Fine Grained Soils
LL = 37
PL = 20
PI = 17
USCS Classification: CL
AASHTO Classification?
A-6
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42. Organic Soils Compressible Undesirable for construction Symboled “pt.”
Peat, humus, and swamp soils
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43. Comparable USCS Soil Type
AASHTO
Soil 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
GC, SC
GW, GP, SW, SP
A-2-5
A-2-6
A-2-7
GM, GC, SM, SC
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
OH, MH, GC, GM, SM
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44. Comparable AASHTO Soil Type
USCS
Soil 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-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 SP
A-3, A-1-b SM
A-2-6, A-4
A-5, A-6, A-7-5, A-7-6, A-1-a SC
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 MH
A-7-5, A-5
A-7-6 CH OH
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45. USDA Classification System
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46. Topic E

47. FAA Classification System
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48. Table 5: FAA Classification
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49. Table 6: Textural Classification
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