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Unified Soil Classification System Training

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Unified Soil Classification System Training

Part B - USCS using Laboratory Data

USDA

cobbles

clay

silt

sand

gravel

2 m

# 4

3”

.05 mm

USCS

cobbles

fines

sand

gravel

# 4

3”

.074 mm

# 200

- Lab Data Classification is byASTM D2487
- Classification of Peat Samples, see ASTM D 4427
- Field Classification is by D2488

- Two Broad Categories
- Fine-Grained - 50% or more finer than the # 200 sieve
- Coarse-Grained - Less than 50% finer than the # 200 sieve

- Fine-Grained Soils
- Organic ( LL ratio < 0.75 )
- Inorganic (no odor and LL ratio not < 0.75)
- Classify by LL, PI
- Modifiers are H or L for LL value, C or M for plasticity and O for organic

Activity 4 - Organic Soil

Solve 4 samples

- H - High LL ( > 50 )
- L - Low LL ( < 50 )
- C - Plastic Fines
- M - Nonplastic or slightly plastic fines
- O - Organic
- Pt - Peat

Activity 5 - Plasticity Chart

Solve 4 samples

Activity 7 - Classify Fine-Grained Samples

Assume 6 samples are not organic and classify by USCS

- Coarse-Grained Soils - 3 Groups
- Clean - Less than 5 % Fines
- Dirty - More than 12 % Fines
- Dual - From 5% to 12% Fines, inclusive

- G - Gravel
- S - Sand
- P - Poorly Graded
- W - Well Graded

% gravel = % finer 3”minus % finer # 4

% sand = % finer # 4 minus % finer # 200

% fines = % finer than # 200 sieve

- To compute % Gravel subtract % finer than # 4 from % finer than 3”
- To compute % Sand subtract % finer than # 200 from % finer than # 4
- Percent Fines is % finer than # 200

Activity 8

For 7 samples, fill out Activity

- To Classify Clean Coarse-Grained Soils, you must first plot grain-size curve and determine three parameters
D10, D30, D60

60

% finer

D60, millimeters

30

10

D30, millimeters

D10, millimeters

Coefficient of Uniformity

High Values Indicate Well-Graded Soil

Coefficient of Curvature

Values Between 1-3 Indicate Well-Graded Soil

Activity 9

Plot Curve from Data, compute CU Value

Activity 10

Plot Curve from Data, compute CC Value

Well graded

Clean Well Graded Sands and Gravels have less than 5 % fines and a wide range of particle sizes that are equally distributed

% Finer

Particle Size

Either Mostly One-Size Particle

Or Gap-

Graded

% Finer

% Finer

Poorly graded

Gap graded

Particle Size

Particle Size

Sands

less than 5 % fines

CU > 6

CC = 1-3

Gravels

less than 5 % fines

CU > 4

CC = 1-3

1. Verify % Fines - Coarse-Grained/Clean

2. Compute % Gravel and % Sand

3. Note which predominates

4. Using provided CU and CC, Determine whether poorly or well graded

5. Determine Correct USCS classification

Activity 12

Review Example Soil

Activity 13

Use Flow Chart, Classify Soil

- Clean Sands and Gravels (< 5% fines)
- Clean Poorly Graded Gravels GP
- Clean Well Graded Gravels GW
- Clean Poorly Graded Sands SP
- Clean Well Graded Sands SW

- If a sample has less than 50 % Fines
- And it has more than 12 % Fines, it is a Dirty Coarse-Grained Soil
- To Classify, follow the flow chart and the following steps

- Determine whether there is a greater % of Sand or Gravel
- % G = % finer 3” minus # 4
- % S = % finer # 4 minus # 200

- Determine where minus # 40 fines plot on plasticity chart

Sands

Gravels

- SC - Fines Plot Above A-Line
- SM - Fines Plot Below A-Line
- SC-SM - Fines Plot in Hatched Zone
- GC - Fines Plot Above A-Line
- GM - Fines Plot Below A-Line
- GC-GM - Fines Plot in Hatched Zone

Activity 16 - Problems

Activity 17 - Example of Classifying Dual-Classification Coarse-Grained Soil

Activity 18 - Problem

Activity 20 - Review Questions

Activity 21 - Comprehensive Problems