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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. Comparison of Particle Size Definitions. # 200. ASTM Standards.

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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

Comparison of Particle Size Definitions

# 200


ASTM Standards

  • Lab Data Classification is byASTM D2487

  • Classification of Peat Samples, see ASTM D 4427

  • Field Classification is by D2488


Comparison of Particle Size Definitions


Activity 2 - Particle Size Comparisons


USCS Flow Chart - Activity 3


Flow Chart Overview

  • Two Broad Categories

    • Fine-Grained - 50% or more finer than the # 200 sieve

    • Coarse-Grained - Less than 50% finer than the # 200 sieve


USCS Overview


Flow Chart Overview

  • 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


USCS Overview


Activity 4 - Organic Soil

Solve 4 samples


Abbreviations Fine-Grained

  • 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


Activity 5 - Plasticity Chart

Solve 4 samples


Activity 7 - Classify Fine-Grained Samples

Assume 6 samples are not organic and classify by USCS


Flow Chart Overview

  • Coarse-Grained Soils - 3 Groups

    • Clean - Less than 5 % Fines

    • Dirty - More than 12 % Fines

    • Dual - From 5% to 12% Fines, inclusive


Coarse-grained Soils


Abbreviations Sands and Gravels

  • 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

Sieve Analyses


Percent Particle Categories

  • 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


Additional Definitions

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

    D10, D30, D60


Determining D10, D30, and D60

60

% finer

D60, millimeters

30

10

D30, millimeters

D10, millimeters


Computing CU and CC

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

Characterizing Clean Sands and Gravels

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

Poorly GradedSands and Gravels


Sands

less than 5 % fines

CU > 6

CC = 1-3

Gravels

less than 5 % fines

CU > 4

CC = 1-3

Clean, Well/Poorly Graded Definitions


Activity 11 - Problems

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


Activity 14 Summary of Classifications of Coarse-Grained Soils

  • 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


Dirty Coarse-Grained Soils

  • 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


Dirty Coarse-Grained Soil

  • 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

Dirty Sands and 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


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