Unified Soil Classification System Training Part B USCS

Unified Soil Classification System Training Part B - USCS using Laboratory Data

Comparison of Particle Size Definitions clay silt 2 m sand cobbles gravel #4 . 05 mm USDA 3” # 200 fines USCS sand . 074 mm cobbles gravel #4 3”

ASTM Standards v Lab Data Classification is by ASTM D 2487 v Classification of Peat Samples, see ASTM D 4427 v Field Classification is by D 2488

Comparison of Particle Size Definitions

Activity 2 - Particle Size Comparisons

USCS Flow Chart - Activity 3

Flow Chart Overview v 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 v 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 v H - High LL ( > 50 ) v L - Low LL ( < 50 ) v C - Plastic Fines v M - Nonplastic or slightly plastic fines v O - Organic v 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 v. 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 v G - Gravel v S - Sand v P - Poorly Graded v W - Well Graded

Sieve Analyses % gravel = % finer 3”minus % finer # 4 % sand = % finer # 4 minus % finer # 200 % fines = % finer than # 200 sieve

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

Activity 8 For 7 samples, fill out Activity

Additional Definitions v To Classify Clean Coarse-Grained Soils, you must first plot grain-size curve and determine three parameters D 10, D 30, D 60

60 % finer Determining D 10, D 30, and D 60, millimeters 30 10 D 10, millimeters D 30, 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

Characterizing Clean Sands and Gravels % F i ne r Clean Well Graded Sands and Gravels have less than 5 % fines and a wide range of particle sizes that are equally distributed Well graded Particle Size

Poorly Graded Sands and Gravels Poorly graded Particle Size Or Gap. Graded % F i ne r Either Mostly One. Size Particle Gap graded Particle Size

Clean, Well/Poorly Graded Definitions v. Sands – less than 5 % fines – CU > 6 – CC = 1 -3 v. Gravels – less than 5 % fines – CU > 4 – CC = 1 -3

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

Dirty Coarse-Grained Soil v Determine whethere is a greater % of Sand or Gravel – % G = % finer 3” minus # 4 – % S = % finer # 4 minus # 200 v Determine where minus # 40 fines plot on plasticity chart

Dirty Sands and Gravels v SC - Fines Plot Above A-Line Sands v SM - Fines Plot Below A-Line v SC-SM - Fines Plot in Hatched Zone v GC - Fines Plot Above A-Line Gravels v GM - Fines Plot Below A-Line v 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