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Published byRonald Osborne Modified about 1 year ago

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

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Comparison of Particle Size Definitions USDA cobbles sandclay gravel 3” 2 .05 mm # 4 silt USCS cobbles sandfines gravel.074 mm # 43” # 200

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

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Comparison of Particle Size Definitions

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Activity 2 - Particle Size Comparisons

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USCS Flow Chart - Activity 3

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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

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USCS Overview

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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

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USCS Overview

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Activity 4 - Organic Soil Solve 4 samples

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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

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Activity 5 - Plasticity Chart

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Solve 4 samples

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Activity 7 - Classify Fine- Grained Samples Assume 6 samples are not organic and classify by USCS

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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

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Coarse-grained Soils

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Abbreviations Sands and Gravels v G - Gravel v S - Sand v P - Poorly Graded v W - Well Graded

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

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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

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Activity 8 For 7 samples, fill out Activity

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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

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

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Computing CU and CC Coefficient of Uniformity Coefficient of Curvature High Values Indicate Well- Graded Soil Values Between 1-3 Indicate Well-Graded Soil

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Activity 9 Plot Curve from Data, compute CU Value

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Activity 10 Plot Curve from Data, compute CC Value

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C haracterizing Clean Sands and Gravels Particle Size % Finer Well graded Clean Well Graded Sands and Gravels have less than 5 % fines and a wide range of particle sizes that are equally distributed

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Poorly Graded Sands and Gravels Poorly graded % Finer Particle Size Either Mostly One- Size Particle Gap graded Particle Size % Finer Or Gap- Graded

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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

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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

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Activity 12 Review Example Soil

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Activity 13 Use Flow Chart, Classify Soil

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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

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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

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Dirty Coarse-Grained Soil v Determine whether there 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

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

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Activity 16 - Problems

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

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Activity 18 - Problem

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Activity 20 - Review Questions

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Activity 21 - Comprehensive Problems

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