This document provides an overview of classifying soils using the Unified Soil Classification System (USCS). It discusses classifying soils as fine-grained or coarse-grained based on the percentage passing through a #200 sieve. For fine-grained soils, classification is based on liquid limit, plasticity index, and organic content. For coarse-grained soils, classification depends on percentage of fines and uses coefficients of uniformity and curvature to distinguish between well and poorly graded sands and gravels. The document outlines steps to classify clean, dirty, and dual-grained coarse soils using flow charts and plasticity characteristics.

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

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

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

4. Comparison of Particle Size Definitions

5. Activity 2 - Particle Size Comparisons

6. USCS Flow Chart - Activity 3

7. 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

8. USCS Overview

9. 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

10. USCS Overview

11. Activity 4 - Organic Soil Solve 4 samples

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

13. Activity 5 - Plasticity Chart

14. Activity 5 - Plasticity Chart Solve 4 samples

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

16. 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

17. Coarse-grained Soils

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

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

20. 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

21. Activity 8 For 7 samples, fill out Activity

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

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

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

25. Activity 9 Plot Curve from Data, compute CU Value

26. Activity 10 Plot Curve from Data, compute CC Value

27. C haracterizing 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 Particle Size % Finer Well graded

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

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

30. 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

31. Activity 12 Review Example Soil

32. Activity 13 Use Flow Chart, Classify Soil

33. 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

34. 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

35. 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

36. 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 Sands Gravels

37. Activity 16 - Problems

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

39. Activity 18 - Problem

40. Activity 20 - Review Questions

41. Activity 21 - Comprehensive Problems