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Soil Classification Sources: Soil Mechanics – Laboratory Manual,B.M. DAS (Chapters 9)

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Presentation on theme: "Soil Classification Sources: Soil Mechanics – Laboratory Manual,B.M. DAS (Chapters 9)"— Presentation transcript:

1 Soil Classification Sources: Soil Mechanics – Laboratory Manual,B.M. DAS (Chapters 9)

2 Soil Classification Systems USCS AASHTO USCS Classification System Class Outlines

3 USCS Classification System Originally developed for the United States Army The method is standardized in ASTM D 2487 as Unified Soil Classification System (USCS) USCS is the most common soil classification system among geotechnical engineers A typical USCS classification would be: SM Silty sand with gravel Group Symbol Group Name -

4 Naming Convention Fine-grained Soil First Letter Second Letter M – SiltL – Low plastic C – ClayH – High plastic O – Organic Coarse-grained Soil First Letter Second Letter S – Sand P – Poorly graded G – Gravel W – Well graded M – Silty C - Clayey

5 Classification of Soils From sieve analysis and the grain-size distribution curve determine the percent passing as the following: > 3 inch – Cobble or Boulders 3 inch - # 4 (76.2 – 4.75 mm) : Gravel # 4 - # 200 ( mm) : Sand < # 200: Fines First, Find % passing # 200 If (5%) or more of soil passes # 200 sieve, then conduct Atterberg Limits test (LL & PL)

6 Grain Size Distribution Curves GRAVEL SAND FINES Cobbles or Boulders

7 Classification of Soils If the soil is fine-grained ( 50% passes #200) follow the guidelines for fine-grained soils If the soil is coarse-grained (<50% passes #200) follow the guidelines for coarse-grained soils Find % Gravel & Sand Calculate Cu & Cc Calculate LL, PL and PI

8 Fine-grained Soils

9 Coarse-grained Soils

10 Example – Soil A Soil A: D 60 = 4.2 mm, D 30 = 0.6 mm, D 10 = 0.09 mm Cu = Cc = 0.95 Gravel = 36% Sand 62-8 = 54% Fines = 8%

11 Example – Soil A (Cont.) Gravel = 36% Sand = 54% Fines = 8% Cu = 46.7 Cc = 0.95 LL = 42 PL = 31 PI = = 11 GO TO Plasticity Chart

12 Example – Soil A (Cont.) LL = 42 PL = 31 PI = = 11 ML

13 Example – Soil A (Cont.) Soil A is then classified as SP-SM – Poorly-grades sand with silt and gravel


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