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Soil Classification

Soil Classification

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Soil Classification

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  1. Soil Classification N. Sivakugan Duration: 7 min. 20 s

  2. Objectives • To develop a systematic way to describe and classify soils; • To group soils of similar geotechnical characteristics; and • To assign symbols.

  3. 0.002 0.075 2.36 63 200 Major Soil Groups Cohesive soils Granular soils or Cohesionless soils Clay Silt Sand Gravel Cobble Boulder Grain size (mm) Fine grain soils Coarse grain soils

  4. Grain Size Distribution Significance of GSD: • To know the relative proportions of different grain sizes. • An important factor influencing the geotechnical characteristics of a coarse grain soil. • Not important in fine grain soils.

  5. sieve shaker soil/water suspension hydrometer stack of sieves Sieve Analysis Grain Size Distribution Determination of GSD: • In coarse grain soils …... By sieve analysis • In fine grain soils …... By hydrometer analysis Hydrometer Analysis

  6. Grain Size Distribution Curve • can find % of gravels, sands, fines • define D10, D30, D60.. as above.

  7. Well or Poorly Graded Soils Poorly Graded Soils Well Graded Soils Wide range of grain sizes present Others, including two special cases: (a) Uniform soils – grains of same size Gravels: Cc = 1-3 & Cu >4 (b) Gap graded soils – no grains in a specific size range Sands: Cc = 1-3 & Cu >6

  8. Relative Density (Dr) • Measure of how densely the grains are packed in a coarse grain soil in %. 0 100 Loosest Densest • Also known as density index (ID).

  9. Granular Soil Consistencies As per AS1726 - 1993 Relative Density (%) Consistency Term 0-15 Very loose 15-35 Loose 35-65 Medium dense 65-85 Dense 85-100 Very dense

  10. water content 0 Shrinkagelimit Plasticlimit Liquidlimit brittle-solid semi-solid plastic liquid Atterberg Limits • Border line water contents, separating the different states of a fine grained soil

  11. Atterberg Limits Liquid Limit (wL or LL): Clay flows like liquid when w > LL Plastic Limit (wP or PL): Lowest water content where the clay is still plastic Shrinkage Limit (wS or SL): At w<SL, no volume reduction on drying

  12. Plasticity Index = Liquid Limit – Plastic Limit water content 0 Shrinkagelimit Plasticlimit Liquidlimit plastic Plasticity Index (PI) • Range of water content over which the soil remains plastic

  13. Intermediate plasticity Low plasticity High plasticity 60 A-LinePI=0.73(LL-20) 40 Liquid Limit 20 0 100 0 20 35 50 Liquid Limit Classifying Fines • Purely based on LL and PI Clays Silts

  14. 0 5 12 50 100 AS 1726 – 1993 Classification coarse grain soils fine grain soils % of fines YB e.g., CH XY e.g., SM XA e.g., GP XA-XY e.g., GP-GC X: Coarse G = Gravel S = Sands Y: Fines M = Silts C = Clays A: Gradation W = well graded P = poorly graded B: Plasticity H = LL > 50 I = 35 < LL < 50 L = LL < 35

  15. Summary • Sieve analysis – for coarse grain soilsHydrometer analysis - for fine grain soils • Classify coarse by GSD and • fines by Atterberg limits(PI-LL chart) .