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Understanding Atterberg's Limits in Soil Consistency for Civil Engineers

Learn about Soil Consistency, Atterberg Limits, Liquid Limit, Plastic Limit, Shrinkage Limit, Plasticity & Liquidity Index, and measurement methods. Discover how soil behaves at different moisture levels.

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Understanding Atterberg's Limits in Soil Consistency for Civil Engineers

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  1. Atterberg's Limits Prof Neelam Belani Assistant Professor Civil Engineering Department IT,NU

  2. Content • Soil Consistency • Atterberg Limits • Liquid Limit • Plastic Limit • Shrinkage Limit • Plasticity Index • Liquidity Index • Plasticity Chart

  3. Soil Consistency Soil consistence provides a means of describing the degree and kind of cohesion and adhesion between the soil particles as related to the resistance of the soil to deform or rupture Soil Behave Like: SOILD at very low moisture content LIQUIDat very high moisture content

  4. Soil Consistency - Atterberg Limits Depending on Moisture Content soil can be divided into: • Solid • Semi-Solid • Plastic • Liquid - Shrinkage Limit (SL) LI = 0 Moisture Content (w) Plastic Limit (PL) Liquidity Index (LI) Plasticity Index (PI) = PL - LL Liquid Limit (LL) LI = 1 +

  5. Liquid Limit - Definition Liquid Limit (LL) is defined as the moisture content at which soil begins to behave as a liquid material and begins to flow (Liquid limit of a fine-grained soil gives the moisture content at which the shear strength of the soil is approximately 2.5kN/m2)

  6. Liquid Limit - Measurement First Method Casagrande Apparatus ASTM D-4318

  7. Liquid Limit - Measurement Liquid Limit (LL) at N = 25

  8. Liquid Limit – Flow Index w1=44 w2=39 N1=20 N2=30 Flow Index

  9. Liquid Limit - Measurement Second Method Fall Cone Method BS1377

  10. Liquid Limit - Measurement Liquid Limit (LL) at d = 20 mm

  11. Plastic Limit - Definition The moisture content (%) at which the soil when rolled into threads of 3.2mm (1/8 in) in diameter, will crumble.

  12. Plastic Limit - Measurement First Method ASTM D-4318 PL = w% at d 3.2 mm (1/8 in.)

  13. Plastic Limit - Measurement Second Method Fall Cone Method BS1377 Plastic Limit (PL) at d = 20 mm

  14. Plasticity Index - Definition Plasticity Index is the difference between the liquid limit and plastic limit of a soil. PI = LL – PL

  15. Plasticity Index - Definition PI (%) = 4.12 IF (%) PI (%) = 0.74 IFC (%) Question!! Which PI is more reasonable for construction projects? The high one or the low one?!

  16. Shrinkage Limit - Definition The moisture content, in percent, at which the volume of the soil mass ceases to change

  17. Shrinkage Limit - Definition

  18. Shrinkage Limit - Measurement

  19. Soil Consistency - Atterberg Limits Depending on Moisture Content soil can be divided into: • Solid • Semi-Solid • Plastic • Liquid - Shrinkage Limit (SL) LI = 0 Moisture Content (w) Plastic Limit (PL) Liquidity Index (LI) Plasticity Index (PI) = PL - LL Liquid Limit (LL) LI = 1 +

  20. Liquidity Index - Definition

  21. Plasticity Chart - Definition • Casagrande (1932) studied the relationship of the plasticity index to the liquid limit of a wide variety of natural soils. • He proposed a plasticity chart

  22. Organic Inorganic Silt Clay

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