Notes on Soil Consistency and Atterberg Limits

Definition of Soil Consistency

• Soil consistency: Degree of firmness of soil.
• Descriptions: Soft, medium, hard.
• Applies primarily to fine-grained soils, especially clays.
• Measured for wet, moist, and dry soil samples.

Importance of Water Content

• Influence of water: Physical properties of soil change significantly with water content.
• Consistency varies with moisture levels.

Atterberg's Four States of Soil

• Albert Atterberg's Classification:
  1. Liquid State: Soil mixed with large amounts of water; behaves like a liquid with zero shear strength.
  2. Plastic State: Soil can be molded; possesses some shear strength.
  3. Semi-Solid State: Cracks upon molding; loses plasticity.
  4. Solid State: Soil has pores partially filled with water; does not shrink anymore.

Transition Between States

• Consistency limits: The water content at which soil transitions from one state to another.
  • Liquid Limit: Water content at which soil changes from liquid to plastic state.
  • Plastic Limit: Water content at which soil changes from plastic to semi-solid state.
  • Shrinkage Limit: Water content at which soil stops shrinking and is no longer fully saturated.

Behavior of Soil with Water Content Changes

• Decreasing water content results in:
  • Transition from liquid to plastic state (increasing shear strength).
  • Transition from plastic to semi-solid (loss of plasticity).
  • Transition from semi-solid to solid (constant volume with decreasing pore water).

Graphical Representation

• With decreasing moisture content:
  • Volume decreases up to the shrinkage limit.
  • Below the shrinkage limit, volume remains constant.

Summary of Atterberg Limits

• Atterberg limits: Critical water contents of fine-grained soils, measured in percentages.
• Determination methods for these limits will be discussed in future lectures.