2.4. Plasticity and structure of soil (Indices of Soil Consistency - Plasticity Index) Flashcards
provides a measure of a soil plasticity: the amount of water that must be added to change a soil from its plastic limit to its liquid limit.
PI = LL - PL or Plasticity Index
Water content where soil changes from plastic to liquid.
Liquid Limit
Water content where soil changes from plastic to semi-solid.
Plastic Limit
More plastic, retains more water.
High Plasticity Index
Less plastic, transitions quickly to solid.
Low Plasticity Index
Liquid Limit (LL): 35–100
Plastic Limit (PL): 20–40
Activity (A): 0.3–0.5
Low plasticity and low swelling potential.
Kaolinite
Liquid Limit (LL): 60–120
Plastic Limit (PL): 35–60
Activity (A): 0.5–1.2
Moderate plasticity and moderate swelling.
Illite
Liquid Limit (LL): 100–900
Plastic Limit (PL): 50–100
Activity (A): 1.5–7.0
Highly plastic and expansive clay.
Montmorillonite
Liquid Limit (LL): 50–70
Plastic Limit (PL): 40–60
Activity (A): 0.1–0.2
Low plasticity and very low swelling.
Hydrated Halloysite
Liquid Limit (LL): 40–55
Plastic Limit (PL): 30–45
Activity (A): 0.4–0.6
Low plasticity and low swelling potential.
Dehydrated Halloysite
Liquid Limit (LL): 150–250
Plastic Limit (PL): 100–125
Activity (A): 0.4–1.3
Moderate to high plasticity.
Attapulgite
Liquid Limit (LL): 200–250
Plastic Limit (PL): 120–150
Activity (A): 0.4–1.3
Allophane
Nonplastic soil
No plasticity, behaves like granular soil (e.g., sand, silt).
PI = 0
Slightly plastic
Very low cohesion, minor deformation before breaking.
PI = 1–5
Low plasticity
Some plasticity, minimal swelling/shrinking behavior.
PI = 5–10
Medium plasticity
Moderate cohesion, workable and moldable soil.
PI = 10–20
High plasticity
Highly cohesive, significant expansion/shrinkage.
PI = 20–40
Very high plasticity
Extremely cohesive, large volume changes with moisture.
PI > 40
