II- Index Properties

Consistency of Soil

1 Basic States:

* Depending on the moisture content, soil behaves like:

a- Solid
b- Semisolid
c- Plastic
d- Liquid

2 Atterberg Limits or Consistency Limits:

* The moisture content (wc) at which the transition from one state to another is defined as:

a- Shrinkage Limit (SL) from Solid to Semisolid.
b- Plastic Limit (PL) from Semisolid to Plastic.
c- Liquid Limit (LL) from Plastic to Liquid.

LIQUID LIMIT:

It is the water content at 25 blows and can be determined by using Casagrande Cup. The slope of the line is defined as the flow index.

Liquid Limit Test

PLASTIC LIMIT

Is the moisture content at which the soil crumbles when rolled into threads of 1/8 in. in diameter.

PLASTICITY INDEX

PI = LL - PL

PLASTICITY CHART

PI vs. LL.

* Line A differentiates between the silt and the clay

SHRINKAGE LIMIT

LIQUIDITY INDEX

ACTIVITY

Is used to identify the swelling potential of clay soils.

3- Moisture Content - Dry Unit Weight Relationship (Compaction)

Soil Compaction

Many civil and environmental engineering applications such as highway embankment, earth dams, landfills, airfields and others require that soft soils be compacted to increase their unit weights. Compaction improves soil properties by increasing its strength, reducing permeability and settlement/swelling potential.

Smooth wheel rollers, sheepsfoot rollers rubber-tired rollers, and vibratory rollers are usually used in compacting soils in the field. Vibratory rollers are used mostly for the identification of granular soils.

Compaction. in general. is the identification of soil by removal of air. which requires mechanical energy. The degree of compaction of a soil is measured in terms of its dry unit weight. When water is added to the soil during compaction. it acts as a softening agent on the soil particles. The soil particles slip over each other and move into a densely packed position. The drive unit weight after compaction first increases as the moisture content Increases (Figure 1). Note that at a moisture content wc =0, the moist unit weight g is equal to the dry unit weight (dry ),

4- SOIL CLASSIFICATION SYSTEMS